Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 130538
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1138 PM CST FRI FEB 12 2016

.SHORT TERM...(TONIGHT THRU SATURDAY NIGHT)
ISSUED AT 255 PM CST FRI FEB 12 2016

MAIN FCST CONCERNS THIS PERIOD...BITTER COLD WIND CHILLS TONIGHT/SAT
MORNING...SNOW CHANCES LATE SAT NIGHT...COLD TEMPS THRU THE PERIOD.

18Z DATA ANALYSIS HAD LOW PRESSURE ASSOCIATED WITH THE SHORTWAVE
ENERGY DROPPING ACROSS THE WESTERN GREAT LAKES MOVING RATHER QUICKLY
TOWARD SOUTHERN QUE. ARCTIC HIGH PRESSURE WAS CENTERED NORTHWEST OF
LK WINNIPEG WITH RIDGING SOUTH INTO KS/OK. BRISK NORTHWEST LOW LEVEL
FLOW BETWEEN THE TWO WAS SPREADING AN ARCTIC AIRMASS SOUTHWARD INTO
THE UPPER MIDWEST. SUBSIDENCE EAST OF THE LOW LEVEL RIDGE AXIS WAS
CLEARING OUT THE CLOUDS OVER MUCH OF THE REGION. EVEN WITH THE
SUNSHINE...MID-DAY TEMPS WERE BELOW ZERO ACROSS NORTHERN MN...TO
AROUND 20 ACROSS SOUTHERN IA. WIND CHILLS ALREADY NEAR/BELOW ZERO
ACROSS MUCH OF MN/IA/WI.

MODEL RUNS OF 12.12Z GENERALLY INITIALIZED WELL. HOWEVER...ALL AGAIN
INITIALIZED SFC PRESSURES ABOUT 2MB TOO HIGH OVER THE NORTH-CENTRAL
CONUS. SOLUTIONS VERY SIMILAR FOR TONIGHT/SAT AS THE TROUGHING OVER
THE GREAT LAKES SHIFTS EAST AND HGTS OVER THE REGION RISE A BIT...
AHEAD OF THE NEXT SHORTWAVE ENERGY INTO WY/MT BY 00Z SUN. TREND
FAVORS FASTER AND STRONGER OF THE EARLIER RUNS WITH THIS FEATURE AT
00Z SUN. THIS SLIGHTLY FASTER/STRONGER TREND CONTINUE SAT NIGHT AS
THE WAVE/TROUGH MOVES INTO WESTERN IA/MN BY 12Z SUN. SOME DETAIL
DIFFERENCES BY SAT NIGHT BUT FCST CONFIDENCE GENERALLY REMAINS GOOD
THRU THE SHORT-TERM.

IN THE SHORT TERM...VERY COLD LOW LEVEL AIRMASS CONTINUES TO SPREAD
ACROSS THE AREA TONIGHT AS THE ARCTIC HIGH BUILDS SOUTH INTO THE
MID/UPPER MS VALLEY. 925MB TEMPS IN THE -18C TO -23C RANGE BY 12Z
SAT. WITH THE SFC RIDGE AXIS REMAINING WEST OF THE AREA TONIGHT...
NORTHWEST GRADIENT WINDS EXPECTED TO REMAIN IN THE 5 TO 10 MPH
RANGE LATER TONIGHT/SAT MORNING. THIS TO KEEP THE BOUNDARY LAYER
STIRRED AND LOWS FROM DROPPING INTO THE -20F TO -30F RANGE IN THIS
COLD AIRMASS. MOST LOWS TONIGHT STILL EXPECTED TO BE IN THE -10F
TO -20F RANGE...BUT IF WINDS DECOUPLE IN THE FAVORED LOW LAYING
LOCATIONS...THE -20F TO -30F LOWS WOULD BE LIKELY IN THESE AREAS.
WIND CHILLS ALREADY LOOKING TO BE -5 TO -20 AT 00Z THIS EVENING
WITH THE 00Z START TIME FOR THE WIND CHILL ADVISORY REASONABLE.
WIND CHILLS BOTTOM OUT AROUND 12Z...THEN LOOK TO RECOVER RATHER
QUICKLY SAT MORNING AS THE SFC RIDGE AXIS APPROACHES/WINDS BECOME
LIGHT AND TEMPS WARM BACK TO NEAR ZERO BY LATE MORNING. LIGHT
WINDS SAT AFTERNOON COMBINED WITH PLENTY OF MID FEB SUNSHINE...IT
WILL NOT FEEL AS COLD AS IT ACTUALLY WILL BE. 925MB TEMPS SAT
AFTERNOON ONLY RECOVER TO THE -14C TO -18C RANGE. IF BOUNDARY
LAYER MIXES THAT DEEP...THESE TEMPS ONLY SUPPORT HIGHS SAT IN THE
5 TO 15 ABOVE...BUT THE MID FEB SUNSHINE AND LIGHT WINDS WILL
ALLOW IT TO FEEL WARMER THAN THAT.

