673 FXUS63 KGRR 060835 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 335 AM EST Sat Feb 6 2021 LATEST UPDATE... Synopsis/Discussion/Marine/Hydro .SYNOPSIS... Issued at 330 AM EST Sat Feb 6 2021 - Light lake effect today, with a system snow boost tonight - Another burst of snow expected Monday night - Snow and cold continues throughout remainder of the forecast && .DISCUSSION...(Today through next Friday) Issued at 330 AM EST Sat Feb 6 2021 -- Light lake effect today, with a system snow boost tonight -- Main question this morning was what to do with the ongoing Winter Weather Advisory headline. The question was what to do given there will be much lighter lake effect today with another burst tonight. First off, know that given low inversion heights and Arctic air in place that any accumulations today will be light, especially east of Highway 131. Given the cold temperatures and at least some light snow showers we have decided to bridge the gap between and extend/expand the Winter Weather Advisory through tonight. So, light lake effect will continue today with accumulations of 1 to locally 3 inches towards Lake Michigan and inch or less amounts inland. The fact that travel conditions will be poor though may the decision to continue the advisory through today fairly easy. Temperatures in the teens will mean roads will remain snow packed and slippery. A shortwave plows into the area from the west this evening which will bring some light synoptic snow to all areas on the order of 1 to 3 inches. The synoptic snow will enhance the continuing lake effect snow, so we expect the highest totals tonight west of Highway 131 on the order of 2 to 4 inches. The main burst of snow will occur between 700pm and midnight. So travel will be impacted during this time with low visibilities and hazardous driving conditions. The system snow shuts down late tonight and we transition back to a pure lake effect regime. The lake effect on Sunday looks pretty light with inversion heights crashing to below 5000ft. The shallow nature of the moisture and the DGZ should result in small flake size and only light accumulations. The snow ramps up once again Sunday night though with another shortwave zipping through the Southern Great Lakes region. Accumulations look lighter with this system though as ridging is in place across the area. Wind flow off the lake is really light, so any lake effect should be confined to the lakeshore counties. -- Another burst of snow expected Monday night -- Another widespread light snow looks to take place Monday night with a shortwave moving through the area. We could be looking at another general 1 to 3 inch snowfall. The "heavier" accumulations look to be along and south of I-96 closer to the better lift. -- Snow and cold continues throughout remainder of the forecast -- Some light lake effect snow will continue from Tuesday into Wednesday before the flow turns off shore. Fairly significant model differences at the end of the week, with the GFS showing a digging deep upper low over the midwest and the ECWMF indicating zonal flow. Given the cold air in place, would tend to side with the GFS here. Bottom line there is not end in sight to the cold air and bouts of snows. Winter is here to stay at least for the next week. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) Issued at 1145 PM EST Fri Feb 5 2021 Primarily IFR conditions will continue overnight due to snow showers and blowing snow. Lighter snow showers and flurries will linger Saturday morning through mid afternoon and conditions will slowly improve to mainly MVFR in that time frame. Steadier light to moderate snow is expected to move in from the west/southwest late Saturday afternoon through Saturday evening and will cause conditions to deteriorate to mainly IFR at all the terminals through 06Z Sun. && .MARINE... Issued at 330 AM EST Sat Feb 6 2021 Have left the two marine headlines as is...Heavy Freezing Spray Warning into this morning and a Small Craft Advisory into Sunday morning. Strongest winds and highest waves will remain in place into the morning hours of today and then a gradual fall off will occur through Sunday. Could see the need to extend the SCA through most of the day on Sunday as it will take some time for the waves to dampen out. Shore ice has expanded significantly in the last 24 hours due to the Arctic air, strong winds and large waves. The South Haven webcam shows ice extending out to about the proximity of the second sand bar, with frazil ice beyond the mounded ice. There is now a buffer in place to protect, at least for a time, against flooding and erosion. That said, lake levels have dropped so much in the last 8 months that the flooding/erosion threat has been fairly significantly mitigated. && .HYDROLOGY... Issued at 330 AM EST Sat Feb 6 2021 River ice has surged obviously in the last 24 hours, with the onset of Arctic air moving into the region. We are not aware of any ice jams at this point, but we are monitoring hydrographs from area rivers and remain in contact with emergency management. Water temperatures are near freezing and we have had plenty of snow, which leads to a quick increase in frazil ice and then a freeze over of the river. The freeze up has been fairly orderly at this point. With a steady freeze over of rivers the situation becomes stable with water flowing underneath the ice on top. Bottom line...river ice has increased, we are monitoring, but all indications at this point are conditions are stable. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Winter Weather Advisory until 8 AM EST Sunday for MIZ037>039- 043>045-050>052-056>059-064>067-071>073. Winter Weather Advisory from 7 PM this evening to 8 AM EST Sunday for MIZ040-046-074. LM...Heavy Freezing Spray Warning until 10 AM EST this morning for LMZ844>849. Small Craft Advisory until 7 AM EST Sunday for LMZ844>849. && $$ SYNOPSIS...Duke DISCUSSION...Duke AVIATION...Laurens HYDROLOGY...Duke MARINE...Duke