bluewave

40°+ Decembers are the opposite the sky is falling for most people off this forum since they can save on heating bills and spend more on the holidays.

So the fist 4 days of December are averaging +5 to +10. The next 4 will average closer to normal. Then we are right back to the 50s by later next week and more days in the +5 to +10 range. So it looks like NYC is on track for another December over 40°. The new 91-20 warmer December average for NYC is 39.1°.

Heavy rains in the Pacific Northwest this time of year are more a La Niña thing. So like in 15-16, the westward lean of the forcing in the MJO 4-7 range resulted in heavier rains displaced further north than usual for an El Nino. So a stronger northern branch of the jet stream. As you mentioned, this is probably why the PNA is struggling to stay positive in early December. Very warm December for much of North America when we have such a strong jet stream off the Pacific and and TPV with the -AO -NAO is located in Eurasia. The competing Nino and Niña-like influences are both warm.

Somewhat similar forcing location this December from the Maritime Continent to the Dateline as we saw during the super El Niño in 2015. So a very westward lean to the forcing for an El Niño December. This is producing the forecast near record atmospheric river to start December into the Pacific Northwest. Time Series Summary for Seattle Tacoma Area, WA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Ending Date Total Precipitation Dec 1 to Dec 10 Missing Count 1 2015-12-10 6.33 0 2 2007-12-10 5.69 0 3 1987-12-10 5.05 0 4 1970-12-10 4.68 0 5 1968-12-10 4.37 0 6 1989-12-10 4.10 0 7 1975-12-10 3.89 0 8 1956-12-10 3.46 0 9 1946-12-10 3.22 0

The main difference in 2010 was that the 60° day occurred when the AO was closer to neutral at -0.3 while this year the AO was still -2.5. Data for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature 2010-11-28 47 2010-11-29 48 2010-11-30 57 2010-12-01 60

Today may be the first 60° day during early December in NYC a few days after the AO going -3.3. It could also be a record for consecutive 50°+ days at the same time. https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.daily.ao.nao.pna.aao.gdas.120days.csv

It’s just that the geographic footprint is much smaller with Arctic outbreaks nowadays like with the record 2021 cold in the Plains not making it to the East Coast. So a smaller percentage of the earths surface is able to experience record cold at any given time than in the past. But even if these outbreaks have a smaller aerial coverage, they can be intense in the more limited areas that get them.

Yeah, winter lovers in Europe can rely solely on the -AO and -NAO and don’t have to worry about a hostile Pacific.

The last time was back in 2002. It has been more common to make it to 50° or warmer on Christmas since 2003. Data for December 25 - NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature Precipitation Snowfall Snow Depth 2022-12-25 28 14 0.00 0.0 0 2021-12-25 52 36 0.16 0.0 0 2020-12-25 61 29 0.92 0.0 0 2019-12-25 47 32 0.00 0.0 0 2018-12-25 40 33 0.00 0.0 0 2017-12-25 38 28 0.23 T 0 2016-12-25 50 36 0.00 0.0 0 2015-12-25 66 57 0.01 0.0 0 2014-12-25 62 44 0.09 0.0 0 2013-12-25 31 19 0.00 0.0 0 2012-12-25 41 32 0.06 0.0 0 2011-12-25 46 31 0.00 0.0 0 2010-12-25 32 25 0.00 0.0 0 2009-12-25 38 33 0.24 0.0 2 2008-12-25 57 33 0.13 0.0 0 2007-12-25 43 35 0.00 0.0 0 2006-12-25 45 39 0.37 0.0 0 2005-12-25 54 39 0.84 0.0 0 2004-12-25 33 25 0.00 0.0 0 2003-12-25 46 33 T 0.0 0 2002-12-25 37 31 1.30 5.0 M

I am not sure if we are ever going to see another March run of snow and cold like from 2013 to 2019 again. It was like someone flipped a switch to warmer in the 2020s. I guess time will tell.

Last December was the warmest on record for a December monthly AO reading of -2.0 or lower in NYC. December 2020 was the warmest on record for a 10" or greater monthly average snowfall and a monthly AO reading from -1.5 to -1.9. https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/monthly.ao.index.b50.current.ascii.table ……………..AO……..NYC T Dec 22….-2.719….38.5° Dec 10….-2.631….32.6° Dec 09….-3.413….35.9° Dec 05….-2.104….35.3 Dec 00….-2.354….31.1° Dec 95….-2.127….32.4° Dec 76….-2.074….29.9° ……………..AO…….NYC S….NYC T Dec 20…-1.736….10.5”…..39.2° Dec 02….-1.592…12.4”…..36.0°

Yeah, the TPV with this -NAO shifted over to Eurasia leaving a mild Pacific air mass in place across North America. As we found out in recent years, -NAO and -AO patterns can be very mild for us. This isn’t like the old days around 2010 when big -AO and -NAO drops meant cold. I think Don had a great post a while back on how the -AO and -NAO has become warmer for us.