HIGH SLIPS QUICKLY EAST SAT NIGHT AS THE NEXT SFC-MID LEVEL TROUGH
CROSSES THE NORTHERN PLAINS. LOWER LEVEL THERMO-DYNAMIC FORCING/LIFT
AND DEEPER MOISTURE SPREAD QUICKLY EAST TOWARD/INTO THE FCST AREA...
WITH GOOD AGREEMENT AMONG THE MODELS FOR SNOW TO SPREAD INTO THE
SOUTHWEST 1/3 TO 1/2 OF THE FCST AREA AFTER MIDNIGHT. TIGHTER
CONSENSUS OF MOST OF THIS REMAINING WEST OF THE MS RIVER THRU
12Z...AND LOWERED SNOW CHANCES OVER THE NORTHEAST END OF THE FCST
AREA LATE SAT NIGHT WHILE MAINTAINING/RAISING TO NEAR 100 PERCENT
ACROSS THE SOUTHWEST 1/3 OF THE FCST AREA. AS MUCH AS AN INCH OR 2
OF SNOW COULD FALL ACROSS THE SOUTHWEST 1/3 OF THE FCST AREA BY
DAYBREAK SUNDAY...AND MAY YET NEED A WINTER WEATHER ADVISORY FOR
THESE AREAS LATE SAT NIGHT AND SUN. MORE ON THAT BELOW. CONTINUED
TO TREND TOWARD COLDER OF GUIDANCE LOWS TONIGHT THEN FAVORED A
BLEND OF THE GUIDANCE HIGHS/LOWS SAT NIGHT. SAT NIGHT LOWS TO BE
IN THE EVENING...WITH STEADY/SLOWLY RISING TEMPS AFTER MIDNIGHT AS
CLOUDS THICKEN AND SOUTHEAST WINDS FOR BOUNDARY LAYER MIXING
INCREASE.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 255 PM CST FRI FEB 12 2016

FOR SUNDAY THRU MONDAY NIGHT...

MAIN FCST CONCERNS THIS PERIOD...SNOW CHANCES/AMOUNTS SUNDAY INTO
SUN NIGHT...WARMING TEMPS THRU THE PERIOD.

MODEL RUNS OF 12.12Z IN GOOD AGREEMENT FOR THE MAIN SHORTWAVE/TROUGH
AXIS TO PASS SUNDAY. TREND IS A BIT FURTHER SOUTH WITH THE MAIN
SHORTWAVE AS IT PASSES SUNDAY. IMPROVING AGREEMENT FOR A SECONDARY
SHORTWAVE TO DROP INTO THE BACK SIDE OF THE TROUGH SUN NIGHT AND
MOVE ACROSS MN/IA/WI MONDAY. DIFFERENCES START TO CROP UP AND
MAGNIFY ON THE NEXT STRONGER NORTHWEST FLOW SHORTWAVE TO DROP INTO
THE LONGWAVE TROUGHING OVER THE UPPER MIDWEST MON NIGHT. GIVEN SOME
DETAIL CONCERNS ALREADY SUNDAY FCST CONFIDENCE IS AVERAGE FOR THE
SUN THRU MON THEN BELOW AVERAGE MON NIGHT.

