SWODY1
SPC AC 301935
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0235 PM CDT MON AUG 30 2010
VALID 302000Z - 311200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NRN AND CNTRL PLAINS
INTO MN...
...NRN HIGH PLAINS...
HAVE OPTED TO ADD HIGHER PROBABILITIES FOR SEVERE ACROSS PORTIONS OF
THE NRN HIGH PLAINS FOR THIS AFTERNOON INTO EARLY EVENING -
PRIMARILY ACROSS SERN MT AND EXTREME NRN WY. THIS UPGRADE IS TO
REFLECT THE INCREASING CONVECTION THAT IS DEVELOPING JUST WEST OF
THE BIG HORN MOUNTAINS IN ASSOCIATION WITH A WELL DEFINED MID LEVEL
VORT MAX. WITH WEAK NELY LOW LEVEL FLOW ACROSS THIS REGION IT
APPEARS THERE IS AN INCREASING THREAT FOR DISCRETE SEVERE SUPERCELLS
CAPABLE OF PRODUCING LARGE HAIL...GUSTY WINDS AND PERHAPS EVEN AN
ISOLATED TORNADO.
FARTHER EAST...EARLIER FORECAST WILL NOT BE MODIFIED SIGNIFICANTLY
ACROSS THE DAKOTAS INTO NEB. LATEST SATELLITE/RADAR IMAGERY CLEARLY
DEPICT A WEAK IMPULSE EJECTING ACROSS WRN SD/NEB - WELL AHEAD OF
UPPER VORT. THIS FEATURE APPEARS TO BE RESPONSIBLE FOR THICKER
CLOUDINESS AND LIGHT PRECIPITATION THAT IS SUPPRESSING SFC
TEMPERATURES SOMEWHAT. EVEN SO...INCREASING LOW LEVEL WARM
ADVECTION AND GRADUAL BOUNDARY LAYER DESTABILIZATION ACROSS THE
PLAINS SHOULD ENCOURAGE STRONG-SEVERE THUNDERSTORM DEVELOPMENT OVER
THE NEXT 2-4 HOURS...ESPECIALLY ALONG LEADING EDGE OF WEAK
PRECIPITATION SHIELD.
..DARROW.. 08/30/2010
.PREV DISCUSSION... /ISSUED 1106 AM CDT MON AUG 30 2010/
...SYNOPSIS...
SIGNIFICANT IMPULSE HAS MOVED THRU WRN U.S. TROUGH AND CURRENTLY
ROTATING NEWD ACROSS CO/WY...WELL DEPICTED ON BOTH W/V IMAGERY AND
UPPER AIR ANALYSIS. SURFACE FRONT HAS STALLED FROM NWRN MN SWWD TO
DEVELOPING SURFACE LOW CENTRAL SD. GULF MOISTURE CONTINUES TO FLOW
NWD THRU THE PLAINS E OF FRONT AND SURFACE LOW ON 40KT LOW LEVEL
JET. THE WAVE/SURFACE LOW SHOULD MOVE NEWD ALONG THE BOUNDARY INTO
ERN ND BY EVE...BEFORE CONTINUING NE WITH FURTHER DEEPENING OVER SE
MB/WRN ONT EARLY TUE. IN THE WAKE OF THE LOW...TRAILING COLD FRONT
EXPECTED TO ACCELERATE SEWD... OVERTAKING PREFRONTAL TROUGH NOW OVER
THE CNTRL HI PLNS.
...NRN/CNTRL PLNS TO UPR MS VLY TODAY/TONIGHT...
BY MID/LATE AFTN A SVR RISK SHOULD EVOLVE FROM ERN ND S/SW INTO
CNTRL/ERN SD AND PARTS OF NEB AS COMBINATION OF SFC HEATING AND
INCREASING LARGE SCALE ASCENT WITH THE APPROACHING UPPER TROUGH WILL
LEAD TO SFC-BASED STORM DEVELOPMENT INVOF DEEPENING SFC LOW...AND
ALONG LEE TROUGH/COLD FRONT.
40-50 KT SSWLY MID TROPOSPHERIC FLOW...INCREASING MOISTURE /PW
1.50-1.75 INCHES/...AND FAVORABLE JUXTAPOSITION OF VERTICAL
SHEAR/BUOYANCY LIKELY WILL YIELD A SEVERAL HOUR WINDOW SUPPORTIVE OF
SEMI-DISCRETE SUPERCELLS POSING A RISK FOR LARGE HAIL AND TORNADOES.
THE TORNADO THREAT WOULD APPEAR TO BE GREATEST OVER THE ERN
DAKOTAS...NE OF DEEPENING SFC LOW. HOWEVER...GIVEN LIKELIHOOD FOR
STORM INITIATION NOT ONLY NEAR SFC WAVE...BUT ALSO SWD ALONG
ACCELERATING COLD FRONT/PREFRONTAL TROUGH INTO NEB...TORNADO THREAT
IN THIS CASE WILL BE ESPECIALLY DEPENDENT ON STORM SCALE
EVOLUTION/INTERACTIONS. GIVEN STRENGTH OF 700 MB
FLOW...STRENGTHENING OF LLJ TOWARD/AFTER DARK...AND COINCIDENT
ARRIVAL OF RICHER LOW LVL MOISTURE FROM IA/ERN NEB...THERE IS THE
POTENTIAL FOR AT LEAST AN ISOLD TORNADO THREAT CONTINUING NEWD INTO
WRN MN AFTER SUNSET. STORMS EXPECTED TO EVOLVE INTO ONE OR MORE
BROKEN QLCSS DURING THE EVENING WITH WIND DAMAGE THE DOMINANT
CONCERN.
..SRN HI PLNS THIS AFTN/EVE...
MORE ISOLD SVR THREAT...POSED BY SCTD MULTICELL CLUSTERS MAY EVOLVE
THIS AFTN/EVE FARTHER S ALONG NNE/SSW LEE TROUGH FROM WRN KS SSW
INTO THE OK/TX PANHANDLES...W TX...AND ERN NM. THIS REGION WILL
REMAIN REMOVED FROM STRONGEST ASCENT/MID LVL COOLING ASSOCIATED WITH
CO/WY SHORTWAVE TROUGH. BUT DEEPLY MIXED BOUNDARY LAYER/STEEP LOW
LVL LAPSE RATES...MODERATE MOISTURE...AND 25-35 KT DEEP SSWLY FLOW
SUGGEST POTENTIAL FOR ISOLD SVR WIND GUSTS THROUGH ABOUT MID EVE.
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