Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

140
FXUS63 KILX 211620
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
1020 AM CST Thu Nov 21 2024

.KEY MESSAGES...

- The first snow of the season will occur across parts of central
  Illinois today. A light slushy accumulation is likely on grassy
  surfaces this afternoon...mainly along and northeast of a
  Bloomington...to Champaign...to Paris line.

- Northwesterly winds will gust 40-50mph today...resulting in
  blustery wind-chill values in the 20s.

&&

.UPDATE...
Issued at 1019 AM CST Thu Nov 21 2024

Late this morning, light to moderate snow is falling across
portions of north central and northeast Illinois and is starting
to spread south of the I-80 corridor. Leading returns on ILX radar
are likely not yet reaching the surface, but do expect snow to
begin to overspread portions of the I-74 corridor by around noon
today. No major changes in thinking in placement and amount of
snow expected today with the highest totals clipping our far NE
forecast area over northern Champaign and Vermilion counties
today. Meanwhile, wind speeds have picked up this morning and we
are starting to see gusts in excess of 40 mph in some of the area
obs.


Deubelbeiss

&&

.SHORT TERM...(Today through Friday)
Issued at 336 AM CST Thu Nov 21 2024

A 993mb low over the upper peninsula of Michigan will track
southward down Lake Michigan then into Indiana by this evening.
CAMs are showing an area of moderate snow associated with the low
expanding southward into the Chicago metro early this morning,
with the snow then dropping southward into the N/NE KILX CWA
toward midday. Based on the trajectory of the low, it appears
precipitation will occur along and east of a Galesburg to
Springfield line...with dry conditions persisting further west.
The heaviest and steadiest precip will be confined to locations
along and east of a Bloomington to Paris line. Thermal profiles
will remain cold enough to support snow initially: however, as
surface temperatures rise, the snow will mix with and/or change to
rain by late afternoon into early evening. Where precip rates are
highest across the NE CWA, snow will be the predominant precip
type the longest. Given expected high temperatures well above
freezing in the upper 30s and lower 40s, significant accumulations
will not occur. Am expecting a slushy accumulation of wet snow on
grassy surfaces along/east of a Bloomington to Paris line...with
perhaps as much as 1-2 inches across the far NE around Danville
and Hoopeston. Any snow that accumulates during the heaviest
period of precip this afternoon will quickly melt once the snow
ends and/or changes to rain this evening. The light rain/snow mix
early this evening will come to an end before midnight as the low
drops toward the Ohio River and decays.

The other big weather story today will be the increasing winds
associated with a tightening pressure gradient on the W/SW
periphery of the low. The HRRR indicates widespread wind gusts
over 40mph across nearly all of central Illinois this afternoon.
In addition, the 00z HREF Grand Ensemble shows a greater than 50%
chance of wind gusts in excess of 45mph along/northeast of a
Macomb...to Springfield...to Lawrenceville line. As a result, have
issued a Wind Advisory for wind gusts of 40-50mph for the entire
CWA from 10am this morning to midnight tonight.

A deep upper low over the Mid-Atlantic states will continue to
influence the weather across central Illinois into Friday. While
conditions will be dry, cloud cover will blanket the region and
N/NW winds will gust 20-30mph throughout the day. High temperatures
will be a few degrees warmer than today in the middle 40s:however,
wind-chills will remain in the 20s and 30s.

Barnes

.LONG TERM...(Saturday through Wednesday)
Issued at 336 AM CST Thu Nov 21 2024

As the upper low moves further away and heights rise, at least
partial sunshine will return and temperatures will reach the upper
40s to around 50 degrees on Saturday. Even warmer weather is on
tap for Sunday as the boundary layer flow becomes southwesterly
ahead of an approaching cold front and afternoon highs climb well
into the 50s to near 60 degrees. The front will drop through the
region mostly dry Sunday night into Monday: however, cannot rule
out a few light rain showers...especially across the E/SE CWA.

After that, colder weather will return for the middle and end of
next week as highs drop back into the 30s and lower 40s. 00z Nov
21 synoptic models are in poor agreement concerning the exact
details:however, all solutions suggest an active weather pattern.
Will need to keep a close eye on subsequent model runs as the
potential exists for another storm system traversing the
Midwest/Ohio River Valley by Wednesday/Thursday...which could
have impacts on holiday travel. Stay tuned to later forecasts.

Barnes

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 542 AM CST Thu Nov 21 2024

Scattered snow-showers will continue to track southeastward across
central Illinois for the next couple of hours...primarily
impacting KBMI and KCMI with 5-6 mile visibility. Other than a
stray flurry or sprinkle, much of the area will remain dry until
midday when an area of snow drops southward out of northern
Illinois. Based on the latest model guidance, the precip will
generally remain along/northeast of a KPIA...to KAAA....to K1H2
line. As a result, have opted to keep KSPI dry and to only feature
a period of very light rain between 19z and 02z at KPIA. Further
northeast, it appears snow will begin at KCMI by 18z before mixing
with and changing to rain by 23z. Scattered rain showers will
linger along/east of I-55 into the evening before the precip comes
to an end after 02z/03z. Ceilings will initially range from low
VFR to high MVFR early this morning, but will lower into the MVFR
category this afternoon through tonight. As the pressure gradient
tightens, northwesterly winds will gust as high as 35-40kt from
late morning through this evening before gradually dropping to
20-25kt overnight.

Barnes

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until midnight CST tonight for ILZ027>031-036>038-
040>057-061>063-066>068-071>073.

&&

$$