STRONGER OF THE LOWER LEVEL THERMO-DYNAMIC FORCING IS SLATED TO MOVE
ACROSS THE FCST AREA SUN MORNING. STRONGER OF THE PV ADVECTION/
DIVERGENCE ALOFT WITH THE SHORTWAVE...AND OVERALL DEEPEST/STRONGEST
LIFT...NOW PROGGED TO PASS ACROSS MAINLY THE SOUTH END OF THE FCST
AREA SUN. MAIN PRECIP BAND...AND HEAVIER OF THE SNOWFALL...WITH THIS
WAVE NOW LOOKS TO FALL ACROSS MAINLY THE SOUTHWEST HALF OF THE FCST
AREA. CONTINUED WITH NEAR 100 PERCENT SNOW CHANCES OVER MUCH OF THE
FCST AREA SUN MORNING...TRENDING DOWN TO 60-80 PERCENT SUN AFTERNOON
AS THE MAIN WAVE WOULD BE MOVING EAST OF THE AREA. BIGGEST QUESTION
IS HOW MUCH SNOWFALL. QUITE A SPREAD AMONG MODELS YET ON HOW MUCH
PRECIP FALLS FROM LATER SAT NIGHT INTO SUN EVENING...SOME WITH 2 TO
3 TIMES AS MUCH QPF AS OTHERS. ALSO QUITE A SPREAD ON EXPECTED
SNOWFALL TO WATER...SOME OF THESE AS HIGH AS 25 TO 1. MODEL
SOUNDINGS SHOWING THE COLUMN TO BE QUITE COLD WITH THE -15C LEVEL
BELOW 700MB WITH A NEARLY ISOTHERMAL LAYER BETWEEN 925-600MB.
FORCING/LIFT SIGNAL NOT ALL THAT STRONG ACROSS MUCH OF THE AREA...
AND WITH LAPSE RATES IN THE 925-600MB LESS THAN 2C/KM...THIS LAYER
WILL BE RESISTANT TO UPWARD FORCING/LIFTING. BULK OF LIFT IS PROGGED
ABOVE 850MB WITH PW VALUES IN THE 1/4 TO 1/3 INCH RANGE. INITIALLY A
VERY DRY LOWER LEVEL AIRMASS TO OVERCOME AS WELL...WHICH MAY
STRUGGLE TO OCCUR OVER THE NORTHEAST 1/3 TO 1/2 OF THE FCST AREA. BY
THE TIME DEEPER SATURATION WOULD OCCUR...MUCH OF THE LIFT WOULD BE
ON ITS WAY OUT WITH THE PASSING SHORTWAVE. ALL THIS POINTS TO SNOW-
WATER RATIOS MUCH LESS THAN 20 OR 25 TO 1. USED SNOW-WATER RATIOS OF
15 TO 17 TO 1 FOR NOW...WHICH STILL PRODUCES 2 TO LOCALLY 5 INCHES
OF SNOW ACROSS THE FCST AREA...HIGHEST OVER THE SOUTHWEST HALF.
CONFIDENCE NOT THAT HIGH IN SNOW AMOUNTS YET AND WILL HOLD OFF ON
ANY POTENTIAL WINTER WEATHER ADVISORY FOR THE POSSIBLE SNOW ON
SUNDAY.

SECONDARY WAVE DROPPING IN FOR SUN NIGHT/MON KEEPS DEEPER CYCLONIC
FLOW OVER THE AREA INTO MON. LINGERING -SN CHANCES OVER MUCH OF THE
AREA SUN NIGHT AND OVER THE NORTHEAST END OF THE FCST AREA MON
REASONABLE. GFS/ECMWF WITH EITHER A STRONGER OR FASTER SHORTWAVE
DROPPING INTO THE TROUGH MON NIGHT ALREADY SPREADS INCREASING
LIFT/MOISTURE BACK INTO THE WEST SIDE OF THE FCST AREA BY LATER MON
NIGHT. DUE TO THE RATHER DRASTIC LOOKING MODEL DIFFERENCES WITH THIS
FEATURE MON NIGHT AND LOWER CONFIDENCE THE SMALL -SN CHANCE OVER THE
WEST END OF THE FCST AREA OKAY FOR NOW. WITH ROUNDS OF LOWER LEVEL
WARM ADVECTION AND THE ARCTIC AIRMASS BEING PUSHED EAST OF THE
REGION...TEMPS TRENDING TOWARD NORMAL BY MON APPEAR REASONABLE. USED
A BLEND OF THE GUIDANCE HIGHS/LOWS FOR SUN THRU MON NIGHT.

FOR TUESDAY THRU FRIDAY...DAYS 4 TO 7...

MAIN FCST CONCERNS THIS PERIOD...-SN CHANCES TUE...SMALL -SN/-RA
CHANCES THU INTO FRI...ABOVE NORMAL TEMPERATURE POTENTIAL BY THU/FRI.

