559  
FXUS63 KARX 121955  
AFDARX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LA CROSSE WI  
255 PM CDT SUN JUL 12 2020  
   
SHORT TERM
 
(THIS EVENING THROUGH MONDAY)  
ISSUED AT 245 PM CDT SUN JUL 12 2020  
 
EARLY AFTERNOON ANALYSIS SHOWED UPPER LEVEL RIDGING STARTING TO  
WORK IN FROM THE WEST, WITH PLENTY OF CUMULUS CLOUDS AROUND THE  
REGION. WATER VAPOR IMAGERY DID SHOW A VERY WEAK WAVE SLIDING  
THROUGH AREAS EAST OF THE MISSISSIPPI RIVER AND MODEL SOUNDINGS  
INDICATED A BIT OF INSTABILITY IN THE CUMULUS LAYER, SO COULD SEE  
A FEW ISOLATED SHOWERS DEVELOP. HOWEVER, WITH A STOUT CAP RIGHT  
ABOVE THE CUMULUS LAYER, THE RIDGING BUILDING IN, AND FAIRLY DRY  
AIR, WOULD EXPECT THOSE TO BE FEW AND FAR BETWEEN IF THEY DEVELOP  
AT ALL.  
 
TONIGHT, COULD SEE SOME PATCHY FOG AROUND THE AREA GIVEN MOSTLY  
CLEAR SKIES AND LIGHT WINDS FOR A BULK OF THE NIGHT, THOUGH A  
TIGHTER PRESSURE GRADIENT WILL BE BUILDING IN FROM THE WEST.  
OTHERWISE, LOW TEMPERATURES WILL BE IN THE 50S TO LOWER 60S.  
 
UPPER LEVEL RIDGING WILL BE IN PLACE OVER THE FORECAST AREA ON  
MONDAY, LEADING TO ANOTHER SEASONABLE AND MAINLY DRY DAY. LIKE  
SUNDAY, COULD SEE A FEW POP UP SHOWERS WITH A BIT OF INSTABILITY IN  
THE CUMULUS LAYER PER SOME MODEL SOUNDINGS. OTHERWISE, THE  
AFOREMENTIONED PRESSURE GRADIENT WILL LEAD TO STRENGTHENING  
SOUTHERLY FLOW AHEAD OF A LOW PRESSURE SYSTEM AND COLD FRONT SLIDING  
THROUGH THE NORTHERN PLAINS. PER THE 12.15Z RAP, SOME RAIN AHEAD OF  
THE FRONT COULD SNEAK INTO THE FORECAST AREA BY LATE MONDAY  
AFTERNOON, THOUGH GENERAL MODEL CONSENSUS WOULD FAVOR ANY  
PRECIPITATION HOLDING OFF UNTIL LATER.  
   
LONG TERM
 
(MONDAY NIGHT THROUGH SUNDAY)  
ISSUED AT 245 PM CDT SUN JUL 12 2020  
 
WE'VE HAD QUITE THE AIRMASS EXCHANGE WITH DEWPOINTS ONLY IN THE  
50S TO LOWER 60S MOST LOCATIONS. DEWPOINTS WILL MOSTLY REMAIN IN  
THE 50S AND 60S, HOWEVER AS WE MOVE TOWARD THE WEEKEND, LOOK FOR  
THE DEWPOINTS TO CLIMB INTO THE 70S. TUESDAY LOOKS LIKE THE  
COOLEST DAY AND SATURDAY THE WARMEST/MUGGY. MOST TEMPERATURES  
SHOULD REACH THE HIGHS IN THE 80S, BUT READINGS WILL BE HELD TO  
THE 70S TUESDAY AND THERE SHOULD BE QUITE A FEW 90S SATURDAY AND A  
FEW STILL SUNDAY DEPENDING ON WHERE THE SURFACE FRONT IS.  
 
