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794
FXUS63 KLOT 301702
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1202 PM CDT Thu May 30 2024

.KEY MESSAGES...

- Dry and pleasant weather persists through Friday as
  temperatures gradually warm.

- Showers and a few thunderstorms on Saturday.

- Periodic chances of showers and storms during the earlier half
  of next week.

&&

.DISCUSSION...
Issued at 306 AM CDT Thu May 30 2024

Through Friday:

Surface high pressure will dominate across the western Great Lakes
today. This will result in more pleasant and sunny late May
weather today. A light onshore east-northeasterly wind through the
day will create the typical "cooler by the lake" conditions again
today. However, temperatures will be a couple of degrees warmer
areawide then those observed on Wednesday. Accordingly, inland
locations are expected to top out in the low to mid 70s, while
areas along the Lake Michigan shore can expect mid to upper 60
degree readings.

Following another cool and quiet night tonight, conditions will
continue to moderate on Friday as the surface flow turns back to
a southerly direction following the eastward departure of the
Great Lakes surface high. Temperatures should thus take another
upward jump Friday afternoon, with most inland locations expected
to top our around the 80 degree mark. A lingering onshore
southeasterly wind component will again result in a bit cooler
weather across the IL shores, however. Skies should start the day
sunny, but increasing cloudiness is expected through the day as
moisture begins to increase in advance of our next approaching
weather maker for Saturday. This will thus make for a partly
cloudy/sunny end to the day.

KJB


Friday Night through Wednesday:

We`re still on track for a rainy start to our upcoming weekend
here as a system of showers and probably some embedded
thunderstorms moves across the area on Saturday. A cutoff low
will spin up over the central Plains late Friday and cling onto
an existing cold front as it begins its trek across the Midwest.
An swath of showers and thunderstorms is then expected to push
into the western CWA early Saturday morning. Confidence in the
path of the low has grown considerably since this time
yesterday. This is good news considering the track should
basically dictate thunder coverage in our area, though some
uncertainty still remains. Models now agree that the low will
pass right through the heart of the CWA or just to our south in
central IL, or somewhere in between. There is strong agreement
that just about all of the available instability suitable for
convection will fail to make it north of the low track.
Therefore, the thunderstorm potential should be confined
accordingly to near and south of the low track while showers
look likely along the cold front north of the embedded
circulation. The majority of guidance does squeeze at least
several hundred joules of tall, skinny CAPE into our south and
southeast promoting what looks like a decent chance for some
embedded general thunderstorms. If a farther north track
verifies, the thunder potential will expand northward deeper
into the CWA.

Such CAPE profiles in a deep moisture-rich environment with
decent synoptic forcing typically amount to a good setup for
soaking downpours and healthy rainfall totals. A lot of models
are resolving a swath of 1-1.5" of QPF focused near and south of
the low track. This raises some concern for a localized
flooding threat, right now favored in our south and southeast
CWA. We should start to see the rain begin to clear away from
west to east by the end of the morning with afternoon and
evening rain chances mainly focused east of I-55.

The rain will help keep conditions relatively cooler for
Saturday with highs progged in the lower 70s. Temperatures
will quickly rebound for Sunday with lower 80s in the forecast.
Conditions will be noticeably cooler along lake on Sunday,
especially along the Illinois lakeshore. Expecting mostly dry
conditions on Sunday, perhaps with a few isolated showers
popping up in the afternoon.

Still eyeing Monday for the potential for stronger thunderstorms
in the region as a cold front looks to move across. Temperatures
well into the 70s with dewpoints slated to reach the upper 60s
should build a noteworthy reservoir of instability ahead of the
front. Medium range guidance continues to offer poor deep layer
shear profiles, certainly more meager than you would want for
deep organized convection. Additionally, forcing for ascent,
both along the boundary and from features aloft, doesn`t stand
out at all. It`s very possible though that the favorable
thermodynamic environment makes up for the poor parameter space
otherwise and fires up some stronger thunderstorms. Although,
modeled CAPE values are generally south of what I would
normally look for in a true high CAPE-low shear severe
environment coming in at 1,500 to as many as 2,500 J/kg. It may
be worth noting that the SLU CIPS, CSU, and GEFS severe prob
guidance continue to highlight Monday across the region,
although the output has become overall more diffuse since
yesterday. Nonetheless, Monday will be one to keep an eye on
over the coming days.

Confidence is high in the early summer-like heat continuing well
into next week with 80s likely through the middle of the week.
Medium range guidance has been consistent in bringing another
storm system through on Wednesday with some impressive
parameter spacing to work with alluding to another possibility
for stronger thunderstorms somewhere in the region.

Doom

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
-- Changed Discussion --
Issued at 1202 PM CDT Thu May 30 2024

VFR conditions with cirrus are expected through the period. NE
winds around 10 knots will diminish tonight while veering SSE by
sunrise Friday. Variability between 160-190 degrees is expected
Friday morning before a lake-enhanced wind shift settles
directions ESE mid to late afternoon.

Kluber
-- End Changed Discussion --

&&

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

&&

$$

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