Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 280559
SWODY1
SPC AC 280557

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1257 AM CDT THU AUG 28 2014

VALID 281200Z - 291200Z

...NO SVR TSTM AREAS FORECAST...

...SUMMARY...
SCATTERED STRONG THUNDERSTORM ACTIVITY IS POSSIBLE TODAY ALONG A
STALLED FRONT ACROSS THE MIDDLE MISSOURI VALLEY...SOUTHWARD INTO THE
SOUTHERN HIGH PLAINS.  ADDITIONAL...BUT MORE WIDELY
SCATTERED...STRONG STORMS ARE POSSIBLE ALONG THE FRONT...FROM THE
MIDDLE ATLANTIC COAST INTO THE LOWER OHIO AND MIDDLE MISSISSIPPI
VALLEYS.

...SYNOPSIS...
THE STRONGER MID-LEVEL WESTERLIES WILL REMAIN GENERALLY CONFINED TO
CANADA AND THE FAR NORTHERN TIER OF THE U.S. THROUGH THIS FORECAST
PERIOD...WITH A NUMBER OF EMBEDDED...PROGRESSIVE SHORT WAVE
IMPULSES.  AS ONE OF THESE FEATURES CONTINUES EASTWARD ACROSS THE
CANADIAN MARITIMES AND NEW ENGLAND TODAY...AN ASSOCIATED SURFACE
FRONTAL ZONE MAY ADVANCE SOUTHWARD INTO SOUTHERN MID ATLANTIC
COASTAL AREAS LATER TODAY AND TONIGHT.  FARTHER WEST...THE FRONT IS
EXPECTED TO STALL OVER PARTS OF THE LOWER OHIO AND MIDDLE
MISSISSIPPI/MISSOURI VALLEYS...BEFORE BEGINNING TO ADVANCE OR
REDEVELOP EAST NORTHEASTWARD AHEAD OF A CLOSED LOW PROGRESSING
SLOWLY EAST OF THE CENTRAL ROCKIES.

THIS LATTER FEATURE IS EMBEDDED WITHIN THE SOUTHERN BRANCH OF SPLIT
HIGH LEVELS WESTERLIES...GENERALLY ON THE NORTHERN PERIPHERY OF
SUBTROPICAL RIDGING.  ASSOCIATED TROUGHING AT LOWER/MID LEVELS IS
FORECAST TO SHIFT ACROSS THE CENTRAL AND SOUTHERN PLAINS...BETWEEN
MID-LEVEL SUBTROPICAL HIGH CENTERS OFF THE PACIFIC COAST AND NEAR
THE SOUTH ATLANTIC COAST.  BUT IT APPEARS THAT A WEAK IMPULSE
EMERGING FROM IT WILL MIGRATE NORTHEAST OF THE MID MISSOURI
VALLEY...TOWARD THE UPPER MIDWEST.  AS IT DOES...MODELS SUGGEST THAT
SOUTHERLY LOWER/MID TROPOSPHERIC FLOW FIELDS AHEAD OF THE LARGER
SCALE TROUGHING...ACROSS THE SOUTHERN PLAINS INTO THE VICINITY OF
THE STALLED FRONTAL ZONE OVER THE MID MISSOURI VALLEY...WILL BECOME
INCREASINGLY WEAK.

...MID MISSOURI VALLEY INTO THE SOUTHERN PLAINS...
WIDESPREAD CONVECTION NOW FORMING ACROSS THE NORTH CENTRAL PLAINS IS
EXPECTED TO SLOW THE NORTHEASTWARD RETREAT OF THE STALLING FRONTAL
ZONE OVER THE MIDDLE MISSOURI VALLEY.  IT MAY NOT BE OUT OF THE
QUESTION THAT A STRONGER CLUSTER OF STORMS COULD FORM ON THE
SOUTHERN PERIPHERY OF THIS ACTIVITY EARLY IN THE DAY.  IF THIS
OCCURS...THERE COULD BE SOME RISK FOR SEVERE WINDS/HAIL ACROSS PARTS
OF SOUTHERN IOWA...AND PERHAPS PARTS OF NORTHERN MISSOURI INTO
ILLINOIS...BEFORE THE SUPPORT PROVIDED BY THE MID-LEVEL IMPULSE
MIGRATING NORTH OF THE FRONT...TOWARD THE UPPER
MIDWEST...DIMINISHES.

LATER IN THE DAY...A CORRIDOR OF STRONGER DESTABILIZATION ALONG THE
PLAINS SURFACE TROUGH...TO THE SOUTH OF THE FRONT...FROM EASTERN
NEBRASKA INTO NORTHWEST TEXAS...SEEMS LIKELY TO BECOME THE PRIMARY
FOCUS FOR VIGOROUS CONVECTIVE DEVELOPMENT.  THIS WILL BE AIDED BY
FORCING FOR ASCENT AHEAD OF THE MID/UPPER TROUGHING...IN THE
PRESENCE OF AT LEAST MODERATE CAPE ON THE ORDER OF 1000 TO 2000
J/KG.  LOCALLY SEVERE WIND OR HAIL MAY NOT BE OUT OF THE QUESTION IN
THE STRONGEST ACTIVITY...BUT THE OVERALL SEVERE THREAT IS EXPECTED
TO BE LIMITED BY THE LACK OF STEEPER LOW/MID-LEVEL LAPSE RATES AND
THE WEAK NATURE OF THE DEEP LAYER WIND FIELDS/SHEAR.

...SRN MID ATLANTIC COAST INTO LWR OH/MID MS VALLEYS...
DEEP LAYER FLOW AND SHEAR ALONG THE AFOREMENTIONED FRONTAL ZONE IS
EXPECTED TO BE WEAK...WITH MID/UPPER SUPPORT FOR CONVECTIVE
DEVELOPMENT CURRENTLY UNCLEAR.  HOWEVER...MOISTURE CONTENT ALONG AND
SOUTH OF THE FRONT REMAINS SEASONABLY HIGH...AND DESTABILIZATION
PROBABLY WILL BE SUFFICIENT TO SUPPORT WIDELY SCATTERED THUNDERSTORM
ACTIVITY WHICH MAY BE CAPABLE OF PRODUCING LOCALIZED STRONG WIND
GUSTS.

..KERR/HART.. 08/28/2014



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