699 
fxus63 kpah 231232 
afdpah 


Area forecast discussion 
National Weather Service Paducah Kentucky 
632 am CST Monday Nov 23 2009 


Update... 
updated aviation discussion. 


&& 


Discussion... 
with respect to current weather...the drier and cooler air that 
was advected into the weather forecast office pah forecast area ahead of the passage 
of the upper low from the lower MS valley to the Tennessee Valley on 
Sunday has ceased and has been replaced by decent warm air 
advection. A good stratus deck...indicative the decent low level 
moisture return...was covering the southern 1/3rd of the weather forecast office pah 
forecast area as of 09z. The kpah VAD wind profile shows that the 
warm/moist air has worked down as far as 925 mb in extreme 
southern Illinois/western Kentucky...with a greater depth of warm moist air 
from surface to nearly 700 mb. Therefore...until there is 
sufficient mixing through the warm later this afternoon...mostly 
cloudy to cloudy skies will be the rule for at least the southern 
2/3rds of the weather forecast office pah forecast area. 


The biggest concern for this morning...based on radar and some surface 
observational trends...is the potential that the lift associated 
with such a warm air advection zone over southeast MO...southwest 
Illinois and The Purchase area of west Kentucky may produce some light 
precipitation. Earlier model runs from the NAM-WRF/sref and European model (ecmwf) 
have been hinting at this possibility. In any case...I may need to 
address this matter before sending out the current forecast package. 


Until the weather forecast office pah forecast area is fully into the warm sector of 
the approaching low over Kansas/northwest MO this afternoon and 
tonight...variable cloudiness will still be a problem. There is 
some potential for fog development over southwest 
Indiana...southeast Illinois...northwest Kentucky late 
tonight...but I suspect that cloud cover will be the dominant 
feature overnight into Tuesday morning. 


The GFS/sref/ECMWF are slightly slower in the eastward translation 
of the upper from Kansas into northern MO by late Tuesday afternoon. 
Although progressive...sensible weather associated with the 
vertically stacked low will remain close to the system. 
Therefore...I have chosen to slow the onset of measurable 
precipitation with the next system until Tuesday morning. 


With respect to any mixed precipitation along the southern edge of 
the evolving Great Lakes closed low/cyclonic circulation...I have 
kept precipitation mostly in the form of rain over southwest 
Indiana and the eastern pennyrile region of western Kentucky...except 
for Thursday morning and again Thursday night...when thermal 
profiles aloft support sufficient cooling in the crystallization 
zone for a mix of rain or snow. Given the warm surface 
temperatures...no accumulation of snow is expected. 


Maximum/min temperatures through Friday were adjusted using a blend of 
spatially adjusted GFS/European model (ecmwf) thermal fields. Dewpoints and winds 
through Thursday were adjusted under a greater influence of NAM- 
WRF/RUC mass/wind fields. 


&& 


Aviation... 
low clouds are currently invading our area from the south. VFR 
conditions will persist at kevv/kowb for a few more hours before 
becoming MVFR...but kpah and kcgi are already there. In addition to 
the ceilings...we will see visibilities drop down into the MVFR category this 
morning. IFR ceilings and scattered IFR visibilities are lurking just to the 
south...so have accounted for this in a tempo group for this 
morning. Confidence is low as to how long these very low 
ceilings/visibilities will remain in place...and if they will return late 
tonight. However...we will at least have MVFR ceilings for the rest of 
the period. Scattered rain showers have developed across the area 
as well and will most likely only affect kpah...possibly kowb/kevv 
later on. The precipitation should move out of the area by 
afternoon. 


&& 


Pah watches/warnings/advisories... 
Kentucky...none. 
MO...none. 
Illinois...none. 
In...none. 
&& 


$$