166 FXUS63 KGRR 100533 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 1233 AM EST Fri Jan 10 2025 .KEY MESSAGES... - Accumulating snow for Friday into Friday night - Arctic air arrives early next week with more snow && .UPDATE... Issued at 933 PM EST Thu Jan 9 2025 No changes to the going fcst and winter headlines at this time. Newer 00Z data continues to support the counties in the advisory since these are the ones which see both the synoptic + lake enhancement event on Friday then the nw flow pure lake effect on Friday night. That being said, from an impact standpoint, even the lower 1-2" inch amounts which occur outside of the current advisory will make for slick travel conditions Friday afternoon and evening, including the Friday evening rush hour. && .DISCUSSION... Issued at 253 PM EST Thu Jan 9 2025 - Accumulating snow for Friday into Friday night Southwest winds will be on the increase later tonight and into Friday as a deeper trough approaches from the west. Moisture advects in and is shown to deepen up through 500 mb Friday morning over the entire area. This axis of deeper moisture shifts east through the CWA during the day. Models are in good agreement in showing and area of light snow spreading into the CWA with inland locations seeing 1 to 3 inches of snowfall. However, closer to Lake Michigan, enhancement is forecast to lead to higher amounts and more impacts. The southwest low level flow during the morning will favor the Holland to Muskegon and possibly southern Newaygo County area for a band of heavier snow. Then as the low level winds shift northwest later in the afternoon and evening the bands should align with this flow and that would support banding into the cities of Holland, Allegan and Kalamazoo. Ensemble snow amounts have been trending up with this system, especially to the southwest of Grand Rapids. We do believe the snow ratio will be a factor in the snow amounts and 10 to 1 is likely a conservative value. Based on all this, we have issued a Winter Weather Advisory for the region we are most confident to see higher snow amounts and associated impacts, which includes Muskegon, Ottawa, Allegan, Van Buren and Kalamazoo Counties. We will have to monitor the next set of counties inland as the western parts of these counties could be impacted by the bands of snow. We did use the term occasional snow as there will likely be some breaks in the snow. - Arctic air arrives early next week with more snow A deeper upper level low drops slowly southward through Ontario Sunday into Monday. This feature is shown to be just north of Lake Superior Monday night. Models are in decent agreement with this scenario. As a result arctic air wraps in south of this feature and into the CWA through this period. The DGZ moistens up here in Michigan later Sunday and it remains moist into Tuesday. In addition, with a tighter pressure gradient, gusty winds can be expected. Ensemble temperature trends have been colder. Given all this, the potential for winter related impacts are on the increase for early next week. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1233 AM EST Fri Jan 10 2025 Not much of a change from the previous forecast. MVFR ceilings will gradually spread over the area with snow starting between 12-15Z for most sites with the eastern terminals more between 14-17Z. Once snow starts expect reductions in visibility along with ceilings dropping to IFR values or lower at times. As mentioned before MKG will likely see the greatest impacts due to lake enhancement which could result in snowfall rates around an inch per hour at times. Elsewhere snowfall rates around 0.25 to 0.50 inch per hour are expected. GRR Airport DSS Update No changes to the airport briefing information provided from the day shift. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Winter Weather Advisory from 8 AM this morning to 4 AM EST Saturday for MIZ050-056-064-071-072. MARINE...Small Craft Advisory until 7 PM EST this evening for LMZ844>849. && $$ UPDATE...Meade DISCUSSION...MJS AVIATION...RAH

NWS GRR Office Area Forecast Discussion