MEDIUM RANGE MODEL RUNS OF 12.00Z/12.12Z IN REASONABLE AGREEMENT FOR
LONGWAVE TROUGHING OVER EASTERN NOAM TUE. HOWEVER CONSIDERABLE
DETAIL DIFFERENCES ON TIMING/STRENGTH OF SHORTWAVES IN THE NORTHWEST
FLOW ALOFT OVER THE UPPER MIDWEST. RATHER GOOD AGREEMENT ON THE
LONGWAVE FEATURES ACROSS NOAM /TROUGHING EAST/RIDGING WEST/
CONTINUES WED...AS DO THE SHORTWAVE DETAIL DIFFERENCES. SIGNAL
CONTINUES FOR THE FLOW TO BE PROGRESSIVE THU WITH LONGWAVE RIDGING
TO BE PUSHED EAST INTO CENTRAL NOAM AS STRONGER ENERGY MOVES INTO
THE WESTERN CONUS. BY FRI...CONSIDERABLE BETWEEN MODEL AND RUN-TO-
RUN DIFFERENCES ON HOW FAST SOME OF THE WESTERN NOAM ENERGY WOULD
MOVE EAST...GFS INTO THE CENTRAL PLAINS WITH SOME OF IT WHILE ECMWF
HAS IT OVER AZ/SOUTHERN CA/NV. FOR THE MOST PART...FCST CONFIDENCE
IN THE TUE-FRI PERIOD IS BELOW AVERAGE.

PERIOD STARTS OFF WITH MID LEVEL TROUGHING OVER THE REGION...WITH
ONE OR MORE SHORTWAVES ROTATING THRU IT. GFS WOULD BRING A STRONGER
ONE OF THESE ACROSS THE AREA TUE WHILE CAN-GEM BRINGS ONE ACROSS
WED. COLUMN REMAINS COLD ENOUGH FOR PRECIP AS -SN THESE PERIODS...
AND SMALL CONSENSUS -SN CHANCE TUE OKAY FOR NOW UNTIL THE DETAILS
SORT THEMSELVES OUT. THU WOULD TREND TO BE A DRY DAY UNDER THE
BUILDING RIDGING ALOFT. HOWEVER MODELS SIGNALING STRONGER LOWER
LEVEL WARM ADVECTION/ISENTROPIC LIFT SPREADING NORTHEAST UNDER THE
BUILDING RIDGING AND THE INCREASING SOUTH/SOUTHWEST LOW LEVEL FLOW
MAY PULL SOME MOISTURE NORTHWARD FROM THE CENTRAL/SOUTHERN PLAINS.
THE GFS WOULD THEN BRING A SHORTWAVE TROUGH ACROSS THE REGION FRI.
COLUMN ALOFT WOULD BE WARMING...WITH ANY SMALL PRECIP CHANCES
THU/THU NIGHT AS -RA/-SN AND MAINLY -RA ON FRI. WITH PLENTY OF
DETAIL DIFFERENCES AND LOW CONFIDENCE BY THU/FRI...STAYED WITH THE
MODEL/ENSEMBLE CONSENSUS PRECIP CHANCES DAYS 6/7. MODEL/ENSEMBLE
CONSENSUS HIGHS/LOWS FOR TUE THRU FRI LOOKING GOOD FOR NOW. BUT...AS
MID CREW STATED...THE STRONG WARM-UP PROGGED TOWARD THE END OF THE
WORK WEEK MAY END UP MUTED...ESPECIALLY IF THE GFS AND ITS FASTER
WESTERN ENERGY THRU THE FLOW ENDS UP MORE CORRECT.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1138 PM CST FRI FEB 12 2016

VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. ARCTIC HIGH
PRESSURE BUILDS INTO THE REGION TONIGHT PROVIDING VFR CONDITIONS
WITH CLEAR SKIES. WINDS WILL BECOME LIGHT SATURDAY MORNING AS THE
HIGH MOVES THROUGH. LOOK FOR AN INCREASE IN HIGH CLOUD COVER LATE
SATURDAY AFTERNOON INTO SATURDAY EVENING AS A STORM SYSTEM
APPROACHES FROM THE NORTHERN PLAINS.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WIND CHILL ADVISORY UNTIL 9 AM CST SATURDAY FOR WIZ017-029-
     032>034-041>044-053>055-061.

MN...WIND CHILL ADVISORY UNTIL 9 AM CST SATURDAY FOR MNZ079-086>088-
     094>096.

IA...WIND CHILL ADVISORY UNTIL 9 AM CST SATURDAY FOR IAZ008>011-018-
     019-029-030.

&&

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...WETENKAMP


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