830 FXUS63 KGRR 210516 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 116 AM EDT Thu May 21 2026 .KEY MESSAGES... - Frost Expected Along and North of M-20 - Periods of Rain Friday through the Weekend - Warming Up Next Week With Slight Chances (20 percent) for Rain && .DISCUSSION... Issued at 143 PM EDT Wed May 20 2026 - Frost Expected Along and North of M-20 Colder temperatures move in tonight with 925 mb temperatures around 4 to 5 C and a weak inversion in place. Lows tonight drop into the low 30s to low 40s from north to south. The best potential for frost will be along and north of M-20 where there is a higher probability (60 to 90 percent) of temperatures falling below 37 F. Therefore this area has been included in the Frost Advisory. Further south temperatures are expected to be largely above 37 F, but some isolated low lying areas could briefly fall below before sunrise. Winds further south are less likely to be calm and therefore will help keep temperatures warmer. Any increase in cloud cover would also keep temperatures from falling lower. - Periods of Rain Friday through the Weekend High pressure sticks around for one more day Thursday. Some showers may try to move in from the west Thursday afternoon, but dry air should keep anything from reaching the ground. Upper level divergence will be present Friday into Saturday with a shortwave moving through. There are some differences with the timing and location of the low as it moves through. Overall the best chances looking at the cluster analysis will be Friday night into Saturday. There will be some instability which could result in some embedded thunderstorms overnight into Saturday. The best chance for any thunder will be south of I-96. Another shortwave moves through Sunday bringing more chances for rain and thunderstorms. The best chances (40 to 50 percent) are along and east of a Kalamazoo to Alma line. - Warming Up Next Week With Slight Chances (20 percent) for Rain Upper level ridging builds in for next week with warming temperatures and some slight chances (20 percent) for rain and thunderstorms. These showers and storms could be more of the afternoon pop up variety as there isn`t any great source of lift for anything more widespread. Temperatures will warm each day with highs in the upper 70s to mid 80s and lows in the 50s. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 115 AM EDT Thu May 21 2026 The majority of the time during this 24 hour forecast period, the area will be mainly under the influence of mid/high clouds based around 12-15k ft agl. The exception to this is an area of low clouds that has formed east of KLAN and KJXN early this morning. The hi-res models have caught on to this for a few runs now. We have brought this low cloud cover in the MVFR category to the I-94 corridor for 2-4 hours this morning. The I-96 terminals may see some of this low cloud cover, but will keep them VFR with sct lower clouds. These lower clouds should move west of the area and dissipate as they move into drier air by 11z or so. Winds from the NE will dominate through this entire period. && .MARINE... Issued at 143 PM EDT Wed May 20 2026 Northerly winds and waves continue to build this afternoon with High Swim Risk Conditions and Small Craft Advisory conditions expected from Grand Haven and to the south. Winds and wave heights will decrease tonight with winds becoming more easterly into Thursday. Winds further offshore will remain from the north before shifting to the northeast Thursday night. Friday winds build once more to Small Craft Advisory levels as a low pressure system tracks toward the area. Rain and a few thunderstorms will be possible Friday night into Saturday with the best chances for lightning south of Grand Haven. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Frost Advisory until 9 AM EDT this morning for MIZ037>040- 043>046. Beach Hazards Statement until 2 AM EDT early this morning for MIZ056-064-071. MARINE...Small Craft Advisory until 2 AM EDT early this morning for LMZ844>846. && $$ DISCUSSION...RAH AVIATION...NJJ MARINE...RAH

NWS GRR Office Area Forecast Discussion