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December 8-10, 2018 Winter Storm


Orangeburgwx
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The NAM used to be biased heavy on qpf, but was adjusted and now maybe is biased a bit light, is that correct?

I do think the level of that initial hit will be important, both the over running which may serve to only moisten the column, and the actual precip from the slp. Then we have the backside ull to deal with. Looks like a broken period of precip over 2 days rather than a continuous period of precip.

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Just now, NCSNOW said:

Nam has position of HP back over western Wisconsin and also slow with the LP. hence position of HP compared to 6z results in CAA being started latter. Also wake up guys, Raleigh want be getting dry slotted. The model only goes out to 84 and has been the slowest with start up time by 6 to 12 hours compared to other models.

Yes, great observation. 84 hrs only takes us to Sunday afternoon and this storm is going to persist through Monday morning, at least. 

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2 minutes ago, tramadoc said:

Look at all the lemmings cliff jumping and climbing back up only to jump again with each successive model run.


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Well, more room for me up here on the cliff with all the folks jumping after that one NAM run. 

If you know things are going to always turn out bad, I'm not sure why you even come on here until 24 hours out before a storm is supposed to hit.

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We can play around with long range NAM soundings, but the trend in this particular model is to delay and lessen the push of cold air and the strength of the high.  There's no question aout that, and it's not good.  That doesn't mean it's right.  And it doesn't matter if it's exactly right.  But if other models continue this trend in one way or another, then we have a problem, assuming you like lots of snow and an all frozen event.

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5 minutes ago, tramadoc said:

Look at all the lemmings cliff jumping and climbing back up only to jump again with each successive model run.


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And look at the lemmings who want to ignore lousy runs and pretend everything is roses.

I'm not jumping off a cliff. Hell, i don't even LIVE in the affected area. I'm certainly not going to let one NAM run change my view of the storm. But pretending like it's not an awful run, especially in an area that is supposed be the NAM's only strength, is foolish. And given that there were subtle warming trends in the 0z suite, it definitely could be a piece of this amazing puzzle we're all trying to put together.  

 

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Winter Weather Update

 

Hi resolution models are starting to paint a picture. Some of you won’t like it. I’m beginning to get concerned for two areas of interest for two very different types of precipitation. 

 

First, the NAM model continues to produce some higher snow totals for places like Asheville N.C. To points East-Northeast Hickory N.C. Including even Boon N.C. The up-sloping snow will get lift from the higher terrain and cause heavy snow in some spots. Elevations 3k, to 4K ft. Will have possible 40mph winds creating blizzard like conditions especially on the east side of the mountains. I’m looking at total estimates later tonight. heavy snow is also possible for places like central north Georgia. The precipitation may be delayed  thanks to the cold air damming of dry air. 

 

Second, I’m growing concern for places south of Interstate 85 across the upstate S.C. and parts of northeast Georgia. A possible ICE storm as far across the state to Sumter and Florence S.C. is even in play. However, rain will often mix with the ice to limit the ice accumulation (as it looks now). That may change if the NAM trends cooler. 

 
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Just now, Cold Rain said:

We can play around with long range NAM soundings, but the trend in this particular model is to delay and lessen the push of cold air and the strength of the high.  There's no question aout that, and it's not good.  That doesn't mean it's right.  And it doesn't matter if it's exactly right.  But if other models continue this trend in one way or another, then we have a problem, assuming you like lots of snow and an all frozen event.

At this point in the game you have to give more weight over the op models (at least I do). Looks like a ice storm. All we need is .25" to reach Winter Storm criteria. 

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2 minutes ago, DopplerWx said:

hr 60 on the 3k nam and the sounding isn't good for kclt. cold rain as precip pushes in. the initial thumping is looking less and less likely now.

nam3km_2018120612_fh60_sounding_KCLT.png

I think you can argue that it’s doing what it’s been showing for a while now and cooling from the top down. It’s snowing just on the other side of the Catawba on that frame.

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Read this RE: NAM.....

Just poured through the hour-by-hour profiles for KCLT in BUFKIT from the 6z NAM.... 12z wasn't in yet. 

Really fascinating. Even out to 3-4z Sunday, the dewpoint is ABOVE freezing from essentially the SFC up to around 5k feet. Then, extremely quickly and dramatically, EXTREME drying kicks in at 2k-4k feet over the next few hours... I mean extreme. Dewpoints drop 10s of degrees C at those layers as strong NE winds kick in at those levels.

That is when the dynamic cooling really starts to kick in.... which is after the end of the 3k NAM's range that someone posted a moment ago. 

Interesting.

Compared to the 6z GFS, the NAM atmospheric profile is warmer by a decent margin than the GFS at precip onset. BUT, this isn't due to a warm nose....it's the initial airmass. At this point, for that aspect of the system, I would still give a slight lean to the globals.

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