748
FXUS63 KGRR 172342
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
742 PM EDT Mon Jun 17 2024

.KEY MESSAGES...

- Hot and humid with p.m. chances for storms through Tuesday

- Heat, humidity, predominantly dry Wednesday through Saturday

- Unsettled beginning Saturday then cooler beginning Sunday

&&

.DISCUSSION...
Issued at 315 PM EDT Mon Jun 17 2024

- Hot and humid with p.m. chances for storms through Tuesday

No changes will be made to the going Heat Advisory with this
forecast package.

We have had a few isolated cells pop up this afternoon along a
line of slightly enhanced convergent flow roughly from south of
Grand Rapids to Saginaw Bay away from the Lake Michigan shoreline.
This slightly enhanced convergence looks like it is the result of
the flow off of the lake, but not a lake breeze with SW flow. This
is interacting with an atmosphere with 3500 J/kg of MU CAPE
available. Obviously plenty of instability, but little to no shear
under the upper ridge to help sustain any updrafts. Thus far, we
have had some winds of 30 mph out of cells. These will continue to
be possible through sunset, when any leftover convection should
come to an end.

The potential for additional diurnal convection looks a little
better for Tuesday afternoon and evening as compared to this
afternoon. Instability looks to be a little less tomorrow
afternoon, but values will still be up around 3150 J/kg. The
difference for Tuesday afternoon is that a short wave riding up
the backside of the upper ridge is forecast to move through the
area Tuesday afternoon. This will provide as a better focus for
convective development. Deep layer shear is still expected to be
quite low around 15-20 knots, so we are anticipating pulse type
storms with some small hail, winds to 40 mph, and locally heavy
downpours.

Once again, convection should come to an end toward sunset Tuesday
evening.

- Heat, humidity, predominantly dry Wednesday through Saturday

No substantive changes to the forecast. We continue to expect highs
in the low 90s and maximum apparent temperatures in the upper 90s.
The Heat Advisory looks good at least through Friday with decent
prospects for eventually expanding this into Saturday. As noted
previously, there are slightly better chances for showers and storms
farther north towards US-10 in the Wednesday into Thursday
timeframe, but overall chances remain low.

- Unsettled beginning Saturday then cooler beginning Sunday

We continue to see a signal for a pattern change over the weekend.
There are timing differences with the approach of an upper PV max
and attendant cold front and convection. Some guidance has this as
early as Saturday afternoon while other guidance has this as late as
Sunday afternoon. Generally speaking, is is hard to transition out
of hot spells like these without some type of severe weather. Even
if convection was to move through our area Sunday morning around the
time of minimum diurnal instability, there still could be plenty of
residual conditional instability given the very ripe, warm and humid
airmass we will have developed over the preceding days.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 742 PM EDT Mon Jun 17 2024

VFR conditions should prevail at most places through Tuesday. The
exception will be isolated thunderstorms bringing very brief IFR
conditions in heavy downpours, mostly on Tuesday afternoon.
Southwest winds around 10 knots could gust to 20 knots at times on
Tuesday.

&&

.MARINE...
Issued at 315 PM EDT Mon Jun 17 2024

We are issuing a Small Craft Advisory and Beach Hazards Statement
for the northern half of the lakeshore starting Tuesday morning,
going through most of Wednesday.

The better gradient between the sfc ridge to our SE, and the low
to our NW will be located over the northern half of our
nearshore/lakeshore areas. It looks to be strong enough to
generate 3-5 ft waves from around Whitehall to Manistee,
especially near Little and Big Sable Points. This will continue
into much of Wednesday, before the gradient weakens enough to not
require them.

The rest of the work week looks like it will be calmer with a
weaker gradient in place. The gradient is not forecast to tighten
up until toward Saturday as a front approaches.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Air Quality Alert until midnight EDT tonight for MIZ037-043-050-
     056-064-071.
     Beach Hazards Statement from Tuesday morning through Wednesday
     afternoon for MIZ037-043-050.
     Heat Advisory until 8 PM EDT Friday for MIZ043>046-050>052-
     056>059-064>067-071>074.
MARINE...Small Craft Advisory from 8 AM Tuesday to 4 PM EDT Wednesday for
     LMZ847>849.

&&

$$

DISCUSSION...NJJ/TJT
AVIATION...Ostuno/TJT
MARINE...NJJ