IWX issues Area Forecast Discussion (AFD) at Aug 1, 11:04 AM EDT010
FXUS63 KIWX 011504
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
1104 AM EDT Sat Aug 1 2026
.KEY MESSAGES...
- Chances (50-90 percent)for showers and storms through the
weekend, with the better chances tapering off from northwest
to southeast Sunday afternoon into Monday morning. Heavy rain,
gusty winds, and lightning are expected within any storms.
Localized flooding is possible, particularly Saturday night
into Sunday. Rain totals in excess of 2 inches are expected
for some areas, and possibly greater than 4 inches in areas
with more persistent rainfall or storm activity.
- There is a marginal risk for isolated strong to severe storms
this afternoon and evening in Indiana and Ohio, generally
south of US 30. The primary threat with any stronger storms
would be damaging wind gusts to 60 mph.
- Dangerous swimming conditions are expected at Lake Michigan
beaches along the La Porte County, IN and Berrien County, MI
shoreline. Life- threatening waves and currents are expected,
especially Sunday. A beach hazards statement is in effect. For
details, visit www.weather.gov/greatlakes/beachhazards
&&
.UPDATE...
Issued at 1047 AM EDT Sat Aug 1 2026
Near term forecast concern is on heavy rain potential and
isolated severe threat.
An impressive low level theta-e ridge is building across the
area this morning downstream of a mid/upper low centered across
west central Illinois. This theta-e ridge will begin to take on
more of a NW-SE orientation later this morning/early afternoon
due to cyclonic flow associated with this system. A band of
showers marking the eastward advance of this low level theta-e
ridge have had some impressive brief rainfall rates of 1 to 2
inches per hour with a pocket of 1 to 2 inch rainfall amounts. A
dry slot has pushed in behind this lead advective forcing band,
but convection is expected to fill in this afternoon/early
evening as upper vorticity advection increases and as modest low
level jet helps advect a 700-1200 J/kg MLCAPE axis northward to
roughly the US 24 corridor. Track of mid/upper level system will
eventually support deformation forced rain showers tonight into
Sunday morning. This leads to some concern for localized areas
experiencing very heavy rainfall amounts, particularly given
high efficiency rainfall expected with high PWATs/deep warm
cloud depths/strong low level moisture convergence. While
uncertainty remains with how extensive flood threat will be for
later today into Sunday, the potential certainly exists for
isolated areas to receive rainfall amounts in excess of 4
inches, particularly where more prolonged deformation sets up.
Will likely go ahead and include all of IN counties in a Flood
Watch valid from later this afternoon through Sunday afternoon.
The period of greatest concern may by this evening through
daybreak Sunday as deformation axis sharpens.
In addition to hydro threat, no change in previous forecast
thinking to the severe weather potential today. A Marginal Risk
of severe weather (mainly iso wind) remains intact roughly
south of US 24 where weak instability/moderate shear environment
should set up. Confidence remains quite low however, with
magnitude of instability being a limiting factor. Low level flow
is backed to the north of sfc reflection of this system for
areas south of US 24, so cannot completely rule out some iso
tornado potential, but this a very low probability and likely
maximized south/southeast of local area.
&&
.DISCUSSION...
Issued at 620 AM EDT Sat Aug 1 2026
The occluding surface low responsible for our active weather this
weekend is centered over southeastern IA/NW IL as of this writing,
with a broad shield of rain showers and isolated storms extending
from up near Milwaukee southeastward into Indy and KY/TN. A 500mb
trough encompasses the Great Lakes region, with the closed
low/associated speed max near the four corners. Ongoing steady rain
showers or drizzle extends from from Michigan City, IN into Marion,
IN and is lifting northeast with time. Beyond that, light east-
northeast flow persists across the forecast area, with some light
shower activity in Lower MI and near Lima, OH.
As the trough aloft/closed low digs southward into southern
IN/KY through Sunday morning, the surface low drifts eastward,
centering around IND by 2 am EDT tonight (models still don't
quite have the exact location pinned down). Shower activity will
become more widespread through the afternoon into tonight as
the better upper level forcing arrives and several waves of
precip rotating around the surface low to our S-SE move through.
