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Storm chasing forecast update 3, for March 13
The Midwest's first big severe weather day will be tomorrow (Friday) evening as the big upper trough approaches, spreading fast upper-level winds overtop of surging low-level moisture. Even though we're approaching the 24-hours-prior mark, some uncertainties remain regarding the magnitude of the tornado threat. St. Louis will be squarely in the highest severe storm risk area (a Moderate Risk on the SPC's map) on Friday evening, with at minimum a powerful (potentially major) damaging straight-line wind event on tap.
The amount of low-level moisture return will dictate the extent of the tornado threat. This increasing moisture will be steadily moving north throughout the day ahead of the storms, and the extent of the tornado threat will depend on how much of this can occur prior to the storms' arrival. Right now, it does appear that enough moisture will make it to the Interstate 64 latitude around the I-57 corridor for the peak tornado risk that should occur an hour or two after sunset, mostly east of St. Louis. However, should the storms' arrival be delayed even an hour or two, that additional moisture could present a much more serious tornado risk for the St. Louis metro and points east.
SPC severe storm, tornado and wind risk areas for Friday evening
Even if storms arrive on time, there will be plenty of a moisture/low-level wind shear combo for a QLCS/mesovortex tornado threat through the metro area into central Illinois during the overnight hours, mainly along and south of the I-70 corridor. Forecasting where these small-scale circulations develop will be next to impossible until the storms are right on our doorstep, with any isolated storms and/or the north side of any gaps in the line being of the most concern.
In any event, these storms are likely to cause numerous to widespread power outages across the metro area and southern Illinois. As this is a solid "home area" risk, currently I am planning on staying close to or in St. Louis. It will be a night to pay attention to the weather via internet, radio and TV sources for warnings and be prepared to take shelter and/or a night without power. Storms will be moving fast, so getting timely warnings is important!
Another ripple in this trough will bring a second and potentially significant tornado event for the Deep South (south of I-40 into Mississippi and Alabama) on Saturday, which could prompt a trip out of the area. This will depend on several factors including how Friday's event evolves. Due to the fast-paced nature of Friday's and Saturday's events, I will likely not have an opportunity to post anything more on this system here until after both events are over.
As this system will bring only Midwest and South events, there is no chance for a Great Plains expedition during its passage through the central USA.
The following table charts the probabilities for a Plains storm chase expedition taking place for the date ranges shown:
| 2025 Plains Chase Expeditions - Probabilities as of March 13 |
| March 13-16 | 0% | |
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