jconsor

I would say the atmospheric coupling with the La Nina event has been uneven. The AAM has averaged near neutral since Nov, with a notable spike from late Nov to the first few days of Dec. I agree with your last three sentences about La Nina's continued influence in the next month or two. Also, in my experience, the CFS is known to be highly +AAM biased.

Getting MJO to phase 7 by mid to late Jan would be helpful. Here are composite for strong MJO phase 7 in Jan - note strong blocking signal from north of AK to NW Canada to Greenland: https://x.com/WorldClimateSvc/status/2006751440753316061

Aside from the 12z and 0z NAM, which look unreasonable and lack a focused WNW-ESE area of heavier precip, there is a good consensus of a peak QPF axis around 0.75-0.8" extending from roughly the PA/NJ/NY border ESE toward NYC and the western third of LI. However in reality the peak QPF axis will likely be more narrow than shown by the HREF. The HREF snowfall amounts are often overdone, but given that I expect ratios of 12 to 13:1 even in NYC and Nassau County, I think they are overall pretty reasonable here. I would conservatively go with 5-8" from Orange, Rockland and Westchester counties SE into Bergen and Passaic Counties in NJ, NYC, Nassau and W. third of Suffolk. Could see local amounts up to 10-12" where best banding sets up (likely N of NYC).

The HRRR tends to be too wet at this range, so precip amounts are likely somewhat overdone. The snow map is using dynamic snow:liquid ratio calculated by the HRRR. What is interesting is the 12 to 13:1 ratios from western LI and NYC to NE NJ.

https://lab.weathermodels.com/models/blend/blend_precip.php has it if you have a subscription.

Firstly, I have noticed that the CPC charts often run a day behind. And yesterday's GEFS had the PNA significantly more negative than today's in the Dec 29-Jan 3. Secondly, the WeathermModels PNA chart looks very similar to the WeatherBell one.

True, but we just had a snowstorm produce widespread 6-8"+ from I-95 south and east (other than lighter amounts in the urban heat island near NYC) with -PNA, though in that case the NAO was slightly positive and AO highly positive. *If* we are going to see a 6"+ snowstorm in a -PNA pattern during a La Nina, it almost definitely will come from northern stream system e.g. a highly amplified clipper/Miller B.

The NWS map looks underdone to me for eastern/central LI and eastern Connecticut. I would expect widespread gusts of 55+ mph and scattered 65-70 mph gusts. HREF *mean* has 70 mph hugging the South Shore of Suffolk County and the Twin Forks, and HRRR is similar. We often overperform in southerly windstorms in the winter ahead of cold fronts.

I agree with you in general. However, there is a timeframe that I think has more potential for a negative tilt, digging trough late next week into next weekend (Dec 11-14). This is the timeframe that both operational models and ensembles show the blocking retrograding from western Greenland to near Baffin Island and then into central Canada, and possibly linking up with western US ridging. The period when blocks retrograde and decay into Central Canada and then link up with western US ridging is the one when significant snowstorms are most likely in the coastal parts of the NE US. Now to clarify, I don't see the potential for a significant (6"+ snowstorm) for the I-95 corridor from NYC to BOS. But my point is that the pattern does match periods which are more favorable for significant coastal storms along with sufficient cold air for snow. Given the northern stream/clipper dominated pattern and the troughs turning negative tilt relatively late, snowfall would be most favored across far northern NY and northern New England, but eastern Long Island to SE New England also climatologically can do well in these types of events if they dig far enough south. The ECMWF and (to a degree) the GEM both show the above-mentioned blocking and negative tilt/digging trough trends late next week into next weekend.

I agree that the -WPO will remain the most dominant influence on the cold through mid-Dec. However, there are increasing indications that in the 10-15 day period (Dec 13 and beyond), the center of the most anomalous ridging will shift significantly NE from the Kamchatka Peninsula/western Bering Sea to the Bering Strait, with the eastern extent of positive anomalous also shifting notably eastward into AK and even parts of the Northwest Territories. Combined with the increased negative anomalies north/NE of Hawaii and below normal heights over the NE US, that suggests a -EPO. This more eastward position of the ridging could theoretically allow the most anomalous cold air to be directed toward the NE US beyond Dec 15, though the lack of ridging over Greenland and the relatively northward position of the polar vortex indicated by the guidance e.g. north of Hudson Bay (I am mainly speaking about EPS and GEPS) would counteract this.

I hear your point about the dangers of oversimplying ENSO-PNA relationships, Don, and wholeheartedly agree. However, from my perspective there is increasing evidence the PNA will average neutral overall (with some periods of slightly positive PNA, especially Dec 7-9 and Dec 14-20) the second and third weeks of Dec. True, the EPS pattern days 3-7 and 11-15 is not fully in line with a canonical +PNA (the positive anomalies are shifted south and west vs. the typical position over western Canada and the NW US, the negative anomalies are concentrated over SE Canada and the NE US vs. the mid-Atlantic and SE US, and the upstream negative anomalies are in the e. Gulf of Alaska vs. the typical position further SW in the north-central Pacific). However, both the EPS and GEPS have been trending toward a more neutral PNA in most of the next two weeks (e.g. Dec 7-10 and Dec 14 and beyond). The charts you showed were from the GEFS, which has the most -PNA (and SE US ridge) biased of all the models recently. Also, looking at the EPS individual members it is evident that a few members with a highly negative PNA are skewing the mean downward Dec 14 onward. A slightly majority of members (about 55-60%) actually show a +PNA during that timeframe! The GEPS is not as aggressive, but still has about 40-50% of members showing a +PNA in the same timeframe. Regarding the last third of Dec, there is too much uncertainty to comment much on that period. While I favor the SE US ridge returning to a degree, I am skeptical of the strength of the NW/N-central US trough and SE US/W Atlantic ridge shown in the past two EPS long-range runs.

Some thoughs on ENSO heading into next hurricane season: https://x.com/yconsor/status/1986046871349936133

Very impressively backloaded hurricane season this year. Here are some stats: https://x.com/yconsor/status/1983980828268097557

Severe damage in Montego Bay: https://x.com/rj_smith_3/status/1983506193994666304

The part of SE Cuba expected to be hit hardest (Santiago de Cuba) has very little precedent for Cat 3s, and none for Cat 4s: https://x.com/yconsor/status/1983236668933988715