964  
FXUS63 KPAH 240009  
AFDPAH  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PADUCAH KY  
709 PM CDT SAT JUN 23 2018  
   
UPDATE
 
 
ISSUED AT 709 PM CDT SAT JUN 23 2018  
 
AMENDED AVIATION DISCUSSION FOR 00Z TAFS.  
 
CURRENT PUBLIC FORECAST IS GENERALLY REPRESENTATIVE OF CURRENT  
CONDITIONS. A BROKEN LINE OF THUNDERSTORMS HAS FORMED ACROSS  
PORTIONS OF SOUTHERN ILLINOIS AND SOUTHEAST MISSOURI EARLY THIS  
EVENING. THE STORMS ARE TIED TO THE EASTWARD PROPAGATION OF A WEAK  
MID LEVEL DISTURBANCE AND LOCATED NEAR THE INTERSECTION OF  
1500-2000 J/KG SBCAPES ACROSS THE SOUTHERN HALF OF THE AREA AND 30  
TO 40 KNOTS OF 0-6 KM BULK SHEAR OVER THE NORTHERN HALF OF THE  
AREA.  
 
NUMEROUS STORMS HAVE DISPLAYED WEAK MID LEVEL ROTATION WITH MINI  
SUPERCELL CHARACTERISTICS. THIS ACTIVITY IS LARGELY EXPECTED TO  
CONTINUE ITS MOVEMENT SOUTHEAST THROUGH MID EVENING, WITH A  
LOCALIZED THREAT OF LARGE HAIL AND DAMAGING WINDS. DESPITE THE MID  
LEVEL ROTATION, THE TORNADO THREAT APPEARS TO BE SMALLER GIVEN  
OBSERVED WEAK 0-1 KM BULK SHEAR. SOME DECREASE IN INTENSITY IS  
EXPECTED BY MID EVENING AS INSTABILITY BEGINS TO DAMPEN DUE TO  
LOSS OF DAYTIME HEATING.  
 

 
   
SHORT TERM
 
(TONIGHT THROUGH MONDAY NIGHT)  
ISSUED AT 149 PM CDT SAT JUN 23 2018  
 
THE SHORT TERM MODELING, ESP THE HRRR, HAS REALLY DOWNPLAYED NEAR  
TERM PCPN CHANCES. WE'VE BOUGHT INTO THAT A LITTLE, BUT WILL  
COLLABORATE FOR BEST FINAL PIC. THAT'S LIKELY TO BE A SLIGHT  
CHANCE TO LOW CHANCE FROM NORTH TO SOUTH ACROSS THE AREA, BASED ON  
CONSISTENCY OF PREVIOUS MODEL SOLUTIONS/INSISTENCE. WHILE  
CONFIDENCE TONIGHT IS DOWN, STILL LIKE TMRW MORNING'S CHANCES  
WITH ALL MODELS SHOWING WAVE OPENING UP AND HIGH CHANCE TO LOW  
LIKELY POPS AS HAS BEEN CONSISTENTLY ADVERTISED. MORE VORT ENERGY  
CONTINUES THESE POPS INTO SUNDAY NIGHT WHILE WE WILL WARM SECTOR.  
 
WE'LL STILL ANTICIPATE MORE OFF AND ON CHANCES INTO THE EARLY WORK  
WEEK, WITH THE NEWLY FORMING LOW MOVING INTO IOWA BY THE END OF  
THE SHORT TERM. HAVING WARM SECTORED BY THEN, TEMPS WILL START TO  
HEAT UP AND JUICE UP, WITH HEAT INDICES REACHING TOWARD TRIPLE  
DIGITS BY MONDAY PM, WHICH COULD BE THE BEGINNING OF CONSISTENT  
SUCH READINGS FOR SEVERAL DAYS IN A ROW, IF NOT THE ENTIRETY OF  
THE WORK WEEK.  
   
