674  
FXUS63 KARX 041706  
AFDARX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LA CROSSE WI  
1105 AM CST SUN DEC 4 2022  
   
DISCUSSION
 
(TODAY THROUGH SATURDAY)  
ISSUED AT 400 AM CST SUN DEC 4 2022  
 
KEY MESSAGES:  
 
- NARROW (40-50 MILES WIDE) BAND OF LIGHT SNOW FALLS MONDAY  
MORNING. STILL ASSESSING THE EXACT BAND LOCATION, BUT AMOUNTS  
ARE EXPECTED TO BE LESS THAN AN INCH WITH MINIMAL TRAVEL  
IMPACTS.  
 
- LOW (20%) RISK OF LIGHT SNOW ON TUESDAY, WITH A STRONGER SYSTEM  
POSSIBLY IMPACTING THE REGION ON THURSDAY.  
 
- MODERATING TEMPERATURES FOR THE UPCOMING WEEK.  
 
UPCOMING WEEK: MODERATING TEMPERATURES  
 
SOUTHWESTERLY FLOW BECAME ESTABLISHED OVERNIGHT AND PERSISTS  
THROUGH MIDDAY MONDAY. AFTER OUR BRIEF BOUT OF ARCTIC AIR  
YESTERDAY, HIGHS TODAY CLIMB BACK INTO THE 30S. WINDS REMAIN  
ELEVATED TONIGHT AND PREVENT LOWS FROM FALLING TOO FAR, ENABLING  
HIGHS ON MONDAY TO STILL REACH THE 30S BEFORE A COLD FRONT PASSES  
THROUGH. THE FLOW WEAKENS FOR TUESDAY AND WEDNESDAY UNDER A PAIR  
OF RIDGES. TUESDAY SHOULD BE THE COOLEST DAY OF THE PERIOD IN THE  
WAKE IF THE FRONT WITH HIGHS ON WEDNESDAY HINGING ON HOW QUICKLY  
RETURN FLOW ARRIVES. BY THURSDAY WE SHOULD SEE AN INCREASING FETCH  
OF SOUTHERLY FLOW AHEAD OF THE NEXT SYSTEM LIFTING FROM THE  
SOUTHWEST. EVEN IN THE WAKE OF THIS LOW THERE IS LITTLE IN THE WAY  
OF UPSTREAM POLAR AIR, THUS TEMPERATURES SHOULD REMAIN SEASONAL  
RIGHT INTO NEXT WEEKEND. THIS IS REFLECTED WELL IN THE NBM  
PERCENTILE PROGS WITH MINIMAL SPREAD NOTED IN THE SEVEN DAY PERIOD  
ASIDE FROM WEDNESDAY.  
 
MONDAY: NARROW BAND OF LIGHT SNOW  
 
DESPITE BEING ONLY ABOUT 24 HOURS OUT, A NUMBER OF SMALL BUT  
MEANINGFUL ISSUES CHIP AWAY AT THE CONFIDENCE FOR THE MONDAY  
MORNING SNOW BAND. CONFIDENCE IS HIGH THAT WE WILL SEE A SNOW  
BAND, BUT IT SHOULD BE VERY NARROW IN NATURE--POSSIBLY ONLY A  
COUNTY OR TWO WIDE--AS IT SLIDES WEST TO EAST THROUGH THE  
FORECAST AREA. THE FORCING FOR ASCENT WILL BE MESOSCALE, MODEST,  
AND BRIEF (2-4 HOURS) IN NATURE AT ANY GIVEN LOCATION. LASTLY, A  
DRY LOWER TROPOSPHERE WILL SUBLIMATE AND FURTHER CONSTRICT THE  
AREAS IMPACTED BY THE BAND.  
 
ALL COMBINED, IT IS EASY TO SEE HOW NORMAL VARIABILITY IN THE  
GUIDANCE AT THIS TIME RANGE FROM AN EVENT COULD MEAN THE  
DIFFERENCE BETWEEN NO SNOW AND A QUICK 0.5-1.0". DID TREND POPS  
HIGHER (AND BROADER) SINCE THE QUESTION HAS SHIFTED TO WHERE WILL  
THE BAND SET UP VERSUS WHETHER A BAND WILL FORM, BUT THE  
AFOREMENTIONED ISSUES PREVENT HONING IN ON A SPECIFIC CORRIDOR  
FOR HIGHER POPS. THAT MAY NOT BE FEASIBLE UNTIL WE ARE 6-12 HOURS  
AWAY FROM THE ONSET OF SNOW.  
 
BOTTOM LINE, IMPACTS FROM THIS SNOW BAND ARE LOOKING TO BE LOW  
AND CONFINED IN SPACE AND TIME. VISIBILITIES MAY BRIEFLY FALL TO  
1/2 A MILE IN THE HEAVIEST SNOW FOR AN HOUR OR TWO. WHEN DEALING  
WITH MESOSCALE SNOW BANDS, THERE IS ALWAYS A RISK THAT IF THE  
FORCING IS STRONGER OR MOISTURE DEEPER THEN EXPECTED, SNOW AMOUNTS  
COULD QUICKLY INCREASE. INDEED, A FEW EXPLICIT MEMBERS DO  
HIGHLIGHT THIS ALBEIT LOW (< 5-10%) POTENTIAL. THE SHORT-LIVED  
NATURE OF THE BAND LIMITS THE PLAUSIBLE RANGE OF SNOW AMOUNTS, BUT  
THE FAR OUTLIER SOLUTIONS ARE NEARING 2".  
 
