SWODY2
SPC AC 020558
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1258 AM CDT SAT APR 02 2011
VALID 031200Z - 041200Z
...THERE IS A SLGT RISK OF SVR TSTMS SUNDAY AFTERNOON AND NIGHT FROM
THE MIDWEST/LOWER OH VALLEY TO THE SRN PLAINS...
...SYNOPSIS...
MODELS REMAIN IN FAIRLY GOOD AGREEMENT SHOWING A FULL LATITUDE
TROUGH AMPLIFYING/DEVELOPING INTO THE CENTRAL U.S. DURING DAY
2...WITH THE 12Z ECMWF/00Z GFS FASTER WITH EWD PROGRESSION THAN THE
WRF-NAM. BY 12Z MONDAY...A POSITIVELY-TILTED TROUGH SHOULD EXTEND
FROM THE UPPER MS VALLEY TO THE SRN HIGH PLAINS. 60-90 METER 500 MB
HEIGHT FALLS ARE EXPECTED FROM OK/KS TO IA/NRN IL DURING THE LATTER
HALF OF THE FORECAST PERIOD. SWLY MIDLEVEL WINDS WILL STRENGTHEN TO
50-60 KT FROM THE SRN ROCKIES TO THE LOWER MO VALLEY AND MIDWEST BY
SUNDAY AFTERNOON...WITH A FURTHER INCREASE SUNDAY NIGHT TO 70-90 KT
FROM THE SRN PLAINS TO LOWER OH VALLEY.
AT THE SURFACE...MODELS HAVE TRENDED NORTH WITH THE INITIAL POSITION
OF LOW PRESSURE AT 12Z SUNDAY...WITH THIS FEATURE LOCATED OVER SERN
SD. THIS LOW WILL TRACK EWD INTO NERN IA BY 04/00Z...AND THEN REACH
THE CENTRAL GREAT LAKES BY 12Z MONDAY. A TRAILING COLD FRONT WILL
ADVANCE SSEWD THROUGH THE CENTRAL AND SRN PLAINS...AND INTERSECT AND
OVERTAKE A DRY LINE FROM ERN KS THROUGH CENTRAL OK TO NRN TX FROM
SUNDAY AFTERNOON TO EARLY MONDAY MORNING. THE NRN EXTENT OF THE
COLD FRONT WILL PROCEED ESEWD THROUGH THE LOWER MO VALLEY REACHING
LOWER MI TO THE OZARKS BY THE END OF THE FORECAST PERIOD.
MEANWHILE...A WARM FRONT WILL LIFT NEWD FROM THE LOWER MO VALLEY
THROUGH THE OH VALLEY TO LOWER GREAT LAKES BY SUNDAY NIGHT.
...SRN PLAINS TO THE MIDWEST/LOWER OH VALLEY...
SLY LOW LEVEL WINDS WILL MAINTAIN MOISTURE RETURN FROM THE SRN
PLAINS THROUGH THE LOWER MO TO LOWER OH VALLEY DURING DAY 2...
BENEATH A STRONG EML/CAP. THIS CAP WILL LIMIT TSTM DEVELOPMENT
THROUGH MUCH OF THE DAY...WITH MODELS SUGGESTING TSTM DEVELOPMENT
WILL BE LIKELY ALONG THE COLD FRONT AS IT ADVANCES INTO NRN/CENTRAL
IL...NRN MO AND INTERSECTS THE DRY LINE IN NERN-ERN KS MID-LATE
SUNDAY AFTERNOON. MODERATE INSTABILITY...STRENGTHENING DEEP LAYER
SHEAR AND STEEP LAPSE RATES WILL SUPPORT ORGANIZED SUPERCELLULAR
STORMS PRODUCING A FEW TORNADOES...LARGE HAIL /SOME SIGNIFICANT/ AND
DAMAGING WINDS. A SECONDARY LLJ IS EXPECTED TO INCREASE TO 45-65 KT
FROM OK TO MO/IL SUNDAY EVENING...FURTHER ENHANCING LOW LEVEL SHEAR
FOR AN INCREASED TORNADO THREAT. AS THE COLD FRONT ADVANCES SWD
OVERNIGHT...STRONG WIND FIELDS COUPLED WITH MODERATE INSTABILITY
WILL SUPPORT A SEVERE WEATHER THREAT PERSISTING WELL AFTER
DARK...ESPECIALLY ACROSS MO/NRN AR TO LOWER OH VALLEY.
UNCERTAINTY EXISTS IN THE GUIDANCE FOR WHETHER TSTMS INITIATE SWD
ALONG THE DRY LINE...S OF THE KS BORDER...THROUGH OK TO NRN TX. THE
00Z WRF-NAM/21Z ETAKF MEMBER OF THE SREF/12Z ECMWF DO NOT INITIATE
ACROSS THESE AREAS...WHILE 00Z GFS TO SOME EXTENT AND THE EACH OF
THE 21Z WRF-ARW MEMBERS OF THE SREF SUGGEST STORMS DO FORM INTO OK/N
TX SUNDAY AFTERNOON. DESPITE THESE DIFFERENCES...STEEP MIDLEVEL
LAPSE RATES /8-9 C PER KM/... MODERATE INSTABILITY AND STRENGTHENING
BULK SHEAR TO 50 KT INDICATES A SLIGHT RISK REMAINS WARRANTED WITH
SWD EXTENT. IF STORMS DEVELOP...THEN THE POTENTIAL WILL EXIST FOR
LARGE HAIL...SOME SIGNIFICANT...PRIOR TO THE COLD FRONT REACHING
THIS REGION AND PROGRESSING SWD INTO TX.
...SRN GREAT LAKES REGION...
MODELS SUGGEST ELEVATED TSTMS WILL BE POSSIBLE EARLY IN THE FORECAST
PERIOD /SUNDAY MORNING/ ACROSS THE UPPER MS VALLEY WITHIN THE NOSE
OF A STRONG SWLY LLJ WHERE WAA WILL SUPPORT THIS ACTIVITY.
STRENGTHENING WSWLY MIDLEVEL WINDS ACROSS THE UPPER GREAT LAKES AND
THE LLJ SHIFTING EWD INTO THE OH VALLEY SHOULD MAINTAIN SUFFICIENT
UVVS FOR CONTINUED CONVECTION/EMBEDDED TSTM DEVELOPMENT TOWARD LOWER
MI BY SUNDAY AFTERNOON. DESPITE EFFECTIVE BULK SHEAR SUFFICIENT FOR
ORGANIZED STORMS...WEAK INSTABILITY SHOULD LIMIT THE OVERALL SEVERE
WEATHER THREAT WITH THIS ELEVATED ACTIVITY.
...CENTRAL TX...
FARTHER S...THE POTENTIAL WILL EXIST FOR TSTM DEVELOPMENT LATE IN
THE FORECAST PERIOD AS THE COLD FRONT ADVANCES SWD INTO THIS REGION.
MODERATE INSTABILITY AND EFFECTIVE BULK SHEAR 30-40 KT SUGGESTS
ORGANIZED STORMS WILL BE POSSIBLE. UNCERTAINTY IN STORM INITIATION
THIS FAR SOUTH AMONGST THE MODEL SOLUTIONS...AND THE MODELS THAT DO
INITIATE OVER THIS AREA SUGGEST THE TIMING IS AFTER 04/03-06Z.
GIVEN THESE FACTORS...ONLY LOW SEVERE PROBABILITIES /5 PERCENT/ ARE
WARRANTED AT THIS TIME.
..PETERS.. 04/02/2011
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