December 2022

[bluewave]

5 hours ago, jm1220 said:

It’s why it’s a fallacy to say “the cutters always work out 6 days in advance but the NYC snowstorms don’t”. We couldn’t care less if the cutter changes 150-200 miles in track, it’s still a cutter and washout. But for Chicago it makes a big difference. A change like that for us is always a big deal. 

Yeah, a cutter can go 5 miles west of NYC or 500 miles west and still be a big rainstorm on Long Island. So there is more leeway for a long range cutter forecast to work out. But a benchmark snowstorm can’t afford to be 500 miles off and still verify. So cutter tracks can start showing up day 6-10 and still work out for us. But we are lucky if a big snowstorm is correctly modeled by day 5. The big ones usually start out suppressed beyond day 5 and correct west the closer in we get. We briefly had a window last Thursday when the cutter was showing up right along the coast or even to the east. But the one cluster the EPS was showing over the Great Lakes turned out to be right. The ensemble mean SE of MTP would have been perfect from 72 hrs out for a KU. But the big westward correction we often get in the shorter range put the storm to our west. The animation below is the one you want to see for snowstorms in our area.

 

 

[Allsnow]

@bluewave nailed this pattern….

[White Gorilla]

3 hours ago, cleetussnow said:

Agree.  I was planning to stockpile some more wood pellets, but my consumption will be half of normal for several weeks at least.  I think we get a 2 to 3 week stretch of winter later in Jan and then we are done.  And that's if we are lucky.  The pacific is setting up hostile as usual.

Just give me one big snow and I won't mind an early Spring.  

[Volcanic Winter]

12 minutes ago, White Gorilla said:

Just give me one big snow and I won't mind an early Spring.  

Here you go man:

[MJO812]

44 minutes ago, brooklynwx99 said:

as far as anything to keep half an eye on over the next few days, I suppose the wave early next week would be worth it

it's too progressive verbatim, but this is the type of thing that models do a pretty bad job with at this range. this is a pretty strong S/W and could pose a threat if it rounds the corner. obviously, this is difficult given the +PNA deamplifying, but this could change given the lead time

so, pretty low chance, but it's something to peek at given the very cold air in place as well as a regime change as the block fades

also worth it given that we're going to absolutely torch after this chance through the New Year

Archambault event?

[eduggs]

19 hours ago, Tatamy said:

Would the same be said for the 0z GEFS mean?  Some interesting outputs on some of the members.

I was wondering the same last night. Hopefully someone with access to the individuals answered it. By now most of those wacky members have probably been weeded out of the suite.

[eduggs]

13 hours ago, LibertyBell said:

If you want cold weather this is the way you get cold weather.

 

I like cold weather for its capacity to facilitate snowstorms. Since this cold likely won't be associated with snow locally, it's the worst kind of cold.

[eduggs]

8 hours ago, JTA66 said:

I wouldn’t buy anything the globals are showing regarding post frontal frozen at this range. If the mesos have this look inside 36 hours, I might get interested.

The raw model output is/was not showing snow locally. 3rd party vendors process the raw data to generate clown maps. Some do a very crude job at it, but it's not the fault of the GFS in this case - it's tropicaltidbits etc.

[wdrag]

6 minutes ago, eduggs said:

I was wondering the same last night. Hopefully someone with access to the individuals answered it. By now most of those wacky members have probably been weeded out of the suite.

I'm pretty sure GEFS and GEPS mean is 10 to 1 and converts sleet as well to 10 to 1.  That can easily inflate numbers-mean. NWS please correct me if necessary on GEFS ensemble being 10 to 1.  Thanks.  Walt

[the_other_guy]

1 hour ago, Rjay said:

Completely disagree with that assertion. 

There at 70+ pages before this was widely accepted as going obviously sideways.

No need to assert anything. It is all right there. you can’t be mad at people after they are saying it never produced. It didnt.

you also can’t be mad at a guy like me that’s calling out another jump… this time on a major “record” warm up two weeks away. 

we have guys swinging the other way talking about how horrible January’s going to be on Dec 19th.

after a while, it’s Christmas week, it’s cold. Possibly record cold right after Christmas. maybe some back end snow. Let’s give it a breather.

 

that isn’t being insufferable, that’s sanity.

 

 

 

 

[Nibor]

9 minutes ago, the_other_guy said:

There at 70+ pages before this was widely accepted as going obviously sideways.

