265  
FXUS63 KLSX 240949  
AFDLSX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
349 AM CST SAT FEB 24 2018  
   
SHORT TERM
 
(THROUGH LATE TONIGHT)  
ISSUED AT 348 AM CST SAT FEB 24 2018  
 
ONGOING HEAVY RAIN EVENT IS OBVIOUSLY THE FIRST CONCERN. THE  
FORECAST LOOKS TO BE WORKING OUT PRETTY WELL WITH A LARGE AREA OF  
RAIN FORCED BY LOW LEVEL MOISTURE CONVERGENCE OVER A QUASI-  
STATIONARY FRONT STRETCHING ACROSS SOUTHERN MISSOURI. RAINFALL  
AMOUNTS SINCE MIDNIGHT RANGE FROM ABOUT 0.20-0.60 INCH STRETCHING IN  
A BAND FROM NEAR VICHY UP INTO THE ST. LOUIS METRO AREA WITH THE  
HIGHER AMOUNTS TO THE SOUTHWEST OF THE STL METRO. THIS WAVE OF RAIN  
SHOULD END FROM SOUTHWEST TO NORTHEAST THIS MORNING FROM ABOUT 12Z  
TO 16Z AS THE 850MB FLOW VEERS AND BECOMES MORE PARALLEL TO THE  
BAROCLINIC ZONE. THE AXIS OF HEAVIEST RAIN IS WITHIN THE  
AREA OF THE FLOOD WATCH SO NO CHANGES TO THE WATCH ARE  
ANTICIPATED AT THIS TIME  
 
MEANWHILE, UP ACROSS NORTHEAST MISSOURI, TEMPERATURES HAVE FALLEN TO  
RIGHT AROUND FREEZING, AND FREEZING RAIN IS CURRENTLY BEING REPORTED  
IN KIRKSVILLE. STILL THINK SOME LIGHT ICE ACCUMULATION ON ELEVATED  
SURFACES IS LIKELY THIS MORNING BEFORE TEMPERATURES CLIMB BACK ABOVE  
32, SO THE WINTER WEATHER ADVISORY STILL LOOKS GOOD.  
 
A STRONG SHORTWAVE WILL DROP INTO THE GREAT PLAINS TODAY FORCING  
CYCLOGENESIS OVER WESTERN ARKANSAS OR EASTERN OKLAHOMA. THE  
RESULTING LOW WILL MOVE NORTHEAST AS THE POSITIVELY TILTED WAVE LIFTS  
INTO THE MIDWEST. WARM MOIST AIR IN THE WARM SECTOR OF THE SYSTEM  
WILL BRING ANOTHER WAVE OF RAIN TO OUR FORECAST AREA ALONG WITH AN  
INCREASED CHANCE FOR THUNDERSTORMS. HIGHEST QPF AND CHANCE FOR  
FLOODING IS SOUTH OF THE I-44 CORRIDOR IN MISSOURI LATE THIS  
AFTERNOON AND THIS EVENING AHEAD OF THE COLD FRONT. ADDITIONALLY,  
THE NAM SHOWS MUCAPE VALUES BETWEEN 500-1000 J/KG IN SOUTHEAST  
MISSOURI THIS EVENING. THE GFS IS NOT QUITE AS AGGRESSIVE WITH THE  
INSTABILITY, BUT THERE WILL BE MORE THAN ENOUGH SHEAR TO PRODUCE  
SEVERE THUNDERSTORMS IF THE HIGHER INSTABILITY CAN BE REALIZED.  
CONVECTIVE MODE WILL BE HIGHLY DEPENDENT ON THE AMOUNT OF  
INSTABILITY WHICH DEVELOPS, BUT COULD RANGE FROM A SEVERE SQUALL  
LINE TO LOW TOPPED SUPERCELLS. REGARDLESS...THE THREAT FOR SEVERE  
WEATHER SHOULD BE LOCALIZED TO SOUTHEAST MISSOURI AND SOUTHERN  
ILLINOIS.  
 
