786 
fxus63 klmk 201714 
afdlmk 


Area forecast discussion 
National Weather Service Louisville Kentucky 
1215 PM EST Thursday Nov 20 2008 


Short term (today and tonight)... 


Colder with northwest flow and low clouds over most areas through the period. 


North Dakota shortwave trough...as seen in water vapor imagery...forecast to 
drop southeastward into the lower Ohio Valley tonight and into eky/Virginia by 12z Friday. 


By 12z this morning...cold front will have exited our forecast area to the southeast 
with cold air advection low clouds upstream about 3-6 hours behind the front. Those 
clouds should overspread much of our forecast area today...especially the northestern half 
of our forecast area. Temperatures will be slow to climb...battling clouds/northwest flow... 
and current forecast maximums below MOS guidance...accepted. 


Tonight...with approach of shortwave...model soundings/time height cross 
sections...GFS in particular...indicate deepening low level 
moisture...up to about 800 mbs into the favorable ice Crystal 
formation layer of -10 to -15 degrees c and steep low level lapse 
rates. Moisture is forecast to be deepest over our northestern most 
counties...where we will keep a chance pop for snow showers tonight. We 
will make a change and insert slight chance probability of precipitation westward to include much 
of scntrl Indiana and the eastern part of central Kentucky. Any snow should be 
ending well before sunrise in all but perhaps our northestern Bluegrass 
region counties. 


Long term (friday through wednesday)... 


Friday through Sunday... 


Cold Canadian high will build southeast across the plains states and 
will be nudging into central Kentucky at the start of the longer 
term. Upper level flow remains amplified through early part of the 
weekend with a deep trough over the area ahead of the high. This 
will keep temperatures quite cool on Friday...even with decreasing 
clouds and plenty of sunshine Friday afternoon. Any lingering 
flurries in the far northeast will move east as the drier air 
spreads east. 


After a chilly start with lows around 20...abundant sunshine will 
help boost temperatures to near 40 in the northeast and the middle 40s 
over the west on Saturday. The moderating trend will continue 
Saturday night and Sunday ahead of the next system that will begin 
diving into the upper Great Lakes Sunday afternoon. 


Sunday night through Wednesday... 
with the next system diving south Sunday night the upper flow again 
becomes more amplified over the eastern U.S. A front trailing from a 
low over the upper Great Lakes will push east across central 
Kentucky late Sunday night and Monday. This will bring showers to 
the region Sunday night and Monday. 


Temperatures will turn cooler Monday night with a chance of snow 
showers or flurries...especially over the east Monday night into 
Tuesday. Latest model runs indicate that this outbreak of cold 
temperatures will not be quite as cold as the one a few days prior. 
Have modified temperatures some...although still stayed cooler than 
guidance most locations. 


&& 


Aviation (18z tafs)... 


A cold northwest flow will continue through this forecast period. 
Strato-cumulus will overspread central Kentucky this afternoon but ceilings 
should remain above 3k feet above ground level. An approaching upper level trough 
will sharpen up across the area tonight which may produce some light 
snow showers or flurries especially over the sdf and Lex taf sites. 
Visibilities may briefly drop into the MVFR range if these showers develop. 


The clouds will clear bwg and sdf by 12z and Lex by 15z Friday. 


&& 


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


$$ 
Weather.Gov/Louisville 


Short term...Kirkpatrick 
long term....mbs 
aviation.....Ja