683  
FXUS63 KPAH 230835  
AFDPAH  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PADUCAH KY  
335 AM CDT TUE MAY 23 2017  
   
SHORT TERM
 
(TODAY THROUGH THURSDAY NIGHT)  
ISSUED AT 335 AM CDT TUE MAY 23 2017  
 
A PERIOD OF UNSETTLED WEATHER WILL OCCUR OVER THE NEXT FEW DAYS  
AS A DEEP 500 MB TROUGH DEVELOPS OVER OUR REGION AND THEN MOVES  
EAST. DESPITE THE IMPRESSIVE LOOK TO THE 500 MB SYSTEM, THERE DOES  
NOT APPEAR TO BE MUCH (IF ANY) POTENTIAL OF SEVERE WEATHER OR  
HEAVY RAINFALL IN OUR AREA.  
 
TODAY AND TONIGHT, A WEAK 500 MB CLOSED LOW OVER THE UPPER  
MISSISSIPPI VALLEY WILL STRENGTHEN AND DROP ALMOST DUE SOUTHWARD.  
THE ASSOCIATED SURFACE COLD FRONT WILL SWING EAST ACROSS SOUTHERN  
ILLINOIS AND SOUTHEAST MISSOURI LATE THIS AFTERNOON AND EARLY  
THIS EVENING. IN ADVANCE OF THE FRONT, A WEAK SOUTHERLY WIND  
COMBINED WITH DAYTIME HEATING WILL RESULT IN MODEST SURFACE-BASED  
INSTABILITY. SHOWERS AND ISOLATED THUNDERSTORMS WILL FORM ALONG  
THE FRONT. AS THE FRONT CONTINUES EAST ACROSS WEST KY AND SW  
INDIANA THIS EVENING, SHOWERS ARE FORECAST TO INCREASE IN  
COVERAGE AS THE STRENGTHENING UPPER LOW APPROACHES. THE THUNDER  
POTENTIAL SHOULD DIMINISH OVERNIGHT AS POST-FRONTAL NORTHWEST  
WINDS COOL THE BOUNDARY LAYER.  
 
ON WEDNESDAY, A RATHER DEEP 500 MB CLOSED LOW WILL DRIFT SOUTH  
INTO SOUTHERN IL OR SOUTHEAST MO BY EVENING. VERY COLD TEMPS ALOFT  
(AROUND MINUS 20 AT 500 MB) WILL CONTRIBUTE TO SCATTERED SHOWERS  
AND EVEN A FEW THUNDERSTORMS. DESPITE THE COLD AIR ALOFT,  
SURFACE-BASED CAPES ARE FORECAST TO REMAIN MAINLY BELOW 500 J/KG  
IN THE COOL NORTHWEST SURFACE FLOW. THIS WEAK INSTABILITY MAY BE  
SUFFICIENT FOR ISOLATED THUNDERSTORMS WITH SMALL HAIL, ESPECIALLY  
IF ANY BREAKS OF SUN CONTRIBUTE TO STRONGER SURFACE HEATING. HIGH  
TEMPS WILL BE ONLY IN THE 60'S.  
 
SCATTERED CONVECTION WILL DIMINISH WITH LOSS OF DAYTIME HEATING ON  
WEDNESDAY NIGHT. THERE WILL BE SOME PARTIAL CLEARING IN SOUTHEAST  
MO AND SOUTHWEST KY OVERNIGHT. OVERNIGHT LOWS WILL BE IN THE LOWER  
50'S.  
 
ON THURSDAY, A BAND OF RAIN OR RAIN SHOWERS IS DEPICTED BY THE 00Z  
MODELS IN A DEFORMATION ZONE ON THE WEST SIDE OF THE DEPARTING  
500 MB LOW. THIS DEFORMATION ZONE IS LIKELY TO BE OVER SOUTHWEST  
IN AND THE PENNYRILE REGION OF WEST KY IN THE MORNING. CLOUDS MAY  
TAKE MUCH OF THE DAY TO EXIT SOUTHWEST IN AND THE PENNYRILE  
REGION, WHERE HIGHS WILL STRUGGLE TO REACH THE UPPER 60'S.  
ELSEWHERE, THE MODELS CONTINUE TO INDICATE ENOUGH CLEARING FOR  
TEMPS TO REACH THE LOWER OR MID 70'S. THURSDAY NIGHT WILL BE  
MAINLY CLEAR WITH LOWS IN THE 50'S.  
   
LONG TERM
 
(FRIDAY THROUGH MONDAY)  
ISSUED AT 335 AM CDT TUE MAY 23 2017  
 
FORECAST CONFIDENCE IS MODERATE THROUGHOUT THE EXTENDED PORTION OF  
THIS FORECAST.  
 