No need to assert anything. It is all right there. you can’t be mad at people after they are saying it never produced. It didnt.

you also can’t be mad at a guy like me that’s calling out another jump… this time on a major “record” warm up two weeks away. 

we have guys swinging the other way talking about how horrible January’s going to be on Dec 19th.

after a while, it’s Christmas week, it’s cold. Possibly record cold right after Christmas. maybe some back end snow. Let’s give it a breather.

 

that isn’t being insufferable, that’s sanity.

 

 

 

 

[nycsnow]

Upton

Winds will also be an issue as the NBM and its 50th percentile
show 35 to 40 kt gusts across the area on Friday, as SE winds
steadily ramp up ahead of the warm front. Winds will veer around
to the S/SW in the afternoon and then W following the cold
frontal passage late afternoon/early evening. Gust up to 40 kt
will be possible throughout the day and even 1-2 hours behind
the cold front, then gradually subside Friday night. There is
lower probability of a high wind event (>=40kt, >G50kt), but
cannot be ruled out.

[eduggs]

I was taking another look at the GFS and CMC 500mb charts for Thursday night into Friday. Yes it's a massive cutter with rain to interior Quebec. But if that strengthening and tilting ULL somehow manages to dive 200 miles further SE, the upper level divergence would start interacting with the coastline and we might start talking about a discrete secondary SLP. Any kind of moisture wrapped back into that arctic air would do wonders for the holiday spirit. Most likely any wraparound snow will remain far to the north and west. But the GFS has been gradually shifting the ULL SE the past few runs. Grasping at straws...

[Roger Smith]

For potential comparison to 23rd-24th change in NYC max temp, these are the top twelve downward differentials from day to day, 1869 to 2022: 

 

_ Rank ___ Dates ___________ From _ To ___ diff

_ 01 _____1918 Feb 20-21 ____59 __ 18 ____-41

_ 02 ____ 1921 Mar 28-29 ___82 __ 42 ___ -40

_ 03 ____ 1927 Dec 8 - 9 ____65 __ 26 ___ -39

_ 04 ____ 1915 Apr 26-27 ___ 92 __ 54 ___ -38

_t05 ____ 1896 Feb 16-17 ___ 44 ___ 7 ___ -37

_t05 ____ 1978 Jan 9-10 ____ 58 __ 21 ___ -37

_t05 ____ 2003 Apr 16-17 ___ 88 __ 51 ___ -37

_t08 ____ 1876 Jan 10-11 ____60 __ 24 ___ -36

_t08 ____ 1911 Nov 12-13 ____69 __ 33 ___ -36 

_t08 ____ 1933 Feb 8 - 9 ____ 60 __ 24 ___ -36

_t08 ____ 1970 Feb 3 - 4 _____56 __ 20 ___ -36

_t08 ____ 2014 Jan 6 - 7 ____ 55 __ 19 ____-36

[donsutherland1]

On 12/3/2022 at 2:51 PM, donsutherland1 said:

Statistically, insight regarding strong AO+ values proved useful in heralding the arrival of AO blocking in late November. A sustained AO- regime commenced on November 23.

https://www.americanwx.com/bb/topic/58336-november-2022/?do=findComment&comment=6681570

Statistical trends in the PNA following the most similar December 3 cases suggest that, just as is shown on the dynamical guidance, the ongoing PNA- regime will be slow to breakdown. By the end of the third week in December, values should be less negative than they currently are. However, the development of sustained positive values by that time seems unlikely (not zero, but still a less than one-in-three probability).

 

Here's how things have turned out so far with regard to the PNA:

[donsutherland1]

Dry but cool weather will continue through Wednesday. A powerful storm could bring heavy rain, high winds, and coastal flooding to the region Thursday and Friday. A general 1"-2" of precipitation appears likely with some locally higher amounts. A light snow accumulation remains possible at the onset of the storm and as it moves away from the region. A flash freeze is possible.

Once that storm passes, the season's coldest air so far will pour into the region. Temperatures could tumble into the teens in New York City. Nevertheless, the core of the Arctic air mass will bypass the New York City region.

