SWOMCD
SPC MCD 181944
OKZ000-TXZ000-182045-
MESOSCALE DISCUSSION 0804
NWS STORM PREDICTION CENTER NORMAN OK
0244 PM CDT WED MAY 18 2011
AREAS AFFECTED...WRN/CNTRL OK...PORTIONS OF N TX
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 181944Z - 182045Z
THE POTENTIAL FOR CONVECTIVE INITIATION APPEARS TO BE INCREASING
THIS AFTERNOON ACROSS WRN OK AND PORTIONS OF N TX...ALTHOUGH SOME
UNCERTAINTY STILL REMAINS. THE ENVIRONMENT WILL BE FAVORABLE FOR
ISOLATED SUPERCELLS CAPABLE OF PRODUCING VERY LARGE HAIL AND
POSSIBLY TORNADOES. THE AREA IS BEING MONITORED FOR A POSSIBLE WW.
STRONG DIABATIC HEATING ACROSS WRN OK HAS RESULTED IN AN EWD
ADVANCEMENT OF A SFC DRYLINE...POSITIONED FROM 40 SSW SPS TO FSI TO
40 NE CSM /PER 19Z SUBJECTIVE ANALYSIS/. THIS FEATURE IS ATTENDANT
TO A DEEPENING SFC LOW...AND A DIFFUSE BAROCLINIC ZONE/WARM FRONT
PROTRUDING ESE ACROSS CNTRL AND SERN OK. THERE IS SOME UNCERTAINTY
REGARDING CONVECTIVE INITIATION AS RECENT SFC OBSERVATIONS HAVE
INDICATED WINDS IN THE POST-DRYLINE ENVIRONMENT HAVE BACKED TOWARDS
THE S /LIMITING LOW-LEVEL CONVERGENCE/. THIS MAY BE OFFSET BY AN
AREA OF IMPLIED ASCENT THAT APPEARS TO BE SPREADING EWD OUT OF THE
SRN HIGH PLAINS...WHERE A BROAD SWATH OF CIRRUS HAS DEVELOPED IN
RECENT VISIBLE SATELLITE/WATER VAPOR IMAGES. AS THIS APPROACHES WRN
OK AND NW TX...WEAKENING CINH AND INCREASING MID-LEVEL ASCENT SHOULD
LEAD TO A MORE FAVORABLE ENVIRONMENT FOR CONVECTIVE INITIATION THIS
AFTERNOON.
RICH BOUNDARY LAYER MOISTURE AHEAD OF THE DRYLINE /LOWER-MID 60S SFC
DEW POINTS/ ALONG WITH STEEP MIDLEVEL LAPSE RATES IN EXCESS OF 7 DEG
C PER KM HAS YIELDED MLCAPE VALUES OF 1500-2000 J/KG...WHICH WILL
SUPPORT A THREAT FOR VERY LARGE HAIL. ADDITIONALLY...ENHANCED
LOW-LEVEL WIND SHEAR RESULTING FROM BACKED FLOW /PARTICULARLY WITH
NWD EXTENT/...ALONG WITH A FAVORED DISCRETE CONVECTIVE MODE DUE TO A
SIGNIFICANT ORTHOGONAL COMPONENT OF THE EFFECTIVE SHEAR VECTOR
RELATIVE TO THE DRYLINE...SHOULD SUPPORT A THREAT FOR TORNADOES IF
LONG-LIVED SUPERCELLS CAN DEVELOP. HOWEVER...CLOUD COVER ACROSS
CNTRL OK HAS LIMITED HEATING/INSTABILITY PRIMARILY E OF I-35...WITH
SOME QUESTION REGARDING MAINTENANCE OF THUNDERSTORMS MOVING E OFF
THE DRYLINE.
..ROGERS.. 05/18/2011
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...FWD...OUN...
LAT...LON 36619876 36569810 36199732 34859686 33919697 33599725
33679820 33849867 34339871 34969856 35659892 36239896
36489880 36619876
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