Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 311742
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1242 PM CDT THU JUL 31 2014

.UPDATE...
ISSUED AT 1227 PM CDT THU JUL 31 2014

UPDATED TO INCLUDE 18Z AVIATION DISCUSSION BELOW.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 348 AM CDT THU JUL 31 2014

EARLY MORNING SURFACE ANALYSIS SHOWED A WEAK ZONAL
PRESSURE TROUGH DRAPED ACROSS THE ARROWHEAD OF MN...WITH THE
SURFACE RIDGE CENTERED ACROSS THE DAKOTAS. AS A RESULT OF THIS
RELAXED PRESSURE FIELD THE WIND WERE LIGHT AND GENERALLY HAD A
SOUTH WESTERLY COMPONENT.

LATER THIS MORNING FORECAST SOUNDINGS SHOW NORTHERLY WINDS
RETURNING AS DIABATIC HEATING MIXES OUT THE NOCTURNAL INVERSION.
WITH RELATIVELY DRY AIR IN PLACE...THE FEW AFTERNOON CUMULUS THAT
DEVELOP WILL HAVE BASES GENERALLY IN THE 4-6KFT RANGE. THIS
AFTERNOON A SUBTLE PV ANOMALY CURRENTLY LOCATED OVER NORTH DAKOTA
WILL SLIDE SOUTHWARD AND DRAG THE SURFACE TROUGH WITH IT. ISOLATED
SHOWERS AND THUNDERSTORMS WILL DEVELOP ALONG THE UPPER MISSOURI
RIVER VALLEY...BUT SHOULD REMAIN SOUTH AND WEST OF THE FORECAST
AREA. MEANWHILE HIRES MODELS SUCH AS THE MPXWRF...NMM...ARW...AND
EVEN THE LAST FEW HOURS OF THE HRRR INDICATE LATE AFTERNOON
CONVECTION ACROSS WESTERN WI AND FAR EASTERN MN ONCE AGAIN.
ALTHOUGH CONFIDENCE IN OCCURRENCE IS HIGH...COVERAGE WILL BE LOW
SO CONTINUE WITH 20 PERCENT POPS. AS WAS THE CASE YESTERDAY...FEW
STRONG WIND GUSTS ARE POSSIBLE UNDER THE HEAVIER PRECIP CORES
GIVEN THE INVERTED V SOUNDINGS. THE ISOLATED CONVECTION WILL TAPER
OFF AFTER SUNSET...WITH ANOTHER QUIET NIGHT IN STORE THURSDAY
NIGHT.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 348 AM CDT THU JUL 31 2014

ONE MORE BROKEN RECORD DAY WILL OCCUR FRIDAY WITH SCATTERED
AFTERNOON SHOWER AND THUNDERSTORM DEVELOPMENT ACROSS EASTERN MN
AND WESTERN WI AS ANOTHER WEAK WAVE ROTATES AROUND THE SLOWLY
DEVOLVING SOUTHERN HUDSON BAY UPPER LOW. ECMWF IS MOT GENEROUS
WITH DEVELOPMENT...WHILE THE GFS AND NAM CONFINE THE BEST
COVERAGE TO SRN WI. MAINTAINED CHC POPS FOR THE EASTERN
AREAS...PRIMARILY BETWEEN 4-7 PM.

THE PATTERN WILL FINALLY DEAMPLIFY SOMEWHAT THIS WEEKEND WITH THE
EASTERN TROUGH EASING AND THE WESTERN TROUGH SPILLING SOUTHEAST
INTO THE PLAINS. THIS WILL KEEP THE UPPER LEVELS WEST NORTHWEST
ACROSS THE MIDWEST FOR THE REMAINDER OF THE LONG TERM. WHILE IT
WILL BRING SLIGHTLY WARMER TEMPS INITIALLY FOR THIS WEEKEND...IT
WILL ALSO BRING INCREASING CHANCES FOR THUNDERSTORMS AND HEAVY
RAINFALL EARLY NEXT WEEK. INTERESTINGLY...FOR THE PAST SEVERAL
WEEKS THE CFS HAS GENERALLY BEEN CALLING FOR A DRY SECOND HALF OF
JULY FOLLOWED BY A DECENT HEAVY RAIN EVENT FOR THE FIRST OR SECOND
WEEK OF AUGUST.

