bluewave

My very rough guess right now is that we are following along the track of November 2018. Very cold Novembers with a -EPO pulse December 1-10. We saw a colder start to December in NYC during 2018. But last year featured a moderating temperature trend after December 10th. December 11-30 also coincided with the milder MJO phases. So we’ll have to reevaluate what the pattern and model forecasts look like once we get past the first week of December. This will be to see if the pattern is following the recent past or it goes in another direction. While the CFS isn’t the worlds greatest model, it does show this pattern progression.

It’s quite possible.

This could be the windiest period around Thanksgiving in years.

While the amplitude has increased in recent runs, the ridge axis remains stuck north of Hawaii and over the SE US.

The fly in the ointment this year has been the unusually strong low over the SW US. So the SE ridge corrects stronger the closer we get to the forecast period. https://ktar.com/story/2850504/hail-falls-across-the-phoenix-area-but-storms-are-heading-out-of-town/

The -NAO blocks this time of year have been fleeting. We had a big -NAO drop at the same time last year. Our best recent success with more sustained -NAO blocking has been later in the season. https://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.nao.index.b500101.current.ascii 2018 11 19 -0.274 2018 11 20 -0.826 2018 11 21 -0.726 2018 11 22 -0.348 2018 11 23 -0.369 2018 11 24 -0.804 2018 11 25 -1.373 2018 11 26 -1.404 2018 11 27 -1.144 2018 11 28 -0.872 2018 11 29 -0.440 2018 11 30 -0.133

It’s not really worth looking at the models past 7 days.The Niña-like SE ridge keeps beating expectations from what is shown at day 10. So the main storm track in the fast Pacific split flow is through the Great Lakes. New day 7 forecast Old day 10 forecast Old day 11-15 forecast

Top 3 coldest first 20 days of November at several of our stations before the temperature moderation. Time Series Summary for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Rank Ending Date Mean Avg Temperature Nov 1 to Nov 20 Missing Count 1 1933-11-20 38.7 0 2 1976-11-20 40.5 0 3 2019-11-20 42.4 0 Time Series Summary for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Rank Ending Date Mean Avg Temperature Nov 1 to Nov 20 Missing Count 1 1976-11-20 41.0 0 2 1967-11-20 41.2 0 3 2019-11-20 41.4 0 Time Series Summary for IGOR I SIKORSKY MEMORI AP, CT Click column heading to sort ascending, click again to sort descending. Rank Ending Date Mean Avg Temperature Nov 1 to Nov 20 Missing Count 1 1962-11-20 41.2 0 2 2019-11-20 42.0 0 3 1967-11-20 42.3 0

We need a strong -NAO event to counter the unfavorable Pacific like we had late in the last few seasons. Root for another -EPO pulse in early December to combine with the weak -NAO. That would be one way we could see some wintery weather. But that is too far out to speculate on now. Otherwise, we get the same default unfavorable Pacific pattern.

I am just weary of the Pacific defaulting back to its multi-year Niña-like base state. Notice how the EPS has the ridge north of Hawaii and SE ridge holding on with the weak -NAO near the end of the month. My guess is that the warm western Pacific and cold Niño 1+2 has a hand in this pattern of the last few years.

This weekend is a great example of what happens with a weak -NAO and unfavorable Pacific. The longer range GFS especially suffers under this type of pattern.

No way to know details like that so far out. But the models continue to show more of a SE Ridge amplification now than several days ago. So we are returning to the default firehose Pacific Jet pattern of the last several years.

Strong winds could be an issue around the Thanksgiving parade if the cutter comes out as intense as the Euro and GFS. We will have to see how models handle the details of this SE Ridge amplification in later runs.

The only recent skill the met community has had with forecasting major SSW’s in advance were the later season ones the last few years.

That would be a very rare occurrence. Only a tiny fraction of major SSW’s have occurred before January. https://www.esrl.noaa.gov/csd/groups/csd8/sswcompendium/majorevents.html

I think it’s a piece of the puzzle. Most of our recent strong Atlantic blocking events have been in JFMAM. The Pacific has been our main driver especially before January in recent years. You can see it now with the EPO reversal.

The recent SSW’s have also been occurring later in the season. It’s rare to get one early.

The Pacific Ocean has a tremendous impact on our weather. The only way to counter an unfavorable Pacific pattern for us is an extreme North Atlantic blocking event. But those have been happening later in the season for us.

That’s why a real -NAO is so important. A -AO with a +EPO and ridge north of Hawaii just won’t cut it. For example, this is what happened last December. We had a mild +EPO/-AO/+NAO pattern. The unfavorable Pacific overpowered the weaker Atlantic blocking for us.

Much milder period coming up around thisThanksgiving than last year. 2018 11/22 28 17 0.00 4th coldest high, 2nd coldest low for Thanksgiving

Notice how the SE Ridge amplification now being shown before Thanksgiving wasn’t even on model radar a few days ago. This is the retrogression of the -EPO ridge back to north of Hawaii. You can see how far off 11-15 day means can be when there are such big changes day 8-10. New run Old run

The warm October and cold November pattern became really well defined following the record summer Arctic melt in 2012. This is also around the time that the mid 1990’s to 2010 colder December -NAO pattern reversed. Since 2011, the December NAO has been in a positive state. We also have seen the -EPO ridge relax in December from very negative November readings. So this has given us the December temperature departure rebound from November. There was also the rapid and historic warming of the entire Pacific Basin in 2013. All these factors have combined to produce these repeating monthly patterns. So we are seeing these relationships between the Atlantic, Pacific, Arctic, and Tropics as the planet continues to warm.

Yeah, the post day 10 performance has been pretty poor from the ensembles. This is often the case as their useful limit is about 7-10 days depending on the pattern. Once in a while we get lucky and day 11-15 shows more skill. But they have been forecasting too much -NAO recently. If we lose the -EPO pattern for Arctic cold, then SE Ridge has found a way to sneak in the closer we get.

That big ridge north of Hawaii isn’t a great look if it verifies like shown. The air mass is largely Pacific in origin. Since the NAO has been verifying more positive recently than long range forecasts, the SE Ridge May correct stronger the closer in we get.

The -EPO relaxation and loss of the record breaking Arctic air mass is right on schedule. This has been one of our famous 2010’s repeating weather patterns. Record cold in November followed by a moderation as we head into December. So we have probably seen our last -20 degree departure for a while in NYC. The only months to feature them in the 2010’s have been November, January, and February. All NYC -20 or lower days since January 2010 Data for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Avg Temperature Departure 2016-02-14 -28.0 2015-02-20 -25.6 2019-01-31 -24.1 2015-02-16 -23.4 2018-01-06 -23.3 2019-01-21 -23.3 2018-11-22 -23.2 2015-02-24 -23.0 2018-11-23 -21.8 2014-01-22 -21.4 2014-02-28 -21.4 2014-01-07 -21.2 2018-01-07 -21.2 2016-02-13 -20.9 2015-02-15 -20.7 2015-02-13 -20.4 2018-01-01 -20.4 2019-11-13 -20.1