976 FXUS63 KGRR 140710 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 310 AM EDT Tue Apr 14 2026 .KEY MESSAGES... - Severe thunderstorms overnight into early Tuesday Morning - Severe Thunderstorms possible late Tuesday into early Wednesday - Flood Potential remains elevated through the week && .DISCUSSION... Issued at 259 AM EDT Tue Apr 14 2026 - Severe thunderstorms overnight into early Tuesday Morning A boundary continues to move through northern lower Michigan overnight through early this morning. Severe storms with large hail have already moved along and north of the US 10 corridor. While there remains some CIN, upwards of -250 J/kg south of that corridor, there is just enough mixed layer CAPE to allow for the strong 0-3KM shear and LLJ to continue storm generation. Latest CAMS, especially the HRRR, have the convection from across Wisconsin swinging through the region This morning with strong to severe storms moving through central Lower Michigan through sunrise. Strongest storms should be north of I 96 with the northern boundary north of US 10. DCAPE with frontal passage will be 600 J/kg at best. However, mid level lapse rates are trending around 7 C/km and the shear vector remains west to east, which could allow stronger winds to mix to the surface around sunrise. So while damaging winds are possible, large hail remains our biggest concern. The line is expected to begin to move into the region around 09, along with the mid level low and corresponding wave. That wave along with the LLJ will move into southern Quebec and to the east by 12Z which will end this morning`s threat of severe weather. - Severe Thunderstorms possible late Tuesday into early Wednesday Any tertiary showers this morning should linger to the south and will be in more stable air and not expected to be strong or severe. Latest SPC Day 1 Outlook for later Today into Wednesday continues to have almost all of lower Michigan in a slight risk. The enhanced risk has shifted to cover most of southern Wisconsin. The temperature of Lake Michigan shouldn`t impede storms as it should provide a cold pool for them to move over. The persistent southwesterly flow should correspond with warm air advection ahead of the incoming surface low. That should allow the atmosphere to recover by late this afternoon ahead of this afternoon and evening`s system. Daytime heating of 70s to low 80s, especially south of I 96 should provide MLCAPE of 1 to 2K J/kg. The wind profiles favor supercell formation. Latest CAMS continue to have storms forming after 22Z and continuing through at least the first half of the overnight period as the strong 850mb jet of upwards of 45 kts should continue to fuel storm generation into early Wednesday. Based on those factors, there remains a good chance for strong to severe storms late Tuesday afternoon with damaging winds and large hail the main threats. However, with low LCL`s and strong shear, an isolated tornado is possible. - Flood Potential remains elevated through the week A flood watch will remain into Wednesday. Heavy downpours from the latest storms has QPE of around 2.0 inches of rainfall with QPF to FFG of upwards of 150 percent. The mid level flow has kept the storms to train through the US 10 corridor and that pattern should continue until the above mentioned boundary moves through after 12Z. The heavy downpour threat will shift to south of the I 96 corridor today, however QPF through Thursday remains a widespread 2 to 3 inches. So urban, stream and flash flooding remains a concern. For information on the increasing flood threat, see the Hydrology section below. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 132 AM EDT Tue Apr 14 2026 Overall and generally, things remain on track as compared to the forecast from 6 hours ago. The main difference is that the showers and storms are further north than previously expected. There have been a few-sct showers and isolated storms in between the terminals. The widespread activity remains well north of the terminals, but will eventually make its way down this south. It looks like the line of storms over Wisconsin will approach KMKG around 08z or so, and press SE thereafter. the majority of sites will see MVFR to LIFR conditions with the visibilities/ceilings with the showers/storms. Conditions will be slow to improve this morning/afternoon after the showers. VFR conditions are likely to return later this afternoon. We will see showers and storms redevelop then toward 23-01z as the next wave of low pressure moves through. We have gone with predominate showers/storms after 23-01z at all sites with LIFR conditions expected. && .MARINE... Issued at 302 AM EDT Tue Apr 14 2026 Special Marine warnings for thunderstorms will continue this morning with hazardous winds and waves for small craft are expected this morning. Strong to severe storms are expected through sunrise. Thunderstorms, possibly severe thunderstorms with hail and wind, are possible over Lake Michigan this evening/tonight and Tuesday evening/night. && .HYDROLOGY... Issued at 302 AM EDT Tue Apr 14 2026 .Update... Based on the fact that another 2 to 3 inches has fallen upstream and should make its way to the Croton gauge later today. ..Previous... The further north you go in the Lower Peninsula, the more significant the flooding situation becomes. Around an inch of rain fell across much of the area along and north of the Muskegon River watershed over the weekend, with a much heavier swath of 2-4 inches across the Manistee River watershed and the headwaters portions of the Muskegon basin. Coming on the heels of one of the wettest springs on record so far, and in the midst of a significantly active (and wet) ongoing weather pattern, the water that`s already on the ground is going to produce renewed flooding on the Muskegon River (and many others rivers further north as well). With another 2-3" of rain over the next few days in the Muskegon, we`re now expecting the most significant flood on the Muskegon River since the flood of 2018. If the next few days of rains overperform (which is entirely possible), the forecasted crests will go even higher. If you live near the Muskegon river, now is the time to prepare for significant flooding. Meanwhile, further south, conditions in the Grand River basin are in slightly better shape, although water is still high from all of the recent rains. We`ve finally dropped below stage at all locations in the basin, but that trend will soon reverse as water levels start to climb again throughout the week. With an additional 2-3" of rain expected in this area as well, it`s beginning to look like the region will generally repeat the flood levels experienced last week. In addition to the river flooding, some of the thunderstorms we`re expecting over the next few days could be very slow moving over the same areas repeatedly. If this happens, some localized rain totals of 4+ inches are possible in the next few days. If this happens over one of the urban areas, significant fast- developing urban flooding is possible. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Flood Watch through Wednesday morning for MIZ037>040-043>046- 050>052. MARINE...Dense Fog Advisory until 8 AM EDT this morning for LMZ844>849. Small Craft Advisory until 4 AM EDT Wednesday for LMZ844>849. && $$ DISCUSSION...Ceru AVIATION...NJJ MARINE...CAS HYDROLOGY...AMD

NWS GRR Office Area Forecast Discussion