October 1, 2009
In a lonely, one-story, concrete building some five miles from the Kansas City International Airport, a group of 40 Aviation Weather Center (AWC) meteorologists toil around the clock. Their job: create the weather forecasts, advisories, warnings, and graphics that flight service specialists and the pilot community rely upon for sound preflight information. Oh, and the AWC also runs the very popular Aviation Digital Data Service (ADDS) Web site.
The yearly output from this squat, bunker-like building is impressive: 30,000 convective sigmets per year; 25,000 Collaborative Convective Forecast Products (CCFPs); 26,300 airmets; 6,600 area forecasts (FAs); and around 21,000 low- and high-altitude significant weather (“prog”) charts. It all adds up to a lot of work by a very small number of meteorologists—all of them working under constant, daily deadlines.
I visited the AWC on July 14, 2009, to get a feel for a day on the job. The day shift begins at 7 a.m. CDT, but waking up on this particular morning wasn’t a problem. Thunder shook my hotel room. Oh, well, I thought, at least I already know one thing about today’s weather—there’s a convective sigmet sitting right over Kansas City. But this early in the morning?
After getting past the rain and the guard desk, AWC Warning Coordination Meteorologist Pat Murphy gave me a quick briefing. Bottom line: The combined staff at AWC has more than 600 years of forecasting experience, and access to some really impressive data sets—all of them provided via immense computer power, and presented on workstation video monitors. This is the National Weather Service’s Advanced Weather Interactive Processing System (AWIPS) system. Another analysis and display program in use is N-AWIPS (National Advanced Weather Interactive Processing System). Altogether, each of the AWC’s eight operational desks (one for convective sigmets, one for CCFPs, three for airmets and area forecasts, one for tropical weather, and two for International Significant Weather and Oceanic charts) have 10 to 12 video monitors. If you can imagine any atmospheric variable or forecast model, it can be called up on AWIPS or N-AWIPS. Some stations have yet another video monitor—one that shows the view from the AWC’s rooftop. Think of it as an electronic substitute for a window.
All of this takes place in a single dark room with a tomb-like silence. Fact is, there’s little time to talk during the shift. There’s too much work. Meals are eaten at the workstation.
Working today’s convective sigmet desk is Andy Fischer, a University of North Dakota graduate. He’s been reviewing data and imagery since he arrived, and now he’s working on 10 active convective sigmets. “There’s a strong wave [a trough aloft] over the northern Plains, with some postfrontal weather over the Dakotas,” he says. “But what I’m seeing now is a continuation of the pattern we had two mornings ago, with a low-level jet stream at 5,000 feet, moving from the south to the Kansas City area. This moist trajectory of warm air is causing a mesoscale convective complex here—something I underestimated.”
Sure enough, there’s a huge, circular precipitation pattern overhead. Fischer speaks in bits of jargon as he drags and drops the redefined boundaries of his updated sigmet, which will be valid for two hours. “Got elevated convection, not surface-based like air mass thunderstorms. Moving east, slowly. Gotta check forecast soundings from the NAM, WRF, and RUC models to see if there might be more problems later today…look for a cap [a wedge of low-level warm air that can inhibit lifting of air parcels heated at the surface]. Yep, by 3 p.m. surface temps will be 95, so the cap near here could break and cause afternoon convection…but low-level humidity could go down, so storms could start to the west of here, at the 700-mb level where temperatures and dew points are forecast to merge.” As for the mesoscale complex, Fischer expects it to die off later in the day, as its precipitation moves into a drier air mass over Missouri.
Fischer draws more convective sigmets over Florida’s panhandle and Minnesota, then posts them. Soon, like all of AWC’s products, they will appear on the ADDS Web site and at flight service stations. It’s only 8:30 a.m., and Fischer has to watch for more signs of convection. As soon as they appear, he begins a mouse-clicking frenzy, checking Skew-T soundings, checking infrared satellite images against sounding plots for cloud top heights, and looking for short-wave troughs aloft for signs of the “spin” that can create lows and accelerate volatile air parcels upward. “Sometimes you can’t even see a short-wave except on a satellite view,” he said. “They can be as small as 100 miles in length.”
