DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 121632
SWODY1
SPC AC 121629

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CDT MON AUG 12 2013

VALID 121630Z - 131200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
BLOCKING PERSISTS WITHIN THE LARGE-SCALE UPPER PATTERN IMPACTING
MUCH OF NORTH AMERICA. A PROMINENT UPPER HIGH CENTER LINGERS OVER
THE CANADIAN NORTHWEST TERRITORIES...WHILE CYCLONIC REGIMES PERSIST
ACROSS THE NORTHEAST PACIFIC THROUGH THE PACIFIC NORTHWEST/BRITISH
COLUMBIA/ALBERTA...AS WELL AS SOUTH OF HUDSON BAY THROUGH THE
NORTHEASTERN QUARTER OF THE U.S. AND THE CANADIAN MARITIMES. TO THE
SOUTH...SUBTROPICAL RIDGING ACROSS THE SOUTHERN TIER OF THE U.S.
REMAINS FLAT...BUT WEAK RIDGING EXTENDS NORTHWARD ALONG AN AXIS
ACROSS THE ROCKIES...TOWARD THE CANADIAN HIGH CENTER...WHILE A
MODEST BELT OF CYCLONIC WESTERLIES CURVES EAST OF THE LOWER CENTRAL
PLAINS THROUGH THE MID ATLANTIC COAST. AMPLIFICATION OF THE
CYCLONIC FLOW IN THE EAST DOES APPEAR LIKELY THROUGH THE REMAINDER
OF THE PERIOD...AS A COUPLE OF SIGNIFICANT SHORT WAVE IMPULSES DIG
SOUTH OF HUDSON BAY THROUGH ONTARIO AND THE UPPER GREAT LAKES
REGION.

IN RESPONSE TO THESE DEVELOPMENTS...COOLER AND DRIER AIR WILL
CONTINUE TO GRADUALLY INFILTRATE PARTS OF THE NORTHERN PLAINS/UPPER
MIDWEST AND GREAT LAKES REGION INTO THE NORTHEAST. AT THE SAME
TIME...THE REMNANTS OF A PRECEDING FRONTAL ZONE...NOW EXTENDING
SOUTH OF THE NEW ENGLAND COAST THROUGH THE NORTHERN MID ATLANTIC
REGION...THE TENNESEE VALLEY AND OZARK PLATEAU...INTO THE SOUTH
CENTRAL PLAINS...ARE ALSO EXPECTED TO SLOWLY SHIFT SOUTHWARD.
MOISTURE CONTENT REMAINS SEASONABLY HIGH ALONG AND SOUTH OF THIS
SOUTHERN FRONTAL ZONE...BUT LOWER/MID TROPOSPHERIC LAPSE RATES HAVE
BECOME RELATIVELY WEAK ACROSS MOST AREAS SOUTH AND EAST OF THE
NORTHERN/CENTRAL HIGH PLAINS.

ACROSS THE WEST...DRYING CONTINUES ACROSS MUCH OF THE SOUTHERN
PLATEAU INTO THE GREAT BASIN...BUT IT REMAINS AT LEAST MODESTLY
MOIST ACROSS PARTS OF THE EASTERN GREAT BASIN INTO CENTRAL AND
SOUTHERN ROCKIES...AS WELL AS ACROSS PARTS OF THE PACIFIC NORTHWEST
INTO THE NORTHERN INTERMOUNTAIN REGION AND NORTHERN ROCKIES.

...OZARK PLATEAU/MID MS VALLEY INTO CENTRAL APPALACHIANS...
THE FRONTAL ZONE IS RATHER DIFFUSE ACROSS THIS REGION...BUT IN THE
PRESENCE OF HIGH MOISTURE CONTENT...AT LEAST A COUPLE OF WEAK
IMPULSES EMBEDDED WITHIN BROADLY CYCLONIC MID-LEVEL FLOW ARE
SUPPORTING AREAS OF ONGOING THUNDERSTORM ACTIVITY. ALTHOUGH
LOW-LEVEL FLOW FIELDS ARE RATHER WEAK...30-40+ KT WINDS AT OR ABOVE
500 MB MAY CONTRIBUTE TO SUFFICIENT SHEAR/MOMENTUM TO SUPPORT ONE OR
TWO ORGANIZING STORM CLUSTERS WITH AT LEAST SOME RISK FOR DAMAGING
WIND GUSTS...PARTICULARLY DURING THE PEAK AFTERNOON/EARLY EVENING
BOUNDARY LAYER INSTABILITY. PEAK WIND GUSTS STILL APPEAR LIKELY TO
REMAIN MOSTLY BELOW THE 50 KT SEVERE CRITERIA...THOUGH...PRECLUDING
AN OUTLOOK UPGRADE TO SLIGHT RISK PROBABILITIES AT THE PRESENT TIME.

...MID ATLANTIC...
LATER THIS EVENING/OVERNIGHT...THE CONTINUED EASTWARD PROGRESSION OF
THE AFOREMENTIONED UPPER IMPULSES...COUPLED WITH LARGER-SCALE TROUGH
AMPLIFICATION ACROSS MUCH OF THE NORTHEAST...MAY CONTRIBUTE TO AT
LEAST MODEST STRENGTHENING OF LOWER/MID TROPOSPHERIC FLOW FIELDS
/20-40+ KT/. DESPITE THE UNFAVORABLE TIME OF DAY WITH RESPECT TO
INSTABILITY...THIS MAY BE SUFFICIENT TO SUPPORT AT LEAST LOW
PROBABILITIES FOR SEVERE WIND GUSTS...AS LARGE-SCALE FORCING ALONG
THE STALLED OR SOUTHWARD ADVANCING FRONTAL ZONE AIDS INCREASING
CONVECTIVE DEVELOPMENT.

...CENTRAL PLAINS...
MID/UPPER SUPPORT FOR CONVECTIVE DEVELOPMENT DURING THE LATE
AFTERNOON AND EVENING REMAINS UNCLEAR. HOWEVER...MID-LEVEL CAPPING
APPEARS WEAK. AND SEASONABLY MODEST BOUNDARY LAYER HEATING AND
MIXING...TO THE SOUTH OF THE CONVECTIVELY ENHANCED LOW-LEVEL
BAROCLINIC ZONE ACROSS PARTS OF SOUTHERN KANSAS INTO NORTHERN
OKLAHOMA...MAY CONTRIBUTE TO THE INITIATION OF AT LEAST SCATTERED
STORMS. AIDED BY HEAVY PRECIPITATION LOADING...THERMODYNAMIC
PROFILES PROBABLY WILL BECOME FAVORABLE FOR AT LEAST LOCALIZED
STRONG DOWNBURSTS...WITH POTENTIALLY DAMAGING SURFACE GUSTS.

..KERR/COHEN.. 08/12/2013

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