[SWODY1] SWODY1

[Severe Weather Outlook Day 1]

ACUS01 KWNS 130459
SWODY1
SPC AC 130458

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
1158 PM CDT WED APR 12 2006

VALID 131200Z - 141200Z

...THERE IS A SLGT RISK OF SVR TSTMS UPPER MS VALLEY REGION TO
PORTIONS NRN/WRN OH...

...SYNOPSIS...
BASIC SYNOPTIC PATTERN WILL BE DOMINATED BY NEARLY ZONAL NRN STREAM
FROM PACIFIC NW TO UPPER GREAT LAKES...HEIGHT FALLS DOWNSTREAM OVER
NEW ENGLAND...AND BROAD SWATH OF MID/UPPER LEVEL RIDGING ACROSS MOST
OF SRN CONUS.  LOW-AMPLITUDE SHORTWAVE TROUGH -- NOW EVIDENT IN
MOISTURE CHANNEL IMAGERY OVER BC AND WA -- IS FCST TO MOVE QUICKLY
EWD ALONG AND  JUST N OF CANADIAN BORDER...REACHING REGION OF LS
NORTH SHORE AND BOUNDARY WATERS OF MN/ONT BY END OF PERIOD.

SFC FRONTAL ZONE - NOW MOVING EWD ACROSS OH VALLEY REGION AND NEARLY
STATIONARY OVER OZARKS -- IS FCST TO RETREAT/REDEVELOP NEWD ACROSS
MID/UPPER MS VALLEY THROUGH THIS PERIOD.  WEAK CYCLOGENESIS IS
REASONABLY FCST ALONG WRN PORTION OF THIS FRONTAL ZONE -- OVER SRN
MN/NRN IA REGION BY 14/00Z.  THIS LOW SHOULD SHIFT ESEWD TOWARD SRN
LOWER MI OR NWRN OH 12 HOURS THEREAFTER.  WEAK COLD FRONT SHOULD
EXTEND FROM LOW SWWD ACROSS IA/SERN NEB DURING LATE AFTERNOON.

...UPPER MS VALLEY...UPPER GREAT LAKES REGION...
MRGL AND HIGHLY CONDITIONAL SEVERE PROBABILITIES ARE FCST DURING
AFTERNOON FROM WARM FRONT SWWD ALONG COLD FRONT.  GREATER CONVECTIVE
AND SEVERE PROBABILITIES ARE AFTER DARK OVER UPPER
MIDWEST...GENERALLY WITHIN ABOUT 250 NM NE OF SFC LOW TRACK.

VERTICAL SHEAR PROFILES AND PROGGED BUOYANCY WOULD SUPPORT SUPERCELL
THREAT DURING LATE AFTERNOON INVOF SFC LOW...OR JUST E OF LOW ALONG
WARM FRONT.  HOWEVER...THIS THREAT IS STRONGLY CONDITIONAL BECAUSE
OF ANTICIPATED STRONG CAP -- EVEN MORE SO THAN SOME MODEL PROGS
INDICATE.  ETA/SPECTRAL FCSTS OF SFC DEW POINTS APCHG 70 DEG F
ACROSS NWRN MO BY 14/00Z AND ASSOCIATED LARGE CAPE/LI FCSTS APPEAR
OVERBLOWN AS WELL...CONSIDERING
1. IMPROBABILITY OF SUCH ROBUST EVAPOTRANSPIRATIVE MOISTENING IN
THAT AREA DURING MID-APRIL AND
2. DRY CHARACTER OF AIR MASS IN UPSTREAM BOUNDARY LAYER...PER
WELL-MIXED OUN/FWD SOUNDINGS.  WHEN COMPARED TO SFC HAND
ANALYSIS...13/00Z ETA INITIALIZED 3-6 DEG F TOO HIGH ON SFC DEW
POINTS IN UPSTREAM BOUNDARY LAYER...S OF WARM FRONT OVER PORTIONS
OK/AR. SPECTRAL BEGAN UP TO 10 DEG F TOO WARM ON SFC DEW POINT IN
SAME AREA.

IF SFC-BASED CONVECTION DEVELOPS NEAR SFC LOW AND WARM
FRONT...BACKED FLOW E OF LOW AND 50-60 KT MIDLEVEL WINDS WOULD
CONTRIBUTE TO FAVORABLE KINEMATIC PROFILES...WITH 0-3 KM SRH 200-300
J/KG AND 60-70 KT SFC-MIDLEVEL SHEARS. HOWEVER...SUCH DEVELOPMENT
WOULD BE VERY ISOLATED...AND MAY NOT EVEN OCCUR.  POTENTIAL FOR
BRIEF WINDOW OF LATE AFTERNOON TSTMS MAY BE SOMEWHAT LARGER ALONG
TRAILING COLD FRONT OVER IA/SERN NEB...WHERE HEATING/MIXING WILL BE
STRONGER.  DAMAGING GUSTS AND HAIL ARE POSSIBLE FROM ANY TSTMS THAT
FORM...BUT CAPPING WILL LIMIT COVERAGE.  

STRONG LOW LEVEL MOIST ADVECTION AND ELEVATED WAA ARE EXPECTED AFTER
DARK...NE OF SFC WARM FRONT.  POTENTIAL IS EXPECTED TO SHIFT ESEWD
FROM SRN MN ACROSS NRN INDIANA/SRN LOWER MI OVERNIGHT. EXPECT
INCREASING CONVECTIVE COVERAGE IN TUNE WITH INCREASING INFLOW-LAYER
MOISTURE CONTENT AND LLJ INCREASING TO 50-60 KT DURING 14/06Z-14/12Z
TIME FRAME.  8-9 DEG C/KM MIDLEVEL LAPSE RATES SHOULD SPREAD NEWD
OVER AREA AS ELEVATED MIXED-LAYER AIR ADVECTS FROM SRN/CENTRAL
PLAINS...CONTRIBUTING TO ELEVATED MUCAPES 1500-2000 J/KG.  IN
ADDITION...FAVORABLE EFFECTIVE SHEAR PROFILES -- ABOVE RELATIVELY
STABLE BOUNDARY LAYER -- WILL SUPPORT ORGANIZED SEVERE RISK WITH
LARGE HAIL THE MOST COMMON SEVERE MODE...AND DAMAGING WIND POSSIBLE
DESPITE SHALLOW/COOL BOUNDARY LAYER.


...WRN NY...NRN PA...
WIDELY SCATTERED TSTMS ARE POSSIBLE DURING AFTERNOON...AMIDST
RESIDUAL/POST-FRONTAL SFC MOISTURE AND BOUNDARY LAYER
HEATING/MIXING.  COLD AIR ALOFT IS EXPECTED INVOF MID/UPPER TROUGH
-- E.G. -23 TO -26 DEG C AT 500 MB -- ALONG WITH VERY WEAK SBCINH BY
MID-LATE AFTERNOON.  BOUNDARY LAYER FLOW IS EXPECTED TO BE
WLY...RESTRICTING BOTH VERTICAL SHEAR AND SFC CONVERGENCE...AND BY
EXTENSION...LIMITING CONVECTIVE COVERAGE. HOWEVER...CONSIDERING COLD
AIR MASS THROUGH MIDTROPOSPHERE...ISOLATED HAIL NEAR SEVERE LEVELS
IS POSSIBLE.

..EDWARDS.. 04/13/2006