Oak Lawn, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

475
FXUS63 KLOT 260512
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1112 PM CST Wed Dec 25 2024

.KEY MESSAGES...

- Low clouds and areas of dense fog and drizzle expected tonight.

- Next chance for widespread rain on Friday morning with above
  normal temperatures expected Friday and Saturday.

- Another system potentially arrives just before New Years Eve
  next week.

&&

.DISCUSSION...
Issued at 218 PM CST Wed Dec 25 2024

Widespread cloud cover seen on satellite imagery has blanketed
Illinois. The forecast area sits between under an upper level
ridge to the east and the next short wave trough to the west.
Higher moisture content is located along and southeast of this
axis from a Gibson City to Valparaiso line. With better
forcing, the best chances for light rain this afternoon look to
be south and east of I-57. However, as the evening approaches,
better forcing is projected to gradually move east of the
forecast area. And while light rain chances diminish, a moist
column and lingering weak forcing could allow for intermittent
drizzle tonight through tomorrow afternoon. As temperatures are
expected to remain in the upper 30s through the night (thanks to
the cloud cover), no freezing drizzle is expected).

Cloud decks are expected to lower through the evening as the
lower levels moisten. Visibilities have already been down below
2 miles just south of the forecast area and most model guidance
is suggesting that with weak south-southeasterly flow the
threat for lower vis and fog will advect north-northwestward
through the forecast area. While fog is expected tonight, there
is uncertainty as to how dense the fog will get. The potential
is certainly there for dense fog, but confidence remains low in
how widespread the dense fog will be. Clouds are expected to
remain around the area on Thursday, but latest high res guidance
is suggesting better mixing tomorrow afternoon which should
help limit fog impacts to the morning.

The previously mentioned trough to the west is projected to
move eastward through Thursday. A surface low is expected to
develop and pass over the area Thursday night into Friday
morning. While significant precipitation is not expected, it is
looking likely that this could be the next chance for greater
rain coverage across the forecast area. However, as another
shortwave trough moves quickly over the Plains Friday morning,
it will likely kick the former trough north into Wisconsin
somewhat quickly allowing PoPs to diminish Friday afternoon into
the evening.

There is still some uncertainty with the track of the kicker
wave as it passes Friday night through Saturday. Models are
continuing to track it farther to the south which keeps much of
the forcing out of the forecast area (focusing it in Indiana and
points east). It was decided to leave the National Blend PoPs
in the forecast for now as there is a chance for some precip
this weekend, but it should be noted that models continue to
trend drier as they continue to project a more southerly track.
Persistent warm air advection from southerly winds ahead of the
troughs will help temperatures warm into the 40s and low 50s
Friday and Saturday - well above seasonal norms.

Ensemble models are suggesting the next wave to arrive sometime
early next week (Monday into Tuesday). Temperatures out ahead
of this wave should remain above freezing allowing for most of
the precip to remain rain. However, as models continue to track
the wave slightly more south of the area, it is allowing the
modeled 850 mb freezing line to drop farther south. Depending on
how this system tracks, there could be some snow that mixes in
on the back side (better chances closer to the Wisconsin state
line) but there remains a lot of uncertainty this far out.
Nevertheless, there is fairly good agreement in the extended
models that that cold air behind this system will continue to
filter into the area from Canada after New Year`s allowing
temperatures to cool below freezing to start 2025.

DK

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1112 PM CST Wed Dec 25 2024

Key Messages:

- LIFR cigs and IFR/LIFR vsbys to prevail overnight into
  Thursday AM with periods of -DZ.

- Increasing potential for a period of near-VLIFR cigs/vsbys at
  ORD/MDW and VLIFR at DPA/RFD early Thursday AM.

LIFR ceilings and IFR visibilities have developed across the
area late this evening and are expected to continue or even
deteriorate further through the remainder of the overnight
hours into Thursday morning. With such a moist low-level
airmass in place, model guidance continues to support a period
of near-VLIFR conditions developing near the Chicago area
terminals though confidence remains too low to include a formal
VLIFR mention with this update. The earlier feared quicker drop
in vsbys ended up not materializing and opted to shift the
1/2SM OVC002 mention back to a later timing (~10-14Z) timeframe
at ORD/MDW in TEMPO groups.

Webcams in and around the RFD area and the northwest Chicago
suburbs combined with continued pessimistic visibility trends
in model guidance have increased confidence enough to introduce
VLIFR conditions at RFD as well as DPA for 1/4SM between
roughly ~9-14Z, though it may persist beyond this time,
particularly at RFD.

Confidence in the timing of improvement in cigs/vsbys Thursday
morning remains on the lower side, but the general expectation
is for cigs/vsbys to very gradually lift mid-late morning into
the afternoon back to IFR and eventually MVFR. Guidance is less
optimistic out toward RFD where low-end IFR may persist for
much of the day. Toward the end of the TAF period Thursday
evening there is another chance (~30%) for light showers and/or
drizzle.

Winds will be light easterly to at times variable overnight
trending ESE and then SSE during the day on Thursday, remaining
under 10kt.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Dense Fog Advisory until 9 AM CST Thursday for the IL and IN
     nearshore waters.

&&

$$

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