SWODY2
SPC AC 241700
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1200 PM CDT THU APR 24 2008
VALID 251200Z - 261200Z
...THERE IS A SLGT RISK OF SVR TSTMS FRI AFTN/EVE FROM THE UPPER
MISSISSIPPI VALLEY SWD INTO THE SRN PLAINS....
...SYNOPSIS...
BROAD CYCLONIC MID/UPPER FLOW...NOW DEVELOPING ACROSS THE PACIFIC
NORTHWEST AND GREAT BASIN INTO THE NORTHERN PLAINS AND UPPER
MISSISSIPPI VALLEY REGION...IS PROGGED TO GRADUALLY SHIFT EASTWARD
THROUGH THIS FORECAST PERIOD. THIS IS EXPECTED TO OCCUR AS A
SIGNIFICANT EMBEDDED SHORT WAVE IMPULSE LIFTS OUT OF THE CENTRAL
PLAINS THROUGH THE UPPER GREAT LAKES REGION...WHILE ANOTHER WEAKER
IMPULSE DIGS THROUGH THE CANADIAN/NORTHERN U.S. ROCKIES. MODELS
SUGGEST THAT THE LEAD SYSTEM WILL BE ACCOMPANIED BY A DEEPENING
LOW/MID LEVEL CYCLONE ACROSS THE UPPER MISSISSIPPI VALLEY/UPPER
GREAT LAKES REGION...SUPPORTING THE SOUTHEASTWARD PROGRESSION OF A
LOW-LEVEL COLD INTRUSION THROUGH MUCH OF THE PLAINS AND MISSISSIPPI
VALLEY BY 12Z SATURDAY.
...SOUTHERN PLAINS THROUGH THE GREAT LAKES REGION...
DETAILS OF PRE-FRONTAL CONVECTIVE EVOLUTION EXPECTED FRIDAY ARE
STILL A BIT UNCERTAIN...PARTICULARLY ACROSS PARTS OF THE UPPER
MISSISSIPPI VALLEY/UPPER GREAT LAKES...WHERE STABILIZING INFLUENCE
OF EARLY DAY CONVECTION AND POSSIBLE SUBSEQUENT MID-LEVEL
SUBSIDENCE/DRYING ARE UNCLEAR. AND...MODELS ARE SUGGESTIVE THAT THE
COLD CORE OF APPROACHING UPPER SYSTEM WILL LAG THE WARM SECTOR
...WHICH COULD RESTRICT THE MAGNITUDE OF PEAK AFTERNOON CAPE.
BUT...THE LOW-LEVEL ENVIRONMENT IS EXPECTED TO BECOME SUFFICIENTLY
MOIST TO SUPPORT AT LEAST WEAK TO MODERATE INSTABILITY FROM THE
MISSOURI OZARKS INTO THE VICINITY OF THE DEEPENING SURFACE LOW OVER
WISCONSIN BY LATE FRIDAY AFTERNOON. COUPLED WITH STRENGTHENING DEEP
LAYER SHEAR...ASSOCIATED WITH A 70-90 KT 500 MB JET STREAK
DEVELOPING ON THE EASTERN PERIPHERY OF AN INCREASINGLY NEGATIVELY
TILTED UPPER TROUGH AXIS...THE ENVIRONMENT ACROSS MUCH OF THE MIDDLE
MISSISSIPPI VALLEY AND UPPER MIDWEST IS EXPECTED TO BECOME FAVORABLE
FOR SEVERE STORMS...INCLUDING SUPERCELLS.
IF STORMS DO NOT INITIATE EARLIER...IT CURRENTLY SEEMS PROBABLE THAT
AT LEAST A BROKEN LINE OF SEVERE STORMS AND EMBEDDED SUPERCELLS WILL
FORM IN ADVANCE OF THE EASTWARD SURGING COLD FRONT BY
25/21-22Z...FROM PARTS OF SOUTHWEST WISCONSIN AND EASTERN IOWA INTO
EASTERN MISSOURI. LARGE HAIL/DAMAGING WIND GUSTS AND ISOLATED
TORNADOES ALL APPEAR POSSIBLE AS ACTIVITY SPREADS EASTWARD THROUGH
MUCH OF SOUTHERN/EASTERN WISCONSIN/ILLINOIS /EASTERN INDIANA AND
LOWER MICHIGAN. THE SEVERE THREAT IS EXPECTED TO WANE WITH DIURNAL
STABILIZATION LATE FRIDAY EVENING ...BUT SPORADIC WIND DAMAGE AND
HAIL NEAR SEVERE LIMITS COULD CONTINUE EASTWARD INTO THE LOWER GREAT
LAKES AND UPPER OHIO VALLEY BY 12Z SATURDAY.
...SOUTH CENTRAL TEXAS INTO THE ARKLATEX...
MODELS SUGGEST THAT LARGE-SCALE FORCING AND DEEP LAYER SHEAR WILL
NOT BE NEARLY AS STRONG AS ACROSS PARTS OF THE UPPER MISSISSIPPI
VALLEY. BUT...A MODERATE TO STRONGLY UNSTABLE AIR MASS IS EXPECTED
AHEAD OF THE SURFACE COLD FRONT APPROACHING REGION LATE FRIDAY
AFTERNOON. THE FRONT/DRY LINE INTERSECTION NEAR THE
AUSTIN/TEMPLE/WACO AREA MAY BE A FAVORED LOCATION FOR STORM
INITIATION...AIDED BY DIVERGENT UPPER FLOW BETWEEN THE POLAR TROUGH
TO THE NORTH...AND A LOW AMPLITUDE SUBTROPICAL WAVE TO THE SOUTH.
CAPE OF 2000-3000 J/KG WILL BE SUPPORTIVE OF INTENSE UPDRAFTS.
AND...MODEST WESTERLY 500 MB FLOW AROUND 30 KTS SHOULD BE SUFFICIENT
FOR AT LEAST ISOLATED SUPERCELLS CAPABLE OF PRODUCING LARGE
HAIL/LOCALIZED DAMAGING WIND GUSTS. A BROKEN LINE OF STORMS MAY
EVENTUALLY EVOLVE ALONG THE FRONT...BEFORE ACTIVITY DIMINISHES
WITHIN A STABILIZING BOUNDARY LAYER LATE FRIDAY EVENING.
..KERR.. 04/24/2008
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