Lesson 4: Avoiding Enroute Thunderstorms


Welcome to lesson four of our six part course on "Thunderstorms and Flying." In this lesson we will learn about and review some of the tips and techniques to get weather information about what lies ahead on your route of flight.

This week's guest "speaker" is Mr. Randy Baker, a meteorologist with the world's largest parcel delivery service. He is a member of the National Weather Association's Aviation Weather Committee. Keeping airplanes out of harms way of thunderstorms, especially in night flying is an ever-present challenge, especially when the aircraft cover the world.

As a meteorologist at a major cargo airline, my knowledge of thunderstorm activity is vital to the daily planning and operation of Flight Operations. Thunderstorms at an airport can totally disrupt loading and unloading of aircraft, fueling operations, maintenance activities, as well as delay arrival and departure operations. A lightning strike can injure workers and shut down computers, even put an aircraft out of service.

Enroute thunderstorms, particularly organized convection, can be even more disruptive. A large squall line can totally shut down traffic through an ARTCC for several hours, causing massive rerouting and weather delays. When located in the Northeast, massive ATC delays and ground stops are common, which will significantly impact our ability to meet our service commitments.

When I look at thunderstorm potential, I need to know not just the likelihood of convection, but also the mode. Will it just be isolated single cells, or will it be more organized, such as Supercells, Multicell Clusters, Multicell Line, or even the Mesoscale Convective Complex? Once I know the level of organization and the potential hazards, I can brief dispatchers, pilots, and operations management as to the potential impact on our operations. It is critical to our success as a delivery service that they all know where the thunderstorms are located in our route structure at all times.
What we need to know to run a successful world-wide business is just what you need to know to conduct safe flights in the United States and around the world. Please learn from this lesson all you can to keep away from the dangers and disruptions of the thunderstorm hazard.

Randy Baker

And now on to our lecture on ways to avoid thunderstorms enroute to your destination. Because thunderstorms are such a dynamic force and a moving target, it is important to keep up with their locations along your route of flight once you know that they may play a role in your day of aviating. How can you do that? There are many ways. The first ways begin during the flight planning process...

Ground-based radar

Radar plays an important role in thunderstorm detection and avoidance. There are ground based radars at detect where thunderstorms are located. Products that display that information are disseminated to you from a variety of distributors. Let's learn more about these radar systems and the products you use.

Radar theory is not easy. The University of Wisconsin at Madison has an internet course on aviation weather with background material on radars and how they work. Please review that basic material now. The Air Force Flight Standards Agency has more advanced material to help you understand the most advanced weather radar system in the world, the next-generation radar, or NEXRAD, composed of the network of WSR-88D Doppler weather radars.
Before lesson one, we asked you to find a vendor of these products on the internet. See where the WSR-88D radars say thunderstorms are a problem right now. If you don't have the link handy you can always see the radar product at the National Weather Service's website. The product you are looking at is called the Radar Composite based on the input from every WSR-88D in the United States. These products are updated every 15 minutes which is two complete scans of the atmosphere for this kind of radar.

Radar Summary Charts is another way to view where thunderstorms are along your route of flight. This is an hourly product. Review AC-0045 Chapter 7 on Radar Summary Charts now .

Satellite images

Another good way to see the locations of thunderstorms while planning your route is to look at satellite images. One of the top meteorologists in the business, Mr. Gary Ellrod from the National Weather Service (and a Councilor of the National Weather Association) has a special "minicourse" on reading the hazards from satellite imagery.

Now is a good time to review AC-0045, Chapter 3 on radar reports and satellite images using the Resource Menu.
The FAA and the National Weather Service's Aviation Weather Center are working on a new satellite imaging technique that overlays satellite-sensed lightning strikes onto images over the Atlantic and Pacific Oceans. This will make thunderstorm identification easier while "over the water." This program was developed by Dr. Alan Nierow, an NWA member, and Mr. Fred Moser. You can see examples of these products at this link.

Lightning data

Lightning data is another source of real-time information on where thunderstorms are located. It collects and distributes cloud-to-ground strike information collected from sensors all over the United States and displays the strike location within a few seconds. This is the most up-to-date information on thunderstorms while you are on the ground. Many airline dispatch offices use this display because of quickness of this information source. View the National Lightning Map at The Weather Channel's website.

Once you are airborne, there are other ways to keep you informed about thunderstorms. If you know that they will impact your flight, you must keep up with their intensity, direction of movement, heights, and other information that will ALWAYS give you options to avoid this hazardous weather condition. Let's look at some of the ways you can keep up with thunderstorms during flight.

Airborne radar

From the June 1998 issue of Flying Safety Magazine comes this portion of the article we first read in lesson one. The article shows different radar signatures that point to significant and severe weather.

