Thursday, May 21, 2009

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 211240
SWODY1
SPC AC 211237

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0737 AM CDT THU MAY 21 2009

VALID 211300Z - 221200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
THE WLYS WILL REMAIN CONFINED TO THE FAR NRN TIER OF STATES AND SERN
CANADA THROUGH FRIDAY AS UPR RIDGE EDGES SLOWLY E FROM THE MID
ATLANTIC CST INTO THE WRN ATLANTIC. FARTHER S...A PAIR OF WEAK UPR
CIRCULATIONS WILL DRIFT GENERALLY E ACROSS THE SOUTHWEST U.S. AS
WEAK UPR LOW RETROGRESSES SLOWLY NW ACROSS THE ERN GULF OF MEXICO.

WITH THE EXCEPTION OF COLD FRONT CROSSING THE UPR GRT LKS AND SRN
ONTARIO/QUEBEC...FEATURES WILL REMAIN WEAK AT LWR LVLS. A DIFFUSE
WARM FRONT WILL DRIFT NW ACROSS THE FL PENINSULA THROUGH THE PERIOD
AS DEEP S/SELY FLOW BECOMES ESTABLISHED E OF RETROGRESSING UPR LOW.

...CNTRL FL...
ERN GULF UPR LOW APPEARS TO HAVE WEAKENED SOMEWHAT RELATIVE TO
YESTERDAY. WATER VAPOR LOOP ATTM DOES NOT SUGGEST PRESENCE OF
UPSTREAM UPR LVL SPEED MAXIMA THAT COULD ENHANCE UPR LVL CIRCULATION
AS OCCURRED LATE TUE/EARLY WED. THUS...LITTLE OVERALL CHANGE IN
INTENSITY OF SYSTEM IS EXPECTED AS IT WOBBLES SLOWLY WNW THROUGH THE
PERIOD.

ALTHOUGH UPR LVL WINDS WILL REMAIN WEAK...LOW LVL FLOW OVER FL WILL
REMAIN SEASONABLY STRONG DUE TO MODERATE PRESSURE GRADIENT BETWEEN
ERN GULF SFC LOW AND WRN ATLANTIC RIDGE. AS A RESULT...0-3 KM WIND
PROFILES LIKELY WILL CONTINUE TO EXHIBIT ENHANCED DIRECTIONAL
SHEAR...ESPECIALLY INVOF DIFFUSE WARM FRONT NOW ROUGHLY BISECTING
THE PENINSULA. COMBINATION OF LOW-LVL VEERING PROFILES AND MOIST
BOUNDARY LAYER ENVIRONMENT COULD SUPPORT A FEW SHOWERS/STORMS WITH
WEAK LOW LVL ROTATION AS SFC HEATING DESTABILIZES REGION. BUT
OVERALL TORNADO RISK APPEARS TOO LOW TO WARRANT INTRODUCTION OF SVR
PROBABILITIES ATTM.

BUOYANCY AND LOW LVL SHEAR MIGHT INCREASE SOMEWHAT LATE IN THE
PERIOD OVER THE FL PANHANDLE AND ALONG THE AL CST AS WARM FRONT
APPROACHES REGION. HOWEVER...WEAK INSTABILITY AND MESOSCALE
UNCERTAINTIES REGARDING PLACEMENT/INTENSITY OF CONVECTIVE FEATURES
PRECLUDES INTRODUCTION OF LATE-PERIOD SVR PROBABILITIES IN THAT
REGION.

...SW U.S. TO CNTRL PLNS...
SCTD DIURNAL STORMS WILL ONCE AGAIN OCCUR OVER PARTS OF THE SW
U.S...WHERE PW VALUES REMAIN RELATIVELY HIGH. COMPARATIVELY WEAK
LAPSE RATES AND WEAK/VARIABLE UPR FLOW SHOULD KEEP ANY SVR WIND
THREAT VERY ISOLD.

FARTHER NE...MID LVL LAPSE RATES ALSO WILL BE SEASONABLY WEAK OVER
THE CNTRL PLNS. THUS...WHILE A FEW AFTN/EVE STORMS WILL FORM
ALONG/BEHIND COLD FRONT FROM ERN CO INTO NEB/KS...DEEP WIND FIELD
AND MOISTURE/BUOYANCY LIKELY WILL BE TOO LIMITED FOR SVR.

..CORFIDI/JEWELL.. 05/21/2009

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