782  
FXUS63 KLSX 131138  
AFDLSX  
 
AREA FORECAST DISCUSSION...UPDATED AVIATION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
538 AM CST WED DEC 13 2017  
   
SHORT TERM
 
(THROUGH LATE TONIGHT)  
ISSUED AT 353 AM CST WED DEC 13 2017  
 
MAIN FOCUS TODAY IS THE FIRE DANGER THREAT AND STRONG WINDS.  
 
THIS CLIPPER IS EXPECTED TO BE SIMILAR TO THE SYSTEM ON MON,  
ALTHOUGH, NOT QUITE AS WARM IN SOME AREAS. SOUTHWEST WINDS WILL  
INCREASE LATE THIS MORNING AND VEER TO BECOME WLY, THEN NWLY THIS  
AFTERNOON AS A CDFNT PUSHES THRU THE AREA. AM CONCERNED THAT GOING  
FORECAST FOR WIND SPEED IS NOT HIGH ENUF AND AN WIND ADVISORY MAY BE  
NEEDED. MAIN AREAS OF CONCERN ARE NRN COUNTIES LATE THIS MORNING AND  
THRU THE AFTERNOON, AND ERN PORTIONS OF THE CWA FOR THIS AFTERNOON  
AND INTO THE EARLY EVENING HOURS. HAVE HELD OFF ON AN ADVISORY FOR  
NOW WITH MDLS SUGGESTING WINDS DIMINISHING SLIGHTLY AS THE LOW MOVES  
SEWD.  
 
HAVE TRENDED AOA WARMER GUIDANCE FOR THE ENTIRE CWA GIVEN THE VERY  
STRONG WAA AND LATER ARRIVAL OF THE CDFNT. GOING FORECAST MAY STILL  
NOT BE WARM ENUF GIVEN SOME GUIDANCE, LIKE THE RAP, SUGGESTING  
WARMER TEMPS. HOWEVER, WITH LOTS OF QUESTIONS AMONG MDLS REGARDING  
CLOUD COVER, DID NOT WANT TO GO TOO WARM ATTM.  
 
WITH DEEPER MIXING, DEWPOINTS WILL REMAIN COOL TODAY, ESPECIALLY  
WITHIN THE WARM SECTOR. THIS WILL RESULT IN RH VALUES DROPPING BELOW  
30 PERCENT FOR THE SRN HALF OF THE CWA. THE LOW RH VALUES COUPLED  
WITH THE STRONG WINDS AND DRY FUELS WILL RESULT IN A HEIGHTENED FIRE  
DANGER THRU THIS AFTERNOON. IF TEMPS ARE TOO LOW AS MENTIONED ABOVE,  
THESE DANGEROUS CONDITIONS MAY EXTEND ACROSS MUCH OF THE CWA. WILL  
ALSO NEED TO MONITOR CONDITIONS FOR A POSSIBLE RED FLAG WARNING WITH  
GOING FORECAST BEING NEAR CRITERIA ACROSS PORTIONS OF SE MO.  
 
LOW CHANCE OF ANY PRECIP WITH THIS SYSTEM, BUT HAVE KEPT A MENTION  
OF SPRINKLES ALONG THE CDFNT AS IT PASSES THRU THE AREA.  
 
TILLY  
   
LONG TERM
 
(THURSDAY THROUGH TUESDAY)  
ISSUED AT 353 AM CST WED DEC 13 2017  
 
COLDER HIGH TEMPERATURES CAN BE EXPECTED ON THURSDAY AS A SURFACE  
RIDGE OVER THE PLAINS BUILDS EAST-SOUTHEASTWARD INTO OUR AREA. LOW  
LEVEL CLOUD COVER WILL ALSO HINDER DAYTIME HEATING. A POSITIVELY  
TILTED UPPER LEVEL TROUGH WILL APPROACH OUR REGION THURSDAY NIGHT  
FROM THE NORTHERN PLAINS. MOST OF THE MODELS DRY UP THE  
PRECIPITATION BEFORE IT GETS INTO OUR FORECAST AREA, ALTHOUGH THE  
OPERATIONAL GFS DOES HAVE VERY LIGHT QPF LATE THURSDAY NIGHT AND  
FRIDAY MORNING MAINLY ACROSS NORTHEAST AND CENTRAL MO. DO NOT THINK  
WE WILL GET ANY MEASURABLE PRECIPITATION, BUT WE MAY GET A FEW  
FLURRIES. WILL SEE THE START OF A WARMING TREND FRIDAY AFTERNOON  
WITH MUCH WARMER TEMPERATURES SATURDAY AS UPPER LEVEL HEIGHTS RISE  
AS AN UPPER LEVEL RIDGE APPROACHES THE REGION, AND THE SURFACE WIND  
BECOMES SOUTH-SOUTHWESTERLY AS THE SURFACE RIDGE SHIFTS SOUTHEAST OF  
OUR AREA. PRECIPITATION WILL SPREAD NORTHEASTWARD INTO OUR FORECAST  
AREA LATE SATURDAY NIGHT AND SUNDAY MORNING AHEAD OF A SOUTHERN  
STREAM SHORTWAVE COMING OUT OF THE SOUTHERN PLAINS. THE OPERATIONAL  
GFS IS A LITTLE SLOWER BRINGING PRECIPITATION INTO OUR AREA THAN THE  
ECMWF MODEL. THE BULK OF THE PRECIPITATION SHOULD SHIFT EAST OF OUR  
FORECAST AREA ALREADY BY SUNDAY AFTERNOON, BUT THERE MAY BE PATCHY  
LIGHT PRECIPITATION SUNDAY AFTERNOON AND EVENING WITH THE APPROACH  
OF A DEEP NORTHERN STREAM UPPER LEVEL TROUGH. THERE WAS STILL SOME  
MODEL UNCERTAINTY AS TO THE POSSIBLE PHASING OF THE NORTHERN AND  
SOUTHERN STREAM ENERGY AND THE TIMING OF THE PRECIPITATION. IT  
APPEARS THAT THE TEMPERATURE PROFILE WILL BE WARM ENOUGH THAT MOST  
OF THE PRECIPITATION WILL FALL AS LIQUID RAIN, ALTHOUGH THERE COULD  
BE SOME SNOW MIXED IN WITH THE RAIN LATE SATURDAY NIGHT AND EARLY  
SUNDAY MORNING. DESPITE A RETURN TO NORTHWEST UPPER LEVEL FLOW BY  
TUESDAY, HIGH TEMPERATURES SHOULD CONTINUE ABOVE NORMAL.  
 
GKS  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)  
ISSUED AT 523 AM CST WED DEC 13 2017  
 
SWLY WINDS WILL INCREASE WITH GUSTS TO AROUND 30 KTS AND BECOME  
WLY THIS MORNING. WINDS WILL BECOME NWLY THIS AFTERNOON AS A COLD  
FRONT PUSHES THRU THE AREA. MVFR CIGS ARE EXPECTED BEHIND THE  
CDFNT. A FAIR AMOUNT OF UNCERTAINTY EXISTS REGARDING HOW LONG  
THESE MVFR CIGS WILL LINGER, BUT HAVE KEPT THESE CIGS A LITTLE  
LONGER FOR NOW. NO PRECIP IS CURRENTLY ANTICIPATED OTHER THAN A  
CHANCE OF SPRINKLES AT KUIN THIS AFTERNOON.  
 
TILLY  
 

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

 
 

 
 
WFO LSX  
 
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