Let's hear from someone who does flying around severe weather for a living. I'll bet he has an interesting story to tell about radar usage.

By the way, he will use the term LEWP. This means Line Echo Wave Pattern and is a squall line that has developed into a wave-like pattern due to acceleration at one end of the line and deceleration along the portion immediately adjacent. A Line Echo Wave Pattern (LEWP) indicates possible tornadoes, large hail and high winds
It is now my privilege to introduce Mr. Jack Parrish, a meteorologist with the NOAA Aviation Operations Center (AOC). It is his responsibility to guide research aircraft around and through thunderstorms and hurricanes, all in the name of science. He has some interesting stories about flying, especially where you don't want to be. Please listen for the lessons from his experiences.


The NOAA Aircraft Operations Center (AOC) flies two types of aircraft, the WP-3D Orions and the Gulfstream G-IV SP, into severe weather. Our remaining fleet of light aircraft, including a Cessna Citation II, several DeHavilland DHC-6 Twin Otters, the AC690A Turbo Commander, several Lake Seawolves, and Bell 212 and Hughes 500D helicopters, fly NOAA missions as well, but encounter severe weather only when necessary, and make all attempts to avoid it. Due to their respective designs, cruise altitudes and true air speeds, we naturally are much more willing to take the P-3s into more potentially severe conditions than the G-IV. Most of this description will fall back on P-3 experiences, with high-altitude insights from the G-IV thrown in when it further clarifies the picture.

The NOAA WP-3Ds have flown near or through virtually all of the different types of hazardous weather prudent pilots avoid, primarily in the United States and offshore waters, but also including severe frontal squall lines off Taiwan, tropical cyclones in Australia, polar lows north of Iceland, mountain winter storms (Foehns) in Austria, and Mistrals over the Adriatic. Again, these discussions are restricted to dealing with typical weather hazards encountered over or near the US.

Every year we fly in hurricanes and tropical storms. What other weather types and hazards the AOC flight crews will deal with depends on research goals for that year. We normally conduct one to three winter /spring projects, from studying continental and oceanic winter storms to California coastal jets to tornado chasing over the Oklahoma prairie.

Flying on a routine basis near and through severe weather requires a few additional capabilities and modes of planning not available to most flight crews. First and foremost, the crew responsible for safe passage through the weather includes the pilots, a flight engineer (P-3), a navigator (P-3), and a flight meteorologist, all highly trained and experienced in the very different types of weather hazards encountered throughout the country. The duties of each of these individuals is specifically segmented to their expertise, so that safe passage through the turbulence is never overwhelmingly on the shoulders of one individual. Of course, the Aircraft Commander (chief pilot) has the final say on what we will and won’t fly through. Second, the P-3s bristle with weather radars, including a nose C-band with turbulence spectra included, a belly 360? scanning C-band surveillance radar, and an X-band tail doppler radar for vertical profiling of thunderstorms.

Third, when going into battle against some of the worst storms on earth, the WP-3D flight crews know they are armed with a formidable flying laboratory. To start with, the P-3 itself is a time-tested, extremely sturdy design, bounced for decades at low altitude over the stormy world oceans by Navy Anti Submarine Warfare crews. The turbulent air speed (about 220 knots) is well suited to the size of convective cells we encounter, along with lots of airspeed above and below 220 knots to get through the worst shears, updrafts and downdrafts. The variable pitch turboprop grants the flight crew plenty of power response when needed, with no noticeable performance degradation regardless of the intensity of the precipitation encountered (although we avoid medium to large hail for all the right reasons). While the rigid wing can offer a jarring ride at times, the aircraft always comes out of the experience as healthy as when it entered the fray, discounting a certain amount of unavoidable leading edge wear and tear.

Modes of Weather

When planning for possible severe weather encounters, the NOAA flight crews consider three different weather modes. The first mode is to reckon with those types of storms and hazards that we are willing to encounter routinely and for lengthy periods, for the sake of accomplishing vital research goals within a sound margin of safety. They might include high winds, up to moderate icing within the deicing/anti-icing capabilities of the aircraft, moderate turbulence in clear air and cloud, moderate to heavy precipitation, including very small graupel, and as much IFR as is needed to accomplish the mission. Notice the repeated use of the term moderate, defining an environment where the aircraft is firmly under control, mostly by the autopilot, and aircraft systems are well able to mitigate the weather hazards. These work environments are identified in tactical planning sessions before take off, using the most recent meteorological products available, including satellite and radar imagery, atmospheric soundings, turbulent indexes and PIREPs, and the latest synoptic forecasts for the degree of expected weather severity in the work area. Armed with this knowledge, we still go into the research area trusting only those indications we receive from our aircraft instruments and real-time ground reports of weather developments. Typical regions that meet this description are most quadrants of a mature winter cyclone, the rainbands surrounding the hurricane eye (and eyewall), stratiform icing areas behind midwestern squall lines, the low altitude coastal jet preceding a landfalling west coast frontal storm, and layers of clear air turbulence near the jet stream. Generally, we are able to operate in these hostile weather environments for long periods, and while crew comfort is obviously degraded, we maintain safe flight in conditions vital to beneficial research.

