Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 250500
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1100 PM CST Sat Feb 24 2018

.UPDATE...
Issued at 825 PM CST Sat Feb 24 2018

Heavy rain is exiting area this evening and have eliminated most
of the Flood Watch for our counties. Have retained it in the far
southeast as they have had radar indicated amounts of 1-2 inches
on top of what they had earlier today. Runoff may remain high for
several hours after the rain has stopped. Either way, rivers,
streams, and low spots are already full.

Front to our west is just now entering our forecast area and
should advect across central and southeast Illinois through the
remainder of the evening brining an end to the patchy dense fog.
light rain is lingering about 50 miles behind the front.

Have adjusted weather and pop grids to match up with timing.
Update FFA and ZFPs have been sent.

&&

.SHORT TERM...(This evening through Sunday)
ISSUED AT 207 PM CST Sat Feb 24 2018

Main focus for this part of the forecast will be through tonight.
Will maintain the flood watch across the southeast third of the
forecast area, with the next wave of rain in Missouri now
approaching the Mississippi River. Areas along I-70 received a
couple inches of rain from the earlier round of rain. Aside from
the NAM, most of the models are focusing the heaviest rains closer
to the Ohio River. However, another inch or more south of I-70 is
certainly plausible, as high precipitable water values linger
through much of the evening. Severe-wise, greatest potential for
any stronger storms will likely be focused in that area between
6-9 pm, when the high shear in the area lines up with a small peak
in MUCAPE.

Further northwest, the warm sector will be more focused east of
I-55, limiting any significant thunder chances west of there. Will
keep a mention of isolated thunder early this evening. The overall
storm system will be occluding, with a smaller low moving across
northwest Illinois this evening. This will linger some
precipitation behind the low for a few hours, but most of the
forecast area should be dry by midnight. However, it will take a
little longer for the eastern CWA to dry out.

With the strength of the system, a short period of stronger winds
is expected toward midnight and lingering until near sunrise.
Some of the gusts will reach 35-40 mph, but should stay below
advisory levels. Breezy conditions will linger into Sunday, mainly
over the northern CWA, due to the pressure gradient between the
storm system and high pressure over the lower Mississippi Valley.

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 207 PM CST Sat Feb 24 2018

The highlight of this period will be with the development of
another strong system over the central U.S. mid week. The latest
European model has made a significant shift, and is now similar to
the GFS strength and position that has been seen in its last few
model runs. These models, and the Canadian, are now all in
reasonable agreement, so it will be interesting to see if this
remains the trend.

Initial rain chances Tuesday night and Wednesday will be tied to
moisture advection accompanying a weaker wave from the southwest.
However, the most widespread PoP`s will be as the system occludes
and lifts northeast. Similar to tonight, the guidance is placing
the heaviest rains near the Ohio River, but plenty of time for
adjustments there. Given the timing, with an overnight passage,
severe potential should be limited.

Temperatures will remain on the mild side, especially on Tuesday
and Wednesday, when highs should reach the 60s in many areas.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1100 PM CST Sat Feb 24 2018

Cold front moving east across central Illinois terminals this
evening should move through KCMI prior to the valid time of this
set of TAFs. Winds are gusting around to around 30 kts behind the
front, however winds should drop off fairly rapidly Sunday as the
gradient loosen significantly as high pressure over the southern
plains moves into the mid-mississippi valley. Biggest question is
speed of clearing. NAM suggests a more gradual clearing trend with
a moist boundary layer trapped near the surface through sunrise.
This seems unlikely given the windy conditions and mixing, but the
winds do drop off fairly quickly. Will not delay clearing as long
as the NAM suggests, but given the moist boundary layer any
partial clearing could redevelop low stratus. Will split the
difference at this point between persistance and the slower
solutions.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Flood Watch until midnight CST tonight for ILZ067-068-071>073.

&&

$$

UPDATE...Barker
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Barker



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