502  
FXUS63 KLSX 290343  
AFDLSX  
 
AREA FORECAST DISCUSSION...UPDATED AVIATION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
1043 PM CDT TUE MAR 28 2017  
   
UPDATE
 
 
ISSUED AT 913 PM CDT TUE MAR 28 2017  
 
LATEST NAM AND HRRR MODEL GUIDANCE IS A LITTLE SLOWER BRINGING  
SHOWERS INTO OUR FORECAST AREA LATE TONIGHT/EARLY WEDNESDAY  
MORNING. IT APPEARS THAT SHOWERS WILL MOVE INTO CENTRAL MO AROUND  
12Z WEDNESDAY MORNING, THEN MOVE INTO NORTHEAST MO AND WEST  
CENTRAL IL LATER IN THE MORNING, MAINLY NORTH AND WEST OF STL AS A  
SOUTHERLY LOW LEVEL JET BRINGS INCREASING TEMPERATURE AND  
MOISTURE ADVECTION INTO THIS AREA. LOWS TONIGHT WILL BE SLIGHTLY  
ABOVE NORMAL FOR LATE MARCH WITH A LOW LEVEL CLOUD COVER ALONG  
WITH GRADUALLY INCREASING EAST-NORTHEASTERLY SURFACE WINDS AS THE  
SURFACE PRESSURE GRADIENT TIGHTENS.  
 
GKS  
 

 
   
SHORT TERM
 
(THROUGH LATE WEDNESDAY AFTERNOON)  
ISSUED AT 327 PM CDT TUE MAR 28 2017  
 
CLOUDS HAVE STAYED LOCKED IN OVER THE AREA AS THE CLEARING OVER EAST  
CENTRAL ILLINOIS THAT WAS WORKING INTO THE EASTERN CWA FILLED BACK  
IN WITH STRATOCUMULUS THIS AFTERNOON. FORECAST SOUNDINGS DO SHOW  
THAT THE LOW LEVELS WILL STAY SATURATED THROUGH THE NIGHT, WITH AN  
INCREASE IN MID-HIGH CLOUDS AS UPPER LOW CURRENTLY OVER NEW MEXICO  
MOVES NORTHEAST INTO THE PLAINS. SHOWERS AND ISOLATED THUNDERSTORMS  
WILL MOVE INTO THE AREA LATE TONIGHT PER THE GFS AND NAM AS THE  
UPPER RIDGE MOVES EAST AND A BAND OF STRONG MOISTURE CONVERGENCE  
SETS UP ON THE NOSE OF A 40KT LOW LEVEL JET. THIS LOW LEVEL FORCING  
COMBINED WITH INCREASED MID-UPPER ASCENT FROM APPROACHING LOW WILL  
BE ENOUGH TO SET UP ONE ROUND OF SHOWERS AND SCATTERED THUNDERSTORMS  
LATE TONIGHT AND TOMORROW MORNING. THEN THERE MAY BE A BREAK DURING  
THE LATE MORNING AND EARLY AFTERNOON BEFORE BOTH MODELS SHOW ANOTHER  
ROUND OF SHOWERS AND THUNDERSTORMS MOVING INTO CENTRAL MISSOURI BY  
LATE AFTERNOON.  
 
WENT CLOSER TO THE GFS MOS TEMPERATURES OVER THE NEXT 24 HOURS.  
 
BRITT  
   
LONG TERM
 
(WEDNESDAY NIGHT THROUGH NEXT TUESDAY)  
ISSUED AT 327 PM CDT TUE MAR 28 2017  
 
PRIMARY CONCERN HEADING INTO WEDNESDAY NIGHT IS THE POTENTIAL FOR  
SEVERE WEATHER. GUIDANCE IS IN GOOD AGREEMENT THAT THERE WILL BE  
THUNDERSTORMS OVER WESTERN MISSOURI AT 00Z MOVING TOWARD OUR AREA.  
FORECAST INSTABILITY FALLS OF PRETTY QUICKLY IN THE EVENING WITH  
MUCAPE VALUES NOT EXCEEDING 500 J/KG ON THE GFS UNTIL AFTER 09Z.  
NAM HAS MORE ENERGY IN THE EVENING PUSHING 1000 J/KG, BUT IT TENDS  
TO BE A BIT TOO HIGH, AND EVEN WITH THAT HIGH BIAS MUCAPE VALUES  
FALL OFF OVERNIGHT. REGARDLESS...WITH 50-60KTS OF DEEP LAYER  
SHEAR, CAN'T SAY THERE WON'T BE SEVERE STORMS; BUT THE THREAT  
SHOULD STAY OVER OUR EASTERN OZARK COUNTIES WHERE INSTABILITY WILL  
BE GREATEST. SHOULD BE A BETTER CHANCE FOR SEVERE STORMS ON  
THURSDAY AHEAD OF THE LOW. SBCAPE INCREASES TO AROUND 2000 J/KG  
DURING THE AFTERNOON. DEEP LAYER SHEAR ISN'T AS IMPRESSIVE  
INITIALLY AT 18Z BUT INCREASES TO 40+ KTS ALONG AND SOUTHEAST OF  
I-44 AND SOUTH OF I-70. 0-1KM HELICITY IS LESS THAN 100 M2/S2 FOR  
THE AFTERNOON HOURS ON THURSDAY SO THINK THE PRIMARY THREATS WILL  
BE HAIL AND DAMAGING WIND RATHER THAN TORNADOES.  
 
