DAY3SVR: Nws Storm Prediction Center Norman Ok

ACUS03 KWNS 200733
SWODY3
SPC AC 200731

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0231 AM CDT THU SEP 20 2012

VALID 221200Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NY/WRN NEW ENGLAND TO
INLAND MID-ATLC......

...SYNOPSIS...
LARGE-SCALE TROUGHING WILL PERSIST FROM GREAT LAKES DOWN MS VALLEY
TO NRN GULF. PRIMARY/EMBEDDED SHORTWAVE PERTURBATION DESCRIBED IN
DAY-2 OUTLOOK SHOULD PIVOT EWD THROUGH MEAN TROUGH POSITION...FROM
IL/LM ACROSS LOWER MI...INDIANA...OH...AND LE. PROGS DO VARY SOME
IN LATITUDINAL EXTENT REGARDING TRACK OF THIS SYSTEM.
NONETHELESS...WHAT AMOUNTS TO JUST MESOSCALE DISCREPANCIES ALOFT
THIS FAR IN ADVANCE NOW OFFERS REASONABLE CONFIDENCE IN
TIMING/PLACEMENT OF ASSOCIATED FRONTAL ZONE AND ACCOMPANYING BELT OF
STG LOW-LEVEL FORCING.

SFC COLD FRONT SHOULD MOVE EWD ACROSS MID-ATLC AND CENTRAL
APPALACHIANS REGIONS EARLY-MIDDLE PERIOD...REACHING ERN NY...ERN
PA...WRN VA...ERN TN...AND NRN/CENTRAL AL BY 23/00Z. FRONT SHOULD
PROCEED EWD TO NEAR WRN MAINE...CAPE COD...ERN NC AND FL PANHANDLE
BY END OF PERIOD. PASSAGE OF FRONT ACROSS OUTLOOK AREA SHOULD BE
TIMED WELL WITH RESPECT TO PEAK WARM-SECTOR THETAE.

...NERN CONUS...MID-ATLC...
AS FRONT AND PERHAPS PREFRONTAL CONFLUENCE LINE PROCEED
EWD...RELATED CORRIDOR OF ENHANCED LIFT WILL IMPINGE ON
PROGRESSIVELY GREATER ATLC-BASED RETURN-FLOW MOISTURE WITH EWD
EXTENT. SFC DEW POINTS MID-50S TO MID-60S F SHOULD BE ENOUGH TO
SUPPORT SFC-BASED CONVECTIVE DEVELOPMENT IN PRESENCE OF SUCH
LIFT...EVEN IF PREFRONTAL DIABATIC SFC HEATING IS MUTED CONSIDERABLY
BY CLOUD COVER. LAPSE RATES ALOFT WILL BE RELATIVELY WEAK...AND
NEITHER BUOYANCY NOR DEEP-LAYER FORCING APPEAR TO BE QUITE AS STG AS
MOST RECENT EVENT IN THIS REGION. STILL...PRESENCE OF AT LEAST MRGL
CAPE JUXTAPOSED WITH STG DEEP-LAYER WIND FIELDS INDICATES
DAMAGING-WIND POTENTIAL. AS SUCH...15% THRESHOLD UNCONDITIONAL
PROBABILITIES ARE IS BEING INTRODUCED ATTM...SUBJECT TO INCREASE IN
FUTURE OUTLOOKS IF INSTABILITY/KINEMATIC TRENDS WARRANT.

OVERALL SVR THREAT GENERALLY WILL LESSEN AND BECOME MORE CONDITIONAL
WITH SWD EXTENT THROUGH CAROLINAS/SERN CONUS...WITH INCREASING
DISTANCE FROM STRONGEST ISALLOBARIC FORCING...MID-UPPER WINDS...AND
FRONTAL LIFT.

..EDWARDS.. 09/20/2012

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