971  
FXUS63 KLSX 261149  
AFDLSX  
 
AREA FORECAST DISCUSSION...UPDATED AVIATION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
649 AM CDT THU APR 26 2018  
   
SHORT TERM
 
(THROUGH LATE TONIGHT)  
ISSUED AT 313 AM CDT THU APR 26 2018  
 
PRIMARY FOCUS IN THE SHORT TERM IS THIS MORNING'S LINGERING SHOWER  
ACTIVITY. THE UPPER LOW AND BETTER LIFT ASSOCIATED WITH THE H8 VORT  
WILL CONTINUE TO PIVOT SOUTHEAST THROUGH ARKANSAS INTO W. TENNESSEE.  
DRY EAST/NORTHEAST SURFACE FLOW WILL CUT INTO THE LOW LEVEL  
MOISTURE, EFFECTIVELY LOWERING RAIN CHANCES FROM NORTH TO SOUTH.  
IT'S REASONABLE THAT MUCH OF THE AREA WILL BE DONE WITH THE RAIN IN  
THE NEXT 4-6 HOURS. FAR SOUTHERN FRINGES OF THE FORECAST AREA MAY  
SEE SCATTERED SHOWERS LINGER THROUGH 13Z-14Z. OTHERWISE, MEASURABLE  
PRECIP IS PRETTY MUCH LONG GONE FOR MOST LOCATIONS BY 12Z. WE WILL  
RECOVER PRETTY WELL WITH RETURNING SUNSHINE AND TEMPERATURES PUSHING  
WELL INTO THE 60S TO NEAR 70 DEGREES.  
 
IT REMAINS PRETTY QUIET THROUGH THE REMAINDER OF THE SHORT TERM.  
JUST A FEW DAYS AGO, IT LOOKED AS THOUGH A DECENT FRONTAL BOUNDARY  
WOULD MOVE THROUGH LATE THURSDAY INTO FRIDAY MORNING TO GIVE US  
ANOTHER CHANCE OF RAIN. TRENDS HAVE REALLY BACKED OFF ON ANY CHANCES  
WITH VERY LIMITED MOISTURE. INSTEAD, THE ELONGATED TROUGH AXIS WILL  
EXTEND FROM THE GREAT LAKES THROUGH THE PLAINS, SERVING BETTER AS A  
WIND SHIFT. I SEE MUCH LESS IN THE WAY OF CAA WITH 850 TEMPS  
MOMENTARILY DROPPING 2-3C. THE BOUNDARY WASHES OUT AS IT PUSHES  
THROUGH FRIDAY MORNING WITH LIMITED NOTICEABLE CHANGE.  
 
MAPLES  
   
LONG TERM
 
(FRIDAY THROUGH WEDNESDAY)  
ISSUED AT 313 AM CDT THU APR 26 2018  
 
HIGH AMPLITUDE WEATHER PATTERN WITH A DEEP LONGWAVE TROF OVER THE  
EASTERN U.S. AND A STRONG RIDGE STRETCHING FROM NORTHERN MEXICO UP  
ACROSS THE ROCKIES INTO SOUTHWESTERN CANADA IS FORECAST TO REMAIN  
NEARLY STATIONARY INTO SATURDAY. NORTHWEST FLOW ALOFT OVER THE  
MISSISSIPPI VALLEY WILL DRIVE ANOTHER COLD FRONT SOUTH THROUGH THE  
MIDWEST ON FRIDAY AND FRIDAY NIGHT. GUIDANCE SEEMS TO BE IN GOOD  
AGREEMENT ON THE MOVEMENT OF THE FRONT THROUGH MISSOURI AND THE  
SOUTHERN 1/2 OF ILLINOIS ON FRIDAY NIGHT. THERE MAY BE A FEW  
SHOWERS OVER SOUTH CENTRAL ILLINOIS AS THE FRONT MOVES THROUGH, BUT  
IT LOOKS DRY OVER MISSOURI.  
 
