‘Tis the season for severe weather — we are in the midst of the month of May, the most active time of the year for severe weather, especially tornadoes. Through at least Tuesday of next week, some parts of the Central US will be at risk for strong, damaging storms. This threat will really begin to ramp up on Thursday, but should become even more significant Friday into Saturday.
On Thursday, the risk for severe weather will span from eastern Wyoming — possibly even farther west into areas near the northern Rocky Mountains — through the southern Great Lakes region. The threat may begin early across the eastern portion of that highlighted zone as low pressure moving across the US/Canada border brings a line of thunderstorms through the upper Midwest Thursday morning. That line — assuming it holds together — may move through Chicago in the afternoon. Those storms will continue to track to the south and east, approaching the Ohio River Valley by the evening.
Meanwhile across the rest of the area we are watching closely for severe weather, the threat won’t really begin until Thursday night. That’s because a weak low pressure system will eject into the western Plains as well as the leeward side of the northern Rocky Mountains. Its stationary front spanning from southern Montana through the Midwest will lead to the development of showers and thunderstorms. According to the NAM model, it shows several supercell thunderstorms forming after sunset across Nebraska and the surrounding areas, which will pose the risk for tornadoes. Then as the night progresses, those storms should evolve into a weaker line of rain and thunderstorms.
Now Friday will likely be a big day for severe weather. It will be a classic setup with a digging jet stream over the western US thanks to an upper-level low. This jet stream will provide the upper-level support needed in the atmosphere for strong storms to form. Meanwhile at the surface, there will be plentiful moisture as it flows in from the Gulf of Mexico, mixing with the hot environment of the Central US. From West Texas up through South Dakota and even into parts of the Midwest, severe storms will be possible. We will especially have to watch west Texas due to the dry line, and central Nebraska thanks to the center of low pressure being located near there. This low pressure will be the ultimate trigger for this active weather Friday into Friday night.
During the day Friday, showers and thunderstorms will become widespread across the northern Plains and upper Midwest, which happens to be north of the stationary front still draped across the region. Some flooding will be possible. Now in terms of the timing of the severe weather, there appears to be some discrepancies among the modeling but there is still time for that to be resolved. As of now, we expect a line of thunderstorms to form across the western Plains along the dry line, which will eventually become the cold front, between the late-afternoon and the first half of Friday night. It’s important to note how much of this threat will take place overnight, so having the severe weather alerts activated on your phone will be beneficial to your safety because tornadoes, damaging winds, and large hail will all be possible.
Based on the forecast sounding from the GFS model (see below) for the Red River Valley Friday night, it shows pretty favorable ingredients for all forms of severe weather. This graphic highlights the significant wind shear that will be in place as well as the instability, conditionally unstable lapse rates, and numerous other variables.
The Midwest will also need to watch for a few stronger storms, especially Friday afternoon, but the activity will be relatively quiet compared to what will be taking place in the Plains.
As we mentioned, this severe weather outbreak will persist into this weekend as well as into at least early next week. On Saturday, the severe weather threat will shift just to the east, still putting much of the Plains at risk. That will shift even further east on Sunday toward the Mid-Mississippi River Valley. Then on Monday into Tuesday, a new storm system will bring the severe weather threat back to the southern Plains and lower Midwest.
We’ll have more details on these upcoming severe risks as the days approach.