Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 180144

Area Forecast Discussion
National Weather Service Lincoln IL
844 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 00Z TAFS through 00Z Monday evening)
Issued at 605 PM CDT Sun Sep 17 2017

The main forecast concern will be with the potential for MVFR or
lower cigs and vsbys in the 09z-13z time frame, otherwise, we
expect VFR conditions for the remainder of this forecast period.
A weak cool front has slipped south of the TAF sites early this
evening and that feature was the focus for scattered showers and
thunderstorms. Other than some isolated showers, the bulk of the
heavier activity has slipped south of the TAF sites with the
front. Not much of a push of drier air into the area behind the
front, so any clearing that may take place late tonight may
be enough to bring some patchy fog and low clouds into parts of
our area towards dawn Monday. What low clouds and fog we do see
in the morning should give way to VFR cigs of the mid and high
level variety on Monday as the next weather system approaches
the area from the west late in the day. Light northeast to east
winds tonight will become southeasterly on Monday with speeds of
10 kts or less.




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