000
FXUS63 KILX 211638
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1038 AM CST Sat Dec 21 2013

.DISCUSSION...
ISSUED 1038 AM CST Sat Dec 21 2013

Current forecast is pretty well on track regarding ongoing winter
storm. Rainfall is becoming more widespread across the forecast
area as forcing ramps up due to the arrival of 140+ kt coupled
upper jet. This forcing should linger into this evening. A slow
rise in surface temperatures continues due to diurnal heating,
heavier relatively warm rain, and latent heat release due icing in
west central Illinois. This gradual warming should push the
freezing rain/rain line further north/west with time (it is
currently a little east of the I-55 corridor), with the freezing
line eventually reaching the Illinois River Valley by this
evening.

See no reason to make major changes to the short term forecast at
this point. Will only make a few tweaks to the hourly, mainly
temperature, trends.

Bak
&&

.AVIATION...
ISSUED 600 AM CST Sat Dec 21 2013

LIFR and local VLIFR cloud heights and vis are expected to
continue periodically today as low pressure approaches from the
southwest. Sub-freezing surface temperatures for all of the
terminal sites at 12z will set the stage for freezing rain and
icing conditions for several hours this morning. As the suns
heating takes effect, the freezing rain should transition to just
rain this afternoon from SE to NW. DEC and CMI should be the first
to warm above freezing, with SPI and BMI next and finally Peoria
around 20z or so.

Cloud heights and vis may briefly climb to IFR this afternoon
during any breaks in the precipitation, but LIFR conditions should
prevail for much of the next 24 hours. A dry slot aloft tonight
should push across all but the PIA terminal, helping to shut down
the steady precipitation. Light snow is expected to affect areas
NW of PIA and possibly PIA airport. A dusting to a half inch of
snow may accumulate on top of any ice in PIA, creating additional
travel problems.

Winds will remain northeast today and much of tonight, until low
pressure passes by to the south of the terminals. Late tonight
winds may shift to the west-southwest behind the departing low.

Shimon
&&

.PREV DISCUSSION...
ISSUED 314 AM CST Sat Dec 21 2013

SHORT TERM...Today through Monday

Vigorous upper low evident on 08z/2am water vapor imagery over
west Texas will track northeastward today/tonight, eventually
reaching northern Illinois by early Sunday morning. Several
forecast concerns remain in play with this feature as it tracks
through the region.

Precipitation Type:
NAM/GFS are both in fairly good agreement with their thermal
profiles, with the GFS being just slightly colder at low-levels.
Forecast soundings suggest rain/freezing rain line will generally
be along the I-72 corridor early this morning. This matches quite
well with 08z/2am obs which indicate temps at or below 32F along
and northwest of a Taylorville to Champaign-Urbana line. Temps
will slowly climb as the morning progresses, with freezing rain
changing to rain across all locations east of the I-55 corridor by
9am, then everywhere along/east of the Illinois River by 3pm.
Given relatively short duration of ice, am only expecting some
very light ice accumulations in the Decatur and Champaign areas
early this morning. Further northwest, between one tenth and one
quarter of an inch of ice is expected along/west of I-55 where
Freezing Rain Advisory remains in effect until 6pm. This will
likely be canceled early if expected temp trends pan out.
Greatest ice accretion will be along/west of the Illinois River
where amounts of one quarter to one third of an inch are likely.

Snow:
Deformation zone snow has shifted further west with the 00z
21 Dec model run, with the heaviest snow focused over eastern
Iowa/northwestern Illinois late tonight. This seems reasonable
given track of 500mb vort max from near Kansas City to Rockford
overnight. As colder air arrives with this feature, freezing rain
will change to snow or a snow/sleet mixture across the Illinois
River Valley after midnight. Minor snow accumulations of around
one half inch will be possible in Peoria, with higher amounts of 2
to 3 inches further northwest around Galesburg and even greater
totals in excess of 6 inches outside the KILX CWA closer to the
Mississippi River.

Heavy Rain:
With impressive amounts of moisture flowing northward ahead of the
approaching system, heavy rain is likely across east-central and
southeast Illinois today/tonight. Precipitable water values will
rise to around 1.50 across the E/SE CWA this afternoon, supporting
the threat for locally heavy rain. Models are in good agreement
with this, suggesting 2 to 4 inches of rain along and southeast of
a Taylorville to Champaign-Urbana line where a Flood Watch remains
in effect until 6am Sunday. The heavy rain, combined with recent
snow melt and the frozen ground, will create copious run-off and
steep rises on many area creeks and streams.

Thunderstorms:
Quite a bit of convection is already evident on satellite imagery
upstream over the Ozarks into southwest Kentucky. While most of
this will remain just south of the KILX CWA today, am expecting a
few thunderstorms to spread as far north as Champaign and
Danville. Greatest chance for thunder will be focused along/south
of I-70 this afternoon and evening as surface low pressure tracks
across far southern Illinois into central Indiana. SPC Day 1 convective
outlook keeps severe weather risk a bit further south, but will
need to keep an eye on the far SE CWA, as strong upper dynamics could
trigger a few strong storms later today.

LONG TERM...Tuesday through Friday

Cold and relatively quiet weather will prevail through the
extended as northwesterly flow takes hold across the central and
eastern CONUS. One weak system could bring a period of light snow
on Christmas Day: however, accumulations are expected to remain
very light amounting to a couple tenths of an inch at best.

Barnes

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH through late tonight FOR ILZ044>046-052>057-061>063-
066>068-071>073.

FREEZING RAIN ADVISORY until 6 PM CST this evening FOR ILZ031-
037-038-041>043-047>051.

WINTER STORM WARNING until 6 AM CST Sunday FOR ILZ027>030-036-
040.

&&

$$