SWODY1
SPC AC 101952
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0252 PM CDT SAT JUL 10 2010
VALID 102000Z - 111200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL
PLAINS...NRN PLAINS AND UPPER MS VALLEY...
THREE CHANGES HAVE BEEN TO THE OUTLOOK FOR THE 20Z ISSUANCE. THE
FIRST IS EXPAND THE SLIGHT RISK AREA EWD TO THE SHORE OF LAKE
MICHIGAN ACROSS CNTRL AND ERN WI WHERE STRONG TO SEVERE
THUNDERSTORMS ARE ONGOING IN A MODERATELY UNSTABLE AIRMASS. ALTHOUGH
DEEP LAYER SHEAR IS NOT THAT STRONG ACCORDING TO REGIONAL WSR-88D
VWPS...OBJECTIVE ANALYSIS INDICATES THAT SFC TO 850 MB LAPSE RATES
EXCEED 8.0 C/KM. THIS ALONG WITH UNIDIRECTIONAL WIND PROFILES SHOULD
BE SUFFICIENT FOR ISOLATED DAMAGING WIND GUSTS. HAIL WILL ALSO BE
POSSIBLE WITH THE MORE INTENSE CELLS. THE SECOND CHANGE IS TO EXTEND
THE 5 PERCENT HAIL AND WIND PROBABILITIES WWD ACROSS ECNTRL CO AND
FAR SE WY. SEVERAL CELLS HAVE INITIATED IN THIS AREA WHERE STEEP
LAPSE RATES MAY CONTRIBUTE TO A THREAT FOR STRONG GUSTY WINDS AND
HAIL. THE THIRD CHANGE TO THE OUTLOOK IS TO MOVE THE 5 PERCENT WIND
PROBABILITY IN ERN NC TO JUST BEHIND A CONVECTIVE LINE ORIENTED
NE-SW ALONG A COLD FRONT.
..BROYLES.. 07/10/2010
.PREV DISCUSSION... /ISSUED 1114 AM CDT SAT JUL 10 2010/
...UPPER MS VALLEY SWWD INTO THE CNTRL PLAINS THROUGH THIS
EVENING...
MORNING WATER VAPOR IMAGERY AND 12Z UPPER-AIR ANALYSIS INDICATE A
COUPLE OF IMPULSES EMBEDDED WITHIN WNWLY FLOW REGIME...ONE OVER THE
ERN DAKOTAS INTO MN AND THE OTHER OVER CNTRL WY. THE FORMER IS
CONTRIBUTING TO ONGOING ELEVATED TSTMS THIS MORNING ACROSS NERN SD
AND CNTRL/SRN MN WITHIN A STEEP LAPSE RATE ENVIRONMENT. CONTINUED
DAYTIME HEATING COUPLED WITH A MOISTENING BOUNDARY LAYER SHOULD
ALLOW THIS ACTIVITY TO BECOME PROGRESSIVELY SURFACE-BASED BY
AFTERNOON...ROOTED WITHIN A MODERATELY UNSTABLE AIR MASS WITH MLCAPE
OF 2000-2500 J/KG. DESPITE A GENERAL WEAKNESS IN THE HIGH-LEVEL
WIND FIELD...FORECAST HODOGRAPHS INDICATE VEERING WINDS WITH HEIGHT
THROUGH THE LOWEST 5-6 KM AGL AND 25-35 KT OF DEEP-LAYER
SHEAR...SUPPORTIVE OF ORGANIZED STORMS INCLUDING SUPERCELLS CAPABLE
OF MAINLY DAMAGING WINDS AND HAIL.
