714
FXUS63 KGRR 061756
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
156 PM EDT Sat Jul 6 2024

.KEY MESSAGES...

- Isolated Showers and Storms Today

- Another round of showers/storms possible early next week

&&

.UPDATE...
Issued at 1210 PM EDT Sat Jul 6 2024

Surface low pressure is centered in Ontario at midday with ridging
just upstream over Wisconsin and Minnesota. This places Southwest
Lower Michigan in a northwest flow. Aloft, a weak shortwave trough
is overhead also moving off to the east. The upper trough will aid
in the development of some showers this afternoon that will likely
persist into the early evening. Model soundings show 500-750 j/kg
of MUCAPE this afternoon which is more than enough for a few
showers. We also expect an isolated thunderstorm or two as well.
The 12Z HREF shows a bit more 50 dbz echo this afternoon in the
4hr max reflectivity swaths. It is still very much isolated, but
it did increase from the 00z run. A cooler than normal afternoon
is expected by July standards with highs for the most part holding
in the 70s due to the clouds.

A quick marine note...our 1-3 foot and low swim risk still looks
good as high resolution models do not support much more than that
based on surface wind day. Highest waves will be from Holland
south this afternoon in the 2-3 foot range.

&&

.DISCUSSION...
Issued at 325 AM EDT Sat Jul 6 2024

- Isolated Showers and Storms Today

Fairly tranquil weather expected over the weekend as upper
troughing prevails, but model soundings show a drying trend
through Sunday. There will be enough moisture and diurnally
driven instability to pop some showers and isolated thunderstorms
today with the greatest coverage this afternoon across interior
zones. With westerly low level flow we expect a lake shadow and
little or no showers across the western zones.

Shower activity diminishes and ends Saturday evening with the loss
of insolation. Model soundings are drying out and surface ridging
builds in on Sunday, so we will continue the dry forecast.

- Another round of showers/storms possible early next week

Another deep trough will swing into the region late Sunday night
through Monday. Latest mid range models are in good agreement on
the position and track of this positively tilted upper level
trough. Copious amounts of mid level moisture will accompany this
trough and coupled with good 500 mb vorticity there should be
enough instability for showers and storms in the Tuesday
timeframe.

The biggest question is how much gulf moisture will
this system tap into. Given the latest ensembles, while there is
anomalous moisture moving through the region by mid week, the best
moisture will be just east of the region. However there are some
outliers that open the possibility for heavier rainfall.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 142 PM EDT Sat Jul 6 2024

A generally BKN cloud deck (3-4kft) continues to impact West
Michigan this afternoon in cool cyclonic flow. July sun has helped
erode the clouds in some areas, while also sparking a few showers
over eastern areas. LAN/JXN may see a stray shower through 22Z
/though thunder not expected at this time/. Expect these clouds to
diminish next several hours, and especially toward sunset, as
ridge of high pressure over upper MS valley moves into the region.
Mostly clear skies tonight with good radiational cooling may
yield MVFR visibilities in fog in the 08-13Z timeframe. A few CU
will form late Sunday morning, along with light southerly winds.

&&

.MARINE...
Issued at 325 AM EDT Sat Jul 6 2024

Winds and waves are expected to remain non-hazardous to boaters
and swimmers over the weekend and into next week. The chance for
thunderstorms is also low until early next week.

&&

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

&&

$$

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