SPC AC 180557
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1257 AM CDT TUE AUG 18 2009
VALID 191200Z - 201200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE ERN PLNS...MID MS
VLY AND PARTS OF THE MIDWEST...
...SYNOPSIS...
SEASONABLY STRONG AMPLIFICATION OF THE UPR TROUGH ACROSS THE CNTRL
PORTION OF THE COUNTRY WILL BEGIN ON WEDNESDAY. LEAD
WAVE...CURRENTLY ADVANCING ACROSS THE UPR GRTLKS REGION...WILL SKIRT
ACROSS NEW ENGLAND EARLY ON WEDNESDAY. UPSTREAM...THE MID-LVL WAVE
OVER CNTRL AB WILL DIG SWD INTO THE DKTS BY WEDNESDAY...EVENTUALLY
CLOSING INTO A LOW THAT WILL REACH THE CORN BELT BY 12Z THURSDAY.
AHEAD OF THIS FEATURE...A STRONG IMPULSE WILL TRAVEL FROM THE GRT
BASIN TO THE CNTRL PLAINS ON TUESDAY...THEN ACROSS THE MIDWEST AND
CNTRL GRTLKS REGION DURING THE DAY 2 PD.
...ERN PLNS TO THE MIDWEST...
MODEL HAVE BEEN TRENDING SLOWER WITH BOTH THE UPCOMING TROUGH
AMPLIFICATION AND NWD RETREAT OF THE WRMFNT...RESULTING IN AN EXTRA
DEGREE OF COMPLEXITY TO WEDNESDAY/S SVR PROSPECTS. THE
AFOREMENTIONED DISTURBANCE EXPECTED TO MOVE INTO THE CNTRL PLNS
TUESDAY WILL LIKELY DRIVE A NOCTURNAL MCS ACROSS KS/N OK TUESDAY
NIGHT. THIS ACTIVITY SHOULD SPREAD ENE ACROSS NRN MO...NRN IL AND
SRN LWR MI DURING THE AFTN. CLOUDS/RAIN WILL REINFORCE AND LIKELY
SLOW THE NEWD RETREAT OF THE WRMFNT. ALONG SRN FRINGES OF THE
MCS...AFTN TSTMS WILL DEVELOP ACROSS CNTRL IL...CNTRL MO WHERE AIR
MASS WILL BE VERY MOIST/WARM BELOW MODESTLY STEEP MID-LVL LAPSE
RATES. PRESENCE OF ENHANCED DEEP LAYER FLOW ALONG SRN PERIPHERY OF
THE SHORTWAVE/MCV WILL BE FAVORABLE FOR SOME STORM
ORGANIZATION/SUPERCELLS WITH LARGE HAIL...DMGG WINDS AND PERHAPS A
TORNADO OR TWO.
MEANWHILE...IN WAKE OF THE MCS...LLVL FLOW WILL BEGIN TO RESPOND TO
THE STRONGER JET STREAK MOVING INTO THE NRN HIGH PLNS WITH
COMPARATIVELY RICHER BOUNDARY LAYER MOISTURE SURGING NWD INTO THE MO
RVR VLY. HERE...COMBINATION OF STRONGER HEATING AND STEEPER MID-LVL
LAPSE RATES SHOULD YIELD VERY UNSTABLE MLCAPES OF 2000-2500 J/KG.
AS STRONGER HEIGHT FALLS SPREAD SEWD...RAPID MASS ADJUSTMENTS WILL
TAKE PLACE DURING THE EVENING WITH STRONG FRONTOGENESIS SPREADING
QUICKLY SEWD INTO THE MID/LWR MO VLY. AT THAT TIME...TSTMS WILL
READILY FORM FROM WRN IA/ERN NEB AND EXPAND ESE INTO NERN KS AND
NWRN MO. PRESENCE OF 40-45 KTS OF 0-6KM SHEAR...MAGNITUDE OF
INSTABILITY AND FORCING WILL BE FAVORABLE FOR INITIAL STORMS TO BE
SUPERCELLS WITH LARGE HAIL. AS FORCING FOR ASCENT
STRENGTHENS...EVOLUTION INTO A QLCS IS LIKELY WITH STORMS MOVING
QUICKLY TOWARD THE MID-MS VLY AND CNTRL IL WITH DMGG WINDS/HAIL
OVERNIGHT. TSTMS WILL TEND TO BACKBUILD/DEVELOP SWWD DURING THE
NIGHT...POSSIBLY AS FAR AS NWRN OK/ERN TX PNHDL WITH AT LEAST LOW
PROBABILITIES FOR DMGG WINDS/HAIL.
...NRN PLNS TO UPR MS VLY...
WARM ADVECTION DERIVED CONVECTION WILL BE ONGOING TUESDAY MORNING
OVER A LARGE PORTION OF THE ERN DKTS WITH AN EWD TRANSLATION INTO MN
DURING THE DAY. IT IS UNCLEAR ON HOW MUCH RECOVERY/HEATING WILL
OCCUR IN WAKE OF THIS ACTIVITY...ESPECIALLY GIVEN MORNING INTERCEPT
OF RICH BOUNDARY LAYER MOISTURE BY NOCTURNAL MCS ACROSS THE CNTRL
PLNS. AT LEAST SOME BUOYANCY CAN BE EXPECTED ALONG THE ADVANCING
FRONT ACROSS THE ERN DKTS INTO WRN/SRN MN WEDNESDAY EVENING. DEEP
LAYER SHEAR WILL BE SOMEWHAT WEAK AS PRIMARY JET STREAM EVOLVES INTO
THE CNTRL PLNS/MO VLY. AS SUCH...IF SUSTAINED STORMS CAN MANAGE TO
THRIVE...IT IS LIKELY THAT ONLY ISOLD DMGG WINDS/HAIL/BRIEF TORNADO
WILL OCCUR.
...NERN STATES...
MODELS ARE MUCH FASTER AT EJECTING THE AFOREMENTIONED LEAD MID-LVL
WAVE AND MOST UPR SUPPORT WILL PASS ACROSS THE REGION PRIOR TO
WEDNESDAY MORNING. CDFNT WILL THEN FOLLOW AND MOVE ACROSS MOST OF
NEW ENGLAND BY MID-DAY. AS SUCH...PREVIOUS SLGT RISK HAS BEEN
REMOVED WITH EARLY DAY TSTM RISK CONFINED TO CSTL AREAS.
..RACY.. 08/18/2009
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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