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fxus63 kilx 180740 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
240 am CDT Thursday Mar 18 2010 


Discussion... 
issued 240 am CDT Thursday Mar 18 2010 


Clear skies prevail over the County Warning Area early this morning...under the 
influence of high pressure ridging extending northeast out of 
Oklahoma. Some light fog forming across the western County Warning Area...where 
cloudiness yesterday held on a bit longer and not as much drying 
out took place. However...some of it is becoming locally 
dense...mainly west of the Illinois River. 


Latest water vapor imagery showing a strong shortwave moving 
southeast across the Canadian prairies. This is the feature that 
will be affecting our weather this weekend. The forecast remains 
complicated...as the models continue to show many discrepancies 
in regards to the weekend storm system. 




Short term...today through Sunday... 


Not much issue in the very short term...as ridging continues 
across the area through early Friday. With abundant sunshine 
expected...have gone a few degrees above the guidance numbers for 
today...resulting in middle 60s over the entire County Warning Area. Guidance numbers 
for Friday also gave middle 60s...and stayed close to them...with an 
increase in cloudiness expected. 


Frontal boundary expected to be knocking on the northwest County Warning Area 
doorstep by late Friday afternoon...and should be just east of 
the I-55 corridor by 12z Saturday. The difficulty arises in the 
development of a surface wave...riding northeast along the 
front...affecting its progress through the area. The various 
models have been having difficulties the last several days trying 
to resolve this feature...and this trend is continuing. The NAM 
and sref models are fast outliers in having the low and front past 
the County Warning Area by late Saturday morning. The GFS has the low spinning 
over southeast Missouri through Saturday night before ejecting 
northeast...the Canadian model has it near Champaign by 12z 
Sunday...and the European model (ecmwf) has slowed things down and keeps the low in 
Arkansas through Sunday morning. Leaned more toward the GFS 
solution for now...as a middle of the Road compromise. 


Forecast soundings indicate a changeover from rain to snow across 
the far northwest County Warning Area by late Saturday morning...with a rain/snow 
mix between the Illinois River and I-55 during the afternoon and 
night. Amounts will be tricky...as ground temperatures are currently well 
into the 40s and would melt quite a bit of the snow that would 
normally accumulate...but an inch or two will be possible 
northwest of the Illinois River despite the potential for some 
heavier periods of snowfall. The southeast half of the County Warning Area is 
currently prognosticated to remain warm enough for rain...with the far 
southeast remaining in the warm sector most of the day. 


Will continue with healthy chance probability of precipitation on Sunday...although dry 
slot wrapping around the low may cut down the chances later in the 
day. 




Long term...Monday through Wednesday... 


No changes were made to this part of the forecast. As the cyclone 
pushes away from the area on Monday...we will be in a split upper 
flow. Next shortwave expected to be digging in the southern stream 
across The Rockies on Tuesday...swinging east through midweek... 
accompanied by the next chance of rain. Temperatures to remain 
rather chilly on Monday in the wraparound behind the low...before 
warming back to normal. 


Geelhart 


&& 


Aviation... 
issued 1200 am CDT Thursday Mar 18 2010 


Surface hi pressure over Kansas/OK will continue moving southward...with light northwesterly winds becoming westerly 
and southwesterly with time. Residual low level moisture creeping slowly eastward through 
western into cntl Illinois with surface dewpoints now upper 30s-lower 40s. MVFR fog 
already being observed northestern MO and western Illinois...so will included 5sm tempo 
2sm for pia/spi...with less fog further east. Pressure gradient will be 
incrsg Thursday afternoon ahead of a cold fnt which will be entering northwestern Iowa by 00z 
Friday. The result will be westerly winds 12-15 knots 18z Thursday to 00z Friday. Winds will 
then decreases Friday evening as boundary layer decouples...with hi clouds incrsg ahead 
of aforementioned cold fnt. 


04 


&& 


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


$$