663
FXUS63 KGRR 271854
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
254 PM EDT Thu Aug 27 2026
.KEY MESSAGES...
- Dry though Saturday
- Showers and Thunderstorms Saturday Night into Next Week
&&
.DISCUSSION...
Issued at 254 PM EDT Thu Aug 27 2026
- Dry though Saturday
We were originally a bit concerned about persistent low cloudiness
lasting into this afternoon due to local observed and forecast
soundings indicating a deep and nearly saturated surface layer.
However, formidable late August insolation is winning the day
growing an even deeper mixed boundary layer. Recent cloud erosion
over our central forecast area was impressively quick. This presumed
lower tropospheric subsidence continues to be well sampled by
GOES-E Lower Level Water Vapor (Channel 10) imagery. Moreover, we
saw slightly divergent surface flow per area observations earlier
today and that may have been an additional mesoscale downward
response in the wake of a subtle low level, low amplitude gravity
wave that appears to have worked southeastward through the flow
while creating local upticks and downticks in the depth and
coverage of stratocumulus observed this morning across much of
Lower MI.
As noted before, there are some model solutions, such as outlier
REFS members, that pop up isolated showers generally along and
southeast of a Lansing to Battle Creek line this afternoon. This
is a low probability outcome (around 10 percent). Thunderstorms
look especially unlikely due to expected strengthening of the
subsidence inversion that will keep conditional instability
confined well beneath the ice production layer.
Friday and Saturday still look dry with rather sharp upper shortwave
ridging upstream over the northern Plains and Upper Mississippi
Valley. Negative differential vorticity advection aloft downstream
of this feature and over the western Great Lakes will promote
continued deep tropospheric subsidence and surface pressure ridging.
- Showers and thunderstorms Saturday night into next week
Our greatest risk for significant weather beyond Saturday looks to
be Sunday night when there could be locally heavy rainfall. The
exact corridor in which this occurs remains in question. The
upper ridge will gradually deamplify while surface high pressure
exits east of the area. A plume of anomalously large PWAT (90+
percentile) will approach from the west and overspread most of
Lower MI by Sunday evening. By Sunday night, medium range ensemble
mean guidance develops a seasonably strong low-level jet (30+
knots at 850 mb and ~90 percentile) over the Midwest that should
be aimed towards Lower MI. This sets up a concern for locally
heavy rainfall; accordingly, WPC does put our area in a Marginal
risk for excessive rainfall from 12Z Sunday through at least 12Z
Tuesday.
Predictability really suffers after the expected round of
precipitation Sunday night into Monday as substantial convective
augmentation of the synoptic flow will be possible. The best guess
right now is continued unsettled conditions with episodic rainfall
through Wednesday. In general terms, there does seem to be a trend
towards the reestablishment of upstream upper ridging starting
Wednesday night that will return subsidence and reduce PWAT
magnitudes to more seasonal levels.
&&
.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 110 PM EDT Thu Aug 27 2026
Scattered diurnal Cu will lift through the afternoon before
dissipating this evening. Can`t rule out an isolated shower (10%)
at LAN/JXN but will leave out of TAFs given low confidence. Patchy
fog is possible once again overnight, but given low MVFR potential
(20%) thanks to dry advection and strong winds just off the
surface will keep all sites VFR. Any fog that does develop gives
way to diurnal Cu once again Friday. Brief periods of MVFR cigs
are possible like we saw this morning, but confidence is too low
in timing and coverage to include in TAFs.
&&
.MARINE...
Issued at 254 PM EDT Thu Aug 27 2026
Winds and waves continue to come down with current observations of
waves around one to two feet. Northwest winds will continue a
steady decline this evening and overnight with an associated
slow reduction in wave heights. Winds become more easterly into
Friday morning. The lake breeze will develop Friday afternoon with
waves heights around a foot or less.
Our next chance for Small Craft Advisory and High Swim Risk
conditions moves in Saturday and continues through at least Sunday
due to stronger southwest winds causing waves to build. Our next
chance for thunderstorms moves in Saturday night and continues
into next week.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...TJT
AVIATION...Thomas
MARINE...TJT/RAH
NWS GRR Office Area Forecast Discussion
