Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 302003
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
303 PM CDT SAT AUG 30 2014

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

WEAK CONVERGENCE ZONE ALONG WITH MLCAPES ARND 500 J/KG HAD
GENERATED A FEW SHRA ACROSS SOUTHERN MN TODAY. BOUNDARY LAYER
MOISTURE REMAINS ROBUST...SO CLDS HAVE BEEN SLOW TO ERODE DURING
THE TYPICAL DIURNAL AFTN TIME FRAME. AS WINDS REMAIN WEAK AND
CYCLONIC CONTINUES DURING THE LATE AFTN/EARLY EVENING...THESE LOW
CLDS 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 CLDS 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 AFTN/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 AFTN
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 AMTS. IN
ADDITION...RESIDUAL CLD CVR FROM DECAYING MORNING TSRA COULD LIMIT
FULL AFTN 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 CDFNT WILL HAVE SHIFTED THROUGH MUCH OF THE MPX CWFA BY
DAYBREAK MON MRNG...WITH IT PROGRESSING JUST BARELY INTO WRN WI
AND SERN MN. SOME LINGERING SHWRS/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 ATMOS MAY PRODUCE ISOLD SHWRS 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 MRNG...
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 ACRS 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 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1141 AM CDT SAT AUG 30 2014

HIGH CONFIDENCE THAT MVFR CIGS SHOULD HOLD ARND THE REGION THRU
THE EARLY AFTN BEFORE ENOUGH MIXING AND DIURNAL HEATING ENABLES
LCL/S TO RISE TO VFR. HOWEVER...SHORT TERM MODELS ARE DEPICTING A
MORE PESSIMISTIC FORECAST THRU THE AFTN...AND INTO THE EVENING.
THERE REMAINS SOME MERIT TO THIS FORECAST AS BOUNDARY LAYER
MOISTURE REMAINS ROBUST AND SFC WINDS BECOME LIGHT THIS AFTN. IN
ADDITION...AS WINDS REMAIN LIGHT AND VARIABLE WITH A RETURN FLOW
FROM THE SE OVERNIGHT...MOISTURE ACROSS WI/IA MAY ADVECT BACK INTO
MN CREATING MVFR CIGS OVERNIGHT. ONLY HAD KSTC WITH THIS SCENARIO
BASED ON LOCATION AND THE AMT OF DEEP MOISTURE IN THE VCNTY. IN
ADDITION...LIFR/VLIFR CONDS ARE VERY POSSIBLE AT KRNH/KEAU IF
SKIES CLEAR. WILL CONTINUE THE SAME TREND FOR THESE SITES. AFT
12Z...MOST AREAS WILL SEE IMPROVEMENT IN THE CIGS WITH GUSTY SE
WINDS DEVELOPING. SHRA/TSRA WILL HOLD OFF UNTIL AFT 18Z.

KMSP...

HIGH CONFIDENCE THAT MVFR CIGS WILL REMAIN NEAR THE AIRPORT
TERMINAL THRU 19-20Z...WITH A SLOW LIFT TO LOW END VFR DURING THE
REMAINDER OF THE AFTN HRS. SOME BREAKS IN THE CLD CVR HAS
ALLOWED FOR VFR CONDS TEMPORARILY...BUT WITH THE AMT OF MOISTURE
IN THE LOWEST 5K...IT SHOULD QUICKLY FILL IN. AS PREVIOUSLY
SAID...AM CONCERN WITH WEAK BOUNDARY LAYER WINDS AND THE AMT OF
MOISTURE HOLDING IN THE AREA FOR MVFR CIGS TO REDEVELOP THIS
EVENING. WILL HOLD OFF UNTIL THE 21Z AMD. OTHERWISE...VFR CONDS
WITH SE WINDS DEVELOPING BY LATE TONIGHT...WITH GUSTY SE WINDS AND
THE CHC OF TSRA AFT 18Z.

/OUTLOOK FOR KMSP/

SUN EVENING...MVFR/IFR CIGS IN +TSRA LIKELY. WNDS SSE AT 10-20 KTS.
MON...MVFR/TSRA ENDING EARLY. VFR BY AFTN WINDS W 10-15 KTS.
TUE...VFR. WINDS WSW 10 KTS.

&&

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

$$

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






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