Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 200021
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
721 PM CDT FRI SEP 19 2014

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 353 PM CDT FRI SEP 19 2014

DURING THE SHORT TERM...CONFIDENCE ON SEEING MUCH ACTIVITY IN THE
MPX CWA THIS EVENING AND OVERNIGHT CONTINUES TO PLUMMET...BUT THIS
HAS BEEN OFFSET BY A SIGNIFICANT INCREASE IN CONFIDENCE FOR SEEING
THUNDERSTORMS SATURDAY AFTERNOON.

THIS AFTERNOON...A WARM FRONT HAD PUSHED UP TO ABOUT THE MN
RIVER...WITH A COLD FRONT EXTENDING FROM A SFC LOW NEAR THE
MN/ND/CAN BORDER TO THE SOUTH ACROSS THE ERN DAKOTAS. BAND OF LIGHT
RETURNS ON RADAR FROM WEST CENTRAL MN TOWARD DULUTH CORRELATES WELL
WITH FGEN THE RAP IS INDICATING IN THE H7-H6 LAYER ON THE NW SIDE OF
A RATHER STRONG CAPPING INVERSION. THIS CAPPING INVERSION LOOKS TO
KEEP THINGS IN CHECK THROUGH 00Z...BUT CAMS BEGIN TO SHOW THE CAP
BREAKING DOWN BETWEEN 00Z AND 03Z THIS EVENING. STORMS LOOK TO
INITIATE ALONG A PREFRONTAL TROUGH THAT IS CURRENTLY TAKING SHAPE
FROM DULUTH...DOWN THROUGH GLENCOE AND OFF TOWARD SIOUX FALLS. THIS
BOUNDARY CAN BE IDENTIFIED IN THE WIND FIELD...WITH STRONG SOUTHERLY
WINDS THAT HAVE BEEN GUSTING TO NEARLY 40 MPH ACROSS IA INTO SRN MN
TO THE EAST...AND MUCH LIGHTER WSW WINDS THAT ARE BACK ACROSS WRN
MN. BY THE TIME 3Z COMES AROUND...WHICH IS WHEN THE HRRR AND HOPWRF
SHOW STORMS INITIATING...SAID WIND SHIFT LOOKS TO BE SITTING NEAR A
FAIRMONT/HASTINGS/RICE LAKE LINE. ANY SORT OF SHORT WAVE TO HELP
KICK OF THUNDERSTORMS DOES NOT LOOK TO ARRIVE UNTIL AFTER 6Z...SO
LOOKS LIKE ISO-SCT STORM COVERAGE IS ABOUT THE BEST THE ERN FRINGE
OF THE MPX CWA CAN HOPE FOR...WITH MOST CAMS REALLY STARTING TO
HIGHLIGHT THE GREATEST STORM COVER BEING DOWN IN IOWA...WHERE BETTER
INSTABILITY WILL RESIDE. GIVEN TREND IN SHORT TERM MODELS...
CONTINUED TO REDUCE POPS/QPF THIS EVENING...AND ALSO SPED UP THE
EWD PROGRESSION OF THE DRY WEATHER AS ALL CAMS SHOW ANY ACTIVITY
THAT DOES DEVELOP THIS EVENING BEING EAST OF THE MPX CWA BY 9Z. THE
ONLY THING TO WATCH OUT FOR WITH POPS FOR LATE TONIGHT INTO SATURDAY
MORNING IS THE NAM DOES SHOW A REGION OF MID LEVEL FGEN WORKING
ACROSS SOUTH CENTRAL MN AS A SHORTWAVE FINALLY WORKS ACROSS SRN MN.
HOWEVER...THIS WOULD NOT BE ANYTHING TOO SERIOUS AND WOULD BE POST
FRONTAL AND NO WORSE THAN WHAT WE ARE SEEING ACROSS CENTRAL MN THIS
AFTERNOON.

