536
FXUS63 KLOT 150219
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
819 PM CST Thu Nov 14 2024

.KEY MESSAGES...

- Low chance (20%) of showers Saturday night into Sunday.

- Periods of rain expected Monday night.

- A cooler weather pattern, potentially accompanied by periodic
  showers, may materialize mid-late next week and continue toward
  the end of the month.

&&

.UPDATE...
Issued at 819 PM CST Thu Nov 14 2024

The only minor change for the evening update was to add a
mention of patchy drizzle to the grids this evening. Recent
PIREPs indicate cloud tops are around 4 kft, and with bases
near 1 kft, this 3 kft-deep layer combined with just a smidge of
ascent has been enough to squeeze out some very light drizzle.
Based on latest model guidance, the deepest moisture is forecast
to focus across roughly the northeastern half of the CWA, and
have generally confined the drizzle mention to these locales.
Based on upstream trends, some visibility reductions into the
3-5 mile range can`t be ruled out, but this generally looks like
a very light drizzle set up. Thankfully, no concerns with FZDZ
this time around. Otherwise, looks like we`ll remain generally
socked in with low cloud cover tonight, with any fog potentially
remaining well west of the region.

Carlaw

&&

.DISCUSSION...
Issued at 136 PM CST Thu Nov 14 2024

Through Friday Night:

We`re firmly entrenched in "stratus season", a common cool season
pattern when relatively stagnant conditions more or less keep
existing low cloud decks locked in. As of early afternoon, with
some exceptions, stratus extends back almost to the IA/NE border
and then up to the eastern Dakotas. With minimal cold and dry air
advection through tonight and then warming aloft on Friday serving
to strengthening an already stout lower level inversion, it`s
tough to pinpoint any timeframes of meaningful clearing.

Some of the global guidance suggests some erosion is possible
from the west Friday afternoon, while higher resolution guidance
(which typically handles these patterns better) supports a mostly
cloudy forecast throughout. Can`t rule out mechanical mixing and
subtle drying resulting in holes in the stratus. However, the low
level flow shifting from northwesterly to light southeasterly
later Friday should cause a back edge of the clouds (if it
approaches parts of our western CWA), to "slosh" back west-
northwest through Friday night. With all the above being said,
bumped up sky cover to overcast tonight and mostly cloudy through
Friday night. This will also limit the diurnal temperature range,
resulting in milder lows (generally solidly above 40F) and
slightly cooler high temps (lower-mid 50s) on Friday.

There are otherwise no weather impact concerns of note. A
marginal thermodynamic setup could result in spotty northwest flow
driven lake effect showers into portions of Porter County
tonight.

Castro

Saturday through Thursday:

A dissipating cold front is expected to be moving across the
area Saturday afternoon into Saturday night. This may allow for
some showers, particularly Saturday night though isolated
showers may persist into Sunday. Low chance pops seem fine for
now with low coverage if anything develops.

The next storm system will develop in the southern Plains Sunday
into Sunday night and lift north to near IA by Tuesday morning.
A warm front will lift north across the local area bringing
periods of rain Monday night which if current timing holds, may
be transitioning to showers or ending by daybreak Tuesday
morning. After high temps in the 50s on Monday, temps may hold
steady or after an evening dip slowly rise back into the lower
to mid 50s Monday night. High temps on Tuesday could be in the
morning with steady or slowly falling temps in the afternoon,
depending on how fast and to what extent cooler air spreads
into the area during the day. Southwest winds may also become
rather gusty Tuesday, perhaps into the 30 mph range.

While a cooler pattern change is still supported by the
ensembles later next week, after Tuesday, there is still some
uncertainty as to when and to what extent this change occurs. As
well as to how long it may persist before temperatures begin to
moderate. If a large upper low were to persist over the area for
several days, the main story might be the cloudy/showery weather
rather than how cold the temps are. But this time period is
still a week away and its too early for details. Given the
warmer blended guidance, all forecast precip types remain liquid
through the end of the period. cms

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 544 PM CST Thu Nov 14 2024

Forecast concerns for the terminals...

- MVFR ceilings to persist through Friday evening


The upper trough and surface low that brought us rain last night
continues to track eastward across lower Michigan this evening.
While rain has come to a close across virtually all of northern
IL and northwest IN, a few scattered lake effect showers
continue to be noted on radar in northern IN. These showers are
expected to remain east of GYY tonight and should pose no threat
to any of the TAF sites but a stray shower could reach VPZ
through midnight.

As the trough continues to move away, high pressure will build
into the area on Friday resulting in light winds through the
period. However, the northwest wind directions tonight and
Friday will become more east-southeasterly as the high pivots
through Friday night. The current MVFR ceilings are expected to
prevail through Friday evening, and possibly beyond, as
lingering low-level moisture becomes trapped beneath the high.
So while some breaks in the clouds may develop Friday afternoon,
BKN to OVC skies are anticipated until at least Saturday
morning.

Yack

&&

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

&&

$$

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