LONG TERM
 
(TUESDAY THROUGH SATURDAY)  
ISSUED AT 149 PM CDT SAT JUN 23 2018  
 
THE EXTENDED PORTION OF THIS ROUTINE FORECAST ISSUANCE BEGINS WITH  
THE TRANSITION OF A NEARLY VERTICALLY STACKED CLOSED SHORTWAVE  
LENGTH LOW MOVING FROM SOUTHERN MINNESOTA/NORTHERN IOWA AT 7 AM CDT  
TUESDAY TO JUST SOUTH OF HUDSON BAY CANADA BY 7 PM CDT WEDNESDAY.  
 
THE SENSIBLE WEATHER FOR THE WFO PAH FORECAST AREA WILL INCLUDE WARM  
FRONTAL ZONE LIFTED AND ISENTROPICALLY LIFTED CONVECTIVE ACTIVITY BY  
TUESDAY AFTERNOON, FOLLOWED BY PRE-FRONTAL AND WEAK COLD FRONTAL  
CONVECTION LATE TUESDAY NIGHT THROUGH WEDNESDAY. WITH THE MIDDLE AND  
UPPER LOW MOVING INTO SOUTHERN CANADA, THE MAJORITY OF THE DEEP  
LAYER SHEAR WILL DRIFT NORTH OF THE WFO PAH FORECAST AREA. THE  
MEDIUM RANGE GFS CARRIES A LITTLE MORE SHORTWAVE ENERGY IN THE WEST-  
NORTHWEST FLOW BEHIND THE AFOREMENTIONED LOW VERSUS THE 00Z SATURDAY  
ECMWF AND 12Z SATURDAY CANADIAN NUMERICAL MODEL GUIDANCE. EVEN THE  
12Z NAM-WRF IS NOT CONSISTENT WITH BRINGING ANY ADDITIONAL SHORTWAVE  
ENERGY BEHIND THE CLOSED LOW VERSUS THE GFS. AT THIS POINT, WILL  
LEAN AWAY FROM A GREATER INFLUENCE OF THE GFS VERSUS A COMBINATION  
OF THE NAM-WRF/ECMWF/CANADIAN SOLUTIONS.  
 
BEYOND THE PASSAGE OF THE CLOSED LOW ON WEDNESDAY AND THE WEAK  
SURFACE FRONTAL ZONE REFLECTION THROUGH THE WFO PAH FORECAST AREA,  
ALL OF THE GUIDANCE BUILD IN A RIDGE OVER THE AREA THROUGH FRIDAY  
MORNING. THE MIDDLE AND UPPER LEVEL RIDGE EVENTUALLY MOVES EAST OF  
THE WFO PAH FORECAST AREA FRIDAY NIGHT INTO THE OHIO VALLEY AND THE  
NORTHEAST U.S. A PROGRESSIVE TROUGH/LOW CENTERED OVER IDAHO WILL  
GRADUALLY SHIFT THE UPPER LEVEL FLOW TO THE SOUTHWEST ON THE EASTERN  
SIDE OF THE TROUGH DURING THE DAY SATURDAY INTO SUNDAY. AGAIN THE  
GFS DIFFERS FROM THE ECMWF AND CANADIAN GUIDANCE BY RETROGRADING THE  
DEPARTING HIGH PRESSURE RIDGE WESTWARD INTO THE OHIO AND MISSISSIPPI  
VALLEY AREA.  
 
EVEN THOUGH LOW LEVEL (BELOW 850 MB) FLOW FROM THE WESTERN GULF OF  
MEXICO ALLOWS FOR A TRAJECTORY OF MOIST AIR THROUGH THE ENTIRE  
FORECAST PERIOD, DEEPER UPPER LEVEL FLOW/MOISTURE/LIFT DOES NOT  
BECOME AVAILABLE UNTIL FRIDAY AND SATURDAY. WITH THAT IN MIND,  
DIURNALLY-BASED POPS/WEATHER (MAINLY AFTERNOON AND EVENING  
TIME FRAME) WILL BE INTRODUCED ALONG THE GRADIENT ZONE OF  
MOISTURE/SHEAR/INSTABILITY IN THE WAKE OF THE RIDGE. THIS WILL MOST  
LIKELY PLACE THE GREATEST POPS/WEATHER OVER EASTERN SECTIONS (MAINLY  
WEST KENTUCKY, SOUTHWEST INDIANA, SOUTHEAST ILLINOIS) OF THE WFO PAH  
FORECAST AREA.  
 
