630 
fxus63 kpah 180154 aaa 
afdpah 


Area forecast discussion...updated 
National Weather Service Paducah Kentucky 
854 PM CDT Wednesday Mar 17 2010 


Update... 
this is an interim evening update to address minor adjustments in 
sensible weather elements. 




Discussion... 
overall...current forecast remains fairly good. Short and medium 
range guidance appears to be handling the mean layer precipitable 
water fairly well...but falters somewhat in the sub- 
synoptic/mesoscale Arena. The 18z GFS/NAM guidance remains 0.5 to 
1 degree celsius too warm at 850 mb at 00z /7 PM CDT/ 
Thursday...with nearly all the guidance too moist at the same 
level. Compared to available GOES sounding data...the mesoscale 
/12-40km/ 18z Wednesday NAM WRF guidance appears to be the 
closest...with the 40km GFS a little more moist than then WRF 
guidance. The best guidance...with respect with near surface 
moisture and temperatures was the 4km arw WRF. The evening update 
was blended with the current forecast in place. 


In addition to temperature...dewpoint...and wind data...adjusted 
the cloud cover to address the slower evolution and transition of 
clearing line to the south...southeast...as the upper low/cyclonic 
circulation continues to move away from the weather forecast office pah forecast area. 
There remains a sharp subsidence/dry advection zone along the 
northern limb of the southeast U.S. Low where it interacts with a 
slight westward tilting upper level ridge. Another temperature 
adjustment may need to be made to address any differential from 
northwest to southeast based on the cloud cover. 


&& 


Aviation... 
/previously issued 205 PM CDT Wednesday Mar 17 2010/ 
VFR ceilings should finally dissipate this evening...with only scattered 
VFR clouds expected thereafter. 


&& 


Fire weather... 
GOES sounding data suggests drier air feeding into the weather forecast office pah 
forecast area from southwestern Indiana this evening. The 4km arw WRF 
guidance appears to be doing fairly well in handling these trends 
this evening and overnight. 


At this time...mixing may be slowed slightly Thursday morning...which 
may slow the degree of mixing and lowered dewpoints until late 
morning and into the early afternoon. The net effect may be a 3-5 
percent increase in minimum relative humidities along and west of 
Interstate 57 in southern Illinois and Interstate 55 in southeast MO. 
For the most part...current minimum relative humidity forecast for 
the weather forecast office pah fire weather forecast area looks 
reasonable...especially over southwest Indiana and the pennyrile 
region of west Kentucky...where drying in the wake of the upper 
low will be maximized. 


For now...will not make any specific changes to minimum relative humidity 
forecast for Thursday...but lower 20s look good for southwest 
Indiana and the pennyrile region of west Kentucky and middle to 
upper 20s over southwest Illinois and southeast Missouri. 


&& 


Pah watches/warnings/advisories... 
Kentucky...none. 
MO...none. 
Illinois...none. 
In...none. 
&& 


$$ 


Smith