DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 292002
SWODY1
SPC AC 291959

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT THU AUG 29 2013

VALID 292000Z - 301200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF CENTRAL
MN...NRN WI...AND THE WRN UPPER PENINSULA OF MI...

PRIMARY CHANGES TO PREVIOUS OUTLOOK ARE TO TRIM MUCH OF THE NRN
PORTIONS OF SLIGHT RISK AREA DUE TO THE STABILIZING EFFECTS OF THE
MORNING MCS...AND THE EWD PROGRESSION OF A SFC WIND SHIFT LINE
ACROSS NWRN MN.

LATEST MESOANALYSIS INDICATES AN EFFECTIVE FRONTAL BOUNDARY
EXTENDING FROM NWRN THRU E-CENTRAL MN EWD ACROSS THE WRN UPPER
PENINSULA OF MI. CLOUD COVER/RAIN-COOLED AIR HAS GREATLY STABILIZED
AREAS N OF THIS BOUNDARY AND IT APPEARS UNLIKELY THAT THIS TREND
WILL BE REVERSED IN THE NEXT FEW HOURS. THIS REGION IS ALSO
EXPERIENCING LARGE-SCALE SUBSIDENCE BEHIND THE SHORTWAVE/REMNANT MCV
ASSOCIATED WITH EARLIER CONVECTION.

ALONG AND TO THE S OF THE SURFACE BOUNDARY...TEMPERATURES HAVE
WARMED INTO THE LOWER 90S...RESULTING IN 1000 TO LOCALLY 2000 J/KG
OF MLCAPE. STRONGER WINDS ON THE SRN PERIPHERY OF THE SHORTWAVE/MCV
HAVE RESULTED IN 40-50 KTS OF DEEP SHEAR IN THIS AREA...MORE THAN
SUFFICIENT FOR ORGANIZED TSTMS INCLUDING SUPERCELLS. UNCERTAINTY
EXISTS REGARDING HOW WIDESPREAD ADDITIONAL TSTM DEVELOPMENT WILL BE
GIVEN THE LIMITING FACTORS ALREADY MENTIONED...BUT WILL MAINTAIN THE
SLIGHT RISK IN AREAS ALONG AND S OF THE SURFACE BOUNDARY FOR THIS
OUTLOOK.

MINOR ADJUSTMENTS TO THE GENERAL THUNDERSTORM LINE WERE MADE BASED
ON CURRENT TRENDS...OTHERWISE NO OTHER CHANGES WERE MADE TO THE
PREVIOUS OUTLOOK.

..BUNTING.. 08/29/2013

.PREV DISCUSSION... /ISSUED 1128 AM CDT THU AUG 29 2013/

...SYNOPSIS...
THE LARGE-SCALE HIGH THAT HAS PERSISTED OVER THE CENTRAL STATES IS
SHOWING SIGNS OF SHIFTING WWD/WSWWD TOWARD THE HIGH PLAINS...AS ONE
PRONOUNCED SHORTWAVE TROUGH EJECTS NEWD OVER THE PAC NW.
DOWNSTREAM...AN INITIAL TROUGH WILL PROGRESS OFF THE MID ATLANTIC
COAST TODAY...WHILE ANOTHER WAVE CRESTS THE RIDGE OVER THE NRN
PLAINS AND BEGINS TO MOVE ESEWD TOWARD THE UPPER MS VALLEY AND LAKE
SUPERIOR OVERNIGHT. OTHERWISE...A PLUME OF RICH MONSOONAL MOISTURE
WILL CONTINUE TO SPREAD NWWD FROM NW MEXICO TO AZ AND THE LOWER CO
RIVER VALLEY...WHERE SCATTERED/MAINLY DIURNAL THUNDERSTORMS ARE
AGAIN EXPECTED.

