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February 11-12 ULL Winter Storm


Upstate Tiger
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1 minute ago, wncsnow said:

Hi Res GFS looks pretty bad too through 60. It also has ice for mountains.

You have any idea how it’s verification scores match up to other low level cold models? I’m not sure I’ve ever seen someone in here touch on it. It’s definitely the warmest. 
 

I’d also like to see RGEM and Canadian cool down somewhat. They’ve been running warmer than other guidance as well. 

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One thing to keep in mind is that ground temps will be quite warm, surface temps may be a tad above freezing even during some of the snow (except in the mountains), so a lot of melting will occur, so accumulations at least on many surfaces will likely be less that what the models are showing. Further melting will happen soon after the event occurs since there will be no real cold air once the ULL departs.

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11 minutes ago, Cheeznado said:

One thing to keep in mind is that ground temps will be quite warm, surface temps may be a tad above freezing even during some of the snow (except in the mountains), so a lot of melting will occur, so accumulations at least on many surfaces will likely be less that what the models are showing. Further melting will happen soon after the event occurs since there will be no real cold air once the ULL departs.

Is there no model or map that takes into account ground temps ?

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Asheville at 8.5” with Kuchera method. Roanoke 7.4. Pretty much entire spine of western NC is 4-8” verbatim with Kuchera on GFS. [mention=14047]BornAgain13[/mention]2-4” type of event down your way. 
Yeah the GFS has been consistent throughout the day. Would love to see the Euro show that for here.

Sent from my SM-N981U using Tapatalk

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I gotta say, I think ground temps are talked about way too much in these situations. Ambient air temps matter and will be a problem for some, but I wouldn't worry too much about ground temps as long as the rates are there. Plus in my experience in top down cooling scenarios, if the rates are persistent they can literally drag freezing air to the surface. Warms up as soon as it moves out, but still aids in accumulation.

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There are positive depth change maps on pivotalweather+ for the ensembles (below), I think the GFS op is free. 10:1 and Kuchera ain't gonna cut it, and in reality, no snow map will capture the differences between what accumulates on trees/vegetation/grass vs pavement. Slower trends could put more of the snow into the day Sunday rather than Saturday night, which could limit accumulations on roadways outside of the mountains.

models-2023021000-f072.snodpc_acc-mean-imp.us_ma.gif.e7afdc17c3eb549cc3b02ba1e0f5d47e.gif

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There is almost better agreement on the freezing rain potential than for snow. A surface high over the Mid-Atlantic could maintain just enough dry air to wet bulb surface temps down to or below freezing near the Blue Ridge (esp. sheltered valleys and some ridge tops) as the heaviest precip moves through. The TROWAL (trough of warm air aloft) provides the melting aloft for that and also contributes to the upright instability that will be crucial for flipping rain over to snow despite marginal boundary layer temps for elevations below ~1500'. The favored zone for heavy snow will be just northwest of the core of the closed 700/500mb circulations, but predicting where and when convection occurs this far out, even on hi-res guidance, is next to impossible. That's why ensembles are still a good tool for a marginal situation like this.

1883583134_ScreenShot2023-02-10at6_15_54AM.thumb.png.e47aafe4b47b76c521b4ff0a75d9f386.pngmodels-2023021000-f072.fram_acc-imp.us_ma.gif.e6017b1eda473974043ff37b3a95029c.gif

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52 minutes ago, purduewx80 said:

There is almost better agreement on the freezing rain potential than for snow. A surface high over the Mid-Atlantic could maintain just enough dry air to wet bulb surface temps down to or below freezing near the Blue Ridge (esp. sheltered valleys and some ridge tops) as the heaviest precip moves through. The TROWAL (trough of warm air aloft) provides the melting aloft for that and also contributes to the upright instability that will be crucial for flipping rain over to snow despite marginal boundary layer temps for elevations below ~1500'. The favored zone for heavy snow will be just northwest of the core of the closed 700/500mb circulations, but predicting where and when convection occurs this far out, even on hi-res guidance, is next to impossible. That's why ensembles are still a good tool for a marginal situation like this.

1883583134_ScreenShot2023-02-10at6_15_54AM.thumb.png.e47aafe4b47b76c521b4ff0a75d9f386.pngmodels-2023021000-f072.fram_acc-imp.us_ma.gif.e6017b1eda473974043ff37b3a95029c.gif

Any analogs you can think of for this sort of ZR event? I figure there isn't really a chance for this to occur below 1,500 ft or so

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10 minutes ago, olafminesaw said:

Any analogs you can think of for this sort of ZR event? I figure there isn't really a chance for this to occur below 1,500 ft or so

Nah, I've only lived in ATL a year. CIPS analogs are below. The shading is probs for >4" of snow based on the 00Z NAM. CIPS doesn't have FZRA as far as I can tell, but you can see the top 15 analogs in that drop down.

image.thumb.png.f56839231f6aca0228b71edbd8d5282f.png

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