803
FXUS63 KGRR 162357
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
757 PM EDT Fri May 16 2025

.KEY MESSAGES...

- Scattered Showers and Storms Tonight

- Gusty Winds and Lingering Rain Showers Saturday

- Cooler Temperatures into Next Week

&&

.DISCUSSION...
Issued at 300 PM EDT Fri May 16 2025

- Scattered Showers and Storms Tonight

Another round of showers and storms is expected to move through
after 8pm tonight. Storms could be strong to severe with damaging
winds being the primary hazard, but can`t rule out hail or a
tornado with this evenings storms.

We`ll need to monitor convection currently in Missouri as it
tracks northeast into southern Michigan and the showers and storms
that develop in Wisconsin as they move across the lake. There is
some uncertainty with the exact variables in play this evening.
Model solutions vary with the amount of instability available
along with the LCL values as storms approach. Hence why we can`t
completely rule out any one hazard.

There is higher confidence in the source of lift with the 500 mb
positive vorticity advection with the upper level low currently
over Minnesota and with the 850mb 40 to 45 knot jet also bringing
with in some moisture. Showers and storms will also be moving into
a more mixed out environment, meaning there is an ample amount of
dry air toward the surface. Downdraft CAPE values will be in the
800 to 1000 J/kg range as storms approach leading to the higher
confidence in the damaging wind potential.

- Gusty Winds and Lingering Rain Showers Saturday

As the previously mentioned upper level low tracks through the
northern Great Lakes, low level moisture and lift will bring some
lingering showers to the area Saturday. It will also bring gusty
westerly winds with gusts in the 30 to 40 mph range. As the low
departs Saturday night winds subside and dry conditions return.
Highs Saturday are only expected to be in the 50s to low 60s.

- Cooler Temperatures into Next Week

Pressure heights increase Sunday into Monday with dry conditions
expected. Thereafter the pattern becomes a little less certain
looking at the ensemble clusters and the 500mb flow. An upper
level low will be in the vicinity but the timing and placement
vary based on each cluster which impacts our rain chances through
the remainder of the week. It does look like most of the rain will
be to our south, but the placement of the low will determine how
far north rain will spread. Either way it doesn`t look like a
total washout, but temperatures will remain on the cooler side
with highs in the 50s and 60s and lows mainly in the 40s. Sunday
night and Monday night there is a chance for temperatures to drop
into the mid to low 30s for areas north of I-96. These
temperatures could result in frost damaging susceptible
vegetation.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 755 PM EDT Fri May 16 2025

Radar has become more active over western Lower during the past
hour or so. Latest models indicate that we`ll see a broken line of
convection move across the terminals this evening with showers
possible overnight. Cigs will fall to MVFR by sunrise and remain
there the rest of the period.

&&

.MARINE...
Issued at 300 PM EDT Fri May 16 2025

Thunderstorms will be possible again tonight and may produce
strong winds. Gusty southerly winds continue and become more
westerly into Saturday as low pressure moves across the northern
Great Lakes. Waves build into Saturday with heights of 4 to 7
feet. Winds and waves gradually subside Saturday night. Northwest
winds may pick back up to Small Craft Advisory levels Sunday
afternoon.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 2 AM EDT Sunday for LMZ844>849.

&&

$$

DISCUSSION...RAH
AVIATION...04
MARINE...04