Big Winter Storm Coming!

A potentially big winter storm is headed our way late tonight through Wednesday. The possibility of 9-12" of accumulation has been forecasted by the NWS in Grand Rapids. Snow ratios are estimated to climb to 20:1, which means 20" of snow for every 1" or water. This correlates to light, fluffy snow. I'm gonna put a final estimate of snow in Battle Creek at 8-11" of accumulation.


Here is the 12z run of the GFS model, which shows snow accumulation in inches. As of this latest run, it is predicting 12-15" which might be overdoing it a little, although even the NAM and GFS profiles as seen through BUFKIT (below) show about 13-14" by Wednesday afternoon.


The two images above are from a forecasting tool called BUFKIT. What you are looking at is an overview of this storm. The first thing to note is these charts are read from right to left. On the x-axis is time and the y-axis can be numerous parameters, but in this case, it shows height (thousands of feet), snow accumulation (inches), and temperature (degrees Fahrenheit). The gray bars indicate snow, with each bar representing a certain amount of time as indicated by the scale on the x-axis. This combined with the snow accumulation on the y-axis can tell you approx. how much snow over any given time period. In this case, I added up both the NAM, and GFS model, both of which indicate a fair amount of snow (~13") by Wednesday afternoon. The red line that oscillates vertically in both directions is the temperature, which can be estimated by reading the temperature scale on the y-axis. The last important factor is the blue and red contoured blobs, which correlate to Omega. Omega is essentially a vertical motion, and when the values are negative, this indicates ascent, or "lift." The larger the negative values, the more lift (Ex. -10ub/s indicates stronger ascent than -5ub/s). This is important, because the more lift you have, associated with moisture indicates heavier snow, as the moisture can be lifted all the way to the DGZ (Dendrite Growth Zone-to be talked about shortly). In short: with moisture supplied, and high omega values (negative), the heavier the snow will be.


The above image shows a thermodynamic profile/sounding/skew-t diagram. This diagram (on the right hand side of the image) depicts a vertical view of what the atmosphere will potentially be like at a certain time-in which case 10:00pm Tuesday. The horizontal gray dashed lines represent height, or in this case pressure (in millibars). The red line is temperature, and the green line is dewpoint. You'll notice the red temperature line is shaded yellow in a certain section. This is the DGZ, or Dendritic Growth Zone. Basically, it's the area where snow is favored to form. The DGZ is between the -12C and -18C isotherms, and indicated on the diagram by the slanted bright teal colored dashed lines. The DGZ here is pretty thick, at almost 200mb, and there is plenty of moisture-indicated by the close distance between the dewpoint, and temperature lines. Also shown on the diagram is the omega, which as you can see jogs over to the left quite a ways. I have marked on there that this correlates to about -9ub/s, which is moderate lift, so heavy snow can be expected in the night period.


Here is an animated gif showing the vertical velocity/omega tomorrow through tomorrow tonight. Omega values shown range from about -5 to -9ub/s.


This last image was just something that I found pretty neat. The low pressure there has some amazing vorticity associated with it, and is the storm that will impact us.