345 
fxus63 kjkl 111108 
afdjkl 


Area forecast discussion 
National Weather Service Jackson Kentucky 
708 am EDT Sat Oct 11 2008 


Short term.../today through Monday/ 


An upper level ridge centered over the upper Ohio Valley will build 
west into the region today with heights rising in the wake of the 
weak middle level SW/v moving from the MS valley and into the Great 
Lakes. This ridge will keep the upper level low off the southeast coast 
suppressed to the south with an overall increase in heights to 
anomalously high levels today and on into sun. The ridge will remain 
place into Monday. At the same time...the upper low will weaken through 
the period and retrograde west or southwest. 


850 mb temperatures will warm today...on the order of 15 to 16c and with 
mostly sunny to sunny skies and the lower levels starting to dry out 
overall...this should lead to record highs today at both loz and jkl. 
The record today at jkl is 80 from 1985 and 2003...while the record 
is 83 set in 1962 at loz. In addition...the rising heights should 
lead to a lowering of the subsidence inversion and mixing and 
advection of drier air should lead to dewpoints drying out down into 
the 40s over much of the area this afternoon...especially in the 
east. Relative humidity there should fall well into the 20s percent range with 
around 30 percent near Lake Cumberland. With the surface high in place to 
the NE and ridge center nearly overhead tonight...a large drop in low 
temperatures should occur tonight. The coldest valleys should fall at least 
to the upper 40s under clear skies...while ridges remain in the upper 
50s. 


The ridge will remain over the area on sun with mostly sunny to sunny 
skies anticipated...so again just a temperature and dewpoint 
forecast. The 1000-500 mb mean layer relative humidity falls below 30 percent on the 
GFS for sun...with the NAM the driest. This is a pattern that is 
usually conducive to dry air mixdown and a significant bottoming out 
of dewpoints and relative humidity. The subsidence inversion will also lower some 
more per NAM forecast soundings. All this points to min afternoon 
dewpoints lower than mav MOS guidance on sun...probably closer to the 
drier NAM and FWC...if not lower still. Dewpoints were trended down 
significantly on sun from the previous forecast...though they could 
end up lower than currently forecast as suggested by the mixed 
dewpoint tool. Min relative humidity on sun should fall at least to the 20 to 25 
percent range...and would not be surprised if it falls below 20 
percent in several locations in the eastern County Warning Area. The consolation is 
that with the ridging in place winds will be light. With roughly the 
same 850 mb temperatures on sun combined with the atmosphere a little drier 
yet...temperatures should average a degree or two above saturdays readings. 
This should again allow maximum T to possibly tie the records of 84 set 
in 1985 at jkl and loz also 84 set back in 1969. 


With the surface high building further southeast along the East Coast on Sun 
night as the center of the upper ridge drifts a little further S and 
SW...the pattern will again be favorable for another a Ridge/Valley 
temperature split. Depending on how far dewpoints fall on Sun 
afternoon...min T could be lower than forecast for valley locations. 
However...trended down a couple of degrees on average for the eastern 
valleys. 


The ridge will remain in place across the area into Monday...though 
moisture...mainly at middle and high levels from what is currently the 
upper low off the southeast coast may begin to be drawn north toward the 
area on Monday. Surface dewpoints also may begin to climb again...but the 
NAM/European model (ecmwf) tend to hold this off a little longer than the GFS...so 
trended Monday dewpoints down a little from the previous forecast... 
more to a compromise between mav and met levels for Monday. 


Long term.../Monday night through Friday/ 


Strong ridging at the surface and aloft will be present at the start 
of the forecast period...meanwhile a deep trough will have dug into 
the western Continental U.S.. as we move toward middle week the original low 
associated with the trough in the east will have lifted into Canada 
while dragging a cold front across the Great Plains and Mississippi 
River valley. Meanwhile...a secondary shortwave will eject eastward 
from The Rockies behind the front. Have leaned with HPC and the 
slower 00z European model (ecmwf) solution as 06z/12z solutions are outliers. With 
the strong ridging in place over east Kentucky have elected to hold 
off slight chance probability of precipitation until Wednesday as the front shears out. The 
best chances for precipitation will not arrive until Thursday/Friday 
as the secondary shortwave arrives...although will stay with slight 
chance probability of precipitation for now as ridging will be tough to overcome. One 
consideration Worth mentioning is that ample moisture will be 
present from a few tropical systems over Baja California...which could warrant 
increased probability of precipitation as we approach next week. 


As far as temperatures go...have pretty much ignored mex(gfs) 
guidance due to strong favor for the European model (ecmwf). Tried to trend upward as 
much as collaboration would allow toward warmer European model (ecmwf) for afternoons 
as 850 mb temperatures are warmer throughout than the GFS. Should expect to 
see some 7-10 degree Ridge Valley splits at the start of the 
forecast...with splits gradually lessening as the system approaches 
middle week and more cloud cover arrives. 


&& 


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


Some patchy River Valley fog will burn off quickly after sunrise 
this morning...with just a brief period of MVFR visible possible at loz 
and sme through 13z. Some patchy MVFR fog should be confined to the 
river valleys tonight...but this will not affect the taf sites. 
Otherwise...high pressure over the eastern Great Lakes will keep VFR 
conditions across the area through the taf period...with east winds 
at 5 to 10 knots. 


&& 


Jkl watches/warnings/advisories...none. 


&& 


$$ 


Short term...jp 
long term....schoettmer 
aviation...wjm