Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 220347

Area Forecast Discussion
National Weather Service Lincoln IL
1047 PM CDT FRI OCT 21 2016

Issued at 904 PM CDT Fri Oct 21 2016

The elongated surface high pressure extending from Lake Superior
to eastern Texas will drift slowly eastward tonight and tomorrow.
A band of mid-clouds is streaming into central Illinois on NW
upper level winds, and the clouds will work to diminish potential
for widespread frost. The overall coverage of clouds is expected
to decrease later tonight, and patchy frost will be possible.
Better chances for frost should remain east of I-55 where the
lower dewpoints and coldest mid-level air will reside. Traditional
cold spots in other portions of central IL could also see low
temps drop far enough for patchy frost.

Winds will be light and variable as the surface ridge axis resides
from N to S through Illinois. Southwest winds will develop
Saturday morning as the ridge axis shifts east of the area.

Minor changes were done to the sky and weather grids tonight. The
latest forecast info is already available.


.SHORT TERM...(This evening through Saturday)
ISSUED AT 215 PM CDT Fri Oct 21 2016

Sprawling ridge of high pressure currently extending from Ontario
to the Southern Plains will shift eastward across the area tonight,
providing mostly clear skies and light winds.  The ridge axis will
be centered over the eastern KILX CWA by 12z Saturday, with some
light return flow developing further west across the Illinois River
Valley.  As a result, am expecting the coldest overnight lows across
the E/NE counties near the Indiana border.  Most model guidance
supports lows in the middle to upper 30s...and with dewpoints
currently ranging from the middle 30s west to the lower 40s east,
think these numbers look reasonable.  Patchy frost will likely
develop overnight, especially east of the Illinois River where winds
will remain lightest.  Given borderline temps in the middle to upper
30s and some high/thin clouds drifting overhead, do not think frost
will become widespread enough to warrant a Frost Advisory.  Once the
ridge axis shifts further eastward, southerly return flow will bring
warmer air back into the area on Saturday.  With south winds and
full sunshine, afternoon highs will reach the lower to middle 60s.

.LONG TERM...(Saturday night through Friday)
ISSUED AT 215 PM CDT Fri Oct 21 2016

High pressure ridge will be east of the CWA Sat night and will
continue to move east Sunday, allowing southwesterly winds to return
to the area. In addition, a cold front will drop into the state from
the northwest and slowly slide through the CWA Sunday afternoon
through night. This front will come through dry since the
southwesterly flow will not bring any moisture back into the area.
Another high pressure area will drop into the state, but this one
will come from the Canadian area and will be cooler. This high
pressure will keep dry conditions in the CWA for Mon through
Tuesday. Then the next weather system and associated precip will
approach the area from the west. Showers and thunderstorms are
expected late Tue night through Wednesday as the cold front moves
into the area. Showers and thunderstorms will begin as only a
chance, but then increase to likely over most of the area during the
day Wednesday. The flow will become more zonal at this point and
this will allow another weather system to move toward the area for
the latter part of the week. This next system looks on the weak side
and will be moisture limited. So, for now will just have a slight
chance of precip, which will not get mentioned in the worded
forecast, but will show up in the grids.

Temps will become warm, above normal, for Sunday, ahead of the next
weather system. However, with the second high pressure area moving
into the region temps will drop back to more seasonable levels for
next week.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1047 PM CDT Fri Oct 21 2016

High pressure will keep VFR conditions over the next 24 hours. The
only clouds of note appear to be a band of mid-level clouds
that look to affect our area through around 09z. Little to no
cloud cover is projected for tomorrow.

The surface high pressure axis will pass across IL the rest of
tonight, and reach near the Indiana border by 12z/7am. That will
set the stage for wind directions to change from light and
variable overnight to SW tomorrow morning. Wind speeds will
gradually increase in speed from the southwest after sunrise.
Sustained winds could climb to 10-12kt for the afternoon on
Saturday, as the surface pressure gradient tightens in the wake of
the ridge axis. Winds speeds will weaken with sunset tomorrow.


.ILX Watches/Warnings/Advisories...


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