Working the “east” desk of this unit is Greg Poulos; Paul Smith is manning the central desk; and Pete Reynolds is in charge of airmets and area forecasts in the western United States. Poulos has 30 years of forecasting under his belt, and had his first day at AWC on September 10, 2001.
Today the East is quiet, compared to the raucous central United States. There’s an east-west stationary front across the southeastern states, some cloudiness over New England, and the chance of low- and high-altitude turbulence. Poulos says, “It helps to look at the previous day in a stagnant pattern like this, because the conditions tend to repeat themselves.”
Poulos calls up models showing low-level humidity in New England, checks METARs for temperature/dew point spreads, then looks at “Ellrod” models showing vertical velocities from 18,000 to 30,000 feet msl. “I’m seeing humidities of 80 percent in northern Maine and New Hampshire, so I feel confident putting mountain obscuration in my airmet. And the kinetic energy shown in the Ellrods make me think that high-altitude turbulence could be a problem. The water vapor imagery backs that up,” Poulos says. “Here, look at that sharp line between that streak of dry air and the clouds next to it. That says ‘jet streak’ to me, which implies turbulence at its margins.”
There will be a low-altitude turbulence airmet for New England, too. “From the surface to 10,000 feet, most low-altitude turbulence in conditions like these is terrain-driven,” Poulos said. “So I look at the 850-mb models to show winds of 25 to 30 knots. With the clear skies of southern New England, and those westerly winds we have, there will be plenty of mixing today with those winds flowing perpendicular to the mountains.”
Poulos also prepares an icing airmet for New England. “The satellite view comes first, then I check the freezing level up there—which is from 8,000 to 15,000 feet. The NAM [North American Mesoscale] model predicts cloud tops at 16,000 to 18,000 feet, but I don’t think they will be that high, so I’m going to say icing is possible to 15,000 feet. It’s colder up there and so there’s not much significant lift in that air mass,” he deduces. “This is where pireps would help us in the forecast,” Poulos adds. “But we don’t have any yet…must be too early.” Poulos tells me to urge pilots to make pireps, no matter the weather. “They are extremely helpful in verifying our forecasts,” he said.
Poulos is predicting morning fog in the Carolinas, southern Georgia, and northern Florida for the following day’s 09-12Z outlooks. “That’s because there will be evaporative cooling to the dew point after showers associated with the stationary front pass-through,” he says. As for Virginia, “there has been IMC in fog for the past three nights, so based on that I’m inclined to predict it again. But the models don’t show any surface humidities at 90 percent or greater, which is my benchmark for fog,” he said. “So, I’ll have to check the latest TAFs to see what the local forecast offices say about this, plus METARs in the area, for close temperature/dew point spreads. If they indicate fog, I’ll say fog.” So it’s an airmet for IFR in mist and fog for Virginia.
It’s now 9:30 a.m. and Poulos has written up his 1500Z airmets, which will be valid to 2100Z, or 4 p.m.—with outlooks to 0300Z, or 10 p.m. His next airmets are posted at 2100Z, which is a problem, because he goes home at 3 p.m. He’ll do as much as he can, then brief the night-shift meteorologist so he can finish the job.
Next comes the area forecast, which Poulos must send out at 1745Z, or 12:45 p.m. CDT. This stirs up a gripe.
“I have to write up a forecast using old TAFs, when I ought to have the latest, considering that my area forecast goes out eight hours,” Poulos said. “So the area forecast has to go out at 1745Z. OK, well, the new TAFs come out—guess when? At 1745Z! The same time! So I have to rely on the latest METARs and computer-model forecast information, checking all that just before post time.”
Meteorologist Paul Smith turns to me and says, “Well, I just finished tearing up my forecast! It was 200 characters too long!” He’s referring to another grievance shared by the AWC staff. Seems that a vestige of the teletype-transmission days of weather products lives on—in the form of a 3,884-character limit on text products. To meet the limit, forecasters must do some heavy text editing. “It’s a real problem, especially when you consider that a CAVU forecast can use up 60 percent of your allotted characters,” said Pat Murphy. “If there’s a lot of adverse weather, we have to be very succinct. So the forecasts are more coarse—meaning essentially that we can’t say all that we know.”
