bluewave

The ensemble means don’t have much skill beyond day 6-10. So reliable model themes start to emerge right around day 8-10. Leaning too heavily on day 11-15 model output usually ends in disappointment.

The forcing came right back to the Maritime Continent as the IOD returned to neutral.

All the models now show the mild Pacific pattern continuing into at least the start of January. The fast Pacific Jet continues to be a dominant theme. This has been our new stuck weather pattern going back to last winter.

That’s why it can be difficult making monthly or seasonal forecasts in weak ENSO regimes. December cold in New England is typically something we see during La Ninas. December to date Recent La Niña composite cold in New England

Sometimes the long range can be more difficult to figure out with multiple areas of weak forcing. Almost impossible to guess which area will tip the scales in one direction or the other. That forcing and Pacific Jet can make the difference in the location and strength of the NEPAC ridge.

The Pacific Jet continues to make headlines.

Have to wait for the CFS best forecast range near the last few days of the month. It doesn’t have much skill before that. Notice the variation in the December forecasts during late November.

Who is proclaiming any day 10 MJO gospel? If you actually read my post, then you see there is a small difference in the tropical forcing between the two models. That may be one of the reasons for the varying solutions. Even low frequency forcing changes can make a big difference in our sensible weather. There is zero risk in pointing this out.

Pretty big model disagreement now showing up to start January. The EPS has a milder MJO than the GEFS. So the EPS has a fast Pacific jet allowing the cold to stay bottled up near Alaska. The GEFS is colder. Small changes in the location of the forcing in the WP can make a significant difference.

In any event, the departures as of the 21st will moderate over the last 10 days of the month. Areas to the south and east of NYC don’t have that much of a cold departure. The biggest heat island locations of NYC and LGA have some of the coldest departures. So there was some decent CAA from the north into NYC. The Northeast was one of the few cold pockets in a mild December across the CONUS. EWR...-2.1 NYC....-2.7 LGA....-2.5 JFK....-2.5 BDR....-2.0 ISP......-1.4 PHL....-1.3

That’s why storm track is so Important. This decade has had numerous events that produced very uneven totals across the region. Sometimes the most extreme storms have big variations over relatively short distances.

There are many different possible combinations of the teleconnection indices. March 2018 was the last strong -EPO and -NAO pattern during DJFM. It was an epic month with Islip picking up an historic 31.8 inches of snow.

Long Island came out of the deep freeze a little earlier than the rest of the region. Highs near 40 today in the warmer spots. ISLIP NY Dec 21 Climate: Hi: 39 Lo: 20 Precip: 0.0 Snow: 0.0

It looks like the cold really builds around Alaska over the next 10 days. Models begin to send it SE right around January 1st. They show the ridge building south of Alaska and over the North Atlantic. Hopefully, the day 11-15 forecasts show some improvement over the last few months.

Cold departures will begin to get smaller with the mild finish to 2019. if the long range ensembles are reliable, then colder weather returns right around the start of the New Year. NEW YORK CITY-CENTRAL PARK KNYC GFSX MOS GUIDANCE 12/21/2019 1200 UTC FHR 24 36| 48 60| 72 84| 96 108|120 132|144 156|168 180|192 SUN 22| MON 23| TUE 24| WED 25| THU 26| FRI 27| SAT 28|SUN CLIMO N/X 31 50| 39 53| 41 49| 39 49| 37 45| 38 46| 44 52| 48 27 40

Up to 37 degrees here on the South Shore. The local landscape crews got some nice weather for the last leaf clean up of the season. Actually feels like spring compared to the deep freeze on Thursday. http://www.nysmesonet.org/mesonow#network=nysm&stid=want