I agree with you on this. It also goes to what I have been saying about the stronger MJO 4-7 with the rapidly warming WPAC as the IOD fades. The reason the models are starting to converge on a warmer solution for December is how strong the MJO 6-7 VP anomalies are forecast to get in the next few weeks. The MJO moving to the Dateline could constructively interfere with the El Niño strengthening it further. Just look at how strong the VP anomalies and WWB are forecast to be. This is why I don’t think the RMM charts will adequately show the strength of this MJO wave. MJO 7 is one of the warmest phases during and El Niño. When you include the lag which take up to 7 days per MJO phase this is why the models have the warmth persisting into so long into mid to late December. The chart below is courtesy of Allsnow who posted it in the NYC forum. My guess is that when the Euro monthly updates on Tuesday, it will have a strong MJO 6-7 look for December.

Again, it’s not canceling winter in December to acknowledge that multiple factors are indicating another 40° or warmer December for NYC to EWR. We have seen this time and time again. It fits the pattern of all the 70° Septembers and 60° Octobers. What is actually happening is that December is becoming a fall month and September a summer month.

Have to head to Eurasia if you want to see any real cold this month.

We haven’t had a really cold December in NYC since 1989 which was the last time NYC averaged in the 20s .

The one antidote to a south based block is a +PNA like we got in December 2020. But the more tucked in storm track near ACY due to the south based block produced 40” in Binghamton instead of Boston.

There were two things at work last December. First, the block couldn’t retrograde sufficiently far enough west to boost the PNA like it did in 2010. Second, the Gulf Stream was much warmer last December than in 2010 which probably helped the block build further south than normal.

More like +2 to +3 by mid month with a possible increase after that. And that is against the new warmer 91-20 climate normals. So NYC is on track for another December near or over 40° which used to be much less frequent in the old days.

After seeing how hostile the Pacific has become since 18-19, the phase NAO and AO isn’t as important as it used to be. 20-21 was the only time the NAO and AO was able to coincide with a favorable Pacific. Last winter the Pacific completely muted a monthly -AO value in the -2.5 to -3.0 range which never happened before. So unless we have Pacific on our side, a -NAO and -AO will be going to waste. Hopefully we get get some semblance of a backloaded El Niño this winter with the Pacific backing off during another -AO -NAO interval.

Do you have the link to those higher res charts?

That last VP frame still shows the MJO forcing the MJO 6 region as the RMMs are chasing convection.

Those were much weaker MJOs through the warm phases than we have seen since 15-16 with El Niños. We never saw MJO 4-6 as strong as 15-16 before with such a strong El Nino. In the old days, stronger MJO 4-6 activity was nonexistent in stronger El Niño’s like we have now. There were several posts in this thread a while back that said that the IOD would shut down the MJO 4-6 phases and it would be nothing to worry about. But I pointed out that there would be a rapid rebound in the WPAC SSTs that we are seeing now. https://phys.org/news/2021-04-distinctive-mjo-super-el-nino.html A research group, led by Dr. Wenjun Zhang from the Nanjing University of Information Science and Technology analyzed MJO activity of the super El Niño event during the Northern Hemisphere winter of 2015/16. Observations show that the western Pacific MJO activity was strongly suppressed during the peak phase of the 1982/83 and 1997/98 super El Niño events. However, during the crest of the 2015/16 super El Niño event, western Pacific MJO-related convection was enhanced. "It is apparent that the enhanced western Pacific MJO is mainly related to its sea surface temperature (SST) anomaly distribution and the associated background thermodynamic conditions." said Dr. Zhang. His team's complete research and data are published in Advances in Atmospheric Sciences. When compared to the previous super El Niño events, the warm SST anomaly, or change from average, of the 2015/16 El Niño was located more westward than during the other two extreme seasons. Additionally, no significant cold SST anomaly was detected in the western Pacific. Accordingly, the moisture and air temperature tended to increase in the central-western Pacific during the winter of 2015/16 unlike the previous super El Niño events. This research highlights that climatologists should consider the SST anomaly distribution of super El Niño events for future MJO activity studies.

You have to be careful using those CPC charts which take 3 month averages. The DJF composite often works better for us each month from December to February. The December general MJO 7 chart is warm for us in addition to the December El Niño composite. Plus there is a lag which can take up to a week after passing through 4-6. So the 7 pattern may take up to a week to show up after first entering 7. That’s why we can’t rush the MJO in the warm phases.

We know this month that the El Niño hasn’t been strong enough to shut down forcing in the warmer MJO 4-7 regions. Beyond this month, it will be a wait and see approach. But even if the forcing shifts over closer to the Dateline and stays there, the record SSTs could easily boost the VP anomalies enough to give us a warm Nino pattern. The SSTs in Nino 4 are close to 15-16 right now. So this isn’t some weak modoki signal like years past with much cooler Nino 4 temperatures. The reason I mention a +2 to +3 average departure in the Northeast is because +2.9 has been the average departure in the Northeast last 8 seasons. Plus it’s nearly impossible to pick out an exact departure ahead of time. Just that based on what I am seeing now the, places like NYC and maybe the entire Northeast have a shot at a record 9th warmer than average winter in a row. Notice aI am not taking the leap which you did mentioning permanent. Since I make the distinction between loading the dice for more frequent warmth but variability always holds the potential for a colder winter emerging here and there. It’s just that I am not sure what a colder signal would look like before the season to be confident enough to forecast a cold winter. Our eventual next cold winter May just be a surprise that we have to deconstruct the hoes and why’s when the season is over.