THE PRIMARY FEATURE THROUGHOUT THE EXTENDED PORTION OF THIS FORECAST  
WILL BE A LARGE UPPER-LEVEL LOW PRESSURE SYSTEM INITIALLY OVER SOUTH  
CENTRAL CANADA. THE GFS PUSHES THIS SYSTEM SOUTHWARD INTO THE  
NORTHERN PLAINS/UPPER MIDWEST BY SUNDAY AND THEN EASTWARD TOWARD  
SOUTHERN ONTARIO BY MONDAY EVENING. THE ECMWF JUST WOBBLES THE  
SYSTEM SLOWLY EASTWARD INTO ONTARIO BY SUNDAY.  
 
WE WILL HAVE SOUTH WINDS TO BEGIN WITH FRIDAY, AND LOW-LEVEL  
MOISTURE WILL BE ON THE INCREASE , WITH SURFACE DEWPOINTS EXPECTED  
TO CLIMB INTO THE 60S DURING THE DAY. FRIDAY IS STILL EXPECTED TO BE  
DRY EXCEPT PERHAPS ON THE WESTERN OR NORTHERN PERIPHERY OF THE  
REGION. THE ECMWF AND GFS BOTH DEVELOP WARM ADVECTION CONVECTION  
OVER OUR REGION FRIDAY NIGHT, BUT THE COVERAGE IS DEBATABLE, WITH  
THE WARM FRONT ALREADY TO OUR NORTH.  
 
AS A MAJOR IMPULSE ROTATES AROUND THE BASE OF THE UPPER TROUGH,  
CONVECTION WILL BE FOCUSED ON OR JUST AHEAD OF THE ASSOCIATED COLD  
FRONT THAT THE ECWMF MOVES THROUGH OUR REGION LATE SATURDAY NIGHT  
INTO EARLY SUNDAY. THE ECMWF THEN DRIES US OUT FOR SUNDAY THROUGH  
MONDAY NIGHT.  
 
WITH ITS UPPER SYSTEM FARTHER SOUTH, THE GFS IS SLOWER TO BRING THE  
COLD FRONT THROUGH THE REGION, AND KEEPS OUR AREA WETTER THROUGH  
SUNDAY AND EVEN INTO SUNDAY NIGHT IN THE EAST. IT DOES KEEP MONDAY  
DRY OVER MOST OF THE AREA, BUT IT BRINGS ANOTHER IMPULSE SOUTHEAST  
AROUND THE DEPARTING UPPER LOW THAT WILL RESULT IN MORE CONVECTION  
MAINLY ACROSS NORTHERN PORTIONS OF THE AREA MONDAY THROUGH NEXT  
TUESDAY. THE ECMWF HAS A MUCH WEAKER IMPULSE THAT MAY FORCE A FEW  
SHOWERS OR STORMS NEAR A WEAK COLD FRONT THAT WOULD MOVE THROUGH  
EASTERN PORTIONS OF THE REGION LATE MONDAY NIGHT INTO NEXT TUESDAY.  
 
THIS FORECAST WILL HAVE MAINLY CHANCE POPS FROM FRIDAY NIGHT THROUGH  
SUNDAY EVENING, AND THEN THERE WILL ONLY BE SLIGHT CHANCES MAINLY  
OVER OUR NORTHERN COUNTIES MONDAY AFTERNOON THROUGH NEXT TUESDAY  
EVENING. TEMPERATURES WILL START OUT NEAR NORMAL FOR HIGHS AND ABOVE  
NORMAL FOR LOWS, AND THEN COOL A CATEGORY OR SO FOR SUNDAY THROUGH  
TUESDAY.  
 
ALL THINGS CONSIDERED IT LOOKS LIKE MEMORIAL DAY WILL BE THE PICK  
DAY OF THE HOLIDAY WEEKEND.  
 

 
   
AVIATION
 
 
ISSUED AT 1205 AM CDT TUE MAY 23 2017  
 
WIDESPREAD MID AND HIGH CLOUDS IN THE 10 TO 15K FOOT RANGE WILL  
CONTINUE THROUGH TUESDAY. SOME OF THE LIGHT RAIN IN TENNESSEE DURING  
THE EARLY MORNING HOURS COULD ARRIVE AS VIRGA IN WEST KY, BUT THE  
MID LEVELS ARE TOO DRY FOR THIS TO REACH THE GROUND. WINDS WILL BE  
LIGHT. TUESDAY EVENING, A COLD FRONT WILL CROSS SE MISSOURI,  
ACCOMPANIED BY SOME LIGHT SHOWERS. AN ISOLATED THUNDERSTORM IS  
POSSIBLE, BUT ODDS ARE TOO LOW TO MENTION IN TAFS. SIGNIFICANT  
CHANGES IN WIND AND CIGS ARE EXPECTED JUST BEYOND THIS TAF PERIOD.  
 

   
PAH WATCHES/WARNINGS/ADVISORIES
 
 
IL...NONE.  
MO...NONE.  
IN...NONE.  
KY...NONE.  

 
 

 
 
SHORT TERM...MY  
LONG TERM...DRS  
AVIATION...MY  
 
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