Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 160551

Area Forecast Discussion
National Weather Service Lincoln IL
1251 AM CDT Sun Jul 16 2017

Issued at 939 PM CDT Sat Jul 15 2017

Quiet weather will remain across central and southeast Illinois
overnight with high pressure lingering over the area. However, a
weak front/trof is sinking toward the area from the upper Midwest.
A broken line of thunderstorms extends along a portion of this
boundary from central Lake Michigan into extreme northeast Iowa.
Expect these storms to slowly dissipate overnight with the loss of
diurnal heating. However, if any of them hold together, they may
impact far northern portion of the forecast area after daybreak.
Expect the better chances to hold off until the front actually
starts pushing into the area by late Sunday morning. It will be
warmer tonight than last night as low-level flow turns more
southerly between departing ridge axis and approaching boundary.
Going forecast is in good shape overall, with only minor tweaks
needed at this time.


.SHORT TERM...(This evening through Sunday)
ISSUED AT 215 PM CDT Sat Jul 15 2017

High pressure was centered just north of Bloomington early this
afternoon, and will be shifting into the Ohio Valley this evening.
This will keep quiet weather going for a good part of the night.
Meanwhile, an upper level shortwave was dropping southeast into
western Ontario, riding along the periphery of the upper ridge
that dominates the Rockies. This wave will be sharpening as it
swings across the Great Lakes on Sunday. Latest model guidance
suggests a few showers/storms with it will be possible as soon as
late Sunday morning across the northern CWA, but main threat
remains with scattered afternoon and early evening storms as the
cold front moves southward across the forecast area. While CAPE`s
are progged to be over 3000 J/kg in the afternoon, the better
shear lags behind the front. Despite that, a few strong to severe
storms will be possible, with most of the forecast area in a
marginal risk in the SPC Day2 outlook. Exception is in the far
north, where the front should pass before the storms really start
to get going.

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 215 PM CDT Sat Jul 15 2017

The primary forecast focus remains with the intense heat expected
most of the week. Have continued the trend of raising the high
temperatures from the model blends, solidly in the low-mid 90s
most areas. ECMWF guidance would suggest some 100 degree readings
would be possible in the sandy regions of the Illinois River
valley by Thursday, but have not gone quite that high yet as
central Illinois usually needs more of a drought situation to get
temperatures into the triple digits. Nevertheless, heat advisories
will likely need to be issued early next week, with heat index
values of 100+ as early as Tuesday across the western CWA and
widespread 105+ Wednesday-Thursday. Late in the week, the longer
range model guidance is coming more into agreement with the ridge
starting to amplify across the Plains, which would push a cold
front through our area on Friday.

With the overall upper pattern, favoring the ridge flattening and
building eastward, models are getting into better agreement with
most of the precipitation to our north. The main threat would be
Thursday night into Friday, as the front slips southward. However,
both the GFS and ECMWF bring the front back northeast on Saturday
as the ridge nudges eastward again.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1246 AM CDT Sun Jul 16 2017

Not much of a shift in the forecast...revolves around a cold front
dropping into the region later today. Mainly a southwesterly flow
with relatively light flow ahead of it... switching around to more
northerly behind the boundary and a chance of scattered showers
and thunderstorms about midday. One adjustment to the forecast
right now is a result of some convection along that same boundary
to the north. The outflow and the thunderstorms may be masking the
actual location of the boundary through the near term...and
hesitate to change too much of the midday timing of the boundary.
May shift thinking by 12z run...but for now, remaining




SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...HJS is the U.S. government's official web portal to all federal, state and local government web resources and services.