Special Weather Statement, NWS Twin Cities, MN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
554 PM CDT SUN JUL 7 2013

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 137 PM CDT SUN JUL 7 2013

LATE THIS AFTN/EVENINGS WX FORECAST IS HIGHLY BASED ON CURRENT
CONVECTION ACROSS SD AND STALLED FRONTAL BOUNDARY INTERACTION FROM
NEAR LXL TO RWF. REGIONAL RADAR STILL HAS REMNANTS OF A SLOWLY
DECAYING COMPLEX OF TSRA ACROSS NORTH CENTRAL SD...WITH A
LINGERING WEAK CIRCULATION IN SOUTH CENTRAL SD. ALTHOUGH MLCAPES
HAVE INCREASED ACROSS WC/SW MN DURING THE DAY...MID LEVEL DRYING
FROM NORTH TO SOUTH ACROSS WESTERN MN...HAS LEAD TO AN OVERALL
DECREASE IN THE REFLECTIVITY RETURNS IN EASTERN SD.
HOWEVER...THESE CIRCULATION ASSOCIATED WITH THE EARLIER COMPLEXES
WILL LIKELY ENHANCE LARGE SCALE LIFT ALONG THE STALLED BOUNDARY
IN SW MN DURING THE LATE AFTN. MODELS ARE ALSO TRYING TO DEVELOP
AN AREA OF SHRA/TSRA ACROSS CENTRAL MN WHERE BETTER SFC
CONVERGENCE IS NOTED. THESE TWO AREAS WILL NEED TO BE WATCHED
BASED ON THE AMT OF CAPE AND SLIGHTLY ELEVATED 0-6KM SHEAR VALUES
WHICH DO INCREASE LATE THIS AFTN/EVENING IN SW/WC MN.
EVENTUALLY...THIS STALLED FRONTAL BOUNDARY WILL MOVE SE AS ANY
COMPLEX THAT DEVELOPS ACROSS SOUTHERN MN...MOVES SE OF THE REGION.
THERE SHOULD BE A LULL IN THE WX FOR LATE TONIGHT...INTO MONDAY
AFTN AS A WEAK RIDGE OF HIGH PRESSURE MOVES OVERHEAD.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 402 PM CDT SUN JUL 7 2013