TUESDAY: SECOND ROUND OF LIGHT SNOW  
 
WE GO THROUGH THIS SAME GAME WITH SNOW POTENTIAL FOR TUESDAY AS A  
WEAK PERTURBATION IN THE CYCLONIC FLOW SPAWNS ANOTHER THIN  
CORRIDOR OF MID-LEVEL ISENTROPIC ASCENT/FGEN FORCING THAT BATTLES  
AGAINST A DRIER NEAR-SURFACE AIRMASS. QPF PROGS DEPICT A NARROW  
REGION OF LIGHT SNOW, BUT CONFIDENCE IN PLACEMENT OF THE BAND IS  
EVEN LESS THAN FOR MONDAY'S EVENT AND HAVE LEFT THE 20% NBM POPS  
UNCHANGED. AS WITH TOMORROW'S BAND, SNOW AMOUNTS SHOULD BE LIGHT  
AND IMPACTS LOW.  
 
THURSDAY: BETTER POTENTIAL FOR WIDESPREAD PRECIPITATION  
 
AS THE LONGWAVE OVER THE WESTERN CONUS PROGRESSES EASTWARD  
MIDWEEK, MEDIUM RANGE SOLUTIONS ARE CONVERGING ON A LEE CYCLONE  
EJECTING FROM THE FRONT RANGE AND TRACKING THROUGH THE MID-  
MISSISSIPPI RIVER VALLEY THURSDAY/THURSDAY NIGHT. TIMING  
DIFFERENCES ARISE AT THIS POINT WITH ABOUT 12 HOURS OF SPREAD  
BETWEEN THE VARIOUS CLUSTERS. THE INTRA-MODEL VARIABILITY IS ALSO  
SOMEWHAT FLUID AND STILL HONING IN ON THE TRACK OF THE LOW.  
COMPARED TO YESTERDAY, THERE HAS BEEN A NORTHWARD SHIFT IN THE  
SYSTEM AND ITS ATTENDANT DEFORMATION BAND--FURTHER INTO THE  
FORECAST AREA. THIS SYSTEM PRESENTS THE NEXT OPPORTUNITY FOR  
WIDESPREAD PRECIPITATION. LOWER TROPOSPHERIC THERMAL PROFILES WILL  
PLAY A KEY ROLE IN PRECIPITATION TYPE AND ONLY A COUPLE DEGREE  
SHIFT COULD QUICKLY CHANGE THE FORECAST. WITH THE GUIDANCE NOW  
LOCKING IN ON THE CYCLONE STRUCTURE, THERE HAS BEEN A NOTABLE  
UPTICK IN THE >3" SNOW PROBABILITIES (30-40%) OVER IOWA WITH THE  
00Z EPS. THIS IS CERTAINLY A SYSTEM TO WATCH OVER THE COMING DAYS.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)  
ISSUED AT 1105 AM CST SUN DEC 4 2022  
 
PERIODS OF LIGHT SNOW MONDAY WITH POTENTIAL FOR VERY NARROW BAND OF  
MVFR/IFR SNOW. POSITIONING UNCLEAR. AMOUNTS WILL BE RELATIVELY  
MINOR, GENERALLY UNDER 1".  
 
CIGS: INCREASING CLOUDS OVERNIGHT WITH A LOWERING TOWARD 12Z.  
POTENTIAL TO DROP INTO MVFR WITH RELATED BANDS OF SNOW, BUT LOCATION  
OF THIS RELATIVELY NARROW BAND OF LOWER CIGS IS UNCERTAIN...AND WILL  
HOLD VFR CIGS FOR THE MOMENT. EXPECT SOME IMPROVEMENT LATER IN THE  
MORNING AS FIRST SNOW BAND EXITS, BUT CHANCE FOR MORE LATER IN THE  
AFTERNOON, AND POTENTIALLY ANOTHER LOWERING IN CIGS.  
 
WX/VSBY: LIGHT SNOW MOVES IN TOWARD 12Z MONDAY. GENERALLY MVFR  
VSBYS, BUT A NARROW BAND OF IFR LOOKS LIKELY. WHETHER THAT WOULD  
IMPACT THE TAF SITES IS UNCLEAR. EXPECT SOME TAPERING OFF IN THE  
LATE MORNING WITH MORE LIGHT SNOW BY MID AFTERNOON. THIS AREA COULD  
SHIFT JUST NORTH OF KRST/KLSE. OVERALL ACCUMULATIONS APPEAR MINOR AT  
THIS TIME.  
 
WINDS: SOUTHERLY INTO TONIGHT, SWINGING NORTHWEST BY MID/LATE  
MORNING MONDAY AS A COLD FRONT PUSHES THROUGH. SOME LLWS CONCERNS AT  
KLSE FROM MID TO LATE EVENING TONIGHT WITH 1.5-2KFT WINDS NEARING  
40KTS.  
 

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

 
 

 
 
DISCUSSION...SKOW  
AVIATION.....RIECK  
 
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