SPC AC 171954

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0254 PM CDT SAT AUG 17 2013

   VALID 172000Z - 181200Z

   ...NO SVR TSTM AREAS FORECAST...

   ...GREAT BASIN/FOUR CORNERS...
   TRENDS IN AFTERNOON RADAR/SATELLITE IMAGERY AND LIGHTNING DATA
   INDICATED SCATTERED TO NUMEROUS TSTMS HAVE DEVELOPED OVER THE FOUR
   CORNERS STATES AND GREAT BASIN WITHIN A MOISTURE PLUME AND FORCING
   FOR ASCENT ATTENDANT TO ONE OR TWO MIDLEVEL SHORTWAVE TROUGHS. WHILE
   WEAK BULK SHEAR WILL LIMIT STORM ORGANIZATION/SUSTENANCE AND HIGHER
   SEVERE PROBABILITIES...FAVORABLE THERMODYNAMICS WILL SUPPORT A
   THREAT FOR A FEW STORMS TO PRODUCE STRONG/DAMAGING WIND GUSTS AND/OR
   SOME HAIL.  FOR ADDITIONAL DETAILS...REFER TO SPC MESOSCALE
   DISCUSSION 1733.

   ...SRN HIGH PLAINS...
   SIMILAR TO FRIDAY...TSTM DEVELOPMENT HAS BEEN CONFINED TO THE HIGHER
   TERRAIN /SANGRE DE CRISTO MTNS AND SACRAMENTO MTNS/ OF ERN NM AND
   ADJACENT PART OF CO.  THE ENVIRONMENT ALONG AND EXTENDING EWD INTO
   THE ADJACENT HIGH PLAINS HAS BECOME MODERATELY UNSTABLE WITH
   EFFECTIVE BULK SHEAR OF 30-40 KT EXPECTED THROUGH THE EVENING. THESE
   FACTORS WOULD SUPPORT AN INCREASE IN STORM ORGANIZATION/INTENSITY
   WITH ACTIVITY THAT IS ABLE TO MOVE OFF THE HIGHER TERRAIN.

   ...NRN ROCKIES INTO NRN PLAINS AND CENTRAL/ERN GULF COAST...
   THE FORECAST FOR THESE REGIONS REMAINS ON TRACK WITH NO CHANGES
   NEEDED TO THE CONVECTIVE OUTLOOK. REFER TO THE PREVIOUS DISCUSSION
   INCLUDED BELOW FOR DETAILS ABOUT THESE THREE AREAS.

   ..PETERS.. 08/17/2013

   .PREV DISCUSSION... /ISSUED 1129 AM CDT SAT AUG 17 2013/

   ...SYNOPSIS...
   THE PRIMARY BELT OF WESTERLIES CONTINUES TO EXTEND IN GENERALLY
   ZONAL FASHION NEAR/NORTH OF THE CANADIAN/U.S. BORDER AREA...WITH A
   STRONG MID LATITUDE PACIFIC JET STREAK LIKELY BEGINNING TO NOSE INTO
   BRITISH COLUMBIA LATER TODAY/TONIGHT.  A NUMBER OF SHORT WAVE
   PERTURBATIONS ARE EMBEDDED WITHIN THIS REGIME...INCLUDING ONE WHICH
   APPEARS TO BE IN THE PROCESS OF CONTRIBUTING TO FLATTENING OF THE
   CREST OF AN UPPER RIDGE...ACROSS THE NORTHERN ROCKIES/PLAINS...THAT
   EXTENDS NORTH OF A SUBTROPICAL HIGH CENTER OVER THE SOUTHERN
   PLATEAU.  BETWEEN THIS LATTER FEATURE AND ANOTHER SUBTROPICAL
   HIGH...OVER THE SOUTHWESTERN ATLANTIC...A CLOSED LOW HAS
   DEVELOPED...AND IS FORECAST TO LINGER...ACROSS THE MIDDLE
   MISSISSIPPI/LOWER OHIO VALLEY REGION.  ALONG AND AHEAD OF A TROUGH
   AXIS TRAILING TO THE SOUTH...THROUGH THE WESTERN GULF OF MEXICO...AN
   INCREASINGLY SHEARED MID-LEVEL PERTURBATION MAY MIGRATE NORTHWARD
   INTO CENTRAL GULF COASTAL AREAS BY 12Z SUNDAY.

