Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 241126
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
526 AM CST TUE FEB 24 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 337 AM CST TUE FEB 24 2015

MAIN FCST CONCERNS THIS PERIOD...-SN CHANCES THIS MORNING...
TEMPERATURES TRENDS AS THE NEXT ARCTIC HIGH BUILDS IN.

DATA ANALYSIS AT 06Z HAD LOW PRESSURE NEAR THE SOUTHWEST SHORES OF
HUDSONS BAY WITH A TROUGH/WARM FRONT TO THE SOUTHWEST TO SOUTHEAST
SD. STRONG PRESSURE GRADIENT/SOUTHWEST FLOW AHEAD OF THIS TROUGH/
FRONT WAS PUSHING WARMER AIR ACROSS MN/IA/WI...WITH TEMPS CONTINUING
TO RISE EARLY THIS MORNING. TEMPS IN THE MID 20S TO LOW 30S ACROSS
WESTERN/SOUTHERN MN NEAR/BEHIND THE FRONT EARLY THIS MORNING.
SECONDARY/NEXT ARCTIC FRONT WAS NEAR THE US/CAN BORDER. FORCING/LIFT
WITH THE TROUGH/FRONT AND SHORTWAVE ENERGY DROPPING SOUTHEAST WAS
TRYING TO PRODUCE SOME SNOW INTO NORTHERN WI...BUT THIS FIGHTING
SOME RATHER DRY AIR IN THE 850-600MB LAYER. SNOW EARLY THIS MORNING
GENERALLY LIMITED TO NORTHERN 1/4 OF MN.

24.00Z MODEL RUNS GENERALLY INITIALIZED WELL. SOLUTIONS QUITE
SIMILAR AS RATHER STRONG SHORTWAVE ENERGY DROPS QUICKLY ACROSS THE
WESTERN GREAT LAKES TODAY AND THE NEXT IN LINE NORTHWEST FLOW
SHORTWAVE MOVES TO NEAR THE US/CAN BORDER BY 12Z WED. TREND FAVORS
FASTER OF THE EARLIER RUNS ON THE PASSING SHORTWAVE TODAY AND
STRONGER OF EARLIER RUNS WITH THE ENERGY DROPPING TOWARD ND LATE
TONIGHT. SHORT-TERM FCST CONFIDENCE IS GOOD THIS CYCLE.

IN THE SHORT TERM...SHORTWAVES AND THEIR FORCING/LIFT MOVE RATHER
QUICKLY SOUTHEAST PAST THE FCST AREA THIS MORNING...AS DOES THE
SFC/LOWER LEVEL TROUGH AND QG/FN CONVERGENCE WITH IT. GIVEN THE FAST
SPEED OF THE FORCING...AND IT STRUGGLING TO OVERCOME THE DRY 850-
600MB LAYER...HAVE LOWER MOST -SN CHANCES SOUTHWEST OF I-94 AND
LIMITED THEM TO MAINLY BEFORE 18Z. THIS AFTERNOON/TONIGHT DRY AS LOW
LEVEL COLD ADVECTION/NEXT ARCTIC HIGH BUILDS INTO THE UPPER MIDWEST.
LEAD TROUGH/WARM FRONT SLIDES INTO/ACROSS THE AREA THIS MORNING...
WITH THE COLD FRONT TO FOLLOW THRU THE EARLY/MID AFTERNOON HOURS.
WARM WEDGE BETWEEN THE 2 FRONTS TO SLIDE ACROSS THE FCST AREA DURING
THE LATE MORNING/EARLY AFTERNOON HOURS. WITH TEMPS ALREADY AROUND 30F
WEST OF THE TWIN CITIES...HIGHS IN THE UPPER 20S TO LOW 30S FOR MUCH
OF THE FCST AREA TODAY CONTINUE TO LOOK GOOD. STEEPER LOW LEVEL
LAPSE RATES AND COLD ADVECTION/SUBSIDENCE TO WINDS BRISK/GUSTY AS
THEY SWING TO THE NORTHWEST THRU THE DAY. STRONGER OF THE LOW LEVEL
COLD ADVECTION/COOLING SPREADS ACROSS THE AREA LATE THIS AFTERNOON/
EVENING WITH THE COLDEST OF THE AIR...SUB-ZERO LOWS TONIGHT...
DROPPING ACROSS THE WI PORTION OF THE FCST AREA. USED A BLEND OF THE
GUIDANCE HIGHS/LOWS FOR TODAY/TONIGHT.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 337 AM CST TUE FEB 24 2015

MAIN FCST CONCERNS FOR WED THRU THU NIGHT...SNOW CHANCE ACROSS THE
SOUTHWEST END OF THE FCST AREA WED...COLD TEMPERATURES THRU THE
PERIOD.