“By definition, we can’t put an IFR or low IFR forecast in our area forecasts,” Smith says. “Because we refer pilots to airmet Sierras for that, up in the forecast header. So to get around that, we’ll put in MVFR instead, just to give a heads-up. Something else we might do to meet the character limits are to say ‘3-mile vis’ instead of ‘3-5 mile vis’, or say simply say BKN skies when we have a good idea that skies will really be SCT to BKN. You can save some space that way. But it’s often hard to come under the character quota when the weather is active.”
Smith checks video monitors, and notes that the mesoscale system (the one that woke me up seven hours ago) has indeed faded away over eastern Missouri—exactly as he and Fischer had predicted. Then it’s back to the area forecast, and preparing for the next round of airmets. AWC will post a sequential loop of airmets (at the time a textual airmet is issued and three, six, and nine hours after) via its new G-Airmet feature (see “ Wx Watch: Greeting the G-Airmet,” June 2009 AOPA Pilot) on the ADDS Web site.
Senior aviation meteorologist Jesse Sparks, like Fischer at the convective sigmet desk, is responsible for putting out oceanic-based sigmets on an event-driven basis. Today, the tropics are fairly quiet. He’s working Sigmet Lima for storms over the Gulf of Mexico; Kilo for a thunderstorm complex over the Turks and Caicos Islands; Juliett for storms ahead of a trough off the North Carolina coast; and a tropical wave moving off Africa’s Cape Verde.
“We have convection today, but nothing really organized,” Sparks says. “Typically, jet streams over the African interior create low-pressure circulations below them, and then they form in a row and go across Africa, moving east to west and then into the Atlantic. I’d say 80 percent of hurricanes start out as Cape Verde circulations.” Today’s Cape Verde actions consists of two circular, adjoining radar signatures that look like a pair of menacing red eyes. But they mean no harm right now, Sparks says.
“We won’t even seriously look at a tropical storm unless there’s an anticyclonic cloud circulation pattern aloft. Basically, this is the exhaust of the tropical system, so this means that there’s an inflow feeding the circulation from nearer the surface. This Cape Verde system isn’t showing that right now—but it may in a few days.”
Sparks’ job may be uneventful today, but by late summer and early fall, this can change quickly as hurricane season reaches peak activity. That’s when a “hot line” connecting the AWC to the National Hurricane Center can light up.
Sparks said the hardest part of his job is that he has to write forecasts for most of the data-sparse Atlantic and Pacific oceans “relying only on satellite and scatterometer data.” Scatterometers are satellite-based detectors that infer surface winds by recording wave movements. “And I only get two scatterometer passes—one in the morning and one in the evening. And rain can block a scatterometer from seeing any waves.”
Meteorologists Ted Hoffman and Richard Douglas write oceanic sigmets and create graphics that feed the ADDS International Flight Folder. These global charts—which cover the altitudes between 25,000 and 63,000 feet—show jet stream flows, turbulence, tropopause heights, volcanic activity, thunderstorms, and tropical weather. Airlines flying long-haul routes consult these charts, which are produced four times per day.
Douglas, whom the staff has given the honorific title of Sensei (teacher), says that he now makes charts covering Antarctica. “Qantas and Air New Zealand now fly across the South Pole to South America, so that’s new for us,” he said. Meteorologists such as Hoffman and the Sensei put out 18,980 of these charts per year. They are valuable products for airlines seeking the fastest travel times with the fewest hazards. Every day, 1,000 flight folders are downloaded, at no charge, to users around the world.
What’s amazing about the AWC is not just its volume of work and level of expertise, but its truly cloistered environment. Sure, the meteorologists use direct observations (pireps, METARs, and satellite and radar imagery) to make their forecasts and warnings. But their work output is chiefly the product of computer-model analysis. In other words, they must rely on their education and expertise in interpreting the models, then temper those interpretations with the wisdom gained in years of forecasting. The choice of models and other forecasting tools are left up to each individual forecaster.
Forecasting can be a lonely calling, packed with what-ifs and when-wills. But if anyone’s up to the task, it’s the AWC team. We’re fortunate to have them by our side.
I’d just like to see aviation forecasts return to the practice of letting each forecaster “sign off” by adding his name to his work. The National Weather Service’s Storm Prediction Center still lets its meteorologists show pride of authorship, but for some reason the AWC has done away with the practice.
E-mail the author at email@example.com.
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