862  
FXUS63 KLSX 230453  
AFDLSX  
 
AREA FORECAST DISCUSSION...UPDATED AVIATION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
1153 PM CDT MON MAY 22 2017  
   
SHORT TERM
 
(THROUGH LATE TUESDAY AFTERNOON)  
ISSUED AT 345 PM CDT MON MAY 22 2017  
 
SOUTHWEST-NORTHEAST ORIENTED AREA OF SHOWERS AND A FEW THUNDERSTORMS  
WILL CONTINUE TO SHIFT MAINLY NORTHEASTWARD OVER THE NEXT SEVERAL  
HOURS. THIS AREA OF PRECIPITATION LOOKS LIKE IT IS MAINLY FORCED BY  
STRONG UPPER-LEVEL JET DYNAMICS IN CONJUNCTION WITH WEAK LOW-LEVEL  
MOISTURE CONVERGENCE. THESE FORCING MECHANISMS BEGIN TO SHIFT SLOWLY  
SOUTHEASTWARD THIS EVENING INTO THE OVERNIGHT HOURS SO HAVE POPS  
ALSO RAISING ACROSS PORTIONS OF CENTRAL MISSOURI INTO WEST-CENTRAL  
ILLINOIS DURING THESE HOURS. VERY LIMITED INSTABILITY AS OF 1900 UTC  
SO THINKING THIS WILL BE MAINLY SHOWERS, ESPECIALLY AFTER MID  
EVENING WHEN THE LIMITED INSTABILITY WE CURRENTLY HAVE IS FORECAST  
TO WANE NOCTURNALLY. LOWS TONIGHT LOOK TO BE NEAR NORMAL FOR MOST  
LOCATIONS IN THE 50S TO NEAR 60 DEGREES.  
 
COLD FRONT WILL VERY SLOWLY PROGRESS SOUTHEASTWARD THROUGH THE  
DAY ON TUESDAY WITH A CONTINUED THREAT FOR PRECIPITATION. CHANCES  
OF THUNDER WILL INCREASE BY MIDDAY AS MIDLEVEL LOW AND ITS  
ASSOCIATED COLD POCKET ALOFT MOVE TOWARD THE AREA HELPING TO  
SIGNIFICANTLY INCREASE MIDLEVEL LAPSE RATES. HIGHEST CHANCE OF  
SHOWERS AND STORMS BECAUSE OF THE TIMING OF THE COLD FRONT WILL BE  
ACROSS CENTRAL PORTIONS OF THE FORECAST AREA. HIGHS ON TUESDAY  
WILL BE DEPENDENT ON FRONTAL TIMING AS WELL AS  
PREVALENCE/THICKNESS OF CLOUD COVER AND PRECIPITATION CHANCES.  
COOLEST LOCATIONS ARE EXPECTED TO BE ACROSS NORTHWESTERN SECTIONS  
OF THE FORECAST AREA WITH HIGHS IN THE LOW 60S AND WARMEST AREAS  
INCLUDING PORTIONS OF SOUTHWEST ILLINOIS AND SOUTHEAST MISSOURI  
TOPPING OUT IN THE LOW 70S.  
 
GOSSELIN  
   
LONG TERM
 
(TUESDAY NIGHT THROUGH NEXT MONDAY)  
ISSUED AT 345 PM CDT MON MAY 22 2017  
 
TRACK OF THE UPPER LOW IS A LITTLE FURTHER WEST TODAY, WITH IT  
MOVING DOWN ALONG THE MISSISSIPPI RIVER ON WEDNESDAY. STILL LOOKS  
LIKE TUESDAY NIGHT INTO WEDNESDAY NIGHT WILL HAVE A CHANCE OF  
SHOWERS UNDER THE UPPER LOW BEFORE DRIER WEATHER IS EXPECTED AS  
SHORTWAVE RIDGE MOVES INTO THE AREA FROM THE WEST. THEN IT LOOKS  
LIKE IT MAY BE ACTIVE FRIDAY INTO SUNDAY AS A FRONTAL BOUNDARY WILL  
BECOME QUASI-STATIONARY OVER THE AREA AND SEVERAL SHORTWAVE TROUGHS  
MOVE ACROSS MISSOURI AND ILLINOIS IN WEST SOUTHWESTERLY FLOW ALOFT.  
THE GFS IS SHOWING THE ATMOSPHERE BECOMING QUITE UNSTABLE WITH QUITE  
A BIT OF DEEP LAYER SHEAR EARLY THIS WEEKEND, SO WILL HAVE TO WATCH  
OUT FOR A FEW STRONG TO SEVERE THUNDERSTORMS. ECMWF AND GFS BEGIN  
TO DIVERGE IN SOLUTIONS BY SUNDAY INTO MONDAY WHICH BRINGS  
UNCERTAINTY IN THE FORECAST BY EARLY NEXT WEEK.  
 
STILL HAVE TEMPERATURES BELOW NORMAL UNDER THE UPPER LOW WEDNESDAY  
AND THURSDAY, BUT THEY WILL CLIMB BACK TO NEAR NORMAL LATE WEEK INTO  
THE HOLIDAY WEEKEND.  
 
BRITT  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)  
ISSUED AT 1150 PM CDT MON MAY 22 2017  
 
MAIN TAF CONCERNS WILL BE ON PRECIPITATION TRENDS ALONG WITH  
LOWERING CIGS. AN AREA OF SHOWERS CONTINUES TO PUSH THROUGH  
NORTH- CENTRAL MO THIS EVENING, TOWARD COU AND UIN. A FEW OF THESE  
SHOWERS MAY JUST BE HEAVY ENOUGH AT UIN TO BRING BRIEF MVFR VSBYS.  
SHOWERS WILL PERSIST OVERNIGHT AT COU/UIN, BUT MUCH OF THE  
ACTIVITY SHOULD STAY JUST NORTHWEST OF THE ST. LOUIS METRO SITES.  
SHOWERS WILL MOVE EAST TOWARDS THE ST. LOUIS SITES BY TUESDAY  
MORNING, WITH A FEW THUNDERSTORMS POSSIBLE ACROSS THE AREA TUESDAY  
AFTERNOON AS A COLD FRONT WORKS THROUGH THE REGION. ALONG AND  
BEHIND THE FRONT, SOME MVFR CIGS LOOK LIKELY TUESDAY MORNING  
MAINLY AT UIN/COU. THE PASSAGE OF THE FRONT WILL BRING A WIND  
SHIFT TO THE WNW TUESDAY AFTERNOON INTO TUESDAY EVENING.  
 
SPECIFICS FOR KSTL:  
VFR CONDITIONS EXPECTED OVERNIGHT, WITH SHOWERS AND A FEW STORMS  
POSSIBLE ON TUESDAY. CURRENT SHOWER ACTIVITY OVER NORTHERN MO  
SHOULD REMAIN JUST NORTHWEST OF THE TERMINAL THROUGH MUCH OF THE  
OVERNIGHT HOURS, BUT A FEW SHOWERS MAY BEGIN TO CREEP INTO THE  
REGION BY TUESDAY MORNING. A BETTER CHANCE FOR SHOWERS AND A FEW  
THUNDERSTORMS WILL COME TUESDAY AFTERNOON AS A COLD FRONT SWINGS  
THROUGH. THIS FRONT WILL BRING A WIND SHIFT TO THE WNW AS IT  
PASSES BY.  
 
KD  
 

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

 
 

 
 
WFO LSX  
 
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