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January 24-26: Miracle or Mirage Thread 2


mappy
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3 minutes ago, Interstate said:

Yes but the GFS has been creeping slowly to the northwest with the sleet line.

Yeah both sides of the argument are maybe meeting in the middle, the GFS "winning" at this point is not really like what it would be like if it "won" with one of its earlier runs, for sure. It would just give its depiction some more credence even if it was over-committed.

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Just now, Maestrobjwa said:

I would ask if that's what we want...but what we want/don't want has changed so many times or had so many caveats I lost count, lol

I think it helps and hurts.  Better moisture but may cause thermals issues.  I’d risk thermals for a better thump which seems to be the case this go around.

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NAM’s are hands down the most aggressive at the handling of the thermal profiles with the warm nose marching northward faster than any other guidance. I do think it’ll come in quick, but perhaps the NAM is too aggressive at this lead. NAM Nest wheelhouse starts tonight and improves stepping through time closer to the event. Curious to see how it responds. The margins are thin when it comes to the handling of the warm nose between 850-700mb. 

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44 minutes ago, SnowGolfBro said:

Any chance the warm layers are being overdone? Is it possible to have a snow/sleet mix after the flip that os more like 6-1 ratio wise?

https://repository.library.noaa.gov/view/noaa/53067
 

Analysis of Model Thermal Profile Forecasts Associated with Winter Mixed Precipitation within the United States Mid-Atlantic Region

This paper looked at overrunning events in a CAD setup in the mid-atlantic and found a warm bias for NAM and NAM3k.

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"Winter mixed-precipitation events across the mid-Atlantic region of the United States from 2013–2014 through 2018–2019 were used to analyze common short-term model forecasts of vertical atmospheric thermal structure. Using saturated forecast soundings of the North American Mesoscale (NAM), higher-resolution nested NAM (NAMnest), and the Rapid Refresh models—corresponding with observed warm-nose precipitation events (WNPEs)—several thermal metrics formed the basis of the analysis of observed and forecast soundings...."

Money part:

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“Well forecast are maximum and minimum temperatures within the warm nose and surface-based cold layer, respectively, but the cold layer is commonly too thin for each of the models, and the warm nose is regularly too thick, particularly within NAM and NAMnest forecasts.......In terms of the nature of bias in precipitation-type forecast, the NAM model is exclusively warm-biased… For the NAM-Nest model, 28.9% of cases are warm-biased while only 3.8% are cold-biased.”

 

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