DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 171631
SWODY1
SPC AC 171629

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CDT SAT AUG 17 2013

VALID 171630Z - 181200Z

...NO SVR TSTM AREAS FORECAST...

...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.

..KERR/COHEN.. 08/17/2013

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