Area Forecast Discussion
Issued by NWS Central Illinois

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058
FXUS63 KILX 140306
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
906 PM CST Fri Jan 13 2017

.UPDATE...
Issued at 855 PM CST Fri Jan 13 2017

No major changes to going forecast and headlines this evening.
First wave of rain and freezing rain has shifted into extreme
southeast Illinois and should move out of our area over the
next hour. Our attention now turns to another band of freezing
rain that is forecast to track out of Missouri late tonight
and into our area after 08z and continue on and off through
the morning before the precip starts to get shunted to our
southeast in the afternoon. RAP/HRRR/and latest NAM showing this
wave for the early morning hours tracking further north than our
initial wave that focused in areas south of I-72 today. Model
consensus suggests a tenth to locally two tenths of an inch
may occur with this second wave, especially along a Taylorville
to Mattoon to Paris line with lighter amounts, generally less
than a tenth of an inch up to the I-74 corridor with the trend
for trace amounts further north. As mentioned above, the precip
should push out of most of the area, except the far southeast
by afternoon. By that time, it appears our surface temperatures
may be close to our just above the freezing mark which should
melt any additional ice the falls Saturday morning.

Have bumped the POPs up further north to reflect the northward
trend in models with the next wave of freezing rain. We should
have the updated ZFP out by 915 pm.

&&

.SHORT TERM...(This evening through Saturday)
ISSUED AT 258 PM CST Fri Jan 13 2017

Will change the winter storm watch over central part of CWA to a
freezing rain advisory tonight through Sunday morning. So a freezing
rain advisory will be in effect from Schuyler, Mason, Logan, DeWitt,
Champaign and Vermilion counties southward. Winter Storm watch
continues north of there from midnight Sat night thru Sunday night.

A frontal boundary over southeast TN into southern AR and central
Texas was causing overrunning of light freezing rain and sleet into
areas south of Taylorville to Paris line at mid afternoon where
temperatures were mostly 30-32F with Lawrenceville up to 33F. Colder
temperatures in the mid to upper 20s north of Lincoln. Mostly cloudy
to overcast skies over CWA at mid afternoon. Strong 1045 mb arctic
high pressure over central WI and sprawled across the Great Lakes
region was giving a ne flow of cold air into central IL.

Still some forecast model differences with handing qpf fields
through Saturday even with the short range/high resolution models.
The HRRR models has area of light freezing rain and sleet
diminishing over southeast IL by 03Z/9 pm this evening with just a
few smaller patches of light qpf thereafter as far north as Canton
and Bloomington. The RAP13 model also diminishing mixed pcpn over
southeast IL but not until late evening and then develops expanding
area of light qpf after 2 am from Peoria south. The NAM12 model
diminishing light qpf in southeast IL early this evening, and then
spreads/develops light qpf ne toward I-72 during overnight. With
stronger arctic high pressure nearby over WI, will keep northern CWA
drier tonight into Saturday. Will bring chance of light freezing
rain northward into central CWA during the evening with likely pops
in southeast IL. Models then diminish qpf from nw to se during
Saturday especially north of I-70. Light rain will also becoming
more likely in southeast IL by Saturday Saturday afternoon. Ice
accumulations up to a tenth inch from I-72 south tonight into Sat
morning (locally one to two tenths along I-70) with less amounts se
of I-70 due to milder air and also north of I-72 in drier air. Lows
tonight range from lower 20s nw of IL river, to 30-32F in southeast
IL from I-70 south. Highs Saturday range from lower 30s north of I-
72 to 35-37F in southeast IL. ENE winds will stay fairly light
during this weekend.

.LONG TERM...(Saturday night through Friday)
ISSUED AT 258 PM CST Fri Jan 13 2017

A lull in the freezing rain threat will exist at the beginning of
the forecast period across most of the forecast area, with the
better chances just to our west/south across Missouri and far
southern Illinois. Our attention to start next week turns to the
vigorous upper low that is currently spinning off the southern
California coast. This feature will eject northeast toward the area
Sunday into Monday, accompanied by a surface low and more widespread
precipitation than is in our vicinity right now.

The initial surge of precipitation associated with the southwest
system will arrive late Saturday night into Sunday. Initially, our
local surface temperatures will be cold enough for freezing rain. As
the precipitation returns, moisture depth is too shallow/warm for ice
crystals, so freezing rain is expected at the onset. Then, as deeper
moisture and cloud ice returns, a period of sleet/snow is possible.
However, the sleet and/or snow should not last long as a deeper
elevated warm layer develops. This signals a south to north return
to freezing rain on Sunday into Sunday night. However, as surface
winds turn more southerly later Sunday into Monday, temperatures
will warm enough for rain. This system does not exit the area until
later Tuesday, and rain chances will linger until the system departs.

Hazardous travel condtions are expected from time to time into
Monday with the periods of freezing rain anticipated. However, a
significant ice storm does not look likely due to the relatively low
rainfall amounts that occur with sub-freezing temperatures, as well
as the diurnal melting that could occur in many areas on trees and
power lines.

Once the current system finally leaves the area early next week, the
rest of the week should be fairly quiet weather wise with warmer than
normal temperatures.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 535 PM CST Fri Jan 13 2017

Initial wave of freezing rain was located just south of SPI and
DEC early this evening with a temporary lull in the precip further
west and south. We expect light freezing rain to develop over
central Mo after 04z and spread into parts of central IL after 08z
and be with us for about a 6 to 8 hour period before all the
precip gets shunted to the south by afternoon. We should also see
a gradual deterioration in the cigs later this evening from south
to north, although some MVFR cigs pushed into PIA and BMI earlier
today from the northeast. Further north towards I-74 there is
quite a bit of dry air in the low levels so any precip to our
south should stay to the south thru the evening with the threat
for precip shifting closer to our northern TAF sites Saturday
morning. Most areas should see IFR cigs with some lower vsbys in
fog as well as we head thru the morning on Saturday with some
improvement in cigs/vsbys during the afternoon, but still looking
like mainly MVFR conditions at that time. Winds will be northeast
to east at 8 to 15 kts tonight and then back more into a north to
northwest direction on Saturday with speeds of 5 to 10 kts.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Freezing Rain Advisory until noon CST Sunday for ILZ040>057-
061>063-066>068-071>073.

Winter Storm Watch from late Saturday night through late Sunday
night for ILZ027>031-036>038.

&&

$$

UPDATE...Smith
SHORT TERM...07
LONG TERM...Bak
AVIATION...Smith



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