508 FXUS63 KGRR 141906 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 306 PM EDT Mon Sep 14 2026 .KEY MESSAGES... - Several rounds of showers and Storms tomorrow - Chances for Rain through the week && .DISCUSSION... Issued at 258 PM EDT Mon Sep 14 2026 - Several rounds of showers and Storms tomorrow Forecast remains fairly consistent. There will be two rounds of showers tomorrow. The first will be early in the morning. It will move across Lower Michigan from the northwest and move eastward with heavy rain possible. Severe winds not expected but there is the potential for strongest storms to overperform. Another line in the afternoon and evening will trek across Southern Michigan along the warm air advection. The best instability will be in IN and OH. However, due to the significant PWATS, upwards of 2 inches, CAPE`s upwards of 1500 J/kg, lapse rates of 7 C/kg through the mid to low levels along with strong low level wind shear and there will be a chance for convection along and south of the I 94 corridor could become strong to severe. SPC continues to have a marginal risk through this region. - Chances for Rain through the week There remains some question about where the frontal pattern shifts this week. If it shifts/expands to the north then quite a bit of southern lower Michigan could receive multiple rounds of showers and storms through Thursday. The zonal flow will keep mid level moisture over the area. If there is enough warm air advection, along with any mid level short wave amplification, and areas could receive periods of heavy rain. NAEFS shows a prolonged period of anomalous moisture along the southern half of lower Michigan. Latest NAEFS PWATs along the I 96 corridor could be around 1.25 inches and increase to 2 inches in northern IN. This moisture boundary remains entrenched over the area through the week and latest ensembles has it shifting northward towards the end of the week. If it shifts southward, then much of the region will remain dry. Another system will lift into the area this weekend and could bring additional shower and thunderstorm chances Saturday. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 205 PM EDT Mon Sep 14 2026 VFR with light winds are expected through evening. Clouds start to thicken below 10,000 feet after 00 Z and through the night, from northwest to southeast. Initially some light rain showers or virga may push in, then instability at around the 7,000 foot cloud layer begins to build enough for a chance of thunderstorms embedded within the batch of rain during the morning hours Tuesday. South of the batch of rain or thunderstorms, there may be a period of LLWS late tonight / early morning. && .MARINE... Issued at 258 PM EDT Mon Sep 14 2026 Conditons deteriorate tonight into Tuesday as an approaching surface low deepens increasing southerly flow. Enough of a signal for 35-40 knot gales exists north of Holland to hoist a Gale Warning, with a Small Craft Advisory south of Holland for 22-33 knot gusts. Gales persist into Tuesday morning with conditions hazardous to small craft continuing into Tuesday night. Will also hoist a Beach Hazards Statement from Allegan County north for waves as high as 12 feet. Due to the refracting waves and strong southerly flow, have expanded the beach hazards to include Van Buren county. The southerly flow could shift just enough that waves miss South Haven, however given latest trends, there is enough concern that waves could grow to the 3-5 ft range bringing a high swim risk. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement from 10 PM EDT this evening through Tuesday evening for MIZ037-043-050-056. Beach Hazards Statement from 10 PM EDT this evening through Tuesday afternoon for MIZ064-071. MARINE...Small Craft Advisory from 10 PM this evening to 5 PM EDT Tuesday for LMZ844-845. Gale Warning from 10 PM this evening to 8 AM EDT Tuesday for LMZ846>849. && $$ DISCUSSION...Ceru AVIATION...CAS MARINE...Ceru

NWS GRR Office Area Forecast Discussion