693  
FXUS63 KARX 201126  
AFDARX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LA CROSSE WI  
526 AM CST WED FEB 20 2019  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 327 AM CST WED FEB 20 2019  
 
MAIN SHORT-TERM FCST CONCERNS ARE SNOW AMOUNTS/POSSIBLE FZDZ TODAY  
INTO THIS EVENING.  
 
DATA ANALYSIS AT 06Z HAD INCREASING MOISTURE/FORCING/LIFT UNDER  
DIFFLUENT MID/UPPER FLOW SPREADING ACROSS THE REGION. THIS AHEAD OF A  
STRONG SHORTWAVE TROUGH LIFTING NE ACROSS THE CENTRAL PLAINS.  
WIDESPREAD SNOW WAS DEVELOPING/SPREADING NE ACROSS THE REGION WITH  
THE LEADING EDGE ALREADY NORTH OF KAUM-KDEH-KPDC-KMRJ LINE, AND  
LIFTING NE AROUND 15 MPH. MOST VSBYS IN THE SNOW FROM SE SD TO SW WI  
AND ACROSS MUCH OF IA IN THE 1/2 TO 2 MILE RANGE, WITH REPORTS OF  
1/2 TO 1 1/2 INCHES OF SNOW IN A RATHER SHORT PERIOD OF TIME MAKING  
ROADS SLIPPERY.  
 
MODEL RUNS OF 20.00Z INITIALIZED WELL. MODELS OFFER QUITE SIMILAR  
SOLUTIONS AS THE VIGOROUS SHORTWAVE TROUGH/ENERGY LIFTS QUICKLY THRU  
THE REGION TODAY THEN HGTS RISE BEHIND IT TONIGHT AS STRONG  
TROUGHING RE-LOADS IN THE SW CONUS. SHORT-TERM FCST CONFIDENCE IS  
GOOD THIS CYCLE.  
 
DEEP LAYERED FORCING/LIFT, FROM LOWER LEVEL WARM ADVECTION/  
ISENTROPIC LIFT AND SOME F-GEN THRU STRONG 500-300MB PV ADVECTION  
AND DIVERGENCE ALOFT WITH AT LEAST PARTLY COUPLED 300-250MB JET  
MAXES, TO BE LIFTING ACROSS THE FCST AREA WITH THE SHORTWAVE THIS  
MORNING INTO EARLY THIS AFTERNOON. THIS WITH AROUND 0.50 INCH OF PW  
IN THE INFLOW AIRMASS. MODEL/ENSEMBLE CONSENSUS OF QPF PRODUCTION  
AND SNOW-WATER RATIOS OF 15:1 SHOW QUICK-HITTER SNOW EVENT FOR TODAY  
LOOKS ON TRACK WITH TOTALS OF 4 TO 8 INCHES, PERHAPS LOCALLY A BIT  
MORE WEST A KRST TO KOLZ LINE. SNOWFALL RATES OF 1 INCH/HR LOOKING  
LIKELY AT TIMES FOR MUCH OF THE AREA THIS MORNING. HAVE EXPANDED  
WINTER STORM WARNING INTO JACKSON/CLARK/TAYLOR COUNTIES WITH 6+  
INCHES OF SNOW NOW EXPECTED THERE, WITH LAYOUT OF THE REST OF THE  
HEADLINES APPEARING GOOD AT THIS TIME. SNOW ON TRACK TO DIMINISH  
FROM SW TO NE DURING THE MID AFTERNOON THRU EARLY EVENING HOURS  
AS THE MID LEVEL SHORTWAVE PASSES AND LIFT WANES.  
 
STILL POTENTIAL FOR LOSS OF ICE NUCLEATION IN THE CLOUD TOPS THE  
SOUTHEAST SIDE OF THE FCST AREA FROM MID MORNING THRU THIS AFTERNOON  
AS MID LEVEL DRYING WOULD WORK AROUND THE PASSING SHORTWAVE.  
CONTINUED WITH A MENTION OF SOME -FZDZ ACROSS ROUGHLY THE SE 1/4 OF  
THE FCST AREA MUCH OF TODAY, WITH A LIGHT GLAZE OF ICE ALONG WITH  
THE SNOW ACCUMULATIONS.  
   
