Post by Zack Fradella on Dec 5, 2017 18:42:02 GMT -6
As is always the case with our winter weather events, how much dynamic cooling occurs during the precipitation will be key?
The NAM goes crazy with snow because it cools the atmosphere off so much in the heaviest precipitation.
The GFS is the exact opposite and doesn't cool much at all. Raw numbers from the GFS are below, the right two numbers are those important atmospheric levels that need to be at or below freezing for snow. No issue there. The precip is still falling according to the GFS at that time. Then look at the boundary layer temp, mid 40's? That will melt any snow. BUT look at your dew point, near freezing. If rain is falling, the temperature will have to dynamically cool closer to the dew point. "Wet bulbing" The GFS doesn't make sense because it has rain falling and temp struggling to fall much.
No, I'm not jumping on the NAM train but we have some interesting model runs coming. I want to see more precipitation than what is being shown and colder temps before I feel comfortable in saying the S word.
TropicalTidbits added a really helpful feature to the NAM and GFS... The total positive snow depth change is likely more realistic than the total snow accumulation. The total positive snow depth change takes more things into consideration rather than just the presumed 10:1 snow to liquid ratio accumlation maps.
The CMC likes a slightly higher latitude for the Gulf disturbance, and that’s making a difference. It looks wetter than the NAM, but that’s probably because of the lower resolution. The GFS still hates all of us.