658  
FXUS63 KLSX 222010  
AFDLSX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
310 PM CDT TUE AUG 22 2017  
   
SHORT TERM
 
(THROUGH LATE WEDNESDAY AFTERNOON)  
ISSUED AT 307 PM CDT TUE AUG 22 2017  
 
A LONGWAVE TROF EXISTED OVER EASTERN NORTH AMERICA THIS AFTERNOON  
WITH A LONGWAVE RIDGE OVER WESTERN NORTH AMERICA, RESULTING IN NW  
FLOW ALOFT FOR OUR REGION. A SURFACE COLD FRONT HAS NEARLY CLEARED  
THE FORECAST AREA, NOW OVER SOUTHERN IL AND SOUTHEASTERN MO AND  
CONTINUES TO CHUG SOUTHEASTWARD. ONE LAST BOUT OF LOW-TOPPED  
SHOWERS CAN BE FOUND RIGHT ALONG THIS FRONT. NORTHWESTERLY SURFACE  
FLOW BEHIND THE FRONT IS BEGINNING TO USHER IN DEWPOINTS IN THE 50S  
INTO NORTHERN MO AND HAS KEPT TEMPS IN THE UPPER 70S TO AROUND 80.  
 
A DISTURBANCE-FREE NORTHWEST FLOW ALOFT AND A COOL CANADIAN SURFACE  
HIGH PRESSURE BUILDING IN FROM THE NORTH WILL BE THE PREVAILING  
THEMES FOR THE FORECAST THRU WEDNESDAY AFTERNOON. THIS WILL  
MAINTAIN A DRY COLUMN WITH FEW, IF ANY, CLOUDINESS ONCE THE LAST OF  
IT EXITS OUR SOUTHERN CWA EARLY THIS EVENING. THE BEGINNINGS OF  
WHAT APPEARS TO BE AN EXTENDED REGIME OF BELOW AVERAGE TEMPS WILL  
BEGIN TONIGHT, WITH NIGHTTIME MINS IN THE 50S AND DAYTIME MAXES  
AROUND 80, OR ABOUT 5 DEGREES SEASONAL NORMS FOR MOST AREAS.  
 
DOES THIS MEAN THAT SUMMER IS OVER?  
 
TES  
   
LONG TERM
 
(WEDNESDAY NIGHT THROUGH NEXT TUESDAY)  
ISSUED AT 307 PM CDT TUE AUG 22 2017  
 
YES, IT MAY BE. A PERSISTENT SURFACE RIDGE WILL EXTEND FROM THE  
GREAT LAKES REGION SOUTHWEST INTO MO WITH UPPER LEVEL NORTHWEST FLOW  
LEADING TO A LONG PERIOD OF RELATIVELY COOL CONDITIONS AND DRY  
WEATHER WEDNESDAY NIGHT INTO THE WEEKEND. ALTHOUGH WEAK NORTHWEST  
FLOW SHORTWAVES WILL MOVE THROUGH THE REGION THE LOW LEVELS SHOULD  
BE TOO DRY FOR ANY PRECIPITATION. WILL HAVE PERSISTENT LOWS IN THE  
MIDDLE 50S TO AROUND 60 DEGREES WITH HIGHS IN THE UPPER 70S TO LOWER  
80S. THIS IS ABOUT 5 TO 10 DEGREES BELOW NORMAL FOR LATE AUGUST. THE  
NEXT CHANCE OF PRECIPITATION WILL NOT OCCUR UNTIL SUNDAY NIGHT  
THROUGH TUESDAY WHEN AN UPPER LEVEL TROUGH DROPS SOUTHWARD THROUGH  
THE NORTHERN PLAINS SENDING A COLD FRONT SOUTHEASTWARD INTO OUR  
AREA. THE REMNANTS OF TROPICAL CYCLONE HARVEY SHOULD MOVE INTO  
SOUTHERN LOUISIANA BY TUESDAY NIGHT, BUT SHOULD NOT HAVE ANY AFFECT  
ON OUR AREA THROUGH AT LEAST TUESDAY NIGHT.  
 
GKS  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)  
ISSUED AT 1250 PM CDT TUE AUG 22 2017  
 
ONE FINAL BAND OF SHOWERS IS MOVING THRU STL METRO NOW BUT SHOULD  
LARGELY BE SOUTH OF THE TAF SITES EXCEPT FOR CPS AT THE VALID  
TIME. OTHERWISE, LOOK FOR VFR CONDITIONS AND DRY WX TO PREVAIL  
AFTER 19Z AT ALL TAF SITES WITH NW SURFACE WINDS THRU THE REST OF  
THE VALID PERIOD. WINDS WILL BE A BIT STRONGER AROUND 10KTS THAN  
TONIGHT OR WEDNESDAY.  
 
TES  
 

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

 
 

 
 
WFO LSX  
 
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