549  
FXUS63 KLSX 251642  
AFDLSX  
 
AREA FORECAST DISCUSSION...UPDATED AVIATION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
1142 AM CDT THU MAY 25 2017  
   
SHORT TERM
 
(THROUGH LATE TONIGHT)  
ISSUED AT 333 AM CDT THU MAY 25 2017  
 
LOW SYSTEM, CURRENTLY CENTERED OVER IN/OH REGION AT THE SFC, WILL  
CONTINUE TO MOVE EWD TODAY. EXPECT CLOUD COVER OVER THE ERN HALF OF  
THE CWA TO GRADUALLY CLEAR OUT OF THE AREA TODAY BEFORE MID CLOUDS  
MOVE INTO THE WRN PORTIONS OF THE CWA.  
 
WITH AMPLE INSOLATION EXPECTED TODAY, HAVE TRENDED TWD THE WARMER  
GUIDANCE DESPITE WEAK ADVECTION. HAVE ALSO TRENDED TWD WARMER  
GUIDANCE FOR TONIGHT AS CLOUDS MOVE INTO THE REGION AND WINDS  
BECOMING SLY ACROSS THE REGION.  
 
EXPECT TODAY TO REMAIN DRY AS WELL AS MUCH OF TONIGHT. HOWEVER, HAVE  
KEPT LOW POPS LATE TONIGHT ACROSS WRN AND NRN PORTIONS OF THE CWA AS  
THE WRMFNT LIFTS THRU THE AREA. THERE ARE SOME MDLS THAT SUGGEST  
TSRA MOVING FURTHER SOUTH IMPACTING SRN PORTIONS OF THE CWA.  
HOWEVER, GIVEN THE STRONG AND DEEP WAA ACROSS THIS AREA, IT WUD SEEM  
THIS AREA WOULD BE CAPPED WITH CONVECTION REMAINING FURTHER NORTH.  
MDLS DISAGREE ON TIMING, BUT WITH A WEAK TROF MOVING THRU IA LATE  
TONIGHT INTO FRI MORNING, HAVE FOCUSED FURTHER NORTH LATE TONIGHT.  
 
TILLY  
   
LONG TERM
 
(FRIDAY THROUGH WEDNESDAY)  
ISSUED AT 333 AM CDT THU MAY 25 2017  
 
SURFACE RIDGE TO CONTINUE WEAKENING AND SHIFT OFF TO THE EAST ON  
FRIDAY AS NEXT SYSTEM MOVES IN. FRONTAL BOUNDARY ASSOCIATED WITH  
SYSTEM TO SINK SOUTH ACROSS FORECAST AREA AND STALL OUT ALONG I-70  
CORRIDOR. LOW LEVEL MOISTURE WILL BE ON THE INCREASE WITH MODERATE  
INSTABILITY. HOWEVER, DECENT CAP SO ACTIVITY WILL BE SLOW TO  
DEVELOP, IF AT ALL. IF ANYTHING DOES FIRE UP BY LATE AFTERNOON/  
EARLY EVENING, IT COULD BE STRONG TO SEVERE.  
 
THE THREAT FOR STORMS WILL PERSIST SATURDAY THROUGH SATURDAY NIGHT,  
WITH MODELS CONTINUING TO INDICATE VERY HIGH CAPES AND STRONG 0-1KM  
SHEAR. AS FRONTAL BOUNDARY LIFTS NORTH AS A WARM FRONT, WILL SEE  
ELEVATED HAILERS DURING THE MORNING HOURS, THEN TRANSITION TO MORE  
OF A SUPERCELL ENVIRONMENT FOR THE AFTERNOON AND EVENING HOURS. SPC  
HAS PLACED AREAS ALONG AND SOUTH OF I-70 IN AN ENHANCED RISK FOR  
SATURDAY/SATURDAY NIGHT.  
 
AS SYSTEM EXITS, WILL SEE SHOWERS TAPER OFF ON SUNDAY. QUIETER  
WEATHER FOR MONDAY AND TUESDAY, THOUGH COULD SEE ISOLATED/SCATTERED  
SHOWERS AND STORMS AS SHORTWAVES ROTATE AROUND UPPER LOW ANCHORED  
OVER GREAT LAKES REGION EACH DAY. WEAK SURFACE RIDGE BUILDS IN BY  
WEDNESDAY.  
 
AS FOR TEMPERATURES THROUGH THE PERIOD, WILL BE NEAR NORMAL OR JUST  
A BIT ABOVE NORMAL.  
 
BYRD  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)  
ISSUED AT 1101 AM CDT THU MAY 25 2017  
 
SURFACE RIDGE AXIS WILL MOVE EASTWARD THROUGH THE TAF SITES THIS  
AFTERNOON CAUSING THE NORTHWEST SURFACE WINDS IN UIN AND THE ST  
LOUIS METRO AREA TO WEAKEN. ONLY FEW TO SCATTERED DIURNAL CUMULUS  
CLOUDS ARE EXPECTED. COULD NOT RULE OUT A FEW SHOWERS/STORMS LATE  
TONIGHT AND FRIDAY MORNING IN THE UIN AND COU AREAS DUE TO WEAK  
UPPER LEVEL DISTURBANCES AND AS A SOUTHWEST LOW LEVEL JET OVER  
SOUTHWESTERN MO BRINGS INCREASING LOW LEVEL MOISTURE INTO THIS  
AREA, BUT THE PROBABILITY OR POSSIBLE COVERAGE IS TOO LOW TO  
WARRANT INCLUDING IN THE TAFS. SHOULD SEE INCREASING MID-HIGH  
LEVEL CLOUDINESS LATE TONIGHT, WITH LOW LEVEL CLOUDINESS FRIDAY  
MORNING THOUGH STILL LIKELY VFR. THE WIND WILL GRADUALLY  
STENGTHEN FROM A SOUTHEAST DIRECTION TONIGHT, THEN SOUTHERLY  
FRIDAY MORNING AS THE SURFACE RIDGE SHIFTS EAST OF THE REGION.  
 
SPECIFICS FOR KSTL: SURFACE RIDGE AXIS WILL MOVE EASTWARD THROUGH  
THE STL AREA THIS AFTERNOON CAUSING THE NORTHWEST SURFACE WIND TO  
WEAKEN. ONLY SCATTERED DIURNAL CUMULUS CLOUDS ARE EXPECTED. COULD  
NOT RULE OUT A FEW SHOWERS/STORMS FRIDAY AFTERNOON DUE TO WEAK  
UPPER LEVEL DISTURBANCES AND AS A COLD FRONT APPROACHES, BUT THE  
PROBABILITY OR POSSIBLE COVERAGE LOOKS TOO LOW TO WARRANT  
INCLUDING IN THE STL TAF FOR NOW. SHOULD SEE INCREASING MID-HIGH  
LEVEL CLOUDINESS LATE TONIGHT, WITH LOW LEVEL CLOUDINESS FRIDAY  
THOUGH STILL LIKELY VFR. THE WIND WILL GRADUALLY STENGTHEN FROM A  
SOUTHEAST DIRECTION TONIGHT, THEN VEER AROUND TO A SOUTHWEST  
DIRECTION FRIDAY AFTERNOON AS THE SURFACE RIDGE SHIFTS EAST OF THE  
REGION.  
 
GKS  
 

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

 
 

 
 
WFO LSX  
 
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