342 
fxus63 klmk 042006 
afdlmk 


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


Short term (tonight and fri)... 


Unseasonably cold with some middle/hi clouds and continued northwest flow. 


Elongated upper level trough extending from the northern plains to the lower 
Great Lakes will move into our forecast area by Friday afternoon while nose of Canadian 
surface ridge reaches the lower Ohio Valley tonight. Hi center then forecast to be 
positioned across the Central Plains/middle MS valley by 12z Friday and from 
the lower msp valley/Tennessee Valley by 00z Sat. 


Approach of trough should result in some increase in middle/high level clouds 
tonight that will linger into at least the first half of the day Friday. 
Current cloud forecast looks to be on course. 


As for temperatures...hrly GFS MOS guidance matches up very well with current 
temperatures and will use this guidance for mins tonight and maximums Friday. So only 
subtle adjustments to going forecast. 


Long term (friday night through thursday)... 


Long term forecast remains generally unchanged Friday night through 
Monday with forecast concerns focusing on the end of the period on 
Tuesday through Thursday. 


Friday night through Sunday night... 


Northwest flow continues over the region as highly amplified ridge 
remains over the western U.S. This pattern will allow for a few 
things. First...Arctic disturbances will migrate through through in 
place across the eastern U.S. This will allow temperatures to remain 
cold...on average around 10 degrees below normal for this time of 
year...as waves of Arctic cold move across the upper Midwest and 
Great Lakes and trickle into the Ohio Valley. Second...this period 
will remain mostly dry. Except for a small chance of very light rain 
or rain and snow showers late Saturday afternoon and very light snow 
showers overnight Saturday...conditions will be dry. Expect quantitative precipitation forecast 
amounts to only top out around .05 at best with this disturbance. 
Expect highs Saturday and Sunday in the middle 30s to near 40 with lows 
Friday night through Sun night in the low to middle 20s. Partly cloudy 
skies Friday night and Saturday morning will give way to mostly 
cloudy skies Saturday night through Sunday morning before some 
breaks allow partly cloudy skies Sunday afternoon and night. 


Monday through Thursday... 


The latter part of the extended forecast will see some bigger 
changes in the way of temperatures and precipitation. On 
Monday...upper ridge across the western U.S. Will will push offshore 
as a potent low pressure system begins to strengthen and dig along 
the Front Range. This will leave a broad trough across the Central 
Plains into the Mississippi and Ohio valleys. Being on the 
downstream side of the trough...dominant northwest flow will turn to 
the southwest ferrying abundant Gulf moisture into the region as 
well as bringing some slightly warmer temperatures to the area for 
Monday and Tuesday. Expect highs in the 40s to near 50 degrees. 
Prefrontal southerly flow along with cloudy skies will also help 
overnight temperatures Monday and Tuesday nights stay warmer than 
they have of late with readings only dropping into the middle 20s to 
low 30s. Rain showers will start developing across the area on 
Monday afternoon as surface high pressure moves northeast across the 
Atlantic coast and surface low builds over the western Gulf Coast. The 
best chance for precipitation will be on Tuesday as cold front 
approaches the area during the day and southwest flow allows 
moisture to continue to stream into the area. Strong upper level jet 
will allow trough to continue digging across Texas and head towards the 
Gulf Coast as well as help create support for large upward momentum 
and increasing frontogenetical forcing across Tennessee/Kentucky and into in/Ohio 
Tuesday afternoon into Wednesday. Expect rain/snow mix on Monday 
night with temperatures warm enough Tuesday to keep precipitation 
all rain with another transition to rain/snow or snow overnight 
Tuesday into Wednesday morning as colder air begins to funnel into 
the area. Expect highs Wednesday in the middle 30s to near 40 with the 
Arctic air arriving Wednesday night into Thursday with overnight 
temperatures Wednesday in the low to middle 20s...highs Thursday in the 30s 
and lows Thursday night in the in the upper teens to low 20s. Model 
consensus has varied quite a bit as far as temperatures forecasts go 
Wednesday and Thursday so confidence is low in these temperatures 
and there is the outside chance they could be a bit colder than 
this. 


&& 


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 


Short term...Kirkpatrick 
long term....ls 
aviation.....Dk