Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 182109
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
309 PM CST THU DEC 18 2014

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 307 PM CST THU DEC 18 2014

A NARROW BAND OF DRIER AIR AROUND 92H HAS LED TO SOME CLEARING OR
PARTLY SUNNY SKIES ACROSS PORTIONS OF CENTRAL AND SOUTHERN MN EARLY
THIS AFTN. IN FAR EC MN/WC WI...EARLIER CLOUD LAYER AND WEAK
CONVERGENCE IN THIS LAYER LED TO A PERIOD OF -SN...WHICH BRIEFLY
CAUSED SOME MINOR ACCUMULATIONS ACROSS THE TWIN CITIES. THIS AREA OF
-SN HAS MOVED OFF TO THE NORTH/NE AND DISSIPATED...OR BECAME VERY
LIGHT FOR RADAR NOT TO DETECT IT.

ALTHOUGH THERE WILL BE A BRIEF PERIOD OF MOSTLY CLEAR SKIES MOVING
ACROSS THE AREA THIS EVENING...IT WILL QUICKLY BECOME CLOUDY AGAIN
AS A WEAK SHORTWAVE MOVES ACROSS THE REGION TONIGHT FROM THE DAKOTAS.
IN ADDITION TO THE INCREASING CLOUD COVER...A WEAK AREA OF LIFT
ACROSS CENTRAL MN MAY PRODUCE SOME LIGHT FREEZING DRIZZLE/FLURRIES.
DEEPER MOISTURE WILL BE NORTH OF MPX CWA...BUT ENOUGH TO INCLUDE
SOME LIGHT PRECIPITATION ACROSS THE FAR NORTHERN CWA BY FRIDAY
MORNING. NO MAJOR PROBLEMS WITH THE FREEZING PRECIPITATION IS
EXPECTED DUE TO LIMITED COVERAGE AND DURATION.

THE STRONG INVERSION THAT DEVELOPED LAST WEEK AND LED TO A LONG
PERIOD OF CLOUDY SKIES...LOW CIGS AND FOG...IS LIKELY TO DEVELOP
ONCE AGAIN BY FRIDAY AFTN AS TEMPS ABOVE THE BOUNDARY LAYER RISE FROM
THE WARMER SW FLOW UNDERNEATH THE CLOUD DECK.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 307 PM CST THU DEC 18 2014

MAIN CONCERNS DURING THE LONG TERM REMAIN FZDZ POTENTIAL
SATURDAY/SATURDAY NIGHT...FOLLOWED BY PRECIP CHANCES SUNDAY THROUGH
WEDNESDAY NIGHT. INCLUDED IN THE PRECIP CHANCE NEXT WEEK IS THE
ISSUE OF P-TYPE SUNDAY NIGHT INTO MONDAY.

FOR THIS FORECAST...MODEL PREFERENCE WAS A BLEND OF THE GFS/ECMWF AS
THE GEM QUICKLY BECOMES AN OUTLIER ON MONDAY NEXT WEEK. DIFFERENCES
BETWEEN THE GFS/ECMWF ARE FAIRLY MINIMAL UNTIL THURSDAY...BUT AFTER
THAT...WE ARE BEYOND THIS FORECAST PERIOD.

THE FIRST PROBLEM WITH THE FORECAST SHOWS UP SATURDAY AS WE GET INTO
INCREASING SRLY FLOW. ONE THING THAT LOOKS LIKE A CERTAINTY IS MORE
TIME SPENT BENEATH A DECK OF STRATUS. STILL QUESTIONABLE SAT/SAT
NIGHT IS IF MOISTURE IS DEEP ENOUGH TO GENERATE DZ. FOR NOW...KEPT
SATURDAY DRY...BUT KEPT THE FZDZ MENTION GOING FOR SAT NIGHT. THE
REASONING HERE IS THAT DURING THE DAY SATURDAY...WE WILL HAVE
SHORTWAVE RIDGING AND SUBSIDENCE WORKING ACROSS THE AREA...WHILE
SATURDAY NIGHT...THE NEXT WEAK SHORTWAVE MOVING ACROSS THE AREA WILL
PROVIDE A LITTLE BURST OF LIFT AND DEEPER MOISTURE. CONFIDENCE IS
STILL LOW ON IF WE WILL SEE ANY DZ OR PRECIP AT ALL...BUT ON
SATURDAY NIGHT...MOST MODELS SHOW SOME LIGHT QPF SPREADING ACROSS
THE AREA...WHICH IS INDICATIVE OF DZ.

