bluewave

CWG did a nice story on this a few weeks back. https://www.washingtonpost.com/weather/2019/12/16/winter-holidays-are-warming-rapidly-mid-atlantic-northeast/ The winter holidays are warming rapidly in the Mid-Atlantic and Northeast The week leading up to Christmas is warming twice as fast as the rest of the winter in many East Coast cities.

This has nothing to do with urbanization. POU had exactly the same +16 high temperature departure as NYC yesterday. Data for POUGHKEEPSIE AIRPORT, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature Max Temperature Departure 2019-12-23 54 16.3 2019-12-24 M M Data for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature Max Temperature Departure 2019-12-23 57 16.3 2019-12-24 M M

Almost difficult to keep up with all these record breaking rainfall events.

The high temperature reached 57 degrees in NYC on Monday. This warmth right before Christmas has become really pronounced since 2001. NYC has gone 17 out of the last 19 years reaching 55 or warmer in the week before Christmas. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Ending Date Highest Max Temperature Dec 18 to Dec 24 Missing Count 2019-12-24 57 1 2018-12-24 61 0 2017-12-24 55 0 2016-12-24 58 0 2015-12-24 72 0 2014-12-24 58 0 2013-12-24 71 0 2012-12-24 56 0 2011-12-24 62 0 2010-12-24 40 0 2009-12-24 39 0 2008-12-24 58 0 2007-12-24 61 0 2006-12-24 59 0 2005-12-24 55 0 2004-12-24 59 0 2003-12-24 56 0 2002-12-24 60 0 2001-12-24 58 0

https://www.nature.com/articles/d41586-018-05978-1 Ocean heatwaves will become more frequent and extreme as the climate warms, scientists report1 on 15 August in Nature. These episodes of intense heat could disrupt marine food webs and reshape biodiversity in the world’s oceans. Scientists analysed satellite-based measurements of sea surface temperature from 1982 to 2016 and found that the frequency of marine heatwaves had doubled. These extreme heat events in the ocean's surface waters can last from days to months and can occur across thousands of kilometres. If average global temperatures increase to 3.5 °C above pre-industrial levels by the end of the century, as researchers currently project, the frequency of ocean heatwaves could increase by a factor of 41. In other words, a 1-in-100-day event at pre-industrial levels of warming could become a 1-in-3-day event. Marine heatwaves have already become more long-lasting, frequent, intense and extensive than in the past,” says lead study author Thomas Frölicher, a climatologist at the University of Bern in Switzerland. He adds that these changes are already well outside what could be expected on the basis of natural swings in Earth’s climate: the study’s analysis determined that 87% of heatwaves in the ocean are the result of human-induced global warming. Going global Scientists have studied heatwaves on land for decades. But it wasn’t until researchers faced episodes of extreme heat in the ocean in the past several years that they started paying more attention to the issue at sea. Those episodes included the massive warm water ‘blob’ in the northeastern Pacific Ocean that killed off sea otters (Enhydra lutris) in Alaska and sea lions (Zalophus californianus) in California, and disrupted fisheries off North America from 2014 to 2015. They also included the massive 2015–16 El Niño that ravaged coral reefs around the world. The emphasis on marine heatwaves is really motivated by the recognition that the same kinds of extremes can happen in the ocean as on land,” says Noah Diffenbaugh, a climatologist at Stanford University in California. He adds that this latest study takes global perspective on these regional issues. The study provides a useful framework for disentangling short-term temperature spikes from long-term warming trends in the oceans, says Kris Karnauskas, a physical oceanographer at the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder. He says that marine heatwaves could be the result of natural temperature swings that become more extreme owing to a warming ocean. Or they could be a signal that global warming is changing how the ocean functions — thus altering the likelihood and intensity of marine warming events. Frölicher says current models suggest that more frequent and intense ocean heatwaves are largely a result of warming oceans. And now, he and his team are working to develop models that can explore marine heatwave trends and their ecological impacts at local and regional levels. https://www.nature.com/articles/s41586-018-0383-9

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