Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 231538

Area Forecast Discussion
National Weather Service Lincoln IL
1038 AM CDT FRI SEP 23 2016

Issued at 1035 AM CDT Fri Sep 23 2016

Updated the forecast to add isolated showers and thunderstorms
into midday north of a Galesburg to Lacon line and also for more
cloud cover into early afternoon over northern CWA. Otherwise rest
of forecast looked on track with another very warm summerlike day
unfolding over central and southeast IL with highs in the mid 80s
to lower 90s (coolest north of Peoria where more cloud cover).

A frontal boundary was near the IA/MO border to just north of
Peoria and Pontiac. A band of convection was diminishing past few
hours north of this boundary and had moved ginto northern Knox and
into parts of Stark counties by mid morning. Expect this
convection to dissipate next 1-2 hours with dry conditions
expected this afternoon across CWA as 591 dm 500 mb upper level
ridge over the Ozarks of southern MO/northern AR builds northward
over the MS river valley, with 500 mb heights of 589 dm over CWA.
This upper level ridge should be strong enough to suppress
redevelopment of convection along frontal boundary sagging
southward into central IL this afternoon. Temps will be cooler
north of boundary especially north of Peoria where more cloud
cover but still should reach mid 80s over Knox, Stark and Marshall
counties. Temps in the upper 80s and lower 90s by mid afternoon
south of I-74.


.SHORT TERM...(Today and tonight)
ISSUED AT 342 AM CDT Fri Sep 23 2016

The surface boundary sitting across northern Illinois this morning
will slowly sag south into the central/southern part of the state.
One would think that showers and storms will develop along this
boundary later this afternoon after max heating of the day. However,
the mid level ridge will be sitting right over the top of the area
and this subsistence should squash any possible convection. So
convection that is ongoing in Iowa will likely remain only in
northern IL today, resulting in a dry forecast for the ILX CWA for
today and into tonight. Any cloud cover will come from the blow-off
from the storms in Iowa. Winds are light now, but should become
southerly again this afternoon, keeping well above normal temps in
the area for another day. Highs should be in the mid 80s in the
north to around 90 in the south, this afternoon. Lows should be in
the middle 60s for tonight.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 342 AM CDT Fri Sep 23 2016

Model performance has been disappointing for the late weekend
system.  The NAM has joined the party at this point, and is in
agreement with the GFS for a new and more progressive approach,
resulting in pops showing up in the forecast for Sunday. Models are
having a major problem with handling this system and pattern shift,
and the ECMWF is the closest to consistent that there is...and
remains slower with the overall upper trof.  All of the models are
splitting the trof/energy and leaving a small closed low over the
SW, resulting in a bit of a breaking up of the dynamics as the
system moves through the Midwest.  With the GFS, the upper low is
deeper, stronger, and further south.  The ECMWF is further north as
a weaker open wave.  The nature and intensity of the sensible
weather at the surface is the question mark...scattered showers vs a
more cohesive line of potential thunder. Rain is the forecast, but
the chances are low at this point, if only for timing and coverage.
This is late Day 3 and into Day 5, Sun night into Tuesday.
Confidence is low presently, but subsequent runs may end up showing
a little more continuity if the trend continues.  Until then, an
unseasonably warm weekend expected.  With the system and front later
in the weekend...the rain chances return, with much cooler temps as
highs on Monday/Tuesday only expected into the 70s.  The cool air is
short-lived however, and the warming trend returns to the latter
half of the week as the mid level ridge shifts into the Midwest yet


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 627 AM CDT Fri Sep 23 2016

VFR conditions will prevail at all sites next 24hrs. Two sites,
PIA and CMI, based on temp/dewpt spread seems to indicate that
some light fog is possible. So have included TEMPO group for each
site for next couple of hours, for 3-4sm. Mid and high clouds is
all expected next 24hrs given the cloud blow-off coming over the
sites from the northwest. Winds will be light and variable.


.ILX Watches/Warnings/Advisories...



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