534 FXUS63 KGRR 022218 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 618 PM EDT Thu Apr 2 2026 .KEY MESSAGES... - Thunderstorms Likely, Severe Thunderstorms Possible This Evening - Thunderstorms Friday Night to Saturday && .DISCUSSION... Issued at 222 PM EDT Thu Apr 2 2026 - Thunderstorms Likely, Severe Thunderstorms Possible This Evening Models have remained pretty consistent on the evolution of the environment, with a warm front surging toward I-96 late this afternoon and storms developing along a prefrontal trough over IL, IN, southern Lake Michigan, and Southwest Michigan. Altogether, the greatest severe weather threat will be between 5 PM and 10 PM, but can`t rule out a couple more isolated storms around 10 PM to 1 AM helping to stir down strong environmental winds above the surface. CAPE in the range of 500-1000 J/kg will develop in the warm sector with most unstable parcels just above the surface, and the greatest concentration of CAPE will be in the warm lower troposphere above the LFC to about 4 km. This limits the hail potential but increases the potential for vorticity tilting and stretching in a highly sheared 0-1 km and 0-3 km layer. Hodographs in the warm sector near and south of I-96 are expected to be elongated and clockwise curved at least in the 0-2 km layer, with less shear above. About 45 knots of 0-3 km shear is possible. The Significant Tornado Parameter south of I-96 is favored to increase to at least 1, perhaps approaching 2-3, between 5 PM and 9 PM. Moisture through the convective layer will be high, with LCLs 1000 meters or lower, increasing rainfall rates but tempering the strength of convective downdrafts and cold pools. But with low- level wind shear being strong, it won`t take strong downdrafts to mix down locally severe wind gusts. The storm mode that evolves over Southwest Michigan this evening could be some mix of quasi-linear segments or semi-descrete supercells. Either way, the small scale and lower-atmospheric mesocyclones or mesovorts that develop in this environment could be capable of producing a tornado or two in our area. Any right- moving mesocyclones are calculated to move northeast around 55 mph, making this evening`s hazards fast-unfolding if the conditional threat is realized. - Thunderstorms Friday Night to Saturday Another wave of low pressure along this regional frontal zone provides elevated warm-advection thunderstorms overnight Friday night and showers/storms in the vicinity of a cold front during the day Saturday. This will be another high-shear low-CAPE sort of environment so can`t rule out a marginal severe threat at this point. The earlier daytime convection timing on Saturday may keep the greater risk farther east. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 615 PM EDT Thu Apr 2 2026 A dynamic system is moving through the area. A warm front is moving north near I-94 and showers and thunderstorms will continue to develop for the next several hours. Additionally, strong low level flow ahead of the low over Iowa will result in LLWS through midnight or so. The trailing cold front will pass over the terminals around 12z Friday putting an end to the precipitation. Cigs/vsbys will slowly lift late morning and early afternoon. && .MARINE... Issued at 222 PM EDT Thu Apr 2 2026 Considered a gale warning for this evening/tonight, but the threat of gales will probably be conveyed with special marine warnings in the vicinity of thunderstorms. South-southwest winds strengthen this evening, but the stable and cool marine air layer is likely to subdue the potential for hours of widespread gales. Instead, gales may be more spurious and thunderstorm-related. Hazardous waves for small craft linger into part of the day Friday while gradually diminishing. Hazardous conditions for small craft are again likely Saturday and Sunday. && .HYDROLOGY... Issued at 222 PM EDT Thu Apr 2 2026 The 3rd (of 4) rounds of rain this week is underway, and is so far unfolding about as expected. An additional 0.5 to 1.0 inches of rain has fallen across the Muskegon River and lower Grand River watersheds. Water levels are beginning to rise. An additional 0.5 to 1.0 for the remainder of today, plus another 0.5 or so on Saturday (Round 4) is raising the possibility of some minor flooding developing along the Muskegon River. It`s also possible that some of the most vulnerable flood locations in the Grand basin could approach flood stage, namely in Comstock Park and also also the Maple River near Maple Rapids, but this will depend on how the rest of today`s rain unfolds. A flood watch is in effect for parts of the Muskegon River, with flooding possible by this weekend. Thankfully the rain rate today is fairly moderate, with locally heavy downpours, but not enough to cause substantial travel impacts or other types of urban flooding. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory until 2 PM EDT Friday for LMZ844>849. && $$ DISCUSSION...CAS AVIATION...04 MARINE...CAS HYDROLOGY...AMD

NWS GRR Office Area Forecast Discussion