Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 291817
AFDMPX

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

.UPDATE...
ISSUED AT 110 PM CDT SUN MAR 29 2015

UPDATED TO INCLUDE 18Z AVIATION DISCUSSION BELOW.

&&

.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 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 110 PM CDT SUN MAR 29 2015

CDFNT CONTINUES TO MAKE EFFICIENT PROGRESS FROM W TO E ACRS THE
WFO MPX COVERAGE AREA TDA...WITH A PRONOUNCED WIND SHIFT AND INCRS
IN WIND SPEEDS ALONG WITH CLEARING SKIES BEHIND IT. FOR THE TAF
SITES NOT YET OUT OF THE CLOUD COVER AND PRECIP...WHICH ATTM IS
SOLELY THE WI TAF SITES...CONDS WILL DETERIORATE TO POSSIBLY IFR
VSBY FOR A BRIEF PERIOD BEFORE MVFR CIGS PREVAIL THROUGH MID-TO-
LATE AFTN. FOR THE MN TAF SITES...THE CLEARING HAS ALREADY
OCCURRED FOR KAXN-KRWF...AND WILL THEN OCCUR SHORTLY THEREAFTER
EARLY THIS AFTN FOR KSTC-KMSP. SKIES WILL THEN REMAIN CLR
OVERNIGHT INTO TMRW MRNG BEFORE HIGH CLOUDS MOVE IN MID-TO-LATE
DAY. WINDS WILL DIMINISH THIS EVE AND OVERNIGHT...EVENTUALLY
DROPPING BELOW 5 KTS OVERNIGHT INTO TMRW MRNG.

KMSP...35-40KT WINDS OCCURRED WITH THE PASSAGE OF THE PRECIP BUT
HAVE NOW DROPPED TO 15-25KT IN THE WAKE OF THE PRECIP. AS SKIES
CLEAR OUT AND BETTER MIXING DEVELOPS TO TAP WINDS ALOFT...WILL
LOOK FOR NW WINDS TO INCRS TO THE 25-35KT RANGE FOR MUCH OF THE
AFTN INTO THE EVE BEFORE DECOUPLING ALLOWS SFC WINDS TO SETTLE
DOWN TO ARND 10 KT. SKIES WILL CLEAR OUT BY ARND 22Z AND REMAIN
CLR OVERNIGHT THRU TMRW AHEAD OF THE NEXT WEAK SYSTEM THAT WILL
REMAIN N OF MSP.

/OUTLOOK FOR KMSP/
TUE...VFR. WINDS NW 5-10 KTS.
WED...VFR. MVFR/-SHRA POSSIBLE IN THE AFTN/EVE. WINDS S 15-25 KTS.
THU...VFR. WINDS W 10-20 KTS.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WIND ADVISORY UNTIL 6 PM CDT THIS EVENING FOR MNZ041>043-047>051-
     054>070-073>078-082>085-091>093.

     FIRE WEATHER WATCH UNTIL 7 PM CDT THIS EVENING FOR MNZ064-073-
     074-082-091.

WI...NONE.
&&

$$

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


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