474 
fxus63 kjkl 041832 
afdjkl 


Area forecast discussion 
National Weather Service Jackson Kentucky 
132 PM EST Thursday Dec 4 2008 


Short term.../the rest of today/ 


Removed morning and afternoon wording from zone forecast text 
product. Hourly observation indicate that temperatures across the area are 
falling a bit more slowly than previously forecast...but overall 
things are still on track for temperatures to fall into and remain in the 
lower and middle 30s this afternoon. A pretty good snow shower was 
ongoing at afd issuance at jkl...with higher reflectivities showing 
up on radar south of the weather office. These higher reflectivities 
are likely large wet snow flakes. Continued with mention of rain and 
snow mix in the forecast for the rest of today...with a general 30-50 
percent chance of precipitation across the board. Latest radar loop 
indicates that new precipitation areas are forming behind the 
departing cold front...but this new activity is not as widespread as 
the previous forecast had indicated. Made adjustments to hourly temperature 
and dewpoint grids based on trends observed in this mornings surface 
observation. The rest of the forecast is in good shape. Update zones have 
already been issued. 


The previous short term forecast discussion follows... 


/tonight through Saturday/ 


Temperatures are expected to fall after frontal passage...dropping into the 
lower to middle 30s during the afternoon. The precipitation may mix with or 
change over to snow briefly before ending. The rain/snow changeover 
line seems to be lining up well with the 1304 h10-800 mb thickness line 
on the RUC. In the past few hours...the Post frontal precipitation has been 
diminishing...with not many stations to our west reporting snow at this time. 
No snow accumulation is expected...although an isolated spot above 
2500 feet neat the Virginia border may see up to a half inch or so. 
Precipitation should taper off from west to east during the day. There will 
be some upslope flow by afternoon...which could help a few more areas 
of light rain and snow to linger in the southeastern County Warning Area into late 
afternoon. 


Dry air rapidly moves in by evening...and this should help cut off 
any precipitation. High pressure also builds in tonight. With partly cloudy 
skies...overnight lows should generally drop into the lower 20s. The 
surface high remains in control on Friday...although some middle and 
high clouds should pass over the region as a weak 500 mb trough swings 
through. Can/T rule out a flurry...but will not include in the 
forecast at this time. Should be rather cold with highs in the lower 30s in 
the north to the upper 30s in the south. Many valley areas will 
likely see temperatures drop into the teens Friday night. On Saturday the 
next clipper system approaches in the afternoon. Will keep slight 
chance to chance probability of precipitation across the area for snow showers. Any snow 
could be mixed with some rain if the boundary layer warms enough. Did 
undercut guidance some for Saturday...considering a cold start and 
increasing cloud cover. 


Long term.../Saturday night through Wednesday/ 


A strong short wave will drop southeast across the area Saturday 
night...with upslope flow developing overnight. This should result 
in an increase in snow showers through the night. Column will cool 
quickly supporting all snow overnight with some light accumulations 
possible in the favored higher terrain of southeast Kentucky. 


Any snow shower activity should taper off quickly Sunday morning as 
the upper trough shifts east away from the region and high pressure 
builds in at the surface. Dropped temperatures a few degrees on Sunday with 
prognosticated 850 mb airmass overhead likely only supporting middle 30s at 
best. 


High pressure with rising heights aloft should support a modest warm 
up on Monday with temperatures warming into the low to middle 40s. 


Models then indicate a shortwave will dive southeast through the 
plains supporting cyclogenesis to our west Monday night. It appears 
like the best time frame for precipitation across the area is on Tuesday 
into Tuesday night based largely on the 03/12z GFS and NCEP 
ensemble. 03/12z European model (ecmwf) is much quicker with the system moving any 
precipitation out quickly Tuesday night. Will continue with chance probability of precipitation 
only Tuesday through Wednesday due to the uncertainty and mention 
only rain until Tuesday night when there is support for a possible 
rain/snow changeover with rain and snow mix possible through the day 
on Wednesday. 


&& 


Aviation.../18z to 18z/...updated 


A cold front has pushed southeast of the area...with light to moderate snow 
and rain showers behind the front as an upper level disturbance 
passes by. Clouds are in the IFR to MVFR range behind the boundary...and 
expect the low clouds to gradually clear out from west to east 
between 19z and 2z...with conditions becoming VFR once the low 
clouds clear out. VFR should then remain through the end of the 
period as high pressure builds into the area. 


&& 


Jkl watches/warnings/advisories...none. 


&& 


$$ 


Short term...wjm/AR 
long term....Abe 
aviation...jp