Area Forecast Discussion
Issued by NWS Chicago, IL

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647
FXUS63 KLOT 141719
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1119 AM CST Thu Nov 14 2024

.KEY MESSAGES...

- Dreary morning expected, as showers transition to a period of
  drizzle and fog.

- Temperatures will be near to above average through early next
  week.

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

&&

.DISCUSSION...
Issued at 259 AM CST Thu Nov 14 2024

Through Friday:

Scattered showers continue to develop and stream northward across
our area just in advance of a sharp mid-level trough/low centered
across far southeastern IA as of this writing. This feature, and
its associated surface low, will quickly slide eastward across
northern IL through daybreak, then across northern IN through the
remainder of the morning. As it does, expect developing showers
to continue for the next few hours (through 5 or 6 am), before the
primary focus begins to shift to the east. While no longer
formally mentioned in the forecast, we still cannot totally rule
out a few lightning strikes with some of this activity early this
morning, but any threat for this will be short lived. Otherwise,
expect a rather dreary morning across the area this morning as
very low clouds, fog and areas of drizzle persist under the low.

Winds will turn northwesterly with the eastward passage of the
surface low this morning. While a gradual visibility improvement
is expected through the morning, it appears cloud cover will hang
on across the area today. Accordingly, temperatures are expected
to remain fairly steady in the low to mid 50s. Drizzle and rain
chances will end for most by this afternoon. However, a low
potential (~20% chance) for some light lake effect showers will
continue tonight across parts of northeastern IN.

Cloud cover may end up lingering across much of northeastern IL
and northwestern IL tonight into the day on Friday as low-level
moisture looks to become trapped under a subsidence inversion
developing off the surface. For this reason it remains a bit
unclear as to how quickly conditions may scatter out on Friday as
a weak surface high shifts overhead. As a result, temperatures
are expected to hold in the low to mid 50s for Friday.

KJB


Friday Night through Thursday:

Heading into this weekend, the synoptic weather pattern will
feature upper-level troughing over the western half of the CONUS
and upper-level ridging over the eastern half of the CONUS.
This upper-level flow configuration will help spawn an initial
weak surface low over the northern Plains late Friday into early
Saturday that will then wander off to the northeast into Ontario
on Sunday, remaining well to our north. Low-level flow to the
south of the low and on the backside of a departing surface high
will be out of the south to southwest, helping high temperatures
to climb into the mid-upper 50s and possibly even low 60s on
Saturday. In spite of increasing cloud cover, continued modest
warm air advection should cause Sunday`s highs to end up being a
few degrees warmer than Saturday`s, so long as the cold front
associated with the aforementioned low slows its southeastward
progress as much as most of the latest forecast guidance says it
will. A ribbon of isentropic ascent ahead of this front could
help generate a few showers in or near our forecast area on
Sunday, though with little additional forcing support, the
overall coverage and duration of any showers should be limited.

Early next week, the primary western CONUS trough will lift
northeastward towards the Midwest, accompanied by a low pressure
system at the surface. While uncertainty remains in how this
trough will interact with another upper-level trough swooping in
from the Pacific Northwest and how quickly the attendant
surface cyclone will occlude and where, every single member of
both the 00Z EPS and 00Z GEFS outputs QPF in our forecast area
late Monday into Tuesday. This lends high confidence to rain
occurring during this time frame regardless of exactly how the
upper-level trough and surface low evolve, though the exact
timing, duration, and quantity of rainfall all remain points of
uncertainty in our forecast that will need to be refined in
forthcoming forecast updates.

The finer scale details of the synoptic pattern evolution will
be of greater relevance for the forecast for Wednesday through
the end of the week, which remains quite uncertain at this
time. While it may still be a few days before we have a better
idea on how all of the puzzle pieces will come together, there
is a fairly strong signal in ensemble guidance that these pieces
will come together in some way that will establish mean upper-
level longwave troughing over the northeastern quadrant of the
CONUS from late next week through possibly the end of November.
If such a pattern were indeed to be established, then cooler
temperatures would be favored to prevail across the region.
These cooler temperatures would potentially be accompanied by
periodically showery conditions as well, including showers that
wouldn`t necessarily be of the liquid variety...

Ogorek

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1119 AM CST Thu Nov 14 2024

IFR to MVFR cigs are expected to prevail through much of the
afternoon before rising and settling near 2000 to 2500 feet
overnight into tomorrow. Timing out when cigs will scatter/erode is
always tough in the current regime (moisture trapped beneath an
inversion, relatively low sun angle), so for now, will offer a
pessimistic forecast with MVFR prevailing through the entire
TAF. Northwest winds will remain generally between 5 to 10 kt
through much of the TAF period before becoming light and
variable tomorrow evening.

Borchardt

&&

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

&&

$$

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