961
FXUS63 KGRR 181125
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
725 AM EDT Thu Sep 18 2025
.KEY MESSAGES...
- Isolated Showers Today, Warm Temperatures Continue
- Weekend Chances for Rain and Storms
&&
.DISCUSSION...
Issued at 350 AM EDT Thu Sep 18 2025
- Isolated Showers Today, Warm Temperatures Continue
Another warm day is in store with highs in the 80s with areas
toward central lower Michigan approaching 90. Winds will remain
light under the influence of high pressure, however a backdoor
cold front will move into the region this afternoon bringing with
in more moisture. The increased moisture, around 250-500 J/kg of
SBCAPE along with lift provided from the front may case isolated
to scattered showers and a few thunderstorms to develop toward the
Tri Cities, Mt Pleasant, Clare area. Lower chances (20 percent)
exist along a Ludington to Grand Rapids to Lansing line.
Any showers diminish around sunset. Behind the front surface
moisture increases as seen in the GFS and NAM soundings. With the
low level saturation advecting into the area fog will be possible
and could be dense. Any fog will then burn off a few hours after
sunrise with cooler temperatures in the low 70s to mid 80s from
Clare to South Haven.
- Weekend Chances for Rain and Storms
This weekend upper level troughing moves into the area along with
warm air advection the low level jet, and positive vorticity
advection. We`ll be on the edge of this lift during the day
Saturday with lakeshore counties having the best chance (30 to 50
percent) for a shower or storm during the day into Saturday night.
Chances increase across the area (40 to 60 percent) Sunday into
Sunday night as we move into the warm sector with signals for a
downward trend through the day Monday as the front shifts through
the area.
Afterward the synoptic pattern becomes more uncertain. Looking at
cluster analysis a wide range of outcomes are present with faster
moving open wave troughs and slower moving closed off lows along
with short wave ridges at times. With this uncertainty see no
reason to adjust NBM PoPs in the extended which keeps largely 20
percent PoPs through the week.
&&
.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 725 AM EDT Thu Sep 18 2025
Light and variable winds become more northwesterly this afternoon
with FEW to SCT cumulus around 4000 to 6000 feet. Any showers and
thunderstorms this afternoon look to be north of TAF sites, but
GRR and LAN have a 20 percent chance this afternoon with better
chances to the north. Winds then shift to the northeast tonight
behind the cold front. Fog is possible for Friday morning mainly
after 9Z, but there is uncertainty with how low visibilities would
fall.
&&
.MARINE...
Issued at 350 AM EDT Thu Sep 18 2025
Light winds continue with low wave heights. Winds will become more
northwesterly this afternoon then shift to the northeast tonight
behind the front. Easterly winds continue through Friday and may
approach Small Craft Advisory levels Friday night. Southerly flow
returns over the weekend with southeast winds Saturday and
southwest winds Sunday along with chances for showers and
thunderstorms.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...RAH
AVIATION...RAH
MARINE...RAH
NWS GRR Office Area Forecast Discussion
