677  
FXUS63 KARX 301853  
AFDARX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LA CROSSE WI  
153 PM CDT SUN APR 30 2017  
   
SHORT TERM
 
(THIS EVENING THROUGH TUESDAY NIGHT)  
ISSUED AT 153 PM CDT SUN APR 30 2017  
 
EARLY THIS AFTERNOON, WATER VAPOR SATELLITE IMAGERY AND SURFACE  
ANALYSIS SHOWED A LARGE, ALMOST VERTICALLY STACKED SYSTEM OVER  
SOUTHERN KANSAS. LOCAL AND REGIONAL RADARS SHOWING TWO MAIN BANDS  
OF PRECIPITATION, ONE FROM NORTHWEST WISCONSIN INTO EASTERN  
NEBRASKA AND THE OTHER FROM CENTRAL ILLINOIS ACROSS SOUTHERN IOWA  
AND NORTHERN MISSOURI INTO NEBRASKA AND KANSAS. IN BETWEEN THESE  
TWO BANDS, NOT MUCH WAS HAPPENING OTHER THAN SOME OCCASIONAL VERY  
LIGHT SHOWERS OR SPRINKLES.  
 
THE 30.12Z MODELS ARE IN AGREEMENT IN MAINTAINING THE UPPER LEVEL  
LOW AS A CLOSED SYSTEM AS IT LIFTS NORTHEAST ACROSS THE GREAT  
LAKES AND INTO SOUTHERN ONTARIO LATE MONDAY NIGHT INTO TUESDAY  
MORNING. THIS WILL TAKE THE SURFACE LOW FROM NORTHEAST KANSAS  
ACROSS EASTERN IOWA TO NORTHEAST WISCONSIN THROUGH MONDAY  
AFTERNOON. SEVERAL SHORT WAVE TROUGHS WILL ROTATE AROUND THE UPPER  
LEVEL LOW AND ARE EXPECTED TO BRING MODERATE TO AT TIMES STRONG PV  
ADVECTION IN THE 500-300 MB LAYER ACROSS THE AREA OVERNIGHT INTO  
MONDAY MORNING. THE BEST LOW LEVEL MOISTURE TRANSPORT WILL OCCUR  
THIS EVENING WHEN THIS WILL BE AIMED RIGHT INTO THE FORECAST AREA.  
THIS WILL THEN MOVE OFF TO THE EAST OVERNIGHT BUT START TO BEND  
BACK TO THE NORTHWEST AROUND THE UPPER LEVEL LOW AND FEED INTO THE  
DEFORMATION BAND. THE FRONTOGENESIS WITH THIS SYSTEM WILL BE DEEP,  
EXTENDING FROM THE SURFACE UP TO 300 MB, AND BE MODERATE TO AT  
TIMES STRONG IN STRENGTH. THIS WILL START TO MOVE IN LATE THIS  
AFTERNOON AND THEN REMAIN OVER THE REGION TONIGHT. THE UPPER LEVEL  
PORTION OF THIS WILL MOVE OFF TO THE NORTHEAST MONDAY WHILE THE  
LOW LEVEL, 1000-700 MB LAYER, WILL BE WEAK BUT LINGER OVER THE  
AREA THROUGH MONDAY. ON THE 290K ISENTROPIC SURFACE, THE UP GLIDE  
WILL ARRIVE IN CONJUNCTION WITH THE FRONTOGENESIS AND SHOULD BE  
ON THE ORDER OF 2 TO 5 UBAR/S THIS EVENING. THIS WILL DIMINISH  
OVERNIGHT INTO THE 1 TO 2 UBAR/S RANGE OVERNIGHT AND THEN CONTINUE  
INTO MONDAY MORNING AS THE TROWAL WRAPS AROUND THE UPPER LEVEL  
SYSTEM TONIGHT AND THEN MOVES ACROSS THE REGION. WITH ALL THIS  
FORCING, EXPECTING THE BAND OF SHOWERS ACROSS IOWA AND MISSOURI  
TO LIFT INTO THE AREA THIS EVENING AND THEN MOVE ACROSS THE AREA  
THROUGH THE NIGHT. EVEN THOUGH THE FORCING WILL BE MUCH WEAKER  
MONDAY, STILL EXPECTING AN PROLONGED PERIOD OF LIGHT RAIN AS THE  
FRONTOGENESIS AND TROWAL/ISENTROPIC UP GLIDE MOVES ACROSS THE  
AREA, BUT THERE MAY NOT BE A LOT OF QPF WITH AMOUNTS GENERALLY  
UNDER A TENTH OF AN INCH. THERE MAY STILL BE A LITTLE BIT OF  
LINGERING PRECIPITATION INTO MONDAY NIGHT WHEN ENOUGH COLD AIR  
WORKS IN THAT SOME SNOW COULD MIX IN WITH THE LIGHT RAIN. NOT  
EXPECTING ANY ACCUMULATION AS AMOUNTS WILL BE VERY LIGHT. ALL THE  
PRECIPITATION WILL THEN END TUESDAY AS THE SYSTEM MOVES OFF INTO  
CANADA.  
   
