bluewave

Yeah, sometimes just cold enough is all we need at the coast for snow with the right storm track and teleconnections. But it’s always nice to have at least some Arctic air nearby to enhance our chances for a higher end event. Even our recent milder snowy Januaries had intervals around storm time with -10 Arctic air available. NYC Jan 18.....-0.9 2018-01-01 19 7 13.0 -20.4 52 0 0.00 0.0 T 2018-01-02 26 13 19.5 -13.8 45 0 0.00 0.0 0 2018-01-03 30 16 23.0 -10.1 42 0 0.00 0.0 T 2018-01-04 29 19 24.0 -9.0 41 0 0.76 9.8 1 Jan 17.....+5.4 2017-01-06 33 25 29.0 -3.8 36 0 0.05 1.2 1 2017-01-07 26 20 23.0 -9.7 42 0 0.32 5.1 T 2017-01-08 25 16 20.5 -12.1 44 0 0.00 0.0 4 2017-01-09 23 14 18.5 -14.0 46 0 0.00 0.0 3 Jan 16....+1.9 2016-01-19 28 16 22.0 -10.3 43 0 0.00 0.0 T 2016-01-20 37 27 32.0 -0.3 33 0 0.00 0.0 T 2016-01-21 36 26 31.0 -1.3 34 0 0.00 0.0 0 2016-01-22 30 21 25.5 -6.9 39 0 0.01 0.2 0 2016-01-23 27 24 25.5 -6.9 39 0 2.31 27.3 6

The EPS is confirming in the week 2 period that the SPV and coldest temperatures will shift over to Eurasia with the SSW. So we just need to work on getting it cold enough for snow with the right storm track. Maybe there could be some Arctic air by later in the month if heights build enough north of Alaska.

Continuation of the mild pattern that began around the solstice. NYC at +5.7 through the first 3 days of January. NYC will remain well above the 33° average for early January. Maybe we can eventually see some upper 20s lows by later next weekend. But the average low is 27°. New York City... Central Park, NY /42 37/41 33/42 31/43 31/40 30/40 29/40......climo 27/38/33 Data for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Avg Temperature Departure 2020-12-21 5.7 2020-12-22 6.5 2020-12-23 5.3 2020-12-24 16.0 2020-12-25 10.2 2020-12-26 -6.5 2020-12-27 -3.8 2020-12-28 8.4 2020-12-29 2.6 2020-12-30 1.8 2020-12-31 8.4 2021-01-01 3.1 2021-01-02 10.2 2021-01-03 2.9

Need to see some lows in the 20s showing up in NYC for more significant snowfall potential. This first week may join the list of years that didn’t fall below 30°. Something closer to the average low of 27° during the 2nd week of the month could allow for snow potential with the right storm track and evolution. Mid 20s lows before or during a storm can signal enough cold air nearby with the right storm details. This is generally what we look for in a mild pattern. ...New York City... Central Park, NY /38 34/44 34/42 34/43 31/43 Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Rank Ending Date Lowest Min Temperature Jan 1 to Jan 7 Missing Count 1 2007-01-07 38 0 - 1907-01-07 38 0 2 2005-01-07 34 0 3 2021-01-07 33 5 - 1966-01-07 33 0 - 1932-01-07 33 0 - 1889-01-07 33 0 4 2020-01-07 32 0 - 1874-01-07 32 0 5 1950-01-07 31 0 - 1880-01-07 31 0 6 1939-01-07 30 0 - 1913-01-07 30 0 - 1906-01-07 30 0

The overpowering -EPO/+PNA along with the +AO forced the best snowfall east of NYC into New England. That may have been the only time that we saw such a combination. Areas to the S and W of NYC had lower snowfall totals. Time Series Summary for Boston Area, MA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Ending Date Total Snowfall Oct 1 to Apr 30 Missing Count 2015-04-30 110.6 0 Time Series Summary for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Ending Date Total Snowfall Oct 1 to Apr 30 Missing Count 2015-04-30 63.7 0 Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Ending Date Total Snowfall Oct 1 to Apr 30 Missing Count 2015-04-30 50.3 0 Time Series Summary for New Brunswick Area, NJ (ThreadEx) Click column heading to sort ascending, click again to sort descending. Ending Date Total Snowfall Oct 1 to Apr 30 Missing Count 2015-04-30 40.3 3 Time Series Summary for Philadelphia Area, PA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Ending Date Total Snowfall Oct 1 to Apr 30 Missing Count 2015-04-30 27.0 0

