Another brisk cold front moves through the Brazos Valley this afternoon and evening, bringing yet another shot of some unseasonably chilly air. Temperatures reached the lower 80s Monday afternoon and will climb into the mid to upper 70s today, not quite as warm because of the increased cloud cover. The cold front will bring about a 25-degree drop in temperatures, knocking lows back down into the 40s Wednesday morning and highs only in the 60s. We'll see a slight chance of showers along the front, and the chance of rain will continue tonight and Wednesday as an upper level disturbance trails the front.
Temperatures for the month of April are running more than two degrees below average here in the Brazos Valley, and several big late winter storms have moved across the nation's mid-section. Why the cooler temperatures this Spring? Look at the jet stream. The strong winds in the upper level flow are what guide the movement of storm systems and fronts at the surface. The upper level flow for much of this Spring has had a high amplitude, more of a north-south flow rather than east-west. That allows the jet stream to go further north, grab the colder air and then carry it further southward than usual.
Even though Spring seems to be hitting the pause button on a weekly basis, there is one really good side effect. The cooler temperatures have kept the severe weather season in check for the most part this year, and the number of tornadoes in March was the lowest in 35 years with only 17 on the books. So far in April, 44 tornadoes have been confirmed, but the numbers could start to climb as the jet stream undergoes some pattern changes.
Computer models are showing this upper level pattern becoming more zonal, or east to west, and then high pressure building over the continental U.S. which is more of a Summer pattern.
And as the cold fronts wane and warmer air spreads northward, severe weather season and the number of tornadoes is likely to be on the upswing.