840
FXUS63 KGRR 251140
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
740 AM EDT Tue Jun 25 2024

.KEY MESSAGES...

- Early Morning Potential for Severe Thunderstorms

- Strong Storms Possible This Afternoon

- Additional Showers Early Wednesday

- Fair weather Thursday then showers and storms Friday/Saturday

&&

.DISCUSSION...
Issued at 241 AM EDT Tue Jun 25 2024

- Early Morning Potential for Severe Thunderstorms

Much of the forecast remains unchanged while we monitor the
cluster of storms currently tracking through northern Wisconsin
that will arrive in lower Michigan within a few hours. As
expected, these storms continue to evolve into a MCS/squall line
with a projected time of arrival into West Michigan around 4 to
6am.

This will largely be a game of monitoring our environment to
estimate the persistence of storms and whether they decay or
prevail. Within the Enhanced Risk upstream of lower Michigan,
these storms are thriving and will evolve in an environment with
3000- 5000J/kg MUCAPE and 50+ knots of Bulk Shear. As the surface
low progresses further east, warm and moist advection will surge
ahead of the storms supporting some ongoing strength. We will not
be as unstable as areas to our west, but a favorable kinematic
environment will support ongoing convection as storms move onshore
and progress east through mid morning. Storms will gradually
enter a weakening stage the further east they progress into lower
Michigan. Damaging wind gusts remain the primary concern as
storms move onshore this morning, but some hail may also occur.

- Strong Storms Possible This Afternoon

The potential for thunderstorms or new convection late tonight
will be dependent on evolution of storms this morning. That is to
say, wherever the frontal boundary sets up is where the best
chance for renewed convection will occur. The strong low- level
jet will weaken as it pivots further south late this morning to
early afternoon, but instability rebounds and may support the risk
for renewed thunderstorms with a damaging wind gust and hail
potential. The main threat area will be near and south of I-96.

- Additional Showers Early Wednesday

Another trough and cold front will sweep through the area
Wednesday morning bringing chance for showers during the first
half of the day. High pressure will fill in during the second half
of the day and into Thursday.

- Fair weather Thursday then showers and storms Friday/Saturday

The flow regime across the Great Lakes this week into next week
features an enhanced belt of westerlies across the northern CONUS in
between subtropical ridging across the southern CONUS and an upper
low across central Canada. Occasional shortwave troughs embedded in
the flow will bring rain chances every couple of days from this
weekend into early next week.

Surface high pressure brings fine summer weather for Thursday into
early Friday before moving east with warm advection pattern
developing by Friday morning. Moisture advection is also increasing
with rain chances by Friday morning as moisture pools ahead of the
the next trough. THere remains some ensemble spread on timing and
and depth of the trough but the consensus has the greatest chance
for showers and storms for late Friday night.

A severe weather threat is possible late Friday night into early
Saturday  as Lower Michigan is in the warm sector and model
soundings show 30 to 35 knots of shear ahead of the cold front.

Surface high builds in behind the front with fair weather for Sunday
into Monday.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 740 AM EDT Tue Jun 25 2024

Squall line with downburst winds in the 40 to 50 knot range moving
through AZO, BTL, LAN and JXN through 13Z then lingering showers
and thunderstorms through about 14-15Z. Wind directions and speeds
will be highly variable this morning due to the effects of
thunderstorm outflows and lingering effects of the cold pool of
air left in the wake of the storms. General winds from the
southwest and west will be established by this afternoon.

Areas of IFR in the lines of storms across southern Lower Michigan
will move out and give way to VFR conditions by late morning into
the afternoon.

&&

.MARINE...
Issued at 241 AM EDT Tue Jun 25 2024

Strong southerly winds early this morning bring waves to
hazardous levels for Small Craft and beaches. Strong thunderstorms
currently in northern Wisconsin will cross Lake Michigan early
this morning bringing significant winds and also a chance for
large hail. Additional showers and storms possible this afternoon
into the evening, and again Wednesday morning.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through this evening for MIZ037-043-050-
     056-064-071.
MARINE...Small Craft Advisory until 8 PM EDT this evening for LMZ844>849.

&&

$$

DISCUSSION...Ostuno/Thielke
AVIATION...Ostuno
MARINE...Thielke