You know that the Pacific is dominating when NYC is struggling to get below freezing during the first week of January. The average low temperature in NYC during the first week of January is 27°. Today looks like the warmest high coming up into the 50s. KNYC GFSX MOS GUIDANCE 1/02/2021 0000 UTC FHR 24| 36 48| 60 72| 84 96|108 120|132 144|156 168|180 192 SAT 02| SUN 03| MON 04| TUE 05| WED 06| THU 07| FRI 08| SAT 09 CLIMO X/N 50s/ 36 43| 37 46| 36 43| 34 45| 33 44| 33 44| 35 44 27 38

That may go to the cold suppression theme during the 1980s. Some our our greatest January Arctic outbreaks occurred during the 1980s. So being a little further south may have benefitted Philly. The 1987 El Niño also favored areas of Central NJ with the slightly further storm track.

The biggest recent disappointment for many came with the January 2015 blizzard shift to the east during the very +AO/+NAO. That was probably the snowiest winter for NYC when one of the lasting memories was such a high profile model error. The biggest recent NYC snowstorms were mostly Atlantic blocking driven rather than Pacific. But I don’t anyone would have predicted so much snow in NYC during such a +AO/ +NAO winter. I don’t even think the Boston crew believed during that fall that they could have had such a snowy winter solely driven by Pacific blocking

We have had a wide temperature range for our 10”+ snowfall months since Dec 09. The Islip data shows a monthly average temperature range from 21.6° to 38.0°. Since the 15-16 winter, the snowiest months have been toward the warmer end of the temperature scale. The main ingredients for a snowy month are teleconnections, storm track, 50/50 low, high pressure to the north, and just cold enough at storm time. Just cold enough often comes down to a low at least into the mid 20s a few days before or during the storm. Sometimes the lows in the 20s before the storm warm to low 30s during storm time. Those are the heavy wet snow events with high water content. Islip.......SN.......TEMP....DEP Dec 09...25.3”....34.5°...-1.1 Feb 10...21.7”....31.4°...-1.4 Dec 10...14.9”....31.5°....-4.1 Jan 11...34.4”.....27.1°...-3.5 Feb 13...31.4”.....32.1°...-0.7 Jan 14...25.2”.....27.7°...-2.9 Feb 14...24.5”....29.7°....-3.1 Jan 15...30.2”.....28.7°....-1.9 Feb 15...13.4”....21.6°.....-11.2 Jan 16....24.8”...33.3°....+2.7 Feb 16....13.2”....35.7°....+2.9 Jan 17....14.0”....36.2°....+5.6 Feb 17....14.7”....37.8°....+5.0 Jan 18....22.0”....30.1......-0.5 Mar 18...31.9”.....38.0°.....-1.3

The current version of the GFS is on track to get retired in February. The new v16 parallel has been doing much better with storm tracks. It looks like they fixed the cold and suppressed bias. Let’s hope the NAM replacement can see the WAA aloft as well as the current NAM did back on December 16-17th with the sleet. https://vlab.ncep.noaa.gov/web/environmental-modeling-center/fv3-convective-allowing-forecast-system UNIFIED FORECAST SYSTEM : CONVECTIVE-ALLOWING FORECAST AND DATA ASSIMILATION SYSTEM

It’s easy to lose track of all the new extremes over the last 10 years.

