GaWx

18Z NAM has a good bit of ZR and less % that’s IP vs 12Z due to warmer atmosphere

RDU. There are no p-type maps or 2 meter temp maps for the JMA at either WB or TT. It is pretty much a given that 2m will be below 32. TT does have 850s at 24 hour intervals for today’s 12Z JMA allowing me to educatedly guess that RDU would be just about all snow (maybe a little sleet). I think that 6” of snowfall from 0.80” qpf would be doable but it is just an educated guess. Regardless, it would be a major hit. If it were mainly sleet (highly doubtful), it would still approach 3” of concrete. ***Edit: I’ll update this when it comes out on WB as they have 850s and qpf at 6 hour intervals through hour 72.

12Z JMA has was appears to be nearly all if not all snow at RDU due to 850s likely staying below 0C most if not the entire time along with ~0.80” qpf suggesting ~~6” of Kuchera snow. A 6” snowfall would be their 4th biggest in La Niña Feb-Apr back to 1886-7! The only larger than 6” were 8.0” on 3/10/1934, 6.9” on 2/6/1984, and 6.2” on 2/17-18/1989. 2/16/96 was very close with 5.6”. In contrast, there have been 8 snowstorms of 6”+ during El Niño Feb-Apr vs the 3 during La Niña at RDU.

Actually, the 12Z WB NAM output shows mainly snow (1.8”) and sleet (0.8”) with only .02” of ZR for RDU due to 850s only getting to barely above 0C for a portion and 925s being near 0C for only a short time before falling to -2 to -3 for most of the qpf: The globals keep RDU in near 100% snow.

12Z Icon qpf: 0.61” RDU

12Z Icon: all snow for RDU; this is 10:1; but even after Kuchera reduction from 6.1” it shows, would likely still be 4-5” hit/major:

12Z NAM fwiw:

12Z NAM: look how much further W is the low compared to other models. But it is the latter hours of the NAM…so take with a humongous grain:

It will still be only Feb 23-24 for the next one and with cold air still nearby.

Don’t forget that there’s another system waiting in the wings once we’re done following this one. There’s always a next time. Maybe that will be more impactful than this one. One never knows, especially since it is still out 6-7 days, a relative eternity!

From JB: Opportunity to learn: Perfect 500 mb forecast, but the surface not responding likely due to lack of focused warm advection The warm advection term is just as important as upper divergence in cyclogenesis and I thought there would be more resistance. AI looks like it will be right. That 9-day call on 500 mb was as good as I can do. In retrospect the development of heavy precip on the gulf coast shuts down any inflow north into the arctic boundary. and the precip weakens in the cold air. Once that convective feedback takes off, there is no chance for the kind of warm advection needed for the more northern route. I obviously thought this was not going to happen to this extent. But that kind of vv there means that is where this wants to form. As it moves along the snow shield to the north weakens instead of the other way. Once the focus gets to the coast its too late and only light snows from the upper low come across.

Indeed, the fact that the best models can and do miss so badly even just a few days out makes this far more interesting than it would otherwise be due to higher uncertainty. Can you imagine how boring forecast discussions would be if the models were perfect?

Yeah, it hasn’t had as big jumps as the Euro op run to run on this.

6Z EPS 10:1 RDU still gets a real nice hit of 4-4.5”

As bad as some in the SE are feeling about the Euro changes, can you imagine how bad the NE is feeling? 6Z 2/16 Euro: 6Z 2/17 Euro: instead it went way SE: 6Z 2/16 Euro: JB still yesterday evening thought even this was going to trend W to W of Hatteras 6Z 2/17 Euro instead trended way east:

JB’s prediction of the low going W of Hatteras on life support now. Meanwhile, here’s the 0Z EPS 10:1 snow. RDU actually rose from 5” on the 18Z to 6” on the 0Z, which is tied with the 0Z of 24 hours ago for the highest!

The 0Z Euro went even further SE… significantly further! The 1” and 0.5” qpf lines have moved 200 miles E/SE vs the 0Z of 24 hours ago! New 0Z Euro Kuchera: RDU down to 4.9” (~1/2 the 18Z); DC down to 0.5” vs 16.7” 24 hours ago: Old 0Z Euro Kuchera:

Look how far the Euro heaviest qpf has trended the last 3 runs. In NC, the 0.5” and 1” lines have shifted E/SE a whopping 100-150 miles! It is due to shift back west some at 0Z. Anyone want to make a prediction of what the 0Z will show? 0Z Euro 18Z Euro

Ok maybe calling it a “major” outlier is too strong. But the UK/CMC have 5-6”. Isn’t that a pretty large difference from 9.8”?

You need JB’s expectation of the low going W of Hatteras due to cold model biases/NW trend to verify.

Wow, 9.8” at RDU! I wouldn’t bet on that much as it is a major outlier to other models and La Niña climo says the chance of that much this time of year there is very low.

Per a video JB released around 11AM today, he’s insisting that the low will go W of Hatteras (100-150 miles W of the model consensus). He’s been insisting on this. His reasoning is that he thinks the models are pushing the cold air boundary out too far due to a bias. He’s saying bet on the common NW trend we talk about. Any chance he’s going to be right? I believe that all of the latest models are well E of Hatteras except the 18Z Icon and NAM, which are only barely off Hatt: 18Z Icon: 18Z NAM:

18Z GFS Sleet: ZR:

The 18Z Icon looks great for RDU: 0.92” qpf. Of this ~0.35” is with snow (say ~3” Kuchera) and ~0.57” is with sleet..1.7” of sleet. Total of ~4.7” snow/sleet RDU with hardly any, if any, ZR.

I see that Dry Fork is only ~6 miles S of Chatham. The following link has Chatham snowfall and other data back ~100 years: https://www.weather.gov/wrh/Climate?wfo=rnk 2”+ Chatham snowfalls 2/15-3/10 during La Niña: there is data going back 30 La Niñas 2/18-19/1989: 10.3” from ? 2/25-26/1934: 9.0” from 1.60” liquid 3/2/2009: 7.7” from 1.09” liquid 2/15/1965: 6.0” from 0.48” liquid 2/24/1989: 5.0” from ? 2/18-19/1972: 4.5” from 0.71” liquid 2/20/2012: 3.2” from 0.40” liquid 2/23/2001: 2.0” from 0.26” liquid 3/2/1939: 2.0” from 0.20” liquid The other 21 La Niñas had no storm of 2”+ during 2/15-3/10. Median largest snow during 2/15-3/10 in any one of the 30 La Niñas was actually <0.5”! -Chance for 0.5”+ storm during La Niña 2/15-3/10 <50% -Chance for 2”+ storm during La Nina 2/15-3/10: 9 out of 30 or 30% chance -Chance for 4”+: 20% -Chance for 7”+: 10% -Chance for 10”+: 3% So, for example: if you get a 4” snowfall, which is looking like a good possibility, you will have done better than 80% of La Niñas during 2/14-3/10. With the current storm threat, you’re in better shape than in most La Ninas this time of year. Regarding snow to liquid ratio for the seven 2”+ snows the liquid is available for: only one storm was >10:1, 2/15/1965. It was at 12.5:1. It was cold with a high of 29 and low of 23. What matters most is the temp aloft like at 850. I bet that was a good bit below 0C. Best to look at Kuchera instead of 10:1 if available.