Sunday, May 18, 2008

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 180544
SWODY1
SPC AC 180542

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1242 AM CDT SUN MAY 18 2008

VALID 181200Z - 191200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE DELMARVA SWWD INTO
N-CNTRL NC...

...SYNOPSIS...

POLAR BRANCH TROUGH /ANCHORED BY VORTEX OVER ONTARIO/ WILL INTENSIFY
THROUGH THE PERIOD AS SIGNIFICANT SHORT WAVE TROUGH CURRENTLY
AMPLIFYING OVER THE UPPER MIDWEST RAPIDLY TRANSLATES EWD ACROSS THE
OH VALLEY INTO THE NERN STATES. AS THIS OCCURS...LOWER LATITUDE
IMPULSE OVER TX WILL WEAKEN WHILE BECOMING ENTRAINED INTO SRN
EXTENSION OF FULL LATITUDE TROUGH DEVELOPING ACROSS THE ERN THIRD OF
THE NATION.

IN THE LOW-LEVELS...PRIMARY SURFACE LOW INITIALLY OVER SERN OH IS
FORECAST TO DEVELOP ENEWD TO NEAR THE PA/NJ BORDER BY LATE
AFTERNOON...AND THEN MORE NEWD THROUGH SRN/ERN NEW ENGLAND TONIGHT.
ATTENDANT COLD FRONT WILL PUSH EWD/SEWD THROUGH THE CNTRL/SRN
APPALACHIANS TODAY AND EVENTUALLY OFF THE ATLANTIC COAST. FARTHER
S...QUASI-STATIONARY BOUNDARY ACROSS THE NRN FL PENINSULA MAY LIFT
NEWD SLIGHTLY BEFORE SHIFTING SEWD AS A COLD FRONT LATER IN THE
PERIOD.

...MIDDLE ATLANTIC STATES SWWD INTO THE SRN APPALACHIANS...

WHILE BOUNDARY LAYER MOISTURE WILL REMAIN SOMEWHAT LIMITED WITH
DEWPOINTS IN THE 50S...LATEST MODEL GUIDANCE SUGGESTS THAT DIABATIC
HEATING WILL RESULT IN DEVELOPMENT OF STEEP LOW-LEVEL LAPSE RATES IN
THE LEE OF THE APPALACHIANS TODAY. THIS IN CONJUNCTION WITH
SIGNIFICANT MIDLEVEL COOLING/DYNAMIC ASCENT ASSOCIATED WITH
ABOVEMENTIONED SHORT WAVE TROUGH WILL CONTRIBUTE TO SBCAPES
APPROACHING 400-700 J/KG IN A NARROW AXIS AHEAD OF SURFACE FRONT.

LOW-TOPPED STORMS DEVELOPING ALONG THE FRONT ARE EXPECTED TO
INTENSIFY BY EARLY AFTERNOON AS THEY SHIFT E OF THE BLUE RIDGE AND
ENCOUNTER THE STEEP LAPSE RATE ENVIRONMENT. FORECAST SOUNDINGS
INDICATE LARGELY UNDIRECTIONAL WIND FIELDS WITH RATHER STRONG DEEP
LAYER SPEED SHEAR AND RESULTANT 50+ KT STORM MOTIONS. THIS
KINEMATIC ENVIRONMENT IN CONCERT WITH THE STRONG DYNAMIC FORCING FOR
ASCENT INDICATE THE POTENTIAL FOR EMBEDDED BOWING STRUCTURES CAPABLE
OF MAINLY DAMAGING WINDS DESPITE THE WEAK CONVECTIVE INSTABILITY.

SCATTERED DIURNAL TSTMS WILL BE POSSIBLE SWWD ALONG THE FRONT INTO
THE TN VALLEY AND EVENTUALLY SRN APPALACHIANS. BOTH VERTICAL SHEAR
AND DYNAMIC FORCING FOR ASCENT WILL DECREASE WITH SWD EXTENT ALONG
FRONTAL ZONE...HOWEVER THE MORE INTENSE STORMS WILL STILL REMAIN
CAPABLE OF LOCALLY STRONG WIND GUSTS.

...UPPER OH VALLEY...

A SECONDARY COLD FRONTAL SURGE MAY FOCUS ADDITIONAL LOW-TOPPED TSTMS
THIS AFTERNOON OVER PORTIONS OF OH INTO WRN PA. SOME HAIL AND
STRONG WIND GUSTS WILL ACCOMPANY THE MORE INTENSE STORMS GIVEN THE
COOL THERMODYNAMIC ENVIRONMENT AND STRONG UNIDIRECTIONAL WIND
FIELDS.

...FL...

AIR MASS ALONG AND S OF WEAK SURFACE FRONT WILL REMAIN QUITE MOIST
WITH DEWPOINTS IN THE 60S TO LOWER 70S. HOWEVER...MIDLEVEL LAPSE
RATES WILL BE RELATIVELY WEAK...LIMITING MLCAPES TO AOB 1000 J/KG.
CONVERGENCE ALONG THIS FRONT IS EXPECTED TO REMAIN SOMEWHAT MARGINAL
GIVEN THE LARGELY WLY LOW-LEVEL WIND FIELDS. HOWEVER...RELATIVELY
WEAK CAPPING AND INCREASED LARGE-SCALE FORCING AHEAD OF APPROACHING
SRN STREAM IMPULSE SHOULD SUPPORT ISOLATED/SCATTERED TSTMS ALONG
FRONT AND/OR DEVELOPING SEA BREEZE CONVERGENCE ZONES. THE PRESENCE
OF 50-55 KT MIDLEVEL FLOW WILL RESULT IN SUFFICIENT DEEP LAYER SPEED
SHEAR TO SUPPORT A FEW ORGANIZED STORMS CAPABLE OF MAINLY STRONG
WIND GUSTS.

..MEAD/CROSBIE.. 05/18/2008

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