Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 190448

Area Forecast Discussion
National Weather Service Lincoln IL
1148 PM CDT Sun Mar 18 2018

Issued at 856 PM CDT Sun Mar 18 2018

A developing area of low pressure is currently centered over
southeast Colorado. This system is forecast to track east,
reaching central Kentucky by Monday evening. This track keeps the
bulk of the associated rainfall south of central Illinois, but
parts of southern Illinois are apt to get pretty wet on Monday.
Breezy easterly winds are expected to develop across the forecast
area Monday to the north of the storm track, and cloud cover will
be considerable even where it doesn`t rain.

Updated forecast through the daytime hours Monday for the latest
trends. Most notable changes were to bump up overnight lows
tonight, increase easterly winds Monday, and delay PoPs across
southern portion of the forecast area until Monday afternoon
(northern portion remains PoP free with this event).


.SHORT TERM...(This evening through Monday)
ISSUED AT 301 PM CDT Sun Mar 18 2018

Sunshine burned off the morning fog by midday, and Central
Illinois had plenty of sunshine for the rest of the day. With the
sun and slightly drier air aloft over the region, temperatures
warmed into the low 50s by this afternoon. Mild weather continuing
into the overnight, with the stratus just to the southwest
potentially creeping into southwestern portions of the state.
Approach of the next system, and its associated precip, from the
southwest is the next main issue for the forecast. Models have
had decent continuity with the last couple of runs, pushing the
upper wave and its surface low into the Ohio River Valley
tomorrow. The northern extent of the wrap around precip is the
main question. With the more southerly track, the northern edge of
the chance pops should land right in the middle of the state.
Thicker cirrus over Central IL moving in from the developing
systems to the SW should inhibit the cooling from dropping as far
as it did last night, even with lighter easterly winds. Tomorrow,
the southern half of the state will see rain chances increasing
through the day with the best chances for measurable precip in the
afternoon hours.

.LONG TERM...(Monday night through Sunday)
ISSUED AT 301 PM CDT Sun Mar 18 2018
Precip associated with that low moving into the Ohio River Valley
will continue through Monday night before moving out of the
region. May see a quick change over to snow on the back side of
the storm in the early hours of Tuesday morning as the storm moves
on. Snow should be confined to a dusting, if that, as the ground
is too warm and will be wet from departing rain. From 09Z to 12Z,
temps approaching zero will potentially bring an additional threat
of glaze/freeze...but that will depend entirely on the speed of
the departure of the storm. A dry period moves in for most of
Tuesday afternoon through Wednesday night as temps remain mild
with highs in the 40s and lows just below freezing. Next pops move
into the forecast for Thursday as models drop a wave into the
northwesterly flow over the region. Both the GFS and the ECMWF are
timing out similarly with the wave/QPF. Simultaneously, a low is
developing over the SW to move up and into the Midwest. Models are
redeveloping the precip over a similar area Thursday night and
into Friday ahead of the system...looking more like a warm frontal
feature potentially too far out ahead of the parent low. A quick
look at 850mb, however... can start to see the SWrly flow ahead of
the midlevel low adding a bit more of an upglide component.
Thursday night, temps dropping again ahead of this point to a
potential for some snowfall mixed in with the precip...but that
southwesterly component/upglide is also accompanied with some
perpendicular warm air advection. FB accumulating up to a half of
an inch of snow Thursday night...but lack any confidence in the
thermal profile this far out. Friday and into the weekend, the low
moves into the region. Unfortunately, the ECMWF and GFS diverge
considerably with a 12-18hr lag in the tracking of the surface
low. As a result, the forecast going into the weekend is dominated
with broad brushed pops.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1147 PM CDT Sun Mar 18 2018

Expect VFR condtions to prevail across the central Illinois
terminals for most, if not all, of the 06Z TAF time. The center
of a storm system will pass south of the area on Monday, causing
winds to shift around to the east later tonight. Gusty winds will
develop by midday Monday. While clouds will increase with the
approach/passage of the system, CIGS are likely to remain at the
VFR level. KSPI & KDEC, closest to the storm track, are most
likely to see any MVFR CIGS and rainfall later Monday as the
system passes nearby.




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