THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NEW ENGLAND TO ERN LOWER MI...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS WI/WRN LM...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS DAKOTAS/NERN WY/SERN MT...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS GA/AL/FL PANHANDLE

Categorical Graphic
Probabilistic Tornado Graphic
Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Probabilistic Damaging Wind Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Probabilistic Large Hail Graphic
Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.

   SPC AC 171958
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0258 PM CDT TUE JUL 17 2012
   
   VALID 172000Z - 181200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NEW ENGLAND TO ERN
   LOWER MI...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS WI/WRN LM...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS DAKOTAS/NERN WY/SERN
   MT...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS GA/AL/FL PANHANDLE...
   
   --- UPDATES ---
   
   ...NERN CONUS...
   SINCE PREVIOUS OUTLOOK...BKN BAND OF STG-SVR TSTMS HAS DEVELOPED
   OVER SERN ONT AND IS MOVING ESEWD...WHILE BUILDING EWD OVER SRN
   QUE...AND MOVING INTO DESTABILIZING BOUNDARY LAYER.  SVR THREAT
   REMAINS CONCENTRATED FROM NRN NY EWD ACROSS PORTIONS VT...NH AND WRN
   MAINE.  REF WW 489 AND RELATED MESOSCALE DISCUSSIONS FOR LATEST
   NEAR-TERM GUIDANCE.
   
   ...SERN CONUS...
   SCATTERED TO LOCALLY NUMEROUS TSTMS WILL POSE CONTINUED THREAT FOR
   DAMAGING GUSTS AND SVR HAIL AS THEY MOVE GENERALLY SWWD ACROSS
   PORTIONS SRN GA/AL AND FL PANHANDLE...AROUND NWRN RIM OF MID-UPPER
   LEVEL VORTEX.  REF WW 488 AND ACCOMPANYING MESOSCALE DISCUSSIONS FOR
   NOWCAST DETAILS.  POTENTIAL BECOMES MORE DISORGANIZED/ISOLATED
   AMIDST SCATTERED TSTMS FARTHER N ACROSS TN VALLEY AND SWRN
   APPALACHIAN REGIONS.
   
   ...NRN PLAINS TO UPPER GREAT LAKES...
   MOST PROBABLE CORRIDOR FOR MCS DEVELOPMENT/MOVEMENT APPEARS TO BE
   ACROSS PORTIONS CENTRAL/NRN SD...BASED ON OBSERVED LOCATION OF
   LOW-LEVEL THETAE PLUME N OF FRONT...WITHIN WHICH CONSENSUS OF
   SHORT-FUSED/CONVECTION-ALLOWING GUIDANCE INDICATES TSTM CLUSTER
   MOVEMENT.  REF SPC MESOSCALE DISCUSSION 1482 FOR DETAILS REGARDING
   STG-SVR CONVECTION OVER WI.
   
   OTHERWISE...MINOR ADJUSTMENTS MADE TO SVR PROBABILITY AND GEN TSTM
   LINES BASED ON CONVECTIVE/INSTABILITY TRENDS.
   
   ..EDWARDS.. 07/17/2012
   
   .PREV DISCUSSION... /ISSUED 1108 AM CDT TUE JUL 17 2012/
   
   ...SYNOPSIS...
   
   SHORTWAVE TROUGH AND ASSOCIATED 50-60 KT MIDLEVEL JET STREAK OVER
   ONTARIO WILL PROGRESS ESEWD ACROSS SRN QUEBEC AND NRN NEW
   ENGLAND...CONTRIBUTING TO INCREASING VERTICAL SHEAR AND LARGE-SCALE
   FORCING FOR ASCENT OVER THESE REGIONS THIS AFTERNOON INTO TONIGHT. 
   ELSEWHERE...A SHORTWAVE TROUGH OVER WRN WY WILL CONTINUE NEWD INTO
   THE WRN DAKOTAS BY TONIGHT...WHILE FARTHER W AN UPPER LOW WILL
   REMAIN QUASI-STATIONARY ALONG THE SWRN ORE/NWRN CA COASTS. 
   FINALLY...AN UPPER LOW OVER NERN FL WILL DRIFT NNWWD TOWARD THE
   SAVANNAH RIVER VALLEY.
   
   AT THE SURFACE...LOW PRESSURE OVER SWRN ONTARIO WILL DEVELOP ENEWD
   INTO NRN ME BY 18/00Z WHILE TRAILING COLD FRONT SETTLES SWD THROUGH
   THE ST. LAWRENCE VALLEY...NRN NEW ENGLAND AND THE GREAT LAKES.  THE
   WRN EXTENSION OF THIS BOUNDARY WILL LINK WITH A SECONDARY SURFACE
   LOW WHICH IS FORECAST TO REMAIN QUASI-STATIONARY ALONG THE SD-NEB
   BORDER.
     
   ...LOWER GREAT LAKES INTO NEW ENGLAND THIS AFTERNOON AND EVENING...
   
   AS MENTIONED ABOVE...DEEP-LAYER WLY WIND FIELD /AND RESULTANT
   VERTICAL SHEAR/ WILL STRENGTHEN ACROSS THE AREA TODAY IN CONCERT
   WITH PROGRESSIVE SHORTWAVE TROUGH.  THIS AIRFLOW REGIME WILL ALSO
   PROMOTE THE EWD ADVECTION OF STEEP MIDLEVEL LAPSE RATES OBSERVED BY
   THE 12Z APX AND DTX SOUNDINGS INTO THE LOWER GREAT LAKES.  WHEN
   COUPLED WITH DECREASING CLOUDS AND BOUNDARY LAYER DEWPOINTS IN THE
   60S...ENVIRONMENT IS EXPECTED TO BECOME MODERATELY UNSTABLE BY
   AFTERNOON WITH MLCAPE VALUES INCREASING TO 1000-2000 J/KG.
   
