Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000 FXUS63 KGRR 240830 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 330 AM EST Mon Feb 24 2020 LATEST UPDATE... Synopsis/Discussion/Marine/Hydro .SYNOPSIS... Issued at 330 AM EST Mon Feb 24 2020 - Precipitation begins this evening becomes lighter into Tuesday - Main burst of snow expected Tues evening through Wed evening - Lake effect snow from Wednesday night into Friday && .DISCUSSION...(Today through next Sunday) Issued at 330 AM EST Mon Feb 24 2020 -- Precipitation begins this evening becomes lighter into Tuesday -- The lead shortwave in a complex interaction of shortwaves that we have been talking about for days is centered over Kansas and Oklahoma this morning. The wave can be seen in the water vapor imagery as well as national radar loops. This wave moves our direction and spreads precipitation into our far southern zones towards I-94 between 400pm and 700pm. Feel the HREF timing is likely the best, holding it off more towards the 700pm time frame. The precipitation will come in as rain and then change over to snow during the night as the column cools down due to wet bulb affects. Snow will start to mix in between 1000pm and midnight changing over to mostly snow in the overnight hours. As we have stated this lead wave weakens as it comes in and so will the precipitation. The HREF shows the precipitation tapering off into Tuesday morning. Some off an on light snow is expected on Tuesday. Any snow accumulation tonight should be on the order of an inch or less. Accumulation on Tuesday will likely be the same, very light. The best chances for some accumulation on Tuesday will be north across Central Lower Michigan as the precipitation is tapering off and in far Southwest Lower where the main synoptic snow will be spreading in. -- Main burst of snow expected Tues evening through Wed evening -- We will qualify any discussion of snow in the Tuesday night and Wednesday time frame as still a bit uncertain given wide disparities in the operational models. The latest run of the GFS as the surface low centered over Benton Harbor MI at 12z Wed. At the same time the operational ECWMF has the low broadly centered somewhere in the West Virginia area. Suffice it to say, details are still a bit ill defined yet. All of that said we continue to believe we are looking at accumulating snow during this time frame as secondary shortwave close off an upper low over the Great Lakes. ECMWF and GFS ensembles are still heavily leaned on here given the operational model disparity. The ensembles show a low track more across Northern Indiana and Ohio which if you were looking for an operational model showing that it would be the NAM. We expect accumulating snow across all of our CWA during this period with the highest amounts likely in the heart of the CWA near the I-96 corridor. We are expecting a 3-6 inch snowfall during this time frame based on ensemble means centered on a line most likely from Holland towards St. Johns. In terms of impacts, travel will be the biggest impact. Some of the heaviest snow will likely occur on Wednesday affecting both the morning and evening commutes. -- Lake effect snow from Wednesday night into Friday -- A prolonged period of lake effect snow looks to occur from Wednesday night into Friday. We will be in deep cyclonically curved northwest flow over Lake Michigan. The lakeshore counties will be the most impacted. Wednesday night could be quite nasty along the lakeshore with winds that will be of gale force variety. As colder air spills in and the snow becomes more powdery, blowing and drifting snow will become a concern. Moisture depth from Thursday through Friday is not all that high, but feel the models may be underdone looking at the 500mb pattern. The snow may actually continue right into Saturday as conditions remain rather stagnant. Additional accumulations are certainly expected west of Highway 131. && .AVIATION...(For the 06Z TAFS through 06Z Monday evening) Issued at 1 AM EST Sun Feb 23 2020 Latest Satellite shows an intrusion of mid to high clouds which also given persistent westerly flow should keep VFR conditions through tonight and through the first half of Monday. The approaching system from the south should bring enough low level moisture to create MVFR cigs along the I-94 TAF sites. The I-96 TAF sites may not see MVFR conditions until after 03Z Tuesday. && .MARINE... Issued at 330 AM EST Mon Feb 24 2020 We dropped the Small Craft Advisory a bit early tonight as wave models are indicating waves are likely below the 4 foot level. Winds and waves will be on the increase for Tuesday into Wednesday as low pressure passes by off to our southeast. The winds will initially be off shore (northeast) Tuesday and Tuesday night. Winds shift on shore out of the northwest Wednesday into Wednesday night. We will likely need a Small Craft Advisory in regard to the wind speeds Tuesday night into Wednesday morning. Conditions look to ramp up to gales as the winds come around to the northwest Wednesday afternoon into Wednesday night. 35 to 40 knot gales look likely centered around Wednesday evening. Water levels are forecast to be elevated in terms of a storm surge especially from South Haven to the south on Wednesday into Wednesday night. The surge looks to be more on the order of a marginal advisory in our far south. && .HYDROLOGY... Issued at 330 AM EST Mon Feb 24 2020 Several sites, Ionia, Maple Rapids, Holt and Eagle are all forecast to have rises that will exceed bankfull in the mid week time frame. We continue to believe that these rises are due to the over estimation in the hydrologic models of snow melt working into the rivers (the Lansing snow depth currently is only 1 inch). There will be some rain that moves into Southern Lower Michigan tonight, but this should not be too heavy on the order of a quarter of an inch. Even if it all fell as rain it would not pose too much of an issue. From Tuesday through the rest of the week the precipitation type will be in the form of snow and not add to rising river levels. So, the bottom line is we do not expect much in the way of river level rises given the precipitation changes over to snow Monday night and the fact that colder weather is forecast. We do expect colder weather to settle back in for Thursday through Saturday so we will once again be monitoring rivers for ice formation. We are looking at highs in the 20s and lows in the teens with snow (lake effect variety late in the week). Frazil ice formation in the rivers will certainly be possible. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ SYNOPSIS...Duke DISCUSSION...Duke AVIATION...Ceru HYDROLOGY...Duke MARINE...Duke

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