It’s possible if the SSW can shift the MJO. Phases 6-7 would be more -EPO in February. Plenty of moving parts so we’ll just have to wait and see how things go. https://iopscience.iop.org/article/10.1088/1748-9326/ab98b5 4. Conclusions The intraseasonal variability in tropical heating related to the MJO can exert an impact on the stratospheric polar vortex (e.g. Garfinkel et al 2012, 2014). However, there has been little written about the propagation features and intensity of the MJO after SSW event occur. In the present study, it is expected that SSWs can affect the MJO based on the above findings. The dominant occurrence of MJO phases 6 and 7; the simultaneously enhanced convective activity over the equatorial Central and Western Pacific during 1 ~ 24 d after onset of SSW events; and then the coherent eastward propagation of tropical intraseasonal convection in the following days all indicate that the influence of SSWs on tropical intraseasonal convection related to the MJO cannot be ignored. Although the dynamic and physical mechanism(s) are unclear, this SSW–MJO link is consistent with the thermal stratification change in the tropical upper troposphere. Presumably, the SSW–MJO link is associated with multiple factors. The responses of static stability in the tropical upper troposphere and lower stratosphere (UTLS) to SSW event described above may not be the sole potential mechanism by which SSW affects the MJO. Other mechanisms, such as vertical wind shear (Ho et al 2009), absolute vorticity (Collimore et al 2003), and tropopause changes (Gray et al 1992), can also be adopted to explain the responses of tropical convection to the anomaly in the UTLS region. Thus, to identify the exact mechanism(s), further studies using both observations and numerical model simulations are necessary. The impacts from SSWs could affect tropical intraseasonal convection related to MJO on time scales exceeding 20 d. More importantly, this work demonstrated the complex relationship between the MJO and SSW. Previous studies have shown a strong impact of the MJO on the NH wintertime stratospheric polar vortex. However, the results of this study allude to the reverse route, i.e. alteration of the tropical intraseasonal convection related to the MJO due to the abrupt change in the extratropical stratosphere. Although the results need to be further confirmed by numerical models that resolve stratospheric processes, this study suggests that SSW is indispensable for the subseasonal-to-seasonal prediction of the evolution of MJO. In this regard, it is also anticipated that the statistical prediction of MJO could be improved by taking variability in the extratropical stratosphere into consideration as a potential predictor especially in boreal winter.

The retrograding block will also have a MJO 3-6 standing wave. We could very well go +EPO/+PNA/-AO/-NAO. So a high water content heavy wet snow for the storms that are cold enough. Maybe a continuation of the tree damage theme as branches could snap under the weight of the snow.

Yeah, we could easily finish with above normal January snowfall and a warm departure. Islip averaged 38.0° in March 2018 and finished with 31” of snow. The NYC average in January is 32.6°. So March 2018 temperatures in a January would have been +5.4. It really comes down to getting a favorable Pacific and storm track with just cold enough for snow. February 2017 was another example on Long Island. Islip recorded 14.7”of snow at an average temperature of 37.8. NYC was able to go to 10.4” in December with a 39.3 average temperature. That’s why I think that we’ll continue to experience great snowstorms even as the winters continue to warm. We showed a few winters ago that we could go 40/40.

Only the 2nd time out of 16 Decembers for NYC in the 39.0° range to reach 10” of snow. 23 1999 39.9 T 24 1889 39.7 6.0 25 1991 39.6 0.7 26 1987 39.5 2.6 - 1911 39.5 8.5 28 1949 39.4 1.3 - 1918 39.4 0.3 30 1974 39.3 0.1 - 1928 39.3 2.0 - 1912 39.3 11.4 33 2020 39.2 10.5 34 1951 39.1 3.3 - 1932 39.1 9.4 36 1986 39.0 0.6 - 1973 39.0 2.8 - 1881 39.0 1.3

31 06:58 SE 35 G 41 7.00 Overcast and Windy BKN006 OVC011 35 34 97% 21 NA 27.42 928.9 31 05:58 SE 39 G 52 5.00 Light Snow Fog/Mist and Windy SCT009 OVC015 35 34 97% 20 NA 27.48 930.9 31 04:58 SE 44 G 54 5.00 Light Snow Fog/Mist and Windy FEW011 OVC017 35 34 94% 19 NA 27.57 934.0 31 03:58 SE 44 G 52 7.00 Mostly Cloudy and Windy BKN024 BKN033 36 33 90% 21 NA 27.65 936.7 31 02:58 SE 44 G 51 7.00 Mostly Cloudy and Windy FEW027 SCT049 BKN055 BKN070 35 35 99% 19 NA 27.72 939.0 31 01:58 E 44 G 61 3.00 Light Snow Fog/Mist and Windy BKN007 OVC012 33 33 33 31 99% 17 NA 27.80 941.8 31 00:58 E 54 G 70 2.50 Light Snow Fog/Mist and Windy BKN008 32 32 99% 14 NA 27.93 946.2 30 23:58 E 60 G 74 2.00 Light Snow Fog/Mist and Windy FEW006 32 32 100% 13 NA 28.06 950.6 30 22:58 E 61 G 83 0.75 Rain Fog/Mist and Windy VV002 32 30 93% 13 NA 28.23 956.3 30 21:58 E 52 G 71 0.63 Rain Fog/Mist and Windy VV001 31 31 99% 13 NA 28.39 961.8 https://w1.weather.gov/obhistory/PASY.html

