246
FXUS63 KGRR 081854
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
254 PM EDT Mon Jun 8 2026
.KEY MESSAGES...
- Rain and Thunderstorms This Afternoon into Tuesday
- Hot Wednesday
- Storms Wednesday night through Thursday night, severe possible
- Dry Friday, thunderstorm chances return for the weekend
&&
.DISCUSSION...
Issued at 254 PM EDT Mon Jun 8 2026
- Rain and Thunderstorms This Afternoon into Tuesday
No real changes to previous thinking. We are now at a short enough
forecast projection time to fully utilize the CAMs for assessing the
heavy rain threat. Starting with the SPC HREF, LPMM/PMM QPF
guidances advertises localized splotches of 2+ inches tonight into
early Tuesday. This looks plausible given that we are looking at
anomalously high precipitable water, nearly 13000 ft warm cloud
depths, and almost stationary Mesoscale Beta Element (MBE) vectors,
indicative of the potential for boundaries to synergize with
convection in a way that keeps precipitation slow-moving. All of
this being said, the individual CAM solutions point towards only
scattered and progressive storms that would reduce the threat for
heavy rain. That, when combined with relatively dry antecedent
conditions, reduces the threat for flooding somewhat; however,
rainfall rates could still be quite significant. Even half an hour
of intense rainfall like this could be enough for localized
flooding, especially across extensively paved areas.
For Tuesday, convection will eventually depart to the east and as
noted previously, thunderstorms could redevelop in the
afternoon/evening timeframe around US-127 during peak diurnal
destabilization. Suboptimal thermodynamics and kinematics will likely
keep this convection sub-severe.
Additional thunderstorms may develop with the warm front late
Tuesday night into Wednesday morning, otherwise chances hold off
until Wednesday night.
- Hot Wednesday
Wednesday looks to be the hottest day of the week with apparent
temperatures reaching or exceeding 100F farther south towards I-94.
Highs around 90F and dewpoints in the low to mid 70s are rather
unusual for this time of year, so people will likely be unaccustomed
to these type of conditions. The area will likely remain under
partly cloudy skies until Wednesday night when the next round of
thunderstorms enters the area.
- Storms Wednesday night through Thursday night, severe possible
An advancing upper level trough will bring increasingly southwest
and slightly difluent flow to the area Wednesday through Thursday.
This will provide ample synoptic forcing for multiple rounds of
thunderstorms. Precipitable water (PWAT) values will remain
anomalously high, approaching two inches, meaning that very
efficient rainfall can be expected with quick accumulations even for
the more rapidly moving storms.
As noted previously, we expect mainly remnant convection from WI
Wednesday night. Downstream conditional instability over Lower MI
will be quite strong with MUCAPE at or above 3000 J/kg. This suggests
an outflow-dominant MCS will be the most likely storm mode, yet
one still with the potential to create expansive damaging wind
gusts.
After a pause in precipitation for the first part of Thursday,
dynamic forcing for the Thursday night round of storms will be
particularly strong with cyclonic breaking of the upper wave across
the area in the 06-12Z Friday timeframe. Although this does coincide
with maximal diurnal stabilization, it`s highly plausible that an
MCS with an already established cold pool will be upstream and
poised to move into the forecast area. Furthermore, the shear and
instability parameter spaces look better balanced compared to
Wednesday night. This means probabilities are better for greater
organization, intensity, and longevity with this particular system
with the main threat being damaging winds.
- Dry Friday, thunderstorm chances return for the weekend
Dry air moves in behind the thunderstorms Thursday night bringing
a break in the rainfall along with cooler temperatures. Rain
chances return for the weekend with an upper level trough in the
vicinity. The best chances (30 to 50 percent) continue to be
Saturday night into Sunday as was also noted previously. This
consistency in model guidance helps confidence a little, but
predictability is simply not great at this time range after a
succession of other precipitation events. So, be prepared for a
possibly ever-changing weekend forecast.
&&
.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 147 PM EDT Mon Jun 8 2026
No real changes to the inherited TAFs except to refine timing of
onset of precipitation tonight based on radar trends and to
advertise IFR ceiling restrictions continuing after 12Z Tuesday.
These TAFs were already quite verbose due to persistent and hard-
to-time probabilities of thunderstorms, so didn`t want to add too
much detail after 12Z, but the upshot is that precipitation will
exit the area from west to east in the 12Z to 18Z Tuesday with a
gradual transition to VFR conditions.
&&
.MARINE...
Issued at 254 PM EDT Mon Jun 8 2026
Waves are expected to remain 2 feet or less through Wednesday
morning as winds remain light. Southeast winds are expected
through tonight before shifting to the southwest behind the low.
Rain and thunderstorms are expected late this afternoon into
Tuesday. Expect low visibilities within any thunderstorms as they
will be capable of heavy rainfall. The increased dew points over
the cold waters of Lake Michigan may also pose a threat for fog as
well. We`ll need to monitor conditions in case a Marine Dense Fog
Advisory is needed.
Winds and waves then pick up Wednesday afternoon into Thursday.
South to southwest winds gusting to around 25 knots will cause waves
to build to 3 to 6 feet especially for areas north of Holland and
around the Sable Points.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...TJT
AVIATION...TJT
MARINE...TJT/RAH
NWS GRR Office Area Forecast Discussion