AN 80KT 300MB JET WILL MOVE ON TO THE WASHINGTON/OREGON COAST SUNDAY  
NIGHT AND TRAVERSE ACROSS THE NORTHERN ROCKIES AND THE NORTHERN  
PLAINS INTO MINNESOTA BY TUESDAY NIGHT. THE 500MB PATTERN HAS A MID-  
TROPOSPHERIC RIDGE FROM MINNESOTA THROUGH THE CENTRAL PLAINS. THE  
500MB TROUGH EXTENDS INTO THE NORTHWEST PART OF THE U.S. FROM A  
CLOSED LOW PRESSURE SYSTEM OVER SASKATCHEWAN FLATTENS THE RIDGE  
MONDAY WITH A BROAD TROUGH THROUGH TUESDAY NIGHT. THE BROAD TROUGH  
REMAINS IN PLACE WITH SOME SLIGHT RIDGING OVER THE WESTERN HIGH  
PLAINS THURSDAY. THE STRONGER SHORTWAVE ENERGY TRACKS ACROSS  
SOUTHERN CANADA WITH A RIPPLY ZONAL FLOW ACROSS THE NORTHERN U.S.  
FRIDAY THROUGH SUNDAY. MEANWHILE...THE SOUTHERN PLAINS REMAINS  
UNDER THE INFLUENCE OF A LARGE HIGH PRESSURE SYSTEM.  
 
A COLD FRONT WILL APPROACH MONDAY NIGHT WITH SOME SPOTTY PRE-  
FRONTAL CONVECTION POSSIBLE, INCREASING BY TUESDAY MORNING.  
SHOWERS AND THUNDERSTORMS BECOME MORE WIDESPREAD ALONG THE FRONT  
AS IT SAGS SOUTHWARD TUESDAY AND PUSHES THROUGH THE AREA TUESDAY  
NIGHT. THERE IS A SEVERE WEATHER THREAT AND POTENTIAL FOR HEAVY  
RAIN TUESDAY AND TUESDAY EVENING. PRECIPITABLE WATER VALUES  
INCREASE TO 1.5 TO 2 INCHES WITH WARM CLOUD DEPTHS NEAR 4KM. THE  
STORMS THAT DEVELOP WILL BE CAPABLE OF PUTTING DOWN HEAVY RAIN AND  
WITH A FRONT IN THE AREA, INCREASE THE PROBABILITY OF TRAINING.  
RELATED TO SEVERE STORMS, INSTABILITY IS MARGINAL...1000-2000J/KG,  
HOWEVER THERE IS INCREASING SHEAR, BOTH 0-6KM SHEAR AND 0-3KM  
SHEAR DURING THE AFTERNOON AND EVENING AS A SHORTWAVE ROUNDS THE  
BASE OF THE LARGER SCALE TROUGH. FORECAST SOUNDINGS SHOW MODEST  
LAPSE RATES. THE MID- LEVEL SIGNAL IS GOOD HOWEVER THE LOW LEVEL  
FORCING IS NOT AS SUPPORTIVE. A STRONGER 850MB JET IS FOCUSED  
WELL TO THE NORTH MONDAY NIGHT AND THE 850MB JET TUESDAY IS  
STRONGER ACROSS MISSOURI. ULTIMATELY SOME OF THESE DETAILS WILL  
CHANGE AS WE GET CLOSER AND TUESDAY INTO TUESDAY NIGHT IS THE BEST  
CHANCE FOR RAIN DURING THE WEEK. THE RAIN MAY LINGER WEDNESDAY  
DEPENDING ON THE PUSH OF THE FRONT. THURSDAY IS DRY. THE  
TEMPERATURES HEAT UP WITH ISOLATED RAIN CHANCES FRIDAY AND  
SATURDAY AND ISOLATED TO SCATTERED SUNDAY DEPENDING ON THE WHERE  
THE FRONT IS.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)  
ISSUED AT 1241 PM CDT SUN JUL 12 2020  
 
VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD, WITH AFTERNOON  
CUMULUS AND LIGHT NORTHERLY WINDS. COULD SEE A FEW SHOWERS  
AROUND THIS AFTERNOON, MAINLY EAST OF THE MISSISSIPPI RIVER,  
THOUGH EXPECT THOSE TO BE FEW AND FAR BETWEEN IF THEY DEVELOP.  
WINDS SWITCH TO SOUTHERLY TONIGHT AND WILL PICK UP A BIT LATER  
MONDAY MORNING. SOME HINTS AT SOME FOG IN THE AREA TONIGHT, BUT  
LATEST GUIDANCE SUGGESTS WINDS ALOFT COULD BE JUST STRONG ENOUGH  
TO PRECLUDE WIDESPREAD DEVELOPMENT, SO DID NOT INCLUDE IN THIS  
ISSUANCE.  
 

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

 
 

 
 
SHORT TERM...CA  
LONG TERM...ZAPOTOCNY  
AVIATION...CA  
 
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