My favorite recent late season event was 3-22-18. Portions of the South shore of Suffolk came in at close to 20”. But you can see those mid 20s lows a few days before the storm. ISP 2018-03-17 47 25 36.0 -3.4 29 0 0.00 0.0 0 2018-03-18 40 25 32.5 -7.2 32 0 0.00 0.0 0 2018-03-19 43 24 33.5 -6.5 31 0 0.00 0.0 0 2018-03-20 37 26 31.5 -8.8 33 0 T T 0 2018-03-21 38 32 35.0 -5.6 30 0 1.70 14.9 0 2018-03-22 47 32 39.5 -1.5 25 0 0.26 3.5 18

It’s an interesting conversation about the right temperatures leading up to a 6”+ or 12”+ event in NYC in our warmer climate. The key seems to be what the low temperatures are doing in the days before or during the event. While we can have highs in the 50s or even 60s right before the storm, we need at least a few days with lows getting into at least the mid 20s or colder. I think getting the lows into at least the mid 20s before or during storm time tells us there is cold enough air supply nearby to be drawn into the developing low. This is when we get favorable storm day teleconnections and storm track and evolution. I added some of our milder events surrounding storms in recent years for illustration purposes in NYC. The cold for the December storm came with the arrival of the event. 2017-02-01 47 33 40.0 6.8 25 0 0.00 0.0 T 2017-02-02 45 32 38.5 5.2 26 0 0.00 0.0 0 2017-02-03 33 26 29.5 -3.9 35 0 0.00 0.0 0 2017-02-04 34 22 28.0 -5.5 37 0 0.00 0.0 0 2017-02-05 43 31 37.0 3.3 28 0 0.00 0.0 0 2017-02-06 49 36 42.5 8.7 22 0 0.00 0.0 0 2017-02-07 42 36 39.0 5.1 26 0 0.27 0.0 0 2017-02-08 62 38 50.0 15.9 15 0 0.03 0.0 0 2017-02-09 44 19 31.5 -2.7 33 0 1.16 9.4 2 2017-02-10 32 19 25.5 -8.9 39 0 T T 8 2017-02-11 48 30 39.0 4.5 26 0 0.00 0.0 5 2017-02-12 40 30 35.0 0.3 30 0 0.46 T 2 2017-01-04 52 34 43.0 10.0 22 0 0.00 0.0 0 2017-01-05 34 27 30.5 -2.4 34 0 0.00 0.0 0 2017-01-06 33 25 29.0 -3.8 36 0 0.05 1.2 1 2017-01-07 26 20 23.0 -9.7 42 0 0.32 5.1 T 2017-01-08 25 16 20.5 -12.1 44 0 0.00 0.0 4 2017-01-09 23 14 18.5 -14.0 46 0 0.00 0.0 3 2017-01-10 46 21 33.5 1.1 31 0 0.00 0.0 3 2017-01-11 52 42 47.0 14.6 18 0 0.52 0.0 0 2017-01-12 66 47 56.5 24.2 8 0 0.05 0.0 0 2017-01-13 62 32 47.0 14.7 18 0 0.00 0.0 0 2016-01-10 59 40 49.5 17.1 15 0 1.80 0.0 0 2016-01-11 40 26 33.0 0.6 32 0 0.00 0.0 0 2016-01-12 44 25 34.5 2.2 30 0 0.00 T 0 2016-01-13 30 22 26.0 -6.3 39 0 0.00 0.0 0 2016-01-14 38 22 30.0 -2.3 35 0 0.00 T 0 2016-01-15 51 34 42.5 10.2 22 0 T 0.0 0 2016-01-16 52 42 47.0 14.8 18 0 0.24 0.0 0 2016-01-17 42 30 36.0 3.8 29 0 0.05 0.4 0 2016-01-18 31 18 24.5 -7.8 40 0 T T T 2016-01-19 28 16 22.0 -10.3 43 0 0.00 0.0 T 2016-01-20 37 27 32.0 -0.3 33 0 0.00 0.0 T 2016-01-21 36 26 31.0 -1.3 34 0 0.00 0.0 0 2016-01-22 30 21 25.5 -6.9 39 0 0.01 0.2 0 2016-01-23 27 24 25.5 -6.9 39 0 2.31 27.3 6 2016-01-24 35 20 27.5 -5.0 37 0 T T 22 2018-03-17 48 27 37.5 -5.1 27 0 0.00 0.0 0 2018-03-18 43 28 35.5 -7.4 29 0 0.00 0.0 0 2018-03-19 47 33 40.0 -3.2 25 0 0.00 0.0 0 2018-03-20 39 30 34.5 -9.1 30 0 T 0.0 0 2018-03-21 39 31 35.0 -8.9 30 0 0.99 8.2 0 2018-03-22 50 32 41.0 -3.2 24 0 0.06 0.2 8 2020-12-13 62 47 54.5 16.3 10 0 0.00 0.0 0 2020-12-14 47 35 41.0 3.1 24 0 0.26 T 0 2020-12-15 39 30 34.5 -3.0 30 0 0.00 0.0 0 2020-12-16 31 24 27.5 -9.7 37 0 0.86 6.5 0 2020-12-17 33 24 28.5 -8.4 36 0 0.66 4.0 9