LONG TERM
 
(THURSDAY THROUGH TUESDAY)  
ISSUED AT 327 AM CST WED FEB 20 2019  
 
FOR THURSDAY THRU FRIDAY NIGHT: MAIN FCST CONCERNS THIS PERIOD ARE  
RETURNING PRECIP CHANCES/TYPES WITH THE NEXT SYSTEM FRI NIGHT.  
 
MODEL RUNS OF 20.00Z IN GOOD AGREEMENT FOR RISING HGTS/BROAD RIDGING  
ALOFT TO BUILD ACROSS THE UPPER MIDWEST THU THRU FRI AS STRONG  
SHORTWAVE TROUGHING SPINS EAST ALONG THE US/MEX BORDER. MODELS  
OFFERING A TIGHTENING CONSENSUS ON THIS TROUGHING AS IT MOVES INTO  
WEST TX FRI NIGHT, BUT DETAIL DIFFERENCES WITH THE NORTHERN STREAM  
PORTION OF THE TROUGH INTO THE NORTHERN PLAINS FRI NIGHT. EVEN WITH  
SOME DIFFERENCES FRI NIGHT, FCST CONFIDENCE THIS PERIOD IS GENERALLY  
GOOD.  
 
MUCH OF THIS PERIOD LOOKING TO THE QUIET-BETWEEN-SYSTEMS PERIOD AS  
HIGH PRESSURE FROM THE PLAINS BUILDS EAST ACROSS THE REGION UNDER  
THE RISING HGTS/BROAD RIDGING/SW FLOW ALOFT. A BIT OF A COOLER DAY  
THU WITH SOME WEAK COLD ADVECTION OVER ANOTHER 4 TO 8 INCHES OF  
FRESH, HIGH ALBEDO SNOW COVER. WOULD HAVE TO WATCH THU NIGHT FOR  
LOWS BOTTOMING OUT AGAIN THU NIGHT (LIKE TUE MORNING) WITH THE  
HIGH OVERHEAD AND THE DEEP SNOW COVER. HOWEVER MID/HIGH LEVEL  
MOISTURE STREAMING NE AHEAD OF THE NEXT TROUGH ALREADY PROGGED  
OVER THE AREA THU NIGHT. LOOKS LIKE LOWS PERHAPS THU EVENING, THEN  
STEADY/SLOWLY RISING TEMPS OVERNIGHT. A MILDER DAY FRI AS  
STRONGER LOW LEVEL WARM ADVECTION SPREADS NORTH ACROSS THE AREA,  
EVEN UNDER MOSTLY CLOUDY SKIES. CONSENSUS HIGHS NEAR TO A BIT  
ABOVE NORMAL FRI REASONABLE.  
 
DEPARTING HIGH FRI LEAVES A DRIER AIRMASS OVER THE AREA FOR FRI, BUT  
INCREASING MOISTURE AHEAD OF BOTH THE SOUTHERN AND NORTHERN STREAM  
PORTIONS OF THE TROUGH TO OVERCOME THIS FRI NIGHT, WITH ENOUGH  
MOISTURE/LIFT IN THE COLUMN FOR PRECIP CHANCES FRI NIGHT. PRECIP  
TYPE IS PROBLEMATIC WITH THE WARM ADVECTION FROM FRI PUSHING AN  
ELEVATED WARM LAYER NORTHWARD INTO THE AREA. THERE ARE ALSO  
POTENTIAL ISSUES WITH WARMER CLOUD TOPS AND LACK OF ICE NUCLEATION.  
PERHAPS SOME -SN ACROSS THE FCST AREA FRI EVENING, THEN MORE OF A  
WINTRY MIX OVERNIGHT WITH A STRONGER SIGNAL FOR LOSS OF ICE IN THE  
CLOUDS.  
 
FOR SATURDAY THRU TUESDAY (DAYS 4 TO 7): MAIN FCST CONCERN THIS  
PERIOD IN THE STRONG SYSTEM LIFTING NE ACROSS THE REGION SAT INTO SUN  
AND PRECIP TYPES/AMOUNTS WITH IT.  
 
MEDIUM RANGE MODEL RUNS OF 20.00Z OFFERING A TIGHTENING CONSENSUS ON  
THE NEXT STRONG SW FLOW TROUGH/SHORTWAVE LIFTS OUT OF TX SAT TO  
LOWER MI BY 12Z SUN. GOOD AGREEMENT ON QUASI-ZONAL FLOW OVER THE  
REGION MON THEN ANOTHER SHORTWAVE TROUGH TO APPROACH FROM THE WEST  
ON TUE. DAY 4-7 FCST CONFIDENCE IS AVERAGE THIS CYCLE.  
 
