018  
FXUS63 KPAH 201158  
AFDPAH  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PADUCAH KY  
658 AM CDT MON AUG 20 2018  
   
UPDATE
 
 
ISSUED AT 658 AM CDT MON AUG 20 2018  
 
UPDATED AVIATION DISCUSSION FOR 12Z TAFS.  
 

 
   
SHORT TERM
 
(TODAY THROUGH WEDNESDAY NIGHT)  
ISSUED AT 330 AM CDT MON AUG 20 2018  
 
THE PRIMARY NEAR TERM CONCERN IS THE POTENTIAL FOR SHOWERS AND  
THUNDERSTORMS THROUGH TONIGHT, IN ADDITION TO THE RISK FOR SEVERE  
WEATHER THIS AFTERNOON AND EVENING.  
 
A RELATIVELY STRONG AREA OF LOW PRESSURE NEAR KANSAS CITY EARLY  
THIS MORNING IS FORECAST TO SLOWLY MAKE ITS WAY EAST TOWARDS THE  
MISSISSIPPI RIVER BY THIS EVENING, THEN WEAKEN AS IT ACCELERATES  
NORTHEASTWARD INTO THE GREAT LAKES REGION ON TUESDAY. ENERGY FROM  
THIS LOW WILL PROVIDE THE NECESSARY FORCING FOR ASCENT--ACTING ON  
A SEASONABLY HUMID AIR MASS TO YIELD A COUPLE ROUNDS OF SHOWERS  
AND THUNDERSTORMS THROUGH TONIGHT. THE FIRST ROUND ACCOMPANIES THE  
PASSAGE OF A WARM FRONTAL ZONE THIS MORNING, WHILE THE SECOND IS  
FORECAST WITH THE APPROACH AND PASSAGE OF A COLD FRONTAL ZONE  
THIS AFTERNOON AND TONIGHT.  
 
A BAND OF SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THE EASTWARD  
ADVANCING WARM FRONTAL ZONE CONTINUES TO MAKE PROGRESS ACROSS  
THE MISSISSIPPI RIVER EARLY THIS MORNING. WHILE THE INITIAL BAND  
IS RAPIDLY DISSIPATING, NEW DEVELOPMENT NEAR THE MISSISSIPPI RIVER  
SHOULD CONTINUE ACROSS SOUTHERN ILLINOIS AND WESTERN KENTUCKY  
THROUGH THE REMAINDER OF THE PRE-DAWN HOURS, EVENTUALLY REACHING  
SOUTHWEST INDIANA AND THE KENTUCKY PENNYRILE REGION AROUND  
DAYBREAK. THIS ACTIVITY SHOULD LARGELY SHIFT EAST OF THE AREA BY  
MID TO LATE MORNING.  
 
WHILE THE MORNING CONVECTIVE ACTIVITY WILL LIKELY LEAVE BEHIND A  
SUBSTANTIAL AMOUNT OF CLOUD COVER, FORECAST MODELS ARE SUGGESTIVE  
THAT SOME SUNSHINE SHOULD BEGIN TO SHOW BY LATE MORNING AND  
AFTERNOON, ESPECIALLY ACROSS THE WESTERN HALF OF THE REGION.  
NUMEROUS SHORT TERM MODELS, INCLUDING THOSE WITHIN THE SPC HREF  
SUITE, DEVELOP A MODERATELY UNSTABLE ATMOSPHERE WITH SBCAPES OF  
1500-2500 J/KG BY MID TO LATE AFTERNOON. THE APPROACH OF A 40-50  
KNOT MID-LEVEL SPEED MAX THIS AFTERNOON SHOULD TRIGGER HELP TO  
TRIGGER NEW CONVECTION WITHIN THE MODERATELY UNSTABLE AIR MASS.  
 
INITIAL DEVELOPMENT APPEARS MOST FAVORABLE WITHIN A ZONE FROM  
SOUTH-CENTRAL INTO SOUTHEAST MISSOURI AND EVENTUALLY INTO  
SOUTHWEST ILLINOIS. FORECAST 0-6 KM BULK SHEAR OF 30-40 KNOTS  
FAVORS MULTICELL AND SUPERCELL STORM MODES INITIALLY, WITH A  
TREND TOWARDS MULTICELL CLUSTERS AND LINES AS THE ACTIVITY  
PROGRESSES EAST ACROSS THE REMAINDER OF THE AREA THROUGH THE LATE  
AFTERNOON AND EVENING HOURS. SPC HAS MOST OF THE FORECAST AREA IN  
A SLIGHT RISK FOR SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING.  
DAMAGING WIND IS THE PRIMARY CONCERN, BUT LARGE HAIL AND A BRIEF  
TORNADO CANNOT BE RULED OUT EARLY ON--PARTICULARLY IN SOUTHEAST  
MISSOURI. A WEAKENING TREND IS EXPECTED BY MID EVENING AS THE  
ATMOSPHERE BEGINS TO STABILIZE IN RESPONSE TO THE LOSS OF DIURNAL  
HEATING.  
 
