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February 9th Coastal Storm Discussion


Baroclinic Zone

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1 minute ago, wxsniss said:

Thanks for all the comments everyone. Lurking > posting due to work but good stuff as always.

For those learning about being in good "cross hairs"... (Mets correct or add anything)

Nice sounding for KBOS off 18z NAM.

1) Dendritic growth zone (DGZ, labeled in blue circle), assuming -10˚C to -20˚C (purple lines), the temperature range at which optimal crystal growth occurs.

2) Within the DGZ, the green line (dewpoint) and red line (temperature) overlap, indicated a saturated column within the DGZ.

3) OMEGA bars on the left indicate upward vertical motion (UVV).

4) The area of maximum UVV (yellow box) colocalizes with the saturated area within the DGZ, parameters for heavy snow with good snow growth.

That pretty much covers it.

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The more I look at this I lean toward a low track closer to the coast...

The primary boundary is aligning parallel to the upper M/A NE coasts within 50 naut miles an is nearly stationary ... that the last ob still initialized it as  cold front.  

- for one, it is nearly parallel to a mid level wind field that is veering aloft as we type and will continue to do so overnight as this trough tightens up and tips the mid llv flow more S-N offshore.

- there are modest pressure rises taking place east of the boundary ... that's not really sending vibes across like it's marching out to sea exactly. 

The best thermal gradient exists in the 850 mb level ..what's new, but as the q-v forcing rips overhead and that level closes off and deepens quickly as a result, I suspect models such as the NAM are too far E with the surface low... Seems the model is too vertically tilted owing to putting too much emphasis on the vestigial primary boundary to track its surface reflection. Maybe..

This system's deep layer structure/evolution would provide for banded heavier QPF embedded in the general zygote CCB head, but it would matter if the system were better vertically integrated because of feed-back processes.  Not that we need those exactly to get what people are after.  You almost don't want this system to be too strong too soon, because it could be too fast and not enough time for instability parameters to gain traction farther west.  You end up with an intense nucleus that way... But that's speculation.

 

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Just now, HoarfrostHubb said:

A few questions...

1) scooter caution flags? If any?

2) What is causing modeling to go nuts with this over the last 2 days?

3) this is a quick mover...how can it drop this much in under 12 hours?

1. Subsidence outside of the f-gen bands, especially north of the main band. Lift above the DGZ, again north of the main band. 

2. Fast moving shortwave was "seen" late by modeling. Only onshore for the last 48ish or so hours.

3. $64,000 question. Forcing is strong, rates will be excellent in good banding, but there is an upper limit.

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1 minute ago, HoarfrostHubb said:

A few questions...

1) scooter caution flags? If any?

2) What is causing modeling to go nuts with this over the last 2 days?

3) this is a quick mover...how can it drop this much in under 12 hours?

1) Yes...well just being nitpicky. Obviously how far west is the deformation band? To the NW of it will be a virtual tailpipe sucking with all that vertical motion within the band. Remember what goes up, must come down. Also, does the band consolidate further east? Where? Will it be as strong? Progressive? What about coastal front/OES? I do worry there may be some subby zones in between the bands..but tough to say. Folks in BOS may be disappointed for awhile and then absolute go ape sh*t after noon.

 

2) First I think we go back to this recent low. It's not the powerhouse once modeled on the GFS. It is weak and that helps keep the baroclinic zone close to the coast. The parent s/w also seems to be modeled stronger which is helping really force and dynamically squeeze out all the PWAT we have. Heavy precip isn't related to intense low....you can have strong mid level forcing aid in this, and we will have this in the morning.

3) There is the potential for 3-4"+/hr snows. It won't take long to drop impressive amounts. 

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1 hour ago, dendrite said:

I had Mar 05 and although it was cool to experience it still made me frustrated when trying to measure. To each his own.

Sucks having to go measure an area to avg with sticking a drift.

1 hour ago, Damage In Tolland said:

I'm so amped up. Treehouse and Trillium drinking like Halloween candy.. let's do this 

Go share a growler with JC-CT so he can man up.

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