623
FXUS63 KGRR 172310
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
710 PM EDT Mon Aug 17 2026

.KEY MESSAGES...

- Showers and storms late Tuesday into Wednesday

- Next round of precipitation Friday night through Saturday

&&

.DISCUSSION...
Issued at 144 PM EDT Mon Aug 17 2026

- Showers and storms latter half of Tuesday into Wednesday

Today`s quaint and idyllic summer time weather, fueled by surface
high pressure, will be driven out, over hill and over dale, by a
southward progressing upper level low. That low, situated over
northern Ontario, will move through bush and through brier, over
park and over pale, bringing with it a system with good barotropic
flow.

 As the low treks southward the upper level trough will
deepen and a mid level long wave trough with a corresponding surface
trough will make its way across WI and through the Great Lakes
tomorrow.  This will swing a cold front through Lower Michigan
Tuesday night into Wednesday.

 The questions through this forecast period is how widespread
showers will be, and the potential for thunderstorms.
 Scattered showers remain likely for the area late Tuesday. PWATS
are currently around 1.5 inches. With a moist mid level, little
directional shear and the good barotropic flow mentioned above,
any showers and storms will be efficient rainers. Given that
potential, WPC has portions of the area in a marginal risk for
excessive rainfall.
 Latest storm total QPF`s are only in the 0.25 to 0.50 inch
range, but that could be significantly higher if; thunderstorms
develop,the front stalls as it moves southward and if there is any
storm entrainment through Tuesday night.

 Some rainfall could linger well into Wednesday if the front
stalls. Other wise, clearer skies with fair weather will return
Thursday.

- Another chance of precipitation Friday night through Saturday

More tumultuous weather is on its way late this week as there is
an increasing consistent signal for a deepening upper level wave
that will move through the Great Lakes Friday night and Saturday.

Latest mid range ensembles shows less anomalous moisture associated
with this system. However, there is great incongruity between the
solutions. So while precipitation will be possible it is to early
to nail down specifics. There remains the potential for rounds of
showers beginning Friday and through the first half of the
upcoming weekend. However, it could become just a mid summer`s
night dream.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 709 PM EDT Mon Aug 17 2026

VFR expected through the period. However, a cold front will be
moving toward Lower MI Tuesday and we`ll see the high cloud deck
lower to around 10k ft by the end of the period.

&&

.MARINE...
Issued at 154 PM EDT Mon Aug 17 2026

Winds and waves will remain calm through tonight and the first
half of Tuesday. Increasing southwesterly flow will build waves
Tuesday afternoon with the potential for a small craft advisory.
 This could be short lived given that the winds quickly shift
due to frontal passage. The greatest area of concern is near shore
waters north of Holland between 18Z and 00Z. However, given the
marginal timing and conditions have held off on an SCA for now.

&&

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

&&

$$

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