   IN RESPONSE TO RECENT AND FORECAST UPPER DEVELOPMENTS...SEASONABLY
   HIGH MOISTURE CONTENT AIR HAS BECOME CONFINED TO A STALLED FRONTAL
   ZONE NEAR CENTRAL/EASTERN GULF AND SOUTH ATLANTIC COASTAL
   AREAS...ALTHOUGH A RETURN OF MONSOONAL MOISTURE IS OCCURRING ACROSS
   PARTS OF THE SOUTHERN PLATEAU.  MID-LEVEL LAPSE RATES ASSOCIATED
   WITH VERY WARM AND CAPPING ELEVATED MIXED LAYER AIR HAVE STEEPENED
   IN A PLUME ACROSS PARTS OF THE NORTHERN PLAINS INTO SASKATCHEWAN AND
   MANITOBA.  THIS MAY BE SHUNTED SOUTHWARD A BIT TODAY...WHILE ALSO
   CONTINUING TO ADVECT EASTWARD TOWARD THE UPPER MISSISSIPPI
   VALLEY...WITH SIMILARLY WARM ELEVATED MIXED LAYER AIR ALSO ADVANCING
   MUCH MORE SLOWLY EAST OF THE CENTRAL AND SOUTHERN HIGH PLAINS.

   ...NORTHERN ROCKIES INTO NORTHERN PLAINS...
   MODEST LOW-LEVEL MOISTURE ALONG/EAST OF A LEE SURFACE TROUGH ACROSS
   THE WESTERN/CENTRAL DAKOTAS INTO SASKATCHEWAN AND MANITOBA MAY BE
   SUFFICIENT FOR THE DEVELOPMENT OF SIZABLE CAPE BY LATE AFTERNOON. 
   THIS ENVIRONMENT...HOWEVER...PARTICULARLY SOUTH OF THE INTERNATIONAL
   BORDER...LIKELY WILL REMAIN CAPPED INTO EARLY EVENING BY THE VERY
   WARM ELEVATED MIXED LAYER AIR.  STORM INITIATION APPEARS MOST LIKELY
   ACROSS THE MOUNTAINS OF WESTERN MONTANA...PERHAPS AIDED BY A WEAK
   IMPULSE ROUNDING THE CREST OF THE FLATTENING RIDGE.  DESPITE WEAKER
   INSTABILITY...DEEP LAYER SHEAR MAY STILL BE SUFFICIENT TO SUPPORT
   ISOLATED SUPERCELLS WITH AT LEAST LOW POTENTIAL FOR SEVERE WIND AND
   HAIL AS THEY PROPAGATE OFF THE HIGHER TERRAIN INTO PARTS OF CENTRAL
   MONTANA.  LATER THIS EVENING...AN INCREASE IN FORCING ASSOCIATED
   WITH LOWER/MID TROPOSPHERIC WARM ADVECTION MAY CONTRIBUTE TO
   WEAKENING INHIBITION AND CONVECTIVE DEVELOPMENT NEAR THE
   INTERNATIONAL BORDER AREA...POSSIBLY SOUTHWARD INTO PARTS OF
   NORTHERN NORTH DAKOTA.  IF THIS OCCURS...THE ENVIRONMENT PROBABLY
   WILL BE CONDUCIVE FOR SUPERCELLS...AND PERHAPS AN UPSCALE GROWING
   CONVECTIVE SYSTEM CAPABLE OF PRODUCING SEVERE WIND/HAIL.

   ...CENTRAL/EASTERN GULF COAST...
   AT LEAST SOME STRENGTHENING IN LOWER/MID TROPOSPHERIC WIND FIELDS
   APPEARS POSSIBLE BY LATE TONIGHT.  ALTHOUGH SUBSTANTIAL UNCERTAINTY
   REMAINS...IT IS NOT OUT OF THE QUESTION THAT THIS COULD CONTRIBUTE
   TO SUFFICIENT SHEAR...IN THE PRESENCE OF SEASONABLY HIGH MOISTURE
   CONTENT AIR...TO SUPPORT LOW SEVERE WIND/TORNADO PROBABILITIES IN
   ASSOCIATION WITH ANTICIPATED CONVECTIVE DEVELOPMENT.

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