Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 292021

Area Forecast Discussion
321 PM CDT Mon Sep 29 2014

.SHORT TERM...(Tonight)

Weak high pressure will continue fair weather into this evening as
few to scattered cumulus clouds with 5-7k ft bases away from the IN
dissipate around sunset. Patchy shallow ground fog will develop
again near rivers and streams in southeast IL during overnight.
A cold front over southeast WI and central IA will push south into
central IL overnight, reaching I-70 by sunrise Tue, and weaken over
southeast IL on Tuesday. Stratus clouds behind/north of the front
will move south into central IL during overnight and especially
affect areas from I-74 north while southeast IL likely stays clear
most of tonight. Light winds into this evening will become northeast
at 5 to 10 mph during overnight over central IL. Lows tonight will
mostly be in the mid 50s with lower 50s north of Peoria.


.LONG TERM...(Tuesday through Monday)

A dry front, located just north of the state is forecast to slowly
drop into the area tonight through tomorrow. NAM-WRF model has been
consistent with forecasting an increase in low clouds across the
northern half of the state tonight and tomorrow. It looks like it
could get to I-74 by morning and could progress further south
tomorrow. How far south it gets will depend on how much of the
southern edge of the cloud deck gets eroded away by the strong sun
during the day tomorrow. So, current thinking is it sill get past
I-74 and could get to I-72 in the eastern part of the CWA. During
the day tomorrow, the sunshine should dissipate a lot of the clouds,
like what is occurring in parts of SD/MN/and IA today. Then mostly
clear and dry conditions are expected tomorrow night through Wed.

A weather system in the western US will the lift northeast into the
northern plains and will have a trailing cold front that will extend
down into the southern plains. Showers and thunderstorms are
expected to develop along and ahead of this front Wed well west of
the CWA. However, these storms will advect eastward into the state
beginning Wed night. A second low pressure area will develop along
the front and will move northeast into the Midwest and bring the
cold front through the area Thur and Thur night. Additional
thunderstorms will develop along the front Thursday and move across
the area during the day and through Thur night. Conditions do not
look right for any of the storms to produce severe weather, but this
could change in the next couple of days. However, lightning and
brief heavy rainfall will be likely with any storms that move
through the area late Wed night and Thursday. Once the front and pcpn
pass, there could be some lingering showers behind the front, so
will be keeping some chance pops in the east for Friday.

Beyond Friday, conditions will improve as a drier and cooler air
mass pushes into the area for the weekend. There is one small, weak
wave that could bring some light showers to the northeastern parts
of the area, along and north of I-74, but its too far away to have
much confidence, so will just have slight chance pops for Sunday,
which will not be mentioned in the worded forecast.

Temps will remain above normal tomorrow, when the sunshine is able
to break through the clouds, and Wed as well. Then clouds and rain
for Thur will keep temps milder and around normal. Once the front
moves through at the end of the week, temps will become much cooler
and actually be below normal for the beginning of Oct.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)

Few to scattered cumulus clouds of 5-7k ft to occur this afternoon
with broken ceilings mainly west and nw of PIA and SPI. Winds to
remain light around 5 kts or less into this evening compliments of
weak high pressure of 1018 mb over IL/MO. A cold front over
southeast WI and northwest IA will push south into central IL
during overnight, and into southern IL during Tue. Broken to
overcast stratus clouds behind the front to move to I-74 from
08-10Z and near SPI and DEC around 12Z. Have ceilings from
700-1500 feet and lowest at PIA and BMI with MVFR vsbys 4-5 miles
possible later tonight into Tue morning. Ceilings to lift to MVFR
after 15Z Tue. Models have trended further southward with stratus
clouds but vary on the cloud bases with NAM model being the lowest
below 1k ft. Winds to switch NE behind the front during overnight
around 5-9 kts.




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