SWODY1
SPC AC 071225
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0725 AM CDT SUN SEP 07 2008
VALID 071300Z - 081200Z
...THERE IS A SLGT RISK OF SVR TSTMS TONIGHT OVER PARTS OF
CO/KS/NEB...
A BROAD UPPER TROUGH IS PRESENT THIS MORNING OVER MUCH OF THE
NORTHERN UNITED STATES...WITH WATER VAPOR IMAGERY SHOWING MAIN JET
STREAM EXTENDING FROM WY ACROSS NEB/IA INTO THE GREAT LAKES STATES.
ONE OF THE STRONGER SHORTWAVE TROUGHS IS CURRENTLY OVER IA/MO AND IS
TRACKING NORTHEASTWARD INTO THE OH VALLEY. SHORTWAVE RIDGING IN THE
WAKE OF THIS SYSTEM WILL HELP TO MAINTAIN/STRENGTHEN THE MID LEVEL
CAPPING INVERSION OVER THE CENTRAL PLAINS THROUGH MUCH OF TODAY.
HOWEVER...AN INCREASING NOCTURNAL SOUTHERLY LOW LEVEL JET WILL
IMPINGE ON WEAK SURFACE BOUNDARY FORECAST TO RETREAT NORTHWARD INTO
KS THIS EVENING AND PROVIDE A FOCUS FOR SCATTERED/NUMEROUS
THUNDERSTORMS. MODELS VARY ON TIMING OF INITIATION...WITH SOME
GUIDANCE NOT SHOWING MANY STORMS UNTIL AFTER 06Z. HOWEVER...ONCE
STORMS DO INTENSIFY...IT APPEARS LIKELY THAT AT LEAST A FEW STORMS
WILL POSE A RISK OF LARGE HAIL AND PERHAPS GUSTY WINDS.
...GREAT LAKES...
WV LOOPS SHOW A RATHER STRONG SHORTWAVE TROUGH OVER MT. THIS
FEATURE IS FORECAST TO AMPLIFY AS IT SWEEPS EASTWARD INTO THE
MIDWEST THIS AFTERNOON. COOL TEMPERATURES ALOFT /-18 TO -20C AT
500MB/ AND RATHER STEEP LAPSE RATES WILL HELP TO DESTABILIZE THE
AIRMASS OVER MUCH OF THE GREAT LAKES...WHERE ISOLATED AFTERNOON
THUNDERSTORMS ARE EXPECTED. CAPE VALUES UP TO 500 J/KG AND STRONG
MID/UPPER LEVEL FLOW WILL PROMOTE THE POTENTIAL OF HAIL IN STRONGER
CELLS. ORGANIZED SEVERE STORMS ARE NOT ANTICIPATED AT THIS TIME.
...NM/WEST TX...
MODEL GUIDANCE IS RATHER CONSISTENT IN SUGGESTING THAT A LOW
LATITUDE IMPULSE WILL LIFT NEWD/NWD FROM NWRN MEXICO THROUGH NM INTO
WRN TX TODAY INTO TONIGHT. FORCING ASSOCIATED WITH THIS FEATURE
COUPLED WITH OROGRAPHIC ASCENT IS EXPECTED TO FOSTER SCATTERED TSTMS
THIS AFTERNOON INTO EVENING. WHILE VERTICAL SHEAR WILL REMAIN
RELATIVELY WEAK...POCKETS OF MODERATE INSTABILITY /MLCAPES
APPROACHING 1000 J PER KG/ MAY SUPPORT A FEW ORGANIZED/LONG-LIVED
STORMS CAPABLE OF MAINLY SOME HAIL.
..HART/GRAMS.. 09/07/2008
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