Des Plaines, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

106
FXUS63 KLOT 220829
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
229 AM CST Sun Dec 22 2024

.KEY MESSAGES...

- 30% chance of light freezing drizzle/drizzle late Sunday
  night through early Monday morning.

- Turning mild with on-and-off chances for rain during the
  Holiday week.

&&

.DISCUSSION...
Issued at 229 AM CST Sun Dec 22 2024

Through Monday:

The primary forecast concern in the short term is the potential
for light freezing drizzle or even some light freezing rain
just before and just after daybreak Monday morning.

High pressure will move to the southeast of the area this
morning with southerly winds steadily increasing with gusts into
the 20-25 mph range this afternoon. This will aid temperatures
warming to near freezing for highs today. Winds may diminish
briefly with sunset but as low level winds steadily increase
this evening, expect gusts into the 25 mph range, perhaps 30 mph
at times tonight. These winds and increasing mid clouds should
allow temps to only fall a few degrees, perhaps into the upper
20s this evening, before becoming steady and then slowly rising
back toward freezing with daybreak Monday morning. However, it
will take some time for the ground and pavement to warm above
freezing after a weekend of sub-freezing temps.

Precipitation chances remain quite uncertain just 24 hours out.
Much of the guidance has slowed the potential onset until the
predawn hours Monday morning, perhaps around daybreak for the
Chicago metro, when the low levels may rapidly saturate and
drizzle may develop and based on both the air temps as well as
the ground temps, it may be freezing drizzle. Some of the
guidance remains mainly dry, while the NAM with its more moist
low levels hints at the potential for at least pockets of light
freezing rain. Confidence in precip trends remains very low and
have made no significant changes, other than delaying the
precip onset by a few hours, now after 3 am in the west. Temps
are expected to slowly warm into the mid 30s by mid morning
Monday as dewpoints creep into the lower 30s, which would likely
end the threat of freezing drizzle or freezing rain. There will
remain a chance of drizzle or light rain into Monday afternoon,
ending from west to east in the afternoon. cms


Monday Night through Saturday:

The Polar jet will be shunted well north of the region into the
high latitudes of Canada as anomalous upper-level ridging builds
across North America this week. The net result of this being the
turn towards a period of above, to much above, normal temperatures
through the Holiday week. Unfortunately, this period of mild
weather will be accompanied by a lot of cloud cover and on-and-off
periods of rain as a parade of mild Pacific impulses traverse the
central CONUS.

A surface cold front is expected to settle south of our area at
the beginning of the period Monday night into Tuesday. This
should push the threat of rain south of the area for most of
Tuesday. Also, with no real push of cold air expected in the wake
of the front, temperatures will remain seasonably mild (in the 30s
to around 40) on Tuesday. On-and-off chances for rain will begin
to enter the picture Tuesday night into Christmas day as the first
in a series of Pacific impulses begin to shift into the central
Mississippi Valley. Rainfall amounts look to remain light on
Christmas Day into Thursday. Also, with temperatures expected to
remain above freezing, even during the night, there is not much of
a threat for freezing precipitation.

Later in the week, and really through next weekend, there
continues to be a signal for an even stronger northward push of
low-level Gulf moisture and warmth into the lower Great Lakes in
advance of a potentially more potent approaching Pacific wave.
This could thus result in even warmer daytime temperatures
(possibly into the low 50s) for next weekend (normals are in the
low to mid 30s). Unfortunately, as mentioned above, these warm
temperatures will also be accompanied by cloud cover and at
least some periods of rain at times. While the official forecast
has continuing rain chances every period through end of the
week, there is likely to be some dry periods in between systems.
However, pinpointing when these dry periods may occur at this
time range remains nearly impossible given the continued model
timing and track differences of each system.

KJB


&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 1100 PM CST Sat Dec 21 2024

Aviation Forecast Concerns for the 06Z TAFs:

- MVFR ceilings possible briefly at GYY around issuance time,
  as lake-effect clouds drift into the vicinity.

- Breezy SSE winds with gusts 20-25 kts develop midday Sunday
  and persist through the period. Strongest winds may occur
  Sunday night, with gusts above 25 kt possible.

- RFD/DPA/GYY may lose gusts with sunset, though would expect
  them to redevelop during the evening. If not, LLWS conditions
  likely as south winds ~45 kts develop above 1500 ft AGL.

- Low probability for -FZDZ to develop toward 12Z Monday. Prob
  too low for TAFs at this time, but may need a mention into
  Monday morning with later forecasts.

Scattered MVFR (2000-2500 ft) deck may briefly affect KGYY
around 06Z this morning, as lake-effect clouds drift west across
the airport. Winds above the surface will be shifting to the
south however, likely pushing these clouds back out over the
lake within a couple of hours.

Surface high pressure ridge over the area at issuance will
maintain calm or light/variable winds into early Sunday, before
winds eventually settle south-southeast and begin to increase
mid-morning. By midday, breezy conditions are expected with
gusts in the 20-25 kt range, as the gradient tightens ahead of
an approaching area of low pressure across the central/northern
Plains. Sites away from the heart of the metro (RFD/DPA/GYY) may
lose gusts with sunset Sunday evening, though at least some
sporadic gusts would likely redevelop during the evening as a
45-50 kt low level jet spreads overhead. If gusts do not
rematerialize, LLWS conditions would likely result given the
strength of the low level jet. (RFD may see a brief period of
LLWS just prior to surface gusts redeveloping). ORD and MDW
typically prone to maintaining gusts in these situations.
Strongest winds, with gusts occasionally above 25 kts, are
likely Sunday night beneath the low level jet.

VFR conditions are expected through the duration of the
forecast, with periods of mid-level ceilings. The only real
concern is for the currently low-probability potential for the
development of light freezing rain/drizzle toward Monday
morning. While this can`t be completely ruled out as early as
10-12Z, most model guidance currently favors this to develop
just beyond the current 12Z end time of the ORD/MDW 30-hour
forecasts. A freezing rain/drizzle may therefore need to be
introduced in later forecasts into Monday morning.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 4 PM this afternoon to 9 AM CST
     Monday for the IL nearshore waters.

     Small Craft Advisory from 6 PM this evening to noon CST Monday
     for the IN nearshore waters.

&&

$$

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