   LATEST CONVECTION-ALLOWING AND MESOSCALE MODEL GUIDANCE SUGGESTS
   THAT TSTMS WILL INITIATE THIS AFTERNOON ALONG COLD FRONT OVER THE
   ST. LAWRENCE VALLEY WITH ACTIVITY GROWING UPSCALE INTO A BROKEN
   CONVECTIVE BAND AS IT PROGRESSES SEWD INTO NRN NEW ENGLAND AND
   UPSTATE NY.  MORE ISOLATED STORM DEVELOPMENT WILL ALSO BE POSSIBLE
   THIS AFTERNOON ALONG DEVELOPING LAKE BREEZE FRONT IN THE LEE OF
   LAKES ERIE AND ONTARIO...AS WELL AS WRN EXTENSION OF COLD FRONT IN
   LOWER MI.
   
   THE STRONGEST LOW AND DEEP-LAYER SHEAR WILL RESIDE FROM THE
   ADIRONDACKS EWD ACROSS NRN PARTS OF VT/NH INTO ME WHERE THE
   POTENTIAL WILL EXIST FOR SUPERCELLS AND BOWING STRUCTURES CAPABLE OF
   A COUPLE TORNADOES...DAMAGING WINDS AND LARGE HAIL.  VERTICAL SHEAR
   WILL DECREASE SWD ACROSS THE SLIGHT RISK AREA...THOUGH THE MODERATE
   INSTABILITY WILL STILL PROMOTE VIGOROUS UP/DOWNDRAFTS CAPABLE OF
   DAMAGING WINDS AND HAIL.
   
   FOR ADDITIONAL NEAR-TERM GUIDANCE...SEE MCD 1480.
   
   ...SERN STATES THIS AFTERNOON AND EVENING...
   
   12Z 500-MB ANALYSIS AND REGIONAL SOUNDING DATA INDICATED A POCKET OF
   COLDER AIR IN THE MIDLEVELS /I.E. -8 TO -9 C/ WHICH WILL COMBINE
   WITH PW VALUES OF 1.75-2.00 INCHES AND DAYTIME HEATING TO YIELD
   AFTERNOON MLCAPE OF 2000-3000+ J/KG.  CONVERGENCE INVOF OF LOW-LEVEL
   CIRCULATION EVIDENT IN VISIBLE SATELLITE OVER CNTRL GA AS OF 15Z AND
   ASSOCIATED SURFACE TROUGH WILL LIKELY SERVE AS THE FOCI FOR
   SCATTERED-NUMEROUS TSTMS THIS AFTERNOON.  WHILE VERTICAL SHEAR WILL
   REMAIN WEAK...THE DEGREE OF INSTABILITY WILL PROMOTE PULSE AND
   MULTICELL STORM CLUSTERS CAPABLE OF LOCALLY DAMAGING WINDS AND SOME
   HAIL.
   
   ...NRN HIGH PLAINS THIS AFTERNOON INTO TONIGHT...
   
   SHORTWAVE TROUGH MENTIONED IN SYNOPSIS WILL AUGMENT LOW-LEVEL
   CONVERGENCE ALONG INVERTED SURFACE TROUGH TO GIVE RISE TO WIDELY
   SCATTERED TSTMS THIS AFTERNOON OVER ERN MT/NERN WY INTO THE WRN
   DAKOTAS.  WHILE VERTICAL SHEAR WILL NOT BE PARTICULARLY
   STRONG...VERTICALLY VEERING WIND PROFILES WILL COINCIDE WITH STEEP
   MIDLEVEL LAPSE RATES AND A MOIST BOUNDARY LAYER TO PROMOTE LOOSELY
   ORGANIZED STORM CLUSTERS WITH A RISK FOR LOCALLY DAMAGING WINDS AND
   HAIL.
   
   ...WI THIS AFTERNOON AND EVENING...
   
   MULTI-MODEL CONSENSUS SUGGESTS AN INCREASING RISK FOR SURFACE-BASED
   TSTMS BY MID-LATE AFTERNOON ALONG THE SWD-MOVING COLD FRONT WITH
   ACTIVITY PERHAPS BEING AIDED BY A WEAK MIDLEVEL IMPULSE CURRENTLY
   OVER NRN MN.  MODIFICATION OF 12Z GRB SOUNDING FOR ANTICIPATED
   AFTERNOON CONDITIONS SUGGESTS THAT CAP WOULD BE ELIMINATED FOR
   SURFACE TEMPERATURES IN THE MID 90S.  GIVEN THE MOIST BOUNDARY LAYER
   AND RESULTANT MLCAPE OF 2000-3000 J/KG...AS WELL AS MODEST WLY
   MIDLEVEL FLOW...SETUP MAY YIELD A FORWARD-PROPAGATING CLUSTER OF
   TSTMS/MCS WITH AN ASSOCIATED RISK FOR DAMAGING WINDS AND HAIL.
   
   ...INTERIOR PACIFIC NW AND NRN INTERMOUNTAIN REGION THIS AFTERNOON
   AND EVENING...
   
   MORNING WATER VAPOR IMAGERY SHOWS A SERIES OF VORTICITY MAXIMA
   PIVOTING AROUND PARENT UPPER LOW.  FORCING ASSOCIATED WITH THESE
   FEATURES WILL COMBINE WITH MODEST LAPSE RATES AND PW VALUES OF
   1.00-1.40 INCHES TO FOSTER WIDELY SCATTERED STORMS CAPABLE OF GUSTY
   WINDS AND PERHAPS SOME HAIL.
   
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