The AO fell reached -4.000 on December 10th. Since 1950, there were 11 cases that saw the AO reach -4.000 or below during December. Mean snowfall for those cases was 9.0" (Median: 9.1"). 64% of such cases saw 6" or more of snowfall in December while 45% of such cases saw 10.0" or more snow. In contrast, during all other December cases, mean December snowfall was 3.5" (Median: 2.5"). 91% of those cases also saw a colder than normal December in the northern Middle Atlantic region. In terms of seasonal snowfall, 64% of those seasons saw 30" or more snowfall in New York City with 45% having 40" or more. Just 18% of such cases had less than 20" seasonal snowfall, both of which had less than 10" for the December-January period.

However, there are cases where Decembers with strong blocking have seen much below normal snowfall. The three cases with less than 1" of monthly snowfall with a monthly average AO of -1.500 or below were: 1985: 0.9" (total seasonal snowfall: 13.0"); 1996: Trace (total seasonal snowfall: 10.0"); and, 2012: 0.4" (total seasonal snowfall: 26.1"). The lowest December snowfall when the AO averaged -2.000 or below was 5.1" in 1976. Total seasonal snowfall was 24.5". There is a chance that the December 1976 record futility could be surpassed this month.

The ENSO Region 1+2 anomaly was -0.1°C and the Region 3.4 anomaly was -0.9°C for the week centered around December 14. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.95°C and the ENSO Region 3.4 anomaly has averaged -0.92°C. La Niña conditions will likely persist through mid-winter.

The SOI was +24.03 today.

The preliminary Arctic Oscillation (AO) was -3.790 today.

On December 17 the MJO was in Phase 3 at an amplitude of 0.644 (RMM). The December 16-adjusted amplitude was 0.602 (RMM).

Based on sensitivity analysis applied to the latest guidance, there is an implied 77% probability that New York City will have a colder than normal December (1991-2020 normal). December will likely finish with a mean temperature near 37.7° (1.4° below normal).

 

[coastalplainsnowman]

How many times in the past 20 years was there, if not total consensus, then at minimum majority opinion that the next three weeks looked bleak, only for things to turn on a dime and for an actual snowy pattern to emerge out of the literal blue within a week?

The answer: frequently enough.  For that reason I really try not to ride the daily highs and lows here.

The mood here is too somber.  C'mon, the season just started! Let's enjoy the ride.  Since I have nothing real to add here will just say happy holidays to all and all the best for 2023.  

 

 

[MJO812]

2 hours ago, eduggs said:

I was taking another look at the GFS and CMC 500mb charts for Thursday night into Friday. Yes it's a massive cutter with rain to interior Quebec. But if that strengthening and tilting ULL somehow manages to dive 200 miles further SE, the upper level divergence would start interacting with the coastline and we might start talking about a discrete secondary SLP. Any kind of moisture wrapped back into that arctic air would do wonders for the holiday spirit. Most likely any wraparound snow will remain far to the north and west. But the GFS has been gradually shifting the ULL SE the past few runs. Grasping at straws...

Nam also did that at 0z

[donsutherland1]

Given all the discussion in this thread--expressions of disappointment and frustration with the pattern evolution--I reviewed my posts concerning the ongoing pattern evolution for December 2022. I appear to have generally highlighted the need for caution. In addition, I mentioned unfavorable outcomes on multiple occasions. But some improvements could have been made, as noted later.

As noted previously, forecasting in the medium-range and extended-range should be viewed in probabilistic, not deterministic terms. I've cited how I believe CPC's probabilistic approach to its 6-10-day, 8-14-day, and experimental 3-4-week forecasts is the way to go. I vigorously disagree with critics who proclaim that probabilistic forecasts are not forecasts. They are. That the critics don't appreciate or understand the application of probabilities is a completely separate issue.

I will note that on social media, particularly Twitter and Facebook, sensationalism remains a genuine issue. Indeed, one tweet even suggested that the coming Great Lakes storm for December 22-24 could be analogous to a combination of the March 1993 superstorm and Blizzard of 1996. The former would be reasonable given the deepening that has been modeled and is still modeled. The latter was favored by only a small number of ensemble members (9/51 EPS members once favored 10" or more snow for NYC--a plurality but not majority--but just two showed 18" or more snow). What is said on social media is beyond what is discussed in this thread here. Social media should not skew perceptions of what is discussed in this thread or elsewhere on AmericanWx.

