345  
FXUS63 KPAH 200725  
AFDPAH  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PADUCAH KY  
225 AM CDT FRI APR 20 2018  
   
SHORT TERM
 
(TODAY THROUGH SUNDAY NIGHT)  
ISSUED AT 215 AM CDT FRI APR 20 2018  
 
WINDS VARY FROM 4-5 KTS IN PLACES, TO CALM. SIMILARLY, TEMPS VARY  
FROM NEAR 40, TO SOME MID 30S ALREADY SHOWING UP. WITH THESE  
TRENDS, WE'LL CONTINUE THE HEADLINE FREEZE/FROST THRU EXPIRATION  
(14Z) THIS MORNING.  
 
THE SURFACE HIGH OVER IA EARLY THIS MORNING MIGRATES EASTWARD TO  
THE GREAT LAKES DURING THE DAY. LIGHT EASTERLIES KEEP DRY/COOL AIR  
OVER THE REGION, AND SOUNDINGS SUGGEST MIX DOWN DEW POINTS IN THE  
UPPER 20S-LOWER 30S THIS PM. THAT'LL MAKE FOR LOW RH READINGS THIS  
PM, PARTICULARLY IN THE OZARKS, WHERE MID 20S PERCENTILE IS  
POSSIBLE, CREATING AN ELEVATED FIRE DANGER WITH DRYING FUELS.  
 
MODELS CONTINUE TO TRACK OUR LATE WEEKEND WEATHER MAKER SOUTH OF  
THE AREA. THE CANADIAN, WHICH HAD THE LANDFALL BEST PEGGED 24  
HOURS AGO, IS FURTHER SOUTH THAN THE OTHERS OPERATIONALLY BY ITS  
EVOLUTION/FORMATION IN THE SOUTHERN PLAINS. THIS TRENDING ADDS  
CONFIDENCE TO THE SOUTHERN TRACK, AND AS SUCH, WE ARE NOT PREPARED  
TO INTRODUCE ANY THUNDER WITH THE RAIN CHANCES, AS MOST MODELS  
KEEP EVEN ELEVATED INSTABILITY SOUTH OF THE FA.  
 
PCPN CHANCES MOVE IN FROM THE SOUTH/WEST SAT NIGHT, AND  
INCREASE/SPREAD ACROSS THE AREA SUN-SUN NIGHT. MOST OF THE  
APPRECIABLE QPF IS OVER BY 12Z MONDAY, WITH NEARLY 1 INCH OF STORM  
TOTAL RAINFALL POSSIBLE ALONG OUR ARKANSAS AND TENNESSEE BORDER  
AREAS, TAPERING TO 3/4 INCHES FROM CGI-PAH-MAD, WITH 1/4 INCH  
AMOUNTS (OR LESS) ALONG/NORTH OF A MDH-OWB LINE.  
 
BELOW NORMAL TEMPS CONTINUE THRU THE QUILT WEEKEND FORECAST. TEMPS  
TODAY AND SUNDAY WILL MAKE THEIR WAY INTO THE LOW END 60S, WHILE  
THE WARM DAY (SATURDAY) MAKES THE BEST PUSH CLOSER TO SEASONAL  
NORMS WITH MID-UPR 60S MOST LOCATIONS, MAYBE 70F ALONG THE TN  
BORDER COUNTIES OF SOUTHWEST KY.  
 
LOWS TONIGHT WILL BE NEAR 40F, WITH MAYBE A 37-38F POSSIBLE IN  
SHELTERED, REMOTE NORTHERN LOCALES. ISOLATED PATCHES OF FROST  
COULD OCCUR THERE, BUT HEADLINES ARE NOT ANTICIPATED.  
   
LONG TERM
 
(MONDAY THROUGH FRIDAY)  
ISSUED AT 215 AM CDT THU APR 19 2018  
 
NOW THAT THE CLOSED LOW IN SOUTHERN CA/NV/AZ IS WITHIN A DENSER  
OBSERVATIONAL NETWORK, THERE SHOULD BE A LITTLE MORE CONSISTENCY IN  
THE RESOLUTION/TIMING OF THE SYSTEM AS IT MOVE IN AND AROUND THE WFO  
PAH FORECAST AREA ON MONDAY. THE CANADIAN GUIDANCE HAS BEEN FAIRLY  
CONSISTENT THE PAST COUPLE OF DAYS WITH THE EVOLUTION OF THIS  
SYSTEM, BUT THE DETERMINISTIC 00Z FRIDAY GFS SEEMS TO HAVE TAKEN  
OVER AS THE PREFERRED MEDIUM RANGE GUIDANCE FOR THIS FORECAST  
PACKAGE. AT THIS POINT, THERE IS MEDIUM TO HIGH FORECAST CONFIDENCE  
(50-70%) WITH THE RAIN CHANCES MONDAY INTO MONDAY EVENING.  
 
