Re: Oklahoma Severe Weather Discussion - May 2011
So going to get kinda serious now about today, Sunday the 22nd. I've been pimping this day out since the 14th that it could be a medium to high end severe weather day. GFS has stuck to its guns for what...8 days straight now. NAM came into line tonight. So what do we have.
Things to watch - 1) Dryline placement. 2) Cap strength. Both of these will be key factors tomorrow. This evening the dryline has backed into western OK extending from Cherokee to Fairview to Weatherford to Mangum. It will probably settle a bit more to the west before daylight. It will then start to move east during the day. Here is the tricky part. GFS and NAM bring it into the OKC Metro area by 6-7PM. However, other short term guidance models (namely the SPC/NSSL model runs and HRRR) accelerate the dryline east past the OKC area by early afternoon. This would take with it the main risk for storms tomorrow. The other issue is going to be cap strength. Forecast soundings have it roughly around a 3, which is pretty tough but not unbreakable. We are going to have some fog tonight with a tone of moisture out there, so the sooner we can get sunshine the more favorable it will be to break the cap.
The models do give their preference on where storms will start, but coverage will be spotty and it really just depends on the dryline position. With the increased moisture out there, the greening up we've done in the last week, and looking at today as an example - it will be rough for the dryline to really push east too far. Today it got right up into the OKC area around 3PM but went back west extremely fast after 6PM. We will just have to wait and see. The main threat area tomorrow will be roughly 20-30 miles east of the dryline location (based on typical initiation point and how far storms will go until getting severe).
So let's look at the conditions, as an average, across the OKC area. I won't focus on specifics for one point because if the dryline is sitting right on I-44 tomorrow...NW OKC will be one thing, Midwest City could be another. So moisture availability looks good tomorrow. Deep moisture, dewpoints in the high 60s and low 70s look likely. MLCAPE across the area will range from 2500 up to 5000 j/kg tomorrow...so plenty of instability. CINH will be relatively high through early afternoon and then fade away...but not completely. Helicity values look solid. Forecast sounding looks good. Almost a due west wind from 500 mb and up, with backing winds at the surface that will be SE to S ahead of the dryline. Additional indices on the sounding look favorable for high end severe weather...strong shear and a moderate cap could make for an interesting day.
So here is the official SPC outlook, which will change through the day. Remember, if you are east of the dryline - you need to be very aware to weather tomorrow. The tornadic probabilities for tomorrow do have a wide around 10%, and this is a hatched area so strong tornadoes are possible. Damaging hail will also be possible - again a hatched area there. Wind is going to be a lesser threat.
The slight risk is along and east of a line from Ponca City to Kingfisher to Frederick. The 10% Hatched tornado risk is along and east of a line from 20 miles East of Ponca City to near Perry to El Reno to Anadarko to Lawton to Waurika.
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1258 AM CDT SUN MAY 22 2011
VALID 221200Z - 231200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF THE SRN PLAINS THROUGH THE MID MS VALLEY...GREAT LAKES ...AND OH VALLEY...
...SYNOPSIS...
CLOSED UPPER LOW OVER THE NRN PLAINS WILL DRIFT SLOWLY EWD INTO THE UPPER MS VALLEY SUNDAY...WHILE UPSTREAM TROUGH AMPLIFIES ALONG THE WRN U.S. COAST. IN BETWEEN THESE TWO FEATURES WEAK SHORTWAVE RIDGING WILL SHIFT INTO THE CNTRL AND SRN ROCKIES. AT THE SURFACE AN OCCLUDED LOW WILL ACCOMPANY UPPER LOW CIRCULATION. ATTENDANT FRONT WILL TRAIL SWWD THROUGH THE UPPER-MID MS VALLEY AND ERN KS. DRYLINE WILL EXTEND FROM THE BIG BEND AREA OF TX THROUGH CNTRL OK INTO KS WHERE IT WILL INTERSECT THE FRONT. WARM FRONT SHOULD CONTINUE TO LIFT NWD THROUGH THE OH VALLEY INTO THE GREAT LAKES.
...SRN PLAINS...
OVERNIGHT CONVECTION IS IN PROCESS OF DIMINISHING ACROSS TX AND THE LOWER MS VALLEY. RICH GULF MOISTURE WITH LOW 70S DEWPOINTS WILL PERSIST BENEATH STEEP LAPSE RATES ASSOCIATED WITH EML PLUME AND WILL LIKELY ADVECT FARTHER NWD INTO SERN KS AND SWRN MO. THE WARM SECTOR IS EXPECTED TO BECOME VERY UNSTABLE AS THE BOUNDARY LAYER WARMS DURING THE AFTERNOON WITH 3000-4000 J/KG MLCAPE. WEAK HEIGHT RISES AND WEAKENING LOW LEVEL FLOW WILL OCCUR OVER THE SRN PLAINS DURING THE DAY AS UPPER LOW DRIFTS TOWARD THE GREAT LAKES. THESE FACTORS ALONG WITH PRESENCE OF CAP ATTENDING THE EML COULD POTENTIALLY LIMIT STORM COVERAGE. NEVERTHELESS...AT LEAST ISOLATED STORMS SHOULD DEVELOP AS THE DRYLINE MIXES EWD ESPECIALLY FROM NWRN TX INTO CNTRL/ERN OK INTO SERN KS WHICH WILL RESIDE WITHIN EXIT REGION OF UPPER JET. GIVEN THE MAGNITUDE OF INSTABILITY WITH HIGH VALUES OF NORMALIZED CAPE AND EFFECTIVE SHEAR SUPPORTIVE OF SUPERCELLS...VERY LARGE HAIL WILL BE LIKELY. LOW LEVEL SHEAR WILL ALSO IMPROVE TOWARD EVENING AS SRN BRANCH OF LLJ STRENGTHENS. THE SHEAR AND INSTABILITY PARAMETER SPACE WILL ALSO SUPPORT POTENTIAL FOR ISOLATED STRONG TORNADOES FROM LATE AFTERNOON INTO THE EVENING. A MODERATE RISK MAY BE NEEDED FOR A PORTION OF THIS AREA IN LATER OUTLOOKS ONCE STORM COVERAGE CONCERNS HAVE BEEN MITIGATED.
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Originally Posted by bucktalk
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