SWODY1
SPC AC 181957
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0257 PM CDT WED APR 18 2012
VALID 182000Z - 191200Z
...NO SVR TSTM AREAS FORECAST...
...SOUTHEAST...
HAVE CONFINED MARGINAL DAMAGING WIND PROBABILITIES TO PARTS OF ERN
SC AND SERN NC AHEAD OF A LEAD MID-LEVEL IMPULSE AND ONGOING TSTM
CLUSTER IN ERN SC /SEE MCD 0565 FOR ADDITIONAL NEAR-TERM
INFORMATION/. ELSEWHERE...MORE ABUNDANT CLOUD COVERAGE AMIDST WEAK
INSTABILITY AND DIMINISHING MID-LEVEL FLOW IN ASSOCIATION WITH THE
DAMPENING SHORT WAVE TROUGH SUGGESTS THE DAMAGING WIND THREAT FROM
ORGANIZED TSTMS IS MINIMAL.
...UPPER MIDWEST...
PREVIOUS FORECAST REASONING REMAINS VALID. HAVE CONFINED MARGINAL
HAIL/WIND PROBABILITIES TO AREAS DOWNSTREAM OF THE COLD FRONT MOVING
SEWD ACROSS THE REGION.
...BLACK HILLS TO MID-MO VALLEY...
PREVIOUS FORECAST SCENARIO APPEARS REASONABLE WITH HIGH-BASED
CONVECTION INITIATING OVER PARTS OF ERN WY TOWARDS THE BLACK
HILLS/WRN NEB PANHANDLE WITHIN A MINIMALLY BUOYANT AIR MASS. AS THIS
ACTIVITY SHIFTS EWD...IT MAY INTENSIFY TONIGHT MAINLY ACROSS NEB AS
MEAGER BUT INCREASING LOW-LEVEL MOISTURE IS ADVECTED N/NWWD IN THE
CNTRL PLAINS.
..GRAMS.. 04/18/2012
.PREV DISCUSSION... /ISSUED 1120 AM CDT WED APR 18 2012/
...SOUTHEAST...
A MID/UPPER LEVEL DISTURBANCE WILL SPREAD EWD ACROSS THE SOUTHEAST
U.S. COASTLINE TODAY AND RESULT IN AN INCREASE IN SCATTERED TSTMS
THROUGH THE AFTERNOON AND INTO THE EVENING HOURS FROM NRN FL TO THE
ERN CAROLINAS. KTLH RAOB DEPICTS DEEP MOISTURE BUT WEAK INSTABILITY
AMIDST MODEST EFFECTIVE SHEAR ON THE ORDER OF 30KT. SOME UPDRAFTS
AHEAD OF WEAK FRONTAL WAVE OFFSHORE OF FL PNHDL COULD EXHIBIT WEAK
ROTATION AND A WATERSPOUT OR TWO CANNOT BE RULED OUT.
HOWEVER...OVERALL SEVERE POTENTIAL APPEARS LOW.
FARTHER EAST...MORNING SOUNDINGS FROM KJAX AND KCHS EXHIBIT
CONSIDERABLE INHIBITION THAT WILL NEED TO BE OVERCOME TO SUPPORT THE
FORECAST OF TSTMS THROUGH THE AFTERNOON. DESPITE LARGE SCALE ASCENT
ACTING TO REMOVE THE CONVECTIVE INHIBITION...GENERALLY WEAK LAPSE
RATES AND VERTICAL SHEAR AOB 30KT SHOULD LIMIT SEVERE POTENTIAL WITH
ONLY A LOW PROBABILITY OF A COUPLE OF STORMS ATTAINING SUFFICIENT
INTENSITY TO POSE A THREAT OF STRONG TO DAMAGING WINDS.
FURTHERMORE...SPC HAIL GUIDANCE INDICATES THAT HAIL SIZE SHOULD
REMAIN BELOW 1 INCH IN DIAMETER.
...UPPER MIDWEST...
A COMPACT AND PROGRESSIVE SHORT WAVE TROUGH CROSSING MN/WI TODAY
PRODUCED 90M 500MB HEIGHT FALLS ACROSS THESE AREAS OVERNIGHT. IN
RESPONSE...1006MB SURFACE LOW...NOW NEAR DLH...IS FORECAST TO TRACK
NEWD ACROSS LAKE SUPERIOR AND INTO SRN CANADA THROUGH THIS EVENING.
A WEAK COLD FRONT TRAILS THE LOW SWWD AND IS FORECAST TO BECOME
QUASI-STATIONARY ACROSS IA. WEAK DESTABILIZATION AND
MESOSCALE/FOCUSED LIFT ALONG THIS STALLED BOUNDARY MAY BE SUFFICIENT
FOR ISOLATED TSTM DEVELOPMENT WITH LOW PROBABILITY HAIL/WIND
POTENTIAL LATER THIS AFTERNOON. THE PROSPECT FOR MORE
ROBUST/WIDESPREAD STORM DEVELOPMENT APPEARS LIMITED BY A NUMBER OF
FACTORS INCLUDING: 1) MEAGER MOISTURE AND 2) LACK OF STRONGER LARGE
SCALE ASCENT DUE TO THE FRONT BEING SITUATED WITHIN AN AREA OF
NEUTRAL HEIGHT CHANGE BETWEEN THE DEPARTING SHORT WAVE MOVING INTO
CANADA AND THE NEXT UPSTREAM SYSTEM MOVING EAST FROM THE
ROCKIES/HIGH PLAINS.
...NRN HIGH PLAINS ACROSS NRN PLAINS LATE...
IN THE WAKE OF THE SYSTEM OVER THE GREAT LAKES/SRN CANADA...ANOTHER
LOW AMPLITUDE SHORT WAVE TROUGH IS FORECAST TO SPREAD EAST FROM THE
ROCKIES TO THE NRN PLAINS THROUGH TONIGHT. LEE TROUGHING AND LOW
LEVEL MASS RESPONSE TO THIS IMPULSE WILL BEGIN TO OCCUR LATER THIS
AFTERNOON BUT...HERE TOO...MOISTURE REMAINS VERY LIMITED.
NONETHELESS...LIFT AND DECREASING STATIC STABILITY ALONG WITH AN
INCREASE IN OROGRAPHIC UPLIFT IN THE LOWER LEVELS ARE EXPECTED TO
CONTRIBUTE TO HIGH-BASED CONVECTION INITIATING NEAR THERMAL/LEE
TROUGH OVER WY BY EVENING. A SMALL CLUSTER STORMS MAY BE MAINTAINED
EAST INTO THE NRN PLAINS OVERNIGHT WITH ONLY A LOW PROBABILITY OF
HAIL/WIND EVENTS ACCOMPANYING THIS ACTIVITY THROUGH EARLY THURSDAY
MORNING.
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