The second mode of severe weather dealt with by the AOC is the occasional encounter with severe conditions unavoidable in carrying out the job. The best example is the intense hurricane eyewall, which may contain severe turbulence, small hail, strong shears, and the possibility of lightning strikes, regardless of quadrant and altitude it is penetrated. Some eyewalls of rapidly-intensifying hurricanes are virtually perfect ‘rings of fire’ on the radar, offering no soft sectors through which to track into the center. Unfortunately, the information obtained in the eye is too crucial to abandon the attempt to reach it, so instead the flight crew will do whatever is possible to mitigate the hazards while carrying out the mission. We do this by considering all that can be known about the storm beforehand in planning, then carrying out all possible steps just before the severe weather impact to minimize the hazard. In planning, we rely on the same products mentioned above, but pay particular attention to satellite-based signatures consistent with rapidly intensifying thunderstorms, and the most recent aircraft experiences in the storm. Then, as the aircraft approaches the possibly severe weather, the on-board radars are closely scrutinized, again for signatures of hazards along the track. Options available to the flight crew include changing altitude (higher is often less turbulent), slight adjustment to track (to avoid hook echoes, doughnuts, extreme gradients), and tracks specifically chosen to keep the plane in the hazardous region for a minimum amount of time. Likewise, optimal airspeeds are chosen to minimize the turbulent effects on the airframe while retaining plenty of cushion above stall speed.

Dealing with this particular type of weather hazard requires the most collective judgement on our part. In these fairly rare events, we’re committing the aircraft to the possibility, if fairly remote, of control problems, and weather impacts that might briefly overwhelm the aircraft systems. The key here is to minimize their impacts and duration. Altitude and airspeed, along with crew readiness, minimizes the former, track adjustment and future track planning handles the latter. The P-3s cross through hurricane eyewalls exceeding 50dBz radar reflectivity when necessary, and the G-IV crosses convective rainbands and occasional eyewalls when required for storm coverage, but we spend as little time in these regions as possible to accomplish the mission.

The third mode of severe weather that the AOC flight crews deal with are those hazards we will not let the aircraft encounter. These include tornadoes or their parent circulations (known as mesocyclones), large hail, very large vertical shears, Line Echo Wave Patterns (LEWPs), very high radar reflectivities, extreme regions of electrification, and low-altitude IFR conditions approaching minimums. Here again the comprehensive suite of airborne radars, aided by other detection instruments and ground communications, forewarns the crew of what to avoid. However, many of these ‘do not enter’ regions are of high interest to weather research scientists, so the job then becomes just how close can we approach such hazards, horizontally and vertically, with a reasonable margin of safety. Again, judgement and experience rule the safe conduction of this type of research flying.

Use of radar for severe weather research

The fundamental use of airborne radar by the NOAA hurricane hunters to observe, avoid, and penetrate severe weather is truly no different than the proper use of radar by any pilot with a healthy respect for controlled flight. The differences are the types of radar we have available, and of course the thresholds of weather hazards we must be willing to encounter. Two simple rules drive our use of radar; first, know how to get the most information possible from your system, and second, thoroughly understand the limitations of radar. Without the first rule, the radar is all but an inert black box, and without the second, it can seem to be a malicious lure to desperate predicaments.

The NOAA flight crews receive about 12 hours of in-house refresher training each year on weather radars, severe weather signatures, and thunderstorm structure (this in addition to periodic simulator and training flights). At least half of this time is spent on having a full understanding of arcane topics such as gain control, characteristics of different radar wavelengths, side lobes, beam filling properties, and most important, tilt management. Knowing how to optimize the forward scanning radars when not manipulating them is given equal priority to rapid control changes when very near weather hazards depicted on the radar; meaning we don’t like to stumble into surprises any more than we care to fall behind the situational curve when maneuvering through well-observed hazards. We also fully brief the type of expected weather hazards unique to certain geographic and seasonal areas before conducting atmospheric research away from home. Guest speakers with local weather expertise are always sought whenever possible.

