Severe Weather Discussion for May 8 – 11, 2011

Severe Weather Discussion for May 8 – 11, 2011.
Issued:  05/06/2011.


–  A few severe thunderstorms are possible in western Oklahoma Sunday and Monday.

–  Severe thunderstorms are possible on Tuesday in western and central Oklahoma.

–  Severe thunderstorms are possible on Wednesday across much of Oklahoma, except the panhandle and far western sections.

–  Fire danger will be extreme in western Oklahoma Sunday – Wednesday.


Large upper trough will take up residence across the western U.S. by Monday and be the primary influence for several runs of severe weather across the state.  SPC has appropriately risked Sunday, Tuesday and Wednesday for severe thunderstorms.  There are lots of considerations for the setup next week, however model agreement leads to decent confidence on the potential for severe thunderstorms.  How significant the event becomes will remain elusive for a few more days.

Sunday will see the continued increase of boundary layer dewpoints in the upper 60s with 850mb dewpoints in the 13-15C range. Models develop a very strong cap across the warm/moist sector as temperatures rise into the 90s.  West of the dryline temperatures will soar into the 100’s with surface dewpoints AOB 40F.  Shortly after 7pm NAM/GFS both forecast the dryline to retreat into the hot air and allow moistening of this airmass.  Models both develop QPF in southwest Oklahoma and this appears reasonable given the rapid moistening of a hot airmass and likely cap breach.  This is very similar to what happened May 9, 2003.  Directional and speed shear will be sufficient for severe thunderstorms, should any develop, with the primary threats very large hail and strong winds.  Since the the storms will be organized and supercells the primary type a tornado or two is possible but not currently expected.

Monday posses a similar setup although the dryline will not surge as Sunday.  Instead, deep layer moisture should continue to stream northward with surface dewpoints near 70F and 850mb dewpoints near 15C.  This yield CAPE values near 4000 J/Kg given temperatures in the 90s.  However, CIN values are a little lower with GFS near -200 J/Kg. but the NAM is around -100 J/Kg.  Tough call on storm development, but if they do develop they’ll be severe and likely supercells.

Tuesday and Wednesday remain the more interesting of the four days and the likely days for moderate risks.  Typically I issue this product only for moderate or greater events, which Sun/Mon don’t appear to warrant.  Since I’m already focusing on next week, makes sense to address it in discussions.  It is also on Wednesday where the models have the most run to run and inter-model disagreement.  Either way, enough confident exists for a risk area and SPC has done such.  18z GFS continues prior trends of ejecting the western U.S. trof slowly east and then through the state on Wednesday.  Deep layer moisture will remain across the state on both days with boundary layer dewpoints near 70F and 850mb dewpoints near 15C, possibly reaching 16C.  CAPE values will be AOA 3000 J/Kg on Tuesday and probably 2500 J/Kg on Wednesday.  This combined with deep layer shear should provide decent environment for supercells.  Storms on Tuesday are likely to be just a few as the cap looks to breach in a few spots.  Wednesday will likely see more widespread activity and early in the day as the cap completely erodes with the upper trof moving across the state.

Suffice it to say, that an active weather weeks looks to be upon us.  Models indicate a pretty significant blocking pattern developing across the lower 48 and this may put the state in a cool pattern with a trof trapped to the east of the state and one off the west coast.


Risk area for any part of Oklahoma (valid:  05/07 Day 2, Day 3):

Slight:  100%, 75%
Moderate:  0%, 0%
High:  0%, N/A

Chase Status:

Level 4 – watching Sunday and expecting higher-end activity Tuesday/Wednesday.

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