901 FXUS63 KGRR 132039 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 339 PM EST Sat Dec 13 2025 .KEY MESSAGES... - Lake Effect Snow Tonight into Tomorrow - Arctic Lows for the next few Mornings - Warmer weather with rain possible Thursday && .DISCUSSION... Issued at 322 PM EST Sat Dec 13 2025 - Lake effect snow Tonight into Tomorrow The arctic front will continue to move southward into Southern Canada this evening into early Monday. Strong NW flow will keep lake effect bands going as a mid level thermal trough deepens due to the arctic air mass moving overhead. That thermal trough will further increase the lake instability. That instability can be inferred by seeing the 80 J/KG of CAPE along the shore line. Using the 925mb-850mb Omega as a proxy the bands become more laminar as they move on shore. While the entirety of the lakeshore will see snow overnight, the greatest intensity will be Holland southward. The lake effect will intensify late tonight into early tomorrow morning. The lake effect will finally be dampened as "warmer air" in the low to mid levels form a thermal ridge. Lake effect showers should linger through Sunday morning and into the early afternoon, but will be light. While there will be some snow inland snow bands, will be hard pressed to infiltrate past the US 131 corridor. As said in previous discussions, temperatures this cold create snow that is more crystalline and not large dendrites. Couple that icy snowfall, along with the fact that the colder temps make salt less effective and you have a recipe for treacherous roadways. - Arctic Lows for the next few Mornings As mentioned above, an Arctic air mass is moving overhead. The 850mb temperatures will drop as low as -25C. That should correlate to t temperatures in the low single digits inland, with the potential for temps to drop below zero. The strong NW flow will continue through the first half of the evening with wind gusts upwards of 35 mph. Winds will finally subside after midnight as the gradient weakens. Any winds along with the frigid temps will couple for wind chills below zero. However, as the strongest winds and cold temps will not coincide, they should not reach any advise criteria. If it does happen it will only be for a brief period early Sunday morning. That said wind chills of -5 to -14 are possible early Sunday morning. The Arctic low will move eastward and "warmer" air will advect in Sunday into Monday. Gusty winds will resume SUnday afternoon with gusts upwards of 25 mph. Lows into Monday are expected to be "warmer" but range between 5 to 12 degrees. There is a small chance Monday with colder air near the surface and slightly warmer air aloft, that freezing drizzle will be possible Monday afternoon. Bufkit soundings do hint at this, though for right now there isn`t enough moisture. However, with an unsaturated DGZ during that timeframe and the above conditions freezing drizzle remains possible and will have to see how that unfolds. - Warmer weather with rain possible Thursday; Snow into Friday The roller coaster of weather will continue through the week as a mid level trough moving through Canada will couple with a ridge building over the plains to advect warm southerly flow into the region through the latter half of the week. Our frigid temps will sky rocket into the low 40s by Wednesday. A more organized low should make its way through the region Thursday into Friday. That low could bring slightly anomalous PWATS. The question is where the moisture will be. If the QPF remains in the warm sector, then heavier rain is likely. As said in previous AFD`s it looks to be a classic thaw and refreeze type of event. So a rain/snow wintry mix is trending Thursday into Friday. With Rain followed by a transition period and then snow, as cold air, as low as -15C, moves through Thursday night into Friday morning. There is some questions on timing and intensity so stay tuned. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1258 PM EST Sat Dec 13 2025 No substantive changes for this update. We continue to see lake effect snow (LES) primarily impacting the MKG, LAN, and BTL terminals with the most dramatic fluctuations at BTL thanks to a particularly well organized LES band undulating over that terminal. GRR, being at the northern edge of the LES region and in an area of broad and weak compensating subsidence, should see low chances (10-20 percent) for IFR restrictions before 00Z this evening. Model guidance indicates increasing boundary layer Richardson number values that will approach or exceed 1 after 03-04Z, meaning a transition from turbulent to laminar flow that in turn will cause LES to become less cellular and more laminar in presentation. Have tried to reflect this in the TAFs, but the exact placement of the bands is uncertain; brief IFR/LIFR conditions at MKG and perhaps AZO/BTL are not out of the question if they end up under a well developed dominant band, but this is too low probability (15-25 percent) to mention explicitly in the TAFs at this time. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Winter Weather Advisory until 11 AM EST Sunday for MIZ037-038- 043-050-056-064-071-072. MARINE...Small Craft Advisory until 7 PM EST Sunday for LMZ844>849. && $$ DISCUSSION...Ceru AVIATION...TJT

NWS GRR Office Area Forecast Discussion