Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 262045
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
345 PM CDT SUN JUL 26 2015

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 340 PM CDT SUN JUL 26 2015

BAND OF ENHANCED INSTABILITY HAS DEVELOPED AHEAD OF A WEAK SFC
TROUGH THAT STRETCHED FROM ABOUT MARSHALL DOWN TOWARD MASON CITY.
CAMS HAVE BEEN SHOWING ISOLATED SHOWERS/STORMS DEVELOPING AHEAD OF
THIS BOUNDARY ALL DAY...AND RADAR CONFIRMS THAT THAT IS INDEED
HAPPENING RIGHT NOW. FOLLOWING THE IDEA OF THE CAMS...THIS LOOKS TO
BE DIURNALLY DRIVEN...SO CARRIED AN ISO THUNDER WORDING IN THE
FORECAST UNTIL ABOUT SUNSET.

FOR THE REST OF THE PERIOD...DECIDED TO KEEP THE FORECAST DRY...AS
ALL OF THE CAMS AND THE ECMWF ARE DRY THROUGH THE PERIOD. WITH THAT
SAID...THERE ARE A COUPLE OF OUTSIDE CHANCES FOR SEEING PRECIP
MONDAY AFTERNOON...BUT RATHER THAN PLASTER LOW END POPS ACROSS A
LARGE SWATH OF THE AREA WHEN MOST PEOPLE WILL NOT SEE
ANYTHING...OPTED TO GO DRY. THE TWO AREAS TO WATCH THOUGH FOR MONDAY
AFTERNOON WOULD BE FAR ERN MN INTO WRN WI AND FAR WRN MN LATE IN THE
AFTERNOON. FOR THE MN/WI BORDER AREA...THEY WILL BE ON THE ERN EDGE
OF A MID-LEVEL WARM BUBBLE AND CAP AND WE COULD SEE A SHOWER OR TWO
POP HERE IN THE AFTERNOON...BUT WITH NO FORCING MECHANISM...FAVORED
A DRY FORECAST FOR NOW. FOR FAR WRN MN LATE MONDAY AFTERNOON...THEIR
CHANCE WILL COME AS THE LLJ AND ASSOCIATED MOISTURE TRANSPORT STARTS
TO PICK UP IN STRENGTH ACROSS THE DAKOTAS. WE COULD SEE ELEVATED
CONVECTION DEVELOP IN THE LLJ DURING THE AFTERNOON THAT MAY SNEAK
INTO WRN MN LATE IN THE AFTERNOON...THOUGH WE ARE NOT EXPECTING
PRECIP CHANCES TO REALLY START RAMPING UP UNTIL 3Z AND LATER ON
TUESDAY...WHICH WILL BE DISCUSSED IN MORE DETAIL IN THE LONG TERM
SECTION.

FOR TONIGHT...WITH THE WARM FRONT LIFT NORTH THROUGH IOWA...WE WILL
HAVE MOIST ESE WINDS THROUGH THE NIGHT. THIS IS A CLIMATOLOGICALLY
FAVORED DIRECTION FOR DEVELOPING LOW STRATUS AND FOG. SREF PROBS FOR
CIGS UNDER 3K FT DO SHOW THIS POTENTIAL FOR ALONG AND SOUTH OF THE
MN RIVER. THROUGH 9Z...THE HRRR SHOWS THE REGION BEING STRATUS
FREE...BUT THE 0-1KM RAP CONDENSATION PRESSURE DEFICITS /CPD/ GET
QUITE LOW IN SOUTH CENTRAL MN...SO WOULD NOT BE SURPRISED IF FOLKS
DOWN ALONG I-90 WAKE UP TO 1-2 MILE VSBYS AND 300 FOOT CIGS MONDAY
MORNING.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 340 PM CDT SUN JUL 26 2015

