Severe Weather Discussion for May 23-24, 2011

Severe Weather Discussion for May 23-24, 2011.
Issued:  05/23/2011.

Highlights:

–  Active severe weather day is expected on Monday across much of Oklahoma.  Primary threats are tornadoes, destructive hail, and damaging winds.

–  Active and potentially significant severe weather day is likely across much of central/eastern Oklahoma on Tuesday.

Discussion:

Overall forecast remains the same as noted a few days ago.  The main difference on Monday will be the lack of dynamic forcing across the region.  However, there could end up being some weak forcing and when combined with CAPE values of 3000 J/Kg and good speed/directional shear, severe thunderstorms are likely.  NAM surges the dryline east in southwest OK and I cannot discount this solution due to it being correct today.  00z NAM shows shortwave ridging to the west of the threat region Monday afternoon with a few small shortwave trofs.  Winds are decent with very favorable turning.  700mb is weaker than I’d expect but this may not be a huge deal.  NAM does seemingly over-convect tonight across northwest Oklahoma.  We’ll see in the morning, but the very high QPF in this area seems odd.    SPC has a moderate up and I’d expect it to continue since the atmosphere hasn’t been modulated across the threat area.  Numerous storms in Texas may somewhat impact moisture return, but not long enough to big a major issue.

Tuesday appears to have significant severe weather potential and the setup is largely unchanged from a few days ago, a rarity.  Wind fields actually increase in response to a shortwave trof moving towards the region on Tuesday while afternoon temperatures in the 80s and dewpoints near 70F yield CAPE values AOA 4000 J/Kg.  The dryline will likely surge to HWY 183 where it should provide a focus for supercell development during the afternoon hours.  Expected shortwave trof, degree of instability, and wind fields all point to a long-lived supercell threat.  SPC noted these issues in the morning Day 3 and see no reason why it won’t continue into the Day 2 outlook.  I went 50% on the High Risk, since this potentially warrants one.  I don’t seem them doing that on a Day 2, but we’ll see!

Probabilities:

Risk area for ay part of OK (valid:  05/23 Day 1, Day 2):

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

Chase Status:

Level 1 – if work allows, will be going out on Monday. Target area is Hobart to Weatherford.

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