091
FXUS63 KGRR 052335
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
735 PM EDT Tue Aug 5 2025

.KEY MESSAGES...

- Slight Chances (20%) for Pop-Up Storms

- Becoming Hot and Humid into the Weekend

&&

.DISCUSSION...
Issued at 315 PM EDT Tue Aug 5 2025

- Slight Chances for Pop-Up Storms

Overall dry conditions are expected through the weekend except
for a couple slight chances for showers and thunderstorms. We`ll
need to monitor some weak shortwaves and positive vorticity
advection riding the ridge into the area. Some CAMs highlight the
potential for an isolated shower or storm toward the Lansing and
Jackson areas later this afternoon and early evening. There is
some moisture available that is seen with the cumulus field that
has developed, however for thunderstorms to develop they`d need to
overcome the warmer air aloft. Overall with the lack of forcing
and the inversion in place, only expect the cumulus field which
will scatter out this evening as the sun sets.

Wednesday there will be some positive vorticity advection moving
through the 500mb flow on the backside of a weak shortwave. The
placement of this lift focuses more so on eastern portions of the
area toward the 127 corridor. Soundings in this area look to
erode the inversion aloft allowing for the chance (20-30 percent)
of showers and storms. These would be your general variety pop-up
thunderstorms that may have some gustier winds in them when they
collapse due to the weak atmospheric wind fields. Similar
conditions are possible Thursday, but confidence is not high
enough at this time to include in the forecast.

- Becoming Hot and Humid into the Weekend

As high pressure shifts east we move more into southerly flow at
the surface advecting a more hot and humid air mass into the area.
Dew points gradually increase into the mid 60s tomorrow and into
the upper 60s to low 70s for the weekend. Air temperatures
gradually increase into the upper 80s to low 90s resulting in heat
indices in the mid 90s over the weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 737 PM EDT Tue Aug 5 2025

Isolated rain showers will impact parts of SW Lower Michigan
early this evening /through roughly 01Z/ before the diurnally-
driven clouds /5-6kft/ dissipate. For the rest of the night,
scattered clouds and light E/NE winds /under 10kts/ will prevail.
Areas of MVFR fog/haze will likely develop once again between
08-12Z. Wednesday`s weather should be similar to today`s, with
diurnal CU developing midday all areas, and a small risk for
showers mainly E of LAN-BTL line.

&&

.MARINE...
Issued at 315 PM EDT Tue Aug 5 2025

Mariners can expect quiet weather to continue on Lake Michigan, as
high pressure located northeast of the Great Lakes provides light
E/SE breezes of generally 10 kts or less (though onshore lake
breezes may develop both this afternoon and Wednesday afternoon).
Waves will generally be calm to one foot. Expect pockets of light
haze or fog, mainly overnight. Winds will remain light through much
of this week, before a modest uptick in southerly winds occurs
Friday and Saturday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Air Quality Alert until midnight EDT tonight for MIZ037>040-
     043>046-050>052-056>059-064>067-071>074.
MARINE...None.

&&

$$

DISCUSSION...RAH
AVIATION...Smith
MARINE...Smith