Monday Night

SPC has placed most of Alabama in a slight risk for severe storms
on Monday night, with areas to our west in a moderate risk.

00 UTC models are now mainly in. Looks like the surface low will stay to our NW, along a track from near Shreveport to Nashville Monday night. The low-level wind fields with this system will be very impressive. Winds just 1,500 feet off the ground will be 45 mph, with winds near 80 mph at 4,500 feet. This shear will cause 0-1 km storm-relative helicity values near 400.

The instability is still the main question, even with the surface low to our north. We could get into the 70s on Monday afternoon, and models bring the 60 dewpoint to near BHM Monday evening. But, the upper-level temperatures will not be too cold until the cold upper-low arrives on Tuesday. The NAM still shows enough instability Monday night for severe storms and tornadoes, the GFS shows less. However, as we saw last week, strong wind shear can make up for a lack of instability. It is still a very difficult forecast, in terms of the significance of this event, since the atmosphere over Alabama will change so rapidly.

It still looks like severe storms are likely, especially from I-65 west, with the main threat being from 5 pm Monday to 5 am Tuesday. Damaging straight-line winds will be a big threat, since low-level winds are so strong and it won’t take much of a storm downdraft to bring some of those winds to the ground. If we get the more unstable air predicted by the NAM, tornadoes may be a problem, also. Right now, the timing is one thing on our side, as the storm should come through during the night. That may be why the moderate risk is confined to Mississippi.

The details of this forecast may change some more, with such a dynamic system. Monday night will definitely be a night to have a source of weather information handy. And, remember, a 70 mph wind, whether it is straight-line or not, can cause significant damage, as we saw last week.

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