714 
fxus63 kjkl 231138 
afdjkl 


Area forecast discussion 
National Weather Service Jackson Kentucky 
638 am EST Monday Nov 23 2009 


Short term.../today through Tuesday/ 


Upper level low that brought rain to portions of eastern Kentucky 
today and tonight has opened up into a wave this morning...basically 
bisecting the commonwealth with the axis stretching roughly from sdf 
to gsp. Light rain showers continue to form in a band along and 
ahead of this axis currently passing northward through our County Warning Area. 
A second upstream disturbance can be seen on the regional water 
vapor loop. This upstream disturbance will pass through the region 
later today as aforementioned trough continues to push off to the 
northeast. With residual moisture in place across the area expect 
this will be enough to keep a chance of showers in the forecast... 
isolated to scattered in nature. Otherwise...short wave ridging will 
develop over eastern Kentucky on Tuesday in response to the approach 
of a deeper low pressure system over the plains. 


For sensible weather...clouds will persist over the area...with only 
some partial clearing expected by Tuesday. Overcast skies will tend 
to keep temperatures down again today. But with decent short wave ridging 
expect temperatures to rebound a bit for Tuesday. Latest MOS 
guidance seems to suggest this line of thought is the right 
direction to take...coming in warmer and in better agreement. Any 
rainfall totals today will be light. 


Long term.../Tuesday night through Sunday/ 


The longwave pattern aloft begins with the models in two camps with 
respect to the handling of the lead closed low over the Midwest and 
its movement to the northeast. The GFS and 00z European model (ecmwf) are quite 
similar with this low...taking it northeast to Chicago-land by 
Wednesday morning...about 6 hours quicker than the NAM cluster. With 
the new European model (ecmwf) basically mirroring the GFS...have gone with a blended 
solution of these two models with the handling of the lead closed 
upper low. The next batch of energy that dives into the upper Midwest 
during the day Wednesday forming a deeper closed low not far from the 
area that the earlier one had occupied 24 hours prior. It is this low 
that will dominate the weather for the Ohio Valley and points east 
through the bulk of the long term portion of the forecast. This 
deep...but initially progressive...low becomes a full latitude trough 
sweeping its elongated band of energy into the the Ohio Valley by 
Thursday morning. From here...with the slower GFS catching up to the 
European model (ecmwf)...the trough further deepens into a bowling Ball of spinning 
energy over southeast Ohio lingering into Friday morning. This now 
consolidated mass them moves east relatively quickly into the North 
Atlantic by Saturday morning with its large influence covering the 
eastern portion of the Great Lakes...Ohio Valley...and the central 
Appalachians. At this point...the GFS is again a more extreme 
solution than the European model (ecmwf)...but still in pretty good agreement for 5 to 
6 days out. Meanwhile...ridging will build into the plains on Friday 
and work east for the remainder of the Holiday weekend. Have 
followed a blended solution for the bulk of the dominant trough... 
with a greater lean toward the new...and less extreme...European model (ecmwf) 
solution for Saturday and Sunday. 


Sensible weather will feature a surface low initially moving into the 
Great Lakes and Northern Ohio valley for midweek dragging a weak and 
relatively moisture starved front across Kentucky. With the 
deepening upper level support taking place to the southwest for 
Thanksgiving day the surface system will be held in place...keeping a 
threat for rain showers in the Holiday forecast. By Thursday night... 
a portion of the surface low will jump to the East Coast and this piece 
will become increasingly dominant through the later part of the 
forecast. The broad...developing coastal system will help to send 
Atlantic moisture across the northern Appalachians and into the Great 
Lakes/Ohio Valley region even as its cyclonic winds bring colder air 
into the area. The combination of upper level energy spinning by... 
more moisture...and upslope flow will prolong the generally light 
showers through the area into Friday and Friday night. Continued cold air advection 
in response to the developing surface low to the east will cool the 
column of air through the region making snow showers a possibility 
along with the rain. These should be most prevalent during Thursday 
and Friday nights when the flakes will not be fighting solar 
insolation. No accumulations are anticipated for most of the 
area...though the upslope flow may contribute some light totals on 
the highest ridges into Saturday morning. Almost all the showers will 
move off to the east by midday Saturday leaving behind cool high 
pressure in its wake. However...this air mass will quickly begin to 
moderate later that night and continue on Sunday returning 
temperatures to near normal by the end of the Holiday weekend. 


Followed the mex numbers fairly close for the bulk of the period with 
minor terrain based adjustments...though did undercut them for highs 
Thursday and Friday with the clouds and cold air advection. As for probability of precipitation...ended up 
similar to the mex guidance...but kept the likely probability of precipitation out of the 
forecast in the north for Friday...awaiting further confirmation with 
subsequent model runs. 


&& 


Aviation.../12z to 12z/...updated 


A couple of upper level disturbances are passing through the 
area...kicking off isolated to scattered showers across the Ohio 
Valley region this morning. Lower IFR to MVFR ceilings to our south have 
rotated northward out of the Tennessee Valley region...dropping ceilings across 
our area as well. Some patchy fog has also developed...causing IFR 
visibilities in some of the valley locations. Low level moisture will 
persist across the area through the entire period. Expect fog will 
become an issue again tonight with stratus likely building down... 
lowering ceilings and visibilities in the process. 


&& 


Jkl watches/warnings/advisories...none. 


&& 


$$ 


Short term...ray 
long term....greif 
aviation...ray