696 
fxus63 kjkl 091201 
afdjkl 


Area forecast discussion 
National Weather Service Jackson Kentucky 
701 am EST Friday Jan 9 2009 


Short term.../today through Saturday/ 


Upper level pattern shows some weak short wave ridging over the area 
today in response to a trough digging into the western intermountain 
region. This trough shears out while sweeping into the Midwest by 
Saturday. At the surface...reflected low pressure wave forms over the 
lower Ohio Valley by early Saturday morning with a cold front 
extending back though the lower Mississippi Valley region. This 
system sweeps through eastern Kentucky by Saturday evening. 


Models handle large scale feature similarly. However...the NAM and 
European model (ecmwf) are about 6 hours slower with the onset of precipitation than 
the GFS...and sref Saturday. In general preferred the faster timing of 
the GFS and sref. Reasoning surrounds the fact that all models have 
eastern Kentucky between a favorable rr quadrant and lf quadrant of separate 
northern and southern jet streams. This produces an area of diffluent 
flow over the area...coupled with a 40kt to 50kt h850 jet nosing its 
way into eastern Kentucky by late Friday night into early Saturday 
morning. Felt this would be enough to justify higher probability of precipitation. GFS forecast 
soundings even hinted at some elevated instability Sat but this was 
only marginal so left any mention of thunder out of the forecast for now. 
Otherwise...made some minor tweaks to isc grids to capture latest 
model trends. Only exception was adjustments to sky grids. Pesky low 
SC deck has been slow to erode and per Sat loop...additional middle 
high level cloudiness will overspread the area a bit this morning 
before some partial clearing works its way back into the area this 
afternoon...especially for our northern zones. This will help keep 
high temperatures down a bit this afternoon as well. 


Long term.../Saturday night through Thursday/ 


The models are in pretty good agreement though the weekend and the 
only differ in the timing of the short waves...but have essentially 
the same patterns in place. Went primarily with European model (ecmwf) for timing of 
the systems...once they started to diverge. Both the models were 
ending the snow showers by 7 am on Sunday. There may be some 
flurries that linger into Sunday morning...but nothing measurable. 
Went with the European model (ecmwf) and slowed the onset of the precipitation of the 
next system to Monday night. The main reason for the change was due 
to the general tendency for the models to be too fast and the better 
verification of the European model (ecmwf). As usual...confidence tends to dwindle 
with time...however feel that the models are correctly forecasting 
the cooler trend. 


We are transitioning to a pretty cold pattern and with that...MOS 
tends to start to move toward climatology. With this in mind...had 
to blend the coldest MOS with some raw model output to get the temperatures 
to better agree with the forecast weather patterns. 


&& 


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


Surface high pressure will transit the area during the forecast 
period. High...middle level clouds are quickly overriding the area as 
low SC exits to the northeast. The scattered to broken deck of high and middle 
level clouds will continue to pass over the area this morning... 
affecting northern portions of the area more than the southern. A 
southerly gradient wind will develop across the area today as well. 
Rain showers are expected to develop toward dawn Saturday...at the 
end of the forecast period ahead of an approaching cold front. 


Hydrology...updated 


River flood advisories continue for a couple of points along the 
Cumberland and Kentucky rivers. Other rivers...creeks and streams 
should be receding at this time. Please see the latest fls products 
for the latest information. Not looking for any Hydro issues for the 
extended period of the forecast due to the anticipated 
progressiveness of the frontal systems forecast to move through the 
area. 


&& 


Jkl watches/warnings/advisories...none. 


&& 


$$ 


Short term...ray 
long term....jj 
aviation...jp 
hydrology...greif/ray