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February 7th Storm Threat Discussion/Obs


mappy
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06Z NAM Nest for Sat night-Sunday. Definitely juicy. This is with the Ferrier rime correction (capped at 10-1). If it's all snow w/o rimed flakes and a >10-1 SLR, we would get more. 

The NAM Nest Ferrier snow maps did a pretty good job in the DC area for the WAA phase in the last event (on Sunday).

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10 minutes ago, WxMan1 said:

06Z NAM Nest for Sat night-Sunday. Definitely juicy. This is with the Ferrier rime correction (capped at 10-1). If it's all snow w/o rimed flakes and a >10-1 SLR, we would get more. 

The NAM Nest Ferrier snow maps did a pretty good job in the DC area for the WAA phase in the last event (on Sunday).

Untitled.png

What is the NAM nest? Like an ensemble of all the different resolutions?

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11Z Sunday over the District per the 06Z 3km NAM. Nice lift in the DGZ. If it comes to fruition, we would see MUCH better dendrites than we saw last Sunday. Thus much better (faster) accumulation efficiency. Like 4+ inches within 12 hours instead of having to wait 24-36 hours (lol).

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27 minutes ago, WxMan1 said:

06Z NAM Nest for Sat night-Sunday. Definitely juicy. This is with the Ferrier rime correction (capped at 10-1). If it's all snow w/o rimed flakes and a >10-1 SLR, we would get more. 

The NAM Nest Ferrier snow maps did a pretty good job in the DC area for the WAA phase in the last event (on Sunday).

Untitled.png

Before the last event on our Philly forum Tony (rainshadow) posted the model that’s supposed to be replacing the NAM soon. I forget what it’s called, but it did an amazing job. I think it begins with a C but idk lol. I’ll see if I can get a snow map off its recent run.
 

I found it...

so supposedly this will be the model replacing the NAM. This was its forecast before the last event

22868309-22A0-4B2E-B526-A8E525AA9447.gif

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54 minutes ago, WxMan1 said:

11Z Sunday over the District per the 06Z 3km NAM. Nice lift in the DGZ. If it comes to fruition, we would see MUCH better dendrites than we saw last Sunday. Thus much better (faster) accumulation efficiency. Like 4+ inches within 12 hours instead of having to wait 24-36 hours (lol).

 

Why is that?  Is it because the sounding you are showing has colder air straight up through the column?

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7 hours ago, MillvilleWx said:

I'll tell you...Easton, MD is looking like a prime spot for this one right now. That and Kent and Arrows area in Queen Anne's. I really hope @CAPE gets crushed someway, somehow. 

If those areas are prime, my yard should be. I usually do better than those areas in marginal temp events because I am further E/NE and away from any moderating influences from the bay.

What do you figure the liquid/snow ratios will be? Even if there is good lift through the DGZ, the lower level temps are super marginal, so I would think maybe 7:1?

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1 hour ago, WxMan1 said:

11Z Sunday over the District per the 06Z 3km NAM. Nice lift in the DGZ. If it comes to fruition, we would see MUCH better dendrites than we saw last Sunday. Thus much better (faster) accumulation efficiency. Like 4+ inches within 12 hours instead of having to wait 24-36 hours (lol).

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Yes, this is a much better sounding compared to what we saw last Sunday, where cloud tops were only around -10C. There's also some convective instabilitiy at cloud top near -20C that would be favorable for ice crystal generating cells; when these ice crystals fall into the saturated dendritic growth layer below, they grow rapidly and stick together, forming fluffy aggregates. If these profiles simulated by the 3-km NAM were to verify, I think the snow-liquid-ratio would be > 10:1 with fairly intense precipitation rates. FWIW, the profiles on the 06z-GFS have similar features around this time.

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1 hour ago, CAPE said:

Given temps, and esp if the best lift ends up along/east of I-95, I hope folks aren't taking any of these snow maps literally. Looking like a 2-4" deal to me, which would be just fine.

1612796400-ASznuTkglsE.png

Thank you for that - good to temper expectations.  Since temps are an issue, do you see this having a big impact on roads Sunday?  It sounds like it will be coming down pretty fast, but I’m wondering about accumulation on surfaces.  

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