THE INFLUENCE OF WEAK RIDGING BOTH AT THE SFC AND ALOFT WILL WANE
STARTING MON NIGHT WHILE A CUTOFF H5 LOW SHIFTS E ACRS CENTRAL
CANADA. THIS LOW WILL OPEN INTO A TROUGH DURG THE DAY ON TUE AND
PICK UP A STRAGGLING CDFNT EXTENDING SWWD FROM MANITOBA INTO THE
DAKOTAS. THIS CDFNT WILL TRAVERSE THE DAKOTAS TUE MRNG THEN SHIFT
THRU MN AND WI DURG THE DAY TUE. THE UPPER LEVEL TROUGH WILL
DEEPEN BEHIND THE FNT...ALLOWING MORE OF A SW FLOW AHEAD OF THE
FNT... MEANING A MORE PRONOUNCED MOISTURE PLUME ALONG WITH
STRONGER LOW LEVEL JETTING. THE ADDITIONAL MOISTURE WILL NOT ONLY
BRING THE SLIGHT RISE IN SFC DEWPOINTS MUCH ALSO INCRS MOISTURE
VERTICALLY... MEANING GREATER PWATS AND INSTABILITY.
OVERALL...PRECIP CHCS RISE TO THE 50-60 PERCENT RANGE FOR TUE INTO
TUE NIGHT AHEAD OF AND WITH THE FROPA. THE OTHER CONCERN IS A
SECONDARY QUASI-STNRY FRONT OVER IA THRU THE LOWER GREAT LAKES.
THIS FEATURE MAY ALSO ACT AS A LOW LEVEL CONVERGENCE BOUNDARY TO
ENHANCE CONVECTIVE COVERAGE. THERE IS ALSO THE CONCERN FOR
STRONG/SEVERE TSTMS WITH THE DEEP MOISTURE IN PLACE...THE STRONG
WARM SECTORING AND THE ADDED DYNAMICS ALOFT. ML CAPES LOOK TO
CLIME TO THE 2000-3000 J/KG RANGE WITH 30-40 KT OF BULK SHEAR WITH
LIMITED CAPPING DUE TO THE STRONG JETTING ALOFT. TOO EARLY TO
PINPOINT BETTER THAN MUCH OF THE MPX CWFA SO THIS SITUATION WILL
CERTAINLY NEED TO BE MONITORED. ONCE THE FRONT MOVES THROUGH THE
REGION BY LATE TUE EVE INTO EARLY MRNG WED...DEEP RIDGING WITH
SOLID NW FLOW ALOFT WILL MOVE INTO THE REGION WED AND LAST THRU
FRI. THE RIDGE WILL THEN GIVE WAY TO ANOTHER FRONTAL SYSTEM
LOOKING TO ENTER THE REGION FRI NIGHT. THERE ARE SOME CONFLICTING
MODEL IDEAS AS TO HOW MUCH EWD PROGRESSION THE FRONT WILL
MAKE...BUT IT APPEARS THE FRONT WILL WEAKEN AS IT RUNS INTO THE
LINGERING RIDGE...THUS DIMINISHING STRONG STORM POTENTIAL BUT
COVERAGE WILL BE ENOUGH TO PUSH POPS INTO THE 40-50 PERCENT RANGE.
CONDITIONS SLOWLY IMPROVE THRU THE WEEKEND BUT THERE WILL STILL BE
THE CHC FOR LINGERING SHWRS AS THE FNT STALLS OUT NEAR TO OVER THE
AREA WHILE THE ATMOS REMAINS QUITE MOIST. AS FOR
TEMPERATURES...THE WARM/HUMID CONDITIONS PERSIST THRU TUE THEN
DRIER/COOLER CONDITIONS MOVE IN BEHIND THE CDFNT. ALTHOUGH NOTHING
SIGNIFICANT...THE NOTICEABLE CHANGES WILL BE HIGHS DROPPING FROM
THE MID-UPR 80S TO NEAR 80 ALONG WITH DEWPOINTS FALLING FROM THE
LWR 70S TO THE UPR 50S. SLOW WARMING TREND IS THEN EXPECTED FOR
THE LATTER HALF OF THE WEEK ALONG WITH A GRADUAL INCRS IN MOISTURE
THAT WILL PUSH DEWPOINTS BACK INTO THE LOW-MID 60S.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 544 PM CDT SUN JUL 7 2013

MAIN AVIATION ISSUES ARE CHANCES FOR SHRA/TSRA THIS EVENING... AND
WIND DIRECTION ISSUES ASSOCIATED WITH ANY PCPN AND WITH THE ACTUAL
SURFACE TROUGH DROPPING THROUGH THE AREA THIS EVENING INTO THE
OVERNIGHT HOURS. DIDN/T STRAY TOO FAR FROM PREVIOUS FORECAST WITH
RESPECT TO THE TIMING OF THINGS... ESSENTIALLY ALLOWING FOR SOME
LIGHT/VARIABLE WINDS ALONG THE TROUGH BEFORE THINGS BECOME
NORTHERLY. ALTHOUGH THERE IS ONGOING CONVECTION... FEELING IS MUCH
OF IT WILL WEAKEN/DISSIPATE WITH THE LOSS OF HEATING BY MID
EVENING AND THERE DOESN/T LOOK TO BE ENOUGH FORCING OR ANY LOW
LEVEL JET TO KEEP ELEVATED CONVECTION GOING. SO... ALTHOUGH THERE
IS A FAIR AMOUNT OF ACTIVITY AT THE CURRENT TIME IT IS
QUESTIONABLE AS TO HOW MUCH WILL REMAIN BY 03Z... SO MAY USE VC IN
THE DOWNSTREAM TAFS UNTIL THINGS LOOK LIKE MORE OF A CERTAINTY
THAT ACTIVITY WILL MOVE INTO A GIVEN TAF AREA.

