Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 310552
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1252 AM CDT SUN AUG 31 2014

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 242 PM CDT SAT AUG 30 2014

WEAK CONVERGENCE ZONE ALONG WITH MLCAPES AROUND 500 J/KG HAD
GENERATED A FEW SHRA ACROSS SOUTHERN MN TODAY. BOUNDARY LAYER
MOISTURE REMAINS ROBUST...SO CLOUDS HAVE BEEN SLOW TO ERODE DURING
THE TYPICAL DIURNAL AFTERNOON TIME FRAME. AS WINDS REMAIN WEAK AND
CYCLONIC CONTINUES DURING THE LATE AFTERNOON/EARLY EVENING...THESE LOW
CLOUDS MAY HOLD ON UNTIL LATER TONIGHT. ONCE WINDS SHIFT TO THE
SOUTHEAST AHEAD OF A DEEPENING AREA OF LOW PRESSURE ACROSS SD
LATER TONIGHT...ANY LOW CLOUDS SHOULD QUICKLY MOVE OUT OR DISSIPATE.
SOME FOG MAY DEVELOP ACROSS WC WI AS THIS AREA WILL BE LAST TO SEE
BOUNDARY LAYER MOISTURE RETREAT ALONG WITH WEAK MIXING IN THE
BOUNDARY LAYER.

A STRONG JET STREAM MOVING INTO THE PACIFIC NW TODAY WILL SET THE
STAGE FOR A VERY ACTIVE SUNDAY AFTERNOON/EVENING ACROSS THE UPPER
MIDWEST. BOTH AMPLE MOISTURE AND INCREASING SHEAR VALUES...ALONG A
DEEPENING AREA OF LOW PRESSURE ACROSS THE NORTHERN PLAINS...SHOULD
LEAD TO WIDESPREAD THUNDERSTORMS DEVELOPMENT BY THE LATE AFTERNOON
AHEAD OF A COLD FRONT. THERE REMAINS SOME DIFFERENCES IN THE
MODELS IN TERMS OF STRENGTH OF THE LLJ ALONG WITH THE UPPER LEVEL
JET CORE TO CONCLUDE WIDESPREAD SEVERE WX ACROSS THE UPPER
MIDWEST. THE UPPER JET CORE...WHICH IS EXPECTED TO BECOME A JET
COUPLET FROM THE NORTHERN AND SOUTHERN JET STREAMS...SHOULD LEAD
TO STRONG UPPER LEVEL DIFFLUENCE BY SUNDAY EVENING. AGAIN...MODELS
HAVE SOME DIFFERENCES IN THIS JET COUPLET WHICH LEADS TO
DIFFERENCES IN TIMING AND PLACEMENT OF THE HIGHER QPF AMOUNTS. IN
ADDITION...RESIDUAL CLOUD COVER FROM DECAYING MORNING TSRA COULD LIMIT
FULL AFTERNOON ISOLATION. THE BEST AREA FOR BOTH JET STRUCTURE/HIGHER
INSTABILITY AND SHEAR VALUES REMAIN ACROSS IOWA. FAR SC/SW MN
COULD ALSO BE IN THIS AREA OF HIGHER SVR WX POTENTIAL. LATER
SHIFTS WILL NEED MONITOR STRENGTH OF THIS JET ALONG WITH TSRA
DEVELOPMENT TOWARD MORNING.

IN ADDITION TO THE SVR WX THREAT...PWATS VALUES RISE INTO THE 1.5"
RANGE. IF ANY TSRA BEGIN TO TRAIN OR BACK BUILD...FLASH FLOODING
IS POSSIBLE...ESPECIALLY ONCE THE LLJ INCREASES DURING THE EVENING
HRS.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 242 PM CDT SAT AUG 30 2014

POTENT COLD FRONT WILL HAVE SHIFTED THROUGH MUCH OF THE MPX CWFA BY
DAYBREAK MON MORNING...WITH IT PROGRESSING JUST BARELY INTO WRN WI
AND SERN MN. SOME LINGERING SHOWERS/TSTMS WILL LIKELY BE ONGOING IN
FAR ERN PORTIONS OF THE CWFA AT THE START OF THIS PERIOD BUT
STRENGTH WILL BE FAIRLY WEAK...MEANING THAT ANY SEVERE POTENTIAL
WILL HAVE BEEN TAPPED BY THIS POINT. SUPPORTING THIS FACT IS THAT
THE UPPER LEVEL TROF AXIS WILL BE E OF THE CWFA AND THE FRONT WILL
BE RATHER STRETCHED OUT BETWEEN THE MAIN LOW PRES CENTER OVER WRN
ONTARIO PROVINCE AND A SECONDARY LOW PRES CENTER OVER KS. HIGH
PRES WILL THEN NUDGE IN FROM THE CENTRAL PLAINS WHILE FLOW ALOFT
IS MAINLY ZONAL WNW-ESE. A FEW BUCKLES IN THE FLOW WITHIN A
PERSISTENTLY DEEP MOIST ATMO MAY PRODUCE ISOLATED SHOWERS FROM TIME TO
TIME LATE MON THRU MUCH OF WED. THIS AREA OF HIGH PRES WILL SHIFT
E INTO THE MID-MISS RIVER VALLEY THEN OHIO VALLEY BY WED MORNING...
ALLOWING FOR A WARMER AND MORE MOIST SLY RETURN FLOW TO DEVELOP BY
MIDDAY WED.

