DAY1SVR: Day 1 Convective Outlook Corr 1

ACUS01 KWNS 251719
SWODY1
SPC AC 251717

DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
1217 PM CDT SUN AUG 25 2013

VALID 251630Z - 261200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE UPPER MS
VALLEY AND UPPER GREAT LAKES...

CORRECTED FOR NDFD GENERAL TSTM POINTS

...SYNOPSIS...
A LARGE-SCALE UPPER RIDGE WILL CONTINUE TO ENCOMPASS MOST OF THE
CONUS...WITH EXCEPTION TO THE PACIFIC COAST WHERE A WEAK UPPER
TROUGH WILL SHIFT FROM CNTRL CA NEWD INTO THE NRN ROCKIES. MULTIPLE
WEAK UPPER DISTURBANCES ARE FORECAST TO PIVOT NEWD AND EWD FROM THE
SOUTHWEST AND ACROSS THE NRN PLAINS AND UPPER GREAT LAKES...ALONG
THE PERIPHERY OF STRONGER ANTICYCLONIC FLOW ALOFT. A WRN EXTENSION
OF A WEAK CANADIAN SFC FRONT WILL BE POSITIONED ACROSS MN AND THE
DAKOTAS...AND WILL SLOWLY SAG S/EWD THROUGHOUT THE DAY. VERY RICH
MONSOONAL MOISTURE WILL REMAIN IN PLACE OVER PARTS OF AZ AND SRN CA
N OF T.D. IVO.

...UPPER MS VALLEY AND UPPER GREAT LAKES...
AN UNCERTAIN/CONDITIONAL RISK FOR DMGG WIND GUSTS AND LARGE HAIL
WILL EXIST THIS AFTERNOON AND EVENING ACROSS THE UPPER MS VALLEY AND
UPPER GREAT LAKES. ONLY VERY WEAK FORCING FOR ASCENT WILL BE PRESENT
IN THE ABSENCE OF ANY NOTABLE UPPER IMPULSES OR MIDLEVEL HEIGHT
FALLS...PRIMARILY VIA LOW-LEVEL WARM ADVECTION AND VERY WEAK SFC
CONVERGENCE ALONG A BOUNDARY SAGGING SEWD ACROSS NRN MN.
HOWEVER...TEMPERATURES ARE FORECAST TO APPROACH 100 F THIS
AFTERNOON...AND A VERY MOIST AIR MASS WAS SAMPLED IN 12Z MPX AND INL
SOUNDINGS WITH PW VALUES EXCEEDING 1.8 INCHES. THIS AREA WILL ALSO
BE LOCATED ALONG THE ERN PERIPHERY OF AN EML PLUME...WHICH WILL
SUPPORT MLCAPE VALUES OF 3000-4000 J/KG...ALTHOUGH WEAK CINH MAY
STILL EXIST DURING PEAK HEATING.

LATEST HIGH-RESOLUTION MODEL GUIDANCE CONTINUES TO EXHIBIT
CONSIDERABLE UNCERTAINTY WITH THE LOCATION/TIMING OF CONVECTIVE
INITIATION THIS AFTERNOON. THE MOST PROBABLE SCENARIO APPEARS TO BE
TSTM DEVELOPMENT BY LATE AFTERNOON INVOF OF THE SFC BOUNDARY ACROSS
CNTRL MN AND NRN WI. MORNING VISIBLE LOOP ALSO SHOWS SOME HINT OF A
WEAK UPPER IMPULSE OVER WRN SD WITH THE PRESENCE OF A MIDLEVEL CU
FIELD...WHICH WILL LIKELY INTERSECT THE BOUNDARY DURING PEAK HEATING
OVER W-CNTRL MN AND COULD SUPPORT TSTM INITIATION. WEAK TO MODERATE
AND NEARLY UNIDIRECTIONAL WIND PROFILES SHOULD MAINLY SUPPORT
MULTICELL CLUSTERS OR MARGINAL SUPERCELL STRUCTURES...WITH
CONVECTION SHIFTING SEWD INTO THE EVENING...POSING A PRIMARY RISK
FOR DMGG WINDS AND LARGE HAIL.

...INTERIOR PACIFIC NW AND INTERMOUNTAIN WEST...
A SHORTWAVE UPPER TROUGH NEAR THE NRN CA COAST THIS MORNING WILL
PROGRESS NEWD INTO INTERIOR PORTIONS OF THE PAC NW...CONTRIBUTING TO
TSTM DEVELOPMENT ACROSS PORTIONS OF ORE/WA AND NRN ID THIS
AFTERNOON. MEAN 0-6 KM FLOW OF 20-30 KT...ALONG WITH STEEPENING
LOW-LEVEL LAPSE RATES...SHOULD SUPPORT A FEW TSTM CLUSTERS CAPABLE
OF PRODUCING STRONG TO ISOLATED SVR WIND GUSTS. HOWEVER...THE SVR
THREAT WILL LIKELY BE LIMITED BY MARGINAL INSTABILITY...WITH
FORECAST MLCAPE VALUES GENERALLY BELOW 500 J/KG.

..ROGERS/THOMPSON.. 08/25/2013

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