MEANWHILE...EXTRAPOLATION OF UPSTREAM WY IMPULSE PLACES IT INTO WRN
SD/NEB PNHDL BY EARLY TO MID AFTERNOON. AIR MASS E OF SURFACE
TROUGH IS EXPECTED TO BECOME RATHER HOT...AND WHEN COUPLED WITH
DEWPOINTS IN THE UPPER 50S TO LOW/MID 60S...ENVIRONMENT ACROSS
CNTRL/ERN SD AND MUCH OF NEB WILL ALSO BECOME MODERATE TO STRONGLY
UNSTABLE WITH MLCAPE RANGING FROM 1500-2000 J/KG OVER SWRN NEB TO
3000-3500 J/KG ACROSS PARTS OF ERN SD. INCREASING INFLUENCE OF
ABOVE-MENTIONED SHORT WAVE TROUGH IN CONCERT WITH THE STRONG
BOUNDARY LAYER HEATING ARE EXPECTED TO FOSTER ISOLATED TO SCATTERED
TSTMS THIS AFTERNOON ALONG THE SURFACE TROUGH WITHIN A KINEMATIC
ENVIRONMENT FEATURING VEERING WIND PROFILES AND 30-40 KT OF
DEEP-LAYER SHEAR.
AS MENTIONED ABOVE...HIGH-LEVEL FLOW WILL REMAIN RELATIVELY WEAK
ACROSS SD...GRADUALLY STRENGTHENING WITH SWD EXTENT OWING TO ZONAL
UPPER-LEVEL JET STREAK IN PLACE FROM THE CNTRL ROCKIES INTO CNTRL
PLAINS. GIVEN SETUP WILL SUPPORT SUPERCELLS CAPABLE OF MAINLY LARGE
HAIL AND DAMAGING WIND GUSTS. THE GREATEST THREAT FOR A TORNADO OR
TWO WILL EXIST ACROSS ERN SD WHERE SLIGHTLY STRONGER LOW-LEVEL SHEAR
WILL COINCIDE WITH THE STRONG INSTABILITY. STORMS MAY GROW UPSCALE
INTO ONE OR MULTIPLE MCS/S TONIGHT WITH AT LEAST AN ISOLATED THREAT
FOR STRONG WIND GUSTS AND HAIL.
FINALLY...AN ADDITIONAL BAND OF TSTMS MAY FORM THIS AFTERNOON INTO
EVENING ALONG COLD FRONT SAGGING SWD INTO ND. WHILE ENVIRONMENT IS
NOT EXPECTED TO BECOME QUITE AS UNSTABLE AS POINTS TO THE
SOUTH...THE PRESENCE OF MODEST CONVECTIVE INSTABILITY AND VERTICAL
SHEAR MAY PROMOTE THE DEVELOPMENT OF A FEW SEVERE STORMS WITH THE
THREAT FOR HAIL AND STRONG WIND GUSTS.
...ERN CAROLINAS SWWD ACROSS GULF COAST STATES THROUGH THIS
EVENING...
12Z REGIONAL SOUNDINGS AND SATELLITE-DERIVED PW DATA INDICATE THE
CONTINUED PRESENCE OF A MOIST/UNSTABLE AIR MASS IN ADVANCE OF
SURFACE FRONT SLOWLY SETTLING SEWD. THESE SOUNDING DATA ALONG WITH
MORE CURRENT VWP OBSERVATIONS SHOW WLY LOW-LEVEL FLOW VEERING TO
WNWLY ALOFT WITH GENERALLY 20-25 KT OF DEEP-LAYER SHEAR. WHILE THE
MAJORITY OF TSTMS FORMING ACROSS WARM SECTOR TODAY WILL BE
PULSE-TYPE...THERE WILL BE SOME POTENTIAL FOR A CLUSTER OR TWO TO
ORGANIZE INTO A MULTICELL COMPLEX /WITH LOCALLY HIGHER WIND THREAT/
SIMILAR TO THAT WHICH OCCURRED OVER THE MIDLANDS AND PEE DEE REGION
OF SC LAST EVENING. DUE TO UNCERTAINTIES IN WHERE THIS MIGHT
ACTUALLY OCCUR...WILL MAINTAIN LOW WIND PROBABILITIES.
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