Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 281947
SWODY1
SPC AC 281945

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0245 PM CDT WED SEP 28 2016

VALID 282000Z - 291200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON INTO
TONIGHT ALONG AND EAST OF THE BLUE RIDGE MOUNTAINS THROUGH THE
PIEDMONT OF THE CAROLINAS AND VIRGINIA...AND PERHAPS ADJACENT
PORTIONS OF THE COASTAL PLAIN...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS SURROUNDING AREAS OF THE
MID ATLANTIC STATES/CENTRAL APPALACHIANS REGION...

...SUMMARY...
THUNDERSTORMS IMPACTING THE PIEDMONT OF THE CAROLINAS AND VIRGINIA
LATE THIS AFTERNOON INTO TONIGHT WILL POSE A RISK FOR SEVERE
WEATHER.  THIS INCLUDES THE POSSIBILITY FOR A TORNADO OR TWO...BUT
LOCALLY STRONG SURFACE GUSTS AND HAIL APPEAR THE PRIMARY POTENTIAL
HAZARDS.

...20Z OUTLOOK UPDATE...
SOME TWEAKS TO PROBABILISTIC AND CATEGORICAL LINES HAVE BEEN MADE TO
ACCOUNT FOR CURRENT TRENDS IN MODEL OUTPUT AND OBSERVATIONAL DATA.
CONSIDERABLE INSOLATION ACROSS THE CAROLINAS INTO SOUTHERN VIRGINIA
APPEARS TO HAVE CONTRIBUTED TO CAPE OF 1000-1500 J/KG ALONG AND
SOUTH OF A LINGERING FRONTAL ZONE EXTENDING ACROSS THE SOUTHERN
DELMARVA PENINSULA AND SOUTHERN VIRGINIA...INTO THE MOUNTAINS OF
SOUTHWEST VIRGINIA AND NORTH CAROLINA.  A RELATIVELY COOL/STABLE
NEAR SURFACE LAYER NOW PRESENT TO THE NORTH OF THE FRONT SEEMS
LIKELY TO HOLD THROUGH TONIGHT ACROSS MUCH OF NORTHERN
VIRGINIA/CENTRAL AND EASTERN MARYLAND...WITH ANY SURFACE PRESSURE
FALLS TO THE LEE OF THE APPALACHIANS FORECAST TO REMAIN WEAK AND
CONFINED TO THE WESTERN CAROLINAS LATE THIS AFTERNOON...PERHAPS
NORTHWARD INTO THE PIEDMONT OF CENTRAL VIRGINIA BY LATE EVENING.

SUBSTANTIVE MID-LEVEL HEIGHT FALLS...THE MID-LEVEL COLD CORE AND
CORE OF STRONGER WINDS ALOFT ASSOCIATED WITH CLOSED LOW NOW DIGGING
INTO THE MIDDLE OHIO VALLEY APPEAR LIKELY TO REMAIN CONFINED TO
AREAS NEAR AND WEST OF THE CREST OF THE CENTRAL APPALACHIANS.
HOWEVER...DEEP LAYER SHEAR CURRENTLY APPEARS SUFFICIENT FOR
ORGANIZED STORM DEVELOPMENT...INCLUDING SUPERCELLS...WHERE THE
BOUNDARY LAYER HAS ALREADY DESTABILIZED ACROSS THE VIRGINIA AND
CAROLINA PIEDMONT.  AND IT STILL APPEARS POSSIBLE THAT AN AREA OF
MID-LEVEL FORCING FOR ASCENT PIVOTING AROUND THE PERIPHERY OF THE
CLOSED LOW COULD AUGMENT STORM DEVELOPMENT TO THE EAST OF THE BLUE
RIDGE MOUNTAINS BY THE 00-03Z TIME FRAME.  ALTHOUGH LOW-LEVEL WIND
FIELDS/HODOGRAPHS ARE CURRENTLY RATHER MODEST TO WEAK...MODEL OUTPUT
SUGGESTS A COINCIDING STRENGTHENING OF SOUTHERLY 850 MB WINDS  ALONG
THE FRONTAL ZONE ACROSS SOUTH CENTRAL VIRGINIA... TO AROUND 30+ KT.
ASSOCIATED ENLARGEMENT OF LOW-LEVEL HODOGRAPHS COULD BE ACCOMPANIED
BY SOME INCREASE IN TORNADIC POTENTIAL BEFORE BOUNDARY LAYER
INSTABILITY WANES OVERNIGHT.

..KERR.. 09/28/2016

.PREV DISCUSSION... /ISSUED 1128 AM CDT WED SEP 28 2016/

...MID ATLANTIC REGION...
A LARGE UPPER LOW IS CURRENTLY CENTERED NEAR CHICAGO...TRACKING
SOUTHWARD INTO THE MID MS AND OH VALLEYS.  CYCLONICALLY CURVED AND
MODERATELY STRONG MID-LEVEL WINDS EXTEND FROM THE BASE OF THE TROUGH
INTO THE MID-ATLANTIC REGION...WHERE A MOIST AND UNSTABLE AIR MASS
IS IN PLACE.  INCREASING DAYTIME HEATING OVER PARTS OF MD/VA/NC IS
LEADING TO POCKETS OF MODERATE CAPE AND THE LIKELIHOOD OF AFTERNOON
THUNDERSTORM DEVELOPMENT.

EARLY INITIATION MAY OCCUR OVER PARTS OF EASTERN VA INTO NORTHEAST
NC.  THIS ACTIVITY MAY INCLUDE ROTATING STORMS CAPABLE OF LOCALLY
DAMAGING WIND GUSTS AND PERHAPS A TORNADO OR TWO.  PLEASE REFER TO
MCD NUMBER 1738 FOR FURTHER DETAILS ON THIS REGION.

BY MID-LATE AFTERNOON...SCATTERED THUNDERSTORMS ARE POSSIBLE
THROUGHOUT THE SLIGHT RISK AREA.  MOST MODEL SOLUTIONS SUGGEST THAT
SOUTHERLY LOW LEVEL WINDS STRENGTHEN JUST AFTER DARK...WHICH WOULD
IN TURN INCREASE THE POSSIBILITY OF A FEW TORNADOES IN THE STRONGEST
CELLS.  OTHERWISE...DAMAGING WINDS APPEAR TO BE THE MAIN THREAT.

...OH VALLEY...
THE CORE OF THE UPPER LOW WILL TRACK ACROSS PARTS OF IL/IND/OH THIS
AFTERNOON...COINCIDENT WITH A POCKET OF COLD MID LEVEL TEMPERATURES
AND VORTICITY ALOFT.  VISIBLE SATELLITE TRENDS SUGGEST THAT LITTLE
IN THE WAY OF HEATING WILL OCCUR AHEAD OF THE SURFACE
BOUNDARY...LIMITING DESTABILIZATION.  WHILE SCATTERED THUNDERSTORMS
ARE EXPECTED IN THIS REGION...THE RISK OF LARGE HAIL APPEARS TO BE
BELOW 5 PERCENT.  NEVERTHELESS SMALL HAIL AND FUNNEL CLOUDS ARE
POSSIBLE IN THE STRONGER CORES THIS AFTERNOON.

$$


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