National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KARX 051707
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1107 AM CST THU DEC 5 2013

.UPDATE...
ISSUED AT 555 AM CST THU DEC 5 2013

HAVE BUMPED DOWN TEMPERATURES A FEW DEGREES ALREADY AS THEY
CONTINUE TO DROP AT A SLIGHTLY FASTER RATE THAN HAD BEEN FORECAST.
THIS MAY BE BECAUSE OF HOW THIN THE CLOUD COVER IS FROM THE
MISSISSIPPI WEST INTO MINNESOTA AND IOWA. THERE MAY BE A LOT MORE
SUN OUT THERE THIS MORNING SINCE WE CAN SEE THE STARS THROUGH THIS
DECK WHICH ALL OBSERVATIONS SAY EXTENDS BACK INTO THE DAKOTAS.
THE 05.12Z MPX RAOB CONFIRMS THAT THERE IS A SATURATED LAYER
BETWEEN 2500-3500FT RIGHT UNDER THE STOUT INVERSION. SO...WHILE IT
APPEARS THAT THERE IS A BROKEN TO OVERCAST STRATUS DECK OUT
THERE...THE QUESTION IS HOW THIN IT ACTUALLY IS AND WHETHER THAT
WILL ALLOW TEMPERATURES TO JUST BACK UP A BIT. AS THE SUN RISES
OVER THE NEXT HOUR OR SO...WE WILL HAVE OUR ANSWER.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 349 AM CST THU DEC 5 2013

MAIN FORECAST CONCERNS THIS PACKAGE...CLOUD TRENDS AND INCOMING
ARCTIC AIRMASS/TEMPERATURES.

06Z DATA ANALYSIS HAD THE DEEPENING SFC LOW OVER CENTRAL LK
SUPERIOR...HEADED RATHER QUICKLY TOWARD ONT. BULK OF THE PRECIP WITH
THIS SYSTEM ALREADY CONFINED TO NORTHEAST MN/FAR NORTHERN WI. COLD
FRONT SOUTH OF THE LOW WAS ALREADY PUSHING ACROSS LK MICHIGAN.
MDT/STRONG COLD ADVECTION AND FALLING TEMPS SPREADING ACROSS THE
REGION. TEMPS ALREADY IN THE SINGLE DIGITS ACROSS WESTERN MN/
NORTHWEST IA...WHERE WIND CHILLS WERE IN THE 0 TO -15 RANGE. PER FOG-
PRODUCT IMAGERY/SFC OBS...SUBSIDENCE WAS DECREASING THE CLOUDS OVER
WEST-CENTRAL/SOUTHWEST MN.

05.00Z MODEL RUNS HAVE INITIALIZED QUITE WELL AND OFFER VERY SIMILAR
SOLUTIONS AS THE SFC-MID LEVEL LOW EXITS NORTHEAST AND ARCTIC HIGH
PRESSURE SETTLES INTO THE NORTH-CENTRAL CONUS. ALL MODELS OFFERING
RATHER GOOD RUN-TO-RUN CONSISTENCY TO THEIR 03.00Z AND 04.00Z RUNS
ON THE MID LEVEL LOW LIFTING THRU ONTARIO AND THE LONGWAVE TROUGHING
REMAINING OVER WESTERN NOAM. CHECK OF OBS VS. MODEL DATA AT 06Z
SHOWED MODELS ALL QUITE GOOD WITH THE SFC LOW STRENGTH/LOCATION AND
DOING A REASONABLE JOB WITH THE COLD AIR POURING IN ACROSS THE
REGION. PER WV IMAGERY MODELS ALL LOOK TO HAVE A DECENT HANDLE ON
THE SHORTWAVE FEATURES OVER NOAM/EASTERN PAC. ONE THING MODELS
APPEAR TO BE STRUGGLING WITH IS CLOUDS/CLEARING OVER CENTRAL/
SOUTHWEST MN. THIS NOT COMPLETELY UNEXPECTED. 925-850MB RH PROGS
WITH 80+ PERCENT RH AND SOUNDINGS SHOWING THIS MOISTURE TRAPPED IN
AN INVERSION INDICATE A LOWER STRATUS DECK SHOULD BE PERSISTING IN
THESE AREAS. GIVEN THE TIGHT MODEL CONSENSUS AND TREND TOWARD DRY
HIGH PRESSURE...FCST CONFIDENCE IS GENERALLY GOOD...BUT FOR CLOUDS/
LOWER LEVEL RH TODAY.

