DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 211958
SWODY1
SPC AC 211956

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0256 PM CDT SAT SEP 21 2013

VALID 212000Z - 221200Z

...NO SVR TSTM AREAS FORECAST...

...SERN STATES...
THE ERN LONGWAVE TROUGH AND ATTENDANT COLD FRONT WILL CONTINUE TO
SHIFT EWD...ALLOWING THE WRN EXTENT OF THE 2 PERCENT TORNADO
PROBABILITY AND GENERAL TSTM AREA TO BE SHIFTED EWD. THE REST OF THE
2 PERCENT TORNADO PROBABILITY FORECAST REMAINS ON TRACK.

EARLY AFTERNOON RADAR IMAGERY SHOWED A COUPLE OF N-S ORIENTED LINES
OF CONVECTION/EMBEDDED TSTMS WITH SOME WEAK ROTATIONAL COUPLETS.
THE DOWNSTREAM ENVIRONMENT IS MARGINALLY UNSTABLE TO SUPPORT FURTHER
TSTMS THROUGH THE AFTERNOON...THOUGH WEAK DEEP LAYER AND LOW LEVEL
SHEAR PER AREA VADS WILL CONTINUE TO LIMIT THE OVERALL SEVERE
WEATHER THREAT.

...DELMARVA INTO SRN NEW ENGLAND...
NO CHANGES FOR THIS OUTLOOK AREA. REFER TO THE DISCUSSION ISSUED AT
1128 AM CDT.

..PETERS.. 09/21/2013

.PREV DISCUSSION... /ISSUED 1128 AM CDT SAT SEP 21 2013/

...DELMARVA INTO SRN NEW ENGLAND...
PROGRESSIVE UPPER FLOW PATTERN WILL CONTINUE DURING THE PERIOD AS A
STRONG SHORT WAVE TROUGH EXTENDING FROM THE GREAT LAKES ACROSS THE
MID-SOUTH AND ARKLATEX REGION MOVES EWD/SEWD THROUGH TONIGHT.
WIDESPREAD CLOUDS AND PRECIPITATION ARE OCCURRING IN ADVANCE OF THE
UPPER SYSTEM AND ASSOCIATED COLD FRONT WITHIN A VERY MOIST AIR
MASS...WITH PW VALUES RANGING FROM 1.5 IN OVER THE LOWER GREAT LAKES
TO AOA 2 IN FROM THE TN VALLEY SWD INTO THE WRN/CENTRAL GULF OF
MEXICO. 12Z RAOBS ALSO INDICATE WEAK LAPSE RATES WITHIN THIS
ENVIRONMENT WHICH IS LIMITING THE MAGNITUDE OF INSTABILITY AND
RESULTANT VERTICAL VELOCITY OF CONVECTIVE UPDRAFTS.

DYNAMIC FORCING FOR LARGE SCALE ASCENT IS EXPECTED TO BE STRONGEST
FROM THE DELMARVA NWD INTO NEW ENGLAND LATER THIS AFTERNOON AND
TONIGHT IN ASSOCIATION WITH INCREASING DCVA AND DIVERGENCE ALOFT
WITHIN THE EXIT REGION OF THE MERIDIONALLY-ORIENTED UPPER JET.
DESPITE WEAK INSTABILITY WITH CAPE AOB 500 J/KG...A FEW LOW-TOPPED
CONVECTIVE CLUSTERS/SHORT LINE SEGMENTS MAY DEVELOP ACROSS THIS
REGION AS THE FRONT MOVES EWD. CG LIGHTNING IS EXPECTED TO BE
LIMITED...HOWEVER...INCREASING SSWLY LOW LEVEL FLOW /40-50 KT AT 850
MB/ SUGGESTS POTENTIAL FOR ISOLATED STRONG WIND GUSTS AT THE SURFACE
AS DOWNWARD TRANSFER OF STRONG HORIZONTAL MOMENTUM OCCURS WITHIN
CONVECTIVE DOWNDRAFTS. A 5% WIND PROBABILITY HAS BEEN INTRODUCED TO
ACCOUNT FOR THIS POSSIBILITY...BUT WEAK INSTABILITY AND RESULTANT
LOW THUNDERSTORM PROBABILITY ARE EXPECTED TO LIMIT OVERALL SEVERE
THREAT.

...SERN STATES INTO ERN PARTS OF SC/NC...
STRONGEST CONVECTION IS CURRENTLY OVER THE CENTRAL GULF OF MEXICO
AND IMMEDIATE COASTAL SECTIONS LA/MS/AL AND NWRN FL. RADAR HAS
INDICATED WEAK ROTATIONAL COUPLETS IN ISOLATED CONVECTIVE CELLS
FARTHER INLAND FROM SERN LA INTO NRN AL EARLIER IN THE MORNING IN
ASSOCIATION WITH 30-40 KT SWLY LOW LEVEL WINDS AND MARGINALLY
FAVORABLE LOW LEVEL SHEAR. A THREAT FOR A BRIEF TORNADO OR TWO MAY
PERSIST INTO THE AFTERNOON OVER PARTS OF AL/GA AND NWRN FL THIS
AFTERNOON...AND THEN REDEVELOP TONIGHT FARTHER TO THE NORTHEAST OVER
THE COASTAL PARTS OF THE CAROLINAS AS THE ENVIRONMENT BECOMES
MARGINALLY UNSTABLE AND STRONGER LOW LEVEL FLOW/SHEAR OVERSPREAD THE
REGION.

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