SWODY1
SPC AC 292000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT THU SEP 29 2011
VALID 292000Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NORTHEAST
STATES/SOUTHERN NEW ENGLAND...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS LOWER MI AND
INDIANA/OH...
...NORTHEAST STATES/SOUTHERN NEW ENGLAND...
STRONGLY SHEARED BUT MODESTLY UNSTABLE ENVIRONMENT MAY YIELD
DAMAGING WINDS AND/OR A TORNADO ACROSS THE REGION INTO THIS EVENING.
HAVE DROPPED THE SLIGHT RISK ACROSS PORTIONS OF PA/NJ/NY IN THE WAKE
OF THE EASTWARD-ADVANCING FRONT/CONVECTIVE BAND.
...SOUTH TX...
SEVERAL CLUSTERS OF STRONG/SEVERE TSTMS ARE ONGOING AT MID-AFTERNOON
ACROSS SOUTH-CENTRAL/FAR SOUTH TX. ADDITIONAL DEEP CONVECTIVE
DEVELOPMENT/MERGERS WITHIN AN UNSTABLE ENVIRONMENT /3000-3500 J PER
KG MLCAPE AS PER LATEST OBJECTIVE ANALYSIS/ WILL CONTINUE TO YIELD
STORMS CAPABLE OF DOWNBURSTS/DAMAGING WINDS ON AN ISOLATED BASIS. TO
ACCOUNT FOR THE POSSIBILITY OF A DEGREE OF CLUSTERING/FORWARD
PROPAGATION...MADE A MODEST SPATIAL EXPANSION OF SEVERE WIND
PROBABILITIES ACROSS FAR SOUTHWEST TX.
...ELSEWHERE...
LITTLE OR NO CHANGES...SEE PRIOR OUTLOOK DISCUSSION BELOW AND ANY
SUBSEQUENT MESOSCALE DISCUSSIONS/WATCHES.
..GUYER.. 09/29/2011
.PREV DISCUSSION... /ISSUED 1125 AM CDT THU SEP 29 2011/
...SYNOPSIS...
A STRONG SHORTWAVE TROUGH WILL CONTINUE TO DIG SEWD TO THE GREAT
LAKES/OH VALLEY...WHILE A PREVIOUSLY CLOSED LOW EJECTS NEWD AS AN
OPEN WAVE FROM VA/MD/PA TO NEW ENGLAND BY TONIGHT. AT THE
SURFACE...AN INITIAL COLD FRONT FROM CENTRAL VA TO ERN PA/CENTRAL NY
WILL PROGRESS EWD TO THE MID ATLANTIC COAST AND SE NEW ENGLAND BY
THIS EVENING. A SEPARATE COLD FRONT WILL MOVE SWD ACROSS THE
CENTRAL/SRN PLAINS AND SEWD ACROSS THE MID MS VALLEY...IN THE WAKE
OF A CYCLONE DEVELOPING SEWD FROM UPPER TO NRN LOWER MI...IN ADVANCE
OF THE AMPLIFYING MIDLEVEL TROUGH.
...ERN PA/NJ/SE NY/SRN NEW ENGLAND THIS AFTERNOON...
CONVECTION IS ALREADY BEGINNING TO DEEPEN AND INCREASE IN COVERAGE
ACROSS ERN PA/SE NY/NJ IN ADVANCE OF THE COLD FRONT...WHERE CLOUD
BREAKS HAVE ALLOWED SURFACE TEMPERATURES TO WARM INTO THE LOW 70S.
LAPSE RATES ALOFT ARE NOT PARTICULARLY STEEP...SO INSTABILITY WILL
BE SOMEWHAT LIMITED THIS AFTERNOON /MLCAPE OF 500-1000 J PER KG/.
HOWEVER...INCREASING MIDLEVEL FLOW WITH THE APPROACH OF THE EJECTING
SHORTWAVE TROUGH WILL CONTRIBUTE TO EFFECTIVE BULK SHEAR OF 40-50
KT...AND THE POTENTIAL FOR BOTH SUPERCELLS AND BOWING LINE SEGMENTS.
DAMAGING WINDS APPEAR TO BE THE PRIMARY SEVERE THREAT THIS
AFTERNOON...THOUGH THE MOIST PROFILES AND MODEST LOW-LEVEL SHEAR
COULD ALSO SUPPORT THE RISK FOR A TORNADO.
...LOWER MI/INDIANA/OH THIS AFTERNOON/EVENING...
A FOCUSED BAND OF ASCENT ALONG THE COLD FRONT WILL SPREAD SEWD FROM
WI/NW IL AS OF LATE MORNING TO LOWER MI/NW INDIANA THIS
AFTERNOON...AND OH THIS EVENING. SOME EROSION OF LOW CLOUDS IN SW/S
CENTRAL LOWER MI WILL ALLOW SURFACE TEMPERATURES TO WARM INTO THE
60S...WHILE 70S ARE EXPECTED FARTHER SW INTO INDIANA WHERE SKIES ARE
CLEAR AS OF 16Z. THIS SURFACE HEATING WILL COMBINE WITH LOW-MID 50S
BOUNDARY LAYER DEWPOINTS TO SUPPORT WEAK INSTABILITY /SBCAPE OF
250-500 J PER KG/. THE INSTABILITY AND ASCENT WILL RESULT IN A BAND
OF LOW-TOPPED CONVECTION ALONG THE COLD FRONT THIS AFTERNOON...WITH
AN ACCOMPANYING RISK FOR DAMAGING WINDS GIVEN THE POTENTIAL FOR
MOMENTUM TRANSPORT OF 40-60 KT L0W-MIDLEVEL FLOW TO THE GROUND.
...CENTRAL FL THIS AFTERNOON...
STRONG SURFACE HEATING IS ONGOING S OF A WEAK FRONTAL
SEGMENT/SURFACE TROUGH THAT IS DRIFTING SEWD ACROSS CENTRAL FL...AND
VISIBLE IMAGERY SHOWS CUMULUS DEVELOPMENT ALONG THE BOUNDARY AS OF
16Z. ADDITIONAL HEATING WILL REMOVE CONVECTIVE INHIBITION AND
CONTRIBUTE TO AFTERNOON MLCAPE OF 2500-3000 J/KG...AS WELL AS DCAPE
NEAR 1000 J/KG. GIVEN THE POTENTIAL FOR BOTH STRONG UPDRAFTS AND
PRECIPITATION LOADING...AND STRONG DOWNDRAFTS...THERE WILL BE A RISK
FOR ISOLATED STRONG/DAMAGING WINDS.
...CENTRAL TX/MIDDLE TX COAST THIS AFTERNOON...
AN OUTFLOW BOUNDARY IS MOVING WWD NEAR MATAGORDA BAY...WITH STRONG
SURFACE HEATING FARTHER INLAND TO THE W/NW OF THE OUTFLOW.
DEWPOINTS IN THE 70S AND AFTERNOON TEMPERATURES IN THE 90S WILL
RESULT IN MLCAPE IN EXCESS OF 3000 J/KG...WHILE LOW-LEVEL LAPSE
RATES WILL ALSO STEEPEN. THE STEEP LAPSE RATES AND LARGE
INSTABILITY MAY SUPPORT A FEW STRONG/DAMAGING DOWNBURSTS THIS
AFTERNOON.
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