Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 031100
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
600 AM CDT MON AUG 3 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 349 AM CDT MON AUG 3 2015

TODAY AND TONIGHT...SFC ANALYSIS DEPICTS A CDFNT FROM THE ERN GRT
LKS WSWWD OVER SRN MI TO NRN IL AND SRN IA. IT IS THIS FRONT
WHICH PUSHED THRU LATE YDA RESULTING IN THE MUCH COOLER/DRIER AIR
EXPERIENCED THIS MRNG WITH CLR SKIES. THIS COOLER/DRIER HIGH PRES
AIRMASS WILL REMAIN OVER THE AREA THRU TNGT...KEEPING MUCH OF THE
CLOUD COVER ASSOCIATED WITH THE DEEP HUDSON BAY UPR LVL LOW TO THE
E OF THE WFO MPX CWFA. THAT SAID...SOME WOBBLING OF THE LARGE UPR
LOW WITH SEVERAL SHORTWAVE SPOKES OF ENERGY ROTATING ARND THE UPR
LOW MAY BRING SOME CLOUD COVER TO FAR NERN PORTIONS OF THE CWFA
THIS AFTN BUT RAIN SHOWERS ARE EXPECTED TO REMAIN WELL OFF TO THE
E. THE UPR LOW WILL BEGIN TO MOVE FURTHER E TNGT WHILE RIDGING OUT
WEST EXPANDS SLIGHTLY EWD...MAKING FOR CLR SKIES UPCOMING TNGT
INTO TUE MRNG. AS ALLUDED TO AT THE START...TEMPERATURES WILL RUN
NOTICEABLY COOLER AND HUMIDITY LEVELS WILL BE MUCH LOWER. HIGHS
TDA WILL HIT THE MID-UPR 70S WHILE DEWPOINTS CAP OUT IN THE LWR
50S...AND THIS WILL BE FOLLOWED BY LOWS EARLY TUE MRNG IN THE UPR
40S TO MID 50S.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 349 AM CDT MON AUG 3 2015

THE LONG TERM PERIOD STARTS OFF QUIET AND PLEASANT. WITH THE UPPER
LOW STILL PARKED OVER HUDSON BAY...THE UPPER MIDWEST WILL CONTINUE
TO BE FED DRY NORTHWESTERLY FLOW FROM CANADA AS SURFACE HIGH
PRESSURE STAYS WITH US THROUGH THE DAY. HIGH TEMPERATURES
APPROACHING 80 WITH DEW POINTS IN THE LOW 50S WILL FEEL VERY
COMFORTABLE FOR MOST. THERE COULD BE SOME CUMULUS DEVELOPMENT
DURING THE DAY AS CU RULE INDICATES SLIGHTLY NEGATIVE VALUES IN
EASTERN MN AND WESTERN WI...COINCIDING WITH CYCLONIC CIRCULATION
ON THE BACK SIDE OF THE LONG WAVE TROUGH.

