206
FXUS63 KGRR 150536
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
136 AM EDT Tue Jul 15 2025

.KEY MESSAGES...

- Frontal System Moves through Wednesday and Thursday

- Brief respite then another weather system possible this weekend

&&

.DISCUSSION...
Issued at 315 PM EDT Mon Jul 14 2025

- Frontal System Moves through Wednesday and Thursday

   Fair weather due to high pressure will continue to dominate the
pattern through Tuesday. While the cumulus field will fill in daily,
with a mix of sun and clouds, it should be a dry forecast into
Wednesday.
 There will continue to be quite a bit of haze today due to smoke
infiltrating the region from Canadian fires. Given the high
pressure and weak flow, it could persist through tomorrow.

   The weather pattern this week will be dominated by a large upper
level low situated over Hudson Bay. That upper level low will be the
driver of a longwave upper level trough that will move through the
US this week. Models are consistent in showing a robust moisture
boundary that will extend across Nova Scotia, Quebec, Ontario and
through the northern Great Lakes early Wednesday. Expect warm air
advection out ahead of that boundary. An upper level shortwave
should move through the Midwest Wednesday, increasing instability
Wednesday afternoon.

   Moisture out ahead of that shortwave, along with diurnal heating
and warm air advection could allow for isolated showers and
storms Wednesday afternoon. While there are some questions on
timing overall, models are in fair consistency on more organized
convection possible late Wednesday into Thursday as the frontal
system brings the previously moisture boundary through the region
as it couples with mid level and upper level troughs.

  Latest NAEFS ensembles has 1.75 PWATS over the area through this
timeframe with broad level moisture through Thursday. While official
QPF remains around a quarter inch there is the potential for heavy
downpours, especially considering the atmospheric set up and
dynamics. Given that, WPC has the region in a marginal excessive
rainfall out look for Wednesday into Thursday.

- Brief respite then another weather system possible this weekend

  Zonal flow will situate itself over the Midwest and Great Lakes
region latter in the week, with high pressure over the mid levels.
This should keep moisture to the south and stifle daytime convection
Friday into Saturday.

The next forecast question will be where and when does the
Saturday/Sunday system progress. There remains timing and strength
issues. Overall trend brings another system with corresponding
showers and storms through late weekend into early next week.


a

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 136 AM EDT Tue Jul 15 2025

The haze that was present earlier has diminished per the
improvement in visibilities at the terminals. KJXN saw the
improvement briefly, and then saw fog settle in. It seems that the
southern terminals have the best chance of some fog with dew
points a bit higher. KJXN will see the worst conditions as is
typical due to the site being in a low spot.

Any fog will burn off/mix out quickly after sunset. Skies should
remain mostly clear outside of any isolated fog/stratus. A few
cumulus clouds are likely, but should not cause any impacts being
few-sct. Winds will become more from the SSW in the afternoon, and
will go light from the SSE after sunset.

There is a small chance of a shower developing at KAZO and KBTL
in the last couple of hours of this forecast period as a few move
up from the south. These should not be anything of consequence.

&&

.MARINE...
Issued at 128 PM EDT Mon Jul 14 2025

Low waves and swim risk through Tuesday with a light southerly
breeze. Thunderstorms are possible between Wednesday and
Thursday. Winds becoming north on Thursday may increase the waves
and swim risk.

&&

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

&&

$$

DISCUSSION...Ceru
AVIATION...NJJ
MARINE...CAS