KMSP...HAVE LOW CONFIDENCE IN SOME OF THE FORECAST SPECIFIC DURING
THE FIRST SIX HOURS... MAINLY WITH RESPECT TO WHETHER SHRA/TSRA
WILL IMPACT THE AIRPORT. UPSTREAM ACTIVITY IS EXPECTED TO WEAKEN
DURING THE MID-EVENING... BUT THE SURFACE TROUGH HELPING TO FORCE
IT IS EXPECTED TO DROP TOWARD KMSP BY THAT TIME... WHICH COULD
SUPPORT KEEPING SOMETHING GOING AS IT WORKS INTO THE AREA. WILL
LIKELY KEEP AN EYE ON THINGS AND AMD FOR TS IF/WHEN IT LOOKS LIKE
IT WILL ACTUALLY HANG ON AND IMPACT THE AREA. OTHERWISE... WINDS
WILL SHIFT WESTERLY AND THEN NORTHERLY WITH TROUGH PASSAGE... BUT
COULD BE A BIT VARIABLE WHILE THE TROUGH DROPS THROUGH...
PARTICULARLY WITH ANY OUTFLOW FROM STORMS... WHICH WOULD BRIEFLY
PRODUCE SPEEDS HIGHER THAN ADVERTISED AND MOST LIKELY FROM THE
NORTHWEST... SO THAT/S SOMETHING ELSE WHICH MAY NEED TO BE AMENDED FOR.

/OUTLOOK FOR KMSP/
MONDAY OVERNIGHT...VFR CONDITIONS EXPECTED... MVFR CEILING AND
VISIBILITIES POSSIBLE LATE WITH A CHANCE OF SHRA/TSRA. VARIABLE
WIND LESS THAN 5 KT BECOMING SOUTHEAST 5 TO 15 KT.
TUESDAY...MVFR CEILINGS AND VISIBILITIES EXPECTED WITH
SHRA/TSRA... IFR CONDITIONS POSSIBLE. SOUTH WINDS 10 TO 20 KT
BECOMING WEST.
TUESDAY NIGHT...MVFR CEILINGS AND VISIBILITIES POSSIBLE EARLY WITH
A CHANCE OF SHRA/TSRA... OTHERWISE VFR. WEST WIND 5 TO 10 KT
BECOMING NORTHWEST 5 TO 15 KT.
WEDNESDAY AND WEDNESDAY NIGHT...VFR CONDITIONS EXPECTED. NORTHWEST
WIND 10 TO 20 KT.
THURSDAY...VFR CONDITIONS EXPECTED. NORTH WIND LESS THAN 10 KT.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&

SHORT TERM...JLT
LONG TERM...JPC
AVIATION...

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1139 AM CDT SUN JUL 7 2013

MNZ041>045-047>070-073>078-082>085-091>093-WIZ014>016-023>028-
081645-
DOUGLAS-TODD-MORRISON-MILLE LACS-KANABEC-STEVENS-POPE-STEARNS-
BENTON-SHERBURNE-ISANTI-CHISAGO-LAC QUI PARLE-SWIFT-CHIPPEWA-
KANDIYOHI-MEEKER-WRIGHT-HENNEPIN-ANOKA-RAMSEY-WASHINGTON-
YELLOW MEDICINE-RENVILLE-MCLEOD-SIBLEY-CARVER-SCOTT-DAKOTA-
REDWOOD-BROWN-NICOLLET-LE SUEUR-RICE-GOODHUE-WATONWAN-BLUE EARTH-
WASECA-STEELE-MARTIN-FARIBAULT-FREEBORN-POLK-BARRON-RUSK-
ST. CROIX-PIERCE-DUNN-PEPIN-EAU CLAIRE-
1139 AM CDT SUN JUL 7 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL AND
SOUTHERN MINNESOTA... AND WEST CENTRAL WISCONSIN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED THUNDERSTORMS WILL BE POSSIBLE THIS AFTERNOON AND EARLY
EVENING ACROSS PORTIONS OF SOUTHERN MINNESOTA AND WEST CENTRAL
WISCONSIN. AN ISOLATED STRONG STORM IS POSSIBLE...BUT SEVERE
WEATHER IS LOW.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THUNDERSTORM CHANCES RETURN FOR MONDAY AFTERNOON AND TUESDAY.
SOME OF THESE STORMS COULD BE SEVERE...ESPECIALLY TUESDAY
AFTERNOON.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION WILL NOT BE NEEDED.

JLT

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