Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 291031
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
531 AM CDT SUN MAR 29 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 528 AM CDT SUN MAR 29 2015

THE EXPECTED STRONG WINDS ARE THE TOP STORY TODAY AS A POTENT
SHORTWAVE SLIDES ACROSS MN/WI.

A BAND OF LIGHT RAIN MOVED ACROSS THE FORECAST AREA EARLY THIS
MORNING WITH GENERALLY BETWEEN A TRACE - 0.05" OF
LIQUID...HOWEVER...RAPID DRYING IS NOW TAKING PLACE ACROSS WESTERN
AND CENTRAL WITH THE DRY SLOT MOVING FROM THE DAKOTAS INTO
MINNESOTA. THIS IS A HIGHLY DYNAMIC WAVE WITH GOOD FORCING...LARGE
500MB HEIGHT FALLS...AND A WELL-ESTABLISHED SURFACE FEATURE. THE
RESULT HAS BEEN A HIGH WIND EVENT ACROSS THE WESTERN/CENTRAL DAKOTAS
OVERNIGHT WITH SFC GUSTS BETWEEN 40-60 MPH. THE WIND WILL SPREAD
EAST ACROSS THE FORECAST AREA THIS MORNING. WE EXPANDED THE WIND
ADVISORY A BIT FARTHER EAST BECAUSE THE MSLP RISE/FALL COUPLET
ACTUALLY MAXIMIZES OVER CENTRAL MN LATE THIS MORNING AND EARLY THIS
AFTERNOON. THERE IS 35-40KTS THROUGHOUT THE LOWER BOUNDARY LAYER AND
NEAR 50KTS AT THE TOP. THIS SHOULD END UP A SOLID WIND ADVISORY
EVENT. WE EXPECT ANOTHER BATCH OF RAIN TO SWING ACROSS THE FORECAST
AREA LATE THIS MORNING...NEAR THE COLD/OCCLUDED FRONTAL
PASSAGE...BEFORE CLEARING OUT LATE THIS AFTERNOON AS THE WINDS BEGIN
TO SLOWLY RELAX. THIS IS A CLASSIC SPRING SYSTEM.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 528 AM CDT SUN MAR 29 2015

GENERALLY A DRY EXTENDED FORECAST...BUT THE MAIN ITEM OF INTEREST IS
WEDNESDAY AFTERNOON WHEN INSTABILITY...SHEAR...AND FORCING YIELD THE
POTENTIAL FOR A FEW AFTERNOON SHOWERS AND THUNDERSTORMS...AND
PERHAPS SEVERE WIND GUSTS. TEMPERATURES WILL CONTINUE TO BE ABOVE
NORMAL ASIDE FROM A BRIEF COOL DOWN ON FRIDAY.

AT THE START OF THE PERIOD MONDAY A WEAK UPPER LEVEL WAVE EMBEDDED
IN NORTHWEST FLOW WILL SLIDE ACROSS NORTHERN MN/WI SPREADING LIGHT
PRECIP TO THOSE REGIONS. THE THERMAL PROFILE WILL BE WARM ENOUGH FOR
MOSTLY RAIN ACROSS OUR FORECAST AREA. MEANWHILE AN UPPER LEVEL
TROUGH APPROACHING THE PACIFIC NORTHWEST WILL MOVE ACROSS THE
ROCKIES TUESDAY NIGHT WITH WARM AIR ADVECTION DEVELOPING OUT AHEAD
OF IT. THIS WILL DRAW UP WARM...MOIST AIR AS H850 TEMPS IN EXCESS OF
10C SPREAD ACROSS THE REGION...WITH 50F SURFACE DEWPOINTS. THE GEM
IS FASTER THAN THE GFS/ECMWF...WHICH DOESNT ALLOW FOR AS MUCH
MOISTURE ADVECTION...AND THEREFORE IS THE DRIEST OF THE 3 MODELS IN
THE LOWER LEVELS. MEANWHILE...THE GFS GENERATES THE MOST PRECIP.

THE MAIN CONCERN WITH THIS SYSTEM IS THE ABUNDANCE OF LOW LEVEL WIND
SHEAR...SPECIFICALLY IN THE LOWEST 3KM. ALTHOUGH DEEP LAYER SHEAR IS
ON THE LOWER END OF THE SEVERE WEATHER SPECTRUM...0-1 AND 0-3KM
SHEAR APPROACHES 30KTS WEDNESDAY AFTERNOON...IN CONCERT WITH A
TONGUE OF 500 TO 1000 J/KG OF MLCAPE. THE UPPER LEVEL SUPPORT IS
RATHER MEAGER..SINCE H500 HEIGHT FALLS FROM THE APPROACHING WAVE LAG
THIS SHEAR/INSTABILITY BY ABOUT 12HRS. HOWEVER...THE LOW LEVEL
CONVERGENCE ALONG THE COLD FRONT MAY BE ENOUGH TO OVERCOME ANY
CIN...AND GENERATE A FEW SHOWERS AND THUNDERSTORMS. ANY STORMS THAT
FORM IN THIS ENVIRONMENT WOULD HAVE THE POTENTIAL TO PRODUCE SOME
STRONG WIND GUSTS...ALTHOUGH THE THREAT FOR WIDESPREAD SEVERE
WEATHER IS LOW AT THIS TIME.

