bluewave

Yeah, it really gets back to the competing influences discussion that we had during the fall. The record +PMM was associated with the more Niño-like pattern so far this winter. But now that the PMM is quickly cooling, the models are showing a transition to a more Niña-like pattern. I mentioned this the other day. Now this new tweet is picking up on the idea. It shows how quickly the SST have cooled west of Central America. I posted for the SST chart not for references to any specific analog year.

Yeah, it’s a very well identified pattern. https://www.climate.gov/news-features/blogs/beyond-data/climate-change-rule-thumb-cold-things-warming-faster-warm-things Colder places are warming faster than warmer places Colder seasons are warming faster than warmer seasons Colder times of day are warming more than warmer times of day

Climate Central compiled all the charts. It’s through the winter of 2019. So the record warmth last winter wasn’t included. https://www.climatecentral.org/gallery/graphics/winter-warming-local-average-winter-temperature-2019

Mild pattern continuing on the 12z EPS through the next week of so. This is what happens when mild Pacific air gets stuck under a south based block. The latest weeklies have the retrogression of the ridge back to the Aleutians with a more Niña--like -PNA by late January.

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.