612 
fxus63 kpah 211201 
afdpah 


Area forecast discussion 
National Weather Service Paducah Kentucky 
601 am CST Sat Nov 21 2009 


Update... 
updated for 12z aviation forecast discussion. 


&& 


Discussion... 
analyzed 00z 500 mb chart shows two distinct short waves...one 
over the upper Midwest...and another in the Southern Plains. 
Models continue to separate these even further apart during the 
day today...with the northern stream wave migrating to the 
east...and a closed low developing over East Texas...which moves 
into the lower Mississippi Valley. All of the associated 
moisture/rainfall with the southern system will stay to our south 
for today. 


Our focus then turns to the southern system. The progression of 
this upper low is not handled very well between the GFS and 
NAM...with the NAM showing the upper low position about 150 miles 
south of where the GFS places it. Nonetheless...both models are 
trending even further south with the precipitation chances for 
tonight...so will take out any mention of precipitation. 


During the day on Sunday...models really dampen out this upper 
level system as it pivots to the northeast. The NAM is slower with 
this weakening trend...but the end result will be that southern 
sections of the County Warning Area will see increase in clouds. 
While some light precipitation cannot be ruled out across portions 
of west Kentucky...it appears chances are very limited. The European model (ecmwf) 
is the only model that even hints at some minor quantitative precipitation forecast in our 
southeastern most counties...as it now has come more in line with 
the GFS and NAM as far as the progression of this system. The GFS 
and NAM have more of an northeastward push to this system before 
it totally deamplifies and becomes absorbed into the flow...thus 
totally voiding our area of precipitation. Even the GFS ensembles show no 
sign of any rain for our region. Will trim back the slight chance 
probability of precipitation and confine it to just a small part of west Kentucky...but would 
not be surprised if the day shift pulls it out altogether. 


On Sunday night and into Monday...another wave approaches from the 
west. However...the GFS brings this system through the area Sunday 
night and exits it on Monday...with little more than a few clouds. 
The NAM...which is even weaker with the strength of the wave...is 
much slower with the progression of this system...and paints quantitative precipitation forecast 
over the area Sunday night and especially into Monday...where the 
quantitative precipitation forecast bullseye is directly over our area. Even though the 00z European model (ecmwf) 
would tend to agree somewhat with the NAM...will ignore this for 
now due to the fact that the NAM shows this feature weakening 
as it approaches the area...and think the NAM may be overdone with 
its quantitative precipitation forecast. 


The next system to affect our area will be in the form of a cold 
front arriving some time on Tuesday or Tuesday night...as a closed 
low pulls eastward out of the northern rockies across the upper 
Midwest and toward the Great Lakes. GFS/European model (ecmwf) have been radically 
different in the speed and eventual interaction of shortwaves in 
the Tuesday-Friday timeframe...but seem to be converging on a more common 
solution with the 00z runs. With this trend in mind...trimmed probability of precipitation 
back to the extreme northwest counties Monday nt and added a slght chance to 
Tuesday night. Regardless of individual model differences...everything 
seems to point toward cooler air arriving for Wednesday with a 
reinforcing shot on Thursday accompanied by 'wraparound' 
clouds...before high pressure builds in with moderating 
temperatures and sunshine Friday into next weekend. Considered 
adding a slight chance to the north on Wednesday but will opt to just 
increase cloud cover during the Wednesday/Thursday period for now. 


&& 


Aviation... 
a weak shortwave passed through the area overnight...and drying in 
the upper levels is now taking place...which is shunting most of 
the cirrus out of the area. However...additional high cloudiness 
will be possible today and tonight...as an upper level system 
moves across the deep south. Some MVFR fog has formed in some 
areas...but this should burn off by 14z/15z. Otherwise...VFR 
conditions will rule into tonight as deeper moisture stays well to 
our south. Winds will be light easterly or southeasterly...and 
winds should stay up late tonight...so the potential for fog 
should be less. 


&& 


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


$$