946 FXUS63 KGRR 160747 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 347 AM EDT Tue Jun 16 2026 .KEY MESSAGES... - Showers and Thunderstorms Tuesday, Marginal Severe Risk - Thunderstorms and Heavy Rain Wednesday, Slight Severe Risk - Quieter Late Week Then Rain and Thunderstorm Chance Sunday && .DISCUSSION... Issued at 347 AM EDT Tue Jun 16 2026 - Showers and Thunderstorms Tuesday, Marginal Severe Risk Ahead of and underneath a mid-upper level shortwave trough, CAPE around 750-1000 J/kg will be maintained from midday through evening. Elevated showers this morning are possible but more likely with embedded thunder during the early afternoon as the lower levels moisten, warm, and destabilize. A short break in the rain is expected followed by another round of thunderstorms late afternoon or evening. Shear is relatively modest at about 20-30 knots 0-6 km with the first round, but greater in the lower levels with the second round with about 20-25 knots wind difference 0-1 and 0-3 km potentially, with some hodograph curvature. Along with a little richer moisture in the lower levels during the second round, rotating updrafts may pose a low but not zero tornado risk especially near/south of I-96 where parameters are higher. 40-60 mph wind gusts are the main threat with thunderstorms today with 500-700 J/kg of DCAPE and mixed lower levels ahead of the storms. Hail may also occur with some storms which would also locally increase the wind threat. - Thunderstorms and Heavy Rain Wednesday, Slight Severe Risk Models continue to show a surface low with MSLP around or below 990 mb tracking from Minnesota to Lower Michigan on Wednesday, which is significant for this time of year at more than 4 standard deviations below normal. Deep moisture will be present during the afternoon with PW values between 1.2 and 1.7 inches. The nose of a 50 to 70 knot 850 mb jet will be over our area between mid afternoon and evening while a coupled jet configuration at 250 mb favors substantial upper-level divergence. 500-1000 J/kg of MUCAPE from elevated parcels may be present during this time. This points to a very high probability of rain along with a few hour burst of heavy rain from thunderstorms in a broad swath of our area, totaling 1 to 2 inches and potentially 3 inches in some places. Flood potential in southern Michigan will have to be monitored. Despite what should be a fairly stable lower atmosphere, the extremely sheared lower levels (50 knot wind difference 0-1 km) may pose some severe wind threat particularly if any gravity waves develop in association with the convection. - Quieter Late Week Then Rain and Thunderstorm Chance Sunday After a breezy day on Thursday, broad high pressure over the region will offer respite late in the week along with cool temperatures. Another upper level trough translating from the western to central CONUS may develop another low pressure system that would bring a rain or thunderstorm threat for Sunday, though the track and magnitude of the low is still in question. Ensemble member QPF for Sunday at this time ranges anywhere between little to no rain and another heavy rain threat. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 211 AM EDT Tue Jun 16 2026 Expecting VFR early this morning with clouds at or above 7,000 feet and 25 knots of wind shear between 1,500 feet and ground from 09 to 12 Z. Showers may develop after 12 Z but are more likely between 16 and 01 Z. Prob30 lines will cover the thunderstorm chances for now, though these may become tempo in the next update. The TS chances may occur in two phases between 16 and 01 Z, with gusty winds greater than 30 knots being a possibility with temporary IFR heavy rain. && .MARINE... Issued at 347 AM EDT Tue Jun 16 2026 Small craft advisory and beach hazards remain in place throughout today as 15 to 25 knot winds build 3 to 6 ft waves and strong currents. Winds relax and waves subside a little Wednesday morning, then southeast winds will become hazardous for small craft in the afternoon and evening. Thunderstorms over Lake Michigan are possible today late morning through late afternoon, and on Wednesday. Thursday will be another breezy day with small craft and beach hazards. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement through late tonight for MIZ037-043-050- 056-064-071. MARINE...Small Craft Advisory until 4 AM EDT Wednesday for LMZ844>849. && $$ DISCUSSION...CAS AVIATION...CAS MARINE...CAS

NWS GRR Office Area Forecast Discussion