FORECAST CONFIDENCE FOR RAIN CHANCES TUESDAY THROUGH THURSDAY ARE  
BELOW AVERAGE (GENERALLY BELOW 40%) AS THERE EXISTS HIGH MODEL  
VARIABILITY IN BOTH THE DETERMINISTIC AND ENSEMBLE GUIDANCE ON THE  
TIMING, EVOLUTION, TRANSLATION, AND PHASING OF THE NORTHERN  
U.S./SOUTHERN CANADIAN BORDER SHORTWAVE DEVELOPING NEXT MONDAY.  
GIVEN THE VARIABILITY, WILL STICK WITH THE LOW POP REGIONALLY  
BLENDED MODEL GUIDANCE AS A STARTING POINT. THE ANTECEDENT EASTERN  
PACIFIC AND WESTERN CANADA CIRCULATIONS SERVING AS A GENESIS  
POINT FOR THE DOMINANT SHORTWAVE ON MONDAY ARE NOT EVEN EXPECTED  
TO MOVE OVER THE NORTHWEST U.S. UNTIL SUNDAY AT THE EARLIEST.  
UTILIZED A BLEND OF THE REGIONALLY BLENDED MODEL INITIALIZATION  
WITH SOME INFLUENCE OF THE CURRENT DETERMINISTIC/MOS GFS GUIDANCE  
AND THE SPATIALLY REDUCED NAM GUIDANCE.  
 
ALL IN ALL, IT APPEARS THAT NEXT WEEK WILL SEE BELOW NORMAL (5-10  
DEGREES BELOW) HIGHS AND LOWS AND MAINLY SHOWERY PRECIPITATION  
WITH THE GREATEST COVERAGE MONDAY, THEN AGAIN WEDNESDAY AND  
THURSDAY. TEMPERATURES MAY REBOUND TO NEAR NORMAL NEXT FRIDAY WITH  
DRY CONDITIONS INTO NEXT WEEKEND.  
 

 
   
AVIATION
 
 
ISSUED AT 215 AM CDT FRI APR 20 2018  
 
DESPITE NEAR DRY ADIABATIC LAPSE RATES IN THE LOWER 4K FT AGL THIS  
PM, CONDENSATION PRESSURE DEFICITS IN EXCESS OF 100 MB SHOULD  
PRECLUDE DEVELOPMENT OF IMPACT LOW VFR BASES. TIME/HEIGHT CROSS  
SECTIONS REVEAL VERY DRY AIR IN THE 850-500 MB LAYER UNTIL LATE  
TONIGHT, WHEN SOME NOMINAL MOISTURE INCREASE DOWN TO ABOUT 600 MB  
MAY PORTEND SCATTERED CIRRUS ADVECTION TOPPING THE H5 RIDGE DURING  
THE LAST FEW HOURS OF THE PLANNING PHASE OF THE FORECAST.  
 

 
   
PAH WATCHES/WARNINGS/ADVISORIES
 
 
IL...FROST ADVISORY UNTIL 9 AM CDT THIS MORNING FOR ILZ080-081-  
084>094.  
 
FREEZE WARNING UNTIL 9 AM CDT THIS MORNING FOR ILZ075>078-082-  
083.  
 
MO...FROST ADVISORY UNTIL 9 AM CDT THIS MORNING FOR MOZ076-086-087-  
100-107>112-114.  
 
IN...FROST ADVISORY UNTIL 9 AM CDT THIS MORNING FOR INZ085>088.  
 
FREEZE WARNING UNTIL 9 AM CDT THIS MORNING FOR INZ081-082.  
 
KY...FROST ADVISORY UNTIL 9 AM CDT THIS MORNING FOR KYZ001>022.  
 

 
 

 
 
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