The two NOAA P-3s and the G-IV are equipped with C-band (5 centimeter wavelength) radars in the nose for guidance around storms. The signal from a C-band radar does not suffer from attenuation in heavy precipitation as much as an X-band (3 centimeter), but requires a larger antenna and more power, so C-bands are rarely seen on light aircraft. On the other hand, X-band radars depict lighter precip better than C-bands, doing a much better job of outlining thunderstorm clouds containing radar scatterers. Beam size and height above ground at various ranges, gain adjustments, reflectivity color thresholds, 0? tilt settings at different altitudes, all impact how to interpret the picture ahead, helping us to make informed decisions with time to spare. We find that little quantitatively useful information is presented on the C-band radars outside of about 100 miles, so as the range decreases to the target ahead, the flight crew frequently changes the range to expand the storm we plan to encounter soonest. Vertically scanning these suspected features using the tilt control gives us a clear picture of their relative height, vertical precipitation gradients, tilt with height, and possibility of hail content, all useful clues about thunderstorm organization upon which we base track decisions. Other than what we see out the cockpit window (precious little on a moonless night or IFR in the top of a hurricane), the ever-evolving story on the nose radar is the best form of life insurance we have, other than the pilot’s skill in the few cases when even this tool fails to keep us far enough from severe turbulence.

Midwestern Thunderstorms

The last section stressed experiences with the stormy tropical environment, generally found between 30? north and south of the equator, especially in that hemisphere’s summer. Much of the hurricane conventional wisdom holds true for Florida summer thunderstorms and sea breeze squall lines as well. That is not to say that there aren’t occasions of very large hailstones, tornadoes, and aircraft killing shears in tropical summer thunderstorms. But by and large, thunderstorms that paint vividly in the tropics contain flight hazards of a lesser degree than similar appearing storms in the mid-latitudes. Why? For numerous reasons dynamic and thermodynamic, some well described in earlier lessons, they simply do not foster the meteorological organization of the granddaddy of all thunderstorms, the supercell.
Over the past several decades, the NOAA WP-3Ds have been involved in numerous studies of hazardous midwestern thunderstorms at their peak intensity, usually between April and June. These missions have concentrated on the complete daily life cycle, from dry line storm initiation, squall line organization, birth and life of the supercell, and into the night and early morning hours studying the Mesoscale Convective Systems (MCS). The nature of these storms is such that we never penetrate the strongest regions displayed on radar, and our dBz thresholds for flying through the precipitation are knocked way down from the tropical environment. However, the destructive potential of the supercell is so extreme that it is a vital research mission to position the aircraft near the worst thunderstorms and profile their evolution with the aircraft radars. Thus, the nature of aircraft safety becomes finding that perfect distance from the storm’s edge that optimizes the data acquisition, yet far enough off to keep the crew safe.

Conducting missions this close to such severe weather has taught us some crucial lessons. Flying ahead of, and above the outflow depicted in the Lesson 2 cross-section at 6000 feet AGL, we have experienced 100 knot inflows trying to draw us into the squall lines body, while visually observing 60-70 knot outflow on the surface directly below the aircraft. Very quick math indicates 170 knots worth of shear somewhere between us and the surface, not a particularly comfortable feeling since we weren’t sure how far below the plane was the meeting of these two opposing winds. In one case, flying just south of a very powerful tornado-producing series of supercells in north Texas, another research turboprop one mile closer to the storm and 1000 feet lower than the P-3 encountered this shear, resulting in crew injury and return to base for medical care. Where the wildest weather was occurring on the ground, radar often (but not always) depicted a hook, scallops, LEWP, protuberance, or extreme gradient.

As we moved from the squall line to the isolated supercell, even more dramatic characteristics usually accompanied the areas of the storms that resulted in tornadoes, hailswaths, and structurally damaging winds. Depending on the radar intensity coupled with what we knew of the upper level winds, wide berth was given to certain sectors where large hailstones could travel miles from the core. Usually, these sectors are areas east to north of the thunderstorm core, depending on flow above 30,000 feet.

Several other factors make these studies among the leading ones we stay up at night anticipating. The growth on the upwind end of a severe squall line is frequently explosive when the thermodynamics are right, and the rising new storms can reach what was moments earlier a safe altitude in very short order, unfortunately at times just before you arrived. Whole regions that are primed with moisture and buoyancy can light off at once, occasionally creating the situation where the aircraft is quickly surrounded by storms, leaving the flight crew with one of those ‘lesser of several evils’ decision. This environment demands very strong situational awareness, when we might otherwise concentrate too much on the research target of interest.