@bluewave had repeatedly expressed a lot of caution, as well. Quite frankly, some of the information in this thread has consistently demonstrated greater insight, knowledge, and expertise than some of the sensationalist posts on Twitter (blizzard of 1996-type calls, 1983/1989-magnitude Arctic outbreak, etc.).

Moreover, that's the norm when this forum is compared to Twitter and other social media forums.  I don't like to have to make such comparisons, but it seems that social media perceptions have skewed perceptions of the better-informed discussions here, so pointing out the contrast is necessary and informative. And yes, "better-informed" is a deliberately-chosen accurate description. Facts, not sentimentalities, are vital.

Having said that, perhaps on my end, I could have been more forceful in highlighting the level of uncertainty and risks for unfavorable outcomes. That this could be the first winter month on record (since 1950 when daily teleconnections data has been available) to see no measurable snowfall in NYC or Philadelphia despite a likely monthly average AO of -2.000 or below speaks to the uncommon nature of what is possibly going to unfold. No measurable snowfall is not yet assured, but the probability of that outcome has increased.

Numerous examples from this thread follow.

December 1: Potential could increase. Percentages provided for days with measurable snowfall and 1" or more snowfall for Boston, New York City, and Philadelphia:

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6709110

Daily Discussion: "With the development of an EPO-/AO-/PNA- pattern, colder air intrusions could become more frequent after the first week of December. The potential for snowfall could also begin to increase."

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6709893

Outcome: December 11-12: Snow coated the ground outside of New York City, including Newark (0.1") and Islip (0.4"). LaGuardia Airport also picked up 0.4" of snow. Another storm brought a moderate to significant snowfall to interior parts of the Northeast during the December 15-18 period, but none to the immediate New York City-Newark areas.

December 2: Blocking patterns can take a long time to deliver snowstorms. November-December 2010 was provided as an example.

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6711095

December 3: PNA: "By the end of the third week in December, values should be less negative than they currently are. However, the development of sustained positive values by that time seems unlikely (not zero, but still a less than one-in-three probability)."

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6711896

Outcome: Through December 19, the PNA has remained < 0

December 3: "With the development of an EPO-/AO-/PNA- pattern following a short-lived rebound in the EPO to positive levels, colder air intrusions could again become more frequent toward mid-December. The potential for snowfall could also begin to increase, as well, as a sustained colder pattern begins to develop, but significant snowfall is not likely during the transition to that colder pattern."

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6712062

December 5: "With the development of an EPO-/AO-/PNA- pattern following a short-lived rebound in the EPO to positive levels, colder air intrusions could again become more frequent toward mid-December. The potential for snowfall could also begin to increase, as well, as a sustained colder pattern begins to develop, but significant snowfall is not likely during the transition to that colder pattern. No severe cold is likely through at least the first three weeks of December. The latest EPS weeklies suggest that near normal to below normal temperatures could prevail during the December 19-26 period."

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6714130

December 11: "A sustained colder pattern is currently developing. The latest EPS weeklies continue to suggest that near normal to below normal temperatures could prevail during the December 19-26 period. No severe cold is likely through at least the first three weeks of December. Afterward, as the PNA goes neutral, the prospect for snowfall and more significant cold could increase."

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6722294

Outcome: 7 of the last 9 days have been cooler than normal in New York City (through December 19th). No severe cold has occurred through December 19th.

December 13: "The probability of snowfall (measurable and significant) is notably higher than climatology during strong blocking patterns, especially when the PNA is positive at this time of year (and all of January).  Higher probabilities are not guarantees. While the extreme blocking during 2010-2011 led to a big December blizzard and very snowy 30 days albeit after a long wait from late November, there have been cases where strong blocking did not produce such an outcome. Winter 1958-1959 is one such example."

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6724692

December 15: "Here's what the two largest clusters look like for 12/23 (the first with 19 members has a Miller B-type scenario and probably comprises all 9 of the individual members showing 10" or more snow in the NYC-EWR areas; the second large group is very unfavorable for the coastal plain)."

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6728734

Note: 9 of 51 EPS (17.6%) members showed 10" or more snow for the December 22-24 period at the time.   