IN PAST EVENTS...THE LOW LEVEL CONVERGENCE AHEAD OF THE FRONT WAS
OVERDONE BY THE FORECAST MODELS 2-4 DAYS AHEAD OF THE EVENT...SO AM
NOT CONVINCED THAT THE GFS`S DEPICTION OF A LINE OF PRECIP WILL
COME TO FRUITION. THE TIME-SHIFTED HOPWRF...WHICH USES GFS
BOUNDARY CONDITIONS...HAVE STORMS DEVELOPING JUST SOUTH AND EAST
OF OUR FORECAST AREA AFTER 00Z THURSDAY...SO AT THIS TIME WILL
SIMPLY CONTINUE TO MONITOR THE POTENTIAL FOR CONVECTION.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1105 PM CDT SAT MAR 28 2015

MINOR TIMING CHANGES WITH REGARDS TO THE PRECIPITATION WITH
THE INCOMING COLD FRONT. STILL APPEARS TO COME IN TWO
STAGES...08Z-12Z AND THEN FROM 14Z-19Z. CONFIDENCE IS INCREASING
ON MVFR CEILINGS SUNDAY MORNING AND COME BKN-OVC012-015 WAS
INSERTED. THREE CONCERNS REMAIN OVERNIGHT. THE FIRST IS THE
POTENTIAL FOR LOW LEVEL WIND SHEAR...ESPECIALLY IN THE AREA FROM
KRWF TO KSTC ON EAST THROUGH THE TWIN CITIES. A CORE OF 50 KT
WINDS NEAR 2K FEET IS SEEN MOVING NORTHEAST ACROSS THE
AFOREMENTIONED AREAS IN THE 09Z-12Z TIME FRAME. LITTLE DIRECTIONAL
CHANGE IS NOTED AND WITH SURFACE WINDS ALREADY FORECAST NEAR 20
KTS WITH GUSTS INTO THE 20S...KEPT THE MENTION OF LLWS OUT OF THE
TAF. THE SECOND CONCERN IS THE THREAT FOR SNOW...SLEET AND LIGHT
FREEZING RAIN FOR THE WI TAF SITES SUNDAY MORNING. WITH CONFIDENCE
ON PTYPE NOT HIGH...KEPT IT TO A MIX OF JUST RA AND SN. THE FINAL
CONCERN IS THE STRONG NW WINDS DEVELOPING BEHIND THE COLD FRONT
BY LATE SUNDAY MORNING. CONFIDENCE REMAINS HIGH FOR NEAR 30 KNOTS
WINDS FROM KAXN THROUGH KRWF ALONG WITH GUSTS APPROACHING 40
KNOTS. CONFIDENCE IS INCREASING LATE THIS EVENING THAT THE
STRONGER WINDS MAY IMPACT EASTERN AREAS OF MN AND WESTERN WI.
HENCE...WIND SPEEDS WERE RAISED A LITTLE AT KMSP AND KRNH.

KMSP...STILL EXPECT A BAND OF LIGHT RAIN TO MOVE THROUGH BEFORE
DAYBREAK WITH THE THREAT OF SHOWERS LINGERING THROUGH THE MORNING.
CONFIDENCE IS INCREASING ON MVFR CEILINGS IN THE MID TO LATE
MORNING HOURS. ALSO BUMPED UP WIND SPEEDS A FEW KNOTS...MAINLY IN
THE GUSTS FOR SUNDAY AFTERNOON WITH NEAR 40 KNOT GUSTS POSSIBLE.

/OUTLOOK FOR KMSP/

MON...VFR. WINDS W 5-10 KTS BECOMING SW.
TUE...VFR. WINDS NW 10 KTS.
WED...VFR. MVFR/-SHRA POSSIBLE IN THE AFTN/EVE. WINDS S 15-25 KTS.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WIND ADVISORY FROM 11 AM THIS MORNING TO 6 PM CDT THIS EVENING
     FOR MNZ042-043-049>051-057>063-066>070-075>078-083>085-092-
     093.

     WIND ADVISORY FROM 9 AM THIS MORNING TO 6 PM CDT THIS EVENING
     FOR MNZ041-047-048-054>056-064-065-073-074-082-091.

     FIRE WEATHER WATCH FROM 1 PM CDT THIS AFTERNOON THROUGH THIS
     EVENING FOR MNZ064-073-074-082-091.

WI...NONE.
&&

$$

SHORT TERM...CLF
LONG TERM...JRB
AVIATION...RAH


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