Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

421
FXUS63 KILX 210936
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
336 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.

&&

.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 06z TAFs through 06z Thursday Night)
Issued at 1100 PM CST Wed Nov 20 2024

MVFR ceilings currently affecting KPIA-KBMI are forecast to expand
south over the rest of the central IL terminals overnight and
persist through Thursday. A disturbance dropping southeast
through the lower Great Lakes will bring -RASN to the area
Thursday afternoon, with a few hours of predominant -SN likely at
KCMI. West- northwest winds gusting near 25 kt will be common
overnight, then increase near 35 kt by midday as the pressure
gradient tightens more, before easing slightly and veering
northwest Thursday evening.

25

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 10 AM this morning to midnight CST tonight
for ILZ027>031-036>038-040>057-061>063-066>068-071>073.

&&

$$