Much of the guidance has a persistent/recurrent rainfall along
and south of US 30 today into tonight as the low pivots, and
then by Sunday a robust deformation zone extending from the low
near Indy (depends on the model) up into southeast Lower MI. The
NAM really latches onto this, and it appears to be the furthest
north of the solutions (centers low from Indy to near
Logansport, IN). This keeps the axis from Logansport into
Hillsdale through much of Sunday. There is still lower
confidence as to whether this feature develops as robustly as
indicated, and if it sinks southeastward with time (thus moving
the precip axis and distributing the rain) or stays in generally
the same location through Sun. If it stays stationary like the
NAM depicts, some areas that see repeated thunderstorms or heavy
rain could end up with 4 inches of rain or more. After a review
of the latest guidance with the neighboring offices, decided
not to issue a flood watch given there are still questions as to
where the band/earlier showers and storms set up and if they
move or stay relatively stationary into Sunday.
There is a marginal risk for isolated strong to severe storms this
afternoon and evening in Indiana and Ohio, generally south of US 30.
The primary threat with any stronger storms would be damaging wind
gusts to 60 mph. Models suggest around 500-1000 J/kg of surface CAPE
this afternoon, with 0-6 km bulk shear around 25-40 knots
along/south of US 30, which is plenty to work with in terms of
stronger storm potential.
Otherwise, low chance pops (20-40 percent) through the work week,
with highs in the 70s, low-mid 80s.
High swim risk and beach hazards statement for La Porte County,
IN and Southern Berrien County, MI from late this afternoon into
Monday morning. Winds strengthen out of the northeast at 15 to
25 knots and become more northerly through Sunday night. Waves
of 1-2 feet today will build to around 3-5 feet by late this
afternoon and evening (highest near New Buffalo, MI into
Michigan City, IN). On Sunday, waves will build to 4 to 7 feet
by the late afternoon.
Northern Berrien County, MI (including Silver Beach) will see
lower wave heights today, generally 1 to 2 feet building to
around 3 feet by late this afternoon/evening. Waves linger in
the 2-3 ft range until late Sunday afternoon, where they build
to 3 to 5 feet. Have a moderate swim risk for today (into early
Sunday), and then a high swim risk for Sunday afternoon into
Monday morning. The Beach Hazards Statement for this county is
in effect starting late Sunday afternoon.
Expect a strong southward flowing longshore current to develop
with the north-northeast flow later today into tonight and
persist through Sunday, in addition to strong structural
currents (particularly on the north sides of piers and
breakwalls). Rip currents are expected, especially where wave
heights are greatest and flow is more northerly. If visiting the
beaches this weekend, monitor the beach forecast.
&&
.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 726 AM EDT Sat Aug 1 2026
A vigorous vort max and a stacked low pressure system moves
southeastward to southern IN from Western IL, which is a slow
pace. A theta-e plume pivots eastward especially through
southern parts of the forecast area bringing the potential for
flooding as well as reduced flight conditions. MVFR conditions
collapse to low MVFR and IFR after 00z tonight. Given cloud
cover, felt more comfortable including showers, but not as
comfortable including thunderstorm potential. It is possible
that MVFR VISBY dips into IFR if thunderstorms do materialize.
Heaviest rain moves through this afternoon and tonight before
slowly departing through the day Sunday.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Flood Watch from 5 PM EDT /4 PM CDT/ this afternoon through
Sunday afternoon for INZ005>009-012>015-017-018-020-
022>027-032>034-103-104-116-203-204-216.
Beach Hazards Statement from 4 PM CDT this afternoon through
Monday morning for INZ103.
OH...None.
MI...Beach Hazards Statement from 5 PM EDT this afternoon through
Monday morning for MIZ277.
Beach Hazards Statement from Sunday afternoon through Monday
morning for MIZ177.
MARINE...Small Craft Advisory from 5 PM this afternoon to 5 AM EDT
Monday for LMZ043-046.
&&
$$
UPDATE...Marsili
DISCUSSION...MCD
AVIATION...Roller
Source:
IWX issues Area Forecast Discussion (AFD) at Aug 1, 11:04 AM EDT---------------
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