Pilots have a built-in dread of inadvertently flying into thunderstorms. But there are some forecast tools that we should all be aware of — and use — in the convective season. Understanding them means fewer surprises, better flight planning, and less chance of stumbling into a storm.
These forecast tools can be found on several popular Internet Web sites. Sure, you can obtain a preflight weather briefing from DUATS, or go old fashioned and get a full, standard preflight briefing over the phone from a flight service specialist. Nothing wrong with that at all. But something very important will be missing: information from the latest storm forecasting technology, and imagery that informs much better than pages of text or a dry recitation of facts. Let's talk about four sites that deserve particular attention.
Meteorlogix
First off, there's the free weather information — provided by Meteorlogix — on AOPA's Web site ( www.aopa.org). There, over on the left side of AOPA's home page, you'll find a link that says "weather." Click on it, and you can select from the "surface weather" menu to get prognostic charts going out to five days; areas forecast to experience thunderstorms are shaded in red. Under the "radar" drop-down menu you can call up national weather radar imagery and view plotted and identified current convective sigmets. Regional weather radar imagery is also available.
For an extra $5.95 per month, AOPA members can subscribe to Meteorlogix's FlightBrief, an online source of aviation weather that has many more features than those on the AOPA home page. For more information or to subscribe, click on "FlightBrief.com" on AOPA Online's weather home page or visit the Web site ( www.flightbrief.com).
One of those features is the thunderstorm outlook. FlightBrief plots convective outlooks for the next 24 and 48 hours — something that can be of immeasurable value for advance planning. The charts use color-coded graphics to illustrate areas where both "general" and severe thunderstorms are expected. (Severe thunderstorms, by definition, imply surface winds of 50 knots or more, hail three-quarters of an inch in diameter, and/or tornados.)
When conditions are right, you'll likely see the terms approaching, slight, moderate, and high associated with the color codes. Approaching simply means that the forecast storms, while still dangerous, aren't expected to reach severe limits. The slight, moderate, and high labels refer both to anticipated coverage and storm severity — all of which are forecast to reach severe limits. Areas labeled slight mean that 2 to 5 percent of the shaded area may have severe thunderstorms; moderate coverage means that 6 to 10 percent of the area could have severe storms; and high implies more than 10-percent coverage by severe storms.
In addition, here's what the severity equivalents of each level of coverage translate into:
Slight risk implies forecasts of five to 29 reports of one-inch or larger hail, and/or three to five tornados, and/or five to 29 wind events with surface winds greater than 50 knots.
Moderate risk implies at least 30 reports of hail one-inch or larger, six to 19 tornados, or numerous wind events — 30 of which may be associated with squall lines or bow echoes and other dangerous radar signatures.
High risk implies a major severe weather outbreak, with at least 20 tornados (at least two of them rated at the F3 or greater level), and widespread wind events with gusts of 80-plus knots.
Storm Prediction Center
Like any other private weather service, Meteorlogix gets its storm prognoses from the National Weather Service's Storm Prediction Center (SPC). At the SPC's Web site ( www.spc.noaa.gov) you can also call up convective outlooks that venture predictions for three days ahead. Click on "Conv. Outlooks" on the left side of the home page to reach the text and graphics for the outlooks, as well as current mesoscale discussions (for those more inquisitive about the storm situation, or those with a meteorological background), fire weather outlooks, and other watches and warnings.
Aviation Weather Center
The NWS' Aviation Weather Center (AWC), together with airline meteorologists, puts out the CCFP — the Collaborative Convective Forecast Product. This shows areas of expected thunderstorm coverage over the next six hours, presented in two-hour intervals. Yellow-shaded plots show how areas of convection are expected to move, expand, or contract in the coming hours.
Aviation Digital Data Service
Forecast storm movement is also available from the Aviation Digital Data Service (ADDS) Web site ( http://adds.aviationweather.noaa.gov/projects/adds/convection/java/). Click on the "National Convective Weather Forecast (NCWF) Java Tool," and a map of the contiguous United States loads. Thunderstorms are shown as blue polygons, sized according to storm dimensions. From the menu below the map, you can select additional data to plot on the base map. These include storm speeds and cloud tops, and extrapolations for predicted storm movements and positions
one hour in the future. Previous storm locations also can be tracked. Storm intensities (using the standard radar reflectivity levels, from one through six) can be scrutinized by zooming in on an area of interest. You do this using the cursor to draw a box around the depicted storm cells. The resulting storm imagery is heavily pixellated, but useful nonetheless.
The Internet leads the way in presenting aviation weather graphics. Years ago, no one could have anticipated .he number and quality of weather products on the Web. Today it's taken for granted, and pilots in particular are the beneficiaries.
You owe it to yourself to check out these sources prior to flying this summer. A picture's worth a thousand words, you know.
E-mail the author at [email protected].
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