776
FXUS63 KGRR 200524
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
124 AM EDT Sun Apr 20 2025

.KEY MESSAGES...

- Showers Late Sunday into Monday

- Windy Day Possible for Monday

- Occasionally Wet Mid to Late Week Period

&&

.UPDATE...
Issued at 913 PM EDT Sat Apr 19 2025

Some high level cloudiness will linger tonight but recent thinning
of the clouds combined with light winds will allow for a chilly
spring night. Lows dipping into the 30s and even some 20s
possible across the far north.

&&

.DISCUSSION...
Issued at 308 PM EDT Sat Apr 19 2025

- Showers Late Sunday into Monday

An upper shortwave trough currently across the southern Plains today
moves in our direction for Easter Sunday. As it does so, surface low
development is well depicted by numerical model guidance. ECE
ensemble members show fairly tight clustering of surface low tracks
from Oklahoma at 12z Sunday to Wisconsin by 12z Monday. While low
level flow will be off the Gulf, the greatest amount of rainfall
will be closer to the low center as opposed to the warm advection
wing that presses through Michigan. Here, rain showers are possible
after 18z Sunday but primarily after dark and into the morning hours
of Monday. Amounts will likely range from a tenth to a quarter of an
inch for most areas, but some swaths of a half inch or more are
possible mainly north and west of a Holland to Mount Pleasant line.
With MUCAPE values reaching a few hundred J/kg, a few embedded
thunderstorms are possible but they will likely be the exception to
the rule.

- Windy Day Possible for Monday

As the mid level dry slot of the system moves in around or after 12z
Monday, we`ll begin to see rain chances diminish across the region
though a scattered shower here and there remains possible during the
day. As this occurs coincident with daytime heating, we`ll see
mixing layer heights reach around 2,000 ft on average, which is
where 35-40 kt winds will be located. Those winds will likely start
to mix down to the surface, and hence we`ll get gusts over 30 knots
(35 mph) for most locations. Further, ECE gust guidance is showing
the probability of hitting gusts of 34 kts or greater (39 mph or
more) to be 90-100% near and south of I-96 on Monday. So, expect a
windy day with SW to WSW winds.

- Occasionally Wet Mid to Late Week Period

Late Tuesday night, a weakening LLJ angles in to western Lower MI as
low level warm air advection takes place. Very weak elevated
instability may be present, though we may lack it completely as
well. Regardless, some showers are possible late Tuesday night into
Wednesday morning.

By next Thursday into Friday, an 850mb thermal boundary will likely
set up across the Midwest and Great Lakes and a surface warm front
may be located somewhere across the state (likely north) at that
time. Weak Gulf flow intersecting with these low level boundaries
should help fire some showers and possibly thunderstorms, though
where exactly those boundaries set up will be key to our rain
chances.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 124 AM EDT Sun Apr 20 2025

The majority of this forecast period should see VFR conditions
rule at all of the terminals. Skies are starting out mostly clear
with just a few wisps of cirrus starting to approach. We will
eventually see the high clouds thicken up, and then a mid deck
developing early this afternoon.

Any rain will be hard pressed to make it to the sfc until late in
the afternoon, developing from SW to NE across the area. This rain
will remain light, even after it starts reaching the sfc. It will
be on and off into the evening hours, before more widespread
showers move in. Enough instability will arrive after about 02-03z
where some thunder will be possible. It is at this time that pcpn
may become heavy enough to reduce visibilities enough to drop into
MVFR.

&&

.MARINE...
Issued at 308 PM EDT Sat Apr 19 2025

The next hazardous period for mariners will be Monday as strong
SW to WSW flow develops over the lake and waves build accordingly.
Monday afternoon should feature the highest wave action with some
6 to 8 footers possible. Hazardous waves may linger into Tuesday
morning before diminishing.

&&

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

&&

$$

UPDATE...Meade
DISCUSSION...Hoving
AVIATION...NJJ
MARINE...Hoving