979
FXUS63 KGRR 041806
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
206 PM EDT Tue Aug 4 2026
.KEY MESSAGES...
- Unsettled pattern over the next 7 days
- Seasonable temperatures are expected through the forecast period
&&
.DISCUSSION...
Issued at 206 PM EDT Tue Aug 4 2026
- Unsettled pattern over the next 7 days
Unsettled conditions are expected over the course of the next 7
days with upper troughing overhead or nearby much of the time. At
the surface, mid summer moisture levels will be in place with dew
points at least in the 60s if not around 70 degrees. This level of
moisture combined with some mid level cooling due to troughing in
the mid levels will set the stage for some build up of afternoon
and evening instability each day. Bottom line is we are looking
periodic chances for showers and storms through the period. The
main question is trying to nail down the time frames for the best
chances for showers/storms.
As for the details, the first good opportunity for showers and
storms will occur Wednesday into Wednesday night as a weak cold
front moves in from the northwest. Chances actually begin late
tonight as the front approaches in the northwest CWA. We have
likely pops at times in our gridded forecast late tonight through
Wednesday night. Most unstable CAPE values increase into the
500-1000 j/kg range at times so thunder is certainly possible.
Locally heavy rain will likely be the main threat.
The front goes south of the forecast area but remains nearby
Thursday into Friday. Some model differences make the remainder of
the forecast a bit lower confidence given a rather benign surface
pattern. Given a predominant northwest flow/upper trough in the
mid level it is hard to rule out at least small pops Thursday
through next Monday. We could see some rain totals add up in spots
through the 7 days, but rivers have plenty of room given low
flows. Some short term advisories are certainly possible given the
moisture values (approaching 2 inches at times).
- Seasonable temperatures are expected through the forecast period
Temperatures look to remain seasonable despite the upper
troughing. 850mb temperatures are in the middle teens C which
make highs in the 80s likely each day.
&&
.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 145 PM EDT Tue Aug 4 2026
SCT to BKN 4-5kft CU field /VFR/ will continue through the
afternoon away from Lake Michigan, thanks to diurnal heating and
dew points in the low-mid 60s. CU will fade later this afternoon
and this evening, as S-SW breezes around 10 kt today become light
tonight.
Attention then turns to a weakening cold front currently over WI.
This boundary will weaken further and essentially wash-out as it
moves into Lower MI early Wednesday. Still, with some moisture
pooling along boundary and weak convergence, a small risk for
showers warranted at MKG /after 08Z/ and GRR /after 12Z/. These
showers may briefly produced MVFR vsbys.
Elsewhere /AZO-BTL-LAN-JXN/ rain-free VFR conditions are expected
through 18Z Wednesday with a light S-SW breeze.
&&
.MARINE...
Issued at 206 PM EDT Tue Aug 4 2026
Small Craft Advisory across our northern marine zones north of
Whitehall continues into this evening. The event looks very
marginal with 3-4 footers potentially in the outer reaches of the
0-5nm nearshore zone. It is for this reason we do not have a
corresponding Beach Hazards Statement out. The winds and waves
both look marginal, but the reason we decided to keep it out is
that the winds are just beginning to increase with Big Sable
recently hitting the 20+ knot range. Given we are just entering
the time frame where the wind peaks, 200pm to 800pm where winds
will peak around 20 knots. Confidence is fairly low though in
reaching Small Craft conditions for any length of time. Feel the
Ludington buoy will likely peak around 3 to 3.4 feet this evening.
Otherwise, southwest winds of 10-20 knots will create some choppy
conditions on Wednesday in the 1-3 foot range. Heading into
Thursday the gradient becomes quite slack and quiet conditions are
expecting on Lake Michigan.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 10 PM EDT this evening for LMZ848-849.
&&
$$
DISCUSSION...Duke
AVIATION...Smith
MARINE...Duke
NWS GRR Office Area Forecast Discussion
