958 FXUS63 KGRR 171055 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 655 AM EDT Fri Apr 17 2026 .KEY MESSAGES... - Dense Fog through this morning with fair weather today - Strong, possible severe storms Friday night - Cooler, Breezy weekend with cooler and drier weather ahead && .DISCUSSION... Issued at 253 AM EDT Fri Apr 17 2026 - Dense Fog through this morning with fair weather today Bottom Line Upfront: Dense fog continues to overspread the region which has reduced visibilities to 1/4SM or less. This fog will continue through most of the morning with fog slowly lifting and visibilities improving late this morning, early this afternoon. Expect impacts to the morning commute. Have issued a dense fog advisory accordingly. The copious amounts of rainfall this week has brought large amounts of low level moisture across Southern Michigan and northern Indiana. Soundings show strong inversion at the surface through the lowest 1KFT with light to calm winds. Dry and slightly warmer air above will keep the cooler, moisture air trapped this morning. The main question is when will the inversion break and the visibilities improve. With high pressure building overhead, not expecting for any flow to mix down. Due to that, will need to wait for daytime heating to allow for warming the surface and dewpoint depression to drop enough for fog to lift and dissipate. This will thus take all morning, with conditions improving slowly with fog lingering through most of the morning and fog finally lifting between 10 AM and Noon. - Strong, possible severe storms Friday night As stated above, High pressure will dominate the weather pattern today which will bring a welcome reprieve to the wet and stormy pattern that has dominated Michigan this week. However, those conditions will be short lived as another frontal system is expected to move through the region tonight and into Saturday. A large barotropic low will be moving through central Canada and its corresponding low and mid levels will swing through an elongated trough and corresponding front through the Great Lakes Friday night into early Saturday. Latest CAMS show steep lapse rates along with good mixed level CAPE. That will correspond with a strong 45KT LLJ that should provide decent shear along and behind the front. Mode of convection should be QLCS with potentially embedded supercells. With soundings being inverted in the lowest levels there is a potential for strong DCAPE which is an indicator that damaging winds and large hail are the main threat. There is also the presence of a cap in the 2 to 5KFT range. This could be a limiting factor. Another limiting factor will be the time of day, as this front should be trekking through the area during the evening. However, there is a good chance that the LLJ and shear overcomes those factors and that any cap could also allow the strongest storms chance to increase enough to break the cap and mix down to the surface with damaging winds. Due to these concerns southwestern lower Michigan is either in a marginal to slight risk. The storms should move through quickly so not expecting training storms. However given the inundation of the region, any rainfall could bring some runoff. QPF remains in the quarter inch to three quarter inch range. Some overperforming storms could have strong enough rain rates to put down an inch but will any heavy downpours will be short lived. Strongest storms should be along and south of the I 96 corridor but as stated above, additional rainfall is expected across Lower Michigan. For more discussion of the rivers please go to the hydro section. - Cooler, Breezy weekend with cooler and drier weather ahead The above mentioned cold front will then usher in cooler northwesterly flow which will allow for cooler temps through the weekend and into early next week. Strong winds with gusts upwards of 30 mph are possible late Saturday. Lows Sunday morning will be at to below freezing with highs on Sunday struggling to get into the mid 40s. While most would not appreciate the cold, it also means dry which given the latest moisture will allow for rivers to recover. A building high over the central US will keep downsloping flow through the region through at least mid next week. Temperatures should rebound back into the mid to upper 60s mid next week. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 657 AM EDT Fri Apr 17 2026 The main aviation concern this morning is the fog. A dense fog advisory will cover all TAF sites. Airport Minimums for visibility are expected this morning. All TAF sites will continue to see Airport minimums through the next 3 hours, potentially until around 15Z. The widespread recent rainfall, calm winds and inversion will keep VLIFR. Cigs will remain to airport minimums as well. The main question remains when will it lift. Latest model soundings give good credence to fog/mist and LIFR and lower cigs continuing through 14Z if not until 16Z. here is a chance MKG improves by 14Z. Cigs and vsbys should finally improve to VFR between 15Z to 18Z. VFR will continue through the daytime with clouds infiltrating tonight with showers and storms possible tonight into Saturday morning. Have adjusted the TAFS for the the incoming convection. Chances for TSRA at times for all TAF sites between 04Z to around 10Z. Due a strong Low Level Jet have put in LLWS. While winds could be 10 to 20 kts at the surface from the southeast or south the LLJ will be from the southwest at 45 to 50 kts between 1 to 2 KFT. Thus LLWS at most TAF sites between 05Z to 10Z. && .MARINE... Issued at 450 AM EDT Fri Apr 17 2026 Dense marine fog will continue today into this evening. Winds and waves will increase late today and continue through the weekend. A small craft advisory will take effect tonight and should continue due to the gusty winds through Saturday into Sunday morning. Marine Dense Fog will continue into this evening. A line of thunderstorms should cross the lake tonight with the potential for winds in excess of 34 knots and potentially some large hail. && .HYDROLOGY... Issued at 432 AM EDT Fri Apr 17 2026 Bottom Line Up Front: Significant flooding continues on the Muskegon River with minor to moderate flooding expected in the Grand River Basin through the coming days. Comstock Park at Grand River could reach Major flood stage by Sunday. While less moisture fell yesterday, another half an inch to an inch of rainfall fell into the Grand River Basin. Scattered rainfall fell through northern lower with isolated half an inch to inch amounts. This will add to what has already fallen into the river system. Major flooding is expected along the Muskegon River at all forecast points. Minor to moderate flooding forecast for much of the Grand River and its tributaries. Comstock Park at Grand River could reach Major flood stage by Sunday. The Kalamazoo River basin saw some precipitation yesterday but no river flooding is expected. Our Saginaw River basin points at the Chippewa River at Mt. Pleasant, and the Pine River at Alma are also forecast to reach minor flood stage. No rainfall is expected during the daytime today. The next chance for more rain will be tonight into early Saturday. Thunderstorms remain expected to bring widespread totals of 0.25-0.75" Friday Night into Saturday. Highest should be along and south of the I 96 corridor, especially near I-94. Given the saturated antecedent conditions, urban and small stream flooding is possible with thunderstorms, particularly Friday Night with potentially heavy rain rates. These storms are expected to move through quickly so not expected storms to train at this time. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Dense Fog Advisory until 11 AM EDT this morning for MIZ037>040- 043>046-050>052-056>059-064>067-071>074. MARINE...Dense Fog Advisory until 8 PM EDT this evening for LMZ844>849. Small Craft Advisory from 8 PM this evening to 8 AM EDT Sunday for LMZ844>849. && $$ DISCUSSION...Ceru AVIATION...Ceru MARINE...Ceru HYDROLOGY...Ceru/Thomas

NWS GRR Office Area Forecast Discussion