420
FXUS63 KGRR 081901
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
301 PM EDT Sat Jun 8 2024

.KEY MESSAGES...

- Showers Possible Through This Evening; Turning Breezy Sunday

- Starting Cool then Warming Trend through Mid/Late Week

- Precipitation Chances Next Week

&&

.DISCUSSION...
Issued at 300 PM EDT Sat Jun 8 2024

- Showers Possible Through This Evening; Turning Breezy Sunday

Regional MRMS imagery this afternoon indicates a broken batch of
showers moving from WI out over Lake Michigan and into central
Lower MI. This is occurring as upper troughing remains entrenched
across the region, courtesy of an upper low located north of Lake
Superior. No lightning has occurred with this activity, and little
to none is expected for our region given almost no atmospheric
instability (SPC Mesoanalysis shows zero MUCAPE across Lower MI).
Thus, we have opted to keep thunder mention out of the forecast
through tonight. Given a fairly dry subcloud layer per 12z model
soundings, expecting mainly light showers across the region. It
will be difficult to accumulate much more than 0.10"-0.25" in any
given area. Showers will come to an end in the 00z-06z time frame.

For Sunday, low level winds (925mb-850mb) are shown to increase to
30 kts or greater by the afternoon. Very steep low level lapse
rates approaching 10C/km from the surface up to nearly 3km will
easily mix down wind gusts of around 30 mph. Would not be
surprised to see some peak gusts reaching the 30-40 mph range. The
HREF max gusts do show some values approaching 40 mph, though the
mean gusts are closer to 30 mph. Sky cover should be partly to
mostly sunny during the morning, though increasing cloud cover is
expected near and north of I-96 during the afternoon as 850 mb RH
is shown to increase in that area.

- Starting Cool then Warming Trend through Mid/Late Week

A cool start to next week following the passage of a cold front
Sunday afternoon. 850mb thermal trough moves overhead with temps
falling towards 4 to 6C Monday. Respondent surface temps in the
upper 60s to 70 degree range are expected Monday afternoon.
Temperatures gradually warm through the week as zonal flow ushers in
warmer air from the west. Highs in the mid to upper 80s look likely
by Thursday.

- Precipitation Chances Next Week

A few embedded shortwaves in the zonal flow will present chances for
showers Tuesday evening and Thursday evening. Few light rain showers
possible Tuesday night, then a better signal for showers and storms
with the passage of cold front Thursday night. Overall evolution of
this window of time will be largely dependent on how convection
evolves over the Plains upstream, so uncertainty remains.


&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 128 PM EDT Sat Jun 8 2024

Light rain is beginning to move through central lower Michigan
this afternoon. Along with these showers, expect slightly reduced
visibility and periods of MVFR and IFR cigs, especially southeast
of GRR. Lightning does not look like a major concern, but a few
flashes of lightning are not out of question. Drier air will move
into the region tonight leading to the return of VFR for Sunday.
Looking into Sunday, wind will turn gusty during the late morning
to afternoon.

&&

.MARINE...
Issued at 300 PM EDT Sat Jun 8 2024

As we head into Sunday afternoon, expect wind speeds to increase
close to advisory criteria as winds shift northerly behind a
front. Waves will likely peak in the 3 to 5 foot range Sunday
evening through Monday. A SCA and BHS will likely be needed for at
least a portion of our marine zones.

&&

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

&&

$$

DISCUSSION...Hoving/Thielke
AVIATION...Thielke
MARINE...Hoving