Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 302104
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
404 PM CDT SUN AUG 30 2015

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 400 PM CDT SUN AUG 30 2015

WATER VAPOR IMAGERY ALONG WITH RAP H5 HEIGHT ANALYSIS SHOWS UPPER
RIDGING BUILDING IN THIS AFTERNOON. A TROUGH EJECTING ACROSS THE
NRN ROCKIES HAS ALLOWED A BROAD AREA OF SFC LOW PRESSURE TO FORM
ACROSS ERN MT/NRN NODAK/SRN CANADA. IT IS THIS LOW THAT HAS
RESULTED IN AN INCREASING PRESSURE GRADIENT AND THE STRONGER SOUTH
WINDS WE HAVE SEEN TODAY.

IT IS THESE SOUTH WINDS THAT MAKE THE FORECAST FOR TONIGHT TRICKY.
NAM BUFR SOUNDINGS MONDAY MORNING LOOK LIKE CARBON COPIES OF THE MPX
SOUNDING THIS MORNING...WHICH OF COURSE WAS ASSOCIATED WITH ANOTHER
ROUND OF LOW STRATUS. STRATUS IS STILL HANGING TOUGH IN IOWA AND
WITH THE PATTERN TO OUR SOUTHEAST NOT MUCH DIFFERENT FROM WHAT WE
HAVE SEEN THE PAST COUPLE OF NIGHTS...EXPECT STRATUS TO EXPAND AGAIN
TONIGHT...THE QUESTION IS JUST HOW FAR NW DOES IT COME. ONE BIG
DIFFERENCE BETWEEN TODAY AND THE PAST COUPLE OF DAYS IS WE HAVE
STRONGER WINDS AND BETTER BOUNDARY LAYER MIXING TODAY. THE GRADIENT
AND ASSOCIATED WINDS WILL REMAIN IN PLACE THROUGH THE NIGHT...ADDING
A LAYER OF UNCERTAINTY TO THE SKY FORECAST. FOR NOW...DID A SOFT
PLAY FOR THE STRATUS...WITH 40/50% COVERAGE FROM SOUTH CENTRAL MN
INTO EAST CENTRAL MN AND WRN WI LATE TONIGHT/EARLY MONDAY MORNING
AND WILL LET FUTURE SHIFTS UP SKY COVER IF NEED BE WHEN THERE IS A
BETTER HANDLE ON WHERE IT IS GOING.

FOR MONDAY...THE PREVIOUSLY MENTIONED LOW WELL SEND A FRONT ACROSS
THE DAKOTAS...APPROACHING WEST CENTRAL MN BY THE AFTERNOON.
HOWEVER...WE ARE NOT ANTICIPATING ANY ACTIVITY ALONG THE FRONT THIS
FAR SOUTH...SO WE REMOVED WHAT SMALL POPS WERE MENTION MONDAY
AFTERNOON IN OUR NW. BESIDE NONE OF THE HI-RES...DETERMINISTIC...OR
ENSEMBLE MODELS SHOWING ANY PRECIP IN OUR AREA...FORECAST SOUNDINGS
AT AXN AND SURROUNDING SITES SHOW A STRONG WARM NOSE BETWEEN H8 AND
H7 THAT LOOKS TO KEEP A LID ON DEEP MOIST CONVECTION THIS FAR SOUTH.
IN ADDITION...THE WAVE AND ASSOCIATED HEIGHT FALLS DRIVING THIS
FRONT ARE GOING FROM MT TO HUDSON BAY...STAYING WELL NW OF THE
MPX AREA...SO FEEL CONFIDENT IN THE DRY FORECAST FOR MONDAY.

BESIDE DRY...ALL OF THE MODELS SHOW 925-850 TEMPS IN WRN MN DROPPING
A COUPLE OF DEGS C MONDAY AFTERNOON COMPARED TO WHAT WE ARE SEEING
TODAY...SO EXPECT HIGHS TO BE NO WARMER THAN WHAT WE ARE SEEING
TODAY AND LIKELY A COUPLE OF DEGREES COOLER IN WRN MN.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 400 PM CDT SUN AUG 30 2015

NO BIG CHANGES TO THE LONG TERM FORECAST AS THE PATTERN STILL
FAVORS RIDGING IN THE CENTRAL CONUS AND ABOVE NORMAL TEMPERATURES
LASTING INTO LABOR DAY WEEKEND.

