281
FXUS63 KLOT 111957
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
257 PM CDT Sat May 11 2024

.KEY MESSAGES...

- Warm, breezy, and dry Mother`s Day

- A few spotty showers, maybe a thunderstorm on Sunday night

- Periods of showers and a few thunderstorms expected Monday
  afternoon through early Tuesday.

&&

.DISCUSSION...
Issued at 257 PM CDT Sat May 11 2024

Through Sunday Night:

The scattered to broken Cumulus field inland of the advancing
lake shadow from the lake breeze push will quickly erode this
evening. Other than some passing high clouds, this should entail
favorable viewing Aurora viewing conditions, with our area
potentially in line again, and higher viewing chances northward
into Wisconsin. Weak high pressure overhead will cause light to
calm winds and on the heels of the low dew points this
afternoon, favorable radiational cooling conditions will support
lows in the mid to upper 40s outside of Chicago (low 50s there).

We`re setting up for the warmest Mother`s Day in quite some
time, with plenty of sunshine, warm advection, and breezy
southwesterly winds. Deep mixing will mix out dew points into
the mid 40s to around 50F and steep low level lapse rates in the
deeply mixed regime will contribute to gusts up to 30 mph. Climo
of progged 925 mb temps supports highs around 80F. With the
favorable set-up to overperform, we`re forecasting low-mid 80s
across northern and central IL (upper 70s to around 80F for
northwest Indiana). Shallow moisture at the top of the mixed
layer should again enable a Cu field in the afternoon. Can`t
rule out a stray shower or sprinkle late in the day (maybe an
isolated t-storm far north), but guidance that shows bonafide
convection appears well overdone with the dew point forecast. As
such, only have a sliver of slight chance PoPs late near the WI
state line.

Any showers and thunderstorms that develop closer to an
approaching cold front Sunday evening across northeast Iowa and
southern Wisconsin will likely being on a steady weakening trend
as they move into far northern Illinois. This will be due to
diurnally unfavorable timing, lack of large scale forcing, and
likelihood of prohibitive MUCIN. Have capped PoPs at low chance
(30%) north of I-88 Sunday evening, with slight ~20%) chances
down to about I-80. Cloud cover may remain scattered enough for
another Aurora viewing opportunity Sunday evening.

The upper level short-wave that will lead to the early work
week rain discussed in the long term section below will be far
enough removed to preclude any real focus for precip. overnight
tomorrow night. Isentropic ascent from a relatively stout low-
level jet will be the main source of lift. With some weak
elevated instability albeit with MUCIN, can`t rule out a few
additional spotty showers and maybe an isolated t-storm.
However, the unfavorable timing and likelihood of capping
supports keeping PoPs in the slight (15-20%) range. Steady
moderate southwest winds with occasional gusts up to 20 to
perhaps 25 mph will keep low temps much milder than tonight, in
the upper 50s to lower 60s.

Castro


Monday through Saturday:

The upper low currently across the Desert Southwest is expected
to be the next notable weather maker across the region late
Monday into Tuesday as it tracks eastward, in concert with an
associated surface low, across the Mid-Mississippi Valley into
the Ohio Valley. Locally, this storm system will favor waves of
showers (along with a few thunderstorms), particularly Monday
afternoon through at least the first half of the day Tuesday.
While this does not necessary look to be a significant heavy
rain maker for our area, persistent rainfall within an
environment featuring 1.3"+ PWATS through Tuesday morning may
result in localized rainfall amounts up around, or a just above,
an inch.

A small threat also exists for a period of thunderstorms with
this rainfall activity, particularly in association with an
approaching back door cold front dropping down the lake Monday
afternoon into the early evening. However, this threat will
quickly shift south of I-80 Monday night into Tuesday as cool
and breezy northeasterly low-level winds develop in the wake of
the front and along the northern/northwestern periphery of the
surface low. As a result, temperatures will be cooler on Tuesday
as inland (lakeshore) temperatures remain in the 60s (50s).

A surface high and upper-level ridge will move over the region
following the eastward departure of this system Tuesday night
into Wednesday. This will support a period of quieter and warmer
weather for the mid-week period (Wednesday into at least the
first half of Thursday). Accordingly, inland temperatures both
days look to rebound back into the 70s, though onshore flow will
keep conditions several degrees cooler near the lake.
Thereafter, there are signs in the ensemble guidance that the
weather pattern could turn a bit more active again, potentially
supporting some additional periods of showers and thunderstorms,
particularly Thursday night into Friday.

KJB

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1225 PM CDT Sat May 11 2024

The primary aviation weather concerns through the 18Z TAF period
include:

* A lake breeze shifting NW winds to easterly this afternoon/evening
  at the Chicago sites

NW winds will continue gusting upwards of 30 kt for the remainder of
the afternoon. A lake breeze just starting to protrude inland early
this afternoon is expected to move across the Chicago terminals in
the late afternoon/early evening abruptly shifting NW winds to
easterly. This wind shift is expected to occur at MDW near 22Z and
at ORD closer to 00Z. Gusts should be cut off behind the lake
breeze, although sustained winds may continue to move at around 10
kt through dusk. Winds will veer to southerly near or under 5 kt for
the late evening and overnight. SW winds will begin gusting into the
teens during the morning, possibly as early as daybreak. More
appreciable gusts into the 20-25 kt range are expected as early as
mid-morning, more likely that they hold off until the afternoon. VFR
can be expected throughout the period.

Doom

&&

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

&&

$$

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