bluewave

Wild snow cover swing for North America. We went from the highest in October to the lowest today.

Warmest first week of December on record for Caribou at +13.6. We would have done better in the snowfall department if we had a colder start like last year. The departures in our area ranged from +0.6 at EWR to +2.9 at BDR.

Following several says of slightly cooler than average temperatures, we will rebound back to 50s. Notice how the day 10 guidance was biased too cold again. So a continuation of the ridge over the area verifying stronger than forecast. KNYC GFSX MOS GUIDANCE 12/07/2020 0000 UTC FHR 24| 36 48| 60 72| 84 96|108 120|132 144|156 168|180 192 MON 07| TUE 08| WED 09| THU 10| FRI 11| SAT 12| SUN 13| MON 14 CLIMO X/N 41| 30 41| 33 45| 38 49| 39 49| 44 56| 49 54| 38 42 31 44 New run Old run

Without some kind of record -EPO or -NAO blocking, we can’t get cold winters anymore. 09-10, 10-11, 13-14, and 14-15 were our only 4 cold winters out of the last 11 years. 09-10 to 10-11 was the strongest -NAO of 187 years that I posted earlier. 13-14 and 14-15 featured the record -EPO patterns. The -EPO developed during the summer of 2013 and intensified during November and carried into the next spring. 14-15 saw a similar extreme -EPO combined with El Niño for the backloaded cold. But since the super El Niño in 15-16, all our winters have been warm with intervals when the unfavorable MJO phases ran the table. Some winters like the 18-19 and 19-20 featured the unfavorable MJO phases dominating for warmth and lack of snow. 15-16 to 17-18 had the unfavorable MJO for warmth but we got intervals of blocking for snowy outcomes. Papers on our only cold recent winters: Winter 2009/2010 temperatures and a record‐breaking North Atlantic Oscillation index https://rmets.onlinelibrary.wiley.com/doi/10.1002/wea.660 The North American winter ‘dipole’ and extremes activity: a CMIP5 assessment https://rmets.onlinelibrary.wiley.com/doi/10.1002/asl2.565

You ask a very good question. As recently as 17-18, portions of Long Island had over 60” of snowfall on the season. But this was also accompanied by record warmth and our first 80° reading on record for February. The record MJO actually had an influence on both. We got the extreme February warmth with a SSW. This was followed by the record snow in March. It turns out that strong MJO phases 5-7 can also lead to SSWs. But this isn’t always the case. So it can just as easily be warm without the snow like we saw last winter with the warm MJO phases. We can also see the MJO in the expanded IO warm pool become more active in phases 1-3 with the record IOD like last November. This may have contributed to the record polar vortex last winter. http://s2sprediction.net/file/documents_publications/wcd-2020-17.pdf Mechanisms and predictability of Sudden Stratospheric Warming in winter 2018 Finally, a composite analysis suggests that teleconnections associated with the record-breaking MJO phase 6 observed in the late January 2018 likely played a role in triggering this SSW event. https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/asl.1005 3.1 The winter 2019/20 NAO and November 2019 IOD

The 10-11 winter was all about a continuation of the 187 year record -NAO pattern that began in 09-10. So the record -NAO had a greater influence than the MJO. We can remember how unfavorable the Pacific was from December 1-25 with all the fantasy snowstorms that showed up with the -PNA. But the -NAO set a record 500 height height anomaly in late December. This allowed a retrogression in heights boosting the PNA and setting up the record 60 inches of snow from late December to late January. But once the blocking faded in early February, we began to move toward a more +EPO +NAO that dominated the 11-12 winter. https://rmets.onlinelibrary.wiley.com/doi/10.1002/wea.660 In conclusion, the winter of 2009/2010 was notable for the record negative NAO index in the 187‐year record of Jones etal. (1997), indicating the very unusual nature of atmospheric circulation over the Atlantic/European region. Despite 2009/2010 being a cold winter over the UK and Europe, it was actually around 0.5 to 1 degC warmer than might have been expected given this extreme pattern of atmospheric circulation. Considering observations averaged across the globe, winter 2009/2010 was one of the warmest on record.

