FXUS63 KGRR 040815 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 315 AM EST Wed Dec 4 2024 .KEY MESSAGES... - Light Snow Through This Afternoon - Lake Effect Snow, Blowing Snow, and Windy Tonight into Thursday - Potential for rain arriving Sunday night && .DISCUSSION... Issued at 313 AM EST Wed Dec 4 2024 - Light Snow Through This Afternoon An upper-low diving towards the region is driving a surface low north of the area today. The warm air advection wing of this system will keep light snow ongoing today, especially near and north of I96 . Accumulations will generally be 3 inches or less by this afternoon keeping travel impacts minimal. There is a low chance of drizzle or freezing drizzle late this morning into the early afternoon once the DGZ dries out. - Lake Effect Snow, Blowing Snow, and Windy Tonight into Thursday Bottom line up front, have upgraded the current Winter Storm Watch into a Winter Storm Warning from this evening to early Friday. Osceola, Mecosta, and Calhoun were also added to the warning. All remaining counties across West Michigan are under a winter weather advisory for the same timeframe. The first phase of the event is expected this evening when an arctic front sweeps across the area. Surface based instability and strong low-level convergence likely leads to the development of snow squalls along the front. Snow squalls will lead to rapid reduction of visibilities to near zero and rapid changes in road conditions. Of particular concern is that these squalls will track along the I96, I69, I94, US131, and US127 corridors during the evening commute. The arctic air behind the front will also lead to any lingering moisture on the roadways quickly freezing. Winds may gust over 40 mph along the front as well given strong mixing. Behind the front snow there may be a brief lull in snow showers before lake effect snow ramps up this evening. Given low-level theta e lapse rates in the negatives and boundary layer winds exceeding 40 knots these snow bands will be able to reach well inland. Two snow maxima are expected. Northwest flow drives the heaviest lake effect snow bands tonight into Thursday across the Grand Haven to Holland to Battle Creek region, and potentially further east if organized banding persists. Second, as low-level flow becomes more northerly into the day on Thursday, several CAM solutions suggest that lake- effect bands are able to get a Lake Superior connection leading to an additional snowfall maximum across the northwestern CWA and enhance snow across the rest of the warning area from enhanced moisture if this occurs. Snowfall totals will vary across counties due to the banded nature of lake effect snow. Across the warning area a general 6 to 10 inches of snow with locally higher amounts possible is favored. In the advisory area where lake effect snow squalls will be more scattered in the post frontal environment a general 2 to 6 inches of snow is expected with locally higher amounts possible. A deep mixing layer tapping into the aforementioned strong boundary layer winds will lead to wind gusts exceeding 40 mph bringing concerns for scattered power outages and blowing snow in addition to the heavy lake effect snow tonight into Thursday. Travel conditions will be hazardous due to occasional whiteouts from snow and blowing snow along with snow covered roads Tonight into Thursday morning. The Thursday morning commute will be particularly impacted, with snow and winds continuing to affect the Thursday evening commute as well. Snow diminishes Thursday night as surface ridging advances into the area. - Potential for rain arriving Sunday night A mid level low that will be over the Southwest U.S. on Friday will lift out into the Plains Sunday and through the Great Lakes region Monday. Warm and moist air advection ahead of this feature will warm temperatures up enough for rain to be the main precipitation type with this next system. An upper level wave digs into the Upper Plains behind the initial wave for Monday. The upper wave then tracks into MI for Tuesday. This feature will extend the precipitation here in MI into Tuesday. As the column cools later Tuesday and more so Tuesday night, any remaining precipitation will mix with and change to snow. Deterministic qpf values from the models generally support around a quarter inch across northern zones with around a half inch over southern Lower MI. Ensemble values show a fair amount of spread, but at this time potential impacts from this event look low. Melting snow will add to the runoff, so we will have to monitor the water equivalent values after the current system is done. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1244 AM EST Wed Dec 4 2024 Strong gusty winds will generate some impacts through the period. Ahead of an arctic front south to southwest winds will gust over 25 knots at times through the morning. Then as the front moves in this afternoon, the winds will veer to the west and gusts will top 30 knots and occasional brief gusts could reach 40 knots, especially after 00z Thursday. Overall, not much precipitation is expected through the morning, with the focus remaining north of KGRR, however that will change as the front moves in during the afternoon. We will see rain and snow arriving and there is still a small chance for a short period for freezing drizzle. As the arctic air flows in during on the backside of the front for the late afternoon hours the snow will expand. IFR and lower conditions are expected. Blowing snow will become an increasing concern, especially after 00z Thursday when the strongest winds arrive and snow intensity increases. GRR Airport DSS Update The potential for visibilities to fall under a mile has increased for later this afternoon. The rapid fall in temperature from 3 pm to 11 pm today is likely to make untreated surfaces icy. Peak wind gusts Wednesday evening and into Thursday could reach 45 mph. && .MARINE... Issued at 313 AM EST Wed Dec 4 2024 Current Gale Warning is already verifying as southwest gales continue through the day. This evening gales turn northwesterly with widespread strong gales and isolated storm force gusts tonight into Thursday with peak gusts along the initial arctic front and again in the hours before daybreak on Thursday. Waves of 15 to 20 feet are expected along with the strong winds. No changes to the gale warning will be made at this time. Snow squalls are expected to develop along and behind the arctic front this evening into Thursday causing rapid reductions in visibilities to under one quarter mile at times. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Winter Storm Warning from 5 PM this afternoon to 1 AM EST Friday for MIZ037>039-043>045-050-056-057-064-065-071>073. Winter Weather Advisory from 5 PM this afternoon to 1 AM EST Friday for MIZ040-046-051-052-058-059-066-067-074. MARINE...Gale Warning until 1 PM EST Thursday for LMZ844>849. && $$ DISCUSSION...Thomas/MJS AVIATION...MJS MARINE...Thomas