...NRN MN/NW WI THROUGH TONIGHT...
AN MCS THAT ORIGINATED OVERNIGHT IN ERN MT/ND HAS MOVED INTO NRN MN
AS OF MID MORNING AND HAS DISPLAYED SLOW WEAKENING SINCE 13Z...ASIDE
FROM SOME RECENT DEVELOPMENT OF STRONGER UPDRAFTS ON THE SRN FLANK
OF THE SYSTEM. THE MCS IS ASSOCIATED WITH A MIDLEVEL TROUGH
CRESTING THE CENTRAL US RIDGE...AND IT APPEARS THAT THE PRIMARY WAVE
HAS BECOME THE REMNANT COMMA HEAD/MCV OVER NW MN. A CORRIDOR OF
LOW-MID 70S BOUNDARY LAYER DEWPOINTS EXTENDS SSEWD ACROSS
CENTRAL/ERN MN ALONG THE SYNOPTIC WARM FRONT WHICH WILL CONTINUE TO
MOVE SLOWLY NEWD TOWARD NW WI THROUGH THE AFTERNOON.

THE SEVERE THREAT THROUGH THE AFTERNOON/EVENING IS COMPLICATED BY
THE STABILIZING IMPACTS OF THE MORNING MCS...IN THE SAME AREA WHERE
MOST MESOSCALE AND CONVECTION-ALLOWING MODELS SHOW DEVELOPMENT OF
ADDITIONAL STORMS AFTER ABOUT 21Z. WILL MAINTAIN THE SLIGHT RISK
SINCE RECOVERY IS POSSIBLE FROM THE S-SW AS THE COLD POOL
ERODES...AND BECAUSE LOW-MIDLEVEL VERTICAL SHEAR WILL BE ENHANCED
S-E OF THE MCV. STILL...THE SEVERE STORM RISK COULD BE DELAYED TO
21Z OR LATER AS THE LOW LEVELS RECOVER IN PROXIMITY TO THE MCV
ACROSS N CENTRAL/NE MN...AND THERE WILL ALSO BE SOME POTENTIAL FOR
ISOLATED SEVERE STORM DEVELOPMENT WHERE THE REMNANT OUTFLOW
INTERSECTS THE SYNOPTIC WARM FRONT INVOF NW WI. THE COMBINATION OF
MODERATE-STRONG BUOYANCY AND THE ENHANCED VERTICAL SHEAR WITH THE
MCV WILL FAVOR SUPERCELLS CAPABLE OF PRODUCING DAMAGING WINDS AND
LARGE HAIL...AS WELL AS A COUPLE OF TORNADOES IN MN IF THE LOW
LEVELS RECOVER AS FORECAST.

...ALONG AND W OF THE ORE/WA CASCADES TODAY...
A PRONOUNCED SHORTWAVE TROUGH AND AN ASSOCIATED BAND OF ASCENT IS
APPROACHING THE ORE COAST AS OF 15Z. THIS WAVE WILL PIVOT NNEWD
OVER WRN ORE AND WRN/CENTRAL WA TODAY. SATELLITE IMAGERY SHOWS
WIDESPREAD CLOUD COVER IN ADVANCE OF THE WAVE...WHICH WILL TEND TO
LIMIT DAYTIME HEATING. HOWEVER...BOUNDARY LAYER DEWPOINTS OF 60-64
F W OF THE CASCADES WILL CONTRIBUTE TO WEAK BUOYANCY TODAY...DESPITE
THE RELATIVELY POOR LAPSE RATES AND CLOUD COVER. DEEP-LAYER SLY
SHEAR WILL BE FAVORABLE FOR SUPERCELLS IF SUFFICIENT DESTABILIZATION
CAN OCCUR IN SMALL CLOUD BREAKS...SUCH THAT ISOLATED DAMAGING GUSTS
AND A BRIEF/WEAK TORNADO WILL BE POSSIBLE.

...NE ID/WRN MT THIS AFTERNOON...
A BROKEN BAND OF HIGH-BASED STORMS IS FORECAST TO DEVELOP FROM
CENTRAL/NE ID INTO WRN MT...BEGINNING AROUND 21Z. INVERTED-V
PROFILES WITH WEAK BUOYANCY ON THE NW EDGE OF THE MONSOONAL MOISTURE
PLUME...AS WELL AS SOMEWHAT ENHANCED MIDLEVEL SWLY FLOW ON THE ERN
FRINGE OF THE PAC NW TROUGH...WILL SUPPORT A RISK FOR ISOLATED
STRONG OUTFLOW GUSTS.

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