THUNDERSTORM THREAT WILL BE COMING TO AN END THURSDAY NIGHT ALTHOUGH  
RAIN WILL LIKELY CONTINUE ON THE WEST SIDE OF THE LOW AS IT PASSES  
FOR A GOOD PORTION OF THE NIGHT. COOLER AND DRIER AIR WILL MOVE  
INTO THE AREA ON FRIDAY AND SATURDAY. OVERNIGHT LOWS WILL DIP INTO  
THE UPPER 30S AND 40S WITH DAYTIME HIGHS MAINLY IN THE UPPER 50S TO  
MID 60S. THERE IS A CHANCE THERE COULD BE SOME RAIN ON SUNDAY AHEAD  
OF THE NEXT SYSTEM AS THE UPPER LEVEL SHORTWAVE DIGS INTO THE  
SOUTHERN PLAINS. HOWEVER THE GFS AND ECMWF DISAGREE ON HOW MUCH  
QPF TO PRINT OUT SO HAVE REDUCED POPS FOR SUNDAY UNTIL WE SEE A  
LITTLE BETTER AGREEMENT. THE SYSTEM LIFTS OUT OF THE SOUTHERN  
PLAINS INTO THE MISSISSIPPI VALLEY ON MONDAY SO RAIN CHANCES FOR  
EARLY IN THE WEEK LOOK GOOD. THE GFS AND ECMWF CAN'T AGREE ON A  
TRACK FOR THE SURFACE SYSTEM JUST YET WITH THE GFS BEING FURTHER  
NORTH AND THEREFORE WARMER THAN THE EC. THINK THE CURRENT HEDGE  
BETWEEN THE TWO WITH HIGHS MAINLY IN THE 60S AND LOWS IN THE MID  
40S TO LOW 50S LOOKS GOOD.  
 
CARNEY  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)  
ISSUED AT 1027 PM CDT TUE MAR 28 2017  
 
CLOUD CEILING AROUND 3000 FEET SHOULD GRADUALLY LOWER LATE  
TONIGHT AND EARLY WEDNESDAY MORNING, EVENTUALLY DOWN TO IFR  
BY LATE WEDNESDAY MORNING. IT APPEARS THAT SHOWERS WILL MOVE INTO  
THE COU AREA AROUND 12Z WEDNESDAY, AND INTO UIN AND POSSIBLY ALSO  
THE ST LOUIS METRO AREA AS WELL LATER IN THE MORNING AS A  
SOUTHERLY LOW LEVEL JET BRINGS INCREASING LOW LEVEL MOISTURE INTO  
THE AREA AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM OVER THE  
SOUTHERN PLAINS. EAST-NORTHEAST SURFACE WINDS WILL STRENGTHEN  
LATE TONIGHT AND WEDNESDAY MORNING AS THE SURFACE PRESSURE  
GRADIENT TIGHTENS. THERE WILL LIKELY BE A BREAK IN THE CONVECTION  
WEDNESDAY AFTERNOON, THEN ANOTHER ROUND OF SHOWERS AND STORMS WILL  
MOVE THROUGH THE TAF SITES WEDNESDAY NIGHT AS A WARM FRONT  
APPROACHES FROM THE SOUTH.  
 
SPECIFICS FOR KSTL: CLOUD CEILING AROUND 3000 FEET SHOULD GRADUALLY  
LOWER LATE TONIGHT AND EARLY WEDNESDAY MORNING, EVENTUALLY DOWN  
TO IFR BY LATE WEDNESDAY MORNING. IT APPEARS THAT SCATTERED SHOWERS  
WILL MOVE INTO THE ST LOUIS METRO AREA IN THE MORNING AS A  
SOUTHERLY LOW LEVEL JET BRINGS INCREASING LOW LEVEL MOISTURE INTO  
THE AREA AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM OVER THE  
SOUTHERN PLAINS. NORTHEAST SURFACE WINDS WILL STRENGTHEN LATE  
TONIGHT AND WEDNESDAY AS THE SURFACE PRESSURE GRADIENT TIGHTENS.  
THERE WILL LIKELY BE A BREAK IN THE CONVECTION WEDNESDAY  
AFTERNOON, THEN ANOTHER ROUND OF SHOWERS AND STORMS WILL MOVE  
INTO THE STL AREA BY LATE WEDNESDAY NIGHT AS A WARM FRONT  
APPROACHES FROM THE SOUTH.  
 
GKS  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
SAINT LOUIS 47 63 56 71 / 5 60 90 80  
QUINCY 42 55 50 61 / 5 70 90 80  
COLUMBIA 47 60 54 67 / 40 70 90 70  
JEFFERSON CITY 49 62 55 68 / 30 60 90 70  
SALEM 48 64 56 72 / 0 30 70 90  
FARMINGTON 50 64 58 71 / 5 50 90 80  
 

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

 
 

 
 
WFO LSX  
 
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