Wintry January 3rd-6th, 2018 Winter Storm The ARCC/Xtreme Weather Special

[Webberweather53]

It's plain and simple.... It's too dry in the lower levels. There will be some snow in the Piedmont, but none of it will ever reach the ground unless those lower levels moisten up a lot. That's the problem.

I call bs on the GFS not pushing the precip at least back to the US1 corridor... Yeah the low levels are dry but the DGZ is saturated and there's lift and the mid level WAA is insane, we have 70 KT southwesterlies at 500 hPa

 

[Cad Wedge NC]

I call bs on the GFS not pushing the precip at least back to the US1 corridor... Yeah the low levels are dry but the DGZ is saturated and there's lift and the mid level WAA is insane, we have 70 KT southwesterlies at 500 hPa

I am not saying I believe it, I am just saying why the models are not allowing the precip back this way. Is the dry air that's being modeled bogus? Maybe....

 

[pcbjr]

For Phil:

That same 18Z RGEM has about 13 straight hours of ZR in Gainesville, FL, (~midnight - 1 PM Wednesday) adding up to a whopping 0.60" of ZR! I suspect that would be an all-time icestorm record for there if that were to verify as I'm not even aware of a single major icestorm on record there! Phil are you aware of any?
Unlike further north in the SAV-CHS corridor, I can more readily buy a lot of ZR because 850s are +4 to +5, which is a common 850 range for major ZR.

For Larry:
No ice storm anywhere like that in my lifetime here (since 1960); the closest was 12/89 that went to ZR but after about a tenth of an inch went to all snow (which kept the snow on the ground longer than one would have anticipated).
Let's see what happens.
Seems like I've lived through the coldest temp on record here, the hottest temp on record here, the most snow on record here, the wettest year ever here (this year, btw), the driest year ever here, missed making your acquaintance here while you slept through our last snow ( ), so why not go ahead and take in the mother of all ice storms here?
Ice ... ???
If you have Tony's cell #, tell him to hop on Delta! - ready when he is ... LOL ...

 

[Cad Wedge NC]

I call bs on the GFS not pushing the precip at least back to the US1 corridor... Yeah the low levels are dry but the DGZ is saturated and there's lift and the mid level WAA is insane, we have 70 KT southwesterlies at 500 hPa

Do you have a link to 700mb UVV's. NAVGEM?

 

[Brett]

12k NAM is out in left field guys, if anything the 3km version looks plausible based on the surface reflections. I still can’t figure why the globals are not slinging more QPF inland given a bombing low off the Carolina’s. End result is the NAM will likely meet the GFS / ECMWF in the middle. If anything I feel less confident how this will play out than 24hrs ago. Moderate snow event for Florence to Norfolk, possiblility for a foot in NE NC and SE VA. Still expect to see a slight NW correction now that we are inside 48hrs, FAY to RWI should do very well.

My NWS in Wakefield has 3-6" expected with high end of 10" in Suffolk Virginia

 

[Bryce Shelton]

00Z runs will hopefully paint us a clearer picture of what is going to happen.

 

[Webberweather53]

I am not saying I believe it, I am just saying why the models are not allowing the precip back this way. Is the dry air that's being modeled bogus? Maybe....

The dry layer at the surface is related to the very fickle spatial distribution of convection offshore and along the SE US coast, earlier runs of the GFS showed more intense convection and spurious potential vorticity maxima which interfered w/ low-level moisture transport. The model is slowly adjusting NW and the last several runs have progressively improved for the piedmont...

 

[Bryce Shelton]

I've been studying the NAM at H5 and the difference between it and the GFS. Through 24 hrs they are tracking very similarly:

3km NAM:

GFS:

After this point, the NAM digs the trailing wave and the lead wave more, and honestly I see nothing implausible about it's solution. I also see the GFS tick closer and closer to the NAM every run. I'm just not sure I see any reason that the NAM is going to dramatically change what it is doing at 500mb.

Glad that you shared this! Very interesting!

 

[Rain Cold]

I've been studying the NAM at H5 and the difference between it and the GFS. Through 24 hrs they are tracking very similarly:

3km NAM:

GFS:

After this point, the NAM digs the trailing wave and the lead wave more, and honestly I see nothing implausible about it's solution. I also see the GFS tick closer and closer to the NAM every run. I'm just not sure I see any reason that the NAM is going to dramatically change what it is doing at 500mb.

It seems like the Nam links the waves sooner. The other models continue to delay the process just a smidge too long. It’s a subtle difference, but it makes a big difference in the outcome here. I would feel so much better if we could see a similar solution across other models.

 

[Rain Cold]

It does. And the reason is because it digs that trailing wave more north-south than the global models, or even the RGEM (which looks very similar to the Canadian). The NAM may be wrong, but if it is, it isn't doing anything that appears exceptionally wonky.

Yep, that makes sense. I’m not sure why it’s on an island digging the waves like it does. Hopefully, we see somebody else join the crowd. We’ve been Nam’ed a lot over the years. And SREF’ed too, for that matter.

 

[Tarheel1]

It seems like the Nam links the waves sooner. The other models continue to delay the process just a smidge too long. It’s a subtle difference, but it makes a big difference in the outcome here. I would feel so much better if we could see a similar solution across other models.

Still seems plausible that the other models could trend towards the NAM. With only minute differences, anything can happen! I'm gonna say NAM holds its ground or ticks west next run!

 

[Metwannabe]

It does. And the reason is because it digs that trailing wave more north-south than the global models, or even the RGEM (which looks very similar to the Canadian). The NAM may be wrong, but if it is, it isn't doing anything that appears exceptionally wonky.