Most of the December snowfall in NYC since 2011 has been before the 20th like this year. After the Boxing Day Blizzard in 2010, we have had very little snowfall after the 20th. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Ending Date Total Snowfall Dec 1 to Dec 20 Missing Count 2019-12-20 2.5 0 2018-12-20 T 0 2017-12-20 7.0 0 2016-12-20 3.2 0 2015-12-20 0.0 0 2014-12-20 1.0 0 2013-12-20 8.6 0 2012-12-20 0.0 0 2011-12-20 0.0 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 Dec 21 to Dec 31 Missing Count 2018-12-31 T 0 2017-12-31 0.7 0 2016-12-31 T 0 2015-12-31 T 0 2014-12-31 T 0 2013-12-31 T 0 2012-12-31 0.4 0 2011-12-31 0.0 0

Looks we are still on track for our annual warm up right before Christmas. The weather also dries out over the next week. So good shopping and holiday travel conditions. NEW YORK CITY-CENTRAL PARK KNYC GFSX MOS GUIDANCE 12/20/2019 0000 UTC FHR 24| 36 48| 60 72| 84 96|108 120|132 144|156 168|180 192 FRI 20| SAT 21| SUN 22| MON 23| TUE 24| WED 25| THU 26| FRI 27 CLIMO X/N 33| 26 37| 32 48| 39 53| 42 50| 38 45| 38 44| 34 44 28 41

These past 2 events were unusual for their intensity across the whole region. Snow squalls usually just affect parts of the area. It’s pretty rare to get two events in the same calendar year that don’t weaken as they cross the area. The one last winter produced the heaviest snowfall rates of the season. This time it was the heaviest rates through at least December. I can’t really remember the last time a snow squall produced the seasons peak snowfall rate. Maybe Uncle can remember if the January 1977 squall was the heaviest rate for that season. Data for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature Precipitation Snowfall 1977-01-28 44 13 0.02 0.2 1977-01-29 13 1 0.00 0.0 1977-01-30 19 10 0.00 0.0 1977-01-31 22 8 0.00 0.0

These snow squalls are very location specific like summer thunderstorms. Last January for me was more extreme with stronger winds and lower visibility. So I guess you were in a better spot for this one than me. But it’s interesting how we got two such potent events this close together in time. Must be a product of the fast Pacific flow and rapid 500 mb wavelength changes. Notice how last year also had short the Arctic outbreak and temperature moderation a few days later. But the lows and highs over the next week will be less extreme. Another version of 2010’s repeating weather patterns. Data for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature Snowfall 2019-01-30 35 6 0.4 2019-01-31 16 2 0.0 2019-02-01 21 11 0.0 2019-02-02 34 16 0.0 2019-02-03 53 33 0.0 2019-02-04 61 41 0.0 2019-02-05 65 44 0.0

Yeah, 4 out of the last 5 years with March being the snowiest month was more like the Rockies and Plains. Welcome to the 2010’s. 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 2014-2015 0.0 0.2 1.0 16.9 13.6 18.6 0.0 50.3 2015-2016 0.0 0.0 T 27.9 4.0 0.9 T 32.8 2016-2017 0.0 T 3.2 7.9 9.4 9.7 0.0 30.2 2017-2018 0.0 T 7.7 11.2 4.9 11.6 5.5 40.9 2018-2019 0.0 6.4 T 1.1 2.6 10.4 0.0 20.5

NYC also has a shot at March surpassing December for average snowfall. 1991-2019 NYC average monthly snowfall. December.....4.9 March............5.1

Yeah, the 2nd lowest by year. Only 2017 dropped below 16 degrees.

You know it’s the 2010’s when Chicago gets record snowfall on Halloween and none on Christmas.

In a decade defined by December warmth, the 16 in NYC is the 2nd coldest December minimum of the 2010’s. The last week of 2017 holds the record for lowest December temperatures of the decade. NYC had 6 consecutive December days below freezing with a low of 9. Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Dec Click column heading to sort ascending, click again to sort descending. Year Lowest Min Temperature Missing Count 2019 16 13 2018 24 0 2017 9 0 2016 17 0 2015 34 0 2014 24 0 2013 19 0 2012 28 0 2011 22 0 2010 19 0 Data for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature 2017-12-26 28 23 2017-12-27 24 17 2017-12-28 18 11 2017-12-29 22 11 2017-12-30 23 17 2017-12-31 21 9