Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 180357

Area Forecast Discussion
National Weather Service Lincoln IL
1057 PM CDT Sun Sep 17 2017

Issued at 835 PM CDT Sun Sep 17 2017

The weak cold front that pushed across our area today has settled
south of the I-70 corridor this evening. We continue to have
scattered showers developing along the frontal boundary early
this evening with short term models suggesting a weak wave of
low pressure will move along the boundary, which is forecast
to stall out in far southeast Illinois tonight. This wave will
keep the rain chances going across southeast IL overnight, while
further northwest, somewhat drier air will work its way southeast
into about the northern half of the forecast area.

The next wave of interest for us was seen on the water vapor loop
extending from Wyoming south northwest Colorado. This feature
will push across the Plains tonight and bring us our next chance
for showers later tomorrow into tomorrow night. Have edged
temperatures down a few degrees across the north based on evening
trends and made some minor adjustments to precip wording in the
southeast along the stalled frontal boundary. The updated forecast
should be out by 9 pm.


.SHORT TERM...(This evening through Monday)
ISSUED AT 241 PM CDT Sun Sep 17 2017
High pressure centered over the Plains this afternoon as an
occluded low moves across southern Canada. A cold front extends
from north of the Great Lakes, through Central IL and back to
Central MO. The cold front has made its way southeast of
Interstate 55. Some scattered showers and thunderstorms are still
developing on radar imagery out ahead of the boundary. Dry air and
limited instability have kept most of the activity contained.
Slightly cooler air behind the boundary will be short lived as the
boundary gets stalled later tonight and wobbles back northward
with warm air moving back northward. However, another wave will
bring a better chance of measurable precip tonight into the weak showers today have slowly been overcoming
the dry air aloft. Temperatures will likely remain cooler in the
NW, north of the boundary.

.LONG TERM...(Monday night through Sunday)
ISSUED AT 241 PM CDT Sun Sep 17 2017

The extended remains much the same, warm and sporadic small pops.
A deep low is digging out a trough over the desert SW, resulting
in a very amplified ridge over the eastern half of the CONUS. Very
warm temperatures will stay in place throughout the week. Guidance
still has 80s...and have tweaked them up in a few places as the
850 temps move into the 16-19C range by mid week. Precip chances
for the most part are shunted off to the NW with the more active
flow ILX is trapped under the ridge with a much weaker
pressure gradient/almost stagnant airmass. Given the multiple
tropical systems in the Atlantic, the strength and duration of the
eastern ridge may be more of a player in the extended than
currently projected. Any small changes may impact the
position/path of the waves ejecting out of the SW. Any shift of
the SWrly flow could result in those weak slight pops coming up.
Confidence for a completely dry forecast is low to moderate. Warm,
however, has considerably more probability.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1052 PM CDT Sun Sep 17 2017

Main forecast concern this period will be with the threat for
MVFR or lower cigs/vsbys in the 10z-13z time frame, especially
from CMI to just east of BMI. Forecast soundings continue to show
the potential for a brief period of low cigs along and east of
I-57 early Monday morning with some westward drift possible just
before sunrise. Otherwise, mainly VFR conditions are expected for
the remainder of the forecast period with shower chances increasing
after 21z at PIA and SPI and after 00z at CMI. Confidence on timing
and especially coverage rather low this far out so will handle with
VCTS or VCSH. Light east to northeast winds tonight will become east
to southeast on Monday but speeds even during the day Monday do not
appear to be much of a factor with most TAF sites seeing 10 kts or




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