Area Forecast Discussion
Issued by NWS Central Illinois

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS63 KILX 211141

Area Forecast Discussion
541 AM CST Sun Dec 21 2014

.SHORT TERM...(Today)

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.


.LONG TERM...(Tonight through Saturday)

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)

MVFR to low VFR cigs expected today with high resolution model
data indicating the potential for the lower cigs to scatter
out at CMI and DEC later this morning into this afternoon.
In addition, some patchy fog and haze was bringing vsbys down
to MVFR as well but expect that to lift after 15z. Low level
southerly flow is expected to continue through tonight which
may effectively lower cigs back to lower MVFR again after 06z
but models have kept that scenario to our west later tonight
but will monitor for that possibility at PIA and SPI after
06z. Surface winds will be southeast to south today at 10 to
15 kts and then winds will tend to back more into a southeast
direction tonight at 8 to 13 kts.




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