773
FXUS63 KGRR 201121
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
721 AM EDT Fri Jun 20 2025

.KEY MESSAGES...

- Several days of high heat coming

- Scattered storms possible today, north late tonight

- A little cooler middle of next week

&&

.DISCUSSION...
Issued at 330 AM EDT Fri Jun 20 2025

- Several days of high heat coming

A building upper ridge will move toward the upper Great Lakes this
weekend. H8 temperatures near 14c Saturday morning will climb to
24c by Saturday evening. Surface temperatures in the mid 90s are
expected Saturday through Monday with mid 80s to lower 90s
Tuesday. When combined with dewpoints in the lower to mid 70s,
apparent temperatures will climb into the lower 100s.
Unfortunately, not much relief will be found at night as lows will
only fall to the mid to upper 70s. We`ve issued an Extreme Heat
Watch along/south of I-96 for Saturday through Tuesday. Since the
northern half of the cwa likely won`t see heat advisory criteria
Tuesday, we`ve excluded those 3 rows of counties from the watch.
However, the northern half of the cwa will see heat advisory
criteria met Saturday through Monday.

- Scattered storms possible today, north late tonight

The upper ridge just to the west will a couple of short waves ride
over the top of it. A weak short wave moving through the pattern
may fire off a couple of storms this afternoon. Otherwise we`ll be
watching for convective development tonight. The nocturnal LLJ
will increase tonight resulting in an MCS developing over the
eastern Dakotas/MN and moving east. The question is whether the
MCS will take a turn to the southeast as it approaches Lake MI.
Most of the CAMS are pointing toward a small turn to the southeast
which would result in the southern flank brushing the far
northeast cwa late tonight and so we have 60 PoPs there for that.
These types of ridge riders tend to be prolific wind producers so
could see a few of the storms strong to severe if the southeast
turn materializes and it brushes the northeast counties.
Sometimes, these nocturnal MCSs will move a bit farther southeast
than expected as they eat into the higher CAPE values to the
south. For this reason, SPC has maintained a marginal risk for
severe storms north of a MKG to TEW line.

- A little cooler middle of next week

The ridge flattens a bit during the middle of next week. That will
result in slightly cooler...highs in the mid 80s...weather as a
frontal boundary drops south. Of course, that boundary may also
act as a focus for shower and thunderstorm development.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 715 AM EDT Fri Jun 20 2025

Mostly VFR across the terminals this morning. The exception is JXN
with 4sm br. This fog will burn off quickly leading to ceilings
around 12k ft today. Lots of clouds from upstream convection
continue to spill in this direction. Showers/storms over Wisconsin
have been moving toward Lower MI all night but eroding as they
near the lake...in line with model trends.

Expect VFR conditions through the period. A minor short wave
moving across the region this afternoon may fire a storm or two
over Mid MI, which may affect LAN, but that`s less than certain
and precipitation was left out of the TAFs.

More convection will may fire along a warm from lifting
northeastward overnight which could affect the terminals after
midnight, but confidence is low on that happening and
precipitation was left out of the TAFs.

&&

.MARINE...
Issued at 330 AM EDT Fri Jun 20 2025

Outside of isolated storms over the lake today, no marine hazards
are anticipated. That will likely change tonight as low pressure
over the Plains moves east. Southwest flow will increase and waves
will build to 6-8 feet Saturday; a small craft advisory will
likely be needed tonight and continuing through the weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Extreme Heat Watch from Saturday morning through Tuesday evening
     for MIZ056>059-064>067-071>074.
MARINE...None.

&&

$$

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