SWODY1
SPC AC 201959
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT SUN MAY 20 2007
VALID 202000Z - 211200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE NRN HIGH
PLAINS...
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF SRN NM INTO SW
TX...
..NRN HIGH PLAINS...
WATER VAPOR IMAGERY SHOWED UPPER TROUGH BEGINNING TO MOVE INLAND
ACROSS WA/ORE THIS AFTERNOON...WITH DOWNSTREAM SHORT WAVE TROUGH
MOVING NEWD ACROSS ID. THIS LEAD UPPER FEATURE IS EXPECTED TO TRACK
NEWD ACROSS MT THIS EVENING...AIDING IN TSTM DEVELOPMENT OVER THE
NRN HIGH PLAINS...AND SHOULD REACH SRN SASKATCHEWAN BY 12Z MONDAY.
SWLY MID LEVEL WINDS WILL CONTINUE TO STRENGTHEN OVER CENTRAL/ERN MT
WITH APPROACH OF ID IMPULSE AND SUPPORT STRONG DEEP LAYER SHEAR FOR
SUPERCELLS.
AT THE SURFACE...STREAMLINE ANALYSIS SUGGESTS A LOW PRESSURE AREA
DEVELOPING ALONG THE NERN WY/SERN MT BORDER AREA...WHILE SEWD
EXTENDING WARM FRONT CONTINUES TO MOVE NWD THROUGH SD TOWARD ND THIS
FORECAST PERIOD. AIR MASS CONTINUES TO MODIFY WITH SURFACE HEATING
NOW OCCURRING ACROSS MUCH OF THE AREA THAT HAD CLOUDS EARLIER TODAY.
THIS COMBINED WITH SURFACE DEWPOINTS IN THE 50S BENEATH STEEP LAPSE
RATES WILL SUPPORT FURTHER DESTABILIZATION WITH MODERATE INSTABILITY
ALREADY EXTENDING FROM SERN MT THROUGH ERN WY TO MUCH OF SD/NEB.
TSTMS HAVE BEGUN TO DEVELOP FROM SOUTH CENTRAL MT/NWRN WY LIKELY IN
RESPONSE TO ASCENT AHEAD OF ID SHORT WAVE TROUGH AND SURFACE
HEATING. ADDITIONAL TSTMS ARE EXPECTED TO DEVELOP AND BECOME SEVERE
AS ACTIVITY SPREADS ENEWD INTO MODERATE INSTABILITY AND WITHIN ZONE
OF STRONG DEEP LAYER SHEAR ACROSS NRN WY INTO SRN/ERN MT. HAIL AND
DAMAGING WINDS SHOULD BE THE PRIMARY THREATS. HOWEVER...STRONGER
AREA OF LOW LEVEL SHEAR ALONG MT/WY BORDER SUGGESTS AN INCREASED
TORNADO THREAT ACROSS THIS AREA.
ACTIVITY MAY CONGEAL INTO FORWARD PROPAGATING LINE SEGMENTS AND/OR
AN MCS ACROSS ERN MT INTO THE WRN DAKOTAS THIS EVENING AS ELEVATED
CAPE/EFFECTIVE SHEAR SUPPORT A CONTINUED SEVERE THREAT OVERNIGHT.
FARTHER S ALONG LEE TROUGH INTO SERN WY AND EAST ALONG WARM FRONT
INTO SD...MODERATE INSTABILITY AND STEEP LAPSE RATES SUGGEST THE
POTENTIAL FOR HAIL AND STRONG WIND GUSTS WITH ANY STORMS THAT CAN
FORM IN THESE AREAS. DESPITE WEAKER DEEP LAYER SHEAR INTO THIS
REGION...VEERING WINDS WITH HEIGHT SUGGEST SOME POTENTIAL FOR
ROTATING UPDRAFTS AND ATTENDANT SEVERE THREAT.
..SRN NM INTO FAR W TX...
ADDITIONAL SURFACE HEATING AND ASCENT ASSOCIATED WITH CYCLONIC FLOW
OVER CENTRAL/WRN NM AND AHEAD OF A MID LEVEL IMPULSE APPROACHING THE
RIO GRANDE VALLEY INTO SW TX SHOULD PROVE SUFFICIENT FOR ADDITIONAL
TSTMS THIS FORECAST PERIOD. MOIST LOW LEVELS WITH SURFACE DEWPOINTS
IN THE 50S COMBINED WITH STEEP LAPSE RATES WILL MAINTAIN MODERATELY
UNSTABLE AIR MASS INTO THE EVENING. 30 KT OF WLY MID LEVEL FLOW PER
WHITE SANDS WIND PROFILER ATOP LOW LEVEL SSELY WINDS SUGGESTS DEEP
LAYER SHEAR SHOULD BE SUFFICIENT FOR MULTICELLS AND A FEW
SUPERCELLS.
.PETERS.. 05/20/2007
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