…Alabama will deal with severe weather threat on Sunday…
We are dealing with another borderline severe weather event on this Sunday in Alabama. Evening run of the NAM showed some interesting results with higher instability in the I-20 corridor starting around noon.
The Storm Prediction Center has much of the state outlooked for the possibility of severe weather tomorrow. It is a developing situation that will have to be monitored durign the next 24 hours. Keep a good source of weather information close at hand starting early tomorrow.
A powerful upper level system is sweeping out of Kansas and Oklahoma. A surface low is just north of Texarkana. The low will intensify rapidly overnight, going from 1001 mb to 988 mb by morning. This low will lift into Illinois during the day.
A powerful line of thunderstorms is pushing through western Louisiana and Southeast Texas tonight. There are two clusters of severe thunderstorm warnings tonight, over NW Louisiana and over SE Texas. The main line is past Shreveport. There is a tornado warning for Chambers and Galveston Counties in Texas at this hour.
That line will move into Mississippi after midnight and into western Alabama early this morning between 5 am and 8 am. I would not be surprised to see a watch issued for western sections during the pre-dawn hours.
Instability values are low across all of Alabama except for southwestern sections, but the strong forcing associated with the upper trough is enhancing the line of storms. Wind damage will be a possibility.
The line should reach the I-65 corridor by lunchtime. Even though instability will be limited, there will be sufficient shear for severe weather as far north of I-20. The primary threat will be damaging winds.
There are signs that instability values should increase this afternoon over the state. SOme indications are that eastern sections might be most affected, from Birmingham east, but it is too early to tell. Thw WRF spreads CAPE of 500 j/kg or greater over the eastern third of the state during the afternoon. THE GFS has been a little less bullish on instability, but as Brian noted, the NAM is stressing higher instability during the afternoon hours at BHM.
Wind fields will be strong at all levels across the state, with indications that an upper level wind max will move across the area this afternoon, enhancing the severe threat especially over southeastern sections.
Winds will be increasing through the night as the low deepens, averaging 10-20 mph overnight. It will be windy on Sunday, and wind advisories will be required.
The best combination of instability and wind shear should be south and east of a line of Birmingham to Atmore Sunday afternoon, where CAPE values could reach 750-1000 j/kg. This is where the best chance of tornadoes will be in Alabama.
Watch the 60F dew point line. This will indicate the northward extent of the severe weather area, with only isolated reports north of it. The latest NAM now has BHM dewpoints in the lower 60s
Please pay close attention to the latest weather information late tonight and on Sunday.
Bottom line is a line of storms in the morning, with some severe weather possible. Then an increased severe weather threat later as instability increases into the afternoon, with damaging winds and a tornado threat possible. The area will be defined as the system evolves.
Churches and other places of worship shoud review their severe weather safety plans before services in the morning and make sure that someone monitors real time weather information.
We will have updates here on the blog during the night and through the day tomorrow.
