910 
fxus63 klmk 231715 
afdlmk 


Area forecast discussion 
National Weather Service Louisville Kentucky 
1215 PM EST Monday Nov 23 2009 


..updated aviation discussion... 


Short term (today and tonight)... 


A short wave trough will traverse the Ohio/Tennessee valleys today 
as a shortwave ridge builds over the middle Mississippi Valley. Low and 
middle level cloud cover will persist through the day as the shortwave 
moves eastward and moisture is advected into the area as easterly 
winds become more southerly. Only some light showers or sprinkles 
will be possible through the afternoon hours...mainly east of 
Interstate 65. By tonight...the shortwave ridge will move over the 
area as a deep low pressure system digs into the Southern Plains. 


Expect high temperatures to be a few degrees cooler given the cloudy 
cover with highs mainly in the middle 50s. Overnight lows tonight will 
fall into the middle 40s under a warm air advection regimen. 


Long term (tuesday - sunday)... 


Tuesday-Wednesday... 


The Ops NAM and GFS models continue their slowing trend that they've 
displayed over the past several days. This slowing trend first 
affects the Tuesday-Wednesday system...which is now mostly a Wednesday system since 
Tuesday begins with the stacked low over eastern Kansas/western MO...well west of 
our County Warning Area. Other than some sprinkles over the west late Tuesday...the 
models do not bring precipitation into our County Warning Area until nearly 12z Wednesday. 
Removed probability of precipitation from Tuesday...and slowly bring low chance probability of precipitation in from 
the west Tuesday night with the highest probability of precipitation remaining over the north. 
Quantitative precipitation forecast amounts will be really light...perhaps a few hundredths most 
places. 


Have probability of precipitation ending by midday Wednesday over the northestern County Warning Area as the 
stacked low moves NE into the Great Lakes by Wednesday night...just in 
time for the next system to arrive. As the Tuesday night-Wednesday morning low 
moves into the Great Lakes...another deeper and colder trough 
quickly dives southeast towards our region Wednesday night. Slowly increase probability of precipitation 
from northwest to southeast ahead of this trough. The really cold air will wait 
until Thursday to filter in...however a rain/snow mix may reach our far 
northwestern County Warning Area very late Wednesday night...but should remain rain showers 
elsewhere. 


Thanksgiving-Friday... 


Chilly and snowy for the holiday? 


Thanksgiving will be cold and will feel even colder with gusty west-northwest 
winds from the cold upper trough settling in over the region. Any 
precipitation from this upper low should remain light but given its 
strength we should get scattered rain and snow showers. Just have 
snow showers over the north in the morning and late in the afternoon 
as even colder air filters in from the northwest late in the Turkey day. 
Actually think the better chance for snow showers mixing in will be 
late in the day. Good day to stay in as highs will not be above the 
middle 40s. 


Thanksgiving night...a changeover to all snow showers is likely as 
the upper trough settles just to our NE and we remain in a cold northwest 
flow. Low-level thicknesses below 1300m and sub-freezing temperatures as 
low as 950mb yield all snow by midnight...with overnight lows in the 
low 30s. However...warm grounds should keep anything from sticking 
to the ground...though slick spots will develop late Thanksgiving 
night into Friday morning. So be careful if you head out to shop 
Friday morning. Slick spots and chilly temperatures will not lead to the 
best travel weather Friday morning. 


For black Friday...a cold north-northwest flow and cloudy skies may keep temperatures 
in the 30s for highs. Light snow showers may still be possible...but 
taper those off from west to east Friday-Friday night. Again...no accums 
are expected. Went on the optimistic side for temperatures with upper 30s 
NE to low 40s SW...but raw GFS numbers suggest even colder temperatures. 
Gusty northwest winds of 25mph will create sub-freezing wind chills 
throughout the day Friday. Friday night lows will again dip into the 
low 30s. 


Saturday-Sunday... 


No changes made. Previous discussion below. 


By Saturday...upper low is forecast to pull out to the northeast and 500 mb 
heights look to rise as surface high pressure builds into the region for 
Sat/sun. Temperatures will slowly modify through the period as this 
cold will not last long in our region. Highs Saturday will range 
from the lower 40s in the NE to the middle and upper 40s in the 
southwest. Further warming is expected for Sunday with highs in the 
upper 40s in the NE with lower 50s in the southwest. 


&& 


Aviation (18z taf issuance)... 


A storm system digging into the Great Plains will keep most rainfall 
off to our west for this forecast package...other than a few stray 
sprinkles or light rain showers early this afternoon that should be 
of little consequence to aviation. Winds will remain light from the 
south and southeast. 


Low level moisture will stay trapped in the region throughout the 
period...resulting in mostly MVFR ceilings with some areas of IFR. 
At this time it appears that the low stratus will be the primary 
challenge to aviation...with any surface visibilities remaining at 
or above 2 miles. If holes can develop in the overcast towards 
morning then some lower visibilities could develop. 


&& 


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


$$ 


Short term........lms 
long term.........Al 
aviation..........13