462
FXUS63 KGRR 152315
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
715 PM EDT Sun Jun 15 2025

.KEY MESSAGES...

- Quiet start to the week...Dry through Monday Night

- Showers and storms mid week...severe weather possible

- Hot weather looking likely next weekend

&&

.DISCUSSION...
Issued at 338 PM EDT Sun Jun 15 2025

- Quiet start to the week...Dry through Monday Night

A quiet start to the week is expected weather wise as surface high
pressure hangs on into Monday. Generally partly cloudy skies are
expected with some high clouds moving through tonight and cumulus
development expected on Monday. Lows tonight will dip into the 50s
again in most areas...warming into the 80s on Monday. Southwest
flow kicks in on the backside of the departing surface ridge and
we will see warmer lows as a result, only dropping into the 60s.

- Showers and storms mid week...severe weather possible

Tuesday looks to be a warm day with southwest flow in place.
850mb temperatures reach the upper teens C which should bring at
least upper 80s for highs for the southeast half of the forecast
area. The surge of moisture into the area at the surface (mid 60s dew
points) will make it feel like mid summer. A cold front will be
poised just upstream, slowly sliding our direction as a mid level
wave moves from west to east across the Northern Great Lakes.
Showers and storms will be possible Tuesday afternoon and evening,
with the best chances over Central Lower Michigan closer to the
front.

The front stalls and becomes stationary Tuesday night over the
CWA, likely becoming a focus for shower and thunderstorm
development. The models are not real bullish though on the threat
of precipitation Tuesday night which is likely due to the fact
there is not a coherent low level jet in the area to focus the
precipitation. With the front, instability and a weak LLJ we do
have 30-60 pops through the course of the night.

The main focus is on Wednesday when the deterministic models try
to bring a low into or through the area. The ECMWF is quicker
pushing the low into the CWA at max heating, while the GFS lags a
bit not bringing it through until Wednesday night. We will likely
see a warm front lifting north through the area during the day
and a cold front sweeping in during the evening. The mid level
wave in both models (GFS and ECWMF) looks potent. The mid level
jet in both the GFS and the ECWMF is in excess of 50 knots. The
ECWMF has a 50 knot low level jet as well. Suffice it to say,
dynamics are in play with this system. Thermodynamics may be in
place as well with MUCAPE values at least into the 1000-2000 j/kg
range with some models indicating higher. Deep layer shear will be
strong given both speed and directional shear. 0-6km shear is in
excess of 50 knots with some suggestion of 60-70 knots. It is day
4, but cannot argue with the Slight Risk that SPC has already
placed us in. Confidence will increase as two factors become more
clear 1) the GFS and ECWMF coming more in line with one another in
timing of the low and 2) some certainty that Tuesday night and
Wednesday morning clouds and precip don`t put a lid on our
instability. Depending on how those two items trend we could be
looking at an episode of severe weather with all hazards in play.
Plenty of time yet to watch how things evolve in the models.
Clearly our focus in the 7 day forecast is on mid week!

- Hot weather looking likely next weekend

Once the mid week system clears to the east heights begin to rise
Thursday night which continues right into the weekend. A strong
mid summer ridge is fully in place by Sunday. 850mb temperatures
rise into the +20 to +22 C range for Saturday and Sunday which
brings a solid likelihood of temperatures reaching at least the
low 90s.

There is a weak shortwave in the models in the Friday night /
Saturday morning time frame that could bring a period of showers
and storms. This wave looks to be associated with a warm front
lifting through the area on the leading edge of the very warm air
before we push fully into the ridge position.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 715 PM EDT Sun Jun 15 2025

SCT to BKN high clouds are expected tonight into Monday. There is
a low (10-20 percent) chance that a high MVFR cloud deck will
develop towards BTL, JXN, and LAN. Otherwise, RH time/height progs
and high resolution guidance suggests a Cu layer develops in the
7-10kft range Monday afternoon persisting through the end of the
TAF window.

For most TAF sites easterly winds subside to 5 knots or less
overnight and increase to 3-8 knots from the south to southeast
Monday. At MKG a westerly lake breeze diminishes after sunset
with light easterly winds overnight. Winds increase to 5-10 knots
from the southeast after daybreak, becoming southwesterly in the
afternoon as the lake breeze develops.

&&

.MARINE...
Issued at 338 PM EDT Sun Jun 15 2025

The rest of Sunday will feature easterly (offshore) flow is expected
near the lakeshore through this evening with northerly flow over the
open lake. Light and variable winds are expected over the lake
Sunday before south to southwest winds of 10-15 knots develop
Tuesday and Wednesday. The other notable weather that may be
impactful to marine interests is several periods of thunderstorms
are becoming increasingly likely between late Tuesday and
Thursday.

&&

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

&&

$$

DISCUSSION...Duke
AVIATION...Thomas
MARINE...Thomas