585
FXUS63 KLOT 241921
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
221 PM CDT Sat May 24 2025

.KEY MESSAGES...

- The pattern through next week will be relatively stagnant with
  below to near-average temperatures for this time of year and
  limited opportunities for widespread, soaking rainfall.

&&

.DISCUSSION...
Issued at 221 PM CDT Sat May 24 2025

Through Monday Night:

Quiet weather conditions will persist the remainder of the
afternoon, albeit with increasing cloud cover into this evening in
advance of our next mid-level impulse dropping southeastward into
the Upper Midwest. This impulse is forecast to slide east-
southeastward across the western Great Lakes tonight into Sunday
along an enhanced belt of uppper-level westerlies and a lower-
level baroclinic zone. Model guidance has trended more bullish
with rainfall prospects across the area tonight into Sunday
morning, owing largely to a stronger low to mid-level
frontogenetic response overhead. While this does not look to be a
significant rain event, it does appear that we will have some
light rain showers developing overhead across northern IL later
this evening and overnight. With this in mind, we have continued
the trend of inching up POPs and going with areal coverage wording
with the rain showers after midnight tonight through Sunday
morning. Fortunately, the threat of rain is expected to gradually
sag southward into central parts of IL and IN later Sunday morning
into the afternoon, so areas along and north of I-80 should dry
out for the afternoon.

Outside of the rain chances tonight into Sunday, Sunday will
again feature persistent onshore flow as surface high pressure
remains anchored over across south central Canada into the western
Great Lakes. This pattern will thus continue to foster the
coolest conditions, with highs in the 50s along and near the Lake
Michigan shore. Farther inland, expect temperatures to generally
top out in the 60s. Similar conditions are slated for Memorial
Day, albeit a couple degrees warmer.

KJB

Tuesday through Saturday...

A blocky upper-level pattern is likely to set up and persist
across North America next week as anomalous upper ridging
dominates across the high latitudes of Canada. This larger scale
pattern will generally favor slow eastward moving and evolving
weather systems across the CONUS through the week. The main system
we will be keeping any eye on for our area is the upper trough
currently shifting onshore across the California coast. This
feature is expected to gradually shift eastward through the
holiday weekend before potentially interacting/merging with a
northern stream wave somewhere over the northern Plains early next
week. As this occurs, ensemble guidance continues to favor the
development of a slow eastward moving closed upper low from the
Upper Midwest into the western Great Lakes during the middle to
latter half of next week.

Unfortunately, the overall complex nature of this evolving
weather pattern continues to stunt forecast confidence to some
degree. This is particularly the case in regards to the exact
track, timing and strengthen of this closed low feature as it
shifts from the Upper Midwest into the western Great Lakes during
the middle to later half of next week. These finer scale details
will ultimately play a large role in how much rain falls across
our area during the midweek period. Nevertheless, our chances for
showers return to the forecast by Tuesday, with our greatest
chances (50-60%) for rain looking to come late Tuesday afternoon
through Tuesday night. Thereafter, additional isolated to widely
scattered diurnal showers and perhaps a few thunderstorms remain
possible (20% chance) through the end of the week as the upper low
tracks over the Great Lakes.

Temperatures through the period are expected to generally be in
the low to mid 70s, particularly for inland areas. However, the
cooler by the lake theme will persist through next week as
persistent onshore flow continues. Accordingly, expect conditions
to remain several degrees cooler along the lakeshore each day.

KJB

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1231 PM CDT Sat May 24 2025

VFR conditions are expected through the current TAF window. Winds
are slowly moving from the southeast to the east-northeast as a
lake breeze increases this afternoon. Wind gusts up to 20 knots
are possible. Since the thinking is for more occasional gusts
to 20 knots rather than sustained, any formal mention of gusts
were left out of the TAF.

Models are showing some consistency for showers overnight, which
increased the chance to around 30 percent. So the VCSH was
converted to a PROB30 for the chances for showers at the
terminals. These showers are expected to be VFR with no impacts
to cigs or vis. No shower mention currently for RFD since the
better coverage is to the south.

Drier conditions on Sunday with a return of east-northeast winds
around or just above 10 knots with gusts up to 20 knots in the
afternoon.

DK

&&

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

&&

$$

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