SWODY1
SPC AC 270553
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1253 AM CDT TUE MAY 27 2008
VALID 271200Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE CNTRL AND SRN
PLAINS EWD INTO THE LOWER MS VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF CNTRL/SRN NEW
ENGLAND SWD INTO THE MID ATLANTIC COAST...
...SYNOPSIS...
A HIGH AMPLITUDE LONGWAVE PATTERN WILL CONTINUE THROUGH THE DAY ONE
PERIOD WITH THE PRIMARY FEATURE OF INTEREST BEING SHORT WAVE TROUGH
WHICH WILL TRANSLATE EWD THROUGH ERN CANADA AND THE NERN STATES.
OVER THE S-CNTRL U.S...HEIGHTS WILL REBOUND IN THE WAKE OF MIDLEVEL
IMPULSE LIFTING NEWD INTO THE NRN PLAINS.
IN THE LOW LEVELS...COLD FRONT ATTENDANT TO ERN CANADA IMPULSE WILL
PUSH EWD/SEWD FROM THE LOWER GREAT LAKES TO THE ATLANTIC COAST BY
THIS EVENING. THE WRN EXTENSION OF THIS BOUNDARY WILL BE MUCH MORE
COMPLEX OVER THE CNTRL/SRN PLAINS INTO OZARK PLATEAU OWING TO
ONGOING TSTMS AND RESIDUAL OUTFLOW BOUNDARIES. HOWEVER...IN
GENERAL...THE SYNOPTIC FRONT IS FORECAST TO SAG SWD THROUGH THE
PERIOD...PERHAPS EXTENDING FROM WRN/NRN TX ENEWD INTO THE LOWER OH
VALLEY BY WEDNESDAY MORNING.
...CNTRL/SRN PLAINS INTO THE LOWER MS VALLEY...
AS MENTIONED ABOVE...FORECAST IS COMPLEX DUE TO THE FACT THAT THE
PRIMARY FOCUS FOR TSTM DEVELOPMENT LATER TODAY MAY WELL BE AN
OUTFLOW BOUNDARY DISPLACED WELL TO THE S OF SYNOPTIC FRONT. CURRENT
THINKING IS THAT REMNANTS OF EVOLVING MCS OVER ERN KS/NERN OK MAY BE
IN PROGRESS AT THE ONSET OF THE FORECAST PERIOD OVER SRN MO/NRN
AR...FOCUSED ALONG NOSE OF SWLY LLJ. LINGERING CLOUDS AND
PRECIPITATION MAY TEND TO LIMIT THE DESTABILIZATION PROCESS AHEAD OF
SYNOPTIC FRONT OVER SERN KS...CNTRL/SRN MO INTO AR.
THEREFORE...NRN/NERN EXTENSION OF SLIGHT RISK AREA IS CONDITIONAL ON
AIR MASS RECOVERY LATER TODAY.
A MODERATE TO POTENTIALLY STRONGLY UNSTABLE AIR MASS /MLCAPES OF
2000-4000 J PER KG/ IS EXPECTED TO DEVELOP THIS AFTERNOON ALONG AND
S OF OUTFLOW BOUNDARY REMNANT FROM EARLIER TSTM ACTIVITY. WHILE
LARGE-SCALE FORCING WILL REMAIN NEGLIGIBLE /PERHAPS EVEN
SUBSIDENT/...MESOSCALE FORCING ALONG SYNOPTIC FRONT AND RESIDUAL
OUTFLOW BOUNDARIES IS EXPECTED TO FOCUS DIURNAL TSTM DEVELOPMENT
LATER TODAY. STRONGER VERTICAL SHEAR IS FORECAST TO RESIDE TO THE N
OF SYNOPTIC FRONT WITH GENERALLY LESS THAN 30 KT OF DEEP LAYER SHEAR
ACROSS AXIS OF STRONGEST INSTABILITY. HOWEVER...GIVEN THE STEEP
LAPSE RATES AND STRONG CONVECTIVE INSTABILITY...THE POTENTIAL WILL
EXIST FOR BRIEF SUPERCELLS AND ORGANIZED MULTICELLS WITH A THREAT OF
LARGE HAIL AND DAMAGING WINDS THROUGH THE EVENING HOURS.
...CNTRL/SRN NEW ENGLAND TO THE MID ATLANTIC COAST...
PERSISTENT SWLY LOW-LEVEL FLOW AHEAD OF COLD FRONT SHOULD SUPPORT
THE NEWD ADVECTION OF AN INCREASINGLY MOIST BOUNDARY LAYER WITH
DEWPOINTS INCREASING THROUGH THE 50S. WHILE MIDLEVEL LAPSE RATES
WILL REMAIN SOMEWHAT MARGINAL...THIS MOISTURE IN CONJUNCTION WITH
DAYTIME HEATING AND RESULTANT STEEPENING OF LOW-LEVEL LAPSE RATES
ARE EXPECTED TO CONTRIBUTE TO A MODERATELY UNSTABLE AIR MASS WITH
MLCAPES OF AROUND 1000 J/KG.
TSTMS ARE EXPECTED TO DEVELOP ALONG THE FRONT BY LATE MORNING/EARLY
AFTERNOON AS LEADING EDGE OF STRONGER HEIGHT FALLS ATTENDANT TO
MIDLEVEL TROUGH BEGIN TO OVERSPREAD DESTABILIZING AIR MASS.
FORECAST SOUNDINGS INDICATE LARGELY WLY TROPOSPHERIC FLOW WITH
DEEP-LAYER SPEED SHEAR RANGING FROM 40-50 KT OVER DOWNEAST ME TO AOB
30 KT NEAR AND S/SW OF THE DELMARVA. THIS ENVIRONMENT SHOULD
SUPPORT EVOLUTION OF A CONVECTIVE LINE ALONG THE FRONT...PERHAPS
COMPOSED OF SHORTER SEGMENT BOWING STRUCTURES CAPABLE OF DAMAGING
WINDS AND SOME HAIL. THE SEVERE THREAT SHOULD DIMINISH THIS EVENING
AS ANY ONGOING STORMS MOVE EWD/SEWD OFFSHORE.
...NRN GREAT BASIN...
A RELATIVELY STEEP LAPSE RATE ENVIRONMENT IS FORECAST TODAY INVOF
WEAK SURFACE LOW AND INVERTED TROUGH DEVELOPING ACROSS REGION.
THESE LAPSE RATES ALONG WITH DEWPOINTS IN THE 40S ARE EXPECTED TO
CONTRIBUTE TO A WEAKLY UNSTABLE AIR MASS LATER TODAY WITH SBCAPES OF
500-1000 J/KG. INCREASING INFLUENCE OF LEFT EXIT REGION OF UPPER
JET STREAK LIFTING NEWD INTO GREAT BASIN SHOULD PROVIDE SUFFICIENT
LARGE-SCALE ASCENT TO SUPPORT DIURNAL TSTMS...A FEW OF WHICH COULD
CONTAIN SOME HAIL AND GUSTY WINDS GIVEN THE STEEP LAPSE RATES IN
PLACE.
..MEAD/JEWELL.. 05/27/2008
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