Several slightly cooler than average days coming up before another rebound back into the 50s. Pacific flow will dominate with the models adjusting for a stronger +EPO. Same theme of long range guidance being biased too cool and showing too much blocking. KNYC GFSX MOS GUIDANCE 12/06/2020 0000 UTC FHR 24| 36 48| 60 72| 84 96|108 120|132 144|156 168|180 192 SUN 06| MON 07| TUE 08| WED 09| THU 10| FRI 11| SAT 12| SUN 13 CLIMO X/N 43| 30 41| 29 39| 32 43| 38 54| 41 50| 46 57| 51 55 31 44

3-21-18 was the last time that a the coast had heavier totals than inland. https://www.weather.gov/okx/storm03212018

https://www.weather.gov/aly/1-3Dec2019Snow Overview A major winter storm impacted eastern New York and western New England December 1-3, 2019. Snowfall began during the late morning and early afternoon of the 1st ahead of a weakening low pressure system approaching from the western Great Lakes. Snowfall rates of 1-2" per hour occurred from the afternoon into the evening, with the heaviest along the I-90 corridor. As the primary low pressure system weakened, it transferred its energy to a coastal low, which strengthened as it remained nearly stationary for much of the 2nd. This allowed snow to continue to accumulate throughout the day. As the low finally pulled away late on the 2nd into the early morning hours of the 3rd, one final heavy snow band crossed the area before the snow finally pulled out prior to daybreak on the 3rd. Storm total snowfall amounts were heaviest in the central Mohawk Valley, Helderbergs, northeastern Catskills, Capital District, southern Vermont, and the Berkshires, where totals of 18-28" were common. The 22.6" recorded at Albany International Airport made this the 8th largest snowstorm on record, the 4th largest December storm, and the largest since the March 1993 superstorm. It snowed for 39 hours and 14 minutes consecutively. Many schools were closed for two consecutive days, and numerous flights were delayed or cancelled. The governor declared a state of emergency for several of the hard-hit counties, and deployed the National Guard to assist in cleanup efforts. Speed restrictions were also placed on area interstate highways. Amounts of 8-18" were common elsewhere, except for southern portions of Dutchess and Litchfield Counties due to warmer temperatures and mixed precipitation, and northern portions of Herkimer, Hamilton, Warren, and Washington Counties which were on the fringe of the heavier precipitation.

The +EPO continues to beat expectations.

That’s why I was pointing out since late November to view those 300+ hr eps forecasts with caution. The EPS skill falls off pretty quickly after the 7-10 day period. But you could see the more Niña-like Maritime continent MJO forcing coming up. Now the EPS is starting to correct for that 7-8 days out with the more +EPO pattern. New Forecast Old Forecast

It’s not persistent forecasting. It’s persistent patterns. Notice how this is the 2nd December in a row with a big storm during the first week of the month. Early last December a low went south of Long Island and produced record snowfall amounts to our north. Just a variation on the same theme. The heaviest snowfall axis this time will be further east into New England. https://www.washingtonpost.com/weather/2019/12/03/northeast-starts-dig-out-after-snowstorm-drops-more-than-two-feet-spots/ 12-02-19

I mentioned that I didn’t look like Hartford would get near another 2nd snowiest snowiest first week of December. The heaviest snows will be to their northeast time time around. But shows how an unfavorable pattern like last December in NYC can produce for New England. Time Series Summary for Hartford Area, CT (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Ending Date Total Snowfall Dec 1 to Dec 7 Missing Count 1 2003-12-07 18.5 0 2 2019-12-07 16.5 0 3 1949-12-07 12.6 0

The +PNA ridge was too flat and merged with the ridge east of New England. Plus we are coming off a record warm November. Great storm track for a change, but very limited amounts of cold air this far south. Just goes to show how New England can get by with what are negative factors for us. Forecast NYC biggest early December snowstorm composite since 2000.