THE ADDITIONAL MOISTURE WILL PRECEDE THE ARRIVAL OF A SLOW-MOVING
LOW PRES CENTER FROM THE NRN ROCKIES WED NIGHT. THIS LOW WILL
STALL OUT OVER THE NRN PLAINS...HELPING SET UP A SFC FRONTAL
BOUNDARY EXTENDING FROM WRN MN ACROSS THE ROCKIES. THIS BOUNDARY
WILL ACT AS A LOW-LEVEL CONFLUENT ZONE AND AID IN PRECIPITATION
DEVELOPMENT THU THROUGH SAT. NOT LOOKING FOR A LOT IN THE WAY OF
QPF NOR STORM STRENGTH...BUT FINDING SOLID DRY TIME WILL BE
DIFFICULT DUE TO SCATTERED SHOWERS FOR MUCH OF THE LATTER PORTION
OF THE WEEK. CANNOT SAY ANY DAY WILL BE A WASHOUT ATTM...BUT ALSO
HARD TO PINPOINT ONE TIMEFRAME OVER ANOTHER FOR BEST TIMING OF
PRECIPITATION.

TEMPERATURES LOOK TO GO ON A SLOW WARMING TREND THRU THE
WORKWEEK...CLIMBING THROUGH THE MID-UPR 70S INTO THE LWR 80S BY
FRI. HOWEVER...THERE WILL BE PLENTY OF CLOUD/RAIN COMPLICATIONS
WHICH ON SMALL SCALES MAY CREATE SOME VARIETY WITH MAX/MIN TEMPS.
BY SAT... THIS LOW PRES COMPLEX WILL SHIFT S AND E OF THE MPX
CWFA...ALLOWING FOR A COOLING OF TEMPERATURES FOR NEXT WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1233 AM CDT SUN AUG 31 2014

WITH THE HRRR ALONG WITH VIRTUALLY ALL OTHER CAMS SHOWING A BAND
OF SHRA/TSRA WORKING ACROSS MN WITH INITIAL ARRIVAL OF THE
LLJ...STARTED TO INTRODUCE VCSH IN THE MORNING TO ALL MN
TERMINALS. THIS SCENARIO SEEMS VERY PLAUSIBLE GIVEN THE FACT THAT
WE ARE CURRENTLY SEEING SCT ACTIVITY CLEAR DOWN INTO NC NEB. THE
ATMO HAS ALREADY TIPPED ITS HAND WHEN IT COMES TO FOG AT EAU...SO
HAVE LEFT THEM DOWN THE REST OF THE NIGHT. WITH THAT SAID...THERE
IS STILL A FAIR AMOUNT OF CLOUD COVER IN THE 050-080 LEVEL IN ERN
MN INTO WRN WI...WHICH MAY LEAD TO A BIT OF VARIABILITY IN THE
VSBYS AT RNH/EAU AS THEY SKIP BETWEEN 050-080 CLOUDS AND CLEAR
SKIES /WHICH WILL BE ACCOMPANIED BY FOG/. STILL A GOOD DEGREE OF
VARIABILITY WITH THE 00Z CAMS IN TERMS OF AFTERNOON
CONVECTION...BUT FORECAST SOUNDINGS DO SHOW A GOOD DEGREE OF
CAPPING TO OVERCOME FIRST...SO DID DELAY AFTERNOON TS MENTION AN
HOUR OR TWO FROM WHAT THE 00Z TAF HAD. IN ADDITION...REMOVED THE
AFTERNOON TS MENTION AT AXN...WITH AXN LOOKING TO MOST LIKELY BE
WEST OF THAT ROUND OF STORMS.

KMSP...BEGINNING TO GAIN CONFIDENCE IN AT LEAST SCT SHRA/TSRA IN
THE METRO AREA THIS MORNING...SO HAVE STARTED WITH INTRODUCING A
VCSH GROUP. BY 9Z...SHOULD HAVE A BETTER FEEL FOR WHETHER OR NOT
WE WILL SEE ANYTHING...SO WILL WAIT FOR THAT AMD TO SEE IF WE NEED
ANY STRONGER SHRA/TSRA MENTION. 00Z TAF LOOKED TO HAVE GOOD TIMING
FOR POTENTIAL AFTERNOON TSRA...SO STUCK WITH THAT. IS POTENTIAL
THAT MSP COULD GET SPLIT BY ACTIVITY TODAY...WITH STRONGER
ACTIVITY REMAINING SOUTH OF THE FIELD WITH BETTER LLJ FORCING DOWN
IN IOWA AND GOING NORTH OF THE FIELD...CLOSER TO THE SFC LOW THAT
WILL BE GOING ACROSS NRN MN. STILL...GIVEN THE STRENGTH OF THE
FRONT/FORCING...ODDS LOOK BETTER THAT MSP WILL SEE SOME TSRA
ACTIVITY THAN STORMS MISSING THE AIRPORT.

/OUTLOOK FOR KMSP/
MON...MVFR/TSRA ENDING EARLY. VFR BY AFTERNOON WINDS WNW 5-10 KTS.
TUE...VFR. WINDS WSW 5-10 KTS.
WED...VFR. CHC MVFR/TSRA LATE. WINDS S 5-10 KTS.

&&

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

$$

SHORT TERM...JLT
LONG TERM...JPC
AVIATION...MPG






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