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As usual this time of the year, while we enjoy some spectacular spring weather, our eyes are focused to the west on the next storm system to impact Alabama. Strong to severe storms could develop in advance of that system tonight over parts of West Texas and West Oklahoma, and SPC maintains a moderate risk of severe weather tomorrow in the general area from Fort Worth to Vicksburg. While all of this is happening, Alabama will enjoy another nice day tomorrow, with sunshine through high clouds and a high in the low 70s.
OUR WEEKEND: Strong to severe thunderstorms will impact Alabama on Saturday. Here are some issues that will come into play concerning the severe weather threat…
NEGATIVES FOR SEVERE WEATHER SATURDAY:
*The upper trough is a positive tilt one; many of our really serious tornado outbreaks here in Alabama are associated with negative tilt troughs, which can enhance upper diffluence and and amount of helicity (veering of the wind with altitude).
*A very stable airmass is in place now, and the degree of recovery (moving from a continental Polar to a maritime tropical airmass) is very much in question.
*The surface low really isn’t all that deep; it will be forming over West Alabama during the day Saturday, and is not forecast to drop below 1000 mb until it moves well northeast of here.
POSITIVES FOR SEVERE WEATHER SATURDAY:
* The NAM brings the dewpoint in Birmingham up to 64 by Saturday afternoon, and it calculates the surface based CAPE at 570 j/kg.
*A 73 knot wind max at 500 mb will be overhead during the event on Saturday, with strong low level winds as well.
*Winds at 200 mb (jet stream level) are forecast to be at 141 knots.
*The 0 to 3 km helicity according to the NAM is forecast to be 729 m2/s2; very impressive.
TIMING
Many questions about the exact time of the rain and storms due to outdoor events. The 12Z run of the GFS is coming in a tad slower; and is in pretty good agreement with the 12Z NAM. At this time it looks like the primary window for severe weather will come from about 9:00 a.m. until 5:00 p.m… with the storms entering West Alabama by mid-morning, then moving through the state during the rest of the day. The storms will end from west to east during the afternoon hours. It might be 6:00 to 7:00 p.m. before the final storms exit the far eastern part of the state and move into Georgia. We will be much more confident over the timing of the system once we begin to see how the system organizes on the east side of the Rockies tomorrow, so check our blog discussions for updates.
HOW MUCH RAIN?
The HPC guys are showing 2.5 inches of rain for Birmingham on Saturday; that seems way too aggressive to me. But, in their defense the NAM is now printing 2.37″ of rain for Birmingham, in pretty good agreement with the HPC outlook. I just have great fear the storms will be moving quickly on Saturday, which will limit the rain totals.
MUCH COOLER SUNDAY: Sunday looks like a blustery day. Clouds could linger most of the day with a very chilly north wind. The GFS continues to drop the temperatures; it now shows a high of only 54 for Birmingham on Sunday, and by Monday morning the low is now down to 33 (for Birmingham). Considering the amazing snow cover over the Midwest, I think these numbers are pretty good. In fact, I would imagine some parts of North Alabama won’t get out of the 40s on Sunday. There is a very real chance of frost and a light freeze Monday morning over much of North and Central Alabama…
NEXT WEEK: A weakening system will bring the risk of a few showers on Wednesday, but the best chance of rain with that feature will probably remain over South Alabama. The rest of next week should be dry.
LONG RANGE: Interesting to see the GFS shows another whopper of a trough over the eastern U.S. in 16 days with more cold air flooding the eastern half of the nation (cold for late April!). That might offer another chance of some frost or a light freeze if that happens to be correct… the latest freeze on record in Birmingham is on April 23; I wonder if that record might be in danger. We will just have to wait and see.
WEATHER PARTY: Get all the latest weather news over on our sister site, WeatherParty.com. Be sure and register while you are there; you can submit stories and vote on them to determine what is published on the front page. Lots of new news over there today… very interesting reading.
I do apologize to the kids at Chelsea Park Elementary… they were scheduled to be on the KIDCAM yesterday on ABC 33/40 News at 5:00, but due to the extended tornado coverage that video never made it out of the camera! They will be on today at 5:00, along with the first graders from Elvin Hill Elementary in Columbiana, where I spoke this morning. Both groups were a great audience.
I will have the next Weather Xtreme video posted by 7:00 a.m. tomorrow!
