221
FXUS63 KGRR 200640
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
240 AM EDT Thu Aug 20 2026
.KEY MESSAGES...
- Dry and less humid today
- Showers with some thunderstorms Friday into the weekend
&&
.DISCUSSION...
Issued at 240 AM EDT Thu Aug 20 2026
- Dry and less humid today
Today should feature dewpoints ranging from the upper 40s over
central interior Lower Michigan to the upper 50s farther south
along the I-94 corridor. This will feel noticeably drier to many.
Maximum temperatures will range from near 80 to the lower 80s,
with maximum apparent temperatures about the same or even slightly
less where dewpoints are lower. Another and more robust measure
of potential heat stress, known as the WetBulb Globe Temperature
(WBGT), gives a reading of lower 70s for this afternoon. So all
of this is to say that it should feel relatively comfortable
outside today.
- Showers with some thunderstorms Friday into the weekend
Certainty is growing that we will see showers and thunderstorms
moving through the forecast area Friday night and exiting to the
east of the area by Saturday afternoon, yielding a dry Sunday. The
exception may be the immediate lakeshore, particularly the Sable
Points area, where lower tropospheric cooling may be sufficient
for lake effect sprinkles.
The growing certainty is related to the most recently available
ensemble guidance, which shows a mean solution of meridionally
deeper upper troughing that`s particularly pronounced into the
Ohio Valley region. The expectation still is that this trough will
become a cutoff low centered somewhere over the north-central
Great Lakes region. The more amplified solution at this location
means more of an equatorward component of the flow aloft over
Lower MI, which is a drier pattern and suggests precipitation will
remain shunted east of our forecast area after Saturday
afternoon. However, it should be noted that ensemble solutions
from as recently as yesterday morning and afternoon showed a
sizable number of members forecasting precipitation through
Sunday. So, although there is growing confidence for a dry Sunday,
this is far from certain.
&&
.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 130 AM EDT Thu Aug 20 2026
Thanks to an incursion of drier air at lower levels the probability
for maintaining VFR conditions through the period is greater than
90 percent, except for JXN and BTL, which have an estimated 30
percent chance of experiencing brief MVFR visibility restrictions
towards sunrise. This reasoning is based upon the presence of a
weak surface boundary in that area where greater dewpoints/RH
values appear to be pooled. The probability of MVFR occurrence is
too low to explicitly mention in the TAFs.
The only other change was to introduce a cloud deck around 8000
feet this morning for the southern terminals associated with
convective debris from thunderstorms to the west and southwest of
the area. These clouds are high enough that they likely wouldn`t
interfere with the previously mentioned possible fog production.
Made minor adjustments to winds this update as well. Based on
high resolution guidance, MKG may see lake breeze augmented winds
more from the northwest this afternoon instead of the typical
west-southwest direction.
&&
.MARINE...
Issued at 240 AM EDT Thu Aug 20 2026
No concerns in the short term. Winds and waves could meet Small
Craft Advisory thresholds by Friday afternoon, mostly around the
Sable Points, due to persistent and moderately strong winds from
the south-southwest over Lake Michigan.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...TJT
AVIATION...TJT
MARINE...TJT
NWS GRR Office Area Forecast Discussion
