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Wintry Machine Learning Mauler 1/30-2/1

Webberweather53 said:
Yeah that’s a good way to think about it.

Sometimes when we’re trying to explicitly resolve convection with the high res CAMs, it can cause more harm than good. The wild swings you’re seeing run to run are part and parcel with that. Things like downstream mass subsidence and divergence/convergence, moisture blocking, how that convection changes the flow pattern ahead of the trough (pumps the ridge) etc. can get all out of whack and cause massive changes between runs over us.

In this setup, we are basically testing the limit of what kind of convective environment we can get at this time of the year over the Gulf Stream and it’s much easier for model biases to show when you push things to the limit like this.
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Why is the 3K NAM 3-7F warmer than the 12K in many cases?
 
Watching the models ebb and flow is annoying but I remind myself that if I had seen this panel in the afternoon on the day before an event in my neck of the woods in NC, without seeing any model data, like it used to be back when I was younger, I would have felt excitement like a kid on Christmas morning. Good vibes only, for sure.

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More interesting discussion from RAH this afternoon on the setup (and the potential dry slot)...

Snow should really increase in coverage and intensity beginning
Saturday morning, with the event likely peaking in the afternoon and
evening as the mid/upper low interacts with the deepening coastal
low and a band of 850 mb frontogenesis sets up. With very cold
temperatures in place, the snow will be of the dry and fluffy
variety as snow to liquid ratios through the event generally range
from 12:1 to 20:1, lowest in the SE and initially, highest in the NW
and by Saturday evening/night. Liquid equivalent QPF for the event
is generally expected to range from a third to three quarters of an
inch, lowest N and highest SE. This generally translates to 4 to 8
inches across most of central NC, but a band of 8 to 12 inches is
likely to set up somewhere over the state with the best chance along
and east of I-95. There is also a scenario where many spots receive
lower amounts that will have to be monitored, which is explained
below.

Despite only being 24 hours from the event, there is still quite a
bit of discrepancy among the models on where exactly the band of
heavier snow will be, and it will depend on where exactly the
elevated frontal zone sets up, as well as how far south the
mid/upper low tracks. This is a complex setup and small shifts in
track and intensity can have a huge effect on how much snow falls.
If the mid/upper low tracks farther south, it will take longer to
interact with the coastal low, keeping the 8+ inch amounts to our
east, and potentially resulting in lower than expected snowfall
totals across a good portion of central NC. This is the scenario
depicted by the 12z NAMNest and 18z HRRR, which depict very light
amounts stretching from the northern Coastal Plain into the NE
Piedmont due to a gap in forcing between the mid/upper low to our
west and the coastal low to our east, a signal that has shown up on
some model runs since yesterday. This is a concerning trend that
will have to be monitored to see if it continues. But until there is
more consistency from run to run, it`s hard to take this one
scenario with too much weight. High-res models have been waffling
back and forth, with a notable shift east in the axis of heaviest
snow in some of the 12z and 18z runs compared to 06z. However, if
the mid/upper low and coastal low interact sooner, as depicted by
models like the 12z GFS and lower-resolution NAM, a larger area of
moderate to heavy snow will develop over central NC. Bust potential
is fairly high and this may be a nowcasting situation where we don`t
know exactly how far inland the heaviest snow will get. For now, a
Winter Storm Warning continues from this evening through Sunday
morning.
 
packfan98 said:
GFS is setting up the dryslot between the Triad and Triangle. Let’s see if it fills in later.
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Yeah, I don't love that but it still ends up with 6" at RDU on Kuchera, so oh well. Everyone else around gets 6-10"+, but you can't win 'em all. Sometimes you gotta take the table scraps. In reality, who knows exactly where the screw zone will be (but it probably will be over MBY).
 
JQPublic said:
The HRRR is within Range Right?
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Not sure if your question was satire or not but no. The last two runs only went to 18 hours which were not the duration. With the models bouncing all over it’s probably time to just look out the window tomorrow and see. It will snow for sure!
 
Btownheel said:
Covering every square mile of NC with at least 3 inches would be pretty freaking cool. I’ve certainly never seen that…(unless 96 did it and I was too young to remember.)


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No ‘96 didnt. The last or closest one would have been March 1980. The whole state got at least 3” except for the extreme southwestern couple counties and those spots got around 2
 
I can’t imagine putting stock into a 18z HRRR run 20+ hours out.

For folks over towards Raleigh, my worry level wouldn’t be too high. Just overreaction to a model that has flopped more than LeBron and can’t even get hour 0 right. (Pretty sure NAM3 isn’t doing well even at hr3 either.)
 

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