Those vendors that show EPS teleconnections have their own custom indices. So they are not using the same methodology as the CPC. It’s an apples to oranges comparison. Plus they don’t have an archive of indices back to 1950 to compare against. https://ftp.cpc.ncep.noaa.gov/cwlinks/ https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/teleconnections.shtml

This was one of the highest daily December +PNA readings on record. It looks like it reached a +1.9. The only other years with a +1.9 that I could find were 2002 and 1989. December 2002 was a moderate El Niño and 1989 was a neutral ENSO. This would be the first for a moderate La Niña. November 2020 reached a -1.32 monthly Niño 3.4 anomaly. Both those Decembers started much colder for NYC than this year with lows under 20 during the first week. So this year is an unusually warm +PNA. This is related to the record warm November lead up to this major amplification of the ridge over Canada. There was no cold to trap underneath for us and the ridge was flatter and extended further east to the Canadian Maritimes.

We would probably need an ENSO time machine for that. https://www.news.gatech.edu/2019/11/25/el-nino-swings-more-violently-industrial-age-hard-evidence-says Blowing models away The physical proof taken from three islands that dot the heart of the ENSO zone has also thrown down scientific gauntlets, starkly challenging computer models of ENSO patterns and causes. A prime example: Previously unknown to science, the study showed that in a period from 3,000 to 5,000 years ago, the El Nino-La Nina oscillations were extremely mild. “Maybe there’s no good explanation for a cause. Maybe it just happened,” Cobb said. “Maybe El Nino can just enter a mode and get stuck in it for a millennium.”

Yeah, it looks like more of a MJO 4 pattern as the AAM and PNA falls. So we get a Niño-like to Niña-like progression this month. Something for all the different ENSO fans.

Yeah, you can see the more poleward +PNA on the NYC biggest early December snowstorm composite since 2000.

The last few years have been oddball combos of Niño and Niña-like features. This year we get the record warmth in November like the November 2015 super El Niño. Then a Niño-like +PNA to start December with a strong STJ. We finally get something resembling a BM track but with a lack of cold. I think the +PNA ridge was just too flat with Pacific air underneath instead of Arctic. This would have been a year when a cold November ahead of the storm could have worked out for us.

6z Euro if it wasn’t posted yet.

I think the main problem was all the antecedent warmth this November. So the big +PNA spike trapped the Pacific air in place. Had this November been cold like last year, the snowfall totals we are seeing to the NW on the models would be closer to the coast. But maybe we can get some flakes down to the coast at the very end of the storm.

We could get another big track jump by 0z or 12z. The ICON just came pretty far west at 18z. Maybe it will take another run or two for the models to converge.

This will be the first storm for the upgraded HRRR once we get within its effective range,

The ridge verifying stronger to our south and east than longer range model guidance has been our new normal in recent years. There have been so many week 2 forecasts that suddenly correct stronger within the day 7-10 range. It would be nice if we had bias corrected model maps to deal with this. Maybe this will be the next step in long range model forecasting. The exception to the rule is strong -AO and -NAO blocking. https://www.ecmwf.int/en/about/media-centre/science-blog/2019/will-machine-learning-replace-conventional-weather How could machine learning be used in numerical weather prediction? There are a large number of possible application areas for machine learning throughout the workflow of numerical weather prediction. Here, the “system” could be a tool to pick and bias-correct observations that are used within data assimilation; a tool to project real-world observations into a representation of variables as they are used within models; or a part of the numerical forecast model – such as the radiation scheme which predicts the heating of the atmosphere given surface temperature, cloud patterns and incoming radiation from the sun. It could also be a tool that is used in post-processing of the output of a weather forecast model, for example to detect extreme weather events in forecasts or to bias-correct forecasts for a specific location.