170 
fxus63 kpah 072122 
afdpah 


Area forecast discussion 
National Weather Service Paducah Kentucky 
322 PM CST Wednesday Jan 7 2009 


Discussion... 
as 2ndary energy rounds base of mean long wave trough tonight...anticipate 
chance Cat development of mainly -sn (maybe -ra/-sn furthest south where 
blayer temperatures slightly warmer) to produce maybe a light dusting by 
morning. All models show this wave primarily east of forecast area by 
12z so we ended probability of precipitation then...although any slowdown could spell a 
little lingering pop early in our farthest southeast counties. 


After that weak ridging holds for a day with return flow slys 
allowing some minor warming Friday into the weekend. This will be 
ahead/in advance of a cold front that passes Friday night. The main 
trend this model run with this front has been to push it entirely 
through the forecast area by 12z Sat (gfs) vs the slower NAM approach which has 
it just exiting our east by then. Either way the resultant precipitation is 
mainly along/ahead of the boundary and so should stay liquid. This 
is important b/c colder air does slam down the backside of this 
system which would change the precipitation over to snow before 
ending...b/c the column does dry out immediately behind the front. 
The other feature of note is strong gradient and differential 
thermal advection will result in brisk winds both ahead of and 
behind the boundary...with perhaps some gusts 15-30 kts late Friday 
night into Sat. 


Sat-Sat night we see near normal early Jan temperatures as NAM rotates -10c 
850 mb cold pool overhead. Surface high/drying column will be only 
saving Grace...although still upper cyclonic flow pattern influence 
suggests some periodic cloudiness hanging around. 


Monday begins the approach and eventual plunge of extremely cold 
Arctic air into the region. The GFS actually lowers 850 mb temperatures 
about 10c during the day while the NAM does so about 5c. We 
forecast a morning high with a steady or falling temperature 
thereafter...behind frontal passage. We carried a slight chance precipitation west/frontal passage like 
our neighbors. Afterwards some of the models hint at trying to 
briefly warm it up Monday night before the most significant Arctic 
plunge takes place Tue-Wed...while others do not. We took a 
collab/middle ground approach to this scenario...allowing for about a 
10f fall overnight. Then Tuesday despite all model relative humidity out of the 
way...significant cold air advection has the models spilling -20 to -25c 850 mb 
temperatures across the lower Ohio Valley...meaning we'll struggle to hit 
the freezing mark for highs. Tuesday night-Wednesday is colder still...with 
lows in the lower teens and highs struggling into/through the 20s. 


&& 


Aviation... 
all taf sites...kcgi/kpah/kevv/kowb will experience periodic VFR 
category middle cloud deck/ceilings through 09-11z Thursday...as a 
secondary impulse rotates around the western limb of the upper 
trough as it begins to broaden again over the northestern U.S. After 
12z...unrestricted ceilings/visibilities can be expected for each 
of the taf locations. 


&& 


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


$$