685 
fxus63 kilx 070156 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
856 PM CDT Monday Oct 6 2008 


Discussion... 
issued 856 PM CDT Monday Oct 6 2008 


Main concern for tonight is the onset of precipitation in our western 
County Warning Area. Radar returns are most virga in east MO and west Illinois...and that 
trend should continue the rest of the night. The 00z sounding here 
at ilx showed plenty of dry air to overcome in the entire column. The 
best axis of moisture remains in c MO...and the eastward progress 
is expected to be slow. Will keep a dry forecast for the rest of 
the night. A few sprinkles may reach Schuyler Colorado by morning...but 
nothing measurable. 


A mild night is in store as clouds help insulate the area...and 
warm air advection flow aloft strengthens. Temperatures will only drop into the middle to 
upper 50s. 


No significant changes are needed in the grids...so no formal zone 
update will be sent. 


Plenty of shower activity still on tap for tomorrow...with a few 
rumbles of thunder from time to time. Chances for severe weather 
are low based on instability params. 


Shimon 
&& 


Aviation... 
issued 700 PM CDT Monday Oct 6 2008...for the 00z tafs 


Saturation of the middle and lower levels is in progress. The main 
line of showers and isolated storms has persisted to our west in 
west MO and west Iowa...closer to the cold front and inverted trough. The 
latest GFS and European model (ecmwf) have precipitation arriving a bit sooner than the 
NAM. Will try to continue a middle morning arrival for pia and 
spi...late morning for Dec and bmi and early afternoon for cmi. 


May need to bump that forward if the 00z models show similar 
trends. 


There will be marginal instability tomorrow...so I went with thunderstorms in the vicinity 
in all taf sites...until the event gets closer. We can fine tune 
any predominant ts or tempo/S for ts later. Ceilings will likely dip 
into MVFR range...but should reach IFR for very long if at all. 
Visible will dip into the MVFR range during steady rain...and a few 
periods of IFR visible will be possible in the heavier showers/storms. 
I left off IFR conditions for this issuance...but may add them at 
the midnight update. 


Shimon 
&& 


Previous discussion... 
issued 250 PM CDT Monday Oct 6 2008 


Main concerns in the short-term package will be onset and ending 
of precipitation with next system moving through the area tomorrow and 
Wednesday. In the long term...the concern is when the next chance of 
precipitation will be. 


GFS and NAM-WRF seem very similar through next 42hrs...Tuesday 
night...but then show some differences in the speed of the front 
as it pulls away from the area on Wednesday. Appears a blend of 
the models is best. 


In the long- term...big differences on what the overall pattern 
and surface pattern will look like through the period. Here...the 
ensemble mean/blend is probably the best way to go since there is 
very low confidence in what the operational models area 
forecasting at this time. 


Short term...tonight through Thursday night 


One more dry night before precipitation arrives in the area. Frontal system 
is still in the plains but showers and thunderstorms are located 
out ahead of the front in eastern Kansas and parts of western MO. This 
frontal system will approach the area overnight with precipitation expected 
not to start until tomorrow morning. As the system and dynamics 
move into the region precipitation will continue across the area Tuesday 
and into Tuesday night. 12z model runs have precipitation ending little sooner 
than first thought so have pulled probability of precipitation for areas along and northwest of 
I-55 for Wednesday...and have kept chance probability of precipitation in the east. Have system 
pushes east later Wednesday and into Wednesday night high prss will build 
into the region bringing dry weather and normal temperatures for Thursday. 


Clouds and precipitation will keep temperatures below normal (lower 70s) tomorrow 
and Wednesday...except in the southeast where precipitation will take longer to 
reach. Then normal temperatures return for Thursday. Guidance looks 
pretty good today. 


Long term...Friday through Monday 


Long wave pattern flattens out for most of the extended time 
period and becomes somewhat zonal. Then next weekend and long wave 
trough builds in the west and County Warning Area returns to southwesterly flow. 
After being dry in the area for several days...a frontal system 
could enter the region and bring the return of precipitation to Illinois for 
Sunday night and possibly first part of next week. However with 
models differing lots with how this will evolve confidence is low. 
So will just follow ensemble blend for now and have precipitation Sunday 
night and leave out chances of precipitation for Monday until models get 
better handle on things. 


Temperatures will warm back to above normal for the extended period. Guidance 
looks fine with temperatures until the weekend...which is too cool given 
expected pattern. So have raised temperatures for Sat through Monday to 
better match current thinking. 


Auten 


&& 


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


$$