Midwestern severe thunderstorms will attenuate radar; cut through a narrow gap in a severe squall line, and you might find something even worse on the other side that was effectively shadowed by the line. Another case of the devil you don’t see being as dangerous as the one you do involves this environment at night. Often the squall line you see vividly on your radar is producing low-level dynamics (outflow) that is busily initiating a pre-frontal squall line that does not show up well (yet) on radar. Why? Because it’s so young thermodynamically that little if any precipitation is evident. But fly through these newly developing convective towers at your hazard. We have, it’s a teeth-rattling trip in the P-3, and very difficult to read the instruments; it’s hard to imagine the control problems a lighter aircraft would have. Another place we particularly dislike is the broad stratiform precipitation region generally northwest of nocturnal squall lines; in the ice above the melting layer, communications becomes very tough, and the P-3 is particularly prone to lightning strikes and static discharges while in this area between 0 C and -5 C.

Use of Radar in Hurricanes

From this point, figuring that we are getting a clear picture of the storm’s reflectivity (and sometimes turbulence spectra, although it thresholds low for our purposes), basic knowledge and experience play into our decisions. For hurricane rainbands, and most tropical thunderstorms, we are aware that the embedded updrafts are not strong enough to maintain large hailstones or produce extreme shears. Reflectivities approaching 60dBz are occasionally flown through, although values in the high 40s and low 50s are more the norm. Very sharp reflectivity gradients on the inside edge of well-organized eyewalls are inevitable and unavoidable; quite often, other than a sharp updraft inward from the gradient, these areas are simply the edge of very heavy rainfall. On the other hand, highly-reflective cells in outer rain bands well away from the high wind hurricane core often possess very disruptive shears, small hail and rotating mesocyclones that occasionally produce small tornadoes (no tornado/waterspout should ever be considered ‘small’ to an aviator). The good news about flying into the hurricane’s eye is that, most often, once inside the ring of greatest weather hazards, there is ample time to maneuver in much calmer conditions while hunting the exact wind center at flight level. Because of this fact, we usually fly attitude and airspeed through the eyewall, regardless of wind shifts while in heavy precipitation, and then make course adjustments once we’re in the clear. During the actual eyewall penetration, close scrutiny is maintained on the upcoming gradients and signs of small-scale rotation (hooks, protuberances, small-scale asymmetries), but the flight crews rarely need to turn away from features on the flight path.

Note: An interesting sidelight to the combination of C-band radars and hurricane eyewall dynamics is that we often encounter our largest updrafts, shears and turbulence exactly where nothing shows up on radar. Here’s why. Well-developed eyewalls tilt outward with height, visually referred to as the stadium effect inside the eye (or the toilet bowl effect if you don’t particularly care for this type of work). The ring of organized updraft that carries moisture rapidly aloft to quickly condense into copious rainfall gradually deflects outwardly as it goes up, eventually spiraling out anticyclonically above the storm as the Central Dense Overcast (CDO). As the rain falls out of this updraft, it becomes the highly reflective eyewall so vivid on radar. On the way inbound to the eye, this bright red band on radar naturally has everyone bracing for the worst, which often doesn’t happen. Then, as the aircraft clears the eyewall rainfall maximum, between the heavy precip and the cloud free eye, we frequently encounter the ‘well organized updraft’. This happens as the cabin is brightening up after the ominous darkness of the eyewall, just as we’re about to break out into the clear, and can profoundly catch the unwary by surprise, just as they’re reaching for their sunglasses.

The AOC flight crews worst hurricane experiences have usually been accompanied by well-known radar limitations that helped mask the true scope of the hazard ahead. In one case, flying an asymmetrical eyewall (most of the strongest eyewall thunderstorms stacked on only one side of the center) at low altitude, the P-3 took repeated 2G ups and downs flying upwind just to break free of the eyewall, only to find ‘new’ intense rainbands just as bad immediately ahead. A combination of attenuation and beam filling had hidden these severe storms from view while we bounced through the eyewall. Twenty minutes and three thunderstorm-filled rainbands later, a beat-up and exhausted crew was thrilled to see the last of that sector. Our toughest recent story, including brief loss of control and failed engine at low altitude in Hurricane Hugo (1989), was an unexpected encounter with a mesocyclone (small-scale rotating system) embedded in the side of an intensifying eyewall. These unique features, larger in spatial scale than a tornado but much smaller than the circulating eyewall, are often invisible to radar, as it was this case.

Thank you, Mr. Parrish. And now back to our lesson...

Having your own sensing system on your aircraft is a very good way to avoid thunderstorms while flying. It is NOT the course's intention to ever endorse any product. However I must let you see the state of radar technology. With that in mind, we will explore the current state of radar and lightning displays for aircraft. Some systems have even evolved to show wind shear locations. The next step for radar, will be to display turbulence locations. That's coming very soon.