FOR SUNDAY...SRLY WINDS WILL BE INCREASING IN STRENGTH...BUT WE WILL
SEE THE ADDED BENEFIT OF SEEING MOISTURE RETURN TO THE DGZ...ALONG
CHANCES FOR PRECIP OTHER THAN DZ. MOISTURE TRANSPORT INCREASES AS
WELL ON SUNDAY...BUT IT IS ORIENTED TOWARD ERN AREAS...SO CONTINUED
TO HAVE CHANCE POPS FOR WRN WI.

SUNDAY NIGHT...THE UPPER WAVE THAT WILL BE WITH US MORE OR LESS TO
CHRISTMAS MAKES ITS APPEARANCE. THIS WILL SEND A SFC LOW ACROSS SRN
MN/NRN IA MONDAY. THE UPPER WAVE WILL STILL BE TAKING ON A NEGATIVE
TILT AND CLOSING OFF...SO THE SFC LOW WILL MAKE IT ONLY AS FAR AS
MICHIGAN BY WEDNESDAY. ALSO ON WEDNESDAY...A SRN WAVE WILL ROUND THE
TROUGH...WITH A COASTAL LOW TAKING OVER BY THURSDAY. THE ECMWF STILL
SHOWS THIS LOW DEEPENING TO UNDER 970 MB...BUT IT IS A BIT FARTHER
EAST THAN EARLIER RUNS. OTHER NOTABLE CHANGE WITH THE SYSTEM IS IN
THE TEMPERATURE DEPARTMENT. BECAUSE THE UPPER LOW GETS SO DEEP...THE
COLD AIR GETS STOPPED UP IN CANADA. WITH THE 17.12 RUNS...THE
ECMWF/GFS WERE SHOWING 925-850 TEMPS COOLER THAN -12C BY
THURSDAY...BUT WITH THE 18.12 RUNS TEMPS IN THAT SAME LAYER ARE
FORECAST TO BE WARMER THAN -10C...SO WE ONLY LOOK TO COOL BACK DOWN
TO ABOUT NORMAL BY THE END OF THE WEEK...WITH THE MOST NOTICEABLE
CHANGE IN THE FORECAST FOR NEXT WEEK BEING TEMPS ABOUT 5 DEGS WARMER
THAN WHAT WE HAD.

AS FOR POTENTIAL SENSIBLE WEATHER NEXT WEEK...WE STILL LOOK TO SPEND
A PROLONGED PERIOD OF TIME WITHIN CYCLONIC FLOW...WHICH LOOKS TO
RESULT IN A PROLONGED PERIOD OF LIGHT TO MODERATE SNOW MONDAY NIGHT
THROUGH WEDNESDAY NIGHT. IN ADDITION...AS THE LOW IS MOVING ACROSS
THE AREA ON MONDAY...IT LOOKS TO BRING A FAIRLY WARM TONGUE OF AIR
UP IN THE AREA...WITH THE ECMWF/GFS SHOWING SFC WET BULB TEMPS
INCREASING INTO THE MID 30S SUNDAY NIGHT INTO MONDAY. FORECAST
SOUNDINGS FROM THE GFS CONTINUE TO SHOW P-TYPE BEING RAIN SUNDAY
NIGHT THROUGH MONDAY MORNING FOR MUCH OF THE AREA OUTSIDE OF CENTRAL
MN AND NW WI. ONCE THIS SYSTEM MOVES OFF TO THE EAST...PROFILES
STILL LOOK TO COOL ENOUGH TO SWITCH THINGS OVER TO SNOW...THOUGH THE
ECMWF IS SLOW ENOUGH IN BRINGING THE COLD AIR IN TO PUSH THE THREAT
FOR A RA/SN MIX OUT INTO TUESDAY IN WRN WI. BOTH THE GFS AND ECMWF
CONTINUE TO SHOW SEVERAL INCHES OF ACCUMULATION NEXT WEEK...BUT WE
GET THOSE SEVERAL INCHES BECAUSE WE LOOK TO PICK UP AN INCH OR TWO
OF SNOW A DAY MONDAY THROUGH WEDNESDAY. WINDS ALSO LOOK TO PICK UP
ON TUESDAY...THOUGH WITH THE SUB 970MB LOW STAYING FARTHER EAST IN
THE LATEST MODELS RUNS...WINDS DO NOT LOOK LIKE THEY WILL BE AS
STRONG AS THEY WERE LOOKING YESTERDAY...BUT STILL WOULD BE STRONG
ENOUGH TO LEAD TO BLOWING SNOW ISSUES DEPENDING ON HOW MUCH SNOW WE
GET NEXT WEEK. STILL LOTS OF UNCERTAINTY SURROUNDING THIS
SYSTEM...BUT GIVEN ITS TIMING DURING A BUSY TRAVEL WEEK...STILL HAS
THE POTENTIAL TO ADVERSELY IMPACT MUCH OF THE AREA IN ONE WAY OR
ANOTHER NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1100 AM CST THU DEC 18 2014

