SPC AC 271728
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CDT FRI APR 27 2012
VALID 281200Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE OH VALLEY
INTO SERN MO...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PART OF THE SRN
PLAINS...
...SYNOPSIS...
BLOCKING UPPER LEVEL FLOW WILL PERSIST THROUGH D2 FROM CANADA INTO
THE NRN THIRD TO ONE HALF OF THE CONUS AS A STRONG RIDGE REMAINS
CENTERED OVER CENTRAL CANADA...AND EXTENDS SSEWD INTO THE GULF COAST
STATES WITH LESS AMPLITUDE. CLOSED LOWS WILL FLANK THIS RIDGE...1/
MOVING SLOWLY NWD THROUGH THE NRN PLAINS...AND 2/ A MUCH LARGER
SYSTEM ENCOMPASSING ERN CANADA INTO THE NERN STATES.
MEANWHILE...MODELS ARE IN AGREEMENT WITH THE WEAKENING OF THE
COMPACT D1 SHORTWAVE TROUGH AS IT MOVES QUICKLY FROM THE UPPER MS
VALLEY THROUGH THE LOWER GREAT LAKES AND BASE OF THE ERN CANADA
CLOSED LOW. MODELS TEND TO AGREE WITH THE TIMING OF A MORE SUBTLE
MIDLEVEL IMPULSE TRACKING THROUGH THE GREAT BASIN AND SRN ROCKIES D1
AND INTO THE MID MS/OH VALLEYS ON SAT.
A WARM FRONT WILL LIFT NWD TO NEAR THE OH RIVER...BUT NWD PROGRESS
WILL BE IMPEDED BY A SURFACE HIGH PRESSURE CENTERED OVER ONTARIO
EXTENDING SWD ACROSS THE GREAT LAKES. THE EJECTING BUT DEAMPLIFYING
WAVE WILL PROVIDE IMPETUS FOR AN ATTENDANT SURFACE LOW TO TRACK SEWD
FROM NRN MO INTO THE LOWER OH VALLEY TO KY...WHILE A TRAILING COLD
FRONT ADVANCES SEWD. BY THE END OF THE PERIOD...THE LOW SHOULD BE
LOCATED E OF THE CENTRAL APPALACHIANS WITH THE COLD FRONT EXTENDING
SWWD THROUGH THE TN VALLEY TO OK...WHERE IT WILL BE RETREATING NWD
AS A WARM FRONT IN THE SRN PLAINS.
...KY/SRN IND/SRN IL/PART OF SERN MO...
ELEVATED SHOWERS AND TSTMS SHOULD BE IN PROGRESS FROM THE UPPER MS
VALLEY INTO A PORTION OF THE OH VALLEY WITHIN ZONE OF ISENTROPIC
ASCENT NORTH OF THE WARM FRONT SAT MORNING. ACTIVITY WILL SHIFT
ENEWD DURING THE DAY AND LIKELY REINFORCE THE WARM FRONT AND SLOW
ITS NWD PROGRESS. ATMOSPHERE WILL DESTABILIZE SOUTH OF THIS FEATURE
AS AXIS OF LOW 60S DEWPOINTS ADVECT NEWD BENEATH PLUME OF STEEPER
MID LEVEL LAPSE RATES. DISSIPATING LOW CLOUDS IN THE WARM SECTOR BY
LATE MORNING OR AFTERNOON SHOULD ALLOW THE BOUNDARY LAYER TO
DESTABILIZE WITH MLCAPE TO 1500 J/KG. POTENTIAL WILL EXIST FOR A FEW
STORMS TO REDEVELOP ALONG THE CONVECTIVELY REINFORCED WARM FRONT...
ESPECIALLY FROM SRN IL...SRN IND INTO THE NRN HALF OF KY WHERE
SHORTWAVE RIDGE WILL BE SUPPRESSED SOME BY THE SUBTLE SHORTWAVE
TROUGH. THIS REGION WILL ALSO REMAIN ON NRN FRINGE OF EML WHERE THE
CAP SHOULD BE SOMEWHAT WEAKER THAN FARTHER SOUTH. OTHER STORMS MAY
DEVELOP ALONG THE COLD FRONT AS IT ADVANCES SEWD. WLY UNIDIRECTIONAL
SHEAR FROM 40-50 KT WILL SUPPORT ORGANIZATION INCLUDING A FEW
SUPERCELLS WITH DAMAGING WIND AND LARGE HAIL THE MAIN THREATS.
FORECAST SOUNDINGS SUGGEST THE POTENTIAL FOR HAILSTONES UP TO...OR
LOCALLY EXCEEDING...2 INCHES IN DIAMETER DUE TO STEEP MIDLEVEL LAPSE
RATES /7.5-8 C PER KM/ ACCOMPANYING THE WEAKER MIDLEVEL IMPULSE.
HOWEVER...UNCERTAINTY IN THE COVERAGE OF THIS GREATER THREAT
PRECLUDES THE INTRODUCTION OF SIGNIFICANT PROBABILITIES AT THIS
TIME.
...OK/N TX WWD THROUGH THE TX PANHANDLE...
TSTM POTENTIAL IS EXPECTED TO REMAIN LIMITED DURING THE DAY ALONG
STALLING FRONT FROM NRN TX INTO THE OZARKS/SRN MO DUE TO A CAPPING
INVERSION AND WEAK FRONTAL CONVERGENCE. THEREAFTER...A STRENGTHENING
SLY NOCTURNAL LLJ WILL CONTRIBUTE TO NWD DESTABILIZATION OVER THE
SRN PLAINS FROM N TX AND OK INTO THE PANHANDLES. ELEVATED STORMS
WILL LIKELY DEVELOP WITHIN THIS ZONE OF ISENTROPIC ASCENT/STRONG WAA
SATURDAY NIGHT. A BAND OF 40-50 KT SWLY MIDLEVEL WINDS EXTENDING
FROM NM ACROSS OK/SRN KS WILL RESULT IN EFFECTIVE BULK SHEAR
BECOMING MORE FAVORABLE /40-50 KT/ TO SUPPORT ORGANIZED STORMS.
ACTIVITY SHOULD DEVELOP FROM S-N WITH MODELS NOW INDICATING STRONGER
MUCAPE 1000-1500 J/KG SAT NIGHT/EARLY SUN MORNING. THIS COMBINED
WITH STEEP MIDLEVEL LAPSE RATES SHOULD PROMOTE STORMS PRODUCING
SEVERE HAIL. THE GREATEST POTENTIAL FOR SEVERE STORMS WILL BE FROM
CENTRAL/SWRN OK INTO ERN PARTS OF THE TX PANHANDLE...AND THUS...A
SLIGHT RISK AREA HAS BEEN INTRODUCED FOR THIS REGION SAT NIGHT.
THERE IS SOME INDICATION FOR SURFACE BASED STORMS SAT EVENING INTO
THE OVERNIGHT PERIOD...BUT CONFIDENCE IS LOWER WITH THIS THREAT. IF
STORMS CAN BECOME SURFACE BASED...THEN THERE WOULD BE A THREAT FOR
DAMAGING WINDS AND A TORNADO THREAT COULD NOT BE RULED OUT.
..PETERS.. 04/27/2012
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