Expand your thunderstorm forecasting skills

4 min read

Ask any experienced meteorologist, and they will tell you that convective forecasts are often quite challenging. Ask any experienced pilot, and they will tell you that convective forecasts are often less accurate or reliable the further you go into the future.

Thunderstorms and clusters of thunderstorms often intensify and weaken constantly over their lifecycle, and the threats they pose can rapidly evolve over time. Even with the volatility and uncertainty surrounding convection, products like the Extended Convective Forecast Product are helpful for determining how thunderstorms may impact your flight.

The Extended Convective Forecast Product (ECFP) Planning Tool – found at https://www.aviationweather.gov/ecfp and in popular aviation apps like ForeFlight in the “Imagery” section under “Extended Convective Fcst”  – is a graphical computer projection of the likelihood of thunderstorms.

The Extended Convective Forecast Product provides guidance on potential thunderstorm development out to 72 hours.

The product was designed to give ATC managers, flight planners, and other groups supporting FAA operations an indication of where weather-related traffic constraints are likely to be focused at a given time. The computer model runs four times each day – at 3, 9, 15, and 21 UTC – with model run data made available about 3 hours after the model run begins.

The ECFP is not a human forecast. This graphical product is created from the Short Range Ensemble Forecast (SREF) Calibrated Thunderstorm guidance. Hashed areas represent a 40-59% probability of thunderstorms, solid lined areas represent 60-79% probability of thunderstorms, and solid blue filled areas represent a greater than 80% probability of thunderstorms. The word “ensemble” refers to a computer modeling system where multiple simulations are compared and aggregated to produce a final result.

The TFM Convective Forecast provides shorter range guidance on thunderstorm development for 2, 4 and 8 hours out.

The ECFP differs significantly from the TFM Convective Forecast (TCF), or Traffic Flow Management (TFM) Convective Forecast. The TCF product is created by a meteorologist and is a high confidence forecast for convection meeting specific criteria. You can view the TCF forecast at https://www.aviationweather.gov/tcf and in ForeFlight under “Convective Forecast” in the “Imagery” section.

The coverage and expected echo tops are specified in TCF forecast. Echo tops are not included in the ECFP product, and the shading in the ECFP product is not the same shading used in the TCF forecast. Meteorologists who produce the TCF forecast may review the ECFP guidance to target convective hot spots in the coming hours and days. You, as a pilot, may do the same during your briefing but know that reviewing radar, surface, SIGMET, PIREP, and other weather trends is essential.

While TCF and ECFP products are useful when investigating the likelihood of convection, we shouldn’t just rely on computer projections. We can also review NOAA Storm Prediction Center (SPC) forecasts, which are found at www.spc.noaa.gov or in aviation apps like ForeFlight. For the next 3 days starting with the current day, you’ll find the general thunderstorm probability and up to 5 categories of increasing convective severity.

The general thunderstorm area is forecast for a 10% or higher probability of thunderstorms. As warranted, SPC will issue a marginal, slight, enhance, moderate, and high risk for severe thunderstorms. For forecast days 4 through 8, the SPC may issue a 15% or 30% severe thunderstorm risk area. These are the equivalent of a slight and enhanced risk, respectively. The Day 1, 2, 3, and 4-8 day forecasts include a text discussion which provides insight on thunderstorm coverage, intensity, and threats. For the day 1 forecast, SPC produces a tornado, damaging straight-line wind, and severe hail forecast.

Not all forecasts go as planned, so it’s always a good idea to do your own reality check. When looking at the potential for convection, ask yourself key questions on the environment you’re flying into or through. Is there a front or area of low pressure in the area? Is air near the surface warm and humid, and is air aloft cold and dry? Is there a significant change in the speed or direction of the wind with increasing altitude? Is it a time of year when thunderstorms or severe thunderstorms are common? All of these factors support convection.

Alternatively, we should look for factors that suppress convection, including sinking air caused by high pressure, cold and dry air near the ground, warm and humid air aloft, increasing temperatures with increasing altitude, and limited to no wind shear. Environmental analysis is critical for understanding how strong and organized storms will be or even if they will form at all.

The Extended Convective Forecast Product is a computer-generated product that can help you see areas where convection may have a significant impact on your flight a day or two out. There are differences between this and the meteorologist-created TFM Convective Forecast. Comparing the ECFP product against Storm Prediction Center forecasts and your own reality check will help you see the value that the ECFP brings to getting to your destination safely.