EARLIER THIS MORNING A CLOUD LAYER ARND 1.5 TO 2.5K AGL MOVED
FROM WC WI...INTO EC MN AS BOUNDARY LAYER WINDS SLOWLY BECAME
ESE/SE THIS MORNING. AS TEMPS IN THE CLOUD LAYER HELD NEAR -10C TO
-12C...ICE CRYSTAL FORMATION CONTD...PLUS THE ADDED AFFECT OF
WEAK CONVERGENCE IN THIS LAYER...LED TO -SN. TEMPS WILL SLOWLY
WARM THIS AFTN AND WINDS WILL VEER TO THE S/SW...SO THE MVFR CLOUD
DECK SHOULD MOVE OFF TO THE N/NE AND ONLY AFFECT KRNH/KEAU THRU
THE NEXT 6 HRS. ELSEWHERE...KSTC WILL SEE VFR CONDS BY 21-23Z. AFT
00Z...ANOTHER AREA OF MVFR CIGS WILL MOVE FROM NE/IA BACK INTO SW
MN AND CAUSE KRWF/KAXN TO LOWER TO MVFR CIGS ONCE AGAIN LATER
TONIGHT. CONFIDENCE REMAINS HIGH ON THE MVFR CIGS FOR EC MN/WC
WI...WITH LOWER CONFIDENCE ON THE RETURN OF MVFR CIGS ACROSS SW/WC
MN AFT 00Z. THIS IS MAINLY A TIMING ISSUE...NOT SO MUCH OF WILL
IT OCCUR OR NOT. LIGHT WINDS FROM THE ESE/SE WILL SLOWLY INCREASE
BY THE END OF THE TAF PERIOD.

KMSP...

LAST BATCH OF -SN SHOULD MOVE THRU THE AIRPORT TERMINAL AREA BY
18-19Z. MVFR CIGS WILL SLOWLY ERODE FROM THE W/SW AND ADVECT INTO
THE METRO AREA BY 20-22Z. TIMING REMAINS THE MAY PROBLEM...BUT
CONFIDENCE IS HIGH ENOUGH TO INTRODUCE VFR CONDS BY 21Z. MVFR CIGS
WILL LIKELY COME BACK INTO EC MN FRIDAY...BUT TIMING REMAINS THE
MAIN DILEMMA. WILL CONTINUE WITH VFR CONDS UNTIL WE HAVE A BETTER
HANDLE ON TIMING. WINDS WILL HOLD FROM THE ESE/SE THRU THE
PERIOD...AND SLOWLY INCREASE FROM 3-5 KTS THIS AFTN...TO 6-8 KTS
BY THE END OF THE TAF PERIOD.

/OUTLOOK FOR KMSP/

FRI...VFR EARLY...POSSIBLY MVFR BY AFTN/EVENING. WINDS SSE 6-8 KTS.
SAT...MVFR CIGS. CHC -FZDZ LATE. WINDS SSE 5 KTS.
SUN...MVFR/IFR. CHC -FZDZ/-RA/-SN. WINDS SSE 7-10KTS.


&&

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

$$

SHORT TERM...JLT
LONG TERM...MPG
AVIATION...JLT






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