Seems I've read it somewhere but wasn't the NAM upgraded? It doesn't seem it's been as crazy with over amped high qpf systems lately, in fact iirc with the early Dec storm it was the first one to show crazy amounts.... most of us dismissed it as being the crazy NAM. We know how that turned out

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[Webberweather53]

I've been studying the NAM at H5 and the difference between it and the GFS. Through 24 hrs they are tracking very similarly:

3km NAM:

GFS:

After this point, the NAM digs the trailing wave and the lead wave more, and honestly I see nothing implausible about it's solution. I also see the GFS tick closer and closer to the NAM every run. I'm just not sure I see any reason that the NAM is going to dramatically change what it is doing at 500mb.

Agreed. The NAM solution is essentially regurgitating back to us what we already see in the mid-upper levels wrt how similar this looks to January 2000... Sure it could be too amped or wet after 36 hours but I don't think the distribution of snowfall in the Carolinas is unrealistic. Other guidance has largely been playing catch up today but we haven't seen any model completely fold to the NAM quite yet. The 0z run infused w/ new RAOB sampling should be interesting, but I'm doubtful there will be any very significant change inside 36 hours

 

[packfan98]

DT just posted a good video that explains what the different models are showing and how the inverted trough can throw the precip further NW. He also goes over the 2000 Carolina Crusher. Good video for those trying to learn about the upper air patterns.

 

[Rain Cold]

Still seems plausible that the other models could trend towards the NAM. With only minute differences, anything can happen! I'm gonna say NAM holds its ground or ticks west next run!

Yep they could. Hopefully, they will soon.

 

[Alex]

DT just posted a good video that explains what the different models are showing and how the inverted trough can throw the precip further NW. He also goes over the 2000 Carolina Crusher. Good video for those trying to learn about the upper air patterns.

Watched it twenty minutes ago and I second this. Nice brief little history lesson on the 2000 storm for me as I barely remember it (14 and living in Fayetteville). Excuse me of this is banter, but could that be part of what the NAM is picking up on, that inverted trough, irt to the distribution, or is it simply picking up something with the energy from the northern stream? I'm a long time reader and rare commenter just west of Raleigh, really trying to get a handle on this storm.

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[WeatherNC]

I would toss the 12k output at this point, and blend a 3k NAM with the RGEM and water that down about 50% based on the Globals. ZR output should be considered suspect in the Coastal Plain from GA north, there will be a very narrow transition zone but the dominant type should be RN or SN with a few pingers for those fortunate to get under the heaviest returns. We are talking a < 20 mile zone not the wide 40-50 mile transitions the 12k NAM shows, more inline with the RGEM.

 

[Webberweather53]

I would toss the 12k output at this point, and blend a 3k NAM with the RGEM and water that down about 50% based on the Globals. ZR output should be considered suspect in the Coastal Plain from GA north, there will be a very narrow transition zone but the dominant type should be RN or SN with a few pingers for those fortunate to get under the heaviest returns. We are talking < a 20 mile zone not the wide 40-50 mile transitions the 12k NAM shows, more inline with the RGEM.

I can buy this, Miller As usually have razor thin transition zones but the most extreme cases (like Jan 1940 for example) actually are strange in that expansive areas of sleet aren't that uncommon. In fact, in that event, heavy sleet was the predominant precipitation type all the way back to central Wake County... As we also recently saw in December 2017 even w/o a substantial CAD in place, we created an in-situ one through low-level CAA capped by intense mid-level diabatic heating and the predominant precip type ended up being sleet all the way back to Greensboro

 

[Rain Cold]

It's funny because all my recent recollections of the NAM is of it being the new "Dr. NO" while the Euro says snow snow snow. The Euro was horrific with the system in December, it had I believe 6 straight runs with RDU near or in the sweet spot, and we know how that turned out. And I know I harp a lot on last January's storm, but that was another epic fail by all the global models. I am not a fan of the Euro or any global inside of 72 hours, and that's just two examples of why.

However, with that said, the NAM scares me. I have seen it do some absolutely mind-boggling wrong things too, but those were before the upgrade. Like I said earlier, if the RGEM would align a little closer with the NAM, I'd essentially be all-in on the NAM solution. The good news to me is that even though the RGEM at H5 looks more like the GFS, the precipitation distribution is still well inland. I am pretty confident if it does trend towards the NAM at H5 it will mimic it at the surface also, perhaps with a little less vigor but still some 12"+ totals between RDU and I-95.

Yeah, good post. Recently, the Nam has done well. But I get NAM PTSD, I guess, because I have a lot of memory of the old NAM pulling out the rug. I don’t like it on an island. That’s risky. But I do think it’s possible.

 

[GaWx]

I would toss the 12k output at this point, and blend a 3k NAM with the RGEM and water that down about 30% based on the Globals. ZR output should be considered suspect in the Coastal Plain from GA north, there will be a very narrow transition zone but the dominant type should be RN or SN with a few pingers for those fortunate to get under the heaviest returns. We are taking <20 mile zones not the wide 40-50 mile transitions the 12k NAM shows, more inline with the RGEM.

I agree with the above for SAV-CHS corridor. However, N FL, which you aren't addressing, is a much different story and is in danger of an unheard of major ZR.
Meanwhile, one of my local mets just gave a forecast that is downplaying this. He had mainly just a no big deal mix (little or no accum) and said temperatures would get up into the high 30s with the precipitation. He's going with the mainly tame solutions of the globals, which do have high 30s vs the wetter models that have 20s. He said there was good agreement of the models, except for one with a crazy solution or something like that lol. In reality that isn't true if you include the RGEM and ICON, among others, that have a lot more than GGEM/Euro/GFS but way less than the insane NAM. Man, this is going to be a nail biter.