278
FXUS63 KIWX 231029
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
629 AM EDT Sat Aug 23 2025

.KEY MESSAGES...

- There are low chances (10-30%) for isolated showers and storms
  today, mainly in the afternoon and evening.

- Significantly cooler than normal temperatures Sunday through
  Tuesday with lake effect rain showers possible at times.

- Dangerous swimming conditions for southeast Lake Michigan
  beaches possible Sunday into Monday.

&&

.DISCUSSION...
Issued at 301 AM EDT Sat Aug 23 2025

Isolated showers and storms are possible today, although
unfortunately, the chances are low (10-30%). A large area of low
pressure is currently centered over the Hudson Bay in northern
Ontario. It`s attendant cold front is draped from Ontario down
across the Upper Midwest. This cold front will move eastward
today and begin a welcome pattern shift towards cooler weather
in the days ahead. The HRRR and NAM are both showing potential
for some prefrontal showers and/or drizzle this morning before
the cold front sweeps through this afternoon and evening,
providing enough lift to warrant isolated showers and storms
developing. Unless under a heavier shower or storm, rain totals
will generally be less than 0.10" today due to mid level dry air
and waning instability.

Behind this front, strong CAA will push a refreshing,
notably cooler airmass across much of the Midwest and Great
Lakes. With cold air moving over the relatively warm waters of
Lake Michigan, expect lake effect clouds and showers late Sunday
into the day on Monday and again potentially on Tuesday.
Soundings near Lake Michigan depict a favorable environment for
lake effect showers with low level convergence along a trough
that pivots through early Monday aided by a strong 500 mb
shortwave, low level cyclonic flow, delta Ts >13C, and tall
inversion heights of 7-8 km. Can`t rule out potential for
waterspouts as well, especially if the low level convergence
sets up near the lake on Monday. Have added in slight chances
(20-30%) for waterspouts to our nearshore zones from 8 PM ET
Sunday to 2 PM ET Monday in collaboration with neighboring WFOs.
With the lake effect showers and breezy northwest winds, it
will feel much more like fall to start the new work week! High
temperatures on Monday and Tuesday will struggle to reach 70
degrees, especially in areas closer to Lake Michigan where there
will be more lake effect cloud cover. Meanwhile, particularly
away from the lake where there will be breaks in cloud cover,
Monday and Tuesday nights will be crisp with near-record lows in
the mid to upper 40s!

As a large area of surface high pressure builds across the central
CONUS midweek, expect dry conditions to persist through much of the
week. Temperatures gradually rebound towards more seasonable
levels by the weekend (with highs near 80 degrees). &&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 102 AM EDT Sat Aug 23 2025

Stayed close to the existing TAFs for the 06z cycle. Stratus
clouds are slowly developing beneath breaks in the upper-level
altocumulus. Ceiling trends will be monitored closely with a
couple of MVFR obs noted upstream in a sea of otherwise VFR
ceilings. A weak cold front is still expected this afternoon.
Radar returns this hour across MN are rather paltry; same for
model guidance locally this afternoon. Thus, the dry TAF
remains.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 624 AM EDT Sat Aug 23 2025

Pre-frontal area of isolated showers is moving across IL this
hour. By my eyes, ASOS/AWOS remains dry beneath these isolated
showers. Dew point depressions are modest, thus an overall dry
atmospheric column is the culprit for the dearth of rain
reaching the ground this hour.

Late this afternoon, the trailing upper-level trough swings
through. High resolution guidance suggests additional isolated
showers are possible at KFWA on either side of 00z. Will pass
this on to the incoming shift for further consideration.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Johnson
AVIATION...Brown