Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 191153
AFDMPX

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

.UPDATE...
ISSUED AT 652 AM CDT TUE AUG 19 2014

UPDATED TO INCLUDE 12Z 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 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 652 AM CDT TUE AUG 19 2014

MRNG FOG/LOW STRATUS AT NRN AND ERN TAF SITES MAKING FOR A
DIFFICULT INITIALIZATION TO THE 19/12Z TAFS. AM THINKING THAT ANY
ISSUES WITH FOG/STRATUS WILL BURN OFF BY 15Z THEN VFR CONDS WILL
PREVAIL. WI TAF SITES WILL THEN BE SUSCEPTIBLE TO AFTN SHRA DUE TO
A LINGERING SFC TROF BEHIND THE LOW PRES CENTER SHIFTING INTO THE
GREAT LAKES TDA. NOT LOOKING FOR ANY RESTRICTIONS WITH ANY
PRECIP...UNLESS AN ISOLD TSTM DOES IMPACT ONE OF THE TERMINALS...
AND THIS POSSIBILITY CANNOT BE RULED OUT. THE WINDOW FOR PRECIP
LOOKS TO CLOSE ARND 20/00Z WITH VFR CONDS RESUMING GOING INTO THE
EVE HRS. LATE EVE THRU THE OVERNIGHT HOURS INTO WED MRNG...WINDS
WILL GO LIGHT TO CALM WITH SKIES CLEARING OUT...MAKING FOR FAIRLY
GOOD RADIATIONAL COOLING CONDS. GIVEN THE EFFICIENT COOLING AND
CALMING WINDS...FOG LOOKS TO BE A GOOD BET AND THE MODELS TEND TO
AGREE. HAVE INDICATED CONDS DROPPING DOWN TO IFR LEVELS BY THE
PRE-DAWN HOURS BUT WOULD NOT BE SURPRISED IF CONDITIONS OCCURRED
EARLIER AND HIT HARDER THAN CURRENTLY ADVERTISED. THAT SAID...
CONFIDENCE WAS HIGH ENOUGH TO ADVERTISE IFR CONDITIONS THIS EARLY.

KMSP...VFR THROUGH THIS EVENING WITH NO PRECIP XPCTD. MVFR FOG TO
DEVELOP OVERNIGHT WITH A GOOD CHC OF IFR /AND POSSIBLY EVEN LOWER/
CONDITIONS TO DEVELOP DURG THE PRE-DAWN HOURS.

/OUTLOOK FOR KMSP/
THU...VFR. CHC MVFR WITH TSRA. 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...DENSE FOG ADVISORY UNTIL 9 AM CDT THIS MORNING FOR WIZ014>016-
     025-027-028.

&&

$$

UPDATE...JPC
SHORT TERM...JPC
LONG TERM...JRB
AVIATION...JPC





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