LONG TERM
 
(WEDNESDAY THROUGH SUNDAY)  
ISSUED AT 153 PM CDT SUN APR 30 2017  
 
NORTHWEST FLOW WILL BE ESTABLISHED BEHIND THE CURRENT SYSTEM. THIS  
WILL ALLOW A SHORT WAVE TROUGH TOPPING THE WESTERN UPPER LEVEL  
RIDGE TO MOVE OVER THE MISSOURI RIVER VALLEY WEDNESDAY. THIS WILL  
THEN FORM ANOTHER UPPER LEVEL LOW OVER THE MIDDLE MISSISSIPPI  
RIVER VALLEY WEDNESDAY NIGHT THAT THEN LIFTS NORTHEAST THROUGH THE  
OHIO RIVER VALLEY THURSDAY AND THURSDAY NIGHT. SOME SHOWERS FROM  
THIS SYSTEM COULD IMPACT THE AREA FROM WEDNESDAY AFTERNOON INTO  
THURSDAY BEFORE THE FORCING SHIFTS WELL AWAY FROM THE AREA. THE  
REST OF THE WEEK THEN LOOKS DRY AS THE UPPER LEVEL RIDGE SHIFTS  
EAST OVER THE MIDWEST.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)  
ISSUED AT 1218 PM CDT SUN APR 30 2017  
 
LOW PRESSURE OVER THE SOUTHERN PLAINS WILL ROTATE NORTHEAST INTO  
THE REGION TONIGHT. MOISTURE SURGING AROUND THIS SYSTEM WILL  
SPREAD SHOWERS AND ISOLATED THUNDERSTORMS INTO THE AREA BY LATER  
THIS AFTERNOON INTO THIS EVENING. WAS NOT CONFIDENT ENOUGH TO  
INCLUDE THUNDERSTORMS IN THE TAFS AS STORMS WILL BE ISOLATED IN  
COVERAGE. THE BULK OF THE RAIN LOOKS TO PUSH NORTH OF THE  
KRST/KLSE SITES AFTER MIDNIGHT. OTHERWISE, LOOK FOR MVFR  
CONDITIONS EARLY THIS AFTERNOON TO DETERIORATE INTO IFR/LIFR  
CONDITIONS AS CLOUD CEILINGS/VISIBILITY COME DOWN WITH THE  
APPROACH OF THE STORM SYSTEM. GUSTY NORTHEAST WINDS ARE EXPECTED  
TO BECOME LIGHT AND VARIABLE AFTER MIDNIGHT AS THE SURFACE LOW  
MOVES IN OVERHEAD. THIS LOW WILL REMAIN OVERHEAD FOR MONDAY FOR  
SCATTERED SHOWERS AMD CONTINUED IFR CONDITIONS.  
 

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

 
 

 
 
SHORT TERM...04  
LONG TERM...04  
AVIATION...DAS  
 
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