450 FXUS63 KGRR 072249 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 649 PM EDT Thu May 7 2026 .KEY MESSAGES... - Frost/Freeze possible again tonight across the north - A few showers possible Saturday with a cold front passage - Cool Sunday through Wednesday - unsettled conditions Tuesday && .DISCUSSION... Issued at 310 PM EDT Thu May 7 2026 Secondary shortwave perturbation working across Wisconsin in advance of a stronger closed wave northwest of Lake Superior will pass over West Michigan this evening. Showers are expanding in coverage with the maturing diurnal boundary layer beneath this forcing feature. Many of the showers will not survive the lake transit - however, the wave will be reintroduced to a mature boundary layer downstream of the lake - especially along and south of the I-96, where more insolation has primed deeper mixing. Net result will be a few hours of potential for scattered showers this evening - mainly along the I-94 corridor. Subsidence kicks in quickly in the wake of this wave, which will support clearing skies - with the earliest clearing occuring across the northern counties of the forecast area. Good outgoing radiative forcing and a decoupled surface layer will once again allow temperatures will drop to around freezing - mainly along and north of US-10. Surface moisture availability with the recent aggressive seasonal green up will put the brakes on the temperature fall. Frost/freeze headlines lay out the best chances for impactful cold conditions. The near surface ridging will linger through Friday providing the region with a quiet and seasonable weather. Longwave troughing aloft is the theme throughout the forecast period. A shortwave handoff from the closed low over Alaska to the trough complex over Hudson Bay will be the next weather maker for the region on Saturday. Still some solution variance associated with the timing and wave alignment within the northwest flow over central Canada on Friday. General consensus is the established longwave trough will be deeper than prior cycles and the shortwave will sling through the Great Lakes earlier on Saturday. Look for a little more movement in the forecast timing of the frontal passage and the associated shower chances. The best chance for showers will be across mid-Michigan and points east, where greater destabilization can occur ahead of the cold front. Cool weather will then settle in for Sunday through Wednesday. A reasonably strong system in the northwest flow is expected in the Tuesday time window. The trajectory of best forcing is still out of focus at this time - so elevated chances for showers will be the going message. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 649 PM EDT Thu May 7 2026 Widespread cumulus persist with cloud bases predominantly in the 6-10kft range at present. Isolated showers are likely to impact AZO/BTL/JXN for the next hour or two, however restrictions are not anticipated given the dry ambient airmass. Light and variable winds and increased dewpoints overnight may lead to a window for light fog development between roughly 08z-13z. Highest confidence is along I-94, however confidence is to low to include restrictions with this package (20% chance of MVFR conditions). Going into the day Friday, High clouds will persist through the rest of the TAF period. Winds will increase from the southwest to 7-10 knots during the afternoon Friday. && .MARINE... Issued at 310 PM EDT Thu May 7 2026 Weak surface high pressure will continue to support onshore flow conditions with wave generally less than 2 feet through Friday. Stronger southerly flow is expected by early Saturday morning as the next system approaches the region. Even with the relatively stable marine boundary layer, gusts will climb to around 20 knots and support a building wave field, higher from Grand Haven north to Manistee. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Frost Advisory from midnight tonight to 9 AM EDT Friday for MIZ037-038-043>046. Freeze Warning from midnight tonight to 9 AM EDT Friday for MIZ039-040. MARINE...None. && $$ DISCUSSION...Mann (DTX) AVIATION...Thomas MARINE...Mann (DTX)

NWS GRR Office Area Forecast Discussion