309
FXUS63 KGRR 071803
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
203 PM EDT Sun Jun 7 2026
.KEY MESSAGES...
- Heavy rain possible Monday night into Tuesday
- Thunderstorms, some severe, likely Thursday/Thursday night
- Possibly dry Friday, then a chance of storms this weekend
&&
.DISCUSSION...
Issued at 203 PM EDT Sun Jun 7 2026
- Heavy rain possible Monday night into Tuesday
The prospects for locally heavy rain beginning Monday night continue
to grow. Forecast soundings advertise precipitable water (PWAT)
values up around 2 inches; this climatologically rare setup has been
supported by ECMWF ensemble guidance, ranking around the 99th
percentile. As one might expect with such a deep and nearly
saturated layer, warm cloud depths around 13000 feet look likely,
supportive of highly efficient rainfall. Finally, and perhaps most
impressively, forecast soundings show a nearly stationary Mesoscale
Beta Element (MBE) motion vector that results from deep, moderately
weak, and highly uniform flow from the altitude at which the low
level jet typically resides all the way through the entire storm
bearing layer. This is very favorable for quasi-stationary back-
building MCSs...a preview of which we have already seen earlier
today across north TX near the Red River (please reference recent
WPC Mesoscale Precipitation Discussions).
The best upper PV forcing and plume of greatest PWAT may still be
slightly upstream at this time, more towards WI, but we still expect
convection to enter far southwest Lower MI around midnight Monday
night and this activity could provide a requisite MBE-caliber
surface boundary to later serve as an anchor point for locally
heavy rain.
The focus for heavy rain continues and perhaps even increases
through Tuesday as the aforementioned forcing and PWAT plume both
cross Lower MI.
Thunderstorm chances around 30 percent continue late Tuesday night
into Wednesday night as a northern Plains upper trough slowly
approaches and provides a steady stream of difluent flow aloft and
implied synoptic ascent coupled with it.
- Thunderstorms, some severe, likely Thursday/Thursday night
The previously mentioned northern Plains upper trough is forecast to
break cyclonically across the western Great Lakes. Moderately strong
southwesterly lower tropospheric flow will yield 0-3 km bulk shear
around 30 knots around the same time ECMWF ensemble mean MUCAPE
climbs to 3000 J/kg. Some mid-level drying will enhance DCAPE as
well, meaning that damaging winds associated with multicell
clusters will be possible from late Thursday into Thursday night.
Temperatures and apparent temperatures could get quite warm prior
to convective initiation, but the duration should be curtailed at
least some.
- Possibly dry Friday, then a chance of storms this weekend
Flow aloft behind the breaking upper trough becomes zonal and then
west-southwesterly, offering many opportunities for transient upper
PV maxima to provide forcing for additional deep convection. But,
predictability with identifying (let alone timing) features such as
these tends to be very poor in a season that already has poor
predictability. It is therefore not surprising that ensemble
solutions are trending towards what are basically climatological
PoPs (20-30 percent) during the weekend.
&&
.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 122 PM EDT Sun Jun 7 2026
VFR expected through this TAF period before turning more active
beyond 18z Monday. Light winds continue through this afternoon and
tonight. ESE winds especially after 12z Monday will pick up a bit,
and may have to trend winds a bit higher with the 00z package.
Can`t rule out some gusts close to 20 kts especially Monday
afternoon, but will take another look. Thunderstorm chances will
be increasing from S to N after 18z Monday and may need to include
mention for some sites with the 00z set.
&&
.MARINE...
Issued at 203 PM EDT Sun Jun 7 2026
No marine headlines are anticipated through at least Tuesday,
although marine fog may be an issue once again mainly over the open
waters tonight. Thunderstorms enter the area Monday afternoon with
better chances Monday night into Tuesday. Additional chances for
storms exist for Wednesday and Thursday.
The next chance for Small Craft Advisory (SCA) conditions looks to
be Wednesday into Thursday with stronger southwest winds. The longer
fetch areas associated with this wind direction (generally from
Grand Haven northward) can expect SCA conditions along with
potentially high risk swim conditions.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...TJT
AVIATION...Hoving
MARINE...TJT
NWS GRR Office Area Forecast Discussion