THE FORECAST BECOMES QUITE MURKY WEDNESDAY AND BEYOND.
DISAGREEMENT AMONG THE LATEST DETERMINISTIC SOLUTIONS WAS
PRONOUNCED. WHILE THE GFS WOULD INDICATE THETA-E ADVECTION AND PV
ADVECTION CAUSING SHOWERS AND THUNDERSTORMS WEDNESDAY FOR WESTERN
MN...THE EC HOLDS THAT ACTIVITY OFF COMPLETELY...AND THE NAM IS A
TAD SLOWER THAN THE GFS AND KEEPS MOST OF THE PRECIP WEST OF OUR
AREA. THE GFS HAS BECOME AN OUTLIER IN HOW QUICKLY THE WAVE MOVES
EAST...SO TRENDED THE FORECAST TOWARD THE ECMWF/NAM...MEANING
BRINGING THE PRECIP IN SLOWER...BUT WITH ALL THE SPREAD IN THE
SOLUTIONS...KEPT SOME 20 TO 30 PERCENT POPS TO EXTREME WESTERN MN
DURING THE DAY ON WEDNESDAY...MAINLY LATE AFTERNOON. ON WEDNESDAY
NIGHT...THE EC AND CANADIAN INDICATE DECENT AGREEMENT IN WORKING A
MID LEVEL WAVE FROM ND ACROSS MN BY THURSDAY MORNING...AND
SPREADING PRECIP THROUGH DURING THAT TIME...BUT THE NAM IS
COMPLETELY DRY AND THE GFS WANTS THE PRECIP CONFINED TO SW MN WITH
THE VORTICITY MAX FROM THE POTENTIAL PRECIP EARLIER IN THE DAY.
THE EC AND GFS FINALLY DO AGREE ON ANOTHER SHORTWAVE QUICKLY
MOVING IN THURSDAY AFTERNOON AND THURSDAY NIGHT SPREADING BROAD
LIFT ACROSS THE AREA AND A SHOT FOR ADDITIONAL RAINFALL.

IN REALITY...DUE TO THE DIFFERENCES IN THE GUIDANCE...THERE IS A
LOT OF 20-40 PERCENT POPS CURRENTLY IN THE FORECAST FROM WEDNESDAY
THROUGH FRIDAY...BUT ONCE THE GUIDANCE CAN START TO OFFER A BETTER
SENSE OF WHAT WE CAN EXPECT TO ACTUALLY OCCUR...POPS WILL LIKELY
BE ABLE TO BE CONSOLIDATED SPATIALLY AND TEMPORALLY.

CONFIDENCE IN THE WEEKEND PRECIPITATION FORECAST IS EXTREMELY LOW
GIVEN THE VARIABILITY IN THE GUIDANCE AND HOW THE VARIOUS
SOLUTIONS FOR HANDLING THE WAVES WE FIRST MUST DEAL WITH
WEDNESDAY THROUGH FRIDAY. THE GFS AND EC BOTH INDICATE A CLOSED
UPPER LOW PROGRESSING EAST-SOUTHEAST FROM SOUTHERN CANADA THROUGH
NORTHERN MN...BUT DIFFER IN BOTH PLACEMENT AND TIMING. THE GENERIC
ALLBLEND OF THE MODELS NOW SMOTHERS THE ENTIRE AREA IN 20-30 POPS
FOR THE ENTIRE WEEKEND...LARGELY DUE TO THE TIMING DIFFERENCES IN
THE HANDLING OF THE UPPER LOW. WE`LL HAVE TO CARRY THESE LOW
END/LOW CONFIDENCE POPS UNTIL MORE CLARITY CAN BE GAINED FROM THE
GUIDANCE IN FUTURE RUNS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 555 AM CDT MON AUG 3 2015

VFR CONDS THROUGHOUT THIS SET AS WRN CANADIAN HIGH PRES MOVES IN
FROM THE NW. FEW/SCT MIDLVL STRATOCU POSSIBLE OVER WRN WI AS
MOISTURE WRAPS AROUND THE LARGE UPR LVL LOW NEAR HUDSON BAY
CANADA. NW WINDS BECOME BREEZY/GUSTY LATE MRNG THRU THIS AFTN
BEFORE SETTLING BACK DOWN THIS EVE AND TNGT.

KMSP...NO SIGNIFICANT WX IMPACTS EXPECTED.

/OUTLOOK FOR KMSP/
WED...MAINLY VFR. CHC MVFR SHRA/TSRA. WIND E 5-10 KTS.
THU...MAINLY VFR. CHC MVFR SHRA/TSRA. WIND SE 5-10 KTS.
FRI...MAINLY VFR. CHC MVFR SHRA/TSRA. WIND E 5-10 KTS.

&&

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

$$

SHORT TERM...JPC
LONG TERM...SPD
AVIATION...JPC


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