Radar displays on the Flight deck

If you are interested, Honeywell describes its commercial aircraft doppler radar in this pdf file

American Airlines' Flight Operations Safety Department published this article on using the newest radar systems. Its called "Weather Radar 101."

By the way, Mr. Tom Horne, Editor-at-Large for AOPA Pilot Magazine and a member of the NWA Aviation Weather Committee, published this article on the "Realities of Radar." You might find it interesting.

Lightning displays on the Flight deck

So what is a lightning display for the flight deck? BF Goodrich, the manufacturer has the following website with a brochure on the product.

For those interested, here is an article from Flying Magazine on Stormscope tips.

The second lightning display is the StrikeFinder manufactured by Insight. Check this website for information on the display.

Some pilots may want to know which is better, radar or lightning displays? I have never flown with a lightning display so it wouldn't be fair for me to say. But I do want you to know some recent findings from science about lightning...

1. Lightning strikes get very numerous during the development stage of thunderstorms with rapid movements of air and water upward. However, as soon as the storm is about to dispense its worst weather hazards like downdrafts, macrobursts, microbursts, and tornadoes, there is a dramatic decrease in the number of lightning strikes. If you see a storm suddenly stop its lightning strikes still don't go there.

2. Lightning displays must assume an average lightning strike to determine distance. Like all things in nature, there is not a standard value to lightning but only a bell-curve distribution of values. Like all things in aviation, please leave yourself room to maneuver away from and around storms. Don't get too close.


There are also ways to get information about thunderstorms from your radio and NAVAIDS. These methods give you the bigger picture and help you see BEYOND your sensors and eyes.

Terry Lankford, a retired FSS specialist, author, and co-chair of the NWA Aviation Weather Committee, is a good source of information on the roles of the Flight Service Stations and how they can assist you in getting the 'big picture.'

by Terry Lankford

Flight Service Stations (FSS) are FAA air traffic facilities that provide preflight and inflight weather briefings, along with flight planning and other services. Selected facilities provide Enroute Flight Advisory Service—radio call "Flight Watch" and Hazardous Inflight Weather Advisory Service "HIWAS" broadcasts. (HIWAS is a continuous broadcast of weather advisories and urgent pilot weather reports (PIREPs) over selected navigational aids.)
The FSS provides pilots with access to aviation weather reports and forecasts. Many contain information on thunderstorms, among these are:




• NEXRAD weather radar (real-time)

• Weather Satellite images(real-time)

• Radar Summary Chart


• Weather Advisories, including Convective SIGMETs (WST), Center Weather Advisories (CWA), and Alert Weather Watches (WW)

• Area Forecasts (FA)

• Terminal Aerodrome Forecasts (TAF)

Significant Weather Prognostic Charts (PROGS)

Although pilots can obtain thunderstorm information through any FSS frequency, Flight Watch is dedicated to weather information. Flight Watch is specifically intended to update information previously received, and serve as a focal point for system feedback in the form of PIREPs.

Case Study

"A Bonanza pilot approached an area of thunderstorms in California's Central Valley. The pilot received the latest weather radar and satellite information, as well as PIREPs and surface observations from Flight Watch. The pilot safely traversed the area with minimum diversion or delay."

This is not a very exciting story, but that's the purpose of Flight Watch, to assist pilots in conducting uneventful flights.
ARTCC controllers are potentially helpful relaying reports of turbulence and icing, and providing advice on the location of convective activity, but the information is limited by equipment, and usually to immediate and surrounding sectors. Their primary responsibility is the separation of aircraft. On the other hand, Flight Watch has only one responsibility, weather. Flight Watch—with real-time—National Weather Service weather radar displays, satellite pictures, and the latest weather and pilot reports—provides specific real-time conditions, as well as the big picture. Additionally, Flight Watch controllers have direct communications with Center Weather Service Unit personnel and NWS aviation forecasters.

Continually updating the weather picture is the key to managing a flight, especially at high altitude in aircraft without ice protection and storm avoidance equipment, and with relatively limited range. A revised flight plan might be required. Flight Watch can provide needed additional information on current weather, PIREPs, and updated forecasts upon which to base an intelligent decision.

Many aircraft are equipped with airborne weather radar and lightning detection equipment. However, these systems are plagued by low power, attenuation, and limited range. A pilot might pick his or her way through a convective area only to find additional activity beyond. Flight Watch has the latest NWS weather radar information. Well before engaging any convective activity, a pilot should consult Flight Watch to determine the extent of the system, its movement, intensity, and intensity trend. Armed with this information, the pilot can determine whether to attempt to penetrate the system or select a suitable alternate. ATC prefers issuing alternate clearances compared to handling emergencies in congested airspace and severe weather.

