SWODY2
SPC AC 240536
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1236 AM CDT SAT MAY 24 2008
VALID 251200Z - 261200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER MIDWEST SWWD
INTO THE CNTRL PLAINS...
...SYNOPSIS...
COMPLEX LARGE-SCALE PATTERN WILL EXIST DURING THE DAY TWO PERIOD
WITH A REX BLOCK OVER WRN N AMERICA AND A DEEP VORTEX OVER NERN
CANADA. MORE SPECIFICALLY...SHORT WAVE TROUGH INITIALLY OVER THE
UPPER GREAT LAKES IS FORECAST TO WEAKEN THROUGH THE PERIOD WHILE
TRANSLATING EWD INTO CONFLUENT MIDLEVEL REGIME OVER ERN ONTARIO INTO
QUEBEC. MEANWHILE...INITIALLY CLOSED CIRCULATION OVER THE NRN
PLAINS INTO S-CNTRL CANADA WILL OPEN AND GRADUALLY PHASE WITH ERN
CANADA TROUGH...EFFECTIVELY LOWER HEIGHTS ACROSS THE UPPER GREAT
LAKES. FINALLY...A SHORT WAVE TROUGH WILL ROUND BROADER...WRN U.S.
TROUGH...WITH THIS FEATURE MOVING NEWD THROUGH THE LOWER CO VALLEY
INTO FOUR CORNERS REGION.
IN THE LOW LEVELS...PRIMARY FEATURE OF INTEREST WILL BE SURFACE LOW
ATTENDANT TO NRN PLAINS MIDLEVEL CIRCULATION WHICH WILL DEVELOP EWD
ALONG THE INTERNATIONAL BORDER FROM N-CNTRL ND INTO THE UPPER GREAT
LAKES. A WARM FRONT WILL PRECEED THIS LOW...LIFTING NEWD THROUGH
THE UPPER GREAT LAKES WITH A TRAILING PRE-FRONTAL TROUGH PUSHING EWD
INTO THE UPPER MS VALLEY BY SUNDAY AFTERNOON. THIS BOUNDARY WILL
EXTEND SWWD THROUGH WRN IA/ERN NEB TO DEVELOPING LOW PRESSURE OVER
ERN CO. A DRYLINE WILL EXTEND FROM INTERSECTION WITH PRE-FRONTAL
TROUGH OVER S-CNTRL NEB/N-CNTRL KS SWD INTO WRN OK AND NWRN TX.
...UPPER MIDWEST INTO THE CNTRL PLAINS...
SWLY LLJ ASSOCIATED WITH LEAD SHORT WAVE TROUGH WILL ENHANCE THE
ADVECTION OF RICH BOUNDARY LAYER MOISTURE /DEWPOINTS IN THE 60S TO
LOWER 70S/ NEWD THROUGH THE WRN PORTIONS OF THE CORN BELT IN ADVANCE
OF PRE-FRONTAL TROUGH SLOWLY SHIFTING EWD. THIS MOISTURE COUPLED
WITH STEEP MIDLEVEL LAPSE RATES OF 7.0-7.5 C/KM WILL RESULT IN THE
DEVELOPMENT OF MODERATE TO STRONG INSTABILITY SUNDAY AFTERNOON WITH
MLCAPES INCREASING TO 2000-4000 J/KG ALONG PRIMARY INSTABILITY
AXIS.
SUBSIDENCE IN WAKE OF LEAD SHORT WAVE TROUGH MAY INHIBIT TSTM
DEVELOPMENT THROUGH MID AFTERNOON...BEFORE HEIGHTS BEGIN TO FALL
WITH APPROACH OF UPSTREAM SYSTEM INTO THE UPPER MS VALLEY. THESE
HEIGHT FALLS COMBINED WITH SUSTAINED LOW-LEVEL CONVERGENCE ALONG
FRONT SHOULD SUPPORT RAPID TSTM DEVELOPMENT LATER SUNDAY AFTERNOON
INTO EVENING ALONG PRE-FRONTAL TROUGH OVER PORTIONS OF CNTRL/ERN
MN/WI SWWD INTO PARTS OF IA/ERN NEB/NRN MO. THE COMBINATION OF
MODERATE/STRONG INSTABILITY AND 40-55 KT OF LARGELY DEEP-LAYER SPEED
SHEAR INDICATE THE POTENTIAL FOR SUPERCELLS AND LARGER-SCALE BOWING
STRUCTURES CAPABLE OF VERY LARGE HAIL...DAMAGING WINDS AND A FEW
TORNADOES. THE GREATEST TORNADO THREAT APPEARS TO BE OVER WI SWWD
INTO ERN IA SUNDAY EVENING WHERE LOW-LEVEL SHEAR IS MAXIMIZED ALONG
AND W OF RETREATING WARM FRONT.
ADDITIONAL TSTMS ARE LIKELY TO DEVELOP SUNDAY NIGHT ACROSS SRN NEB
INTO KS AS STRENGTHENING LLJ ENHANCES CONVERGENCE AND LIFT ALONG AND
N OF W-E ORIENTED BAROCLINIC ZONE. THE MAJORITY OF THIS ACTIVITY IS
EXPECTED TO BE SLIGHTLY ELEVATED WITH LARGE HAIL BEING THE PRIMARY
SEVERE WEATHER THREAT.
...SRN PLAINS...
LATEST MODEL GUIDANCE REMAINS CONSISTENT IN SUGGESTING THAT
ISOLATED...DIURNAL TSTM DEVELOPMENT WILL OCCUR SWD ALONG THE DRYLINE
SUNDAY AFTERNOON INTO EVENING. FORECAST SOUNDINGS INDICATE THE
PRESENCE OF STEEP LAPSE RATES AND DEEPLY MIXED BOUNDARY LAYER
CONDITIONS WITH MLCAPES OF 1000-1500 J/KG. VERTICAL SHEAR WILL
REMAIN SOMEWHAT MARGINAL /I.E. EFFECTIVE BULK SHEARS OF AROUND 30
KT/...HOWEVER A FEW ORGANIZED/ROTATING STORMS ARE POSSIBLE WITH A
THREAT OF LOCALLY DAMAGING WINDS AND HAIL.
...OZARK PLATEAU INTO LOWER MS VALLEY...
A VERY MOIST BOUNDARY LAYER WILL EXIST ALONG WRN PERIPHERY OF ERN
U.S. ANTICYCLONE WITH DEWPOINTS IN THE 60S TO LOWER 70S. THIS
MOISTURE COMBINED WITH MIDLEVEL LAPSE RATES OF AROUND 7 C/KM WILL
RESULT IN MODERATE TO STRONG INSTABILITY WITH MLCAPES OF 2000-3000
J/KG. LARGE-SCALE FORCING FOR ASCENT WILL REMAIN MINIMAL...BUT
PRESENCE OF LOW-LEVEL CONFLUENT FLOW SHOULD PROVIDE THE FOCUS FOR
SCATTERED...DIURNAL TSTM DEVELOPMENT. A FEW OF THE MORE INTENSE
STORMS WILL BE CAPABLE OF STRONG WIND GUSTS AND PERHAPS SOME HAIL
GIVEN THE STRONG INSTABILITY.
..MEAD.. 05/24/2008
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