THE LONGWAVE RIDGE AXIS WILL CONTINUE TO SHIFT EAST ON
TUESDAY...BUT THE BIGGEST RESERVOIR OF WARMTH WILL LINGER FROM THE
FOUR CORNERS UP THROUGH THE NORTHERN PLAINS. THE NAEFS
STANDARDIZED 850MB TEMPERATURE ANOMALIES ARE COMMONLY BETWEEN TWO
AND THREE SIGMA OVER THE NEXT WEEK IN THESE AREAS. AS THE 500MB
RIDGE AXIS SLIDES EAST ON TUESDAY THE LONGWAVE PATTERN LOSES SOME
OF ITS AMPLITUDE AND THE 850MB TEMPERATURE ADVECTION DECREASES
BEFORE REACHING THE FORECAST AREA. AS A RESULT...THE FORECAST AREA
WILL MAINTAIN MID 80S FOR HIGHS AS WE HEAD TOWARD MID WEEK...BUT
THE TEMPERATES WILL NOT APPROACH THE MID /AND EVEN UPPER/ 90S
THAT ARE CURRENTLY BEING OBSERVED IN THE DAKOTAS THIS AFTERNOON.
WESTERN MN IS ALREADY SEEING DEWPOINTS IN THE UPPER 60S AND
EASTERN MN AND WESTERN WI WILL SOON FOLLOW...THESE DEWPOINTS WILL
LINGER THROUGH THE WEEK AND THE DEWPOINT WILL MOST LIKELY HIT 70
DEGREES IN MANY LOCATIONS THIS WEEK. IN THE WED-THU TIME
FRAME...MUCH OF THE 12Z GUIDANCE HINTS AT THE CHANCE FOR RAIN WITH
MOISTURE TRANSPORT EMBEDDED IN THE LOW LEVEL SOUTHWEST FLOW. THE
FORCING ISNT EXTREMELY...BUT THERE IS ELEVATED INSTABILITY AND
THE CAP ISNT OVERLY STRONG EITHER WITH THE 12-14C AIR AT 700MB
REMAINING WEST OF THE AREA IN THE DAKOTAS. THEREFORE...WE
MAINTAINED THE SMALL POPS IN THE FORECAST...BUT ADMITTEDLY THERE
IS LOW CONFIDENCE ON TIMING/AMOUNTS AND EVEN IF THERE WILL BE MUCH
CONVECTIVE INITIATION LOCALLY.

THE PERSISTENT TROUGH OVER THE GULF OF ALASKA AND PACIFIC
NORTHWEST FINALLY LOOKS TO MAKE SOME EASTERN PROGRESS AS WE HEAD
TOWARD THE BACK HALF OF LABOR DAY WEEKEND. THE OPERATIONAL
GUIDANCE AND ENSEMBLE OUTPUT HAS SLIGHTLY SLOWED THE ARRIVAL OF
THE COLD FRONT...BUT AT THE VERY LEAST WE CAN SAY NEXT WEEKEND
LOOKS MORE UNSETTLED WITH A PATTERN SHIFT LOCALLY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1251 PM CDT SUN AUG 30 2015

STRONGER WINDS AND ASSOCIATED MECHANICAL MIXING HELPED CLEAN
STRATUS OUT MUCH FASTER THIS MORNING THAN WHAT WE SAW YESTERDAY.
REALLY...THE ONLY QUESTION THIS TAF PERIOD IS WHERE DOES THE
STRATUS RETURN TONIGHT. FORECAST SOUNDINGS FROM THE NAM LOOK LIKE
CARBON COPIES OF THIS MORNINGS SOUNDING HERE AT MPX...SO STRATUS
IS LOOKING LIKE A REAL POSSIBILITY FOR A THIRD NIGHT IN A ROW. ONE
BIG DIFFERENCE THOUGH BETWEEN TODAY AND YESTERDAY AS WE HAVE
STRONGER WINDS TODAY...WHICH MEANS BETTER BOUNDARY LAYER MIXING.
THIS IS WHAT ADDS UNCERTAINTY TO THE STRATUS FORECAST FOR
TONIGHT...IS THIS MIXING ENOUGH TO KEEP THE STRATUS FARTHER EAST
TONIGHT. FOR NOW...PLAYED UP THE STRATUS THREAT AT WIS TERMINALS
WHERE WINDS ARE WEAKEST TODAY...BUT IT IS CERTAINLY POSSIBLE TO
SEE STRATUS AS FAR WEST AS MSP/STC AGAIN TONIGHT.

KMSP...WILL BE VFR WITH SOUTH WINDS THE REST OF THE DAY. CURRENT
THINKING IS BETTER MIXING TODAY WILL MAKE IT MORE DIFFICULT TO GET
THE STRATUS GOING TONIGHT...BUT IF YOU WERE TO GO STRAIGHT OFF THE
NAM BUFR SOUNDING...MSP WILL SEE A REPEAT PERFORMANCE ON THE
STRATUS FOR A THIRD NIGHT IN A ROW. DECIDED TO GO THE SCT008 ROUTE
FOR NOW UNTIL THERE IS MORE CONFIDENCE ON WHERE STRATUS WILL END
UP TONIGHT.

/OUTLOOK FOR KMSP/

TUE-THU...VFR WINDS S 5-15 KTS.


&&

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

$$

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


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