359
FXUS63 KGRR 060608
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
208 AM EDT Sat Jul 6 2024

.KEY MESSAGES...

- Chance for Isolated Severe Storms This Afternoon and Evening

- Additional Showers Possible Saturday Afternoon

- Dry and warm Sunday

- Unsettled with showers/storms later Monday into Tuesday

- Heat slowly starts to build late week

&&

.DISCUSSION...
Issued at 316 PM EDT Fri Jul 5 2024

- Chance for Isolated Severe Storms This Afternoon and Evening

Thinking has not changed from earlier as we expect a continued
chance for showers and storms through mid evening. Much if not all
of the activity should come to an end by 900pm as the showers and
storms rotate to the north and east out of the forecast area.
Storms moving in from Wisconsin and over the lake will likely
diurnally fade over Lake Michigan as we head towards 900pm or so.


As for the threat, the setup consists of a low centered near
Baldwin with a warm front to the east down U.S. 10 and a cold
front stretching south down the lakeshore counties. The cold front
has caught up with the lake breeze at this point. Scattered storms
will continue to occur near both frontal boundaries through
800pm-900pm. The CAPE / Shear balance is definitely to levels that
warrant a close watch today for severe weather. MUCAPE values have
hit 1500 j/kg and deep layer shear is on the order of 40-50 knots.
Storm organization is expected with that level of shear and we
have seen that with rotation contained within storms today. Wind
to 60 mph and hail to around 1 inch in diameter are the main
threats. Locally heavy rain cannot be ruled out either as
precipitable water values are in the 1.25 to 1.50 range.

Little if any showers and storms are expected overnight as there
is a healthy diurnal component to the ongoing activity. Widespread
stratus looks to develop tonight, but fog looks to remain above
levels that would be concerning to travelers.

- Additional Showers Possible Saturday Afternoon

Another mid level shortwave rotates in from the north on Saturday
and we expect a diurnal flare of showers once again especially in
interior portions of the state (up along U.S. 10 and down U.S.
127). There is less in the way of instability on Saturday (750
j/kg and lower) so we expect more showers than storms, but we
cannot rule isolated thunderstorms. The precipitation will once
again fade diurnally with the setting sun. Expecting mainly dry
conditions Saturday night.

- Dry and warm Sunday

West Michigan will close out the holiday weekend with pleasant weather
Sunday; partly to mostly sunny skies, low (<10%) chances for rainfall,
and high temperatures in the lower 80s. This, thanks to a ridge of
surface high pressure expected to be overhead early Sunday. This
feature will migrate to the east by Sunday night, allowing southerly
winds and WAA to develop, and thus set the stage for potential
showers/storms to start the workweek.

- Unsettled with showers/storms later Monday into Tuesday

The Monday-Tuesday timeframe will feature a rather summer-like pattern,
with warmth, humidity, and a chance (30-50%) for showers and storms.
Ensembles agree that weak 500 mb troughing aloft, with an embedded
short wave, will impact the region. The associated surface low/front
will move from the upper MS valley to the Great Lakes late Monday,
before moving east of the area late Tuesday. Modest /at best/ synoptic
support for ascent, together with daytime heating, will generate
scattered showers/storms. Current indications suggest the best coverage
from late Monday through Tuesday. Overall support/dynamics suggest low
severe weather threat, though an isolated summertime severe storm not
out of the question. Highs in the mid 80s Monday will drop off to
around 80 Tuesday.

- Heat slowly starts to build late week

Aforementioned upper troughiness will move east of the Great Lakes
during the middle and latter parts of next week, and this will allow
500 mb heights across the Great Lakes to slowly rise. Surface high
pressure over the upper Great Lakes Wednesday is currently forecast to
shift east to New England by late week. This setup supports increasing
warmth with limited shower/storm chances. High temperatures in the
lower to middle 80s can be expected Wed/Thu/Fri, and West Michigan
*may* potentially make another run at 90F next weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 143 AM EDT Sat Jul 6 2024

Cool, moist flow will continue overnight. Lows in the 60s and a
capping inversion will couple with the rainfall from earlier an
MVFR to IFR cigs are expected between now and 12Z. MKG and BIV are
already IFR with GRR, AZO and BTL expected to have periods of IFR
now through 12Z. Cigs will slowly lift and improve by 15Z. The
cool, moist flow will continue today and showers will be possible
this afternoon at LAN. Otherwise, VFR will then dominate the
pattern.


&&

.MARINE...
Issued at 316 PM EDT Fri Jul 5 2024

Low pressure will move off to the east of Lake Michigan tonight
which will set up a northwest flow tonight into Saturday. Winds
look to peak late tonight and into Saturday midday in the 10-20
knot range. This should keep waves/currents below Beach Hazards
Statement and Small Craft Advisory levels. Northerly flow events
though have a tendency to overperform in the summer so we will be
vigilant tomorrow (Sat) in watching the wave field on webcams and
via buoys. As of now we expect waves to remain in the 1-3 foot
range. Cannot rule out a midday to afternoon bump into the 2-4
foot range, but we think it should remain below the 3-5 foot
advisory level.

Beyond Saturday afternoon winds look light for Saturday night and
Sunday so the later half of the holiday weekend looks good for
swimmers and boaters. Winds do try to increase again Sunday night
possibly reaching the 15-20 knot range. Chance of reaching
advisory level again though look low.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Duke/Smith
AVIATION...Ceru
MARINE...Duke