bluewave

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

It was a very impressive first half of November for early record snow and cold. You can see the beginning of the -EPO relaxation with the North American snow extent peaking. We’ll have to see how the record +IOD interacts with the MJO and El Niño. Even weak El Niño patterns like we have now are usually back-loaded winters with mild Decembers. The one exception to that is getting a -NAO. But we have been in a mild December +NAO streak since 2011. Daily EPO 2019 10 23 -43.21 2019 10 24 -36.14 2019 10 25 -49.33 2019 10 26 -193.78 2019 10 27 -286.38 2019 10 28 -273.06 2019 10 29 -225.04 2019 10 30 -191.46 2019 10 31 -179.78 2019 11 01 -191.50 2019 11 02 -233.94 2019 11 03 -260.13 2019 11 04 -268.09 2019 11 05 -261.25 2019 11 06 -237.61 2019 11 07 -181.25 2019 11 08 -150.84 2019 11 09 -175.85 2019 11 10 -217.23 2019 11 11 -197.04 2019 11 12 -92.56 2019 11 13 -67.49 2019 11 14 -10.10 2019 11 15 42.49

Looks like the Arctic air mass that dominated the first half of November will be replaced by more of a Pacific one. So any cold we get should be much less intense. Probably have to wait for the next big -EPO drop to see Arctic air again.

It works out to a -5.7 departure for the first 16 days of the month. About 3 to 4 weeks early early for those temperatures which are average for December 1st.

Suffolk is living up to its snowy 2010’s reputation.

Some of the models were showing this snow on Long Island. Islip now has 2 days with reported snow by November 17th. This was the 2nd coldest start to November for Islip behind 1976. 17 Nov 7:56 am 34 28 79 23 NNE 17 4.00 Lt Snow BKN031,OVC039 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 16 Missing Count 1 1976-11-16 40.6 0 2 2019-11-16 41.5 0

While we have seen record cold during recent Novembers, this year Is showing us something more impressive.

Rare to see the relative humidity drop under 10% at White Plains. This looks like the lowest relative humidity of the 2010’s. White Plains FAIR 39 -15 9 NE14 https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=157&network=NY_ASOS&station=HPN&year=2019&var=min_rh&dir=below&thres=10&dpi=100&_fmt=png

Relative humidity down to 13% now in NYC. This has to be a new record for NE flow in November. Central Park FAIR 40 -7 13 NE14G23

Today could be one of the driest days that we have seen this time of year on a NE wind. The relative humidity is already down to 30% with dewpoints falling to near 0. The NWS even put out a special statement. This is essentially an Arctic backdoor with the temperatures modifying due to the NE flow. But the dryness remains. East Hampton FAIR 32 5 32 NE12G21 Willimantic FAIR 27 -1 30 N8 There will be an enhanced risk of fire spread today with gusty winds and low relative humidity. Winds will be out of the north to northeast at 10 to 20 mph with gusts mainly between 20 and 30 mph. Relative humidity is expected to lower to around 15 to 25 percent.

It may not make much of a difference for us if the AMO goes more negative in the future. The waters of the NW Atlantic have seen some of fastest rates of increase. Perhaps a combination of the upward global SST trend and the slowing AMOC. So we get the persistent cool pool south of Greenland and warm SST’s off the East Coast. This effect could mute any influence on our weather of a more -AMO. The 1980’s were a much colder SST and global climate era. http://www.realclimate.org/index.php/archives/2016/05/amoc-slowdown-connecting-the-dots/