599 FXUS63 KGRR 121656 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 1156 AM EST Thu Dec 12 2019 LATEST UPDATE... Synopsis/Update/Marine .SYNOPSIS... Issued at 1155 AM EST Thu Dec 12 2019 - Warm advection light precipitation this afternoon into tonight (light snow to drizzle) over northern CWA - Some freezing drizzle may mix in across Central Lower Tonight - Cold front brings lake effect snow Saturday night into Sunday morning. Expect some light accumulations west of US-131 - Some snow possible into Southern Lower Michigan early next week. Indications are the main system impacts will miss our area to the south and east. Colder with lake effect into Wednesday. && .UPDATE... Issued at 1155 AM EST Thu Dec 12 2019 No significant changes will be made at this time to the going forecast. A mid level shortwave is moving our direction from the upper midwest out of MN/WI. The wave will spread warm air advection precipitation into Central Lower Michigan this afternoon and evening. At this time, the dominant precipitation types looks to be rain and snow transitioning over to some drizzle overnight. Surface temperatures will be somewhat marginal however across interior Central Lower Michigan, around 32F. Not out of the realm of possibilities that we see a bit of freezing drizzle, but confidence at this time is low. We could see some light accumulation of snow centered from Scottville to Reed City on the order of 1-3 inches in spots by Friday morning. At this time though we are not thinking of issuing a Winter Weather Advisory, but we will be taking another look through the course of the afternoon. && .DISCUSSION...(Today through next Wednesday) Issued at 258 AM EST Thu Dec 12 2019 There are three major systems heading our way in the next week. First is a weak system that should bring us mostly light snow to drizzle northwest today and freezing drizzle tonight. Then a major east coast storm will pull cold air into this area late Saturday into midday Sunday, that will bring a 1 to 3 inch lake effect snow event with it. Finally there is still the potential for a major snow storm later Monday into Tuesday morning. Afternoon and overnight system... We have a weak shortwave tracking through the Great Lakes today but the problem is there is a much stronger system upstream, on the southern branch of the polar jet, coming on shore as I write this. That will cause our system today to minor out as it moves through the area. Which means the front stalls near us tonight as the next upstream system pushes warm air back toward us due to the digging trough, which by sunrise Friday will be over the midwest. The warm advection lift precipitation will mostly be north of our CWA today into early tonight. However as the front stalls we have a persistent southwest winds (50 to 60 knots between 900 and 800 mb) which brings warm air into our area. Our surface temperatures will rise above freezing south of Route 10 by midday. The freezing level rises to near 2000 ft by evening. So any light snow with the warm advection push (near route 10 this afternoon) will change to light rain or drizzle by late in the day. Tonight the deep moisture moves out so the DGZ will not be saturated but the speed convergence and stalled front will trap low level moisture and cause some drizzle tonight, mostly from the lake shore to US-131. The question is will the surface temp fall below freezing? Inland north of GRR has the best chance but that area may be to far inland to see much drizzle. So for now no weather advisory but we may need one if the next shift believes there is a greater risk of accumulating freezing drizzle. Saturday evening lake snow event.... This is the big east coast storm that will bring the cold air back into our area. However the cold air push will be shortlived as an even strong system comes onshore over the western CONUS Saturday. That will force the shortwave trough brining the cold air in east. Even so we get about 18 hours of cold enough air and deep enough moisture for lake effect snow. This seems like a 1 to 3 inch sort of event. The Monday system... The GFS has been forecasting this for nearly a week now and the ECMWF has since the 10th /00z run been bringing the storm closer to us on the operational runs. The 12/00z run brings snow to GRR from the ECMWF. Since this is polar closed upper low dropping south into and southern stream system, this will be watched closely to monitor evolution. && .AVIATION...(For the 12Z TAFS through 12Z Friday morning) Issued at 632 AM EST Thu Dec 12 2019 A weak area of low pressure will track towards the Western Great Lakes today. The most likely impact at TAF sites will be southerly winds gusting between 20 and 30 knots, potentially higher at MKG. Low-level jet will bring a core of higher winds aloft, with 40-50 knots at 2000 feet causing low-level wind shear from late morning into tonight. Precipitation will be limited at TAF sites with this system and mostly affect central and northern Michigan. Temperatures look warm when precipitation arrives into MKG, and will carry only a rain mention. As we cool overnight, there is some potential for light snow or freezing drizzle there, but by then much of the precipitation will have ended. Watching potential for drizzle or freezing drizzle overnight not just at MKG, but also GRR. && .MARINE... Issued at 1155 AM EST Thu Dec 12 2019 6 to 10 foot waves are still expected this afternoon and evening from Holland north up the lakeshore. The hardest hit areas will be on the south sides of the points, from Ludington State Park down to Ludington and from Little Sable Point down to Whitehall. The waves in these locations will be more directly onshore given the southwest trajectory. Winds and waves steadily decrease tonight with a relatively calm period from Friday into Saturday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Lakeshore Flood Advisory until 7 AM EST Friday for MIZ037-043- 050-056. LM...Small Craft Advisory until 7 AM EST Friday for LMZ844>849. && $$ UPDATE...Duke SYNOPSIS...WDM DISCUSSION...WDM AVIATION...HLO MARINE...Duke

NWS GRR Office Area Forecast Discussion


Free website templates courtesy of JustDreamweaver.com