743 
fxus63 klmk 212308 
afdlmk 


Area forecast discussion 
National Weather Service Louisville Kentucky 
608 PM EST Sat Nov 21 2009 


..updated aviation discussion... 


Short term (tonight and sunday)... 


Surface high pressure centered over Ohio will move NE into the New 
England state tonight. Expect mostly clear skies overnight with an 
increase in clouds over the southern forecast area (fa) toward 
sunrise ahead of the next weather system. Low temperatures will be in the 
upper 30s over the Bluegrass/southeast Indiana to low 40s elsewhere 
across the region. 


The next weather system sits to our south over Louisiana and Texas. 
This system will weaken at the surface and move north up into the 
Tennessee Valley on Sunday. Although most models keep the precipitation 
south of our forecast area...the 12z GFS has a good handle on the current 
precipitation field and it does bring some up into our far southern 
counties Sunday afternoon. Therefore...will continue a 20% pop in 
our southern counties along the Tennessee border for the afternoon hours. 
With a notable amount of more clouds in the southern forecast area...will see 
high temperatures range from the middle 50s over south central Kentucky to upper 50s 
over southern Indiana/north central Kentucky. 


Long term (sunday night - saturday)... 


Sunday night through Saturday... 


Sunday night through Wednesday night... 


In the medium range...the deterministic and ensemble model guidance 
is in general agreement with the synoptic pattern across North 
America. Cut off 500mb over the MS Delta Region is forecast to lift 
northeast and weaken as another strong 500 mb wave drops southeast out 
of Canada and into the plains. Associated with the lifting 500 mb 
wave...a surface area of low pressure looks to move up out of the Gulf 
and track NE along the southeast coast. With this track...some 
light shower activity seems possible over our southeast sections 
late Sunday and early Monday before quickly moving off the 
northeast. Overall...the trend in the model data is drier than 
previously forecast. Lows Sunday night look to drop into the lower 40s 
in the north with middle 40s in the south. Highs Monday should warm 
into the lower to middle 50s. 


Next weather system will begin to affect the region by late Tuesday 
in the form of a large closed low pressure system rolling eastward 
across the plains. Associated surface low looks to move from the plains 
and then into the Great Lakes states with a large 500 mb gyre left 
spinning across the Great Lakes region. Shower chances look to 
increase Tuesday afternoon ahead of the surface cold front which looks 
to push through the region Tuesday night/early Wednesday. Here we'll be 
running the highest pop chances for this forecast period. As 
initial low moves off the northeast...large lobe of vorticity will 
drop down out of the upper Midwest around the periphery of the large 
500 mb circulation in the lakes. This will lead to additional chances 
of light precipitation into Wednesday night. Temperatures will start off 
Tuesday in the lower to middle 40s with highs topping out in the 
low-middle 50s. Much cooler weather will move into the region 
Wednesday with overnight lows in the middle-upper 30s and highs on 
Wednesday in the upper 40s to the lower 50s. Lows Wednesday night look to 
drop into the middle 30s. 


Thanksgiving day through Saturday... 


Very large 500 mb cut off low is forecast to move slowly eastward through 
the Great Lakes region. Surface low will looks to be stacked right 
underneath of the upper low with much of our region being locked 
into a northwest flow situation. Lots of low-level moisture looks 
to stay in the region...so Thanksgiving day looks to be very cloudy 
and cool with some showers moving through the region. Temperatures 
will continue to cool with highs in the upper 30s to the lower 40s 
in the north and middle 40s down south. The raw model data is 
cooler...and the trend in the data continues to go down. So further 
adjustments to temperatures may be required in subsequent forecasts. Northwest 
flow looks to continue Thursday night and into Friday. Enough moisture 
looks to be available Thursday night for some light rain showers 
early...with a transition to snow showers possible late Thursday night or 
Friday morning. Surface and upper level lows look to pull out quickly 
for Friday and Saturday with a drying trend expected. Highs 
Friday/Sat will range from the upper 30s-lower 40s in the north to 
the middle 40s in the south. Again the raw model guidance is cooler 
and the trend is cooler...so further adjustments downward may be 
required. 


&& 


Aviation (00z taf issuance)... 


An area of low pressure moving across the Gulf Coast states will be 
responsible for gradually increasing clouds Sunday and an eat to 
southeast flow. With clear skies and calm winds for most of the 
night will will continue to mention MVFR and occasional IFR visibilities 
with fog being the restriction. Otherwise expect some middle level 
clouds to overspread the area after 16z. 


&& 


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


$$ 


Short term........aml 
long term.........Mj 
aviation..........ja