282 FXUS63 KGRR 071021 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 621 AM EDT Mon Sep 7 2026 .KEY MESSAGES... - Mostly sunny today, cool tonight - Chance of showers/storms Tuesday night/Wednesday, weekend && .DISCUSSION... Issued at 300 AM EDT Mon Sep 7 2026 - Mostly sunny today, cool tonight High pressure stretching from western Quebec southwest across the western Lakes will bring another day of tranquil weather with seasonal highs in the upper 70s, followed by lows in the lower to mid 50s tonight. The ridge will then begin to drift eastward tonight. - Chance of showers/storms Tuesday night/Wednesday, weekend South winds will increase Tuesday as the surface high moves east and the upper ridge moves overhead. What we`ll see is an increase in heat and humidity as temperatures climb into the lower to mid 80s dewpoints rise into the 60s. The upper ridge will be flattened by a short wave moving across the northern tier of states behind a surface cold front. The LLJ increases to 40 kts Tuesday night ahead of the cold front. As precipitable water values increase to 2 inches, we may see some heavy rain develop as convection develops along/ahead of the front. Latest RRFS progs show convection developing over the northern half of the cwa after 06z Wednesday. This is also where the nose of the LLJ is and highest MUCAPE. It`s worth noting the GFS is not bullish on CAPE Tuesday night and the RRFS has backed off a bit too. That said, we`ll need to watch for localized flooding as the upper flow becomes more parallel to the frontal boundary, which could lead to training echos. Given the high PWATs, upper short wave, and approaching cold front, PoPs in the 90 percent range seem reasonable late Tuesday night and Wednesday. Once the front moves south Wednesday afternoon, the precipitation will go with it, leading to a couple of dry days late in the week. Highs will fall back into the 70s and dewpoints will retreat to the 50s. The next cold front will approach Saturday. At this point, models show the best upper dynamics well north into Canada which may result in lower PoPs...20-30 percent...late Saturday into Sunday. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 617 AM EDT Mon Sep 7 2026 Some patchy fog is possible for the first hour or two before temperatures begin to rise. High clouds are spilling over the ridge and will be present through the period. Fog is again possible after midnight tonight at JXN. && .MARINE... Issued at 300 AM EDT Mon Sep 7 2026 High pressure overhead will result in winds and waves well below advisory criteria. However, as the high drifts east late tonight, south winds will begin to increase and a small craft advisory will likely be needed Tuesday afternoon into potentially Thursday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...04 AVIATION...04 MARINE...04

NWS GRR Office Area Forecast Discussion