Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 021815
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
115 PM CDT TUE SEP 2 2014

.UPDATE...
ISSUED AT 1036 AM CDT TUE SEP 2 2014

MORNING UPDATE CONSISTS OF ADDING IN SOME SLGT CHC POPS FOR THIS
AFTN MAINLY ALONG AND N OF THE I-94 CORRIDOR. SHORT-TERM MODELS...
SPECIFICALLY THE HRRR/HOPWRF/RAP COMBINATIONS...INDICATE MODEST
INSTABILITY WITHIN THE WNW-ENE FLOW ALOFT. SOME SAGGINESS IN THE
NRN FRINGES OF EXITING HIGH PRES HINT AT WEAK SFC CONVERGENCE
PERTURBATIONS...ALONG WITH SOME BUCKLING IN THE UPPER FLOW. THESE
INGREDIENTS MAY ALLOW FOR SOME ISOLD SHWRS...POSSIBLY EVEN A
TSTM...DURING THE MID-TO-LATE AFTN HOURS. MOST AREAS WILL REMAIN
DRY...AND COVERAGE WILL BE SPARSE SHOULD ANYTHING DEVELOP. QPF
WILL ALSO BE QUITE LOW...BUT THIS IS SIMPLY DECENT SHORT-TERM
MODEL AGREEMENT THAT THE DAY MAY NOT BE COMPLETELY AND SOLIDLY
DRY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 410 AM CDT TUE SEP 2 2014

A COOL AND DRY DAY IS EXPECTED ACROSS EASTERN MN AND WESTERN WI
WITH ISOLATED SHOWERS THIS MORNING MOVING EAST AND OUT OF THE
FORECAST AREA WITH TIME.

VAD WIND PROFILES FROM KABR...TO KMSP...TO ARX ARE ALL SHOWING
NORTHWEST FLOW FROM 2-10KFT THIS MORNING. THERE IS ONGOING WEAK
LOW-LEVEL COLD ADVECTION THIS MORNING WHICH SHOULD KEEP HIGH TEMPS
TODAY SLIGHTLY COOLER THAN YESTERDAY EVEN WITH EXPECTED AFTERNOON
SUNSHINE. THE HIGH CLOUDS THIS MORNING ARE THE REMNANTS OF A
COMPLEX OF THUNDERSTORMS THAT DEVELOPED IN SD/NE LAST EVENING.
THE CLOUDS ARE THINNING WITH TIME WITH NO NEW UPDRAFTS AND ARE
ALSO MOVING EAST AT GOOD CLIP /35-40KTS/. SO...THE CLOUDS SHOULD
BE OUT OF THE PICTURE QUICKLY THIS MORNING. PLEASANT TEMPERATURE-
DEWPOINT COMBINATION TODAY IS TYPICAL FOR EARLY SEPTEMBER WITH 70S
OVER 50S. THERE IS GOOD COVERAGE IN LIGHT SHOWERS ACROSS FAR
SOUTHERN MN AND IN NORTH CENTRAL IA EARLY THIS MORNING TIED TO PV
ADVECTION AND THE UPPER JET OVER IA. THE VORTICITY ADVECTON WILL
ALSO QUICKLY MOVE EAST OF THE FORECAST AREA THIS MORNING. THE
LIGHTNING HAS REALLY DROPPED OFF...WITH JUST A COUPLE STRIKES IN
IA WHERE THERE ARE STILL MUCAPE VALUES BETWEEN 500-1000J/KG. THE
NORTHWEST FLOW WILL BE SHORT LIVED...HOWEVER...WITH THE LOW LEVEL
FLOW TURNING BACK TO THE SOUTHWEST BY 12Z WEDNESDAY ACROSS WESTERN
MN. THE WARM ADVECTION HAS THE POTENTIAL TO GENERATE ISOLATED TO
SCATTERED WEAK THUNDERSTORMS LATE TONIGHT ACROSS THE WESTERN
FORECAST AREA.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 410 AM CDT TUE SEP 2 2014

WARM AND HUMID WEATHER IN THE MIDDLE OF THE WEEK WILL GIVE WAY TO
A COOL CRISP FALL AIRMASS FOR THE WEEKEND. TEMPERATURES WILL RUN
FROM ROUGHLY 5 TO 10 DEGREES ABOVE NORMAL ON WEDNESDAY...TO 5
DEGREES BELOW NORMAL OVER THE WEEKEND.

EARLY MORNING WATER VAPOR IMAGERY WITH GFS 02.00 500MB HEIGHTS AND
WINDS IDENTIFIED A VIGOUROUS SHORTWAVE CRAWLING DOWN THE BRITISH
COLUMBIA COAST. OVER THE NEXT 36 HOURS THIS PV ANOMALY WILL
TRANSITION EASTWARD ALONG THE INTERNATIONAL BORDER AND CAUSE A
SURFACE LOW TO DEVELOP OVER THE HIGH PLAINS...WITH THE WARM SECTOR
OVERSPREADING THE UPPER MIDWEST DURING THE DAY ON WEDNESDAY. A
SURFACE WARM FRONT WILL LIFT NORTHWARD...AND BOUNDARY LAYER
DEWPOINTS OF NEAR 70F WILL BECOME WIDESPREAD ACROSS SOUTHERN MN BY
WEDNESDAY EVENING.

