908  
FXUS63 KARX 172030  
AFDARX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LA CROSSE WI  
230 PM CST WED JAN 17 2018  
   
SHORT TERM
 
(THIS EVENING THROUGH THURSDAY)  
ISSUED AT 230 PM CST WED JAN 17 2018  
 
AT 2 PM, A TIGHT SOUTHWEST SURFACE PRESSURE GRADIENT WAS BRINGING  
SLIGHTLY WARMER AIR INTO THE REGION FROM THE CENTRAL PLAINS.  
TEMPERATURES RANGED FROM THE UPPER TEENS INTO MID-20S.  
 
FOR TONIGHT, A SHORT WAVE RIDGE WILL BUILD ACROSS THE REGION. THIS  
WILL KEEP SKIES MAINLY CLEAR. THIS WILL ALLOW A NOCTURNAL INVERSION  
TO BUILD ACROSS THE AREA. THIS INVERSION WILL BE THE STRONGEST IN  
CENTRAL WISCONSIN WHERE WINDS WILL FALL TO AROUND 5 MPH DURING THE  
OVERNIGHT. DUE TO THIS, LOWERED THE TEMPERATURES A FEW DEGREES  
LOWER THAN MOS.  
 
ON THURSDAY MORNING, A SHORTWAVE TROUGH WILL MOVE QUICKLY SOUTHEAST  
ACROSS THE NORTHERN MINNESOTA AND NORTHERN WISCONSIN. WITH LIMITED  
MOISTURE ACROSS THE REGION. ONLY EXPECTING SOME CLOUDS WITH ITS  
PASSAGE.  
 
WITH 925 MB TEMPERATURES AROUND 3C WARMER THAN THIS AFTERNOON, THE  
HIGH TEMPERATURES SHOULD EASILY CLIMB INTO THE LOWER AND MID-30S ON  
THURSDAY AFTERNOON. THIS SHOULD ALLOW THE LOW WATER SNOW CONTENT TO  
COMPRESS EVEN MORE.  
   
LONG TERM
 
(THURSDAY NIGHT THROUGH WEDNESDAY)  
ISSUED AT 230 PM CST WED JAN 17 2018  
 
HIGHLIGHTS THROUGH THIS PERIOD INCLUDE MILD TEMPS INTO THE WEEKEND  
FOLLOWED BY A POTENTIAL IMPACTFUL SYSTEM SUN/MON.  
 
THE UPPER AIR PATTERN WILL CONTINUE TO FLATTEN LATE THIS WEEK. ON  
FRIDAY VERY MILD 850 MB TEMPS AS HIGH AS 10-12C WILL OVERSPREAD  
THE AREA AHEAD OF A PACIFIC COLD FRONT SWEEPING THROUGH LATE  
ASSOCIATED WITH A LOW PRESSURE SYSTEM PASSING WELL NORTH ACROSS  
CANADA. THESE 850 MB TEMPS CORRESPOND TO NAEFS STANDARD ANOMALIES  
OF +2 TO +3. WITH SOUTHERLY WINDS BECOMING MORE SOUTHWESTERLY  
AHEAD OF THE FRONT, THIS SET-UP WOULD SUPPORT HIGHS AT LEAST INTO  
THE LOW 40S IN SPOTS, DEPENDING ON HOW THICK ANY MID/HIGH CLOUDS  
ARE ALONG WITH INFLUENCES FROM THE SNOWCOVER. BEHIND THE WEAK  
FRONT, LITTLE CHANGE IN TEMPS IS EXPECTED, WITH WELL ABOVE AVERAGE  
HIGHS ON SATURDAY, ALBEIT WITH MORE CLOUD COVER THAN FRIDAY.  
 
THE MAIN PERIOD OF INTEREST REMAINS THE SUNDAY-MONDAY TIMEFRAME AS  
WE CONTINUE TO MONITOR A STORM SYSTEM EXPECTED TO LIFT UP TOWARDS  
THE AREA FROM THE SOUTHWEST. 17.12Z GUIDANCE INDICATES THE UPPER  
SHORTWAVE TROUGH EJECTING FROM THE ROCKIES WILL BE CLOSED OFF  
SOMEWHERE ACROSS THE MIDWEST BY MONDAY. PLENTY OF GULF MOISTURE  
SHOULD BE TAPPED WITH THIS SYSTEM AS STRONG NORTHWARD LOW-LEVEL  
MOISTURE TRANSPORT INCREASES AHEAD OF THE LOW. THERE ARE STILL  
CONSIDERABLE DIFFERENCES AMONG MODEL SOLUTIONS WITH THE PLACEMENT  
OF THE SURFACE LOW TRACK, IMPACTING HOW MUCH WARM AIR IS FED  
NORTHWARD INTO THE AREA, AND CONSEQUENTLY PRECIP TYPES. THE 17.12Z  
DETERMINISTIC MODELS (EC/GFS/CANADIAN) SHOWED A BIT OF A WESTWARD  
SHIFT WITH THE SURFACE LOW TAKING IT UP THROUGH IOWA AND  
WISCONSIN SUNDAY NIGHT INTO MONDAY WITH PERHAPS SOME LIGHT MIXED  
PRECIP SATURDAY NIGHT INTO SUNDAY AND THE BULK OF THE PRECIP  
HOLDING OFF UNTIL LATER SUNDAY INTO MONDAY. HOWEVER, GIVEN THE  
LACK OF CONSISTENCY AMONG SOLUTIONS WITH PLACEMENT/TIMING OF THE  
LOW AND STILL LARGE ENVELOPE OF POSSIBLE SOLUTIONS IN THE ENSEMBLE  
GUIDANCE WHICH WOULD HAVE SIGNIFICANT IMPACTS ON PRECIP TYPES AND  
AMOUNTS, CONFIDENCE IN SPECIFICS REMAINS LOW. WHILE CONSENSUS  
CONTINUES TO INCREASE THAT AN IMPACTFUL STORM SYSTEM WILL AFFECT  
THE UPPER MIDWEST DURING THE LATER SUNDAY-MONDAY TIMEFRAME, IT  
REMAINS TOO EARLY TO DISCERN IMPACTS TO THE LOCAL AREA.  
 
BEHIND THE SYSTEM, NOT MUCH IN THE WAY OF COLD AIR IS EXPECTED, SO  
TEMPS LOOK TO REMAIN NEAR SEASONAL AVERAGES INTO THE MIDDLE OF NEXT  
WEEK. THERE COULD BE A FEW UPPER WAVES IMPACTING THE AREA WITHIN  
WEST TO NORTHWEST FLOW, BUT NOTHING SIGNIFICANT.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)  
ISSUED AT 1134 AM CST WED JAN 17 2018  
 
THE PRIMARY CONCERN FOR THIS TAF PERIOD WILL BE THE LOW LEVEL WIND  
SHEAR FROM LATE THIS AFTERNOON TO AROUND 18.08Z. IT WILL RANGE  
FROM 40 TO 45 KNOTS DURING THIS TIME FRAME.  
 

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

 
 

 
 
SHORT TERM...BOYNE  
LONG TERM...JM  
AVIATION...BOYNE  
 
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