836
FXUS63 KGRR 281616
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1216 PM EDT Fri Jun 28 2024

.KEY MESSAGES...

- Increasing Showers and Storms Tonight into Saturday

- Cool High Pressure Sunday/Monday

- Rain chances mid/late week

&&

.UPDATE...
Issued at 1215 PM EDT Fri Jun 28 2024

High pressure is situated off to the east of the Great Lakes
across Southern New England and the Middle Atlantic states at
midday. Low pressure is located upstream with a low in Minnesota.
Ceilings are still high base across Western Lower Michigan with
most sites reporting 9,000 feet or higher. South Haven and Grand
Rapids are both reporting some light rain, but we are not even
seeing the pavement turn wet here at the office due to how light
the precipitation is. We will likely continue to see some light
rain try to advect in from the west this afternoon especially over
the southwest CWA towards South Haven and Covert. The
precipitation is associated with a warm front aloft and a
shortwave in the mid levels moving our direction from Iowa. 850mb
dew points rise from below 0C earlier this morning to around +12C
this afternoon. That moisture flux is resulting in instability
and an increase in precipitation ahead of the shortwave. Bottom
line a mainly cloudy afternoon with increasing chances for rain
showers. Highs in most areas will hold in the 70s.

&&

.DISCUSSION...
Issued at 335 AM EDT Fri Jun 28 2024

- Increasing Showers and Storms Tonight into Saturday

Lingering surface high pressure keeps conditons quiet this morning
while focus turns to this afternoon and into Saturday for showers
and storms.

Starting this afternoon, mid-level shortwave energy embedded in
ridging will trigger increasing shower activity. Low level profiles
look quite dry, so wouldn`t expect too much precipitation to reach
the surface and a few "virga showers" across the area. Profiles
moisten up into Saturday morning as the parent low moves across
southern Ontario and a trailing cold front approaches. As a
secondary low develops along the southern edge of the front south
of the state line, a warm front will lift north and trigger
elevated showers across southern Michigan early Saturday. Diurnal
instability will build into the early afternoon ahead of the
lagging cold front. Favorable deep-layer shear will support at
least an isolated severe thunderstorm threat Saturday afternoon
and evening as the cold front sweeps through. Damaging wind gusts
and hail will be the primary hazards to monitor for.

- Cool High Pressure for early Next Week

Upper troughing with Canadian surface high building overhead will
provide dry and cool weather for Sunday into Monday. Lows Sunday
night expected to dip down into the 40s in the rural areas and even
some upper 30s in the cold hollows. The surface high moves east on
Tuesday with warm advection and moisture return ahead of the next
shortwave trough.

- Rain chances mid/late week

Shortwave ridging late Monday into Tuesday is flattened and replaced
by low amplitude troughing on Wednesday, which persists the rest of
the week. Low confidence in the timing/details of rain given
individual model and ensemble spread but the general consensus is
that a cold front will bring showers and thunderstorms late Tuesday
night into Wednesday with the front hanging up just south of Lower
Michigan and another surface low forming along this baroclinic zone
by the Fourth of July.

At this point it looks like bulk of showers and storms may remain
just to the south of Lower Michigan after Wednesday but chance POPs
in the forecast will cover the potential for the front/sfc low to
move further north.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 732 AM EDT Fri Jun 28 2024

VFR conditions will continue into this evening then areas of MVFR
will develop tonight as rain showers become more widespread along
with ceilings in the 1500 to 2500 feet AGL range. Southeast winds
will gust to near 20 knots today. There could be a thunderstorm
overnight but coverage is low enough to leave out of the forecast
for now.

&&

.MARINE...
Issued at 335 AM EDT Fri Jun 28 2024

Wind shifts southerly this morning and builds. Waves will
increase and will become hazardous to small craft after daybreak.
A moderate swim risk is expected for beaches north of Grand Haven.
A small craft advisory remains in place for Muskegon, Mason, and
Oceana Counties, and wave heights will need to be monitored for
potential Beach Hazards Statement. Southerly winds will make
beaches on the south side of south piers especially vulnerable to
structural currents and turbulent waves. For today this will
include Grand Haven State Park and Pere Marquette Park in
Muskegon.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 2 AM EDT Saturday for LMZ847>849.

&&

$$

UPDATE...Duke
DISCUSSION...Ostuno/Thielke
AVIATION...Ostuno
MARINE...Thielke