SPC AC 221251

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0751 AM CDT TUE APR 22 2014

   VALID 221300Z - 231200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NWRN WY...SERN
   ID...SWRN MT...

   ...SUMMARY...
   THUNDERSTORMS MAY PRODUCE DAMAGING WIND AS THEY MOVE NORTHEASTWARD
   ACROSS PARTS OF SOUTHWESTERN MONTANA...NORTHWESTERN WYOMING AND
   SOUTHEASTERN IDAHO...INCLUDING YELLOWSTONE NATIONAL PARK.  ISOLATED
   STRONG TO SEVERE THUNDERSTORMS MAY OCCUR OVER THE CENTRAL-NORTHERN
   HIGH PLAINS.

   ...SYNOPSIS...
   IN MID-UPPER LEVELS...PROGRESSIVE AND FAIRLY HIGH-AMPLITUDE
   SHORTWAVE PATTERN WILL PERSIST OVER CONUS THIS PERIOD.  NRN-STREAM
   TROUGH -- CURRENTLY OVER UPPER GREAT LAKES AND LOWER MI -- IS FCST
   TO MOVE EWD TO SERN ONT...NY AND PA BY 00Z.  PROXIMAL/TRAILING
   PERTURBATION -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER
   BOUNDARY-WATERS REGION OF MN/ONT -- IS FCST TO DIG SEWD ACROSS LOWER
   MI BY 00Z.  THIS FEATURE WILL CONTINUE TO STRENGTHEN AND BECOME MAIN
   BASAL VORTICITY MAX FOR NRN APPALACHIANS/MID-ATLC SHORTWAVE TROUGH
   OVERNIGHT.

   SRN-STREAM SHORTWAVE TROUGHS -- INITIALLY OVER DEEP S TX AND MS --
   WILL BECOME BETTER-PHASED TODAY.  BY 00Z...ASSOCIATED VORTICITY AXIS
   SHOULD EXTEND FROM SC ACROSS FL PANHANDLE TO NWRN GULF...THEN SW-NE
   ACROSS FL PENINSULA BY 12Z.  UPSTREAM...MAJOR/HIGH-AMPLITUDE TROUGH
   WILL MOVE INLAND OVER W COAST STATES DURING NEXT FEW
   HOURS...REACHING FROM WA CASCADES ACROSS WRN NV TO SRN CA BY 00Z AND
   NRN ROCKIES TO UT/AZ BY 12Z.

   AT SFC...11Z ANALYSIS SHOWED COLD FRONT EXTENDING FROM LOW OVER
   ONT/QUE BORDER SWWD ACROSS NWRN OH...WRN KY...SERN AR AND S-CENTRAL
   TX.  BY 00Z...LOW SHOULD MOVE TO NEAR NRN TIP OF NH...WITH FRONT
   SWWD ACROSS SERN NY...ERN VA...AL AND SRN LA...BECOMING
   QUASISTATIONARY OVER S TX.  BY 12Z...FRONT SHOULD EXTEND FROM SE TX
   ACROSS CENTRAL GULF COAST REGION TO SC AND ADJOINING ATLC
   WATERS...WHILE DISSIPATING OVER CENTRAL/S TX.  WRN-CONUS COLD FRONT
   SHOULD STRENGTHEN TODAY OVER ID AND NRN NV...MOVING EWD TO ERN
   BORDERS OF MT/WY AND CENTRAL CO BY END OF PERIOD.

   ...NRN ROCKIES...
   SCATTERED TO WIDELY SCATTERED TSTMS SHOULD MOVE NEWD ACROSS THIS
   REGION LATE AFTN AND EVENING...OFFERING SPORADIC DAMAGING GUSTS AND
   ISOLATED HAIL.  DESPITE LACK OF MOISTURE...ENOUGH POTENTIAL FOR
   ORGANIZED TSTM WIND EVENT IS APPARENT THAT SVR PROBABILITIES HAVE
   BEEN BOOSTED TO CATEGORICAL THRESHOLDS IN YELLOWSTONE REGION.

