Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 151952

Area Forecast Discussion
National Weather Service Lincoln IL
252 PM CDT Sun Sep 15 2019

Issued at 251 PM CDT Sun Sep 15 2019

After morning rain dissipated, partly to mostly sunny skies and
warmer air prevailed over central and southeast Illinois, this
afternoon. Fog is possible across the area tonight, as winds
become light and low level moisture lingers. Unseasonably warm
temperatures and dry weather will dominate the region, for the
first half of the week.


.SHORT TERM...(This evening through Monday)
ISSUED AT 251 PM CDT Sun Sep 15 2019

A weak surface front will track across the area tonight. Upper
level support is negligible and with the loss of diurnal
instability, expect a dry frontal passage. High pressure building
in from the west later tonight, will allow winds to go light/calm.
With lingering low-level moisture, added areas of fog where the
more substantial rains fell this morning, mainly north of a
Rushville to Danville line. Will need to monitor for potential
dense fog development late tonight through mid-morning across the
north, which latest high-res guidance is suggesting.

Fog and/or low clouds may be prevalent across the north half of
the CWA through mid Monday morning, as forecast soundings show
shallow moisture trapped under subsidence inversion. This should
erode by late morning. Mostly sunny skies and light northeast
winds will dominate the day, with the surface ridge axis off Great
Lakes high shifting overhead. We will see a return to summer
warmth with highs in the mid to upper 80s and mid 60s dewpoints.


.LONG TERM...(Monday night through Sunday)
ISSUED AT 251 PM CDT Sun Sep 15 2019

A deepening west coast longwave trough will allow upper level
ridging to strengthen from the lower Mississippi Valley, northeast
into the Great Lakes for the first half of the week.  With
588-590 DM 500 MB heights through the period and 850 MB temps at
+16-20C, July- like warmth will prevail. 85-90 degree highs are
forecast, and with normal highs dropping into the upper 70s this
week these numbers will be around 10 degrees above normal. However
with east to southeast surface flow off high pressure to the
northeast, dewpoint will stay tolerable in the 60s, keeping peak
heat indices within a few degrees of max temps.

Wednesday night into early Thursday, a shortwave disturbance will
temporarily flatten the ridge, with thunderstorms likely well to
our northwest. We have a low thunderstorm chance primarily
northwest of the IL River as this disturbance tracks east
Thursday. Beyond this system dry weather looks to dominate
through the end of the week, along with more unseasonably warm

For next weekend, medium range guidance is in good agreement that
the western trough lifts northeast through the Plains and into
the Great Lakes. This would bring a more difluent southwest flow
and deeper moisture east into the region. With significant timing
differences on better periods of upper level forcing, low chance
pops from NBM look reasonable at this range.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1204 PM CDT Sun Sep 15 2019

Convective system has decayed across the area by midday, leaving
mid to high level clouds and southeast winds in its wake.
Southwest wind around 10-12 kts will develop this afternoon as
pressure gradient tightens ahead of an approaching surface trough.
Clouds will continue to thin and dissipate through afternoon, with
mostly clear skies expected through much of the overnight. The
surface trough will pass through the region overnight. Light
northeast winds will be prevalent behind the boundary. Guidance
has been hinting at MVFR clouds and slightly reduced visibility
behind the boundary affecting the I-74 sites towards sunrise.
Will monitor this for next fcst issuance.




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