502 FXUS63 KGRR 122319 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 619 PM EST Fri Dec 12 2025 .KEY MESSAGES... - Light Lake Effect Snow through Saturday - Arctic Cold into Early Next Week The Moderating && .DISCUSSION... Issued at 256 PM EST Fri Dec 12 2025 - Light Lake Effect Snow through Saturday A shortwave trough and advancing arctic front is currently across Wisconsin with low level convergence generating an area of snow. The snow should expand as it gets a boost from Lake Michigan with the trough raising inversion heights to around 10 kft this evening. Lake effect snow will perk up in southwest flow behind the front,switching to northwest overnight. Given strong lake instability and persistent onshore flow, we expect some localized amounts over 4 inches of snow before inversion heights fall and snow showers decrease on Saturday night. However, snow amounts will be limited in most places to 1 to 3 inches by inversion heights at or below 5 kft and small flake size, as the DGZ is near or below the ground. - Arctic Air into Early Next Week then Moderating Arctic air surges in on Saturday, with a lobe of the polar vortex reaching Lower Michigan Saturday night. We will see apparent temperatures fall to near of below minus 10F away from Lake Michigan and a Cold Advisory may be needed. 850 MB temperatures near or below minus 20C and should result in high temperatures being confined to the teens on Saturday and Sunday then slowly moderating into Monday. The surface high moves east with milder Pacific air arriving for mid-week and the potential for rain on Thursday. Colder air moves in for the end of the week, completing a freeze-thaw-refreeze cycle. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 619 PM EST Fri Dec 12 2025 Snow will increase in coverage over the next several hours leading to MVFR visbys across the terminals, with a 20-30% chance of IFR. Widespread MVFR cigs are present and will persist through the TAF period. Have leaned on the NAMNEST for snowfall timing given its success at handling this afternoon`s snow. There first looks to be a main batch of snow behind the front, followed by lake effect in the several hours to follow. Tonight`s snow diminishes after 07-12z from west to east. Coverage of snow increases again after 18z Saturday as 1) Warm air advection snow clips the I94 terminals, with MVFR visbys possible. 2) Lake effect increases in coverage for MKG and GRR after 21z with the approach of a mid- level wave. Widespread coverage holds off until after 00z but enough of a signal is there to warrant PROB30s for MVFR. In the post frontal airmass that overspreads the area tonight into Saturday, gusts to around 20 knots are likely, with gusts to 30 knots possible at MKG. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory until 7 PM EST Saturday for LMZ844>849. && $$ DISCUSSION...Ostuno AVIATION...Thomas

NWS GRR Office Area Forecast Discussion