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fxus63 kjkl 042007 
afdjkl 


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


Short term.../tonight through Saturday night/...updated 


Overall the GFS model seems to be handling the current synoptic 
pattern the best...and is the preferred model of the HPC according to 
their latest discussion...so the GFS model was used for the forecast 
through 12z Sunday. All the models agree that once the isolated rain 
and snow showers that are ongoing across the area move off to the 
east...things will be high and dry for tonight through late Saturday 
afternoon. Low level cloud cover will continue to blanket the area 
behind a departing cold front through late this evening. The latest 
satellite imagery reveals a distinct clearing line situated just to 
the west of the jkl forecast area. The area of clearing will expand 
slowly eastward with partly cloudy skies expected by 6z tonight 
across the entire area. Typical upslope induced cold air low clouds 
will remain in place for the next couple of days as well. Skies will 
remain partly cloudy until an area of low pressure moves across the 
Great Lakes late Saturday into Sunday. As this trough digs into the 
Ohio Valley Saturday night...low and middle level clouds will blanket 
the area...bringing scattered rain and snow showers to eastern 
Kentucky. The latest GFS model soundings dont support much 
snowfall...with only a brief period Saturday night favorable for 
dendritic Crystal growth. Bottom line...the latest MOS data supports 
a chance of precipitation Saturday evening into Sunday morning. 
Temperatures will remain just warm enough for all rain for most of 
Saturday afternoon. There could be a brief period of rain snow mix 
middle afternoon Saturday...before a transition to all snow around 
sunset Saturday. The system responsible for the precipitation will 
move through the area fairly quickly...so little if any snow 
accumulation is expected. The exception will be the higher elevations 
east of the weather office...where a light dusting might occur along 
the ridgetops. 


Went a bit warmer than MOS for highs on Friday...per the trends 
observed in the MOS data over the past 4 or 5 runs and accounting for 
partly cloudy skies that could aid in some enhanced daytime heating 
where breaks in the clouds occur. Went a few degrees cooler than MOS 
for highs on Saturday...as cloud cover will be on the increase 
throughout the day...with mostly cloudy conditions expected by late 
morning. Considering the amount of cloud cover expected Saturday 
night...the mavmos lows seemed a bit too cold...so went with the 
metmos numbers for now to account for this...going a bit warmer than 
the met MOS for Saturday nights lows. Dewpoints were in good shape 
already. Only a few minor tweaks were needed to touch up the wind 
grids...as that portion of the forecast was already in good shape as well. 


Long term.../Sunday through Thursday/...updated 


The long term models are in agreement that a mean trough will be in 
place through the period east of The Rockies over the Continental U.S. And 
North America. However...there are differences in timing and 
individual shortwaves...as well as how cold the airmass will be. The 
0z and 6z GFS runs are generally faster with timing...with lower 
heights across the Ohio Valley Tuesday through Thursday and considerably colder 
with the airmass the last two days of the period. The 12z GFS was 
less phased with northern and southern stream SW/vs by 0z to 12z 
Wednesday. The 12z GFS is also slower with this southern SW/v. The 3/12z 
and 0z European model (ecmwf) both tend to close off a SW/v emerging from The Rockies 
into the plains on Monday into Tuesday...and the 12z run also maintains 
that trend. This scenario would lead to a slower more western 
secondary surface low track...while the 0z and 6z GFS as well as the 
3/12z and 0z GFS ensembles and 12z Canadian appear to support more of 
a phased trough...and a more eastern secondary surface low...or perhaps 
none at all. The 12z less phased GFS has a secondary low developing 
over the Gulf Coast states Tuesday and Tuesday night and then tracks this 
system NE east of the Appalachians Wednesday and Wednesday night. The 


The 0z naefs...0z Canadian as well as 0z GFS ensemble generally 
support the quicker solutions...but the 12z GFS ensemble is 
generally in line with the 6z GFS run...with a weak or no secondary 
surface wave. Confidence in cold front timing Tuesday into Wednesday and the Tuesday 
through Thursday period overall is rather low as timing and phasing of 
individual SW/S is in question and if/when they phase will determine 
how cold the airmass will be a the end of the period. Obviously 
this will play a large role in determining the sensible weather. For 
now...opted to go warmer than the 0z mex numbers that appeared to be 
too low given the very cold forecast 800 mb temperatures toward the end of the 
period. Overall...compromised more toward the warmer 12z mex 
numbers. If the systems end up being more phased it will end up 
cooler at the end of the period...while if they are less phased it 
could end up several degrees warmer. 


&& 


Aviation.../18z to 18z/ 


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...Arkansas 
long term...jp 
aviation...jp