923
FXUS63 KGRR 202235
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
635 PM EDT Thu Aug 20 2026
.KEY MESSAGES...
- Scattered showers/thunderstorms late Friday into Saturday
- Cooler and comfortable Sun-Tue then midweek rain chance
&&
.DISCUSSION...
Issued at 204 PM EDT Thu Aug 20 2026
- Scattered showers/thunderstorms late Friday into Saturday
Increasing low-level moisture returns Friday in a weak warm-air
advection zone, ahead of a cold front that is expected to pass
through with a deepening upper-level trough Friday night into
Saturday morning. Models generally have CAPE values around
500-1500 J/kg with about 20 knots of deep layer shear. Scattered
showers and thunderstorms may develop from late in the day Friday
and through the night into part of the day Saturday. Severe
weather potential appears low at this time, though isolated and
temporary intersections of better low-level shear and CAPE can`t
be ruled out. Average QPF is approximately 0.1 to 0.25 inches, but
realistically rain totals could be more hit-or-miss, with
isolated spots of over an inch possible.
- Cooler and comfortable Sun-Tue then midweek rain chance
Ensemble agreement in the general pattern from the weekend into
mid next week is fairly good, with troughing over the Great Lakes
evolving into a cutoff low over northeastern parts of the region.
This would likely put Lower Michigan into a northwest flow of
somewhat cooler and drier, more comfortable air Sunday and Monday.
There is a slight chance of daytime showers popping up inland on
Sunday during peak heating underneath the upper-level trough.
Somewhat warmer and more moist air then returns Tuesday ahead of
the next cold front with a chance of showers/storms from late Tue
into Wed.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 634 PM EDT Thu Aug 20 2026
Scattered diurnal Cu will diminish over the next 1-2 hours with
mainly high clouds overnight. High clouds will thicken into Friday
as a warm front approaches the area. There is a low (10-20
percent) chance of MVFR fog at AZO, BTL, JXN, late tonight. Light
and variable winds overnight increase to 7-12 knots from the
southwest Friday. After 18z, scattered showers and isolated
thunderstorms are possible at all terminals, best chance at
LAN/JXN. Given low confidence in terminal impacts have introduced
the risk with a PROB30 for showers and kept thunder out of the TAF
at this time.
&&
.MARINE...
Issued at 204 PM EDT Thu Aug 20 2026
Low waves and low swim risk through early Friday morning.
Southwest winds increase on Friday 10-15 knots gusting to 20-25
knots, particularly north of Whitehall, where a small craft
advisory and beach hazards statement may be needed for the
afternoon. Then behind a cold front and amid northwest flow of
cooler air during Saturday and Sunday, hazardous waves and
currents are likely for swimmers and small craft.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...CAS
AVIATION...Thomas
MARINE...CAS
NWS GRR Office Area Forecast Discussion