A SMALL CHANCE OF SHOWERS AND THUNDERSTORMS LINGERS INTO TUESDAY  
ACROSS NORTHERN AND EASTERN SECTIONS OF THE FORECAST AREA IN  
CLOSER PROXIMITY TO THE DEPARTING LOW. THEREAFTER, DRY CONDITIONS  
ARE FORECAST TUESDAY NIGHT THROUGH WEDNESDAY NIGHT AS AN EXPANSIVE  
DOME OF HIGH PRESSURE BUILDS EAST FROM THE PLAINS. DURING THIS  
TIME, THE REGION WILL BE SITUATED IN NORTHWEST FLOW BETWEEN AN  
UPPER LOW OVER THE NORTHEASTERN U.S. AND AN UPPER RIDGE OVER THE  
SOUTHERN PLAINS. SO AFTER HIGHS IN THE MID 80S TODAY, TEMPERATURES  
ARE FORECAST TO PEAK IN THE UPPER 70S TO LOWER 80S BOTH TUESDAY  
AND WEDNESDAY. LOWS SHOULD DROP FROM THE UPPER 60S TONIGHT INTO  
THE UPPER 50S BY WEDNESDAY NIGHT, RESULTING IN WHAT COULD BE THE  
COOLEST NIGHT LOCALLY SINCE LATE MAY OR EARLY JUNE.  
   
LONG TERM
 
(THURSDAY THROUGH SUNDAY)  
ISSUED AT 330 AM CDT MON AUG 20 2018  
 
THE MEDIUM RANGE MODELS/ENSEMBLES WERE IN GOOD AGREEMENT THROUGH THE  
EXTENDED FORECAST PERIOD.  
 
THE PAH FORECAST AREA WILL BE UNDER THE INFLUENCE OF AN AREA OF HIGH  
SURFACE PRESSURE AND NORTHWESTERLY MID LEVEL FLOW BY THU. THU NIGHT  
SHOULD BE DRY, BUT BY EARLY FRI, SHOWERS AND TSTMS ARE POSSIBLE OVER  
PARTS OF SOUTHEASTERN MO AND SOUTHWESTERN IL. A TIGHT LOW PRESSURE  
SYSTEM WILL PASS THROUGH THE UPPER MIDWEST, LOWERING MID LEVEL  
HEIGHTS HERE SOMEWHAT BUT WITH NO SURFACE BOUNDARY TO SPEAK OF. DUE  
TO THE PRESENCE OF THE RIDGE OF HIGH PRESSURE IN THE DEEP SOUTH,  
DEEP MOISTURE FETCH WILL BE LIMITED FOR US. ALSO, IT APPEARS THE  
BEST MID LEVEL VORTICITY SIGNAL WILL MOSTLY PRECEDE THE BEST FETCH  
OF MOISTURE. THEREFORE, POPS AND QPF FROM FRI THROUGH SAT MORNING  
WILL BE LIMITED WITH THIS SYSTEM, AND WILL BE PRIMARILY IN THE  
WESTERN AND NORTHERN SECTIONS OF THE REGION. AT THIS TIME, WE WILL  
LIMIT TSTM COVERAGE TO ISOLATED.  
 
THE REMAINDER OF THE WEEKEND SHOULD BE DRY FOR THE PAH FORECAST AREA  
UNDER INCREASING HEIGHTS ALOFT AS AN EXPANSIVE RIDGE OF HIGH  
PRESSURE BEGINS TO BUILD OVER THE SOUTHEASTERN QUADRANT OF THE  
COUNTRY. THIS RIDGE MAY CONTINUE TO BUILD EVEN FURTHER BEYOND THE  
SEVEN DAY PERIOD, POSSIBLY TAKING TEMPS TO WELL ABOVE AVERAGE.  
 
WE WILL START OUT RELATIVELY COOL ON THU, WITH HIGHS AROUND 80, AND  
LOWS FRI MORNING RANGING FROM THE UPPER 50S NORTH TO THE LOWER 60S  
SOUTH, AND WE WILL BE BACK TO AROUND AVERAGE LEVELS BY THE WEEKEND.  
WITH SURFACE DEWPOINTS BACK IN THE LOWER 70S, WE COULD FLIRT WITH  
100 HEAT INDICES PRIMARILY IN PARTS OF SOUTHEASTERN MO BY SUN.  
 

 
   
AVIATION
 
 
ISSUED AT 658 AM CDT MON AUG 20 2018  
 
PRIMARILY VFR CONDITIONS ARE FORECAST THROUGH THE PERIOD, ALTHOUGH  
PATCHY MVFR CEILINGS ARE POSSIBLE DURING THE MORNING. SCATTERED  
SHOWERS REMAIN POSSIBLE ACROSS THE EASTERN HALF OF THE AREA  
THROUGH MID MORNING, SO INCLUDED A VCSH MENTION AT BOTH KEVV AND  
KOWB. THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER SOUTHERN MISSOURI  
THIS AFTERNOON. THESE SHOULD IMPACT THE FORECAST TERMINALS DURING  
THE LATE AFTERNOON AND EARLY EVENING HOURS. CONDITIONS COULD BE  
BRIEFLY REDUCED TO MVFR OR IFR IN THIS ACTIVITY, BUT DID NOT  
EXPLICITLY MENTION THE REDUCTION AT THIS POINT DUE TO UNCERTAINTY.  
SOUTHERLY WINDS AROUND 10 KNOTS ARE FORECAST TODAY, WITH GUSTS TO  
15 KNOTS DURING THE LATE MORNING AND AFTERNOON.  
 

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

 
 

 
 
UPDATE...RJP  
SHORT TERM...RJP  
LONG TERM...DB  
AVIATION...RJP  
 
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