515 
fxus63 kilx 211743 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
1143 am CST Sat Nov 21 2009 


Discussion... 
issued 1042 am CST Sat Nov 21 2009 


Moisture continues to spread northward from a storm system over 
eastern Texas. Latest satellite imagery indicates partly to mostly 
cloudy conditions along and west of I-55...with sunny skies further 
east. Based on general north/NE drift of cloud cover and drier airmass 
poised to the east...think abundant sunshine will prevail across 
the east/southeast kilx County Warning Area for the balance of the day. Meanwhile...quite a 
bit of cloud cover will continue to plague locations from I-55 
west. Have updated forecast to better reflect sky trend and to 
lower high temperatures by a couple of degrees across the Illinois River 
valley. Should see afternoon highs ranging from the middle 50s 
west of the Illinois River...to the lower 60s south of I-70. 






&& 


Aviation... 
issued 1143 am CST Sat Nov 21 2009 


A storm system over Texas continues to push middle-level moisture 
northward across western Illinois. Latest satellite imagery 
indicates scattered-broken clouds with bases around 7000ft along and west 
of I-55...with clear skies further east. Clouds will tend to 
dissolve as they try to move northeastward into a drier airmass 
beneath surface high pressure centered over Indiana. As a 
result...will only carry scattered clouds at kcmi and kdec. Further 
west...will maintain broken middle-deck at kpia and kspi through the 
afternoon into the evening. 12z NAM-WRF and GFS relative humidity profiles 
indicate a drying trend overnight...so will scatter out the clouds 
across the western terminals between 05z and 06z. Winds through 
the entire 18z taf period will remain light out of the E/se. 


Barnes 
&& 


Previous discussion... 
issued 205 am CST Sat Nov 21 2009 


Latest surface map showing the County Warning Area underneath an east-west high 
pressure ridge...centered in southeast Ohio. Satellite fog 
imagery showing patches of stratocumulus clouds across the east 
central County Warning Area around Champaign and Danville...as well as scattered 
near the St Louis area. Dense fog has mainly been patchy thus 
far...with average visibilities over the County Warning Area in the 3 to 7 mile 
range. 


Main short term concern involves the fog this morning. In the 
longer range...evolution of the next storm system in the Tuesday- 
Wednesday time frame is the primary forecast concern. 


Short term...today through Monday... 


The fog has been slower to evolve than last night...but latest 
surface plot showing fog becoming more widespread across Iowa and 
adjacent areas of Missouri and Illinois. RUC model supports some 
expansion of this area...and will keep the dense fog advisory 
going across the northern County Warning Area. Across the south...believe the fog 
will be more patchy in nature...due to the drying that took place 
in the sunshine on Friday. 


Other than that...models in decent agreement through Monday... 
keeping things dry. Temperatures expected to remain several 
degrees above normal. Met/mav MOS guidance fairly close and did 
not significantly deviate from it. 


Long term...Tuesday through Friday... 


Main forecast challenge involves evolution of upper trough that 
will move into the Pacific northwest on Sunday. The major models 
all have a closed circulation developing over the Central Plains 
by Tuesday morning...but the speed and track of the surface 
features remain in question. GFS has slowed a bit but continues to 
be the faster of the extended models...bringing the cold front 
through the County Warning Area by about midday Tuesday and having wraparound 
precipitation affecting the area Tuesday night. Meanwhile...the European model (ecmwf) 
places the surface low in southeast Nebraska at 12z Tuesday and 
moves it to near Rockford by 12z Wednesday...with the surface 
front passing through our area shortly afterward. Trended toward 
the slower solution and thus reduced probability of precipitation to slight chance across 
the eastern County Warning Area Monday night. Went ahead and added some low chance 
probability of precipitation Tuesday night and Wednesday across the north...as that area 
should at least be getting some wraparound precipitation from the 
GFS solution...or from the front itself in the European model (ecmwf) solution. 
Southern County Warning Area is not as clear cut at this time...and will not 
change the probability of precipitation in that area. Until more consistency develops. 
1000-500mb thickness...as well as BUFKIT soundings...would suggest 
that precipitation type would be a concern as well. Currently plan to 
limit any mixed precipitation to the far northern County Warning Area for Tuesday night. 


Both models showing weak troughs moving through on Thanksgiving 
day...followed by high pressure ridging building in from the west. 
However...no changes were made to this portion of the forecast. 


Geelhart 




&& 


Ilx watches/warnings/advisories... 
none. 
&& 


$$