THE COLD FRONT WILL MOVE THROUGH QUICKLY BETWEEN 00Z AND 05Z  
TONIGHT, BRINGING THE WET WEATHER TO AN END FOR THE TIME BEING.  
INCREASING PRESSURE GRADIENT BEHIND THE FRONT WILL LIKELY PRODUCE  
STRONG AND GUSTY WINDS AFTER FROPA WITH GUSTS TO AROUND 35 MPH  
LIKELY...PARTICULARLY IN NORTHEAST MISSOURI INTO CENTRAL ILLINOIS.  
 
CARNEY  
   
LONG TERM
 
(SUNDAY THROUGH FRIDAY)  
ISSUED AT 348 AM CST SAT FEB 24 2018  
 
THERE IS FAIRLY GOOD AGREEMENT AMONG THE MODELS THAT THE PERIOD FROM  
SUNDAY THROUGH MONDAY NIGHT WILL BE RATHER TRANQUIL WITH ABOVE  
NORMAL AND SLOWLY MODERATING TEMPERATURES. SOUTHWEST FLOW ALOFT WILL  
PERSIST IN THE WAKE OF THE UPPER TROF EXITING THE GREAT LAKES INTO  
SOUTHEAST CANADA WHILE WEAK HIGH PRESSURE TO THE SOUTH OF THE CWA  
DOMINATES. A FAST-MOVING LOW-AMPLITUDE SHORT WAVE TROF WILL TRAVERSE  
THE REGION ON SUNDAY NIGHT. MOISTURE APPEARS TO BE QUITE LIMITED  
WITH THIS WAVE AND PRESENT INDICATIONS ARE IT WILL BE JUST  
ACCOMPANIED BY SOME MID CLOUDS.  
 
TEMPERATURES WILL CONTINUE TO MODERATE MONDAY AS 1) HEIGHTS RISE  
ALOFT ASSOCIATED WITH MODEST RIDGING OCCURRING IN RESPONSE TO  
UPSTREAM AMPLIFICATION FEATURING A DIGGING/DEEPENING WEST COAST  
UPPER LOW/TROF, AND 2) SOUTHERLY FLOW RETURNS BRINGING WEAK WAA. A  
BETTER BOOST IN THE WARMING APPEARS ON TAP FOR TUESDAY AS FLOW ALOFT  
BECOME MORE SOUTHWESTERLY AND WAA INCREASES IN RESPONSE TO  
STRENGTHENING SOUTH-SOUTHWEST LOW LEVEL FLOW.  
 
FROM TUESDAY NIGHT THROUGH THE END OF THE WEEK THE GFS AND ECMWF  
BEGIN TO DIVERGE IN THE DETAILS OF THE FORECAST. THIS IS MOST  
PROMINENT BEGINNING LATE WEDNESDAY NIGHT WHEN THEY DEPART  
SIGNIFICANTLY WITH THE HANDLING OF THE EJECTING WEST COAST UPPER  
TROF. FIRST ON TUESDAY NIGHT THE ECWMF IS RATHER STINGY WITH THE  
AMOUNT AND NORTHERN EXTENT OF A LIGHT PRECIPITATION EVENT AS A WEAK  
IMPULSE ALOFT TRAVERSE THE AREA. THE WETTER GFS SOLUTION APPEARS TO  
BE A REFLECTION OF BETTER LOW LEVEL MOISTURE RETURN. THE GFS THEN  
HAS THE WEST COAST TROF EJECTING ACROSS THE PLAINS AND THROUGH THE  
MS VALLEY WEDNESDAY NIGHT INTO THURSDAY BRINGING STRONG LARGE SCALE  
ASCENT AND ACCOMPANIED BY A A WELL DEVELOPED SURFACE LOW AND  
WARM/COLD FRONTAL SYSTEMS. ALTERNATIVELY THE ECWMF HAS A COLD  
FRONTAL PASSAGE DUE TO A WEAK NORTHERN STREAM SHORT WAVE WITH THE  
WEAKENING WEST COAST TROF LAGGING BACK INTO THE SOUTHERN ROCKIES AND  
SOUTHERN PLAINS. OVERALL THE GFS HAS SLIGHTLY BETTER CONTINUITY.  
WHILE THE GEFS SHOWS A GOOD DEAL OF SPREAD, IT HAS MORE MEMBERS THAN  
NOT CLOSER TO THE OPERATIONAL GFS SOLUTION, SUGGESTING THEN ANOTHER  
WET PERIOD FROM WEDNESDAY AFTERNOON INTO THURSDAY MORNING.  
 
