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Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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283 FXUS63 KGRR 290538 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 138 AM EDT Sat Jun 29 2024 .KEY MESSAGES... - Showers and storms tonight into Saturday - Dry and comfortable Sunday through Monday - Unsettled and warmer much of the holiday week && .UPDATE... Issued at 942 PM EDT Fri Jun 28 2024 The 00Z run of the HRRR is quite startling in that it paints a narrow swath of 4+ inches of rain overnight along the I-94 corridor between Kalamazoo and Jackson. There is a decent theta-e surge and a low-level wind confluence axis that makes localized heavy rain seem plausible. The 00Z SPC HREF Prob Matched Mean (PMM) and Local PMM guidance should lend a bit more insight once it becomes available in the next hour or two. Not going to completely bite on a single deterministic run at this point, but certainly there is some concern since this could cause pronounced localized flooding should this come to pass. Otherwise, no changes to the forecast planned in terms of overall coverage and timing of anticipated thunderstorms. && .DISCUSSION... Issued at 337 PM EDT Fri Jun 28 2024 - Showers and storms tonight into Saturday Some light rain is falling in places this afternoon across Southwest Michigan. This rain is falling from high cloud bases that from the most part are above 5,000 feet. This precipitation is associated with a weak shortwave moving through the area as well as the initial surge of moisture advection. The most substantial rainfall will occur tonight into Saturday as an upper trough digs into the northern Great Lakes driving a cold front through the area on Saturday. Instability tonight is not all that substantial, but on the order of 500-1000 j/kg. The HREF would suggest some embedded storms within a broader area of rain showers. Not expecting anything close to severe tonight given the limited instability. We are likely looking at 0.25 to 0.50 inch rainfall amounts in many areas tonight with local amounts towards an inch in the heavier swaths. On Saturday the cold front will bisect the area at daybreak with storms mainly expected southeast of a Holland to Clare line. As we work through the day, the best chance for storms in the afternoon and early evening will be near and south of I-96. Showers and storms on Saturday will be a bit more transient so rainfall totals will be lower, ranging from trace amounts to 0.30 to 0.40. We are in a SPC marginal risk for severe weather, but we expect instability to be muted by clouds and morning precipitation. Chance for any severe weather look low. HREF tries to indicate some scattered showers and storms moving back into Central Lower Michigan during the late afternoon and evening ahead of the main upper shortwave. This activity will be scattered and given the drier air moving in we have a lower confidence in this occurring. There are hints at some lower clouds developing Saturday night in the wake of the precipitation. We have brought some of these clouds into Central Lower Michigan at this time. - Dry and comfortable Sunday through Monday After the unsettled weather in the first couple of periods of the forecast, the area will see dry weather and cooler temperatures make their way over the area for Sunday and Monday. This will be the result of a fairly decent upper ridge and Canadian sfc high moving over the area. This will provide for strong subsidence to cap any clouds that try to grow at all in the vertical. 850 mb temperatures on Sunday around 7 to 9C will support max temperatures in the low to mid 70s. Return flow setting up on Monday will support highs in the upper 70s. - Unsettled and warmer much of the holiday week The upper ridge responsible for the dry weather Sunday and monday will slip east of the area by Tuesday. This will allow a long wave trough over the Pacific NW to move over the upper midwest. Deeper flow from the SW will bring warmer and more moist air to the state. Embedded short waves in the flow will bring multiple chances of showers and a few storms to the area for Tuesday and Wednesday. Details at this point are obviously a bit up in the air, but we can expect temperatures to warm back into the 80s with more humid air, and occasional chances for rain. There has been some decent agreement that much of the wet weather may settle just south of the area on the Holiday. The short waves moving through Tuesday and Wednesday flatten out the upper jet a bit. They will also lay out a front that looks to stall out over the southern portion of our area, or just south of the state. This will take the better chances of rain further south. However, this could end up being a scenario where waves ride along the front, and MCS activity just north of the front could be found. For this reason, small rain chances will be maintained for the holiday. The uncertainty by next Friday with respect to frontal and wave positions will obviously be fairly high due to the sequence events that takes place leading up to then. There is some hint that maybe a short wave ridge may build in on Friday in the wake of the early week trough, and the next trough reloading over the western portion of the country. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 128 AM EDT Sat Jun 29 2024 Based on radar trends, newer model data and lightning plots, I added more widespread shower and thunderstorm activity to the TAF forecasts for the remainder of tonight. Convective cells with occasional lightning strikes were already approaching the KJXN TAF site. Further west and northwest, the cells crossing Lake MI had a few lightning strikes in the as well and they were rapidly moving onshore. Given the very moist airmass moving, it has not take much of a cell to send VSBY`s down into the IFR category as evidenced by the brief IFR conditions as KAZO and KBTL in the past hour. Through the remainder of the night, the atmosphere only becomes more unstable and the latest model data shows the convection increasing. However, between 10 and 13z the strongest cells dissipate from west to east. IFR is likely to overspread the area as the strongest cells shift east of the TAF sites. It`s a very moist airmass moving in and with a cold front approaching from the northwest, that will keep low level convergence going which will support low ceilings and even some drizzle. However the low cloud conditions are expected to lift into the MVFR/VFR range mid to late afternoon. An isolated shower/storm is possible then, but the coverage at this time looks to thin to warrant adding them to the TAF forecast. && .MARINE... Issued at 337 PM EDT Fri Jun 28 2024 We have extended the current Small Craft Advisory (SCA) through 800am on Saturday from Grand Haven northwards. South winds of 15 to 25 knots will produce marginal SCA conditions of 3-5 feet tonight. The highest waves per the WaveWatch3 model look to remain offshore which is why we do not have a corresponding Beach Hazards Statement (BHS) out. After tonight, the focus will shift to our next wave event which develops behind a cold front Saturday night and Sunday. 4 footers develop just after midnight Saturday night and will continue through the day on Sunday. Waves will peak on Sunday morning in the 4 to 6 foot range. A SCA and BHS will be likely on Sunday. That said, weather conditions will not be ideal for a beach day with water temperatures in the 60s (and falling). Air temperatures on the beach will likely hold in the 60s as well, so we are not expecting a high beach population and even less so in the water. A north wind is the direction that are biggest upwelling occurs with. As a north wind commences, each layer below the surface turns a bit to the right due to Coriolis. Therefore the general flow below the water surface (in a north flow above the water) is offshore and upwelling occurs. So, with air temps in the 60s and falling water temperatures we are not expecting lots of people in the water. We will message it with full force on Saturday a day ahead of the actual event. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory until 8 AM EDT this morning for LMZ847>849. && $$ UPDATE...TJT DISCUSSION...Duke/NJJ AVIATION...MJS MARINE...Duke