bluewave

Updated for Dec 16-17,2020 https://nwschat.weather.gov/p.php?pid=202012171928-KOKX-NOUS41-PNSOKX 1 S EAST TREMONT 12.4 IN 0145 PM 12/17 TRAINED SPOTTER

While we have surpassed many previous snowfall records since 1994, that winter really stands as the last widespread severe ice storm. I had an ice storm in Long Beach on Valentine’s Day 2007 and Feb 2, 2011. But neither one of those were on par with Jan 1994. Jan 94 was my only ice storm in Long Beach lasting over 12 hours. It was remarkable how even Long Beach was able to stay in the 20s with freezing rain from the early morning into the night.

This looks like the 5th earliest 10” snowstorm for NYC. #1 Nov 26-27, 1898....10.0”. #2 Dec 5-7.......2003....14.0” #3 Dec11-12...1960.....15.2” #4 Dec 15th.....1916.....12.7” #5 Dec 16-17....2020.....10.0”

Once the models saw the SSW in February, they began to move toward the cold and snowy March.

That’s been my whole point since October. There have been too many competing influences since at least October to use ENSO as a sole indicator. Think of it more like a collection of overlapping influences adding their various inputs to what becomes the actual pattern. Front-loaded doesn’t mean that there can’t or won’t be other periods of active winter weather. On the whole though, La Ninas have been known for early wintery periods. The best winter DJF snowstorm of the 95-96 La Niña was on January 6th and the 00-01 La Niña December 30. The greatest winter snowstorm of the 17-18 La Niña was January 4th. But that doesn’t preclude a March 2018 or even 2001. The super El Niño in 15-16 had the historic event later in January. The 82-83 super El Niño had the best snowstorm of the season in February. Same for the snowiest month during the 09-10 El Niño in February which had a strong backloaded period late winter. So while there has been many overlapping influences, at least we got some element resembling a La Niña this month.

The last few months have been an extreme example of mixed influences. But at least we can say some element of La Niña has shown up. The La Niña front-loaded early winter snowfall period has worked out. Numerous La Ninas in NYC had a 6”+ storm and or monthly snowfall total for December.

Before I changed the title of the winter thread that I started back in October, it was about the MJO staying in 4-5 for October. I changed the title of the thread for a broader winter discussion. I actually deleted my first post which didn’t look like it may work out in November as not to get hopes up too high. It was about October La Niña forcing and seasonal snowfall. Cases focused near the Maritime Continent 4-5 usually had better snow outcomes than the IO phases back to 2000. I included the last 2 winters due to the strong Niña-like background state focusing the ridge north of Hawaii. But We have seen many Niño-like influences this month like the record NP warmth and the +AAM spike and strongest +PNA for a moderate La Niña in December. The MJO in October seemed to be hinting a better snowfall outcome this winter than the last two. Perhaps, the MJO in October can be a precursor to the amount of blocking in the winter during a La Niña even if many Niño-like features are present. There were so many conflicting features during October and November that it was really tough to know how everything would interact with each other until we got to December. This will be a first for such an extreme November to December AO reversal especially for a La Niña with record warmth in November. October 2020 forcing closer to snowier La Niña composite since 2000 Snowier outcomes Less snowy

This could be the first time that the AO was positive for nearly every day in November and negative for so many days in December.

Great day to finish any yard clean ups with a top 5 warmest 12-13 in tap. Data for December 13 - NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature Precipitation Snowfall Snow Depth 2015-12-13 67 55 0.00 0.0 0 1923-12-13 64 42 0.10 0.0 0 1984-12-13 63 46 0.00 0.0 0 1946-12-13 63 36 T 0.0 0 1919-12-13 61 42 0.07 0.0 0 1990-12-13 60 41 0.00 0.0 0 1968-12-13 60 36 0.00 0.0 0 1949-12-13 60 36 0.17 0.0 0

Today should be the warmest day of the month so far with widespread 60s. KEWR GFS MOS GUIDANCE 12/13/2020 0000 UTC DT /DEC 13 /DEC 14 /DEC 15 / HR 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 18 00 X/N 63 37 44 29 40 TMP 51 50 50 55 60 59 53 47 42 40 39 39 41 41 38 37 34 32 30 38 32

