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fxus63 klmk 041723 
afdlmk 


Area forecast discussion 
National Weather Service Louisville Kentucky 
1225 PM EST Thursday Dec 4 2008 


Near term (this afternoon)... 


Updated for current cloud trends and to lower maximum temperatures by 1-3 degrees. 
Kept mention of light rain/snow mix in our far eastern counties through 18z 
via the web forecast...however for those same counties...stated becoming 
mostly sunny in the zone forecast...as back edge of clearing continues to 
make progress southeastward. Temperatures will not climb until clouds disperse...then 
only minor rises. 


Short term (today and tonight)... 


Rain line just moving east of a line from Louisville to Bowling 
Green as of 3am EST/2am CST...with only an extremely thin band of 
light snow following behind this rain. This band of snow has been 
thinning as it moves east and will likely only drop a few flakes in 
the central zones as it moves through over the next couple of hours. 
Rain in the far eastern zones will continue into the morning commute 
but should exit by middle to late morning. Some flurry potential exists 
in the east through middle morning...though the air mass will only be 
cold enough to produce just a few very light and brief snow showers 
there as well. Freezing temperatures are trailing the light band of 
snow currently on the radar by an hour or two and should not be in 
place to make for a widespread frozen Road surface problem this 
morning. 


The temperature gradient will range from around 40 degrees in the 
far east and southeastern zones to the lower 30s in the western 
zones by sunrise. These lower 30s will work into the eastern zones 
this afternoon and evening. 


Should see some clearing of skies from west to east this afternoon 
as well...with mostly clear skies tonight and much colder 
temperatures. Lows by early Friday should be well into the 20s 
across the entire region. Some very patchy fog could develop toward 
morning in favorable fog formation locations...but widespread fog is 
not expected at this time considering how dry air mass moving into 
the region is expected to be. 


Long term (friday through wednesday)... 


An amplified 500mb ridge off the Pacific northwest coast will remain 
in place. This will allow repeated intrusions of Arctic air across 
the upper Midwest and the Great Lakes. Cold temperatures of at least 
5 to 10 degrees below seasonal norms will continue this weekend into 
early next week across the entire region. 


Friday through Sunday... 


A strong jet maximum rounding the ridge across the Pacific northwest 
Friday will dive southeast into the mean longwave trough centered 
across the western Great Lakes by late Saturday. Upper air 
divergence associated with the left front quadrant of this jet and 
isentropic lift across an elevated baroclinic zone will spread light 
snow across Wisconsin...northern Indiana and into Ohio. 


A few days ago...the forecast track of this Alberta clipper was 
farther south....bringing a chance of light snow to southern Indiana 
and the Bluegrass. However...both the GFS and the NAM have trended 
north with the best lift and the track of the associated weak 
surface low (now forecast to move across michigan). Forecast 
soundings show middle level cloudiness late Saturday...but remaining 
unsaturated at the lowest levels during the period of best lift. 


Will only mention a chance of flurries or slight chance of light 
snow across our northeastern counties late Saturday. 


Cold weather will continue throughout the weekend. Arctic surface 
high pressure will migrate east over the state late Friday...setting 
up a brief episode of southwest flow late Saturday ahead of the 
Great Lakes disturbance. Another shot of Arctic air will move 
directly into the state Sunday. High temperatures may rebound into 
the middle 40s across our southern counties Saturday afternoon before 
diving again Sunday. 


Friday looks partly cloudy as some middle level moisture will move 
across the state. Cloudy skies late Saturday will clear by Sunday as 
colder air arrives. 


Monday through Wednesday... 


Early next week looks increasingly stormy...with a good chance of 
some type of wintry precipitation across some portions of Illinois 
or Indiana. The latest operational runs of the European model (ecmwf) and the GFS 
have varying solutions hinging on each model's different handling of 
persistent ridging off the Pacific northwest coast. Both show energy 
diving southward across the northern rockies east of this ridge 
early Tuesday with bitterly cold Arctic air in place across the 
upper Midwest. By early Tuesday...an expected trough will develop 
across the Southern Plains and moisture will move north into the 
lower Ohio Valley. The placement and orientation of this boundary 
will determine temperatures and precipitation type. The operational 
GFS is the coldest and farthest southeast with the track of a 
surface low. It deepens the low and moves it across eastern 
Tennessee late Tuesday. The European model (ecmwf) is warmer and keeps the bulk of 
precipitation liquid late Tuesday into early Wednesday. 


Currently these models have a great amount of spread...resulting in 
a low confidence forecast for temperatures Tuesday and Wednesday. 


In any case...temperatures should moderate Monday under partly 
cloudy skies as southerly flow begins on the backside of high 
pressure over the Atlantic coast. 


&& 


Aviation (18z tafs)... 


VFR weather as high pressure ridge moves in. Some high clouds through the 
period with northwest flow. 


&& 


Lmk watches/warnings/advisories... 
Kentucky...none. 
In...none. 
&& 


$$ 
Weather.Gov/Louisville 


Near term....Kirkpatrick 
short term...maczko 
long term....jsd 
aviation.....Dk