Downers Grove, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

023
FXUS63 KLOT 231745
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1145 AM CST Mon Dec 23 2024

.KEY MESSAGES...

- Chance of sprinkles/light showers today - threat for any
  freezing drizzle has diminished.

- Warmer with periodic rain chances midweek into the weekend.

&&

.UPDATE...
Issued at 844 AM CST Mon Dec 23 2024

Set-up for drizzle and freezing drizzle thankfully ended up not
coming to fruition this morning, with larger T/Td spreads
resulting in higher ceilings and much shallower saturation
depths. Since any obs of light precip. have been few and far
between early this morning, and also haven`t noted any recent
mPing reports of precipitation falling, light radar echoes over
the area are likely not reaching the ground. Updated the
forecast to remove any freezing drizzle mention and indicate low
chances for sprinkles/light showers. Temperatures are warming a
bit faster than earlier forecasts as well, so nudged up forecast
highs into the upper 30s to lower 40s (locally mid 40s in the
Sterling to Pontiac corridor).

Castro

&&

.DISCUSSION...
Issued at 300 AM CST Mon Dec 23 2024

Through Tuesday:

The primary forecast concern continues to center around the
threat for a period of light freezing rain or drizzle this
morning before surface temperatures warm safely above freezing.

A potent mid-level trough, currently sliding eastward into the
Upper Midwest, will shift into the western Great Lakes later
today as an associated surface cold front crosses the area. While
the track of this impulse is expected to favor most of the
precipitation falling north and northeast of our area today, we
continue to monitor a small window in which a period of light
freezing precipitation could materialize this morning. If this
does occur, the best chances for it would primarily be to the
east of I-57.

Lower-level moisture transport is now well underway west-
southwest of the area early this morning, thanks to a
strengthening southwesterly low-level jet. This has been noted
by the quick northward development of a VFR stratus deck into
western IL over the past couple hours. This stratus deck is
expected to overspread our area through mid-morning. In spite of
this increase in lower-level moisture, questions remain with
regard to the quality of low-level saturation (which is
typically necessary to support drizzle) across the area this
morning. Forecast guidance suggests that the developing stratus
deck this morning will remain based above 1500 ft AGL, which is
typically not good for supporting drizzle. Based on the current
large dewpoint depressions across the area, as well as the
reported bases of the developing stratus deck upwards of 5,000
ft, I have reservations on how much if any drizzle/freezing
drizzle may develop this morning.

Even the prospects for light rain/freezing rain looks low
through mid-morning as soundings suggest the presence of a dry
layer around 4,000 ft deep based just above the developing
stratus deck. With this dry layer potentially not eroding,
except for areas east of I-57 into parts of northwestern IN
later this morning, the potential window for any freezing rain
looks minimal (an hour or two at most). Accordingly, with
confidence only growing lower with the occurrence of any
impactful freezing precipitation this morning, no advisory is
planned. Instead, we will continue the going SPS to highlight
the small chance (20%) for some possible slick conditions later
this morning.

Temperatures will warm above freezing for the afternoon, so
there is not anticipated threat for freezing precipitation after
noon. Most locations look to remain cloudy but dry through the
afternoon. However, some instances of light rain or sprinkles
may occur across portions of northeastern IL and northwestern IN
into the afternoon (about a 20-30% chance) as the surface cold
front shifts across the area. This front will settle south of
the area tonight. Once it does, precipitation free weather is
expected through Christmas Eve as a surface ridge of high
pressure settles in across the western Great Lakes. Wind speeds
should abate tonight in association with this approaching
surface ridge, and with lingering low-level moisture we will
have to monitor the potential for low ceilings and/or fog late
tonight into Tuesday morning.

KJB


Tuesday Night through Sunday:

A series of waves is expected to move across the region midweek
into the weekend bringing periodic chances for rain. Temps will
also be warming each day with 50s expected Friday/Saturday.

Still some uncertainty for the first of these waves Tuesday
night into Wednesday which may just brush the southeast cwa.
Lower blended pops have followed the most recent model trends,
keeping the northwest cwa mainly dry. Given how moist the low
levels will be, its possible that some patchy drizzle occurs
with light fog, even if rain or showers don`t materialize.
Regardless, cloudy/damp conditions appear on track. There is
also some uncertainty for precip type late Tuesday night into
Wednesday morning as the precipitation begins. It appears temps
may fall into the lower 30s by daybreak Wednesday morning so
will need to monitor for any possible light freezing rain.
However, by that time, surface temps should be around or above
freezing, with no real cold air expected before that time
period. For now, have continued with all liquid rain for this
time period.

No organized weather is expected Thursday/Thursday night, though
with the continued moist low levels, can`t completely rule out
some drizzle but no mention for now. The next system arrives
Friday with winds turning southerly and this is when the warmest
air arrives as temps look to push well into the 50s for highs
with periodic chances for rain into Saturday with highs still
well in the 50s. Instability currently looks to remain far
enough south to continue with no thunder mention at this time.
The last of these waves is expected to move across the region in
the Sunday time frame, with a cold front moving across the area
with cooler temps, though likely still above normal for late
December. cms

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1145 AM CST Mon Dec 23 2024

The primary aviation weather concerns for the 18Z TAF period
include:

* Continued MVFR cigs throughout the period with IFR possible
  this evening and tonight

* Potential vsby restrictions overnight due to fog, primarily at
  RFD

MVFR cigs are hanging over all sites this afternoon and are
expected to prevail into this evening. We may see a brief
period of scattering to VFR during the early-mid evening before
MVFR fills back in. Cigs may drop to IFR late in the evening
which could hang on through the night. Confidence in timing and
overall presence of IFR cigs is on the lower side, but the
seemingly highest IFR potential exists very late this evening
through the early overnight hours. We look to return to MVFR by
dawn and remain as such through the day on Tuesday.

Additionally, areas of fog may materialize overnight into early
Tuesday. As of this afternoon, the greatest potential for seeing
any impactful vsby restrictions exists out near RFD. Meanwhile,
SW winds gusting as high as 20 kt early this afternoon will
gradually subside to under 10 kt by this evening. Direction will
veer through the evening to near-northerly before flopping over
to NNE early Tuesday. Expect NNE winds below 10 kt during the
day.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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