AFTER A CLEAR SATURDAY...CLOUDS WILL INCREASE AND CHANCES OF
STORMS WILL REENTER THE PICTURE LATE SATURDAY NIGHT ACROSS CENTRAL
MN...EXPANDING SOUTHEAST THROUGH WESTERN WISCONSIN SUNDAY WITH A
WEAK SHORTWAVE.

THE MAIN SHOW WILL ORIGINATE OVER THE DESERT SOUTHWEST WITH
MONSOONAL MOISTURE. THIS DISTURBANCE WILL TRACK NORTH AND EAST
AROUND THE UPPER RIDGE CENTERED OVER THE SOUTHERN PLAINS EARLY
NEXT WEEK. MODELS ARE IN GENERALLY GOOD AGREEMENT WITH THE OVERALL
SCENARIO SET TO PLAY OUT...BUT AS CAN BE EXPECTED 5 TO 6 DAYS
OUT...DIFFERENCES ARE SIGNIFICANT ENOUGH TO REDUCE CONFIDENCE ON
PLACEMENT AND TIMING OF THE BEST RAINFALL. GENERALLY PREFER THE
ECMWF AND GFS ENSEMBLE MEAN WHICH ARE FAVORING SIMILAR SOLUTIONS
AND ARE QUITE DIFFERENT THAN THE OPERATIONAL GFS WHICH IS MUCH
FURTHER NORTH THAN THE REST OF THE GUIDANCE ENVELOPE.

MID LEVEL WINDS SHOULD BE SUFFICIENTLY WEAK TO GREATLY LIMIT THE
THREAT FOR SEVERE WEATHER...BUT MAY FAVOR A HEAVY RAIN SCENARIO
WITH A SLOW MOVING OR BACK BUILDING MCS ALONG THE STATIONARY FRONT
TUESDAY NIGHT/EARLY WEDNESDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1227 PM CDT THU JUL 31 2014

RATHER BENIGN PATTERN THROUGH MIDDAY TMRW. WILL LOOK FOR
PREVAILING VFR CONDS THRU THEN...INCLUDING THE WI TAF SITES. NOT
SEEING NEARLY THE INDICATORS THAT WERE PRESENT THE PAST FEW DAYS
FOR CREATING ISOLD SHWRS/TSTMS THAT MAY IMPACT NWRN WI THEN DRIFT
SEWD TO NEAR KRNH-KEAU. A STRAY SHWR CANNOT BE RULED OUT...BUT
CHCS TOO LOW FOR INCLUSION AND WILL MONITOR/AMEND AS NEEDED. A
MORE PRONOUNCED SFC TROUGH IN CONJUNCTION WITH AN UPPER LEVEL
DISTURBANCE WILL APPROACH THE AREA BY MIDDAY TMRW...MAINLY OVER
WI. THIS COMBINATION MAY PRODUCE SCATTERED SHWRS/TSTMS BY EARLY-
TO-MID AFTERNOON TMRW...PARTICULARLY OVER WRN WI. TIMING IS STILL
AN ISSUE...LOOKING TO BE CLOSE TO THE 18Z CUTOFF...SO THE THINKING
WAS TO INCLUDE A TEMPO UP TO 18Z TMRW THEN LATER TAFS CAN BETTER
REFINE THE THINKING OF PRECIP INTO THE AFTN HOURS. WINDS AOB 10 KT
THROUGHOUT THIS SET.

KMSP...VFR WITH NO CONCERNS THROUGH 18Z TMRW. HOWEVER...AS PRECIP
DEVELOPS OVER WRN WI TMRW AFTN AND SPREADS W...SOME DEGRADED CONDS
COULD IMPACT MSP LATER TMRW AFTN. ATTM...HAVE KEPT CONDS AS VFR
BUT MVFR CONDS CANNOT BE RULED OUT.

/OUTLOOK FOR KMSP/
SAT...VFR. WINDS VARIABLE 5 KTS.
SUN...VFR WITH MVFR/TSRA POSSIBLE. WINDS SW 5-10 KTS.
MON...VFR WITH MVFR/TSRA POSSIBLE. WINDS SW 5-10 KTS.

&&

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

$$

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






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