729 
fxus63 kpah 231137 
afdpah 


Area forecast discussion 
National Weather Service Paducah Kentucky 
537 am CST sun Nov 23 2008 


Update... 


Updated for 12z aviation forecast discussion. 


&& 


Discussion... /issued 340 am CST sun Nov 23 2008/ 


Discussion... 
main concerns for this forecast are probability of precipitation through Monday. 


The 00z models continue to agree that a clipper system...currently 
emerging from the northern rockies...will descend toward the quadrant 
state today and tonight...and pass through the region Monday. To our 
south...satellite imagery indicates a large area of low VFR stratus 
over Arkansas and southwest Tennessee...which is indicative of 
increasing low-level moisture. 


As the clipper approaches...it will induce strong warm advection 
from the surface through at least 700mb beginning this afternoon. At 
06z...the 00z GFS has a 50kt low level jet at 850mb. Model soundings from the 
00z NAM and GFS indicate that there could be just enough elevated 
instability for a few thunderstorms to develop anywhere across the 
quadrant state. 


The main problem is timing. The GFS is a bit faster with the onset 
of precipitation...and it is also more agressive with quantitative precipitation forecast than the 
NAM. They both hold off quantitative precipitation forecast until after 00z. The models tend to be a 
tad slow with the onset of precipitation with these massive 
warm...moist advection situations...so would prefer the faster 00z 
GFS timing. A quick look at the 03z sref quantitative precipitation forecast probabilities shows a 
20-30 percent chance of measurable precipitation into southeast 
Missouri by 00z. This is faster than the 21z sref...and supports our 
preference for a faster onset of precipitation. 


Decided to add a slight chance of showers to southwest portions of 
southeast Missouri 21z-00z this afternoon...just in case the faster 
trend is better. Also spread 50+ probability of precipitation further north and east this 
evening...and increased probability of precipitation to categorical levels over the eastern 
2/3 of the area overnight tonight. Models are continuing to indicate 
ongoing showers/storms over much of west Kentucky at 12z...so 
indicated a sharp gradient of probability of precipitation Monday morning from no pop far 
west...to likely southeast. Mentioned a slight chance of thunder 
with all likely or better probability of precipitation...and ran with HPC quantitative precipitation forecast. 


The models continue to be awfully warm for Monday...considering 
there will be lots of cloud cover and modest cold advection behind 
the front. Stayed at or up to a category below coolest guidance for 
Monday. Generally stayed below guidance for highs through Tuesday. 
For lows...went at or just above guidance for tonight...with the 
warm advection scenario expected...and the frontal passage not 
expected until 12z or later Monday morning. Otherwise consensus 
guidance looks fine for lows. 


A brief look at the 00z GFS and European model (ecmwf) indicates much uncertainty for 
the Thanksgiving weekend forecast. Probability of precipitation currently in for Thursday 
night through Friday night...but could see probability of precipitation anytime from 
Thursday through Saturday...depending on which model solution you 
want to follow in a rather chaotic...blocky flow pattern over the 
U.S. Will leave the forecast for Wednesday and beyond alone...and 
will not envy the day shift trying to figure this one out. 


&& 


Aviation... 
clear skies will prevail this morning...with a south wind picking 
up by middle morning along with some passing cirrus. By this 
afternoon...we should see a scattered-broken VFR deck as low level moisture 
to our south creeps northward. Cold front will approach from the 
west later today. Light rain will overspread the area from west to 
east during the evening...beginning around 03z Monday at kcgi and 
kpah...and a few hours later at kevv and kowb. MVFR ceilings but 
unrestricted visibilities will accompany the rainfall in the evening 
hours...but lower ceilings and MVFR visibilities expected during the overnight 
hours. 


&& 


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


$$