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fxus63 kilx 211126 
afdilx 


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


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 




&& 


Aviation... 
issued 525 am CST Sat Nov 21 2009 


Main forecast concern will be with the potential for locally dense 
fog through 14z this morning. Fog development this morning has been 
quite a bit slower than last night at this time. One negative 
factor for the formation of widespread fog has been with some 
scattered-broken stratocu that has been pushing eastward across parts of the 
area early this morning. Will still include a tempo group through about 
15z for the threat of visibilities dropping to IFR/LIFR conditions 
for a brief time. Fog should lift by 15z with forecast soundings 
indicating a moist layer between 900-800 mb (3500-4500 feet) into 
this afternoon suggesting a scattered to broken deck...especially across the 
western taf sites (pia and spi). Surface winds will be light east 
to southeast into tonight with speeds at or below 10 kts. 


Smith 
&& 




Ilx watches/warnings/advisories... 
dense fog advisory until 9 am CST this morning for ilz027>031- 
036>038-040-041. 


&& 


$$