232
FXUS63 KGRR 150726
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
326 AM EDT Sun Jun 15 2025

.KEY MESSAGES...

- Dry today and Monday

- Increasing humidity, showers/storms mid week

- Hot next weekend

&&

.DISCUSSION...
Issued at 326 AM EDT Sun Jun 15 2025

- Dry today and Monday

A line of showers has developed along a weak h8 convergent
boundary from CAD southwest across LDM to Wisconsin. This will
likely dissipate later this morning. Otherwise, IR loop shows a
bkn-ovc mid deck over the northern two rows of counties with
mainly bkn high clouds covering the rest of the cwa.

Expect a mix of clouds and sun today across the cwa with highs
around 80 and dewpoints in the upper 50s. The high over Ontario
the past several days will move east Monday, resulting in higher
heights and warmer temperatures; highs in the mid 80s.

- Increasing humidity, showers/storms mid week

Dewpoints will surge into the mid 60s Tuesday and the air will
feel rather summer-like, compared to the lower humidity values of
late. Southwest flow will increase Tuesday ahead of a low that
will move toward the state Wednesday. Moisture transport vectors
increase considerably Tuesday night into Wednesday. Instability
will also increase, and with it, so will chances for showers and
thunderstorms. There hasn`t been much change in ECMWF ensemble
mean QPF over the past few model runs. Still looking at a half
inch to inch of rain across much of the cwa. In fact, each
ensemble member produces precipitation. LREF ensemble mean
suggests a 50-70% chance of half inch of of rainfall during this
time frame an a 25-35% chance of an inch. Precipitable water
values increase to 1.75 inches late Tuesday into Wednesday,
pointing toward some heavier rainfall possible. Any rainfall
would be beneficial given the dry conditions in place across much
of the cwa.

As for chances for strong/severe storms mid week, some model
discrepancies exist between the operational ECMWF and GFS models.
Specifically, the GFS is a bit quicker moving the trailing cold
front across the cwa compared to the ECMWF, which would lower the
chances for strong/severe convection. We`ll start to get a better
indication on timing over the next day or so as the time frame in
question comes into the CAMs.

Precipitation chances will linger into Thursday when the trailing
upper wave moves through.

- Hot next weekend

A building dome of high pressure over the MS/western OH Valleys
will result in an increase in heat across the Great Lakes. We may
be looking at 90 degrees by Saturday/Sunday. If dewpoints push 70
degrees, heat indices will increase to the mid 90s.



&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 123 AM EDT Sun Jun 15 2025

High broken clouds cover the terminals early this morning. IR loop
also shows bkn-ovc mid clouds north of I-96. This deck is expected
to sink south today resulting in 6-10k ft ceilings at most of the
TAF sites.

An onshore wind will develop at MKG by early afternoon. Otherwise,
expect northeast winds again today.

&&

.MARINE...
Issued at 326 AM EDT Sun Jun 15 2025

High pressure over Ontario will produce a northeast wind flow this
morning. A lake breeze will develop this afternoon. However, wind
speeds will remain in the 5 to 15 mph range.

Thunderstorm chances will increase late Tuesday and continue
through Thursday.

&&

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

&&

$$

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