Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 162000
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
300 PM CDT Sat Sep 16 2017

.SHORT TERM...(This evening through Sunday)
ISSUED AT 300 PM CDT Sat Sep 16 2017

A gradual increase in deep moisture will accompany an approaching
cool front - which extended from northeast MN through western IA
to the OK panhandle at 2 pm. There is quite a bit of dry air in
the mid levels of the atmosphere, however, that will need to be
overcome first before any of the precipitation makes it to the
ground. Forecast soundings and most of the short range models
indicate this won`t happen in west central IL until well after
midnight, and east of the IL River until daybreak or shortly
afterwards.

The front is expected to reach the IL River valley early Sunday
afternoon, and east of I-55 by dusk. This will result in
increasing t-storm chances in eastern IL during the afternoon, and
in parts of southeast IL toward evening. The clouds and periods of
rain will keep temperatures on Sunday a good 10 degrees cooler
than today`s highs, but still a bit warmer than normal for mid-
September.

&&

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 300 PM CDT Sat Sep 16 2017

Our warmer than normal pattern is expected to continue into next
weekend, with unsettled weather into mid-week.

The 12z model runs are all pushing the cool front a bit farther
south late Sunday - toward the I-70 corridor - than their
previous runs. This looks reasonable based on the expected upper
level ridge axis just north of the Ohio River valley. The impact
on our weather would be for showers/t-storms to remain in eastern
IL through Sunday evening and primarily in southeast IL Sun night.

The models are also fairly consistent in showing a shortwave
trough ejecting from the upper trough axis near the Rockies toward
the Midwest Monday. This should allow the front to lift back north
as a warm front, and give the forecast area the best chances for
thunderstorms with moderate/heavy rain Monday. Moderate
instability and increasing deep layer shear Monday afternoon-
evening could result in some strong storms north of a Springfield-
Danville line, although the best ingredients appear to be off to
the west (as seen in the SPC Day 3 outlook).

With Hurricane Jose making its way up the eastern seaboard, our
weather pattern into mid-week will be rather stagnant with plenty
of warm and humid air, and summer-like, diurnally driven showers
and t-storms Tuesday and Wednesday.

Mid and upper level ridging is expected to strengthen from the
eastern Great Lakes to the lower Mississippi Valley by Thursday,
in response to a digging upper level trough in the intermountain
region. This will keep any synoptic low level boundaries well to
our west. The resulting weather will be more of the same with
unseasonably warm and humid temperatures and perhaps and isolated
t-storm into early next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1256 PM CDT Sat Sep 16 2017

VFR conditions can be expected in eastern IL and most of central
IL during much of this TAF period.

This afternoon, mixing in the lower atmosphere will result in
periods of wind gusts over 15kts in parts of central IL, mainly
from PIA-BMI-CMI. The diurnally driven cumulus field will
primarily be scattered around 4500-6000 feet, but a few clusters
of broken cloud cover are possibly - primarily early this
afternoon.

The 12z ILX sounding indicated some increasing low level
moisture, but a very dry layer aloft. This will play a role later
tonight in delaying the onset of scattered showers in central IL
until just after daybreak. Thus, held off on MVFR visibility and
VCSH until 14z or later along and west of the I-55 corridor.
Scattered showers and a few t-storms should hold off in the rest
of central and eastern IL until 18Z or later Sunday.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Miller
LONG TERM...Miller
AVIATION...Miller



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