Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 200930

Area Forecast Discussion
330 AM CST Sat Dec 20 2014

.SHORT TERM...(Today)

Latest satellite data indicating a shortwave trof near Omaha which
is expected to push across our area later this morning. Upstream
surface observations across central and east central Iowa have had
some reports of some very light freezing drizzle and flurries to the
east of the main area of lift, with even some very light flurries
reported this past hour in St. Louis. A secondary shortwave was
noted over parts of southern Missouri into the lower Ohio Valley
that has produced a band of light snow which extended along and
south of the I-70 corridor early this morning. That system will
shift off to our east over the next few hours taking the light snow
out of southeast Illinois by dawn.

As the compact shortwave over the Missouri Valley tracks across the
area, many of the forecast soundings are not showing much in the way
of support for widespread precip as high pressure at the surface is
still holding firm over east central Illinois this morning. We see
moisture in the 850-800 mb layer over most of the area with not a
great deal above that until later this morning when the main area of
lift associated with the vort max swings thru. Much of the stratus/low
level moisture will remain to our west thru the morning as well before
tracking slowing into west central Illinois this afternoon. Will carry
chances for flurries this morning, mainly over west central Illinois
ahead of the vort max, as we see some mid level moisture/lift track
just to the west of our forecast area. Most of the short term high
resolution models continue to suggest as the shortwave moves across
the remainder of the state, moisture profiles will not support much
in the way of precip further east this afternoon. Despite the more
widespread cloud cover over our area today, we should see afternoon
temperatures a few degrees warmer than yesterday with readings
ranging from the mid 30s north to around 40 south.


.LONG TERM...(Tonight through Friday)

Fairly quiet weather expected tonight through Sunday night across
central and southeast IL as surface ridge shifts east into New
England and the mid Atlantic states Sunday. Temps to gradually
modify next few days with increasing southerly flow especially by
Monday. Added patchy drizzle/freezing drizzle to the IL river valley
overnight with the low clouds as surface temps are close to
freezing. Mostly cloudy skies expected Sunday with more low clouds
prevailing over northern counties. Highs in the lower 40s Sunday
which will be a bit above normal highs in the mid to upper 30s.
Added slight chance of light rain late Sunday night around Galesburg
with best rain chances arriving during the day Monday especially by
Monday afternoon NW areas and Monday night into Tue across area.
Strong low pressure near Pacific NW to track into MN Monday night
and increase chances of rain over IL ahead of approaching low
pressure and cold front. Milder highs in the 40s Monday and Tue with
Lawrenceville around 50F.

Forecast models then deepen another area of low pressure from the
southern plains into KY by dawn Wed and then into eastern lower MI
or just east of there by sunset Wed. Colder air to be drawn into IL
Tue night and Wed with rain changing to snow during Tue night and
continue good chances of light snow Wed. Could be some light snow
accumulations overnight Tue night into Wed especially over
eastcentral IL. Windy conditions expected Wed and Wed night as
deepening low pulls away with strong west winds gusting 25-35 mph.

Dry conditions expected on Christmas Day over the state as IL will
be inbetween strong low pressure exiting into eastern Canada and new
low pressure developing over Texas Panhandle by sunset Thu. This low
pressure ejects ne into the western Great Lakes by sunset Friday and
returns good chances of precipitation with southeast IL mainly rain
and a mix of rain/snow over central IL. Extended models show active
weather pattern looks to continue beyond day 7.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)

VFR conditions will begin the TAF period for most of the TAF
sites...with the exception being CMI where MVFR VIS is already in
place. Some of the issues with the TAFs tonight are the timing of
MVFR VIS and lowering CIGs. The surface high that was over
Illinois earlier is slowly pushing east with light to calm winds
remaining over much of central Illinois. Winds are also slowly
shifting to the east southeast allowing the low level moisture to
filter in both from the east and the west. Locations over Missouri
and Indiana have MVFR VIS and CIGs with locations in Missouri
under IFR CIGs. Given the complexity involved with timing of lower
VIS and CIGs...confidence is fairly low in the TAF forecast past
the first 6 hours. Currently have MVFR conditions over PIA
starting at 08Z for BMI and DEC...and at 12Z for SPI.
Mainly went with the HRRR since it seemed to have a pretty good
handle on the previous forecast. Also included a TEMPO group for
CMI as all guidance had IFR VIS over the site between 09Z and 13Z.
Only included a TEMPO for now since confidence in the timing is
lower. VFR conditions could resume around 16Z for the sites after
the next upper level wave moves through Illinois...but this could
change with the next TAF issuance.





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