SPC AC 181937
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0237 PM CDT MON MAY 18 2009
VALID 182000Z - 191200Z
...NO SVR TSTM AREAS FORECAST...
LITTLE CHANGE TO LATE MORNING FORECAST REGARDING CONVECTIVE
POTENTIAL ACROSS THE CONUS. ONE AREA WHERE THUNDERSTORMS MAY NOT BE
AS ROBUST AS EARLIER THOUGHT WILL BE ACROSS THE CNTRL FL PENINSULA.
WIDESPREAD PRECIPITATION ALONG/NORTH OF SWD-SAGGING BOUNDARY WILL
PREVENT STRONG UPDRAFTS THE REST OF THE PERIOD...FOR THIS REASON
HAVE OPTED TO REMOVE LOW PROBABILITIES FROM THE CNTRL PENINSULA.
ELSEWHERE...SCATTERED CONVECTION IS DEVELOPING AS SCHEDULED ACROSS
THE HIGHER TERRAIN OF THE SWRN U.S. FROM THE MOUNTAINS OF CO/NM INTO
SRN CA. GUSTY WINDS MAY ACCOMPANY THIS HIGH BASED ACTIVITY AS NOTED
BY 45 MPH WIND GUST IN SAN BERNARDINO COUNTY CA.
..DARROW.. 05/18/2009
.PREV DISCUSSION... /ISSUED 1117 AM CDT MON MAY 18 2009/
...SYNOPSIS...
EXPANSIVE UPPER RIDGE CENTERED OVER THE SRN GREAT BASIN WILL EXPAND
EWD OVER THE CNTRL CONUS AS DEPARTING ELONGATED E COAST UPPER TROUGH
SLIDES EWD INTO WRN ATLANTIC. WATER VAPOR IMAGERY INDICATES A LEAD
SUBTLE FEATURE MOVING EWD ACROSS THE PACIFIC NW TOWARDS THE NRN
ROCKIES IN ADVANCE OF LARGER SCALE FEATURE SITUATED OFF THE PACIFIC
NW/BC COAST. FURTHER E...STRONG UPPER DISTURBANCE OVER WRN ONTARIO
WILL GLANCE PARTS OF THE UPPER MS RIVER VALLEY/UPPER GREAT LAKES
REGION.
AT THE SURFACE...A COLD FRONT WILL SLOWLY SAG SEWD OVER THE
CNTRL/SRN FL PENINSULA. FURTHER N...A COLD FRONT ANALYZED OVER
PARTS OF NRN MN/ND LATE THIS MORNING WILL SLIDE SEWD TOWARDS THE
UPPER GREAT LAKES WHEREAS TRAILING PORTION OF THIS BOUNDARY WILL
REMAIN QUASI-STATIONARY WITH WWD EXTENTION IN WRN MT.
...CNTRL/SRN FL...
SCTD SHWRS/TSTMS WILL CONTINUE TO DEVELOP ALONG FRONT OVER FL
PENINSULA IN ASSOCIATION WITH SRN PERIPHERY OF LARGE SCALE TROUGH
OVER THE E COAST. WARM/MOIST AIRMASS S AND E OF FRONT HAS
CONTRIBUTED TO MODERATELY CONVECTIVE INSTABILITY SAMPLED BY 12Z AREA
RAOBS. VEERING BUT MEAGER FLOW ALOFT WILL LIMIT SEVERE
POTENTIAL...BUT DEEP MOIST PROFILES AND RELATIVELY COOL MID-LEVEL
TEMPS /AOB -10 DEG C/ MAY SUPPORT AN ISOLD DMGG WIND GUST/LARGE HAIL
THREAT WITH STRONGER STORMS.
...MT...
MORNING UPPER AIR/GPS PW DATA SHOW DRY AIRMASS OVER THE NRN ROCKIES.
MID-LEVEL HEIGHT FALLS WILL GRADUALLY SPREAD EWD OVER THE PACIFIC
NW/NRN ROCKIES REGION IN ADVANCE OF E PACIFIC UPPER TROUGH. STRONG
DIABATIC HEATING IN COMBINATION WITH ELY UPSLOPE/FRONTAL FORCING
WILL PROBABLY LEAD TO ISOLD TSTMS LATE THIS AFTERNOON/EVENING.
STEEP MID-LEVEL LAPSE RATES IN LEE OF NRN ROCKIES MAY RESULT IN
MODEST CONVECTIVE INSTABILITY /BELOW 1000 J/KG MUCAPE/ WITHIN MORE
THAN ADEQUATELY SHEARED ENVIRONMENT...SUPPORTING AN INCLUSION OF LOW
HAIL/WIND PROBABILITIES.
...UPPER MS RIVER VALLEY/UPPER GREAT LAKES...
DESPITE STEEPENING LAPSE RATES ON SRN PERIPHERY OF ONTARIO
DISTURBANCE...ONLY TEMPERED BOUNDARY LAYER MOISTURE MODIFICATION IS
EXPECTED IN ADVANCE OF COLD FRONT MOVING SEWD OVER AREA. AS
SUCH...LATEST MODEL GUIDANCE SUGGESTS ONLY ISOLD TSTMS DEVELOPING
DURING THE EVENING/OVERNIGHT HOURS. WITH MODESTLY STRONG DEEP LAYER
SHEAR FORECAST...STRONGER UPDRAFTS MAY POSE A BRIEF SEVERE HAIL/WIND
THREAT.
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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