THE DEEP UPPER TROUGH TO OUR NORTHWEST OF THE FORECAST AREA WILL
PASS THROUGH THE NORTHERN ROCKIES...THEN BECOME A CLOSED OFF LOW
OVER AS IT MOVES EAST NORTHEAST ALONG THE US/CANADIAN BORDER AND
INTO SOUTHERN SASKATCHEWAN AND MANITOBA ON TUESDAY. THIS LOW IS
HIGHLY ANOMALOUS FOR LATE JULY WITH 150-160 METER 12HR 500MB
HEIGHT FALLS ALONG THE BORDER AND 180-200 METER FALLS NORTH OF THE
BORDER TUESDAY NIGHT...IT LOOKS MORE LIKE A SPRING/WINTER UPPER
LOW. THEREFORE...THE BEST SEVERE THREAT IS NORTH AND WEST OF THE
FORECAST...HOWEVER...LOCALLY WE EXPECT A LINE OF THUNDERSTORMS TO
PASS THROUGH THE FORECAST AREA MONDAY NIGHT INTO TUESDAY MORNING. LIFT
WILL ACCOMPANY THE APPROACHING TROUGH ALONG WITH A NOCTURNALLY
FAVORED TIME FOR STORMS TO DEVELOP WITHIN A LLJ/WARM AIR ADVECTION
REGIME ON MONDAY NIGHT. PWATS THAT APPROACH 2" - 2000 J/KG OF
MLCAPE - A 13500FT WARM LAYER - SUGGEST HEAVY RAIN AND THE THREAT
FOR FLASH FLOODING IS PROBABLY THE BIGGEST HAZARD. THE 925-700MB
MOISTURE TRANSPORT LEANS OVER THE FORECAST AREA DURING THE DAY
TUESDAY WITH THE SURFACE TROUGH PASSING THROUGH. THEREFORE...WE
COULD KEEP SHOWERS/STORMS MOST OF THE DAY AND AT THE VERY LEAST
CLOUD COVER COULD MEAN HIGHS ARE CLOSER TO 80 THAN THE UPPER 80S
CURRENTLY IN THE FORECAST. THE SPEED OF THE WARM FRONTAL PASSAGE
IS STILL SOMEWHAT UNCERTAIN...BUT THE MOISTURE TRANSPORT IS SOLID
BY TUESDAY MORNING. THE PRONOUNCED UPPER TROUGH AND BEST DYNAMICS
ARE NORTH OF THE AREA. THE COLD FRONT SHOULD FINALLY CLEAR THE
FORECAST AREA TUESDAY NIGHT...BRINGING IN LESS HUMID AIR WED-FRI AS
A SURFACE HIGH PRESSURE SYSTEM SLIDES ACROSS THE MID-MISSISSIPPI
RIVER VALLEY BENEATH NORTHWESTERLY FLOW ALOFT WHICH WILL PERSIST
THROUGH THE REMAINDER OF THE FORECAST PERIOD. WE ALSO THINK
WEDNESDAY COULD BRING W-NW WIND GUSTS BETWEEN 30-40MPH IN THE COOL
ADVECTION BEHIND THE COLD FRONT. TEMPERATURES SHOULD ALSO
GRADUALLY MODERATE BY FRIDAY BEFORE ANOTHER COLD FRONT MOVES
THROUGH THE ARE FOR THE FIRST HALF OF THE WEEKEND.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1219 PM CDT SUN JUL 26 2015

MAIN QUESTION THIS PERIOD IS WHETHER OR NOT WE SEE LOW STRATUS/FOG
DEVELOP TONIGHT TO THE NORTH OF A WEAK WARM FRONT THAT WILL BE
LIFTING NORTH OUT OF IOWA. WE WILL HAVE A VERY MOIST...LIGHT EAST
FLOW IN THE LOW LEVELS ALL NIGHT...WHICH IS A FAVORABLE DIRECTION
FOR GETTING LOW CLOUDS...BUT WITH NOTHING OUT THERE NOW...WILL
SIDE WITH CLIMATOLOGY AND MENTION NOTHING MORE THAN SOME MVFR BR.
SREF PROBS FOR CIGS UNDER 3K FT WOULD SAY BEST SHOT AT SEEING
STRATUS WOULD BE ALONG AND SOUTH OF THE MN RIVER...IMPLYING RWF
HAS THE GREATEST CHANCE AT SEEING STRATUS TONIGHT. ALSO HAVE HIGH
CONFIDENCE IN THIS TAF PERIOD BEING DRY AT ALL TERMINALS...WITH
TSRA CHANCES NOT STARTING TO RAMP UP UNTIL AFTER 3Z TUESDAY.

KMSP...GFSLAMP HAS BEEN BACKING AWAY FROM FOG/STRATUS TONIGHT SO
HAVE KEPT MSP VFR THROUGHOUT...THOUGH THE EXPECTED ESE WIND
THROUGH TONIGHT IS A FAVORABLE DIRECTION FOR GETTING FOG/LOW
STRATUS. WE LOOK TO BE CAPPED MONDAY AFTERNOON...SO NOT EXPECTING
ANYTHING UNTIL STORMS SHOW UP MONDAY NIGHT...WHICH MODELS THIS
MORNING SHOW MOVING INTO MSP BETWEEN 9Z AND 12Z TUESDAY.

/OUTLOOK FOR KMSP/
TUE...IFR/MVFR IN TSRA EARLY THEN VFR. WINDS S BCMG SW 10-15 KTS.
WED...VFR. WINDS W 15-20G30KTS.
THU...VFR. WINDS W 10-15 KTS.

&&

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

$$

SHORT TERM...MPG
LONG TERM...CLF
AVIATION...MPG



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