Severe Weather Discussion for May 10-11, 2011

Severe Weather Discussion for May 10-11, 2011.
Issued:  05/09/2011.

Highlights:

–  One or two severe thunderstorms are possible Tuesday evening.  Primary threats are large hail and damaging winds.

–  Severe thunderstorms are possible on Wednesday.

Discussion:

Basics aspects of the forecast are unchanged yet again tonight.  Although there are complicating issues, especially for Wednesday.

On Tuesday, closed low remains well west of the region with 70F surface dewpoints to the east of a quasi-stationary dryline in western Oklahoma.  SPC has a slight risk for a small part of south-central Oklahoma, for what may be nocturnal activity.  00z NAM develops activity in Texas tomorrow late afternoon and dissipates it by early morning.  Given progged CAPE values of 2500-3000 J/Kg in this area, a large hail threat is likely.  So far we haven’t seen any heat bursts but wouldn’t be shocked to get something like that given very strong cap.  Additionally, NAM develops very light QPF along the dryline in NW OK tomorrow afternoon.

Setup for Wednesday has become much more muddied that prior forecasts and the 00z NAM did not alleviate this much.  All models develop convection in Texas Wednesday late morning into the afternoon hours.  The new NAM actually creates a robust line that moves across central Texas.  This appears to occur in response to a ill-timed subtropical shortwave trof.  Models have not been doing that great with this setup and I’m not quite sure if the NAM’s low QPF is enough to reduce surface temperatures Wednesday afternoon.  Even if a cirrus shield invaded the region, temperatures should hold steady much as they did today.  When OUN’s sounding launch, CAPE values were near 4500 J/Kg.  So, the thermo side of things will be difficult to pin down IMHO.  Wind shear wise, the 700mb winds could be stronger and the NAM will under forecast winds from time to time.  The rest of the wind fields are decent, although not overly impressive.  However, given the potential for high instability, it may not matter too much.  At this juncture, thunderstorms seem likely on Wednesday, question remains if the potential of the event can be fully realized.

I don’t have a gut feeling on what SPC will do on the morning Day 2, I know a slight risk is a given.  Whether or not they go moderate is iffy.  I went ahead and put 50% in there to hedge my bets.  I see arguments both ways.  They may do it at 17:30z after 12z GFS/NAM runs.

We’re very much interested in chasing on Wednesday and will likely go if conditions warrant.

Probabilities:

Risk area for any part of OK (valid:  05/10 Day 1, Day 2):

Slight:  75%, 100%
Moderate:  0%, 50%
High:  0%, 0%

Chase Status:

Level 3 – monitoring Wednesday.

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2 Responses to Severe Weather Discussion for May 10-11, 2011

  1. Wade says:

    I live in Central Texas (Waco) just how severe would you say this can get Wed. Night?

    • Brett LaBare says:

      Higher risk is further north from N TX thru OK. Still in a risk towards Waco though. Keep an eye on the sky!

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