Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 121658
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1058 AM CST Thu Jan 12 2017

.UPDATE...
Issued at 1055 AM CST Thu Jan 12 2017

Updated the forecast at 9 am to allow the freezing rain advisory
to expire along and northwest of I-55. A 2nd update recently done
to address diminishing precipitation trends, temperatures and
also adjusted cloud cover today as low clouds holding on longer
over central IL.

Late morning surface map shows a strong cold front pushing
toward far southeast IL, approaching Lawrenceville, Mount Carmel
airport and Fairfield. This front was marked by a narrow band of
showers and isolated thunderstorms. Temperatures were in the mid
60s ahead of cold front over Lawrence county and fall into the
35-45F range just behind the front. The freezing line (temp of
32F) extended near a Taylorville to Rantoul line while temps were
in the low to mid 20s over the IL river valley. Most of the
measureable precipitation has ended over central IL at late
morning with patchy freezing drizzle and drizzle remaining with
the stratus clouds below 1k ft.

The cold front will sweep through Lawrence county during next hour
with temperatures fallling into the mid 30s to lower 40s during
the afternoon in southeast IL. Little temperature rise is expected
over central IL with the freezing line staying near or getting a
bit south of I-72 this afternoon. 1030 mb arctic high pressure
over Saskatchewan and ridging into the central plains, will build
into the upper Midwest into this evening and help to break up the
low clouds during the afternoon especially north of I-70. Have
chances of showers and isolated thunderstorms over southeast IL
into midday, then drier conditions expected rest of the afternoon
and tonight and precipitation shifts south of CWA with the front.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 432 AM CST Thu Jan 12 2017

Rain and isolated thunderstorms are quickly moving through the CWA
this morning. Unfortunately, areas north of I-72 are seeing surface
temperatures falling to below freezing. So any precipitation will be
freezing rain this morning. Sleet is also occurring under the heavier
showers and thunderstorms. The precipitation should end across most
of the area later this morning, but the impact of the slick roadways
will likely continue until the air temperature rise to above
freezing. However, this will not occur everywhere and some areas
will remain below freezing through the afternoon. Some clearing in
the clouds is expected early this afternoon, but diurnal CU/SC is
expected to develop along the edge of the clearing since the CWA
remains in a somewhat cyclonic flow. The frontal system responsible
for this mornings precip will move south of the CWA this afternoon
and bring an end to all precip early this afternoon. Dry weather is
expected tonight but some clouds will linger in the area. Daytime
highs will likely be now/this morning and then temps will fall
during the day as colder air advects quickly into the area. Lows
tonight are expected to range from 14 in the northwest to 27 in the
southeast.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 432 AM CST Thu Jan 12 2017

Difficult forecast is taking shape for the weekend for Central
Illinois.  Issues remain with timing as the trof deepens over the
desert SW and some weak ridging and easterly flow erodes the
northern edge of the precip associated with the stalled boundary.
However, freezing rain is expected to dominate the system through
the weekend.  A Winter Storm Watch has been issued to cover the
threat of higher potential accumulations...but freezing rain will be
expected over all of Central Illinois at some point through the
weekend.

The frontal boundary moving through the Midwest now will stall to
the southeast. Models have varied the location of the boundary that
becomes the focus for precipitation in several waves through the
weekend.  Recent runs have moved much of the precip further south
and dries out the forecast tonight...only to bring a wave through on
Friday, spreading freezing rain northward through the day, with the
better chances later in the afternoon and into the overnight hours.
Freezing rain will be the predominant weather across the southern
half of Illinois for Saturday morning until warmer temperatures
spread northward, slowly transitioning the precip over to all rain.
Temperatures drop again quickly after sunset and freezing rain takes
over...into Sunday morning.  The main push of precip has previously
been in place for Sunday as the main low to the SW ejected across
the southern Plains and into the region.  However, every run slows
the approach of the low, further complicating the end of the weekend
in the Midwest.  Sundays precip slowly changing over to rain as the
warm air advects into the region...but now the northern extent of
the precip is becoming an issue. With the freezing rain threat
concentrating through much of the weekend over the southern half of
the state...the slow accumulations of ice starting to reach close to
warning criteria, albeit showery and periodic.  Have issued a watch
for the higher accumulations...but details will continue to shape
the forecasts for the next 24-48 hrs ahead of the system.

The forecast through the first of next week is now dominated with
widespread likely pops in the form of rain with above normal
temperatures spreading into the state and remaining the rule through
mid week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 556 AM CST Thu Jan 12 2017

Rain and freezing rain already moving across the TAF sites this
morning. Based on HiRes models...the precip should end later this
morning. All sites will have IFR and LIFR conditions with cigs
below 1kft, as the precip moves through. Even after the precip
ends later this morning, the IFR conditions will likely continue
into the afternoon. Even if breaks do occur in the clouds, diurnal
CU/SC will develop and fill in any holes. Plus, satellite shows
clouds extending back across IA and parts of NE. Conditions should
begin to improve late this afternoon with lower clouds pushing off
to the east as a large high pressure area moves into the region.
Could be some cirrus advecting into the area and this will last
into the evening and tomorrow night. Low pressure area is making
for variable winds at CMI while other sites will see north-
northwest winds this morning, becoming northwest for the rest of
the TAF period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Friday afternoon through Sunday morning
for ILZ040>057-061>063-066>068-071>073.

&&

$$

UPDATE...07
SHORT TERM...Auten
LONG TERM...HJS
AVIATION...Auten



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