455
FXUS63 KGRR 031052
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
652 AM EDT Fri Jul 3 2026
.KEY MESSAGES...
- Thunderstorm chances continue through the holiday weekend
- Warm and humid conditions to persist
&&
.DISCUSSION...
Issued at 415 AM EDT Fri Jul 3 2026
- Thunderstorm chances continue through the holiday weekend
Thunderstorm chances will continue each day from today through
Sunday across Southwest Lower Michigan. We are in a
marginal/slight risk of severe weather today and a general
thunder risk for Saturday/Sunday via the Storm Prediction Center.
A diffuse stationary boundary remains in place across the
Southern Great Lakes this morning which is being augmented by
thunderstorm outflow. Rich boundary layer moisture remains in
place which will aid moderate instability once again today and
over the weekend as well. It is not until we get into Sunday night
and Monday before we get into less humid/unstable air.
Thunderstorms today will be driven by weak shortwaves moving
through the upper flow and localized convergence at the surface.
The SPC HREF shows a lull during the morning hours in the wake of
the current activity with a diurnal boost to the activity this
afternoon and evening, especially for areas near and south of
I-96. Machine learning output via Nadocast shows wind as the clear
main threat.
Saturday and Sunday the thunderstorm chances continue with
Saturday`s threat being driven by convective vort`s and Sunday`s
by a stronger wave moving through. Instability is still fairly
significant both days with the GFS showing north of 2,000 j/kg of
MUCAPE. Cannot rule out severe weather either day, especially on
Sunday when convection will get more of a synoptic boost from a
mid level wave and a surface cold front.
Heavy rain potential will exist today through Sunday as well with
PWAT values near 2 inches all three days. The flooding threat
would be short term excessive rain where storm drains will not be
able to keep up with the volume of water.
- Warm and humid conditions to persist
850mb temperatures remain warm today and on the forth. Highs today
will still reach the 90s over much of the area. 80s will be more
common on Saturday. We will maintain the current Heat Advisory as
is.
&&
.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 652 AM EDT Fri Jul 3 2026
VFR conditions are in place across all of Southwest Lower Michigan
at 12z. Showers have cleared to the east of all of the TAF sites.
We expect VFR conditions to prevail into the mid afternoon hours
or roughly through 20z or so. Conditions have stabilized in the
wake of the overnight showers and storms and it will take time to
build instability for new activity later today.
By mid afternoon we feel instability will have returned and a
round of showers and thunderstorms are likely between 20z and 03z.
Some storms will press in from the west while others develop
overhead. There is a slightly better chance of seeing
showers/storms at the I-94 TAF sites, but all TAF sites will
likely see some activity later today.
Winds are somewhat variable to begin to the day, but we expect
southwesterly winds to fill in at 5-15 knots at all sites today.
&&
.MARINE...
Issued at 415 AM EDT Fri Jul 3 2026
A fairly light wind regime is expected for the holiday weekend.
Winds for the most part will be in the 5 to 15 knot range from
today through Sunday. There is a brief window this evening where
southwest winds increase aloft and some of this wind could mix to
the surface. On Saturday we may see a southwest wind of 10 to 20
knots develop. Overall though it looks like waves of 1-3 feet or
less through the holiday weekend given the lighter winds. We
therefore are not expecting any wind/wave events to advisory
levels. We will see occasional thunderstorms today through Sunday,
some mariners and beach goers alike (both of which will be
plentiful this weekend) will need to keep an eye to the sky for
the threat of lightning.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 8 PM EDT this evening for MIZ046-051-052-
056>059-064>067-071>074.
MARINE...None.
&&
$$
DISCUSSION...Duke
AVIATION...Duke
MARINE...Duke
NWS GRR Office Area Forecast Discussion
