005
FXUS63 KGRR 050008
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
808 PM EDT Thu Jul 4 2024

.KEY MESSAGES...

- Chances for showers and storms Friday into Friday Night

- Mainly dry this weekend with seasonable temperatures

- Seasonably warm with a risk for showers/storms next week

&&

.DISCUSSION...
Issued at 353 PM EDT Thu Jul 4 2024

- Chances for showers and storms Friday into Friday Night

Chances for an isolated rain shower will continue this afternoon
and evening as a shortwave slides through the Southern Great
Lakes. Chances for a widespread wetting rain are very low given
the dry air that remains in place below cloud base.

The focus really shifts to Friday afternoon and evening as a
deeper trough moves in from the west. The HREF shows precipitation
trying to slide in during the morning and then a distinct
redevelopment in the afternoon after about 100pm-200pm. Deep layer
shear is formidable with 40-50 knots. MUCAPE values reach around
1000 j/kg. Given the deep layer shear there will be storm
organization. The HREF shows multiple updraft helicity swaths
especially in our northeast CWA, so there is a severe threat. We
are not expecting widespread severe storms, but some localized
wind/hail is certainly possible. We would not be surprised to see
the marginal severe threat area expand from SPC into more of our
forecast area with later updates as we head into day 1 (Friday).
Precipitation will be very much diurnally driven so we expect a
loss in coverage and intensity quickly after sunset.

- Mainly dry this weekend with seasonable temperatures

In the wake of Friday`s system, look for weak cyclonic flow to
linger into Saturday at the surface and aloft - especially early
Saturday. This may support a stray diurnal shower (20%) east of US-
127, though most areas will remain dry. With some clouds around
Saturday /again, mainly early/ highs will only reach the mid 70s -
just a bit below normal for early July. Models agree that surface
ridging will then provide dry and warmer weather Sunday, as high
temperatures reach the lower 80s.

- Seasonably warm with a risk for showers/storms next week

The early and middle part of next week will feature a continued
summerlike pattern, with periodic chances (30-50%) for showers and
storms. Timing the specific windows for the shower/storm risks will
be difficult, given the interplay between daytime heating, and the
passage of weak upper disturbances embedded within broad/weak 500 mb
trough located over the northern Plains and Great Lakes.

The next impulse aloft and associated weak surface trough are
forecast to move into the Great Lakes from the WNW Monday and
Tuesday, bringing a chance (40-50%) for showers and storms. At this
time, the signal for strong to severe storms appears low. Ensemble
data suggests the aforementioned broad/weak troughing aloft over the
northern CONUS will start to give way to higher heights. However,
this weakly forced summertime set up, coupled with daytime heating,
will still support a low (20-30%) chance for storms through late
week. Highs will be within a few degrees of normal for early-mid
July (low to mid 80s). All in all, a very normal pattern for early-
mid July.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 753 PM EDT Thu Jul 4 2024

A few very isolated showers have formed this evening around West
Michigan as max diurnal heating has been reached over the last few
hours. Most places will remain dry, though one of these showers
just went over the Grand Rapids airport. These will all diminish
over the next few hours, resulting in a VFR night with generally
light winds. Latest model guidance suggests some low clouds may
form/move into the I-94 corridor after midnight, taking advantage
of weak flow and plenty of humidity/moisture in the lowest levels
of the atmosphere. Currently not thinking this will be an overly
significant impact to the TAF sites, but will monitor future
trends. Meanwhile, better chance for showers and some storms is
still expected by tomorrow morning along the lakeshore and
spreading inland by late morning. In general it seems like this
line of showers/storms will come through a bit too early to take
advantage of the diurnal instability, but some storms may produce
gusty winds and hail through early afternoon Friday.

&&

.MARINE...
Issued at 353 PM EDT Thu Jul 4 2024

There are limited chances for significant wind in the next few
days, so we are not expecting Beach Hazard Statements or Small
Craft Advisories. Tonight, wind is lighter than 10 knots. On
Friday into Friday night we have a low that moves through the
area, so south winds will shift to the northwest through that
period. Winds will reach the 10 to 20 knot range at times Friday
and Friday night. This should not be enough to create winds/waves
that reach BHS/SCA criteria.

&&

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

&&

$$

DISCUSSION...Duke/Smith
AVIATION...AMD
MARINE...Duke