Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 141655

Area Forecast Discussion
National Weather Service Lincoln IL
1055 AM CST Sat Jan 14 2017

Issued at 1055 AM CST Sat Jan 14 2017

Updated the forecast this morning to add McLean, Tazewell and
Fulton counties into the freezing rain advisory, which goes
through Sunday night. The band of freezing rain reached as far
north as a Canton to East Peoria to Lexington line, with patchy
freezing drizzle north of there. Temperatures rise just above
freezing (33-35F) in southeast IL from I-70 south where light
freezing rain turned to light rain. Meanwhile subfreezing
temperatures of 28-32F north of I-70 and as cold as 25F at
Galesburg. Radar mosaic loop showing light freezing rain already
starting to diminish from the west as a weak short wave was
shifting southeast of the IL river at late morning. Latest high
resolution models continue to show light precipitation diminishing
from nw to se during late morning and afternoon as short wave
departs central IL. Just light patches of qpf mainly south of I-72
from mid afternoon into this evening. Temperaturess should only
climb a few more degrees reading lower 30s north of I-72 and
35-37F from I-70 south.


.SHORT TERM...(Today and tonight)
ISSUED AT 302 AM CST Sat Jan 14 2017

A short-wave trough evident on 08z/2am water vapor imagery over
Kansas will track eastward...spreading freezing rain across much of
central and southeast Illinois this morning.  Latest radar imagery
already shows precip developing/pushing into west-central Illinois
around Quincy.  Based on radar timing tools and 07z HRRR, the
freezing rain will reach the I-55 corridor from the Lincoln area
southward by around 10z/4am...then will reach east-central Illinois
by 12z/6am.  Given current trends, it appears the northern KILX CWA
will largely be missed by this initial wave of wintry precipitation.
As a result, have only carried low chance PoPs for freezing rain
this morning from the Peoria area northward.  Further south, will go
with categorical PoPs along/south of a
Danville line...where a Freezing Rain Advisory will remain in effect
through the entire day.  The precip will tend to track eastward into
Indiana and come to an end across central Illinois by early
afternoon, so the Advisory may be cancelled early.  Total ice
accumulations will generally be around one tenth of an inch, with
the greatest amounts focused between the I-72 and I-70 corridors.
This amount of ice will be enough to create hazardous driving
conditions, particularly on secondary roads and overpasses.  Further
south, surface temperatures will warm sufficiently to change the
precip to light rain by afternoon south of I-70, mitigating ice
accumulations there.

As has been seen for the past couple of model runs, a distinct lull
in the precip will be observed this afternoon into tonight after the
first wave passes through the area.  Have gone with mostly dry
conditions accordingly, with low chance PoPs gradually returning
from the southwest after midnight.  Based on model consensus...kept
freezing rain chances limited to locations along/southwest of a Robinson line after midnight.

.LONG TERM...(Sunday through Friday)
ISSUED AT 302 AM CST Sat Jan 14 2017

The second round of wintry precipitation will arrive across the area
on Sunday, although models continue to delay onset and downplay QPF
as it tries to push into prevailing high pressure centered over the
southern Great Lakes.  In fact, areas along/north of I-74 will
likely stay dry until afternoon.  Thanks to cold/dry northeasterly
flow around the high, the warm layer aloft will cool by 1-3
degrees...resulting in only partial melting of ice crystals. This
will support a mix of freezing rain and sleet...with perhaps even
some light snow at times across the central and northern CWA.
Meanwhile, surface temps climbing into the middle to upper 30s will
lead to a transition to all rain along/south of I-70 by afternoon.
Mixed precipitation will continue across the remainder of the area
into Sunday night before surface temps slowly climb and the freezing
precip changes to all rain by Monday morning.  The Winter Storm
Watch for areas along/north of a Canton to Bloomington line Sunday
afternoon and night will remain in effect: however, with only light
icing expected and precip mixing with and changing to rain
late...this will likely be dropped in favor of a Winter Weather
Advisory by later shifts.  Overall ice accumulations from the second
wave will amount to less than one tenth of an inch.

Main upper system currently over Baja California will approach from
the southwest on Monday...with its associated surface low tracking
from Oklahoma Monday morning to Lake Michigan by Tuesday morning. As
the low approaches, rain will become widespread across central
Illinois on Monday.  Then as the area punches into the warm sector,
GFS MUCAPE values of 200-400J/kg support the potential for isolated
thunder Monday night as the low lifts into the Great Lakes.  Any
lingering showers will come to an end Tuesday morning, followed by
warm and dry weather Wednesday and Thursday.  The next chance for
precip will hold off until the end of the week: however, model
agreement remains will only mention low chance PoPs for
showers on Friday at this time.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 559 AM CST Sat Jan 14 2017

Cigs and vsbys will remain IFR or LIFR for the first 4 to 6 hours
of this TAF period as freezing rain and/or freezing drizzle
advance eastward across central Illinois. PIA has lingered at
MVFR at TAF issuance time, but could dip to IFR for an hour or
two through 15z. Ceilings will improve to MVFR this afternoon as
precipitation comes to an end or shifts south of the terminal
sites. Cigs should improve to VFR tonight as north winds bring a
drying trend to the cloud bearing layer. Surface temperatures are
expected rise close to or just above the freezing mark this afternoon,
so what icing does occur this morning should begin to melt this
afternoon. Winds will not be much of a factor during this TAF
period, with the east to northeast winds at 4-8 kts this morning
becoming north to northwest by afternoon with speeds of less than
10 kts.


Freezing Rain Advisory until noon CST Sunday for ILZ040>057-

Winter Storm Watch from late tonight through late Sunday night
for ILZ027>031.

Freezing Rain Advisory until 6 AM CST Monday for ILZ036>038.



LONG TERM...Barnes
AVIATION...Shimon is the U.S. government's official web portal to all federal, state and local government web resources and services.