We will have to deal with a very mild start to January before we can get to the retrograding -AO block and Pacific improvement by mid-January. Looks like we are close to a new all-time lowest pressure near Alaska. So my guess is that the early part of January will represent the peak +EPO. The hope is that the -AO retrogression will allow the EPO to back off enough for more ridging to build over Western North America and more +PNA. Every model group shows this scenario so it looks like it could really happen. So we’ll just have to watch for the 11-15 means to make it to day 7 for verification and forecast purposes.

Something similar happened after the February 2018 SSW. The SPV wound up in Asia. But due to the improvement on the Pacific side, we got the record snows. So the key going forward will be the ability to get a successful NAO retrogression and Pacific improvement.

Yeah, looks just like the December pattern this year. https://advances.sciencemag.org/content/4/7/eaat6025 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.

The EPS gradually transitions the main NH blocking from the Kara-Barents regions of Europe over to the Davis Strait by the 2nd week of January. December featured a very strong block in this region and an intense East Asian Jet which carved out a deep trough over the North Pacific. This lead to the strong Pacific influence that we are experiencing from late December into early January. The shift in heights could allow the North Pacific Jet to buckle and allow a retrogression of the Greenland block. This would represent some improvement by mid-January in the EPO. Sometimes that’s all we need to get the ball rolling toward a MECS regime by mid to late January.

Several times since 1995 NYC has had a snowy December following an extremely high ACE hurricane season. Accumulated Cyclone Energy - Atlantic hide Season ACE TS HU MH NYC Dec Snowfall 2020 180.1015 30 13 6 10.5 2019 132.2025 18 6 3 2.5 2018 132.5825 15 8 2 T 2017 224.8775 17 10 6 7.7 2016 141.2525 15 7 4 3.2 2015 62.685 11 4 2 T 2014 66.725 8 6 2 1 2013 36.12 14 2 0 8.6 2012 132.6325 19 10 2 0.4 2011 126.3025 19 7 4 0 2010 165.4825 19 12 5 20.1 2009 52.58 9 3 2 12.4 2008 145.7175 16 8 5 6.0 2007 73.885 15 6 2 2.9 2006 78.535 10 5 2 0 2005 250.1275 28 15 7 9.7 2004 226.88 15 9 6 3.0 2003 176.84 16 7 3 19.8 2002 67.9925 12 4 2 11.0 2001 110.32 15 9 4 T 2000 119.1425 15 8 3 13.4 1999 176.5275 12 8 5 T 1998 181.7675 14 10 3 2.0 1997 40.9275 8 3 1 T 1996 166.1825 13 9 6 T 1995 227.1025 19 11 5 11.5

It will be interesting to see if the Bering Sea low can break the all-time record. The last January with a NW PAC low with a 932 mb pressure or lower was 2013. That also occurred around the time of a SSW. It will be interesting to see if the weeklies are correct about the -NAO retrogression and EPO improvement by mid-January. https://www.wunderground.com/blog/weatherhistorian/bering-sea-superstorm-bottoms-out-at-924-mb.html https://csl.noaa.gov/groups/csl8/sswcompendium/majorevents.html JAN 2013 7-Jan-13 6-Jan-13 7-Jan-13 6-Jan-13 N E

Makes sense that a really amped up solution would be warm at the coast with such an unfavorable Pacific. The closed low went north of us this run. We needed a perfect thread the needle UL track and storm spacing to get at least a change to snow after such a mild start to the storm.