WEATHERAmerica SUMMARY, Saturday, April 20, 2024

[Larry Cosgrove]

Is "Tornado Alley" about to light up with severe thunderstorms and heavy rain threats?

Most probably yes. At this time of year, when a broad 500MB trough is matched against ridging along the Eastern Seaboard, the result is a three-way convergence of cP/cT/mT air masses from Texas into the middle and lower Missouri Valley. If enough energy and cold air are present aloft in the body of the trough complex, repeated pulses of convective formation will occur to the right of the dry line and along/below the surface warm front. This type of alignment is present during the 6-10 and 11-15 day forecast periods. If the longer term models are correct, the pattern goes nowhere.

Ultimately this configuration must retrogress and retreat northward as we get closer to summer. In these days of warmer temperatures related to climate change (observed since 1990, so no ignoring or discarding the effects), it is wisest to boost subtropical high cores at 500MB 5 to 10 degrees in Latitude, So using the analog projections (which go into the latest summer season forecast), the heat ridge over Oaxaca state in Mexico should be in Texas, and the ridging over Puerto Rico across the Sargasso Sea. The northward translation of these features would probably get underway during the middle of next month. As we progress into the JJAS time frame, a conjoined Sonoran + Bermudan ridge complex will probably scorch most of the eastern 3/4 of the USA, with the only cooler values evident along the West Coast and possibly Quebec into New England.

If you are into excess heat and humidity (with severe weather across southern Canada), this should be a very interesting summer. In the meantime, buckle up your safety belts and hunker down for repeated cases of intense convection from Texas into Nebraska and Iowa.