Some parts of the Plains, South and Midwest could pick up nearly 10 inches of rainfall in a week’s time, much of it falling on soils already saturated by recent deluges. Louisiana, Mississippi and other parts of the Deep South, which have already seen up to two feet of rain since the start of April, could be affected.
The heavy rains could spark pockets of flash and urban flooding, particularly in Texas and Oklahoma.
Severe thunderstorms on the Plains
Friday marked the start of a pattern switch in the skies above North America. The jet stream, a river of swift upper-level winds, will dive south over the Intermountain West and ride north over the Plains. That will pump warm, moist Gulf of Mexico air northward over the central United States this weekend, providing fuel for thunderstorms.
Severe thunderstorms are possible from the Texas and Oklahoma panhandles north to the Kansas and Colorado high plains Friday afternoon, some posing a risk for large hail or damaging winds. Moisture is lacking for now, though, translating to high cloud bases and a low tornado risk.
Additional storms will fire up Saturday from Colorado south into Mexico, affecting places including Denver, Amarillo and Lubbock. Humidity will rise gradually, making for a marginal chance of a tornado or two. Once again, wind and hail will be the main threats. The risk area expands east to include Oklahoma City on Sunday.
By Monday, a dryline will take shape — that’s the boundary between humid air to the east and arid desert air blowing in from the west. It will stretch through the Texas Hill Country north into the Panhandle and up into Oklahoma. As the dryline sharpens, “forcing,” or the impetus for triggering a storm, strengthens. However, a “cap” of mild, dry air several thousand feet above the ground will suppress storm growth, so anything that emerges will be isolated.
Severe thunderstorms are again possible Tuesday across the Plains ahead of an upper-level disturbance bringing a lobe of high-altitude cold air and spin. Texas and Oklahoma again appear favored. The active pattern continues the majority of next week with no immediate end to thunderstorm activity in the forecast.
Fortunately, while wind and hail will be an issue with storms, tornado risk will be more isolated, thanks to comparatively tame upper-level winds.
Flood concerns rise
Arguably more problematic will be the odds of flooding, which will extend well east of the Plains and into parts of the Midwest and the South. Storms each day may have a tendency to merge at night, racing east and dumping a quick inch or two of rain along the way. That will be an issue for places that see multiple waves of storms over the course of several days.
That axis of moisture and storminess will stretch northeast around a high-pressure system parked over the Southeast. That means that, in addition to the Texas, Oklahoma and Kansas corridor, a broader area from Louisiana and Arkansas through Missouri, Illinois and Indiana could receive appreciable rainfall.
Most will see a general two to four inches, but localized totals of six to 10 inches can’t be ruled out through late next week, especially along and east of Interstate 35 in Oklahoma and Texas.
Louisiana could get in on the action, too, though the greatest rainfall may stay just to the west. New Orleans has had approximately 24 inches of rain since April 1, more than three times the average. Any additional rain in Louisiana or Mississippi would result in more flooding.
Looking ahead, it appears the pattern will continue to remain active for potential severe weather deeper into May.
The National Weather Service Climate Prediction Center, meanwhile, is calling for toasty weather over much of the Lower 48, with the exception of the Upper Midwest, over the next month. Drier-than-average conditions will persist in the West, while the pattern will support more rainfall than is typical in the East.