546
FXUS63 KGRR 081050
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
650 AM EDT Mon Jun 8 2026
.KEY MESSAGES...
- Rain and Thunderstorms This Afternoon into Tuesday, Hot
Wednesday
- Chances for Storms Wednesday Night through Thursday Night,
Severe Possible
- Dry Friday, but Rain and Thunderstorm Chances Return for the
Weekend
&&
.DISCUSSION...
Issued at 307 AM EDT Mon Jun 8 2026
- Rain and Thunderstorms This Afternoon into Tuesday, Hot
Wednesday
An active stretch of weather is expected this week starting with
later this afternoon into Tuesday.
The shortwave trough over Missouri will slowly move northeast
bringing with it plenty of moisture with precipitable water values
around 2 inches. Instability will be increasing through the day
with MUCAPE values around 500 to 1000 J/kg continuing overnight.
While severe thunderstorms are not expected, localized heavy
rainfall is possible. In this high moisture environment any
thunderstorm will produce heavy rainfall rates. Coverage however
will be scattered and areas that see storms linger over the
longest or train over repeatedly will have the best chance to see
1 inch or more of rain. The HREF localized probability-matched
mean shows pockets of 1 to 3 inch amounts across the forecast area
over 24 hour period. These amounts may cause brief localized
flooding.
As the shortwave departs Tuesday instability will increase during
the afternoon with mean MUCAPE values around 1000 to 1500 J/kg
mainly along and east of US-131. We could see some additional
thunderstorms as the 850mb front moves through during the
afternoon. Some stronger storms are possible with sub-severe winds.
Additional thunderstorms may develop with the warm front late
Tuesday night into Wednesday morning, otherwise chances hold off
until Wednesday night.
Wednesday looks to be the hottest day of the week with 925mb
temperatures around 25 C with highs in the upper 80s to low 90s.
Dew points in the 70s would result in heat indices in the 90s with
some spots approaching 100.
- Chances for Storms Wednesday Night through Thursday Night,
Severe Possible
An advancing upper level trough will bring southwest flow to the
area Wednesday through Thursday. This will set the stage for
multiple rounds of thunderstorms within a very moist environment.
Each round of storms will likely see perceptible water values
around 2 inches. The difference with this set up compared to
tonight into Tuesday`s is that the trough is stronger with upper
level jet support along with a stronger low level jet. This will
bring the potential for severe thunderstorms with a Mesoscale
Convective System (MCS) set up for both Wednesday night and
Thursday night. We may be on the edge for Wednesday night as
thunderstorms move in from Wisconsin and weaken as they track
eastward across the lake into Michigan. The best potential for
severe storms will be across western portions of the forecast area
with winds as the primary concern.
Depending on how fast we can clear out Thursday morning will
determine if we see storms develop during the day ahead of the
next MCS Thursday night. The low level jet will not be present
during the day but will ramp up again Thursday night bringing
plenty of shear with the shortwave trough. Winds will again be the
primary concern with the line of thunderstorms.
Both rounds will be capable of heavy rainfall and could lead brief
minor flooding, especially in known trouble spots.
- Dry Friday, but Rain and 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. However
rain chances return for the weekend with the upper level trough
remaining in the area. The best chances (30 to 50 percent) are
Saturday night into Sunday. However the pattern is rather messy,
with not much agreement between the various clusters of ensembles.
Expect more clarity as we get closer.
&&
.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 650 AM EDT Mon Jun 8 2026
High clouds will be present for most of the day with easterly
winds becoming southeasterly. Between 20Z to 06Z isolated to
scattered thunderstorms will be possible. Hit and miss showers and
thunderstorms will continue through the overnight, therefore kept
and thunderstorm mention in the Prob30 group into Tuesday morning.
Thunderstorms will be capable of heavy rainfall. Depending on how
fast thunderstorms move or if multiple thunderstorms train over
the same area, rainfall amounts could exceed an inch by Tuesday
morning.
Ceilings will gradually lower to MVFR and then IFR levels by 12Z
Tuesday.
&&
.MARINE...
Issued at 307 AM 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.
Southwest winds gusting to around 25 knots will cause waves to
build to 3 to 6 feet especially for areas north of Holland.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...RAH
AVIATION...RAH
MARINE...RAH
NWS GRR Office Area Forecast Discussion
