417 
fxus63 kpah 080113 
afdpah 


Area forecast discussion 
National Weather Service Paducah Kentucky 
812 PM CDT Tuesday Oct 7 2008 


Updated aviation section for 00z tafs 


Discussion /208 PM CDT Tuesday Oct 7 2008/... 


Main question for this forecast package is when to end rainfall 
from this current system. 


A large area of showers and scattered thunderstorms spent the 
entire morning moving across the County Warning Area. The bulk of 
the heaviest rainfall has just moved east of our area. Scattered 
rain showers developed in its wake but coverage was 
limited...until just recently. 


Models seemed to be a little slow in bringing precipitation across 
our area today...but now have sped things up a bit...and we need 
to lower probability of precipitation for Wednesday and eliminate them altogether for 
Wednesday night. A slow moving surface/upper system continues to lurk 
to our west. Even though there is a lull in the precipitation 
right now...models still want to ramp up precipitation for this 
evening. Already seeing signs of new development to our west 
across Missouri and Arkansas and even further south into Tennessee and 
MS. Even within the last half hour...we have noticed new 
development over extreme southeast Missouri and far southern 
Illinois. Storm Prediction Center just highlighted the area just to our south for the 
possibility of severe weather...so this will have to be watched 
closely. The latest laps data indicates the atmosphere has gotten 
fairly unstable over the Missouri bootheel and areas south. 


The latest GFS and NAM bring the main h50 trough and associated 
vorticity maximum toward the area this evening. Unlike yesterday...where 
the models wanted to develop a closed low (or two) as this trough 
moved east...todays models wait until tomorrow afternoon to close 
off the upper low to our south. So that in turn has allowed for 
the system to speed up a little. The upper trough should move 
through the area during the early morning hours tomorrow...and be 
east of the region by late afternoon. Like yesterday...the models 
differ on rainfall amounts...but do show the best chances early 
this evening. After midnight...it gets a little more tricky as to 
figuring out just how much rain we might get. It appears the 
deepest moisture will be in our eastern sections...so the highest 
probability of precipitation will be oriented that way. By Wednesday afternoon...we should 
really see things come to an end. 


In the wake of the trough...middle level ridging should take over by 
Wednesday evening. After a cool day tomorrow...Thursday should be 
much warmer as 850 mb temperatures rise to about 13 to 15 degree c. The weekend 
will be even warmer. 


As for the extended period....as expected the 06z GFS is coming 
into better agreement with the 00z Tuesday European model (ecmwf)...however there is 
still a considerable timing difference. In contrast the 12z Tuesday 
GFS is much better with the timing. The main difference continues 
to be the GFS closed and slower and more intense upper low vs the 
open and faster European model (ecmwf). The GFS run apparently took on a negative 
tilt to the upper trough which help speed it up. Will continue to 
lean toward the European model (ecmwf) due to its better continuity. Pulled already 
low probability of precipitation for Sunday...mainly due to weak signals and especially 
for collaboration. At the most could possibly see isolated warm air advection 
showers. As for temperatures followed HPC and collaboration needs for 
extended although the mex is catching onto the slower front 
arrival and warmer temperatures. 


&& 




Aviation... 
widespread showers will gradually diminish overnight. Despite 
decreasing precipitation coverage...ceilings and visibilities will lower as low level 
winds become light over rain moistened ground. Expect IFR conditions 
through the early morning hours before improvement occurs. The 
combination of diurnal heating and drier air in the wake of a cold 
front will scatter out the low clouds by evening. 


&& 


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


$$ 


Short term...CW 
long term....kh 
aviation...my