WITH ANY OF THE CONVECTIVE ACTIVITY DURING THE EXTENDED FORECAST  
PERIOD, GENERAL MOST UNSTABLE CAPE VALUES WILL BE 1500-2500 J2/KG2,  
WITH 0-6 KM CUMULATIVE SHEAR BETWEEN 15-30 KNOTS. THERE MAY BE THE  
POTENTIAL FOR ISOLATED TO SCATTERED STRONG TO SEVERE THUNDERSTORMS  
TUESDAY AND WEDNESDAY.  
 
THE MORE LONG TERM CONCERN WILL BE THE HEAT AND HUMIDITY FOR THE  
EXTENDED PERIOD. AFTERNOON AND EVENING HEAT INDEX VALUES WILL EXCEED  
100 EACH DAY IN SOME PART OF THE WFO PAH FORECAST AREA THROUGH THE  
EXTENDED FORECAST PERIOD. FROM WEDNESDAY THROUGH SATURDAY, SEVERAL  
LOCATIONS WILL SEE HEAT INDEX VALUES TOP OUT NEAR 105 DEGREES,  
ALTHOUGH ANY OCCURRENCE ON WEDNESDAY WILL BE CONDITIONAL BASED ON  
PRECIPITATION AND CLOUD COVER. MORE WIDESPREAD HEAT INDEX VALUES  
NEAR 105 WILL BE EXPECTED THURSDAY THROUGH SATURDAY AND MAY WARRANT  
A FUTURE HEAT ADVISORY ISSUANCE.  
   
AVIATION
 
 
ISSUED AT 149 PM CDT SAT JUN 23 2018  
 
VFR CONDITIONS MAY TEMPORARILY RESTRICT TO MVFR, WITH VICINITY  
MENTION OF PCPN POSSIBLE LATE THIS PM, AND DURING THE LATE  
NIGHT-EARLY MORNING TIME FRAME. SHOULD SEE BEST CHANCE OF  
DETERIORATED CONDITIONS (CIGS AND VSBYS) COMING THEN, WHEN WAVE  
OPENS UP/LIFTS ACROSS MID MS VALLEY AND SPREADS BEST SUCH CHANCE  
PCPN SOUTHWEST TO NORTHEAST ACROSS THE AREA.  
 

 
   
AVIATION
 
 
ISSUED AT 709 PM CDT SAT JUN 23 2018  
 
A WEAK MID LEVEL DISTURBANCE WILL KEEP THE POTENTIAL FOR WIDELY  
SCATTERED THUNDERSTORMS IN THE FORECAST THROUGH MID EVENING,  
ESPECIALLY OVER THE SOUTHERN HALF OF THE AREA. INCLUDED A VCTS  
MENTION AT KCGI AND KPAH. MAINLY DRY WEATHER SHOULD PREVAIL FROM  
LATE EVENING THROUGH THE OVERNIGHT AND INTO MUCH OF SUNDAY  
MORNING. THEREAFTER, A BETTER CHANCE OF SCATTERED THUNDERSTORMS  
RETURNS TO SOUTHERN PORTIONS OF THE REGION SUNDAY AFTERNOON IN  
ASSOCIATION WITH INCREASING MID LEVEL ENERGY ALONG AN APPROACHING  
BAROCLINIC ZONE. THIS CHANCE SHOULD SLOWLY SPREAD NORTHEAST INTO  
THE REMAINDER OF THE REGION SUNDAY NIGHT. VFR CONDITIONS SHOULD  
LARGELY PREVAIL THROUGH THE FORECAST PERIOD, WITH THE EXCEPTION OF  
BRIEF REDUCTIONS DUE TO THUNDERSTORM ACTIVITY. WINDS WILL BE LIGHT  
AND VARIABLE TONIGHT, THEN SOUTHWEST AROUND 5 KNOTS ON SUNDAY.  
 

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

 
 

 
 
UPDATE...RJP  
AVIATION...RJP  
 
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