506
FXUS63 KGRR 032326
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
726 PM EDT Wed Jul 3 2024

.KEY MESSAGES...

- Warm and Partly Cloudy Independence Day

- Showers and Storms Likely Friday

- Unsettled Pattern Next Week

&&

.DISCUSSION...
Issued at 254 PM EDT Wed Jul 3 2024

- Warm and Partly Cloudy Independence Day

Not much change to this part of the forecast. Dry weather is
expected with rain chances creeping into far southwest Lower
Michigan beginning well after dark on July 4, so little to no
disruptions to nighttime fireworks are expected at this time.
Dewpoints should be in the lower 60s during the day, resulting in
apparent temperature/heat index readings in the mid 80s, which is
near or slightly below expected highs in the upper 80s for areas
away from the lake.

- Showers and Storms Likely Friday

The primary timeframe to watch for impacts will be late Friday
morning into the afternoon. Synoptically, a positively tilted trough
approaches the area causing a surface low to deepen as it passes to
our northwest. The dynamics are decent with a 50 knot westerly mid-
level jet and 30 knot southwesterly low-level jet setting up across
lower Michigan.

Ample moisture will be in place and dewpoints climb near 70 with
PWAT values exceeding 1.5 inches. The key to severe potential will
be the extent of morning convection ahead of the front. Current
trends support an earlier frontal passage (late morning into early
afternoon) supporting less instability, as well as more showers and
storms ahead of the front. These outcomes would limit potential for
strong storms even with decent deep layer shear. However, if we can
get some instability to build (which won`t be difficult given the
high dewpoints), ample moisture and the strong kinematics mean some
gusty winds from water loaded downdrafts cannot be ruled out. This
will need to be monitored closely over the next day or two to see if
trends more towards a severe weather risk. Regardless of any severe
weather potential, showers with embedded thunderstorms are likely as
the front moves through so will keep the high PoPs in place for
Friday.

- Unsettled Pattern Next Week

The shortwave and associated surface low take their time to exit
west Michigan so rain showers continue into Saturday. A brief break
comes in late Saturday into early Sunday as high pressure pushes
through the state.

The overall pattern remains quite unsettled Sunday into mid next
week. A longwave trough sets up across the eastern half of the CONUS
while strong ridging sets up across the western half. The general
expectation in these kinds of patterns is for shortwaves to rotate
through the larger scale flow pattern; bringing occasional chances
for showers and storms. However, at this range, exact timing of any
precipitation is uncertain as it depends on how the upper-low
evolves in terms of its strength and position. Even though several
chances of rain are possible, dry weather will be predominant much
of the time. The other good news is that while temps will be
slightly cooler, significant drops in temperature are not
expected due to the low amount of change in the predominant
airmass temperature.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 726 PM EDT Wed Jul 3 2024

VFR will persist through the forecast period as high pressure
rolls into the region. There are signals that MKG may see fog
early Thursday morning but there is low confidence that visibility
will be greatly impacted. Winds turn calm overnight then build to
around 5 knots Thursday.

&&

.MARINE...
Issued at 254 PM EDT Wed Jul 3 2024

Main concern in the very short term is persistent and localized
shallow marine fog being noted by some of our webcams in the
Holland to South Haven vicinity. Expectation is that this will
scour out later today based on visible satellite trends. Fog
could return again tonight, but if it does, it`s not expected to
be widespread enough to warrant headlines. The immediate lakeshore
could see some rapid changes though.

Otherwise, winds and waves are expected to remain below advisory
criteria through the period.

&&

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

&&

$$

DISCUSSION...TJT/Thomas
AVIATION...Thielke
MARINE...TJT