24.00Z MODELS TRENDING TOWARD A COMPROMISE AS THE SHORTWAVE ENERGY
NEAR THE ND/CAN BORDER WED MORNING DROPS SOUTHEAST TOWARD IA/MO WED/
WED NIGHT. TREND FAVORS STRONGER OF THE EARLIER MODELS WITH THIS
FEATURE. TIGHTENING CONSENSUS FOR ANOTHER COLD MID LEVEL TROUGH TO
SLIDE ACROSS THE UPPER MIDWEST THU/THU NIGHT...WITH YET ANOTHER
ARCTIC HIGH TO DROP INTO THE NORTHERN PLAINS/UPPER MIDWEST UNDER IT.
FCST CONFIDENCE IN THE WED THRU THU NIGHT PERIOD IS GENERALLY GOOD.

STRONGER SHORTWAVE DROPPING TOWARD WESTERN IA WED THEN NORTHERN MO
WED NIGHT GENERATES MORE DIVERGENCE/LIFT ALOFT AS IT PASSES. BULK OF
THIS REMAINS WEST OF THE FCST AREA BUT DOES CLIP MAINLY THE
NORTHEAST IA PORTION OF IT. ROUND OF LOWER LEVEL THERMO-DYNAMIC
FORCING AND STRONGER 850-500MB QG CONVERGENCE SIGNAL ACCOMPANY THIS
WAVE...ALSO CLIPPING THE SOUTHWEST END OF THE FCST AREA. HOWEVER...
MODEL SOUNDINGS/X-SECTIONS SHOW THIS FORCING/LIFT IS ONCE AGAIN
BATTLING DRY AIR IN THE 900-700MB LAYER AND NORTHERLY FLOW OUT OF
THE NEXT ARCTIC HIGH BUILDING INTO THE NORTH-CENTRAL CONUS. CAN-GEM
THE MOST ROBUST WITH SATURATION AND SNOW INTO THE FCST AREA WED
WHILE GFS AND HI-RES NMM/ARW TEND TO KEEP ANY SNOW WED/WED EVENING
OUT OF THE FCST AREA. FOR NOW WILL MAINTAIN A SMALL -SN CHANCE
ACROSS MAINLY THE NORTHEAST IA PORTION OF THE FCST AREA WED...WHICH
BLENDS WELL WITH NEIGHBORING GRIDS. ONCE THIS WAVE PASSES...WED
NIGHT THRU THU NIGHT DOMINATED BY THE NEXT ARCTIC HIGH AND ITS COLD
AIRMASS SETTLING INTO THE REGION. 925MB TEMPS OF -13C TO -16C ACROSS
THE FCST AREA AT 00Z THU COOL TO AROUND -19C TO -20C FOR THU NIGHT.
850MB TEMPS FOR THE SAME TIME TRENDING 2 TO 3 STANDARD DEVIATIONS
BELOW NORMAL. WED NIGHT THRU THU NIGHT TO CONTINUE THE TREND OF MUCH
BELOW NORMAL TEMPERATURES WE/VE SEEN MUCH OF FEB. MAY YET NEED MORE
WIND CHILL ADVISORIES FOR LATE WED NIGHT/THU MORNING WITH SUB-ZERO
TEMPS AND NORTH WINDS OF 5-10MPH. USED A BLEND OF THE GUIDANCE
HIGHS/LOWS FOR WED THRU THU NIGHT...BUT WITH LIGHT WINDS/DECOUPLING
THU NIGHT LOWS COULD BE MUCH COLDER IN SHELTERED LOW LAYING AREAS.

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

MAIN FCST CONCERNS THIS PERIOD...SNOW CHANCES SAT NIGHT/SUN...
CONTINUED BELOW NORMAL TEMPERATURES THRU THE PERIOD.