   STG LARGE-SCALE ASCENT/COOLING ALOFT WILL PRECEDE MID-UPPER-LEVEL
   TROUGH...ACTING IN TANDEM WITH LIMITED NEAR-SFC HEATING TO STEEPEN
   LOW-MIDDLE LEVEL LAPSE RATES.  IR IMAGERY SHOWS THICK HIGH CLOUDS
   ABOVE OUTLOOK AREA ATTM...BUT ALSO...RELATIVE SLOT OF CLEARING OVER
   PORTIONS NRN NV/SRN ID THAT SHOULD WORK NEWD OVER THIS AREA BY AFTN.
   LOW-LEVEL COLD FRONT AND RELATED FORCING...ALONG WITH OROGRAPHIC
   LIFT IN LOCALIZED UPSLOPE AREAS...SHOULD INITIATE CONVECTION THIS
   AFTN OVER PORTIONS SERN ID AND WRN MT...WHICH WOULD MOVE RAPIDLY
   NEWD AMIDST STG DEEP SHEAR.  MAIN LIMITING FACTOR WILL BE LACK OF
   MORE SUBSTANTIAL LOW-LEVEL MOISTURE...WITH PRECONVECTIVE SFC DEW
   POINTS MAINLY IN 30S F AT LOWER ELEVATIONS THANKS TO ANTECEDENT
   RAIN.

   TSTMS SHOULD BE SOMEWHAT HIGH-BASED...OFFERING BOTH
   MOMENTUM-TRANSFER POTENTIAL FROM STG FLOW ALOFT AND EVAPORATIVE
   ACCELERATIONS THROUGH WELL-MIXED SUBCLOUD LAYER.  COLD-POOL
   GENERATION AND BOWING ARE POSSIBLE IF ACTIVITY CAN AGGREGATE
   DENSELY.  THREAT SHOULD DIMINISH WITH NEWD EXTENT AFTER DARK AS
   FOREGOING BOUNDARY LAYER BECOMES MORE STABLE AND ALREADY MEAGER CAPE
   DIMINISHES.

   ...CENTRAL/NRN HIGH PLAINS...
   SUSTAINED SFC HEATING SHOULD BE SUFFICIENT TO ENCOURAGE ISOLATED TO
   WIDELY SCATTERED TSTMS BY LATE AFTN OVER HIGH PLAINS...SOME OF WHICH
   MAY FORM IN AND MOVE EWD/NEWD FROM CENTRAL ROCKIES.  DRY AIR MASS
   WILL KEEP MLCAPE VERY WEAK -- BELOW 500 J/KG MOST AREAS. 
   HOWEVER...ISOLATED DAMAGING GUSTS AND HAIL NEAR SVR LEVELS CANNOT BE
   RULED OUT GIVEN FAVORABLE LOW-MIDDLE LEVEL LAPSE RATES AND
   WELL-MIXED SUBCLOUD LAYER.

   ...MID-ATLC TO SRN APPALACHIANS REGION...
   WIDELY SCATTERED TO SCATTERED TSTMS MAY DEVELOP INVOF SFC COLD FRONT
   THIS AFTN AND EARLY EVENING...WITH A FEW VERY LOCALIZED/ISOLATED STG
   GUSTS POSSIBLE.  SFC DIABATIC HEATING WILL DESTABILIZE PREFRONTAL
   AIR MASS...BUT IN PRESENCE OF MEAGER MOISTURE SUCH THAT ONLY NARROW
   SLIVER OF 500-1000 J/KG MLCAPE IS EXPECTED AT MOST.  VERTICAL SHEAR
   AND LOW-LEVEL CONVERGENCE ALSO SHOULD BE WEAK...WITH FLOW VEERING
   AHEAD OF FRONT AND STRONGEST NRN-STREAM FLOW LAGGING BEHIND. 
   OVERALL SVR POTENTIAL APPEARS TOO CONDITIONAL AND MRGL ATTM TO
   SPECIFY A 5% AREA WITHIN THIS LONG CORRIDOR.

   ..EDWARDS/ROGERS.. 04/22/2014

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