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Dec 29-Jan 2 potential storm event


Brian D
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I think analyzing the NAM is as simple as tossing its BMJ parameterization scheme which does terribly with antecedent dry air. Look at the composite reflectivity vs the precip output and that should be all you need to see. It will take some time to top down saturate, but with robust moisture transport and strong forcing you shouldn't lose 3 hours of precip. The NAMs have it snowing hard aloft at 21z. If anything, skew timing earlier and account for possibly earlier northward surge of warm nose and the forecast is in decent shape.

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Just now, cyclone77 said:

Feeling pretty good about a quick 5-6" before quick shift to sleet.  HRRR drops 1.5" precip so could get quite the sleet storm tomorrow eve before changing to frz rain/rain.

As RC stated above, sleet is not going to end up being the primary p-type in most places, a brief transition between snow and zr. 

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This sounding below demonstrates the NAM's dry air issues pretty well. It's over LaSalle or Kendall County valid at 21z. If you go to the Precipitation Type parameter on COD, this area is not being counted as snow by the model. Yet you look at that sounding and that's very clearly a snow sounding, a good WAA snow sounding at that. 850 mb is a pretty good proxy for saturation level at which snow reaching the ground is a decent bet. Since the NAM is 3 hour time steps, not counting these areas of the grid space of having qpf as snow cuts into the qpf and snow totals unrealistically. This is an area where meteorologists and weather enthusiasts can add value to the model forecasts when we know their typical biases. cceb91650678537d5bd222ff09be7a6f.jpg

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