499 
fxus63 klmk 211111 
afdlmk 


Area forecast discussion 
National Weather Service Louisville Kentucky 
611 am EST Sat Nov 21 2009 


..updated aviation discussion... 


Short term (today and tonight)... 


Current water vapor imagery shows low pressure spinning over Texas 
which is causing higher clouds to spread across the region from 
mainly the Ohio River southward. With high pressure at the surface 
in place and some low-level moisture...fog will again be a problem 
this morning. The higher clouds could help mitigate how dense the 
fog becomes however the clouds are thin so they should not totally 
preclude fog from forming. Locations across southern Indiana where 
less cloud cover resides and any low-lying areas like river valleys 
could see patchy dense fog by sunrise. Fog should lift quickly after 
sunrise with early morning lows generally in the upper 30s to around 
40. Some middle 30s will be possible over sheltered regions in the 
Bluegrass. 


For today...surface high pressure will slowly move eastward and the 
upper low over Texas will help push surface low pressure over the western 
Gulf northeastward towards the Appalachians. The system will be over Alabama 
by late tonight...with its precipitation field stretching downstream as far 
north as Tennessee by early Sunday morning. The past four model runs 
of the Ops NAM and GFS have slowed the progression of the low and 
thus onset of precipitation so will remove precipitation from our southeastern County Warning Area for 
late tonight and keep today and tonight dry. Will however continue 
to increase the cloud cover over the southeastern County Warning Area. 


Concerning temperatures...with NE winds at the surface and possibly more clouds 
from the southern stream low...think temperatures will be similar to 
yesterday and went closer to raw GFS values rather than MOS 
guidance. Upper 50s to low 60s looks reasonable for highs. Lows 
tonight will be a bit warmer from added cloud cover from the 
approaching low. 


Long term (sunday - friday)... 


No major changes made to the ongoing extended forecast this morning. 
Lowered probability of precipitation across northern portions of the forecast area on Sunday 
but left some slight chance and chance probability of precipitation across the southeast 
with the best chance for some light showers in the Lake Cumberland 
area and possibly moving into the Bluegrass region in the afternoon. 


Monday continues to look dry as the system across the southeast 
moves eastward and the upper low over the northern plains continues 
to migrate toward to Midwest. The GFS and European model (ecmwf) are still quite 
different in their solutions for this system with the GFS bringing 
the trough and attendant cool front through the region on Tuesday. 
The European model (ecmwf) continues to be the slower model with a bit more southerly 
track...bringing the system through on Wednesday. 


Both models do show the trough lingering across the Midwest/Ohio 
Valley through Thursday so cloudy and cool conditions are expected 
but pinpointing shower activity remains difficult. Therefore will 
leave Wednesday and Thursday forecast as is with a Wednesday being 
dry and Thursday possibly seeing some showers...mainly over the 
Bluegrass region. By Friday a broad upper level ridge moves eastward 
into the Central Plains and the Ohio Valley region will return to 
drier conditions. 


Temperatures will be near normal Sunday through Wednesday with highs 
in the 50s and lows mainly in the 40s. By Thursday temperatures take 
a colder turn with highs in the 40s for Thursday-Friday and lows dipping 
to around freezing. Expect skies to be partly to mostly cloudy 
through the extended period. 


&& 


Aviation (12z taf issuance)... 


Surface high pressure overhead will gradually shift to the northeast 
during this taf period. Other than MVFR visibilities at sdf/Lex due to br 
and IFR-LIFR visibilities at bwg due to fog...conditions should be VFR 
after 14-15z and through the rest of the taf period. Will keep an 
LIFR tempo in at bwg for a few hours this morning. 


Middle-to-high level cloudiness should continue to stream northeastward 
from Texas...mainly affecting bwg...but perhaps sdf and Lex as well. 
NAM BUFKIT soundings show few clouds around 3-4kft...but for the 
most part all cloud cover will be 20kft or higher. Winds will be 
light and out of the east-northeast. 


After 00z tonight...fog should not be a problem with increasing 
boundary layer winds from an approaching low pressure system from 
the Gulf. Again...only clouds around 15kft should push in from the 
south...keeping VFR conditions. 


&& 


Lmk watches/warnings/advisories... 
Kentucky...none. 
In...none. 
&& 


$$ 


Short term........al 
long term.........Lms 
aviation..........al