GLASS  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)  
ISSUED AT 1147 PM CST FRI FEB 23 2018  
 
PRECIPITATION HAS NEARLY OVERSPREAD ALL TAF SITES AND WILL REACH  
UIN IMMINENTLY. PCPN SHOULD BE ALL RAIN EXCEPT COULD MIX WITH SOME  
SNOW IN UIN INITIALLY. IFR CONDITIONS HAVE ENVELOPED ALL TAF SITES  
EXCEPT UIN AND WILL LIKELY REACH THERE BY 09Z. AFTER A BREAK IN  
THE RAIN FOR MOST OF THE MORNING AND EARLY AFTERNOON, ROUND TWO OF  
THE RAIN WILL MOVE BACK IN DURING SATURDAY AFTERNOON AND EXIT IN  
THE EARLY EVENING. ROUND TWO OF THE RAIN WILL BE MORE CONVECTIVE,  
AND HAVE ADDED IN SOME VCTS TO ACCOUNT FOR IT FOR NOW. LIGHT  
NE SURFACE WINDS WILL GRADUALLY VEER E AND STRENGTHEN BY SATURDAY,  
AND FURTHER VEER TO SW AND W DURING SATURDAY EVENING. WINDS  
NOTABLY WILL STRENGTHEN SIGNIFICANTLY WITH ADVENT OF SW TO W  
DIRECTION AS THE DRY LINE/COLD FRONT PASSES AND WILL SEE GUSTS TO  
25-30KTS.  
 
SPECIFICS FOR KSTL: IFR CONDITIONS WILL PREVAIL UNTIL PASSAGE OF  
DRY LINE/COLD FRONT SATURDAY EVENING. STEADY RAIN WILL EXIT BY  
MID-MORNING WITH ROUND TWO RETURNING BY LATE AFTERNOON. COULD SEE  
SOME THUNDER NEARBY WITH THE SECOND ROUND. AFTER WINDS VEER  
GRADUALLY FROM NE TO SE TO SW BY SATURDAY EVENING, LOOK FOR  
SUBSTANTIAL STRENGTHENING WITH DRY LINE/COLD FRONT PASSAGE WITH  
GUSTS TO 30KTS.  
 
TES  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
SAINT LOUIS 55 34 57 34 / 100 80 0 5  
QUINCY 48 29 50 29 / 80 80 0 0  
COLUMBIA 53 30 54 30 / 80 80 0 5  
JEFFERSON CITY 55 31 56 31 / 90 80 0 0  
SALEM 57 37 53 34 / 100 90 0 0  
FARMINGTON 60 35 57 33 / 100 80 0 5  
 

 
   
LSX WATCHES/WARNINGS/ADVISORIES
 
 
MO...FLOOD WATCH THROUGH THIS EVENING FOR CRAWFORD MO-FRANKLIN MO-  
GASCONADE MO-IRON MO-JEFFERSON MO-MADISON MO-OSAGE MO-  
REYNOLDS MO-SAINT CHARLES MO-SAINT FRANCOIS MO-SAINT LOUIS  
CITY MO-SAINT LOUIS MO-SAINTE GENEVIEVE MO-WARREN MO-  
WASHINGTON MO.  
 
WINTER WEATHER ADVISORY UNTIL 9 AM CST THIS MORNING FOR KNOX MO-  
LEWIS MO.  
 
IL...FLOOD WATCH THROUGH THIS EVENING FOR BOND IL-CLINTON IL-FAYETTE  
IL-MADISON IL-MARION IL-MONROE IL-RANDOLPH IL-SAINT CLAIR  
IL-WASHINGTON IL.  
 

 
 

 
 
WFO LSX  
 
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