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February 19-20 Major Winter Storm Threat


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1 hour ago, BornAgain13 said:

I mean. Realistically, how far south and east can it go? 

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.
 

 

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8 minutes ago, GaWx said:

I see that Dry Fork is only ~6 miles S of Chatham. The following link has Chatham snowfall and other data back over 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 2/15-3/15 <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, you’ve done better than 80% of La Niñas during 2/14-3/10.

 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.
 

 

Thank you! That's so cool!

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RAH discussion.  They are seeing the same as everyone else on this board.  We will all know either late Monday or early Tuesday.

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 400 PM Sunday...

A southern stream shortwave will move east from the southern Plains
on Tuesday night to the Deep South on Wednesday, while a separate
northern stream closed mid/upper low drifts SE from the Northern
Plains to the Upper Great Lakes region. The southern wave and upper
divergence from the right entrance region of an associated upper jet
streak will spawn a surface low that develops on a cold front along
the Gulf Coast on Tuesday night and early Wednesday. This low will
then deepen and moves NE in a classic "Miller A" track along or just
off the Southeast US coast on Wednesday afternoon and evening. With
a cold dry air mass in place ahead of the system, confidence is
increasing in a period of frozen precipitation across most of
central NC from late Wednesday morning into Wednesday evening.
However, how impactful it is still remains to be seen, with both
precipitation types and amounts will very much up in the air. This
does not look like an all snow event, as there is almost definitely
going to be significant warming aloft with southerly flow at 850 mb.
At this time, the most likely part of the region to stay all or
mostly snow is the far northern Piedmont, with a fairly large
corridor of mainly sleet and freezing rain to the south. Our
southern tier of counties including FAY are most likely to stay all
or mostly rain.

A lot will depend on the degree of phasing that can occur between
the southern stream and northern stream wave, the latter of which
also has an associated jet streak which dives into the Central
Plains and mid-MS Valley. The ECMWF (and to some degree the
Canadian) has a faster and deeper northern stream mid/upper low
compared to the GFS, allowing for stronger height falls and greater
energy interaction between the two systems. This results in a deeper
coastal low and would bring a high impact winter storm to central
NC, with colder temperatures and greater QPF amounts. The GFS would
be more of a moderate/nuisance type event that only lasts for 6-12
hours before we are quickly dryslotted after 00z Thursday. This is
borne out in their respective ensembles as well, with the EPS
ensembles depicting a 50+% probability of warning criteria snow (>=
3 inches) across roughly the northern half of the region while the
GEFS only have 20-40% probabilities that are confined to our
northern tier of counties. Deterministic and ensemble guidance has
also been depicting potential for significant amounts of freezing
rain somewhere across central NC, perhaps exceeding a quarter inch,
with the greatest probabilities from around Raleigh to the south and
east. The NAM is surprisingly the warmest out of all guidance, with
mostly liquid for a good part of the area, but considering this
storm is at the very end of its range, will mostly disregard it at
this time.

It should be noted that neither the GFS or ECMWF has complete
phasing between the two waves, and the overall trend in both
deterministic and ensemble guidance has been slightly downward in
terms of overall QPF with a faster exit of precip, so will need to
see if this trend continues. Yesterday the ensemble mean QPF was in
the 1 to 2 inch range, while today it is more like the 0.5 to 1.5
inch range, lowest west and highest east. If this trend continues,
we would be looking at more of a nuisance type event like the GFS
has, but that is a big if. Stay tuned as details should become
clearer, hopefully by tomorrow when the southern wave reaches the
West Coast and we can get better sampling. As for timing,
precipitation still looks to start from SW to NE on Wednesday
morning, ending from SW to NE during the evening or early overnight
hours. Temperatures will be highly dependent on the ultimate
evolution of the system, but Wednesday is likely to be quite chilly
with temperatures stuck in the lower-to-mid-30s during the day,
maybe even upper-20s in the far north. Forecast lows Wednesday night
are in the upper-teens to mid-20s.
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Eric Webber's thoughts from the other place.

 

It's going to hold steady or trend south a little more from here in general imho. While we could get a sizable north shift here, the pattern does not favor a big one this time around unless we see seismic changes with the chunk of the vortex that's getting trapped underneath this west-based -NAO blocking ridge.

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10 minutes ago, olafminesaw said:

Don't love the trend towards late development, meaning pretty dry West of Durham 

snku_acc-imp.us_ma (3).png

I’m nervous anywhere west of 95 imo. Take that as you will because I’m genuinely not trying to sound trollish, but that northern stream is crushing the system 

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11 minutes ago, PackGrad05 said:

18Z ICON looks almost identical with placement, amounts slightly lower.  Still massive gradient across central NC/Wake

Filled in the snow hole back here in the west, I'll take that as a plus for MBY for the time being.

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