Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 070318

Area Forecast Discussion
National Weather Service Lincoln IL
918 PM CST Wed Dec 6 2017

Issued at 918 PM CST Wed Dec 6 2017

Second of three batches of clouds will continue to move across the
area this evening. The last batch of clouds will get here around
midnight and last 3-4 hours during the overnight period. During
the breaks in clouds, temps should fall. So still expecting
overnight lows to drop into the mid to upper teens in the the low to mid 20s in the south; which is very close to
current dewpoints. Northwest winds will also continue overnight.
Scattered flurries will still be possible across the central part
of the state with this next batch of clouds and forecast handles
this ok. So for now, forecast looks good and not update planned at
this time.


.SHORT TERM...(This evening through Thursday)
ISSUED AT 310 PM CST Wed Dec 6 2017

A weak shortwave will push across central Illinois late this
afternoon and evening, with some sprinkles or flurries possible.
Based on satellite and radar trends, it appears the better
potential for precip will be in our SW counties, south of a line
from Rushville to Effingham. It appears that the band of clouds
associated with the wave will depart to the southeast of our
counties toward late evening. However, the clearing will be
short-lived, as another disturbance arrives in NW Illinois late
tonight. Clouds will overspread central IL from the NW after 3 am,
but no precipitation is expected with that system as it progresses
across Illinois Thursday. Our coldest air of the season will
settle into the area Thursday, with 850mb temps dropping about
8-10C from this afternoon to Thursday morning. That will support
overnight lows in the upper teens north of Lincoln, with low 20s
elsewhere in our forecast area. Highs on Thursday will struggle to
climb through the 20s, under prevailing clouds and sustained
chilly NW winds. A few southern areas may climb into the low 30s,
otherwise 20s will prevail for highs, with wind chills remaining
the teens.

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 310 PM CST Wed Dec 6 2017

The early portion of the extended will be dominated by our a
potential for measurable snowfall in a large portion of our
forecast area, especially the NE half. A clipper system is
projected to move from Manitoba Canada on Friday to far southwest
Michigan by Noon on Saturday. A cold front will be dragged across
Illinois during that time. Moisture will be limited due to the
origin region of the system being northern inland Canada, and
southerly flow will not establish enough ahead of the system to
provide a moisture source. That will limit snowfall potential.
There are model differences with timing and coverage of precip,
but the consensus points toward the period from midnight Friday
night and Noon or early afternoon on Saturday. The GFS is the most
aggressive with the southward extension of snowfall into central
Illinois, with the ECMWF keeping most of the measurable snow in NE
Illinois. The Canadian GEM is in the middle of those two, and
slightly delayed by 4-6 hours. Snowfall totals are a tough call at
this point, but it appears that amounts should remain less than a
half inch, with a few areas N of I-74 climbing to around an inch.
Models typically overestimate snowfall based on QPF, and the GFS
is indicating a couple inches for Champaign, with an inch from
Peoria to Effingham and a half inch from Springfield and
Jacksonville toward Flora. Those numbers appear overdone based on
available moisture, so we have just increased the coverage of
chance PoPs Friday night to cover all the way south to Springfield
and Mattoon, and kept snowfall amounts at a half inch or less.
Once the wave starts to materialize in N Canada tomorrow, we
should get a better picture of snowfall potential.

The Saturday cold front will usher in a reinforcing push of cold
air, primarily affecting Saturday night. Lows will dip close to
Thursday nights lows, ranging from 15 near Galesburg, to 19 near
Lawrenceville. The cold pocket will shift eastward on Sunday,
allowing for a brief warming trend, with highs Sunday in the mid
to upper 30s, and highs Monday in the upper 30s to low 40s.

Another cold blast of air will arrive for Monday night into
Tuesday as a cold front pushes across the area. At this point,
Monday evening looks to be the primary period of rain-snow
potential. That will not be enough time for accumulations of
significance, but any light snow can create slippery travel. The
GFS is the most aggressive with the southward push of cold air
behind that front, with the ECMWF indicating more of a glancing
blow from the cold pool. The Canadian has a similar 500mb trough
placement as the GFS, but not as cold. The end result will still
be a return to much below normal temps for Tuesday and Wednesday.
A weak shortwave is indicated for Tuesday night and Wednesday in
the ECMWF, with measurable snowfall possible. The GFS and Canadian
are weaker and slower with that potential shortwave, so slight
chance PoPs were the only addition for the Tues night-Wed time
frame next week for now.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 534 PM CST Wed Dec 6 2017

All sites are VFR and will remain that way the remainder of the
night. However, a band of rain/snow is moving across parts of
central IL early this evening and looks like it will affect
SPI/DEC/CMI next 1-2hrs. So now have a TEMPO group for an hour or
two for brief period of cigs below 3kft and vis less than 6sm.
Satellite shows a break in clouds behind this back to the
northwest, but another area of clouds will advect into the area
this evening. These clouds will be MVFR and arrive around midnight
at PIA and BMI, and then later for the other three sites. These
clouds will also eventually depart the area but mid clouds will
remain for a few hours, before clear skies return tomorrow
afternoon. Winds will be west and then become northwest overnight
and continue through tomorrow. Wind speeds will be 08-12kts




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