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Area Forecast Discussion
Issued by NWS Central Illinois
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989
FXUS63 KILX 010528
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1128 PM CST Tue Jan 31 2017

.UPDATE...
Issued at 900 PM CST Tue Jan 31 2017

An elongated area of lift is extending from Missouri across west-
central and central Illinois this evening, as evidenced by radar
returns and cooler cloud tops in the satellite loops. High res
models continue to point toward increasing frontogenesis in the
800-700mb layer, peaking between 07z-09z/1-3am. The trend has been
for that forcing to focus slightly higher than 800mb, so chances
are remaining low for any measurable rain or snow from this push
of energy. The 00z KILX sounding confirms dry air between
700-850mb to start this event, so will stay the course mentioning
only sprinkles or flurries. Air temps are holding on the warm side
due to the blanket of cloudy cover, tipping the scales toward
sprinkles over flurries. Low temps tonight may end up a couple
degrees warmer than previous lows, so will bump them up a degree
or two with the evening update. Precip chances should advance east
of Illinois by 12z/6am, with mostly cloudy skies persisting
through the day on Wednesday. Updated hourly temp/dewpoint trends
as well as sky and weather conditions to match latest trends.
Forecast update will be sent shortly.

&&

.SHORT TERM...(This evening through Wednesday)
ISSUED AT 301 PM CST Tue Jan 31 2017

Gusty W/NW winds this afternoon will diminish to less than 10mph by
evening as high pressure currently over the Plains builds eastward.
Despite the presence of surface ridging, a weak upper-level
disturbance will spread clouds and some very light precipitation
into the area tonight.  Frontogenetical forcing increases markedly
as the wave approaches from the northwest between 03z and 09z,
particularly within the 800-700mb layer.  The main mitigating factor
for measurable precip reaching the ground will be a dry layer below
850mb.  Some top-down moistening occurs overnight: however, the
profile never fully saturates.  As a result, have opted to go with
just sprinkles/flurries from mid-evening through the overnight
hours.  Based on trajectory of system...have kept the far northern
KILX CWA from the Peoria area northward dry...with sprinkles and/or
flurries further south and east.  Low temperatures will drop into
the lower to middle 30s.  Lift quickly decreases by 12z Wed,
spelling an end to any light precip by Wednesday morning.  The
remainder of the day will be mostly cloudy and dry with high
temperatures in the upper 30s and lower 40s.

.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 301 PM CST Tue Jan 31 2017

Forecast issues for today center on the couple of systems moving
through region, mainly weekend and early next week.

Morning upper air and moisture channel imagery shows flat ridge in
the west US and flat trough approaching WV. In weak NW flow over IL,
minor system to move through area in next 24 hours.

Then starting for wed night, surface ridge of high pressure builds
into area, and brings in cooler, more near normal temperatures for
area through rest of week.

By Sat, high pressure finally east of area, with southerly flow over
IL. Upper flow becomes zonal and first minor surface low develops
in lee of rockies. Weak upper wave moves through mid MS River
Valley and brings light pcpn to region, mainly Sat night. Will be
some light snow, and mixture r-s- in the south sections, ending by
noon Sun. Amounts vary light with this rapidly moving system.

A second cold front will move into area Monday, bringing light
pcpn, possibly a mixture again. the front will stall and by Tues,
a stronger low pressure system will move out of the Rockies into
IA, with significant mainly rainfall ahead of the system over IL.
Timely details are still uncertain, as this is a week out in
advance. However there may be enough warm air brought up with this
system from the south, that sct storms may be possible.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1128 PM CST Tue Jan 31 2017

Radar images are showing the affects of increasing frontogenesis
in the 700-800mb layer, but there have been no reports of any
precip reaching the ground to this point. The highest radar
returns so far have been in the 25-27dbz range, with cloud bases
at 6000-7500FT. High resolution models continue to point toward
an increase in F-gen between 06z-09z tonight, mainly affecting the
southern terminals of SPI, DEC, and CMI. Have kept a VCSH for a
few hours at the start of this TAF period to account for some
precip reaching the ground, most likely in the form of sprinkles
based on low level thermal profiles. Even during peak forcing for
precipitation, it appears the cloud bases will generally remain
VFR, but could approach MVFR for a couple hours from 07z to 10z.
Dry air in the lowest levels will limit potential for measurable
rain/snow. Surface dewpoint depressions have narrowed some, but
are still 5 to 10F late this evening. The forcing for precip is
expected to quickly shift east of Illinois by 12z, with lingering
VFR mid-clouds the remainder of the TAF period.

Winds will remain light west the rest of the night. Once this shortwave
passes, winds will become NW tomorrow morning and increase to
10g18kt during the afternoon. There is some indication the
pressure gradient could support sustained 10kt into the evening
tomorrow.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Shimon
SHORT TERM...Barnes
LONG TERM...Goetsch
AVIATION...Shimon
National Weather Service Regional Headquarters
