Sunday, April 24, 2011

An Active Two Days Ahead

The next two days across East Texas could be very active weather wise, potentially life threatening. Two mid level disturbances will be moving through the area over the next 48 hours. The first is progged to move through Monday afternoon and evening and the second 24 hours later late Tuesday. As these systems move through the area strong to severe storms will develop across the area with a few of these storms producing very large hail and isolated strong tornadoes. So, I thought I would give a detailed look at how the atmosphere is setting up for what could be a historic weather day.

Monday the first mid level disturbance will swing through the Red River Valley by the evening hours dragging a dryline into the western counties of East Texas. Along this dryline thunderstorms will develop as peak heating provides plenty of instability. MLCAPE values will approach 2500 J/kg and combine this with 0-6km shear between 50 and 60 knots, the atmosphere is primed for robust rotating updrafts capable of producing strong supercells. By looking at the sounding for Tyler at 7PM Monday,
we can see there is ample instability for storms along with a fairly decent amount of low level turning of the winds with height. This will increase the tornado threat with any supercell that develops. Right now it appears that isolated supercells will develop wets of the Trinity River around 3PM and make their way across East Texas during the late afternoon and evening hours. In addition to a tornado threat, the amount of instability and shear will combine to make very large hail a significant threat. I would not be surprised to see a few reports of hail between baseball and softball size Monday afternoon and evening.

Now normally when we see a significant severe weather event here in East Texas the following day is usually calm. With this event, another mid level disturbance is forecast to move through the area. This system will develop a surface low near the Metorplex. This low is forecast to move northeast towards Texarkana during the overnight hours. This will bring another dryline through East Texas followed by a cold front. By looking at the forecast sounding for Tyler
we once again see an ample amount of instability but this time the low level turn of the winds with height is much stronger thanks to the aforementioned surface low. 0-1km SRH is forecast to be over 300 Tuesday afternoon making significant tornadoes a threat. In fact the significant tornado parameter is peaking at 13.6 Tuesday afternoon just north of Tyler.
Whenever we see values this high we become very concerned about the possibility of EF-4 and EF-5 tornadoes. The last time I saw a STP value actually that high was the day of the Yazoo City EF-4 tornado last year.

A lot could change between now and late Monday and Tuesday. Tuesday significant tornado threat is dependent on the actual track of a low pressure that has yet to develop. But right now it does look like a very active day for areas east of I-35 Monday and Tuesday and that includes all of East Texas. The Storm Prediction Center has all of East Texas under a slight risk of severe weather including a hatched outlook, meaning significant severe weather is a threat. More than likely much of East Texas will be under a moderate risk of severe weather come tomorrow. As for Tuesday's official forecast. Most of East Texas again is under a slight risk but if the current forecast holds true, I think we will once again be under a moderate risk if not a high risk on Tuesday afternoon.

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