The AO volatility continues to make headlines. This could be one of the greatest +November to -December reversals on record. Notice how a very +AO in November usually carried over to December. The one exception was 1978. 2020 2.419 3.417 2.641 0.928 -0.027 -0.122 -0.412 -0.381 0.631 -0.072 2.086 2015 1.092 1.043 1.837 1.216 0.763 0.427 -1.108 -0.689 -0.165 -0.250 1.945 1.444 2013 -0.610 -1.007 -3.185 0.322 0.494 0.549 -0.011 0.154 -0.461 0.263 2.029 1.475 2011 -1.683 1.575 1.424 2.275 -0.035 -0.858 -0.472 -1.063 0.665 0.800 1.459 2.221 1994 -0.288 -0.862 1.881 0.225 -0.115 1.606 0.351 0.828 -0.084 0.174 1.779 0.894 1978 -0.347 -3.014 0.502 -0.967 0.059 0.635 -0.604 -0.354 -0.099 0.895 2.470 -0.980

We may just have to take it week by week and month by month. Past expectations based on canonical El Niño or La Niña patterns haven’t been working out since 18-19. Too many competing warm SST blobs for the seasonal models to handle. https://www.climate.gov/news-features/blogs/enso/csi-enso-case-missing-central-pacific-rainfall CSI ENSO: The case of the missing central Pacific rainfall Author: Nat Johnson February 28, 2019 As Emily’s most recent post describes, the tropical Pacific Ocean and atmosphere have finally coupled, allowing NOAA to declare that weak El Niño conditions are present. It’s nice to see the atmosphere and ocean in a cooperative mood, but ENSO forecasters are left with a mystery: why did the expected atmospheric response go missing for so long? In this blog post, we’ll put our detective hats on and look for clues.

You can see how many competing influences there were this month in that 500mb height anomaly map. This may be our first December with a configuration like that. No wonder none of the seasonal model forecasts had a look like that. We were discussing in the other thread back in November how unusual the combination of conflicting SST features were. This could be the 3rd winter in a row that a straight ENSO (El Niño-La Nina) based expectation forecast doesn’t work out.

We’ll see if the MJO can weaken by January.

The EPS has had the mid-December storm signal for weeks now. But it also had a moderation in temperatures around the solstice. What it missed was the warm up this weekend.

Starting the day with a heavy frost here in SW Suffolk. But there was a very wide temperature spread across Long Island this morning. The breeze off the ocean kept the South Shore beaches 10° to 20° warmer than areas of the island that were able to radiate. Long Island New York CITY SKY/WX TMP DP RH WIND PRES REMARKS Jones Beach N/A 45 N/A N/A SW7G13 N/A Wantagh N/A 32 30 93 NW3 N/A Hempstead NOT AVBL Matinecock Pt N/A 39 N/A N/A SW2 N/A Farmingdale PTCLDY 30 27 88 CALM 30.22R MacArthur/ISP PTCLDY 27 26 96 CALM 30.22R Shirley PTCLDY 28 23 81 CALM 30.23R Mt Sinai Harb N/A 36 N/A N/A S3 N/A Westhampton PTCLDY 20 17 88 NW3 30.24R East Hampton FAIR 24 23 94 CALM 30.22F Southold N/A 28 28 100 SW1 N/A Montauk N/A 36 34 92 CALM 30.24S

