Elmhurst, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

884
FXUS63 KLOT 221142
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
542 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 /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 542 AM CST Sun Dec 22 2024

Aviation forecast concerns through the period include:

- Breezy SSE winds with gusts 20-25 kts this afternoon and
  tonight.

- 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.

- Chance (~30%) for a 2 to 4 hour period of -FZDZ 11-14Z Monday
  morning.

A surface ridge of high pressure is beginning to slide east of
the area early this morning. As it continues to do so, winds
will settle into a southerly direction after daybreak this
morning. Southerly winds will then be on the increase through
the morning as the surface gradient tightens in advance of low
pressure shifting out across the Plains. Gusty south winds of 20-25
kt are then expected this afternoon. While these wind gusts may
briefly abate at KRFD and KDPA after sunset this evening, it
appears gusty winds will redevelop during the evening as a 45+
kt low-level jet shifts overhead. With the expectation for some
continued gustiness tonight, we have opted to leave the mention
of LLWS out of the TAFs.

VFR conditions are expected today, and most of tonight, with
only some mid-level ceilings expected. However, this looks to
change very late tonight into early Monday morning as increasing
low-level moisture leads to the development of a low stratus
deck, potentially in the IFR or low MVFR category. Concerns
also continue for the development of a period of freezing
drizzle early Monday morning. Confidence continues to be low
with the extent of freezing drizzle, especially since
temperatures will be hovering right around the freezing point.
Nevertheless, there appears to be about a 2 to 4 hour window
favorable for freezing drizzle at the terminals early Monday
morning (~11 to 14Z). Accordingly, we have opted to include a
PROB30 mention for -FZDZ in the latest 30 hour ORD and MDW TAFs.
The threat of freezing precipitation will come to an end by mid
morning as temperatures warm above freezing. Lower cloud cover
may persist for much of the day, however.

KJB

&&

.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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