MEDIUM RANGE MODEL RUNS OF 24.00Z CONTINUE TO ADVERTISE A PATTERN
SHIFT DURING THE FRI-MON PERIOD...TOWARD MORE TROUGHING OVER THE
WESTERN CONUS AND RISING HGTS OVER EASTERN NOAM. SURPRISINGLY GOOD
BETWEEN MODEL AND RUN-TO-RUN CONSISTENCY FRI INTO SUN...AT LEAST
WITH THE LONGER WAVE FEATURES. PLENTY OF LONGWAVE AND SHORTWAVE
DETAIL DIFFERENCES BY LATER SUN AND MON...BUT THIS NOT UNEXPECTED
WITH A POTENTIAL PATTERN TRANSITION IN THE DAY 6/7 TIME-FRAME.
FCST CONFIDENCE IS GENERALLY AVERAGE IN THE FRI THRU MON PERIOD.

ARCTIC HIGH PRESSURE TO BE OVER THE AREA TO START THE PERIOD...
DRIFTING SOUTHEAST FRI/FRI NIGHT...WITH A RETURN OF LOW LEVEL WARM
ADVECTION AND SLOW MODERATION TEMPS FRI INTO SAT. HGTS CONTINUE TO
RISE SAT AS TROUGHING DIGS INTO THE WESTERN CONUS. BY SAT NIGHT...
SOUTHWEST FLOW ALOFT STARTS TO SPREAD MOISTURE NORTHWARD AHEAD OF
THE WESTERN TROUGHING AND TOWARD/INTO THE FCST AREA. PLENTY OF
DETAIL DIFFERENCES WITH THIS...SFC FEATURE POSITIONS AND SHORTWAVE
ENERGY IN THE FLOW TO AID IN LIFTING. LATEST TREND/CONSENSUS
INDICATES THE DEEPER MOISTURE/GREATER LIFT...AND SNOW CHANCES SAT
NIGHT/SUN MAY REMAIN SOUTH OF THE FCST AREA. UNTIL THE DETAILS
SETTLE DOWN...SNOW CHANCES IN THE 30-50 PERCENT RANGE /HIGHEST
SOUTH/ FOR SAT NIGHT/SUN APPEAR REASONABLE. TEMPERATURES BY THE
WEEKEND LOOKING TO COME OUT OF THE DEEP-FREEZE AS THE LOW LEVEL FLOW
BECOME SOUTH AND SOUTHWEST...BUT STILL REMAINING BELOW NORMAL. HIGH
PRESSURE/DRIER AIR RETURN MONDAY HOWEVER THIS HIGH LOOKS TO BE MORE
OF PACIFIC/WESTERN CAN ORIGIN VS. ARCTIC. MODEL/ENSEMBLE CONSENSUS
OF HIGHS/LOWS FOR FRI THRU MON APPEARS WELL TRENDED AT THIS TIME.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 526 AM CST TUE FEB 24 2015

THE WARM FRONT WAS STARTING TO APPROACH BOTH TAF SITES FROM THE
WEST...WHICH HAS ALLOWED THE GRADIENT TO RELAX AND THE GUSTS TO
CALM DOWN. ONCE THE WARM FRONT GOES THROUGH...THE WINDS WILL COME
AROUND TO THE WEST AND WILL ALSO SEE THE CEILINGS COME DOWN TO
EITHER MVFR OR LOW VFR. UPSTREAM OBSERVATIONS INDICATE SOME LIGHT
SNOW IS FALLING OVER NORTHWEST MINNESOTA AND THE 24.08Z HRRR
INDICATES THIS SHOULD HOLD TOGETHER LONG ENOUGH TO PRODUCE A SHORT
WINDOW OF SOME LIGHT SNOW. THE UPSTREAM OBSERVATIONS INDICATE
EITHER IFR OR MVFR VISIBILITIES WITH THE LIGHT SNOW.
HOWEVER...WITH THE HRRR SHOWING A DIMINISHING TREND AS THE SNOW
WORKS INTO DRIER LOW LEVEL AIR...WILL ONLY TAKE THE VISIBILITY
DOWN TO MVFR. THE SNOW SHOULD END AS THE COLD FRONT COMES THROUGH
AND SWINGS THE WINDS AROUND TO THE NORTHWEST. THE 24.06Z NAM SHOWS
GOOD LOW LEVEL LAPSE RATES DEVELOPING BEHIND THE FRONT FOR ANOTHER
ROUND OF WIND GUSTS OF 25 TO 30 KNOTS. VFR CONDITIONS EXPECTED TO
DEVELOP DURING THE AFTERNOON AS THE CLOUDS SCATTER OUT AND THEN
LOOK FOR THE GUSTS TO DIMINISH AROUND SUNSET WITH THE SUSTAINED
SPEEDS DROPPING BELOW 10 KNOTS THIS EVENING.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

SHORT TERM...RRS
LONG TERM...RRS
AVIATION...04



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