December 16: "Phasing events are complex and details matter greatly. At extended ranges, even the best models don't fully resolve the details.  With the PNA forecast to be rising to neutral or somewhat positive levels coupled with a strongly negative AO, the region has its highest probability relative to climatology for at least an appreciable snowfall. Nearly half of all December 16-31 days with 4" or more snowfall in either New York City, Newark, or Philadelphia during 1950-2021 have occurred with an AO-/PNA+ pattern (and two thirds of storms with daily snowfall of 4" or more in all three cities). There are no guarantees, of course. Some similar patterns deliver very little (December 1950). Others deliver large amounts of snow (December 2010 into January 2011)."

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6732883

December 16: "Late next week could see another storm bring precipitation to the region. Model solutions range from accumulating snow in the New York City-Newark area to a potential Ohio Valley/Great Lakes blizzard. Details remain to be sorted out, but the latter scenario is currently the favored one on the ensembles. Once that storm passes, the season's coldest air so far will pour into the region."

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6734163

December 17: "A powerful storm could bring heavy rain, high winds, and coastal flooding to the region late next week. A light snow accumulation remains possible at the onset of the storm and as it moves away from the region. Once that storm passes, the season's coldest air so far will pour into the region. Temperatures could tumble into the teens in New York City."

https://www.americanwx.com/bb/topic/58472-december-2022/?do=findComment&comment=6737090

 

 

[eduggs]

Great post Don. You bring so much to these discussions. I think we mostly fail to meet you on your level.

My only quibble with your excellent analysis is the your handling of sample size and its impact on confidence and uncertainty. But I don't even have a good solution for dealing with small sample sizes in weather-related statistics other than a big shrug. Sometimes there just might be too much uncertainty to draw conclusions.

[eduggs]

GFS still shifting ever so slightly southeastward at h5. We just need 3 or 4 more like that with no steps backward to make things interesting.

The ICON shifted a little as well but the RGEM appears not to have.

[MJO812]

Let's see where this goes

[MJO812]

6 minutes ago, MJO812 said:

Let's see where this goes

Dies out but now it's showing a clipper coming down.

Cmc also has this 

[brooklynwx99]

GFS is quite interesting for early next week... really close here to buckling the trough

obviously, this won't do it this run, but continued amplification of the PNA ridge would allow this to work. something to keep an eye on 

[eduggs]

5 minutes ago, brooklynwx99 said:

GFS is quite interesting for early next week... really close here to buckling the trough

obviously, this won't do it this run, but continued amplification of the PNA ridge would allow this to work. something to keep an eye on 

I think we just need a slightly different orientation of the height field. If that ULL is slightly less suppressive or a lobe retrogrades west and dives into the trof, that would work.

[eduggs]

The Canadian has the day 8 threat.

[MJO812]

3 minutes ago, eduggs said:

The Canadian has the day 8 threat.

The PNA might help us out this time around.

[donsutherland1]

10 minutes ago, eduggs said:

Great post Don. You bring so much to these discussions. I think we mostly fail to meet you on your level.

My only quibble with your excellent analysis is the your handling of sample size and its impact on confidence and uncertainty. But I don't even have a good solution for dealing with small sample sizes in weather-related statistics other than a big shrug. Sometimes there just might be too much uncertainty to draw conclusions.

I agree with this quibble. I’ve sometimes mentioned sample size limitations and probably, but should do so more often. I note some cases/examples, e.g., 1958-58 in my commentary for purposes of illustration, but avoid references to analogs, as such references would go beyond the strength of relationships. Even an outcome that is 50% above climatology can still be a fairly low probability outcome. 10”+ snowstorms are uncommon events by any measure.

Skill clearly dissipates as timeframes grow. Coefficients of determination also leave large parts of explanation beyond limited numbers of variables, especially as one considers the synoptic scale. Further complicating things is the reality of a dynamic climate that is altering existing relationships among variables.

In the extended range, to use an analogy, one is always peering into the fog or mist of uncertainty. That’s why I embrace probabilistic language such as “likely,” and like CPC’s approach.

Finally, models and ensembles have come far—and they consistently outperform the human level of skill—but they still have real limits. Machine learning/AI holds additional promise. How to convey the inherent uncertainty and limitations is a continuing question. I don’t have definitive answers to this question. Critiques are both welcome and helpful.

[SnoSki14]

3 minutes ago, MJO812 said:

The PNA might help us out this time around.

Don't get your hopes up. I'm quietly looking at it and that's it. I fully expect failure 

[MJO812]

1 minute ago, SnoSki14 said:

Don't get your hopes up. I'm quietly looking at it and that's it. I fully expect failure 

Okay