642  
FXUS63 KLSX 231037  
AFDLSX  
 
AREA FORECAST DISCUSSION...UPDATED AVIATION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
537 AM CDT TUE OCT 23 2018  
   
SHORT TERM
 
(THROUGH LATE TONIGHT)  
ISSUED AT 332 AM CDT TUE OCT 23 2018  
 
NORTHWEST UPPER LEVEL FLOW HAS TAKEN HOLD ACROSS THE REGION IN THE  
WAKE OF A TROUGH THAT PASSED WELL TO OUR NORTH. THE SURFACE CYCLONE  
ASSOCIATED WITH THE TROUGH IS CURRENTLY OVER THE GREAT LAKES WITH A  
WEAK SURFACE COLD FRONT EXTENDING BACK INTO THE MID MISSISSIPPI  
VALLEY. THE COLD FRONT WILL CONTINUE TO SLIDE SOUTHEAST TODAY AS  
HIGH PRESSURE BUILDS INTO THE UPPER MIDWEST BENEATH UPPER LEVEL  
HEIGHT RISES. THIS WILL RESULT IN ANOTHER DAY OF CALM WEATHER, WITH  
HIGH TEMPERATURES ACROSS ALL BUT THE FAR SOUTHERN PORTIONS OF OUR  
AREA ABOUT 5-10 DEGREES COOLER THAN WHAT WE SAW ON MONDAY.  
   
LONG TERM
 
(WEDNESDAY THROUGH MONDAY)  
ISSUED AT 332 AM CDT TUE OCT 23 2018  
 
THE SURFACE HIGH WILL GRADUALLY SHIFT EAST ON WEDNESDAY AS THE  
COOL, DRY AIR MASS BUILDS INTO THE NORTHEASTERN CONUS. THEREFORE  
ANOTHER LARGELY CLOUD-FREE DAY IS EXPECTED ON WEDNESDAY. TEMPS  
WILL BE SIMILAR TO TUESDAY ACROSS OUR NORTH, BUT FOR AREAS ALONG  
AND SOUTH OF I-70, TEMPERATURES WILL BE ANOTHER 5-10 DEGREES  
COOLER THAN ON TUESDAY.  
 
ON THURSDAY, THE UPPER LEVEL RIDGING WILL BREAK DOWN AS A TROUGH  
PUSHES INTO THE REGION. MEANWHILE, A PLUME OF MID LEVEL MOISTURE  
ASSOCIATED WITH HURRICANE WILLA WILL PUSH INTO THE REGION. THE  
CYCLONIC VORTICITY ADVECTION ASSOCIATED WITH THE SHORTWAVE,  
COUPLED WITH THE MOISTURE FROM WILLA, HAS MUCH OF THE FORECAST  
GUIDANCE PAINTING VARIOUS AMOUNTS OF PRECIP ACROSS THE REGION ON  
THURSDAY EVENING/NIGHT. THE NAM/GEM SATURATE THE AIRMASS QUITE A  
BIT FASTER THAN THE GFS/EURO, AND THEREFORE PUT DOWN ABOUT TWICE  
AS MUCH QPF AS THE MORE CONSERVATIVE SOLUTIONS. GIVEN THE VERY DRY  
AIRMASS CURRENTLY IN PLACE AND THE FACT THAT THE DRYNESS WILL BE  
REINFORCED BEHIND TODAY'S FROPA, IT STANDS TO REASON THAT THE  
ATMOSPHERE WILL TAKE A WHILE TO SATURATE ON THURSDAY NIGHT.  
THEREFORE I'M INCLINED TO LEAN ON THE GFS/EURO A BIT MORE THAN THE  
NAM/GEM. REGARDLESS, WE SHOULD SEE AT LEAST SOME SPOTTY LIGHT  
SHOWERS BEFORE THE SHORTWAVE CLEARS THE AREA ON FRIDAY MORNING.  
 
AFTER A QUIET DAY ON FRIDAY, ANOTHER SHORTWAVE EMBEDDED IN THE  
NORTHWEST UPPER FLOW WILL RACE THROUGH THE REGION LATE FRIDAY AND  
SATURDAY. WITH NOTHING TO SCOUR THE MOISTURE BEHIND THURSDAY NIGHT'S  
PRECIP, THERE WILL LIKELY BE SUFFICIENT MID AND LOW LEVEL MOISTURE  
IN PLACE TO SUPPORT ANOTHER ROUND OF LIGHT RAIN ON SATURDAY AS THE  
SHORT WAVE MOVES THROUGH. BEYOND THAT, WE WILL REMAIN ENTRENCHED  
IN NORTHWEST UPPER LEVEL FLOW. ALL FORECAST GUIDANCE SHOWS  
EMBEDDED SHORTWAVES INTERMITTENTLY PASSING THROUGH THE REGION,  
THOUGH THERE IS LITTLE CONSENSUS ON TIMING THIS FAR OUT.  
REGARDLESS, THESE PASSING WAVES HAVE RESULTED IN A FEW PERIODS OF  
LOW PRECIPITATION CHANCES THROUGH EARLY NEXT WEEK.  
 
BSH  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)  
ISSUED AT 531 AM CDT TUE OCT 23 2018  
 
PATCHY FOG IN LOW LYING AREAS SHOULD DISSIPATE QUICKLY AS THE SUN  
COMES UP THIS MORNING. AFTERWARD, SKIES WILL STAY MOSTLY CLEAR  
SAVE FOR A FEW HIGH CLOUDS STREAMING INTO THE AREA FROM THE WEST.  
OTHERWISE, A WEAK COLD FRONT WILL MOVE SOUTH OUT OF THE AREA,  
LEAVING NORTHERLY FLOW IN ITS WAKE.  
 
BSH  
 

 
   
LSX WATCHES/WARNINGS/ADVISORIES
 
 
MO...NONE.  
IL...NONE.  

 
 

 
 
WFO LSX  
 
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