325
FXUS63 KGRR 180536
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
136 AM EDT Fri Jul 18 2025
.KEY MESSAGES...
- Showers and Storms Saturday and Saturday Night
- Showers and Storms Potentially Mid Next Week
- Building Heat Next Week
&&
.DISCUSSION...
Issued at 343 PM EDT Thu Jul 17 2025
- Showers and Storms Saturday and Saturday Night
The weather looks quiet and more comfortable tonight through
Friday night. High pressure will drift through the Great Lakes
region during this time, so we expect dry conditions and lower
humidity.
On Saturday a shortwave trough moving along the Canadian / U.S.
border will push a cold front into the area. The front will
translate off to the south of the state Saturday night.
Precipitation chances increase during these two forecast periods
with almost the entire area peaking at about 60 pct chances for
rain. This system is not strong by any means, but the wind in the
profile is of moderate strength. The low level jet at 850mb`s
peaks at around 20-25 knots and the mid level jet at 500mb`s
around 40 knots. Deep layer shear in the ECMWF reaches 30-40
knots, so there will be some storm organization. The main
shortwave is well north of the area, but we do see some
convectively driven vorticity maxima moving through our area.
Surface dew points reach the low 70s with MUCAPE values of at
least 1,000 to 2,000 j/kg will be possible. So, with both
sufficient CAPE and shear and a source of lift with the front, not
out of the realm of possibilities of seeing some scattered strong
to severe storms. At this point we are in a day 3 general thunder
from SPC, but could see this trending up across the southern half
of Lower Michigan ahead of the front at peak heating.
- Showers and Storms Potentially Mid Next Week
The next chances for rain come mid next week as potentially a warm
front moves through the area on Wednesday. Wednesday night into
Thursday a stationary boundary may be situated across the area
providing more chances for showers and storms. Given the range in
the forecast, 6-7 days out, and the fact we are likely dealing
with a MCS augmented frontal boundary the mid next week forecast
is low confidence.
- Building Heat Next Week
It does look like we build heat next week but again it could be
modulated by MCS`s moving through the region. 500mb heights rise
into the 590`s though which makes some semblance of heat very
likely. We should at least be around 90 next Wednesday and
Thursday in areas that remain precip free. IF MCS`s stay to the
north we could be into the 90s.
&&
.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 136 AM EDT Fri Jul 18 2025
Light winds and low clouds will continue through a good portion of
the TAF period. Ceilings should remain VFR but should remain at
4-5k feet.
&&
.MARINE...
Issued at 343 PM EDT Thu Jul 17 2025
Observations at several buoy sites and land bases stations show
gusts in the 20-25 knot range and waves over 4 feet. Winds and waves
will diminish through the evening into the early overnight hours, so
no changes to the Small Craft Advisory or Beach Hazards Statement
are needed. Winds and waves are forecast to remain below hazardous
levels Friday through the weekend as the gradient remains weak. The
noted potential for upwelling in the current northerly flow is
already underway according to observations. The Ludington Buoy has
dropped from 75F yesterday afternoon to 65F this afternoon. As long
as the flow remains offshore in the northerly flow, cooler water
temps from upwelling are possible.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Duke
AVIATION...Maczko/Thomas
MARINE...Thomas
NWS GRR Office Area Forecast Discussion
