Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 191815
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
115 PM CDT TUE AUG 19 2014

.UPDATE...FOR 18Z AVIATION DISCUSSION BELOW

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 358 AM CDT TUE AUG 19 2014

TODAY AND TONIGHT...SFC ANALYSIS DEPICTS A LOW PRES CENTER
CROSSING INTO NWRN WI EARLY THIS MRNG...WITH A CDFNT DRAGGING
OVER SERN MN INTO FAR SWRN WI. ALOFT...A UPR LVL LOW OFFSET TO THE
NNW FROM THE SFC LOW WILL ACCOMPANY THE SFC LOW TO THE E INTO THE
GREAT LAKES TDA. THIS WILL DRAG ANY REMAINING SHOWERS/T-STORMS OFF
INTO WI. HOWEVER...IN ITS WAKE WILL BE PLENTY OF LLVL MOISTURE
ALONG WITH COOLER AIR THAT MAY WELL BE CONDUCIVE TO FOG
DEVELOPMENT. KEY FACTOR FROM THIS MRNG COMPARED TO YDA
MORNING...WHERE DENSE FOG WAS PREVALENT OVER WRN MN...IS THAT
WINDS ARE SHIFTING TO NW BEHIND THE SFC LOW AND AT SPEEDS IN THE
5-10KT RANGE...HELPING KEEP THINGS MIXED JUST ENOUGH TO AVOID MORE
WIDESPREAD FOG COVERAGE. GOING BEYOND DAYBREAK...A LINGERING NW-SE
TROUGH EMANATING FROM THE NWRN SIDE OF THE SFC LOW WILL FOLLOW THE
LOW AND MAKE ITS WAY INTO NWRN MN INTO WRN WI. THIS SFC TROF WILL
ACT AS A LLVL CONVERGENCE BOUNDARY FOR MOISTURE AND LIFT WHILE THE
SHORTWAVE TROUGH AXIS ALOFT...WHICH CONTAINS THE UPR LVL
LOW...MOVES ATOP SFC TROUGH... HELPING AID LIFT FOR ERN PORTIONS
OF THE MPX CWFA. THIS COMBINATION WILL BE ENOUGH TO PRODUCE
SCATTERED SHWRS/TSTMS MAINLY THIS AFTN OVER ERN PORTIONS OF THE
CWFA. NOT LOOKING FOR A LOT OF COVERAGE NOR INTENSITY BUT PRECIP
MENTION IS CERTAINLY WARRANTED. AS FOR CENTRAL-WRN MN...HIGH
PRESSURE WILL START TO MAKE INROADS TO THE UPR MISS RIVER
VALLEY...ALLOWING FOR CLEARING SKIES WELL IN THE WAKE OF THE SFC
LOW. PRECIP OVER THE ERN PORTIONS WILL STEADILY SHIFT OFF TO THE E
THIS EVE WHILE SKIES CLEAR OUT...ALLOWING FOR DECENT RADIATIONAL
COOLING CONDS OVERNIGHT TNGT INTO WED MRNG. THE CONCERN AGAIN
BECOMES FOG DEVELOPMENT. WITH WINDS DROPPING OFF AND COOLER BLYR
AIR ATOP STILL MOIST DEWPOINTS SHOULD MAKE FOR AT LEAST AREAS OF
FOG...IF NOT THE PROTOTYPICAL WIDESPREAD FOG. AM NOT QUITE
CONFIDENT ENOUGH TO GO WITH DENSE FOG MENTION ATTM...BUT WOULD NOT
BE SURPRISED IF THAT IS INDEED THE CASE 24 HOURS FROM NOW.
TEMPERATURES TDA WILL BE A LITTLE COOLER BEHIND THE DEPARTING SFC
LOW PRES SYSTEM. WILL LOOK FOR HIGHS FROM THE LWR 70S TO LWR
80S...THE LOWER END OF THAT RANGE IN WRN WI AND THE HIGHER END OF
THAT RANGE IN SWRN MN WHERE CLEARING WILL BE MOST EFFICIENT.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 358 AM CDT TUE AUG 19 2014

TWO MAIN ROUNDS OF CONVECTION WILL DEVELOP LATE WEDNESDAY INTO
THURSDAY...AND AGAIN FRIDAY NIGHT INTO SATURDAY. THE PREVIOUS
FORECAST WAS IN VERY GOOD SHAPE...SO DID NOT MAKE ANY SIGNIFICANT
CHANGES.