So how do you get in touch with your FSS? Typically, pilots access the FSS for preflight briefings by telephone. The universal number is 1-800-WX-BRIEF (1-800-992-7433).

Inflight, pilots can obtain weather information through the FSS "Inflight Position" or "Flight Watch." FSS communication frequencies are published on aeronautical charts and in the Airport/Facility Directory. Flight Watch uses the common low altitude frequency of 122.00 MHz. For high altitude flights, each Air Route Traffic Control Center (ARTCC) has been assigned its own discrete frequency.

When contacting an FSS facility use the aircraft's complete identification, approximate location, and the frequency you expect a response (except Flight Watch).

For example:

"Rancho Radio, Cessna One One One Five Romeo, Fresno, listening One Two Two point Five Five, Over."
"Oakland Flight Watch (or Flight Watch), Piper Two Eight Six Two Tango, Monterey, Over."

Its really important that you know that you are part of the aviation weather system, too!

PIREPs are the most important ingredient for Weather Advisories and forecast amendments. Certain phenomena can only be observed by the pilot. An urgent need exists for information on weather conditions at flight altitudes, along routes between weather reporting stations—especially in mountainous areas—and at airports without weather reporting service. In many cases the pilot is the best and only source of actual weather conditions. The need for accurate pilot reports cannot be overemphasized.

ARTCC and tower controllers do accept PIREPs, but weather is a secondary duty and, unfortunately, PIREPs aren't always passed along. If at all possible, PIREPs should be reported directly to an FSS or Flight Watch.
Because of the hazardous and transitory nature of thunderstorms, PIREPs of thunderstorm related phenomena are paramount. As well as "ride" reports, the location and movement of convective activity is important. For the departure and arrival phase the existence of gust fronts and low-level wind shear (LLWS) should be reported. Many automated weather observations have limited, or no, thunderstorm reporting capability. Therefore, PIREPs may be the only information available about convective activity in the vicinity of the airport.

You can take a tour of the ABQ Flight Service Station if you want.

Let's now explore the local FSS that you deal with. Go to the FAA's FSS links page and find out which FSS serves your area. .
(The link provided in the original program is no longer active. Since the FAA frequently changes its web site, the best bet is simply to go to, and search from there for the particular information you need. Be patient -- it can be a difficult process.)

Hazardous Inflight Weather Advisory Service

HIWAS is a significant way to find out about the big weather picture. Recorded by FSS, they are broadcast on the frequencies of selected NAVAIDS. The station and frequencies are usually on the enroute charts you fly with or check the FSS websites in the previous paragraph of this course.

Center Weather Service Unit (CWSU) at ATC facilities and thunderstorms
The following lesson on the role of the meteorologist at the CWSU's came from Mr. S. Douglas Boyette who is a former dispatcher who has worked with the National Weather Service since 1986. He now serves as an Aviation Forecaster at the CWSU in Memphis, Tennessee.

Role of the ARTCC Meteorologist Pertaining to Thunderstorms

The FAA presently maintains Center Weather Service Units (CWSUs) within each of their 21 Air Route Traffic Control Centers across the lower 48 states and Alaska. Each of these CWSUs are staffed by National Weather Service meteorologists, generally operating during the peak traffic hours between 5:30 am and 10:00 pm seven days a week. The CWSUs came into being in 1980 due to a recommendation by the NTSB.

After examining a crash involving a Southern Airways DC-9 that flew into the hail shaft of a thunderstorm, the NTSB felt that having a meteorologist in each ARTCC would enhance safety. The ability to quickly pass hazardous weather information to the FAA personnel in direct communication with the pilot was the driving force.

Although low ceilings/visibilities, turbulence and icing can play havoc with en-route air traffic, thunderstorms cause the most trouble. Organized convection, such as squall lines or large clusters of thunderstorms (referred to as Mesoscale Convective Systems--MCS), produce most of the weather-related problems for both the airlines and controllers. Airlines generally do not prefer flying their passengers into thunderstorm activity, therefore en-route deviations or other "traffic management unit" (TMU) initiatives must be undertaken by the FAA. The end result? Obviously delays, but delays are a trade-off many people will accept if it means a safe flight.