It could mean climate model studies that show a more -NAO and others a +NAO could both be correct. A corals study that came out in 2009 indicated that the NAO has exhibited wider swings as the climate has warmed. The last 10 years since this study came out featured record -NAO/-AO and +NAO/+AO intervals. We have never seen a decade with such wild swings from record highs to record lows. https://www.sciencedaily.com/releases/2009/01/090113101200.htm Swings In North Atlantic Oscillation Variability Linked To Climate Warming Date: January 14, 2009 Source: Woods Hole Oceanographic Institution Summary: Using a 218-year-long temperature record from a Bermuda brain coral, researchers have created the first marine-based reconstruction showing the long-term behavior of one of the most important drivers of climate fluctuations in the North Atlantic. Using a 218-year-long temperature record from a Bermuda brain coral, researchers at the Woods Hole Oceanographic Institution (WHOI) have created the first marine-based reconstruction showing the long-term behavior of one of the most important drivers of climate fluctuations in the North Atlantic. The North Atlantic Oscillation (NAO) is a wide-ranging pressure seesaw that drives winter climate over much of North America, Europe and North Africa. Past reconstructions of the NAO have relied mainly on terrestrial, or land-based records, such as tree ring chronologies combined with ice cores and historical climate data. Those records do not fully capture oceanic processes linked to NAO variability, and short instrumental records from relatively few locations limit the understanding of ocean–atmosphere dynamics with regard to NAO behavior. “By analyzing the coral, we were able to look at changes in the ocean relative to changes on land,” said Nathalie Goodkin, lead author of the study published in the December issue of the journal Nature Geoscience. “Because they are slow growing and have long life-spans, corals can provide high resolution records that are well dated and centuries long.” As they grow, corals accrete seasonal and annual growth layers, similar to tree rings. The proportions of trace elements versus the major element (calcium) found in the layers of the skeleton largely depend on the temperature of the seawater in which it was formed. By analyzing the strontium to calcium ratio in the Bermuda brain coral, Goodkin and colleagues — WHOI scientists Konrad Hughen, Scott Doney and William Curry — were able to reconstruct monthly changes in ocean temperatures and evaluate variability of the NAO during both cold and warm periods from the Little Ice Age (1800–1850) to modern day. The research team found the variability of the NAO decade-to-decade (multi-decadal scale) has been larger, swinging more wildly, during the late twentieth century than in the early 1800s, suggesting that variability is linked to the mean temperature of the Northern Hemisphere. This confirms variability previously reported in past terrestrial reconstructions. “When the Industrial Revolution begins and atmospheric temperature becomes warmer, the NAO takes on a much stronger pattern in longer-term behavior,” said Goodkin. “That was suspected before in the instrumental records, but this is the first time it has been documented in records from both the ocean and the atmosphere.” The North Atlantic Oscillation is described by the NAO index, calculated as a weighted difference between the polar low and the subtropical high during the winter season. (For more information about the NAO index, see animation.) In a positive phase, both the low-pressure zone over Iceland and high pressure over the Azores are intensified, resulting in changes in the strength, incidence, and pathway of winter storms crossing the Atlantic. In a negative phase, a weak subtropical high and a weak Icelandic low results in fewer and weaker winter storms crossing on a more west-east pathway. The NAO index varies from year to year, but also exhibits a tendency to remain in one phase for intervals lasting more than a decade. An unusually long period of positive phase between 1970-2000 led to the suggestion that global warming was affecting the behavior of the NAO. “Anthropogenic (human-related) warming does not appear to be altering whether the NAO is in a positive or negative phase at multi-decadal time scales,” said WHOI paleoclimatologist Konrad Hughen. “It does seem to be increasing variability. Clearly, this has implications for the future.” “As temperatures get warmer, there’s potential for more violent swings of the NAO — the phases becoming even more positive and even more negative,” Hughen added. “If the NAO locks more into these patterns, intense storms will become more intense and droughts will become more severe.” The climatic influence of the NAO extends from the eastern United States to Western Europe, impacting human activities such as shipping, oil drilling, fisheries, hydroelectric power generation and coastal management. Improving the ability to predict shifts in the phase and intensity of the NAO is a prerequisite to mitigating the economic impacts of future climate change. While additional modeling and palaeoclimatic studies are needed, a broad distribution of marine records could advance our knowledge of NAO variability and serve to improve future projections, said Goodkin, now an assistant professor in the Department of Earth Sciences at the University of Hong Kong. A WHOI Ocean and Climate Change Institute Fellowship, and grants from the National Science Foundation and Woods Hole Oceanographic Institution supported this work.

This almost reminds me of how quickly the Kara Barents block built back across the North Pole to Greenland at the end of December 2015. We had an intense PV that December with the historic warmth and near record +AO. It suddenly reversed at the end of the month. We saw a near record +AO and PV this November with the record warmth. There have been some recent studies linking that KB block to the low sea ice. At the beginning of the month, it was one of the strongest +PNA rises that we ever saw during a moderate La Niña December. So we are getting several overlapping influences all at the same time. https://advances.sciencemag.org/content/4/7/eaat6025 A stratospheric pathway linking a colder Siberia to Barents-Kara Sea sea ice loss View ORCID ProfilePengfei Zhang1,2,*, View ORCID ProfileYutian Wu2, Isla R. Simpson3, Karen L. Smith4, Xiangdong Zhang5, View ORCID ProfileBithi De1 and Patrick Callaghan3 See all authors and affiliations Science Advances 25 Jul 2018: Vol. 4, no. 7, eaat6025 DOI: 10.1126/sciadv.aat6025 Article Figures & Data Info & Metrics eLetters PDF Abstract Previous studies have extensively investigated the impact of Arctic sea ice anomalies on the midlatitude circulation and associated surface climate in winter. However, there is an ongoing scientific debate regarding whether and how sea ice retreat results in the observed cold anomaly over the adjacent continents. We present a robust “cold Siberia” pattern in the winter following sea ice loss over the Barents-Kara seas in late autumn in an advanced atmospheric general circulation model, with a well-resolved stratosphere. Additional targeted experiments reveal that the stratospheric response to sea ice forcing is crucial in the development of cold conditions over Siberia, indicating the dominant role of the stratospheric pathway compared with the direct response within the troposphere. In particular, the downward influence of the stratospheric circulation anomaly significantly intensifies the ridge near the Ural Mountains and the trough over East Asia. The persistently intensified ridge and trough favor more frequent cold air outbreaks and colder winters over Siberia. This finding has important implications for improving seasonal climate prediction of midlatitude cold events. The results also suggest that the model performance in representing the stratosphere-troposphere coupling could be an important source of the discrepancy between recent studies.

