-- Discussion containing changed information from previous version are highlighted. --
638
FXUS63 KGRR 061413
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1013 AM EDT Thu Jun 6 2024

.KEY MESSAGES...

- Scattered Showers Thursday and Friday

- Some Showers Possible Saturday; Likely Drying Out Sunday

- Steady Warming Trend Next Week & More Dry Than Wet

&&

.UPDATE...
-- Changed Discussion --
Issued at 1008 AM EDT Thu Jun 6 2024

Skies are generally clear across the cwa, but diurnal cu is
expected to develop. Colder air aloft and subsequent increase in
mid level instability will likely result in showers developing
after 12z over the northern half of the cwa. Cooler air is flowing
into the region and highs in the lower 70s are expected today.
-- End Changed Discussion --

&&

.DISCUSSION...
Issued at 256 AM EDT Thu Jun 6 2024

- Scattered Showers Thursday and Friday

An initial wave of showers is crossing the CWA ahead of a cold
frontal boundary this morning providing light (under 0.1 inch)
rainfall. Enough instability exists for some scattered thunderstorms
up towards Newaygo/Ludington but any thunderstorms will be just
garden-variety storms given low instability and no deep-layer shear.
These showers will clear the area around daybreak as the front
passes through.

The area generally remains dry through the mid-afternoon hours.
However, the progression of a -10C to -15C mid-level cold pool
associated with a 500mb trough should be enough to ignite scattered
instability-driven showers across the northern 2/3 of the CWA with
the greatest concentration near US10 where the heart of the cold
pool is. Highs will be slightly below normal for this time of year
ranging from around 70 near US10 to the mid 70s near I94.

Instability driven showers continue Thursday night and into the
start of Friday as the upper-level cold pool remains in the region.
However, by Friday afternoon showers diminish as the upper-level low
and associated cooler air push off to the east. Highs Friday will be
in the mid to upper 60s.

- Some Showers Possible Saturday; Likely Drying Out Sunday

Good model agreement exists regarding upper troughing into the
weekend. This will ensure cooler than normal temperatures along with
some diurnal showers on Saturday and perhaps a few thunderstorms
(less likely). A notable disparity exists with how the models are
handling 850 mb winds across the Midwest and Great Lakes Saturday
morning through Saturday night. The 00z GFS follows previous runs in
showing a much stronger and more convergent low level jet over the
region 12z Saturday through 00z Sunday, helping drive greater
coverage of showers. The GEM and ECMWF do not show this, and their
respective ensemble suites show little in the way of precipitation
Saturday but do have some increase in precipitation coverage
Saturday evening and Saturday night. While the NBM POPs on Saturday
(30-40%) may be a touch high due to the GFS/GEFS influence, will
maintain those for now and see how the deterministic and ensemble
runs trend for precip coverage. The latest 00z guidance favors
Sunday largely drying out aside from an isolated shower possible
near US 127 during the afternoon.

Temperatures over the weekend will be cooler than average, with mid
to upper 60s north of I-96 and upper 60s to low 70s south.

- Steady Warming Trend Next Week & More Dry Than Wet

Model guidance favors incremental warming from Monday through
Thursday (and beyond). A shortwave trough is forecast to move
through the Great Lakes region late Tuesday into Wednesday. Some
increase in low level moisture and surface dew points is shown.
There is at least a low threat for some showers for that time
period, but probably not enough instability forecast to include
mention for thunderstorms.

850 mb temperatures should be climbing up especially from mid to
late next week. GEFS/ECE/CMC ensemble suites largely agree on this
point. This is thanks to an increasing prospect for rising upper
heights across our part of the country. This far out, the degree of
height rises can be pretty iffy given unresolved upper waves that
can dampen out those heights. However, confidence is growing in
temperatures reaching the 80s by late next week, and some ensemble
guidance (ECE/CMC) supports the potential for 90s along with
humidity as we enter into the heart of mid June.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 729 AM EDT Thu Jun 6 2024

As the morning progresses, expect wind speeds to increase with
gusts commonly around 25 kts or slightly greater. Scattered to
broken clouds with bases down to 6000 ft are likely to develop
this afternoon. A few showers may develop later this afternoon and
evening but the bulk of them will likely stay north of the
terminals. Model guidance favors cloud bases lowering down to
around 4000 ft later tonight.

&&

.MARINE...
Issued at 256 AM EDT Thu Jun 6 2024

The current Beach Hazards Statement and Small Craft Advisory look to
be in good shape. West to northwest winds of 20-25 knots gusting to
30 knots at times are expected to develop today with waves
increasing into the 3 to 5 foot range as a result. The highest waves
will be between South Haven and Muskegon where the flow will provide
the best fetch for wave development. These conditions will continue
through Friday afternoon before 2-4 foot waves and 15-20 knot gusts
become the theme for the weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Friday afternoon for MIZ037-043-
     050-056-064-071.
MARINE...Small Craft Advisory until 4 PM EDT Friday for LMZ844>849.

&&

$$

UPDATE...04
DISCUSSION...Hoving/Thomas
AVIATION...Hoving
MARINE...Thomas