Numerous rounds of low pressure moving from the northern Rocky Mountains through the Northern Plains will lead to the development of some severe thunderstorms through this weekend across the region. The pattern is rather messy and there’s no organized storm system, but multiple rounds of disturbances will be strong enough to spark off recurring rounds of thunderstorms in this part of the country.
As our Chief Meteorologist Joshua Feldman has noted, Lee Cyclogenesis will occur again as yet another low pressure forms on the leeward side of the Rocky Mountains. Attached to this low pressure will be a warm and cold front. These fronts will be the main instigators for the development of thunderstorms later today. As daytime heating increases, instability will rise with CAPE (Convective Available Potential Energy) values exceeding 3000 J/kg in some areas. When values reach this level, instability will be plentiful for thunderstorms to get going.
Severe thunderstorms will be possible across most of the Dakotas and into northern Minnesota and Wisconsin. The best risk for these strong storms will be found in North Dakota. This is due to the state having the most conducive environment based on its proximity to the triple point, which is where the fronts and low pressure meet. This morning, there is a MCS (Mesoscale Convective System) located over Iowa. This system will weaken midday as it tracks toward the Mississippi River. Meanwhile over the Northern Plains and Upper Midwest, it will be dry and sunny much of the day. Then at around 3pm CDT, a few showers and thunderstorms will begin to pop over eastern Wyoming, western Nebraska, and parts of Colorado. These storms will then organize into a line of scattered storms by sunset as they track to the north and east. New storms will also develop associated with this line further north over North Dakota. Given the scattered nature of these storms, not everyone will be affected by them. A few storms may also develop in the evening over the Upper Midwest, but the main, isolated risk for severe weather will be early in the morning on Friday.
A few tornadoes will be possible near the North Dakota-Canadian border as well because that is where the best wind shear will be located. The primary threat with this severe weather event will be the risk for damaging winds in excess of 58 mph and very large hail greater than one inch in diameter.
On Friday, the risk for severe weather threat will be much lower, but there is still much uncertainty and most of it will depend on how thunderstorms act Thursday night and what kind of environment they leave behind. A cluster of thunderstorms is possible over Minnesota Thursday night and may lead to hail and damaging winds reports into Friday morning across parts of the Mississippi Valley. The outflow boundary associated with these storms may promote the development of new storms Friday evening back into the South Dakota and Minnesota. Meanwhile farther west, a surface trough, which is an elongated area of low pressure, will likely allow for the development of scattered showers and thunderstorms across the Northern and Central Plains Friday evening into Friday night. Damaging winds and large hail are the main risks, but an isolated tornado cannot be ruled out.
The severe weather risk will then ramp up again on Saturday, again across similar areas including the Upper Midwest and Northern Plains. Clusters of strong to severe thunderstorms are expected to develop in the mid-afternoon and continue overnight associated with a broad area of low pressure. These clusters will form ahead of a stationary boundary draped across the weekend, and paired with somewhat strong winds aloft, moderate instability, and moisture, will promote strong thunderstorms.
We’ll have more details on these upcoming severe weather threats in the coming days.