bluewave

You know it’s a mild winter pattern when even the mountain areas can’t build much of a snowpack.

It will be interesting to see the new EPS weeklies later. The latest GEFS weeklies have a pretty fast retrogression of the ridge back to the Aleutians by late January. This would allow a more La Niña-like -PNA to emerge by later in January into February. So hopefully we can maximize our snowfall potential after January 10th before a possible shift later on.

Stating that we could see a La Niña-like pattern in February means that the ridge could pull back to the Aleutians and the PNA falls. It doesn’t speak to what type of snowfall opportunities that we will see. There also isn’t much correlation between the strength of the La Niña and this February pattern. For example, 16-17 featured one of the weakest La Ninas during February. But it had near record warmth with a memorable blizzard. February 2011 had a much stronger La Niña with the PNA drop. But it was cooler than 16-17 with less snow. So specific temperatures and snowfall can be quite variable within a February La Niña pattern should it arise this year.

I can still remember how surprised everyone was when the La Niña pattern showed up in February 2011. We could have surpassed 95-96 if that pattern didn’t reverse. That’s why I am always cautious when dealing with La Ninas in February.

It may be that the record off equator North Pacific warmth allowed a more Niño-like pattern to dominate since December. But this off equator North Pacific warm has steadily declined in recent weeks. So it’s possible that a more La Niña-like pattern finally emerges in February.

It will be interesting to see how long we can keep it going. I am not aware of another La Niña that had +PNA for the whole winter. The +1.58 PNA for December was out of place for a La Niña. https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.pna.monthly.b5001.current.ascii.table

Hopefully, the EPS is rushing the flip to La Niña in February. Forecasts past week 2 have lower skill. Sometimes week 3 and beyond just defaults to a climo type composite for the ENSO at the time.

New 30 year climate normals will be warmer and snowier.

The only thing we can say about the day 10 to 5 EPS corrections is that the Davis Strait blocking is weaker and the +PNA is stronger. New run Old run

When the 510 Arctic thickness line drops down near the Northeast. Usually this time of year it’s a -10 departure or lower. Highs often stay in the 20s with lows in the 10s. Lows below 10 are usually reserved for the strongest Arctic outbreaks. https://www.weather.gov/source/zhu/ZHU_Training_Page/Miscellaneous/Heights_Thicknesses/thickness_temperature.htm The 5,700, 5,400 and 5,100 thickness lines will be shown in solid yellow. A thickness of less than 5,100 is associated with arctic air while a thickness of 5,700 or greater is associated with tropical air.

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