SWODY1
SPC AC 181244
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0744 AM CDT SUN MAY 18 2008
VALID 181300Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE MID
ATLANTIC REGION...
...THERE IS A SLGT RISK OF SVR TSTMS OVER A SMALL PORTION OF THE TN
VALLEY...
...SYNOPSIS...
A STRONG POLAR VORTEX ENCOMPASSES MUCH OF SRN ONTARIO/QUEBEC AND THE
GREAT LAKES REGION THIS MORNING WITH SEVERAL SHORT WAVE TROUGHS
EMBEDDED WITHIN THE LARGER-SCALE CYCLONIC CIRCULATION. PRIMARY SHORT
WAVE TROUGH OF INTEREST FOR TODAY WAS DIGGING TOWARD THE OH VALLEY
WITHIN 70-75 KT MID LEVEL FLOW. THIS FEATURE WILL PRODUCE MODEST
HEIGHT FALLS AND A STRONG FRONTAL PASSAGE ACROSS THE APPALACHIANS
AND MID ATLANTIC REGION THROUGH THIS EVENING.
AS THE COLD FRONT ADVANCES ON THE ERN SEABOARD...THE LARGE UPPER
RIDGE THAT HAS DOMINATED THE WEST WILL BE TEMPERED SOMEWHAT ACROSS
THE NRN ROCKIES AS A FAST-MOVING LOW AMPLITUDE DISTURBANCE TRACKS
FROM BRITISH COLUMBIA TO THE NRN PLAINS. DPVA WITH THE UPPER WAVE
WILL INDUCE WEAK CYCLOGENESIS ALONG THE LEE/THERMAL-TROUGH ACROSS
NERN MT LATER TODAY. THIS LOW WILL DEVELOP SEWD ACROSS THE MO RIVER
VALLEY THROUGH EARLY MONDAY. ISOLATED HIGH-BASED TSTM DEVELOPMENT IS
ALSO POSSIBLE ACROSS PARTS OF ID...WRN MT...AND WY AS THE RIDGE
BREAKS DOWN IN THESE AREAS TODAY.
...OH VALLEY TO THE MID ATLANTIC...
STRONG IMPULSE AND ASSOCIATED MID LEVEL JET NOW DIGGING SEWD
ACROSS THE MIDWEST WILL SPREAD QUICKLY EWD THROUGH THIS AFTERNOON.
FRONTAL WAVE IN RESPONSE TO THIS FEATURE WILL TRACK FROM OH THIS
MORNING TO SRN PA/NRN VA THIS AFTERNOON AS ASSOCIATED COLD FRONT
TRAILS FROM THE LOW SWWD ACROSS THE APPALACHIANS TO THE TN VALLEY
WITH TIME.
MOISTURE TRANSPORT IS MAXIMIZED THIS MORNING IN THE WARM CONVEYOR
BELT AHEAD OF THE LOW AND FRONT...GENERALLY WEST OF THE APPALACHIANS
TO THE OH VALLEY. AIR MASS TO THE EAST OF THE APPALACHIAN CREST IS
LIKELY TO BECOME ONLY MARGINALLY UNSTABLE AHEAD OF THE LOW AND FRONT
TODAY GIVEN LIMITED LOW LEVEL MOISTURE /DEWPTS IN THE 50S/.
HOWEVER...SURFACE HEATING AND STRENGTHENING ASCENT/MOISTENING ACROSS
THIS AREA WILL LIKELY SUPPORT POCKETS OF MUCAPE AROUND 500 J PER
KG...ESPECIALLY FROM NRN NC TO SERN PA.
GIVEN RAPID EWD TRANSLATION OF THE SHORT WAVE...SURFACE LOW...AND
FRONT...THE CHANCE FOR LOW-TOPPED TSTMS SHOULD INCREASE QUICKLY
THROUGH THE EARLY AFTERNOON FROM PA SWWD ACROSS VA. THE POSSIBILITY
FOR SEVERE STORMS WILL ALSO INCREASE AS GREATER INSTABILITY IS
REALIZED AND ACTIVITY IS FOCUSED/SUSTAINED NEAR THE LOW AND ALONG
THE TRAILING FRONT. MEAN WLY DEEP-LAYER FLOW OF 45-50KT AND
UNIDIRECTIONAL SHEAR WILL ACCOMPANY THE SYSTEM ACROSS THE REGION AND
CONTRIBUTE TO A FEW BANDS/LINES OF ORGANIZED STORMS...AND PERHAPS A
SUPERCELL OR TWO...THROUGH THE AFTERNOON. WHILE DAMAGING WIND
POTENTIAL MAY BECOME THE MAIN THREAT FROM THIS ACTIVITY...COLDER
TEMPERATURES ALOFT AND THE POTENTIAL FOR A COUPLE/FEW ROTATING
STORMS ALSO SUGGESTS THE CHANCE FOR SEVERE HAIL.
A SECONDARY COLD FRONTAL SURGE MAY CONTRIBUTE TO ADDITIONAL
LOW-TOPPED TSTMS THIS AFTERNOON OVER PORTIONS OF OH INTO
WRN PA/NY. SOME HAIL AND STRONG WIND GUSTS WILL ACCOMPANY THE MORE
INTENSE STORMS GIVEN THE COOL THERMODYNAMIC ENVIRONMENT AND STRONG
UNIDIRECTIONAL WIND FIELDS AND FORCING.
...APPALACHIANS SWWD TO TN VALLEY...
BROAD SRN STREAM TROUGH NOW CROSSING THE LWR MS VALLEY WILL
EVENTUALLY BE ABSORBED WITHIN THE AMPLIFYING LARGE SCALE TROUGH
ACROSS THE ERN U.S. INTO MONDAY. PRIOR TO THIS HAPPENING...LIFT WITH
THIS DISTURBANCE MAY ENHANCE TSTM DEVELOPMENT WELL AHEAD OF AND
ALONG THE FRONTAL SYSTEM MOVING ACROSS THE APPALACHIANS AND THEN
SETTLING OVER THE TN VALLEY LATER TODAY THROUGH TONIGHT.
CLOUD SHIELD WITH THE SRN IMPULSE WAS CURRENTLY SPREADING ENEWD
ACROSS THE TN VALLEY AND MAY INHIBIT GREATER HEATING AND
DESTABILIZATION FROM ERN TN TO WRN NC. HOWEVER...LOW LEVEL THETA-E
RIDGING...AND THE POTENTIAL FOR DIFFERENTIAL HEATING ACROSS THE
CLOUD SHIELD...COULD RESULT IN AN AXIS OF GREATER DESTABILIZATION
AND MORE ROBUST TSTM DEVELOPMENT FROM AL TO NRN GA/SERN TN THIS
AFTERNOON.
STRENGTHENING LARGE SCALE ASCENT AND MODEST UNIDIRECTIONAL
DEEP-LAYER FLOW ACROSS THESE AREAS...COINCIDENT WITH PEAK IN DIURNAL
TSTM POTENTIAL...COULD RESULT IN A FEW SEVERE HAIL/WIND EVENTS.
..CARBIN/CROSBIE.. 05/18/2008
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