FOR SATURDAY WE WILL SEE A BREAK IN THE ACTION THROUGH THE
MORNING...BUT THE STRONG SHORTWAVE AND ASSOCIATED JET STREAK
CURRENTLY MOVING INTO WRN ALBERTA WILL BE DIVING SE ACROSS NRN MN BY
SATURDAY AFTERNOON. THERE IS GOOD AGREEMENT BETWEEN THE
DETERMINISTIC MODELS AND CAMS WITH A LINE OF STORMS DIVING SE OUT OF
NRN MN DURING THE AFTERNOON OUT AHEAD OF THE WAVES PV FEATURE AND AT
THE NOSE OF A 120+ KT NWRLY JET STREAK. GIVEN STRONG MODEL
AGREEMENT...INCREASED POPS SIGNIFICANTLY SATURDAY AFTERNOON FROM THE
LOW CHANCE CATEGORY TO KNOCKING ON THE DOOR OF GOING CATEGORICAL.
MAIN QUESTION IS HOW FAR SW WILL WE SEE ACTIVITY. GIVEN THE TRACK OF
THE PV ANOMALY AND JET STREAK...FORCING FROM THOSE FEATURES LOOKS TO
BE CENTERED ALONG AND NORTH OF THE I-94 CORRIDOR...BUT SREF PROBS
AND CAM REFLECTIVITY FORECASTS DO SHOW THE LINE TAILING BACK INTO SW
MN...SO DID DRAG POPS AS FAR SW AS THE MN RIVER. FOR THE SEVERE
THREAT...THE BIG LIMITING FACTOR WILL BE THE MEAGER INSTABILITY
/MUCAPE AROUND 500 J/KG/ AND WEAK MID-LEVEL LAPSE RATES.
HOWEVER...FORECAST SOUNDINGS SHOW WINDS OF 50 KTS OR MORE GETTING
DOWN TO NEAR 10K FEET. WITH THE CAMS SHOWING A NICE LINE OF STORMS
DEVELOPING...COULD SEE THESE STORMS BE ABLE TO TRANSFER SOME OF THIS
MOMENTUM TO THE GROUND...WHICH WILL POSE A RISK FOR DAMAGING
WINDS...BUT THE LACK OF INSTABILITY AND WEAK MID-LEVEL LAPSE RATES
SHOULD KEEP ANY HAIL SIZES IN CHECK.

NOT MANY CHANGES WERE MADE TO THE REST OF THE FORECAST...OTHER THAN
TO COOL HIGHS TOMORROW SOME WHERE WE HAVE LIKELY POPS IN THE
AFTERNOON...AS THE ARRIVAL OF CLOUD COVER AND RAIN LOOKS TO PUT AN
EARLIER END TO DIURNAL RISES IN THOSE LOCATIONS.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 353 PM CDT FRI SEP 19 2014

ANY THUNDERSTORM ACTIVITY ONGOING AT THE BEGINNING OF THE PERIOD
WILL BE QUICK TO SWING EAST THANKS TO THE VERY FAST 90-130 KT
UPPER LEVEL FLOW CONTRIBUTING TO THE SOUTHEASTWARD DIGGING TROUGH.
CYCLONIC FLOW WILL REMAIN OVER PORTIONS OF CENTRAL AND EASTERN
WISCONSIN INTO SUNDAY AND MAY ALLOW FOR A FEW SHOWERS TO DEVELOP
IN THE AFTERNOON. HOWEVER...THE SURFACE RIDGE BUILDING EAST INTO
THE PLAINS WILL KEEP THE REMAINING AREAS DRY AND MAINLY CLEAR. THE
TROUGH WILL LIFT OUT BY MONDAY WITH SEASONAL TEMPS AND CLEAR SKIES
ACROSS THE ENTIRE UPPER MIDWEST THROUGH EARLY NEXT WEEK.

A MAJOR PATTERN SHIFT WILL TAKE PLACE NEXT WEEK AND LIKELY PERSIST
THROUGH THE REST OF SEPTEMBER. THE SURFACE HIGH WILL MAKE STEADY
PROGRESS EAST AND EVENTUALLY PARK ITSELF OVER NEW ENGLAND FOR
MIDWEEK AND BEYOND. MEANWHILE...MID LEVEL HEIGHTS WILL BUILD OVER
THE MIDWEST WITH THE CENTER LOCATED SOMEWHERE NEARBY FOR LATE WEEK
AND NEXT WEEKEND. THIS WILL ALLOW FOR A WARMER AND DRIER THAN
NORMAL PATTERN TO SET UP FOR A GOOD PORTION OF THE LONG TERM.
THERE WILL BE A BRIEF HIATUS IN THIS EVOLUTION MIDWEEK AS LOW
LEVEL MOISTURE INCREASES AND A DISTURBANCE LIFTS NORTH UP AND
AROUND THE BUILDING RIDGE FROM THE DESERT SOUTHWEST /CURRENTLY
LOCATED OVER CALIFORNIA/. CLOUDS AND SCATTERED SHOWERS/THUNDERSTORMS
WILL KEEP TEMPERATURES DOWN A BIT TUESDAY AND WEDNESDAY. WITH THE
BUILDING MID LEVEL HEIGHTS...MID LEVEL LAPSE RATES WILL BE RATHER
MEAGER WHICH WILL LIMIT ANY SEVERE THREAT GREATLY. KEPT POPS LOW
DUE TO THE LACK OF INSTABILITY AND A SLOW WEAKENING/ABSORPTION OF
THE SYSTEM INTO THE ZONAL FLOW ACROSS CANADA.

