Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 161616
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1016 AM CST Mon Jan 16 2017

.UPDATE...
Issued at 1015 AM CST Mon Jan 16 2017

Updated the forecast to cancel the winter weather advisory by 9 am
for northern CWA, as temperatures have slowly risen just above
freezing. Lacon still had a temperature of 32F, but was getting no
reports of ice in our northern counties. Temperatures currently
range from low to mid 30s from I-72 north to the upper 30s and
lower 40s south of I-72.

Also expanded the dense fog advisory to include Vermilion, Edgar
and Clark counties until noon. Widespread dense fog covers much of
CWA this morning with vsbys 1/4-1/2 mile. HRRR model shows vsbys
improving from sw to ne through the afternoon, and may need to
extend dense fog advisory into part of the afternoon.

Late morning surface anaylsis shows 1010 mb low pressure over
central KS with a warm front over sw MO and ne AR to near the
KY/TN border. Widespread light rain showers were along and nw of
I-55 with another band of rain showers lifting ne into sw IL and
eastern MO. Latest forecast models lift surface low pressure ne
from central KS into nw MO by sunset and into nw IL by
06Z/midnight tonight. This spreads band of showers ne across rest
of CWA during early/mid afternoon, with isolated thunderstorms
possible sw of Springfield to Effingham line late this afternoon
and isolated thunderstorms possible across area this evening.
Highs late this afternoon range from lower 40s north of Peoria, to
the mid 50s along highway 50 in southeast IL.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 329 AM CST Mon Jan 16 2017

08z/2am obs continue to show temperatures hovering near 32F along
and north of a Rushville to Bloomington line.  With radar echoes
moving across the Illinois River Valley, cannot rule out some patchy
freezing drizzle for the next couple of hours before readings climb
above freezing by dawn.  Will therefore continue the Winter Weather
Advisory for the far N/NW KILX CWA, but this will likely be
cancelled shortly after sunrise.

The main short-term forecast challenge will be the development of
widespread fog today.  Thus far the lowest visibilities have been
centered from the St. Louis area northward to around Quincy.  HRRR
has been consistently showing dense fog spreading N/NE into central
Illinois: however, this has simply not materialized yet.  With warm
front well to the south and E/SE boundary layer flow expected to
persist all day, think visibilities will eventually decrease
across all of central and southeast Illinois this morning.  Based
on latest trends and HRRR signal, have expanded the Dense Fog
Advisory northward to include all locations along/south of a
Canton...to Decatur...to Robinson line.  If the HRRR verifies,
the Advisory may need to be expanded to include nearly the entire
CWA later this morning.  The only potential fly-in-the-ointment
will be the development of scattered rain showers that could mix
the atmosphere sufficiently to prevent widespread dense fog
northward to the I-74 corridor.

Showers will eventually become widespread this afternoon/evening as
low pressure and its accompanying warm front lift northward into the
area.  Forecast soundings indicate MUCAPE values increasing into the
200-400J/kg range this evening as the CWA punches into the warm
sector.  Will therefore carry categorical PoPs for showers and also
mention isolated thunderstorms.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 329 AM CST Mon Jan 16 2017

As low pressure tracks into the Great Lakes, it will pull a weak
cold front through central Illinois late tonight.  Most of the
precip associated with this system will exit Illinois by early
Tuesday morning: however, with a trailing upper-level wave not
expected to pass until evening, will continue slight chance PoPs for
showers across the far north through Tuesday afternoon.  High
pressure will build into the region on Wednesday, bringing sunshine
and mild temperatures in the 40s.

Once the high shifts off to the east, deep-layer southwesterly flow
will establish itself across the Mississippi/Ohio River Valleys,
leading to warm and unsettled weather for the end of the week.  00z
Jan 16 models have come into much better agreement concerning two
waves expected to impact the region...the first coming Thursday
night into Friday and the second arriving on Sunday.  Temperatures
will be warm enough to support all rain...as highs climb into the
50s through the period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 610 AM CST Mon Jan 16 2017

Cigs will remain LIFR for most of the 12z TAF period as the air
mass remains unchanged until tomorrow. Visibility will likely dip
to LIFR and possibly VLIFR at all TAF sights as the morning
progresses, based on HRRR and RAP output and upstream
observations. Both of those high res models show a band of low
visibility progressing northward into the I-74 corridor later this
morning and eventually lifting to LIFR or possibly IFR levels for
a few hours. Rainfall coverage should increase today, and become
widespread this afternoon and evening. Vis is expected to drop
again this evening as rainfall remains widespread through
midnight. Rain will begin to diminish from SW to NE after
midnight.

Winds will start out easterly this morning at 4-8kt, then become
southeast later this morning. Wind speeds are expected to increase
to 10-16kt later today or this evening as low pressure approaches
closer to western Illinois and the pressure gradient tightens.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon CST today for ILZ027>031-036>038-
040>057-061>063-066>068-071>073.

&&

$$

UPDATE...07
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Shimon


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