Scientific Forecaster Discussion

000 fxus63 kgrr 221152 afdgrr Area forecast discussion National Weather Service Grand Rapids Michigan 652 am EST Fri Feb 22 2019 Latest update... aviation Synopsis... issued at 330 am EST Fri Feb 22 2019 - rain showers and a few storms become likely by Saturday night, with a possible brief period of freezing rain at the onset Saturday especially up north - confidence continues to increase for a high wind event centered around Sunday and into Sunday night - colder next week with chances for snow showers && Discussion...(today through next thursday) issued at 330 am EST Fri Feb 22 2019 We will be holding on to the Winter Storm Watch as is with it focused mainly around the high wind potential for Sunday, with some snow showers and blowing snow possible. We are also monitoring the ice potential for the onset of the precipitation, and whether a headline would be needed for that. Quiet and tranquil weather is expected for the first 24 hours, with a decent amount of sunshine expected after some light fog early this morning. High clouds will dominate the sky with some patchy low clouds here and there. We should stay dry through tonight, except for some very light pcpn that may bring trace amounts of some mixed pcpn toward 12z as the initial moisture transport moves through. Low level moisture will be quite limited, which should the pcpn amounts. We expect that the core of the precipitation will occur over the area beginning late Sat afternoon and linger into Sunday. This is when we see the main push of moisture transport arrive via a 60 knot low level jet that surges in through 06z sun. Our thinking at this time is that most of the area should see temperatures warm above freezing by the time most of the precipitation arrives. A small chance exists that some locations up north could see temps hold around freezing that would allow for some light accumulations of freezing rain at the onset. As the main batch of precipitation arrives late Saturday and Saturday evening, a thunder threat does exist over most of the area. The instability is sufficient with air parcels at and above 850 mb. Elevated Li/S are a little below zero c, and there is a couple hundred j/kg of MUCAPE. We do not anticipate severe weather at this time with CAPES on the limited side, and instability based at and above 850 mb. It is possible some higher wind gusts could occur with the convection. The thunder threat should last through 06z, along with a surge of temps maybe into the 50s across the south. After 06z, we will see the occluded front race through the area. Rain showers will linger behind the frontal passage, and change to snow for a short time frame before temporarily diminishing as the system pcpn moves out. The bigger thing going on is we will see the winds ramp up first at the frontal passage, then again after a short break before 12z Sunday. Models and respective ensembles are in fairly good agreement with bringing the strong winds to the area around or just after 12z sun. This is when we have good cold air advection, and a strong pressure rise/fall couplet moving through as a result of the deepening low. There is a good chance that most of the area will see wind gusts of 50+ knots, or 60 mph for much of Sunday. We have 50 knots of wind only 1k feet above the sfc which will be mixed down easily with the cold air advection. The other factor on Sunday is how much snow shower activity will be present with lake effect becoming possible, and obvious blowing and drifting that would occur. Over lake instability is obviously sufficient with 850 mb temps dropping to the negative mid teens c. Moisture is not bad with it being present to almost 10k feet. The limiting factor seems to be that we do not appear to have the northern jet core south of the area. The southern branch is south, but the deep cold air is not really there. The models and their ensembles are limited with snow accumulations. The northern two rows look favored for a few inches of snow with the departing system, and lake effect coming from Northern Lake Michigan with a northwest flow. It will not take much drier snow to fall to be able to blow around with the magnitude of wind. Winds will only slowly diminish Sunday night through Monday, with some lake effect remaining. Conditions should improve with regards to wind by Tuesday. We could remain in between systems then for much of the week, as high pressure will slowly ooze through the area. Temps will remain cold, and a few snow showers will be possible. Conditions do not look favorable for significant accumulations with short waves not coming right through the area. && Aviation...(for the 12z tafs through 12z Saturday morning) issued at 652 am EST Fri Feb 22 2019 Some light MVFR fog/haze (3-5sm) is expected for a couple of hours this morning and should be gone by 1430z or so. After that, VFR weather is expected the remainder of the day and tonight as well. Ceilings will be above 10,000ft today and will lower late tonight to around 8,000ft. Wind will be less than 10 knots today. && Hydrology... issued at 232 PM EST Thu Feb 21 2019 The ice jam on the Grand River in Portland remains in place, and is expected to hold in through the end of this week. Fluctuations can be expected in river levels. High temperatures will reach into the 40s this weekend. The snow melt and expected rainfall of a half inch to three quarters of an inch will cause river ice to breakup and move downstream, possibly leading to ice jams. This may also bring a few sites, mainly on the Grand River, to around bankfull. Temperatures will cool back down next week to below freezing with lows into the single digits. This will lead to ice formation on area rivers and could lead to stabilization of the rivers. && GRR watches/warnings/advisories... Winter Storm Watch from Sunday morning through late Sunday night for miz037>040-043>046-050>052-056>059-064>067-071>074. && $$

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