The days of severe weather began this Monday, and the threat will worsen midweek as our storm system organizes and the ingredients needed for severe weather correlate closer together.
On Tuesday, severe storms will be focused in the Central Plains and Upper Midwest. Large hail, damaging winds, and several tornadoes are all expected with many of these storms. According to the Storm Prediction Center, the highest risk for these strong storms will be in northeastern Kansas, southeastern Nebraska, northwestern Missouri, and southwestern Iowa. This is the area where the best overlapping of ingredients will be found. Temperatures will be warm with highs mainly in the 80s. There will also be a moderate to high about of moisture with dew points in the 60s and 70s as well as instability, or Convective Available Potential Energy (CAPE), with CAPE values generally between 1200 and 3500 J/kg. In terms of winds, the strongest of winds in the low-level jet at 850 mb (5,000 feet) will be found in this area. These winds will come out of the south-southwest while winds at the jet stream level (300 mb or 30,000 feet) come out from the west. The strongest of these jet stream winds will be back to the west over the Rockies, so that will be one of the limiting factors. Therefore, widespread tornadoes are not expected but there will be a fairly high amount of spin present in the atmosphere, which may allow for several tornadoes to form.
Now let’s talk timing for Tuesday: There will be three different clusters of isolated to scattered storms present at sunrise, located over: northern Minnesota, eastern Nebraska/western Iowa, and eastern Kansas. Most of these storms will then dissipate by midday ahead of the main batch of storms that develop late in the day due to the daytime heating. Scattered showers and thunderstorms will first develop throughout the Central Plains and portions of the Upper Midwest by the late-afternoon. A more intense batch of thunderstorms is then expected to organize in the evening over eastern Nebraska and Iowa. This batch will track to the northeast toward southern Minnesota and Wisconsin overnight. Based on the future radar from the NAM model, this storm cluster may take on a “bowing-out” shape, which is an indicator for damaging winds. Meanwhile to the south and west, spotty storms, some of which will be supercells, may develop in Nebraska and Kansas. This is the type of storm that has the best chance at producing tornadoes. Now in the Southern Plains, many of the ingredients needed for thunderstorms and severe weather will be present, especially CAPE, but there will be a “cap,” or warm air aloft, which will prevent anything more than isolated storms to develop.
The biggest day for severe weather is expected to be on Wednesday. A much larger spacial area is at risk for severe storms, spanning from the Quad Cities through the Rio Grande Valley. The best chance for the most intense storms will be found in eastern Kansas and central Oklahoma, the two states that have been tornado-less through April, which is a new record. The reason why this day is expected to be more active and feature the strongest of storms is because of the better atmospheric setup. Temperatures will remain in the 70s, 80s, and even 90s while dew points increase into the 60s and 70s. There will also be higher CAPE values. Typically, the higher the CAPE values, the taller the thunderstorm, thus making it easier for hail to grow in size, especially because there will be cold air aloft. The upper-level winds will also be in a more favorable position with the 300 mb winds coming out of southwest at a stronger speed than on Tuesday while the 850 mb winds come out of the south with speeds up to 70 mph. It’s not the perfect setup for tornadoes because of the 45 degree turn in wind opposed to the 90 degree turn, but there will still be spin in the atmosphere which will allow for some tornadoes to form.
During the morning Wednesday, a few thunderstorms may be found in the Central Plains while that squall line that moved through the Upper Midwest Tuesday night tracks through Lower Michigan. Spotty damaging winds are possible there. Once the afternoon arrives, the activity will begin to increase with scattered showers and thunderstorms forming or becoming more widespread in the Central Plains and into the Upper Midwest. Storms will then form along a dry line during the evening hours in from West Texas up through central Oklahoma and eastern Kansas. This threat will continue into the overnight hours, so it’s important to have weather alerts activated on your device for your location because there is a significant risk for tornadoes in the middle of the night, especially in the Southern Plains. Rounds of showers and thunderstorms will also move through from the Upper Midwest through the Great Lakes and into the interior Northeast.
Now on Thursday, the risk for severe weather will continue, but it won’t be as widespread. Severe storms are even possible in portions of the interior Northeast, where even an isolated tornado is possible. Otherwise, some severe storms will be possible from the eastern Southern Plains up through the Midwest. Storms will be tracking east ahead of a cold front from eastern and southern Texas up through Iowa, where the low pressure will be located, during the day. Spotty storms are possible near the central Gulf Coast. Storms will also span through the Great Lakes and portions of the Northeast. Then overnight, storms are expected to dissipate for the most part in Texas while storms continue to track east into the Mid-Mississippi and Ohio River Valleys.
On Friday, the severe weather risk will be low, but isolated strong storms will be possible in the Northeast. A heavier cluster of storm may develop and persist through much of the day in the Rio Grande Valley of Texas. Otherwise, the line of storms will move through the Ohio and Tennessee Valleys during the day as well as into the Mid-Atlantic and Northeast, affecting areas mainly north and west of I-95. It’s not until Friday night when the storms will really weaken and much of the precipitation dissipates before the front reaches the coast. Nonetheless, scattered showers and thunderstorms will be possible from the Carolinas up through Maine overnight while heavier storms persist in the Rio Grande Valley.
Heavy rain and some flooding is possible, especially in the Rio Grande Valley and the Corn Belt. This is where a large area will receive two to four inches, and in some cases up to half a foot of rain.