THE FRONT SHOULD BE DOWN OVER THE BOOT HEEL OF MISSOURI AND INTO  
WESTERN KENTUCKY AND NORTHERN TENNESSEE BY 12Z SATURDAY MORNING.  
MODELS ARE VERY CONSISTENTLY SHOWING STRONG COLD ADVECTION BEHIND  
THE FRONT AS A 1025+ CANADIAN HIGH DROPS INTO THE MIDWEST. ENSEMBLE  
MOS TEMPERATURES FOR SATURDAY AND SATURDAY NIGHT KEEP FALLING A FEW  
DEGREES WITH EACH RUN. ORIGINALLY LOOKED LIKE HIGHS AROUND 70  
SATURDAY AFTERNOON...BUT LATEST GUIDANCE STRUGGLES TO PUSH US OUT OF  
THE LOW TO MID 60S. 2 METER TEMPS OFF THE RAW MODELS ARE EVEN  
COLDER IN THE MID 50S TO LOW 60S! IT DOESN'T LOOK LIKE WE'LL SET  
ANY RECORDS FOR COOLEST MAXIMUM TEMPERATURE FOR APRIL 28, BUT IT MAY  
GET WITHIN 5-10 DEGREES. REGARDLESS, IT DOES LOOK LIKE THERE WILL BE  
PLENTY OF STRONG LATE APRIL SUNSHINE WHICH WILL MAKE IT FEEL WARMER  
THAN IT REALLY IS.  
 
THE HIGH WILL SHIFT SOUTHEAST SATURDAY NIGHT. LIGHT WIND AND CLEAR  
SKY SHOULD PRODUCE EXCELLENT RADIATIONAL COOLING CONDITIONS. 2  
METER TEMPERATURES AT 12Z ON SUNDAY MORNING ARE APPROACHING LEVELS  
WHERE WE MIGHT NEED TO BE CONCERNED WITH FROST. WILL HOLD OFF  
MENTIONING FROST IN THE FORECAST AT THIS TIME SINCE THIS IS STILL 4  
DAYS AWAY AND THERE'S SOME VARIABILITY IN THE FORECAST.  
 
THE UPPER LEVEL PATTERN GETS IN GEAR AND SHIFTS EAST SUNDAY INTO  
MONDAY. THIS WILL PUSH THE SURFACE RIDGE EAST ACROSS THE  
APPALACHIANS AND JUST OFF THE EAST COAST BY TUESDAY. THE WARM  
SOUTHERLY FLOW ON THE WESTERN SIDE OF THE RIDGE WILL PUSH  
TEMPERATURES UP TO NEAR NORMAL ON SUNDAY AND THEN ABOVE NORMAL FOR  
MONDAY THROUGH WEDNESDAY NEXT WEEK. THE NEXT LONGWAVE TROF IN THE  
PATTERN IS FORECAST TO DIG INTO THE WESTERN CONUS AND MOVE VERY  
SLOWLY EASTWARD THROUGH THE MIDDLE OF NEXT WEEK. THIS WILL SET UP A  
MORE SPRING-LIKE WARM AND WET WEATHER PATTERN WITH SOUTHWEST FLOW  
ALOFT AND AN ACTIVE SOUTH-SOUTHWESTERLY LOW LEVEL JET OVER THE MID  
MISSISSIPPI VALLEY. IT SHOULD CERTAINLY FEEL A LOT MORE LIKE LATE  
APRIL/EARLY MAY WITH THE POTENTIAL FOR THUNDERSTORMS AND  
TEMPERATURES IN THE UPPER 70S TO LOW 80S.  
 
CARNEY  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)  
ISSUED AT 649 AM CDT THU APR 26 2018  
 
LOCALIZED AREAS OF IFR/LIFR FOG DEVELOPED OVERNIGHT, MAINLY AROUND  
KCOU AND KCPS. REMNANT FOG WILL DISSIPATE WITH SUNRISE AND DRIER  
WORKING INTO THE REGION. MVFR CIGS SOUTH OF ST. LOUIS CONTINUE TO  
DEPART TO THE SOUTHEAST THROUGH THE MORNING. VFR CONDITIONS ARE  
EXPECTED FOR THE REMAINDER OF THE FORECAST PERIOD. WIND WILL  
REMAIN RELATIVELY LIGHT TODAY OUT OF THE NORTHWEST.  
 
SPECIFICS FOR KSTL:  
 
OVC/BKN CLOUD DECK WILL CONTINUE TO DEPART TO THE SOUTHEAST THIS  
MORNING. VFR CONDITIONS ARE EXPECTED THROUGHOUT THE FORECAST  
PERIOD WITH FEW/SCT HIGH CLOUDS. NORTHWEST WINDS WILL BE  
RELATIVELY LIGHT TODAY THROUGH EARLY FRIDAY. NORTHWEST WIND WILL  
BRIEFLY SHIFT OUT OF THE WEST-SOUTHWEST OVERNIGHT AHEAD OF A  
BOUNDARY, THEN BACK TO THE NORTHWEST FRIDAY MORNING. SIMPLIFIED  
THE TAF TO JUST A COUPLE OF LINES GIVEN THE VFR CONDITIONS AND  
WINDS REMAINING BELOW 10 KTS.  
 
MAPLES  
 

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

 
 

 
 
WFO LSX  
 
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