232
FXUS63 KGRR 251814
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
214 PM EDT Wed Jun 25 2025

.KEY MESSAGES...

- Several Rounds of Showers and Storms Over The Next Week

- Hot and Humid Weather Returns Thursday

&&

.DISCUSSION...
Issued at 214 PM EDT Wed Jun 25 2025

- Several Rounds of Showers and Storms Over The Next Week

This afternoon should be dry for most, though widely scattered
showers and thunderstorms may develop. The best chance is for areas
near and south of I94 near a slow moving boundary. Cannot completely
rule out an isolated gusty storm, however the passage of the
aforementioned boundary will leave little in the way of surface
based instability. This should keep the best potential of damaging
winds south of the area.

Precipitation returns late tonight and early Thursday morning. The
best chance for precipitation will be across Central and Northern
Lower Michigan where low-level jet convergence will enhance forcing,
though isolated WAA driven showers may occur across Southern
Michigan. Forecast soundings suggest enough instability will be
present to support isolated thunder.

Tonight into Thursday sees the frontal boundary lifting north as a
warm front keeping scattered showers and storms in the forecast.
Exact timing and placement of any thunderstorm activity remains
unclear given the reliance on the location of the warm frontal
boundary. With the boundary comes higher dewpoints and thus surface
based instability. While shear will generally be marginal (20-30
knots) strong instability will be present with MLCAPE values aoa
2500 J/kg. This will be supportive of isolated strong to severe
damaging winds from wet microbursts in any storms that develop.

A cold front then swings through Friday as a low pressure system
moves through the region. Frontal timing will determine how much, if
any, of the area will be at risk for strong to severe storms as this
front comes through. As of now the best potential for thunder is
across our southeastern forecast area towards Lansing/Jackson Friday
afternoon. Winds are the main concern if a stronger storm can
develop, though confidence is low given variance in forecast frontal
timing.

The other concern is for locally heavy rainfall given the very moist
airmass and weak flow in place. In particular any training resulting
from storm redevelopment along outflow boundaries may support minor
flooding over urban/poor drainage areas. This will be a concern
through Friday when the cold front scours out some of the moisture.

We dry out Saturday behind the front as a period of weak ridging
crosses the area. The arrival of a longwave trough and a parade of
embedded shortwaves will bring the potential for showers and storms
back later Sunday into the work week next week.


- Hot and Humid Weather Returns Thursday

Heat index values have largely held in the 80s today thanks to
persistent cloud cover, though isolated values in the low 90s may
approach I94. Hot and humid conditions return Thursday through the
weekend as dewpoints climb into the mid 60s to mid 70s and highs
climb into the 80s to low 90s. This may result in heat indexes
approaching 100F during this period.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 125 PM EDT Wed Jun 25 2025

A stalled frontal boundary near I-94 is resulting in cooler but
cloudy/showery conditions north the boundary and a bit more
sunshine south of the boundary...closer to the I-94 terminals.
Considerably drier air...dewpoints in the 40s/50s was noted over
the northern half of Lower MI and some of that drier air will try
to work south later this afternoon on northeast winds. Eventually,
later tonight, the frontal boundary will move north again. We`ll
see some fog develop and then burn off by mid morning. MVFR
cigs/vsbys are are expected late tonight.

&&

.MARINE...
Issued at 156 PM EDT Wed Jun 25 2025

Northeast winds will become southerly tonight around 10-15 knots
and continue through the weekend. Thus, wind and waves will not be
hazardous to boaters nor beach goers. Scattered thunderstorms
through Friday, however, will pose a threat.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Thomas
AVIATION...04
MARINE...04