AT THE START OF THE PERIOD A SHORTWAVE WILL LIFT FROM THE WYOMING
FOOTHILLS UP ACROSS NORTHERN MINNESOTA. THIS DRAG A WARM FRONT
UP FROM THE SOUTH...WHICH WILL BE THE FOCUS FOR SHOWERS AND
THUNDERSTORMS LATE WEDNESDAY INTO THURSDAY. CONFIDENCE IS HIGH
THAT AN MCS WILL DEVELOP THURSDAY NIGHT AND BRING HEAVY RAIN
ACROSS THE UPPER MIDWEST. A FEW LOCALIZED AREAS SHOULD SEE AROUND
2 INCHES. SEVERE WEATHER IS ALSO POSSIBLE WITH THE ELEVATED
CONVECTION. BUFR SOUNDINGS SHOW 30-40KTS OF 1-6KM SHEAR...WITH A
VEERING WIND PROFILE...SO STORMS MAY BE FAIRLY ORGANIZED WEDNESDAY
NIGHT. AT THIS TIME...SEVERE WIND WOULD BE THE PRIMARY
THREAT...WITH A SECONDARY THREAT OF HAIL...AND NEARLY ZERO THREAT
OF TORNADOES.

THIS CONVECTION WILL LINGER INTO THURSDAY AS THE FRONT LIFTS
NORTHWARD. THE GFS CONTINUE TO SHOW ANOTHER SHORTWAVE EJECTING
NORTHEAST FROM THE CALIFORNIA TROUGH ON FRIDAY...BUT THE ECMWF AND
GEM REMAIN DRY SO DO HAVE HAVE MUCH FAITH IN THE GFS SOLUTION.
THIS IMPACTS THE REST OF THE FORECAST AS WELL...WITH THE GEM AND
ECMWF IN GOOD AGREEMENT ON PRECIP ACROSS THE SOUTHERN HALF OF THE
CWA FRIDAY NIGHT INTO SATURDAY. THEREFORE CONTINUED LIKELY POPS
SATURDAY NIGHT...WITH A BLENDED SOLUTION CARRIED ON THROUGH THE
WEEKEND. TEMPERATURES WILL DEPEND ON CLOUD COVER AND LOCATION OF
THE WARM FRONT...NEAR 90 SOUTH OF THE FRONT...AND UPPER 70S ALONG
AND NORTH OF THE FRONT.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 115 PM CDT TUE AUG 19 2014

MVFR LEVEL CLOUDS WILL BE BROKEN AT TIMES GENERALLY ALONG/NORTH OF
THE INTERSTATE 94 CORRIDOR THIS AFTERNOON...AFFECTING KSTC-KRNH-
KEAU. THIS WILL ALSO BE THE AREA MOST SUSCEPTIBLE TO SHOWER/TS
ACTIVITY...ALTHOUGH SHOWERS IN THE VICINITY OF KMSP WILL ALSO BE
POSSIBLE THROUGH THE AFTERNOON. SKIES CLEAR THIS EVENING...AND
THEN FOG BECOMES A CONCERN YET AGAIN AS WINDS BECOME
CALM...ESPECIALLY FOR KRNH AND KEAU WHERE THE SURFACE RIDGE AXIS
WILL LIE. HAVE INCLUDED 1/2SM FG MENTIONS AT SAID SITES...BUT THAT
COULD EASILY BECOME 1/4SM FG IF SKIES CLEAR EFFICIENTLY. VSBYS AT
THE OTHER SITES SHOULD PRIMARILY BE IFR. FOG SHOULD BURN OFF
14-15Z ON WEDNESDAY...WITH SOUTHEAST WINDS AROUND 5 KTS AND A FEW
CUMULUS CLOUDS DEVELOPING.

KMSP...
FEW-SCT MVFR LEVEL CLOUDS WILL BE POSSIBLE AT THE START OF THE TAF
PERIOD...ALONG WITH SPOTTY SHOWERS NEAR THE FIELD THROUGH THE
AFTERNOON. SKIES CLEAR TONIGHT AND WINDS BECOME NEARLY CALM. FOG
WITH VSBYS OF 2-5SM WILL BE POSSIBLE BETWEEN 08Z AND 13Z. A FEW CU
AROUND FOR WEDNESDAY BUT OVERALL A BENIGN WX DAY.

/OUTLOOK FOR KMSP/
THU...VFR. CHC MVFR WITH TSRA...ESPECIALLY IN THE MORNING. WINDS SE 5-10
KTS BECMG SW.
FRI...VFR. CHC MVFR WITH TSRA. WINDS NE 5-10 KTS.
SAT...VFR. CHC MVFR WITH TSRA. WINDS SW 5-10 KTS.

&&

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

$$


SHORT TERM...JPC
LONG TERM...JRB
AVIATION...LS






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