PRECIP CHANCES WILL FOLLOW THIS WARM FRONT...BUT BY WEDNESDAY
AFTERNOON BUFR SOUNDINGS SHOW A STOUT CAP DEVELOPING ACROSS
SOUTHERN MN...SO HAVE BROKE POP GRIDS INTO 3HR BLOCKS TO BETTER
DEPICT THE TIMING AND LOCATION OF EXPECTED CONVECTION. THE 02.00
WRFARW AND WRFNMM HAVE PRECIP FOCUSED NORTH OF THE WARM FRONT...SO
FEEL COMFORTABLE SHAVING OFF POPS FROM SOUTH TO NORTH THROUGHOUT
THE DAY ON WEDNESDAY. LATE WEDNESDAY EVENING THE BOUNDARY LAYER
WILL DECOUPLE AND SHOULD SEE AN MCS DEVELOP ON THE NOSE OF THE LOW
LEVEL JET ACROSS CENTRAL MN WHICH SHOULD SHIFT EAST SOUTHEAST
OVERNIGHT. VEERING WINDS IN THE EFFECTIVE LAYER WILL SUPPORT
ORGANIZED CONVECTION SO SUSPECT TO SEE A FEW STRONG/SEVERE
STORMS...WITH THE BEST CHANCES ALONG AND NORTH OF I-94.

THIS CONVECTION WILL EXIT THE REGION BY THURSDAY MORNING...AND
WILL SEE TEMPERATURES SURGE ACROSS SOUTHEASTERN MN AND WESTERN
WI AHEAD OF A COLD FRONT THAT IS FORECAST TO PASS THROUGH THE
REGION DURING THE DAY ON THURSDAY. FORECAST SOUNDINGS SHOW AN
EXTREMELY UNSTABLE ENVIRONMENT BY LATE AFTERNOON ACROSS
WISCONSIN...SO COULD SEE ANOTHER ROUND OF SEVERE STORMS IF THE
SURFACE CONVERGENCE ALONG THE FRONT IS ENOUGH TO BREAK THROUGH THE
CAP.

IN THE WAKE OF THIS FRONT IS A MUCH COOLER...DRIER AIRMASS. LOW
TEMPERATURES THURSDAY NIGHT WILL FALL INTO THE 40S ACROSS THE
NORTHWEST CWA. NORTHWEST FLOW AND SURFACE HIGH PRESSURE SUPPORT
DRY WEATHER THROUGH THE WEEKEND.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1258 PM CDT TUE SEP 2 2014

RATHER BENIGN START TO THE 02/18Z TAFS WITH LOTS OF SUNSHINE AND
ONLY MINIMAL CLOUD COVER. THAT BEING SAID...EARLIER RUNS OF
HRRR/HOPWRF LOCAL MODELS INDICATED SOME WEAK MIDLVL PERTURBATIONS
ON THE BACKSIDE OF DEPARTING HIGH PRES ALONG WITH SOME KINKS IN
THE WNW-ESE FLOW ALOFT. THIS COULD BE ENOUGH TO SPARK SOME ISOLD
SHWR/TSTM DEVELOPMENT LATER THIS AFTN INTO THE EARLY EVE...BUT
CHANCES AND COVERAGE ARE TOO LOW FOR INCLUSION SO HAVE OMITTED IT
ATTM BUT WILL CONTINUE TO MONITOR.

GOING THROUGH TNGT AND INTO WED...A WMFNT WILL SLOWLY LIFT N OVER
THE CENTRAL PLAINS ON INTO THE UPR MISS RIVER VALLEY. SOME ISOLD
TO SCTRD -SHRA LOOK TO DEVELOP OVERNIGHT OVER MAINLY SWRN MN...
BUT THEN THE BULK OF THE ACTION WILL TRANSITION TO CENTRAL MN BY
LATE DAY WED...LIKELY PAST THE TIME PERIOD OF THIS 18Z TAF.
NEVERTHELESS...THERE ARE SOME INDICATIONS THAT THE PRECIP MAY
OCCUR FASTER THAN WHAT IS BEING ADVERTISED SO IF ANYTHING... THE
TIMING OF THE PRECIP MAY NEED TO BE ADJUSTED EARLIER. AS FOR TSTM
POTENTIAL...TSTM PARAMETERS ARE FAIRLY WEAK SO HAVE OMITTED TSTM
MENTION ATTM.

KMSP...FAIRLY HIGH CONFIDENCE IN VFR CONDS THROUGH THE OVERNIGHT
HRS. LOW CHCS OF ISOLD SHWR/TSTM THIS AFTN...BUT AM GROWING MORE
CONFIDENT THAT PRECIP SHOULD EVADE MSP. GOING THRU TMRW...CHCS DO
INCRS OF SEEING SHWRS/TSTMS IN AND AROUND MSP...ESPECIALLY LATE
AFTN INTO THE EARLY EVE. AM NOT THINKING TSTMS WOULD IMPACT MSP BY
00Z SO HAVE OMITTED IT ATTM...BUT THERE IS STILL SOME POTENTIAL
THAT FLIGHT CONDITION REDUCING PRECIP COULD IMPACT MSP PRIOR TO
00Z TMRW EVE.

/OUTLOOK FOR KMSP/
WED...VFR. CHC MVFR/TSRA. WINDS S 10-15 KTS.
THU...VFR. CHC MVFR/TSRA LATE. WINDS S 10-15 KTS BCMG W LATE.
FRI...VFR. WINDS NW 10 KNOTS.

&&

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

$$

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





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