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SPC has now defined a slight risk of severe thunderstorms for a large part of Alabama today. Pretty much a classic case of good dynamics, and marginal thermodynamics. A strong, negatively tilted upper trough will sweep through the Deep South today, and a good surface low over Central Illinois and very respectable wind fields at the surface and aloft. However, surface dewpoints are pretty low now, meaning very limited instability. As I write this update, Birmingham’s dewpoint is only 49. We do note the dewpoint at Mobile is up to 62, and we will be watching the progress of that airmass during the day today.
Seems like the “sweet spot” for the stronger storms might be between Montgomery and Birmingham sometime between 11:00 a.m. and 5:00 p.m. Remember, when it comes to thunderstorms, expect the unexpected, so we will be watching the radar screens closely today.
I still don’t think rain totals will be all that heavy; the NAM shows 0.40″ for Birmingham with today’s event, while the GFS indicates only 0.29″.
TOMORROW/FRIDAY: These days should be very nice with ample sunshine and comfortable afternoons. However, the models have backed way off on the degree of warming. Just a couple of days ago, the GFS was showing low 80s tomorrow and mid 80s on Friday. Now the GFS and the NAM are giving us a high near 70 tomorrow, with only low to mid 70s on Friday. The air advecting into Alabama tonight and tomorrow will be coming across the snow cover over the Midwest, and I think the cooler temperatures are correct.
SATURDAY: Another strong system will impact Alabama as we begin the weekend. Again, the GFS shows a positive tilt upper trough, suggesting the greatest threat will probably come from a squall line with strong, perhaps damaging straight line winds. It is also interesting to note the GFS is trying to push the line through here Saturday morning, which would mean very limited instability. On top of that, the surface low really doesn’t deepen until it is well to the northeast of Alabama. So, it remains to be seen if this will be a big threat.
The line of storms should enter West Alabama in the 6:00 a.m. to 8:00 a.m. time frame, then moving quickly through the state, finally moving into Georgia sometime between 1:00 and 4:00 p.m. The 00Z GFS is a little faster than this… lets watch the 12Z run before we make any more changes.
With the line moving through pretty quickly, I figure rain amounts on Saturday will be on the one-half to one inch range. The guys at HPC are really aggressive on the QPF (expected rain) here for the next five days… their graphic is showing between 3 and 4 inches. Seems to be that is overdone, I am afraid the combined rain total from today’s system and the one on Saturday will be closer to one to one and a half inches for most Alabama communities.
SUNDAY: Clearing, windy, and cooler weather is likely Sunday. The latest GFS now prints 42 for Birmingham Monday morning; I still think colder spots in North Alabama will reach the 30s with some potential for scattered frost.
NEXT WEEK AND BEYOND: The 00Z GFS brings back a chance of rain at the middle of next week on Wednesday, but the surface low is near Panama City, and the heaviest rain remains south of here. The model run has also backed off on the strength of the system around April 24, but that is all voodoo for now.
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This morning I will be speaking to the kids at the all new Chelsea Park Elementary School in Shelby County; then I will be back in the office and should have the afternoon Weather Xtreme video posted by 3:30, assuming the thunderstorms around here don’t get out of hand. J.B. will have updates on the blog through the day as the storms develop…..