In today’s world, there are rush hours in aviation just like on the ground. Since most of the major airlines operate under a hub and spoke concept, this requires large numbers of aircraft to depart and arrive into a handful of airports in distinct "rushes" each day. These rushes translate into large numbers of airplanes flying along the same airways at the same time. Throw large areas of convection into the mix and you have trouble, especially if the cloud tops are higher than FL410. For example, in the spring (and sometimes fall), long squall lines commonly form ahead of advancing cold fronts. A solid line of thunderstorms may develop from Chicago to Dallas and block off several major airways, requiring TMU decision-makers both locally and at the Central Flow Command Center in Washington, DC to orchestrate "programs" to effectively steer aircraft around the weather. Coordination is essential since there is no desire to re-route traffic unnecessarily. Meteorologists at each center are involved in these coordination events by providing two scheduled stand-up briefings each day for facility supervisors, supplementing those with various as-needed short-term forecasts for their respective TMUs. Center meteorologists are also involved on more of a national scale, by participating in the Collaborative Convective Forecast Product (CCFP). This product is issued every four hours by forecasters at the Aviation Weather Center (AWC) during the thunderstorm season. It is crafted upon completion of an Internet chat session, in which meteorologists from the CWSUs, airlines and AWC confer about the impending situation. The product is designed to better pinpoint areas of thunderstorms that will impact flight operations. Command Center personnel use the information from the CCFP in putting together their plan of action each day. If CWSU meteorologists can provide effective input about expected thunderstorm conditions several hours prior to an event, dollars can potentially be saved by avoiding unneeded delays and re-routes. Conversely, if action plans call for air traffic to be routed into areas that have a high probability of becoming blocked by thunderstorms, input from center meteorologists could perhaps save lives, and most certainly time and money. Yes, it is sometimes quite difficult to be accurate when forecasting thunderstorms, but therein lies the ultimate goal of the CWSU meteorologist: the safe and efficient flow of air traffic through their airspace.

CWSU meteorologists also issue short-term hazardous weather advisories in the form of a Center Weather Advisory, or CWAs. The CWA is similar to an AIRMET or SIGMET, but is usually issued for small-scale events, or in rapidly developing situations not yet covered by AIRMETs or SIGMETs. An example of a CWA pertaining to thunderstorms might be a rapidly developing, but isolated supercell. The storm may contain a tornado, but since it is isolated, most aircraft will have no trouble deviating around it. This information is mostly useful to smaller, lower flying aircraft, especially those without on-board radar, however if the storm is heading for an airport the impact would obviously affect larger commercial aircraft as well. This could include aircraft hundreds of miles away that are heading to that particular airport, who may need to be placed into en-route holding to allow for spacing should the thunderstorm temporarily close the field.

Want to interact with ATC? See where there are real-time CWAs happening now.

View the CCFP for today.

NWA Aviation Weather Committee member Steve Walden sent in this briefing showing just what an ATC enroute controller sees with the current and with the new radar screens. This program is called the WARP.

Pilot to Metro (USAF)

For members of the United States military, there is usually a weatherman only a radio call away while airborne. Usually, your needs are one of the highest priorities of the base weather stations.

The staff of the Directorate of Weather at Headquarters USAF prepared a lesson on the Pilot-to-Metro Service (PMSV) and the important information available on thunderstorms for this course.

Finally, contact your Dispatcher (if you are flying commercially and have one) for the big picture as time allows.

B efore we end this lesson, we want to make you aware of some research that taking place to help you and those involved with aircraft operations know where thunderstorms are located.

For those of you who fly over the ocean, there is the National Center For Atmospheric Research's Oceanic Convective Nowcasting project.

Well, thank you for joining us again for Lesson 4. We hope you've picked up some pointers on places to get thunderstorm information while you are airborne.
Your "homework" for the next lesson is to read the Microburst Handbook for Visual Identification.
Study Questions:
1. What is the difference between an older weather radar and the newer doppler radar?
2. What is the name of the new weather radar network now used in the United States?
3. How long does it take a WSR-88D to make one scan of the atmosphere and update a picture?
4. What does the word MESO mean on a Radar Summary Chart?
5. What does the word HAIL mean on a Radar Summary Chart?
6. What is the different types of satellite images?
7. How do you identify thunderstorms on a visible image?
8. How do you identify a thunderstorm on an IR image?
9. How fast does the National Lightning map update?
10. What is an LEWP?
11. What are the hazards that Mr Parrish mentions he has seen in thunderstorms?
12. How does Mr Parrish say NOAA crews avoid the worst weather?
13. What hazards do the NOAA crews avoid?
14. What is the most important lesson the NOAA crews receive about their radar?
15. What is attenuation?
16. What has happened that put NOAA crews in the worst hurricane experiences?
17. What is the newest technology on aircraft radars?
18. What is a lightning display?
19. How can the FSS help you avoid thunderstorms on the ground and in the air?
20. What is a HIWAS? How will it help you?
21. Do PIREPs help others?
22. What is a CWA? Who creates them? What is the CWSU?
23. When is there a meteorologist on staff at an ATC facility? When ISN'T there a meteorologist on staff?
24. What is the CCFP?
25. What is the role of the Central Flow Command Center?