Thanks. Maybe the record off equator SST warmth in the North Pacific for a La Niña is also giving us a blocking assist. https://www.aos.wisc.edu/~dvimont/MModes/PMM.html

We need the block to press hard enough so the low tracks out near the benchmark. That would put the coast in a great spot for some of the higher accumulation potential. But a track a little too close to the area would focus the higher accumulations near or north of I-80. So plenty for the models to work out over the next week. My guess is that the snowfall accumulation from this storm in NYC could determine the snowfall outcome for the entire season. La Niña winter snowfall has been very sensitive in NYC to December snowfall. The 3 inch number has been pretty important. Over or under that amount in December has predicted how the snowfall would go for the rest of the season. It may be that a strong enough block in December for a significant 3.0”+ snowfall signals further winter or early spring blocking. La Niña years highlighted Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2019-2020 0.0 0.0 2.5 2.3 T T T 4.8 2018-2019 0.0 6.4 T 1.1 2.6 10.4 0.0 20.5 2017-2018 0.0 T 7.7 11.2 4.9 11.6 5.5 40.9 2016-2017 0.0 T 3.2 7.9 9.4 9.7 0.0 30.2 2015-2016 0.0 0.0 T 27.9 4.0 0.9 T 32.8 2014-2015 0.0 0.2 1.0 16.9 13.6 18.6 0.0 50.3 2013-2014 0.0 T 8.6 19.7 29.0 0.1 T 57.4 2012-2013 0.0 4.7 0.4 1.5 12.2 7.3 0.0 26.1 2011-2012 2.9 0.0 0.0 4.3 0.2 0.0 0.0 7.4 2010-2011 0.0 T 20.1 36.0 4.8 1.0 T 61.9 2009-2010 0.0 0.0 12.4 2.1 36.9 T 0.0 51.4 2008-2009 0.0 T 6.0 9.0 4.3 8.3 T 27.6 2007-2008 0.0 T 2.9 T 9.0 T 0.0 11.9 2006-2007 0.0 0.0 0.0 2.6 3.8 6.0 T 12.4 2005-2006 0.0 T 9.7 2.0 26.9 1.3 0.1 40.0 2004-2005 0.0 T 3.0 15.3 15.8 6.9 0.0 41.0 2003-2004 0.0 0.0 19.8 17.3 0.7 4.8 0.0 42.6 2002-2003 T T 11.0 4.7 26.1 3.5 4.0 49.3 2001-2002 0.0 0.0 T 3.5 T T T 3.5 2000-2001 T 0.0 13.4 8.3 9.5 3.8 0.0 35.0 1999-2000 0.0 0.0 T 9.5 5.2 0.4 1.2 16.3 1998-1999 0.0 0.0 2.0 4.5 1.7 4.5 0.0 12.7 1997-1998 0.0 T T 0.5 0.0 5.0 0.0 5.5 1996-1997 0.0 0.1 T 4.4 3.8 1.7 T 10.0 1995-1996 0.0 2.9 11.5 26.1 21.2 13.2 0.7 75.6

You have to wonder if that block suddenly getting stronger close to the Siberian Arctic got an assist from the record warmth and low sea ice. New run Old run

Another big warm up into the weekend following some days that were slightly below normal. So the first 2 weeks of December will average warmer than normal. Very little cold air around following the 4th warmest November on record for the CONUS. KNYC GFSX MOS GUIDANCE 12/10/2020 0000 UTC FHR 24| 36 48| 60 72| 84 96|108 120|132 144|156 168|180 192 THU 10| FRI 11| SAT 12| SUN 13| MON 14| TUE 15| WED 16| THU 17 CLIMO X/N 52| 40 53| 46 57| 52 59| 39 47| 33 42| 38 47| 44 47 30 43

Looks like Newark was the big local ASOS winner. SNOWFALL (IN) TODAY 0.3

Steady light snow in SW Suffolk and 35°.

NYC down to .50 mile vis in snow. https://mesowest.utah.edu/cgi-bin/droman/mesomap.cgi?state=NY&rawsflag=3 12:31 34.0 28.0 31.7 79 6.9 17.3 29.63 29.80 Snow 0.50 2300 0.00