ATTENTION THIS PERIOD IS SQUARELY FOCUSED ON THE SW FLOW WAVE TO  
LIFT TOWARD/ACROSS THE REGION SAT/SAT NIGHT. PRESENT CONSENSUS TRACK  
PUTS THE FCST AREA IN THE DEFORMATION BAND OF PRECIP ON THE NW SIDE  
OF THIS SYSTEM AS IT PASSES. INITIALLY THE COLUMN IS LOOKING RATHER  
WARM FOR SAT WITH BL TEMPS IN THE 30S 850MB TEMPS ABOVE 0C ACROSS  
MUCH OF THE FCST AREA. BULK OF ANY PRECIP SAT LOOKING TO BE -RA OR A  
-RA/-FZRA MIX. BY SAT NIGHT AS THE MID LEVEL LOW/SHORTWAVE APPROACH  
BROAD/STRONG DYNAMIC LIFTING OF THE COLUMN COOLS IT WITH PRECIP SAT  
NIGHT RAPIDLY CHANGING TO SNOW. SEVERAL INCHES OF SNOW THEN POSSIBLE  
SAT NIGHT INTO SUN MORNING, ALONG WITH STRONG WINDS FOR BLOWING/  
DRIFTING OF ANY NEW SNOW. HIGH PRECIP CHANCES LOOK IN ORDER FOR  
LATER SAT INTO SUN MORNING, BUT GIVEN INHERENT TRICKINESS WITH  
PRECIP TYPES DRIVEN BY BL TEMPS AND WARM LAYERS ALOFT, PRECIP TYPES  
AND ANY SNOW AMOUNTS ARE FAR FROM CERTAIN. AND ALL THIS COULD STILL  
SHIFT NORTH OR SOUTH OF THE FCST AREA WITH LATER MODEL RUNS. FOR NOW  
THE MODEL/ENSEMBLE CONSENSUS IN THE FCST GRIDS (ITS STILL 4-5 DAYS  
AWAY) IS A GOOD PLACE TO START. AFTER A BRIEF BREAK SUN NIGHT INTO  
MON, THE NEXT SHORTWAVE COMING EAST ACROSS THE NORTHERN PLAINS  
SPREADS SNOW CHANCES (COLDER COLUMN WITH THIS ONE) BACK INTO THE  
FCST AREA FOR TUE.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)  
ISSUED AT 526 AM CST WED FEB 20 2019  
 
MVFR/IFR CIGS AND IFR VSBYS IN SNOW ARE GOING TO PREVAIL AT THE TAF  
SITES THRU THE MORNING INTO THE EARLY AFTERNOON HOURS. BY THE TIME  
THE SNOW STARTS TO TAPER OFF DURING THE MID AFTERNOON HOURS, SNOW  
AMOUNTS OF 4-6 INCHES ARE EXPECTED AT KLSE, WITH 6-8 INCHES AT KLSE.  
AS THE SYSTEM QUICKLY LIFTS NE OF THE AREA, VSBYS EXPECTED TO BACK  
UP TO VFR BY 00Z THU. HOWEVER, AS IS TYPICAL BEHIND WINTER SYSTEMS,  
AN MVFR STRATO-CU DECK IS SET TO LINGER FOR A TIME AFTER THE PRECIP  
EXITS. THIS MVFR DECK LOOKS TO PERSIST AT THE TAF SITES THROUGH THE  
EVENING HOURS, THEN GRADUALLY BREAK UP/BECOME SCATTERED AFTER  
MIDNIGHT. BRISK E/SE WINDS THIS MORNING WILL SWING SOUTH THRU THE  
AFTERNOON, THEN BECOME WESTERLY DURING THE OVERNIGHT HOURS TONIGHT.  
 

 
   
ARX WATCHES/WARNINGS/ADVISORIES
 
 
WI...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR WIZ032>034.  
 
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR  
WIZ041>044-053>055-061.  
 
WINTER STORM WARNING UNTIL 9 PM CST THIS EVENING FOR WIZ017-029.  
 
MN...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR MNZ079-  
086>088-094>096.  
 
IA...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR IAZ008>010-  
018-019-029.  
 
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR IAZ011-  
030.  
 

 
 

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