IN THE SHORT TERM...STRONGEST OF THE LOW LEVEL COLD ADVECTION MOVES
ACROSS THE AREA THRU ABOUT 15Z THIS MORNING. THIS COLD ADVECTION
PLUS SFC-850MB CYCLONIC FLOW CONTINUE TO PUT THE SQUEEZE ON THE WRAP
AROUND MOISTURE THRU THE MORNING. CONTINUED THE MENTION OF FLURRIES
THRU THE MORNING ACROSS MAINLY THE NORTH HALF OF THE FCST AREA...
CLOSER TO THE SFC-500MB LOW. WITH SATELLITE AND SFC OBS SHOWING
DECREASING CLOUDS/CLEARING SPREADING SOUTHEAST TOWARD THE FCST AREA
EARLY THIS MORNING...WILL TREND SKY GRIDS TOWARD MORE SUNSHINE THIS
MORNING...ESPECIALLY OVER THE SOUTHWEST HALF OF THE FCST AREA WHERE
SFC-850MB WINDS WOULD ADVECT THE CLEARING. WOULD EXPECT DIURNAL
STRATO-CU REDEVELOPMENT FOR THE LATE MORNING/AFTERNOON HOURS WITH
THE COLD AIRMASS AND STEEP LOW LEVEL LAPSE RATES WITH SOME BOUNDARY
LAYER WARMING DUE TO SUNSHINE ON SNOW-FREE LANDSCAPE. SNOW-FREE
ACROSS ALL BUT THE NORTH END OF THE FCST AREA. WITH THERE APPEARING
TO BE MORE SUNSHINE TODAY AND STRONGEST OF THE LOW LEVEL COLD
ADVECTION EAST OF THE AREA...HAVE OPTED FOR A BIT OF A TEMPERATURE
RISE TODAY. 925MB TEMPS TONIGHT FALL TO THE -16C TO -20C RANGE BY
12Z FRI. NORTHWEST WINDS OF 10-15MPH TO KEEP THE BOUNDARY LAYER
STIRRED...BUT STILL APPEARS LOWS TONIGHT HEADED TO THE -5F TO +5F
RANGE. SUB-ZERO LOWS OVER THE NORTHWEST/NORTH ENDS OF THE FCST AREA
COUPLED WITH THE WINDS RESULT IN WIND CHILLS OF -20 TO -25 LATE
TONIGHT/EARLY FRI MORNING FOR PORTIONS OF SOUTHEAST MN AND NORTH-
CENTRAL WI. WILL ISSUE A WIND CHILL ADVISORY FOR THESE AREAS FOR
06Z-15Z FRI. IT IS ON THE EARLY SIDE FOR WIND CHILLS THIS COLD. WILL
LIKELY NEED ANOTHER WIND CHILL ADVISORY FOR PORTIONS OF THE AREA
LATE FRI NIGHT/SAT MORNING BUT WILL ADDRESS THAT LATER. WITH SOME
SUNSHINE TODAY AND RELATIVELY SNOW-FREE GROUND...LEANED TOWARD
WARMER OF GUIDANCE HIGHS. WITH THE WIND FOR BOUNDARY LAYER MIXING
USED A BLEND OF THE GUIDANCE LOWS.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 349 AM CST THU DEC 5 2013

MAIN FORECAST CONCERNS FOR FRIDAY THROUGH SATURDAY NIGHT...ARCTIC
HIGH PRESSURE...COLD TEMPERATURES AND NEED FOR MORE WIND CHILL
HEADLINES LATE FRI NIGHT/SAT MORNING.

05.00Z MODELS REMAIN IN VERY GOOD AGREEMENT FOR THE FRI THRU SAT
NIGHT PERIOD AS 500MB HGTS GRADUALLY RISE AND THE FLOW GOES BACK TO
THE SOUTHWEST AHEAD OF THE NEXT WESTERN CONUS TROUGH. MODELS
CONVERGING ON A COMPROMISE OF THEIR EARLIER SOLUTIONS THRU 12Z SUN.
FCST CONFIDENCE GOOD FOR THE FRI THRU SAT NIGHT PERIOD AS COLD...DRY
HIGH PRESSURE DOMINATES THE REGION.