AS MENTIONED ABOVE...THE MID LEVEL RIDGE WILL LIKELY BE CENTERED
OVER THE MIDWEST BY NEXT WEEKEND. SUMMERLIKE TEMPERATURES SHOULD
MAKE A RETURN AS 850 MB TEMPS REACH BETWEEN +15 TO +20C. SINCE THE
MAJORITY OF SOUTHERN MINNESOTA DID NOT HAVE A HARD TIME REACHING
THE LOWER/MIDDLE 80S TODAY...WE STAND A PRETTY GOOD CHANCE AT
REACHING THE 80S AGAIN LATE NEXT WEEK WITH A STRONGER RIDGE AND
WARMER TEMPS ALOFT. DRY WEATHER WILL PREVAIL UNTIL THE WESTERN
TROUGH BEGINS TO ADVANCE EASTWARD - NOT UNTIL WELL AFTER THE
CURRENT FORECAST PERIOD.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 720 PM CDT FRI SEP 19 2014

MAIN CONCERN OVER THE NEXT FEW HOURS IS TSRA DEVELOPMENT FROM
SOUTH CENTRAL MN THROUGH THE SOUTH METRO AND INTO WEST CENTRAL WI.
VISIBLE IMAGERY SHOWING TOWERING CU FROM SOUTHWEST OF KMSP ON BACK
TO NORTH OF KFSD. AT THIS TIME...CONFIDENCE REMAINS HIGH THAT A
FEW STORMS WILL DEVELOP/MOVE INTO KEAU IN THE 01Z-04Z TIME FRAME.
KRWF...KMSP AND KRNH WILL SEE SOME LIGHT SHOWERS THIS EVENING AS A
BAND OF MID LEVEL FRONTOGENESIS MOVES THROUGH. PREVAILING
CONDITIONS EARLY TONIGHT WILL BE VFR. HOWEVER...LATE IN THE
NIGHT/EARLY SATURDAY MORNING IN THE WAKE OF A COLD FRONT...MVFR
CIGS/VSBYS ARE LIKELY FROM KSTC THROUGH KRNH AND KEAU. A VERY
NEGATIVE CU RULE IS SEEN ACROSS EASTERN MN AND WESTERN WI ON
SATURDAY. THE CONCERN IS THAT BKN-OVC MVFR CEILINGS MAY PERSIST
LONGER THAN CURRENTLY FORECAST FOR KSTC...KRNH AND KEAU. THEREFORE...
WITH CONFIDENCE NOT HIGH ON EXTENDING THE MVFR...USED BKN035-040.
ANOTHER COLD FRONT WILL BLAST THROUGH THE AREA SATURDAY AFTERNOON
AND EVENING. THIS FRONT WILL BE ACCOMPANIED BY VERY STRONG WINDS
ALOFT. SEVERAL CONVECTION ALLOWING MODELS INDICATE A BKN LINE OF
STORMS MOVING INTO KAXN AROUND 21Z. THE LINE HEADS SOUTHEAST AT
NEAR 50 KNOTS REACHING THE TWIN CITIES BY 23Z. CONFIDENCE IS
PRETTY HIGH ON THIS FEATURE AND USED TEMPO GROUPS FOR THE MN TAF
SITES AS THE LINE SHOULD NOT REACH INTO WESTERN WI UNTIL AFTER
21/00Z. THE STORMS THAT DO DEVELOP WILL HAVE THE CAPABILITY TO
PRODUCE STRONG TO SEVERE WIND GUSTS FROM THE NORTHWEST.

KMSP...STORM DEVELOPMENT THIS EVENING...IF IT OCCURS...WILL STAY
JUST SOUTH OF THE AIRFIELD. THERE WILL BE LIGHT SHOWERS MOVING
THROUGH FROM THE WNW. ANOTHER PERIOD FOR TSRA WILL BE LATE
SATURDAY AFTERNOON (23Z-02Z) WHEN A LINE OF STORMS IS EXPECTED TO
MOVE THROUGH AHEAD OF A STRONG COLD FRONT. LIGHT NNE WINDS EARLY
THIS EVENING WILL VEER TO THE SSW LATE IN THE EVENING THEN BECOME
NW 10-15 KNOTS SATURDAY MORNING.

/OUTLOOK FOR KMSP/
SUN...VFR. WINDS NW 10-15 KTS.
MON...VFR. WINDS W 5-10 KTS.
TUE...VFR. WINDS SE 5-10 KTS.

&&

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

$$

SHORT TERM...MPG
LONG TERM...BORGHOFF
AVIATION...RAH






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