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Weather Threats: Winter 2020-21 Edition Part II


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I think it's safe to say "here we go" for Sunday - Tuesday in the Midwest and Northeast!   The pattern features a west-based -NAO, 50/50 low, large shortwave, confluence ahead of it over New

the fact that we have the signal for an Arctic jet-infused Miller A while a historic blizzard is ongoing and before a highly anomalous blocking pattern resets is totally astounding   LFG

Well, 3rd time is the charm, am I right?    The synoptic evolution preceding this, and during, renders a very impact and high-potential situation here with an anticyclonic wavebreak over S. Que

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18 minutes ago, Thundersnow3765 said:

I'd be watching for north bumps with the Thursday overrunning event from where the Euro solution is now. Systems primarily driven by warm air advection, like this one, have a classic tendency to end up more north than modelled as the warm air advection itself tends to be undermodelled. The NAM and other CAMs usually do better with modelling the strength of the WAA and as such the NAM may be the more correct solution atm.

Well the NAM looks to be caving to the globals this run

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18 minutes ago, Thundersnow3765 said:

I'd be watching for north bumps with the Thursday overrunning event from where the Euro solution is now. Systems primarily driven by warm air advection, like this one, have a classic tendency to end up more north than modelled as the warm air advection itself tends to be undermodelled. The NAM and other CAMs usually do better with modelling the strength of the WAA and as such the NAM may be the more correct solution atm.

Nams going to be well south of its 12z run for thursday

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20 minutes ago, Thundersnow3765 said:

I'd be watching for north bumps with the Thursday overrunning event from where the Euro solution is now. Systems primarily driven by warm air advection, like this one, have a classic tendency to end up more north than modelled as the warm air advection itself tends to be undermodelled. The NAM and other CAMs usually do better with modelling the strength of the WAA and as such the NAM may be the more correct solution atm.

NAM is sig. further south with the overrunning this run.

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4 minutes ago, Stormlover74 said:

Nams going to be well south of its 12z run for thursday

18z Nam is further south with the overunning. I think this one might be done for Philly north.

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Almost like it's out to make me look bad, the NAM shifted significantly south at 18z. That doesn't change the bulk of my argument however, and it is true that systems primarily driven by warm air advection tend to trend northward on model guidance as the distance out becomes shorter for the reasons I mentioned above.

 

So why did the NAM shift south? TPV placement. It's definitely a wildcard here and is still shifting around significantly. You can see how it really flattened heights out this run.

1243554806_namconus_z500_vort_us_fh48_trend(2).gif.d88c7a18feefdd6e3c07667c1b032ab7.gif

 

 

 

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Just now, Jake302 said:

We're not in the NAM's useful range. I lend more weight to the GFS and euro with even more weight to the euro.

After last week no model can be trusted 3 days away from the event

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1 minute ago, rossi said:

It’s 3 days away; didn’t you learn from last weeks storm that wAs out to sea

Apples to oranges when we look at setup. This is only two days from impacting the areas.

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The other risk you run with a more flat suppressed solution is a lack of forcing for precipitation. The disturbance gets sheared out by the fast zonal flow and only produces minor snow accumulations this run, east of the mountains, as a result.

 

snku_acc.us_ma.png

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A fair amount of whiffs on the eps for the Thursday Friday system. Nam is in those camps. All we can do is watch for trends. I don’t know think we can use the rule of if always comes north,  but we’ll see

B1349169-4962-4EE7-B39E-AAEE35BEBAE7.png

35598B3C-6C5E-4298-82BE-0EC4311A9628.png

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2 minutes ago, rossi said:

Agree completely; how many times have we seen it come north & DC gets less

The GFS has the heaviest axis just to the north of DC and the Euro has it just to the south of the DC area. The reality is that it's going to be somewhere in the middle. It is highly unlikely that the heavy axis goes south of the Euro and/or north of the GFS at this stage. We are only 54 hours until it's gonna start snowing.

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