NORTHWEST WINDS OF 10-20 MPH CONTINUE ON FRI...WITH 925MB TEMPS
HOLDING IN THE -16C TO -20C RANGE. NOT EXPECTING MUCH OF A TEMP RISE
ON FRI WITH THE NORTHWEST WINDS BLOWING COLD AIR OFF THE SNOWPACK
ACROSS ALL BUT SOUTHEAST MN. SOME SUNSHINE AND THE LOCALLY SNOW-FREE
GROUND OVER MUCH OF THE FCST AREA WILL ALLOW FOR SOME TEMP RISE
FRI...VS. VIRTUALLY NO TEMP RISE IF WE HAD SNOW COVER. 925MB TEMPS
DIP A BIT MORE FRI NIGHT. NORTHWEST WINDS AROUND 10 MPH TO KEEP THE
BOUNDARY LAYER STIRRED FRI NIGHT...BUT WITH A COLDER DAY FRI...
APPEARS LOWS HEADED BELOW ZERO FOR MOST OF THE FCST AREA. THE WINDS
COMBINED WITH SUB-ZERO TEMPS AGAIN SEND WIND CHILLS INTO THE -20 TO
-25 RANGE ACROSS ABOUT THE NORTH HALF OF THE FCST AREA BETWEEN
ROUGHLY 06Z-15Z SAT. IF FCST WINDS/LOW TEMPS HOLD...WILL NEED
ANOTHER WIND CHILL ADVISORY FOR LATE FRI NIGHT/MUCH OF SAT MORNING
BUT WILL NOT DOUBLE UP THE HEADLINES AT THIS TIME. LITTLE 925MB TEMP
CHANGE FOR SAT...WITH HIGHS LOOKING TO BE SIMILAR TO THOSE OF FRI.
CENTER OF THE SFC-925MB HIGH SLIPS EAST OF THE AREA SAT NIGHT...WITH
SOME LOW LEVEL WARM ADVECTION SPREADING ACROSS THE AREA ESPECIALLY
BY LATER SAT NIGHT. THE TRANSITION TO SOUTHERLY 850MB FLOW AND
SOUTHWEST 700-500MB FLOW SAT NIGHT SENDS INCREASING MOISTURE AND
SOME LIFT INTO THE AREA SAT NIGHT. ADDED A SMALL -SN CHANCE TO THE
WEST END OF THE FCST AREA LATE SAT NIGHT. APPEARS LOWS SAT NIGHT TO
BE DURING THE EVENING...WITH STEADY/SLOWLY RISING TEMPS AS CLOUDS
INCREASE AND THE LOW LEVEL WARM ADVECTION SPREADS IN. FCST GRIDS FOR
SAT NIGHT CARRYING A NON-DIURNAL TEMP TREND WITH LOWS AROUND
MIDNIGHT. USED A BLEND OF THE NUMERICAL GUIDANCE HIGHS/LOWS FOR FRI
THRU SAT NIGHT.

FOR SUNDAY THROUGH WEDNESDAY.../DAYS 4 TO 7/...

MEDIUM RANGE MODEL RUNS OF 05.00Z IN QUITE GOOD AGREEMENT SUN/MON AS
THE TROUGHING/ENERGY LIFTING OUT OF THE ROCKIES AT LEAST PARTLY
PHASES WITH SHORTWAVE ENERGY DROPPING OUT OF CENTRAL CAN. ECMWF
CONTINUES TO SHOW THE BETTER RUN-TO-RUN CONSISTENCY FOR SUN/MON WITH
OTHER MODELS CONVERGING ON ITS SOLUTION AS THE ROCKIES PORTION OF
THE SHORTWAVE ENERGY LIFTS ACROSS THE MID/UPPER MS VALLEY. BETWEEN
MODEL AND RUN-TO-RUN CONSISTENCY REMAINS REASONABLE TUE AS LONG-WAVE
TROUGHING REMAINS OVER THE REGION. ECMWF/GFS APPEAR REASONABLY
SIMILAR AT 500MB WED BUT SAME CANNOT BE SAID AT THE LOWER LEVELS.
FCST CONFIDENCE GOOD SUN/MON...THEN BELOW AVERAGE BY WED.

