668 
fxus63 klmk 211901 
afdlmk 


Area forecast discussion 
National Weather Service Louisville Kentucky 
305 PM EDT Thursday Aug 21 2008 


Short term (tonight and friday)... 


Scattered showers possible west while the east should remain dry. 


A couple of systems will affect the forecast area over the next 24 
hours. Over the western portion of the County warning forecast area we will find a moist 
southerly flow tapping moisture from the Gulf of Mexico. This in 
combination with a weak upper level system over the middle 
Mississippi Valley will keep showers and isolated thunderstorms 
moving across western Kentucky and into the wester tier counties of 
our forecast area. Across eastern Kentucky the flow will remain out 
of the southeast which will remain dry coming from the subsidence of 
ts Fay and even some downslope from the mountains. So we will keep 
the Bluegrass region dry. Dew point temperatures will continue to 
rise tonight which will again limit temperatures from dropping much 
below the 70 degree mark. Louisville will again remain the warm 
spot. 


Even with the cloud cover temperatures Friday should warm to around 
90 degrees. 


Long term (friday night through thursday)... 


Upper air pattern for early next week will feature an amplified but 
progressive series of ridges and troughs that will March through the 
Canadian prairies. The first trough will weaken over the Great Lakes 
Sunday while another stronger trough will be entering the Pacific 
northwest. By early Wednesday...this western trough will have 
migrated over the northern rockies...while the earlier trough over 
the Great Lakes will have been replaced by a ridge. 




Friday night through Sunday... 


Deep low pressure will move well north of Lake Superior 
Saturday...with its attendant cold front moving across Michigan and 
Illinois late Saturday. Southerly flow along the western side of 
ridging across New England will bring ample Gulf moisture north from 
Texas through the western Great Lakes. 


However... the strength and position of the eastern ridge will 
continue to bring southeasterly flow across our forecast area and 
will keep much of this return moisture to our west. Weak 500mb 
troughing across Missouri Saturday and Sunday will focus precipitation to 
our west. 


Will take out chances for scattered convection Saturday east of 
Interstate 65...while allowing for only a chance on Sunday due to 
the arrival of a weakening cold front. 


Temperatures will stay warm through the weekend. Highs will range 
near 90 while overnight lows will warm substantially compared to 
last week. 






Monday through Thursday... 




The eventual evolution of the circulation and moisture of former 
T.S. Fay is uncertain. Initially likely near southern Alabama 
Monday...the remnant low is handled by the GFS and the ecwmf 
differently. The GFS stalls this feature over Alabama...eventually 
bringing any residual moisture east across the Gulf states. The 
European model (ecmwf) brings a circulation Tuesday and Wednesday northeast across 
eastern Tennessee. Both scenarios miss central Kentucky and southern 
Indiana...and it is looking increasingly unlikely that tropical 
storm related moisture will alleviate our dry spell. 


Cool Canadian high pressure will move across the Great Lakes late 
Monday and Tuesday. However...the drier air will not sag much south 
of central Indiana. Antecedent moisture and the possible presence of 
a residual boundary south of the Ohio River may sparked scattered 
convection Monday and Tuesday. 


&& 


Aviation (18z tafs)... 


An upper level low moving through the middle Mississippi Valley has 
taped Gulf moisture. Showers and thunderstorms have been moving 
through western Tennessee and Kentucky. We still expect the bulk of 
this activity to remain west of the bwg and sdf taf sites for this 
taf period. Even if a brief shower moves across the area VFR 
conditions are expected. We also expect clouds to remain above 8k 
feet. 


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


$$ 


Short term...ja 
long term....jsd 
aviation.....Ja