066 
fxus63 kjkl 211905 aaa 
afdjkl 


Area forecast discussion...updated 
National Weather Service Jackson Kentucky 
305 PM EDT Thursday Aug 21 2008 


Short term.../tonight through Sunday/...updated 


18z surface analysis shows high pressure off to the northeast keeping 
east Kentucky dry and mostly sunny...while to the west broad low 
pressure is allowing for more clouds and even a few showers. 
Meanwhile Tropical Storm Fay is spinning nearly in place along the 
northeast Florida coast. Sunnier skies today has promoted better 
mixing and thus drier afternoon dewpoints/relative humidity across the area than 
yesterday...but these are still a far cry from the very dry 
afternoon/S of Monday and Tuesday. With the dry air and sunny skies 
temperatures are having little trouble running up into the lower 90s 
for afternoon highs. 


The longwave pattern aloft is similar from all models as the eastern 
ridge evolves into a large subtropical ridge that will spread across 
the southern portion of the nation for the weekend. This ridge will 
build atop the upper low associated with T.S. Fay and serve to block 
its movement north. From the Pacific northwest...during this time...a 
deep trough will roll east through southern Canada helping to flatten 
the northern extent of the eastern ridge. There are slight timing 
differences with this feature heading into the weekend with the 00z 
Thursday European model (ecmwf) representing a compromise between the GFS and NAM. Its 
reasonable solution with the upper pattern and ensemble support makes 
the European model (ecmwf) the model of choice for the latter part of the short term 
and into the long term portion of the forecast. The wave originating 
in the Pacific northwest then crosses north of the Great Lakes for 
Sunday but too far north to have much affect on whatever remains of 
Fay. 


Sensible weather will continue our rain-free existence well into the 
weekend as low pressure holds to the west...Fay stays south and late 
in the short range...a front...associated with the upper level 
trough...approaches from the northwest. The moisture from Fay and 
approaching front will give US a better chance of seeing showers or 
thunderstorms during the day Sunday. Otherwise...persistence will 
hold sway with partly to mostly clear skies and dry conditions...a 
small ridge to valley split during the nights...and highs around 90 
each afternoon. Any early morning fog is expected to be confined to 
the river valleys and the deeper sheltered areas further east. 


For temperatures...leaned mostly toward persistence and that meant 
the mav numbers were generally favored. As for probability of precipitation...kept things dry 
up until Sunday comparable to MOS guidance...though would not rule 
out a stray shower or thunderstorm at peak heating each afternoon... 
especially in the west or higher terrain in the east. Therefore have 
not zeroed out probability of precipitation completely through Sunday. 


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


Into the extended...the models continue fairly similar aloft with 
the northeast trough pulling east and ridging builds through the 
central United States. Again...ridging builds north of Fay/S remains 
keeping the movement slow and encouraging dissipation. The models 
begin to diverge later in the period from late Tuesday on as the 
European model (ecmwf) maintains the circulation from Fay...taking it up into the 
Tennessee Valley. On the other hand the GFS...thanks to stronger 
influence from another Pacific northwest trough moving through the 
northern plains...losses the circulation of Fay. This upper trough 
pushes east building a ridge over the northeast...in the process. The 
model differences magnify by Thursday with the GFS much more 
progressive with the large northwest trough compared to the 
flatter...slower European model (ecmwf). Have leaned closer to the GFS solution and 
for weather specifics blended in the frontal and pressure pattern 
guidance from HPC for the latter part of the forecast. 


Sensible weather in the extended will feature the slow convergence of 
the stalling front to our northwest and the remnants of Fay. Rather 
than combining to produce a good and much needed soaking...the 
preferred medium range solution from the GFS and HPC keeps the rains 
from Fay to the south before slipping them off to the east late in 
the period. Accordingly...the main rain threat for most of next week 
will come from the stalled front northwest of US or right overhead. 
This will keep a medium and somewhat diurnal chance of rain in the 
forecast from Sunday night through Thursday. It would also keep temperatures 
a tad cooler from greater clouds and increased moisture. However... 
barring a solid move northward by a still potent Fay early in the 
period...the drought conditions look to worsen. 


&& 


Aviation.../18z to 18z/ 


Expecting scattered cumulus clouds to form after 19z today across the 
entire forecast area. Latest visible satellite imagery shows that 
some cumulus clouds are already popping up along the Virginia and 
West Virginia borders. With strong cap in place in forecast 
soundings...not expecting clouds to last long after the sun GOES 
down...so will be clearing thing out after 2z this evening at all taf 
sites. Patchy fog is likely to form in river valleys...particularly 
in areas adjacent to lakes and rivers....overnight tonight. The taf 
sites will remain fog free as the surface is simply too dry for fog 
to form at these locations. With widespread haze already in place 
across the forecast area today...decided to keep visibilities in the 
aviation grids at 8sm for both this afternoon and tomorrow after 
15z...as the stagnant air mass currently in place is expected to 
remain in place for at least the next couple of days. 


&& 


Jkl watches/warnings/advisories...none. 


&& 


$$ 
Short term...greif 
long term...greif 
aviation...Arkansas