AFTER THE COLD OF THE NEXT FEW DAYS...ATTENTION TURNS TO THE
POTENTIAL ACCUMULATING SNOW EVENT FOR THE ENTIRE FCST AREA CENTERED
ON SUN AFTERNOON/EVENING. TIGHTENING MODEL CONSENSUS SPREADS
INCREASING 925-500MB MOISTURE AND DEEP LAYERED FORCING/LIFT
ACROSS THE AREA SUN/SUN NIGHT. GIVEN THE GOOD/IMPROVING MODEL
AGREEMENT...RAISED -SN CHANCES SUN/SUN NIGHT ABOVE THE
MODEL/ENSEMBLE CONSENSUS...TOWARD 30-55 PERCENT SUN AND TO AROUND
60 PERCENT SUN NIGHT. NO PROBLEM WITH THE AIRMASS/DEPTH OF
MOISTURE BEING COLD ENOUGH FOR ALL SNOW WITH THIS SYSTEM. FAIRLY
GOOD CONSENSUS FOR 1 TO 2 TENTHS OF AN INCH OF QPF ACROSS THE AREA
SUN/SUN NIGHT. SNOW-WATER RATIO IS A QUESTION THOUGH...WITH THE
DENDRITIC GROWTH ZONE /DGZ/ MAINLY IN THE SFC- 750MB LAYER...
RESULTING IN A RATHER DEEP DGZ. HOWEVER...BULK OF THE LIFT IS
ABOVE THIS LAYER...AND WIND IN THE LAYER PROGGED TO BE IN THE
10-20KT RANGE...TO BREAK UP SNOW CRYSTALS. IF WINDS BELOW 700MB
END UP LIGHTER AND THERE ENDS UP BEING MORE 850-700MB LIFT...SOME
VERY FLUFFY SNOW COULD FALL SUN/SUN NIGHT. FOR NOW APPEARS 1 TO 3
INCHES OF SNOW LIKELY FROM THIS SYSTEM. ANOTHER ROUND OF VIGOROUS
LOW LEVEL COLD ADVECTION FOLLOWS FOR MONDAY. WITH PROGRESSIVE
SHORTWAVES IN THE FLOW...LOW LEVEL WARM ADVECTION ALREADY RETURNS
MON NIGHT...AHEAD OF THE NEXT NORTHWEST FLOW WAVE/LOW TO PASS
NORTH OF THE AREA ON TUE. SMALL -SN CHANCE ACROSS THE NORTH PARTS
OF THE FCST AREA ON TUE REASONABLE WITH PASSAGE OF THE LOWER LEVEL
TROUGH/FRONT. GFS MAINTAINS NORTHWEST LOW LEVEL FLOW AND LOW LEVEL
COLD ADVECTION BEHIND THE TUE SYSTEM IN TO WED WHILE ECMWF IS MORE
PROGRESSIVE WITH SOUTHWEST FLOW AND MDT/STRONG WARM ADVECTION
ACROSS THE REGION ON WED. 925MB TEMPS EITHER -16C TO -20C WED
/GFS/ OR -10C TO -14C /ECMWF/ DEPENDING ON MODEL OF CHOICE. FOR
NOW FOLLOWED THE MODEL/ENSEMBLE CONSENSUS FOR HIGHS/LOWS IN THE
SUN- WED PERIOD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1107 AM CST THU DEC 5 2013

VFR CONDITIONS EXPECTED THROUGH THE PERIOD. THE AREA OF LOW
PRESSURE THAT BROUGHT PRECIPITATION TO THE REGION WEDNESDAY IS
OVER ONTARIO AND CONTINUES TO MOVE OFF TO THE NORTHEAST. HIGH
PRESSURE WAS OVER EASTERN MONTANA INTO NEBRASKA. THE GRADIENT
BETWEEN THESE TWO WILL CONTINUE TO GRADUALLY WEAKEN ALLOWING THE
WINDS TO SLOWLY DIMINISH THROUGH THE PERIOD. EXPECT THE DIRECTION
TO REMAIN WEST/NORTHWEST THROUGH THE PERIOD. THE GUSTS WILL
CONTINUE THROUGH TODAY AND INTO THE NIGHT AT KRST AS GOOD LOW
LEVEL LAPSE RATES WILL PERSIST TO KEEP THE MIXING GOING. DID DROP
THE GUSTS AT KLSE AFTER SUNSET AS A WEST/NORTHWEST WIND IS NOT A
CLIMATOLOGICALLY FAVORED DIRECTION FOR GUSTS TO OCCUR AS THE
VALLEY TENDS TO GET CUT OFF FROM THE BETTER MIXING.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM CST FRIDAY FOR
     WIZ017-029.

MN...WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM CST FRIDAY FOR
     MNZ079-086-087-094.

IA...NONE.
&&

$$

UPDATE...HALBACH
SHORT TERM...RRS
LONG TERM....RRS
AVIATION...04