bluewave

I will take it a step further than that and say whether for positive or negative the winter outcomes can be traced back as early as the previous spring or summer. The record breaking warmth and ridging last winter in Canada was becoming evident in May 2023 which carried right through last winter. The 22-23 winter deep trough in the West pattern became established in November. The very strong SPV pattern in 19-20 began with the near record IOD and IO forcing in the fall. The cold and snowy 13-14 and 14-15 winter patterns first began to set up with the record TNH during the summer of 2013. The great backloaded 12-13 progression followed the early peaking El Niño around Labor Day even though no official Nino was declared. The amazing 09-10 and 10-11 blocking patterns first became evident in the summer of 2009 with one of the coolest June and July periods around NYC and record summer blocking.

I was looking more at the big burst of IO forcing which preceded the record breaking AO rise. https://www.nature.com/articles/s41612-022-00279-x#:~:text=Arctic oscillation (AO)%2C which,the positive trend of AO. Arctic oscillation (AO), which is the most dominant atmospheric variability in the Northern Hemisphere (NH) during the boreal winter, significantly affects the weather and climate at mid-to-high latitudes in the NH. Although a climate community has focused on a negative trend of AO in recent decades, the significant positive trend of AO over the last 60 years has not yet been thoroughly discussed. By analyzing reanalysis and Atmospheric Model Inter-comparison Project (AMIP) datasets with pacemaker experiments, we found that sea surface temperature warming in the Indian Ocean is conducive to the positive trend of AO from the late 1950s. The momentum flux convergence by stationary waves due to the Indian Ocean warming plays an important role in the positive trend of AO, which is characterized by a poleward shift of zonal-mean zonal winds. In addition, the reduced upward propagating wave activity flux over the North Pacific due to Indian Ocean warming also plays a role to strengthen the polar vortex, subsequently, it contributes to the positive trend of AO

Driest first two months of fall for many locations.

These strong 500mb ridges are usually located further north in Canada allowing moisture to undercut. But this one was right across the CONUS with too much high pressure for it to rain. Very rare situation to say the least.

I started out in the mid-80s with the Alden Difax weather model printer at the college weather lab. The models were really primitive back then with only black and white and very low printed resolution. Plus they were often incorrect even the day before especially with snowstorms. Then in the 90s I didn’t get online until January 97. So I missed the whole 95-96 weather season online. I got a Pentium 150 with a 56k dial up. I quickly found Walt’s great AFDs out of Boston and tried to learn all the different terms he was using in his long range discussions. My first forum experience was back on Eastern during 2006 just reading the comments. Then I joined in 2007 and have been on the forums ever since.

I think the comments were added to the wrong date since there wouldn’t have been frost that morning as Jersey City had a low of 45° also. A few days later it dropped to 34° at both sites. So that is probably the date that frost was recorded. The temperature shelter in 1924 was down on the platform. So it was a good sitting before it became overgrown with trees and went into deep shade when the NWS left NYC in the 90s. The anemometer was always on top of the castle. But now the trees have grown higher than the top of the castle. So the winds are too low. This is why the strongest gust was back in the 1970s before the trees were blocking the wind. Data for October 18, 1924 through October 18, 1924 Click column heading to sort ascending, click again to sort descending. NY BEDFORD HILLS COOP 50 NY WORLD TRADE CENTER WBAN 46 NJ JERSEY CITY COOP 45 NY NY CITY CENTRAL PARK WBAN 45

While the Euro had the general ridge and trough locations correct for October, the pattern verified much more amplified than forecast. http://seasonal.meteo.fr/content/PS-previ-cartes?TSPD_101_R0=0804515747ab2000263c57679892e0481ee247a166d03c175ce873dc1d66636a0d5c36e7e8a9cf5f08c0aa925214300096df27d4518308136ac5ee301211eb4b4b0904e4c8bf3eb9f6b53626dc172c2d2096614d7cdda80bf8d8617544ad2c09

A top 10 warmest October for spots like JFK with the average high in 2nd place. Time Series Summary for JFK INTERNATIONAL AIRPORT, NY - Month of Oct Click column heading to sort ascending, click again to sort descending. 1 2017 71.0 0 2 2024 70.5 4 3 1971 70.2 0 4 2007 70.1 0 5 2021 69.9 0 6 1963 69.2 0 7 1995 69.0 0 8 1949 68.7 0 9 1984 68.6 0 10 1990 68.4 0 Time Series Summary for JFK INTERNATIONAL AIRPORT, NY - Month of Oct Click column heading to sort ascending, click again to sort descending. 1 1971 63.5 0 2 2017 63.2 0 3 2021 63.0 0 - 2007 63.0 0 4 1984 61.7 0 5 1995 61.6 0 6 1990 61.3 0 7 2024 61.1 4 - 1949 61.1 0 8 1954 60.1 0 9 2013 60.0 0 10 1975 59.9 0

ISP tied the lowest October dew point on record at only 12°. The relative humidity was 2nd lowest at 17%. So places like the Pine Barrens can experience some strong radiational cooling tonight. MacArthur/ISP MOSUNNY 57 12 17 https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=153&network=NY_ASOS&zstation=ISP&month=oct&sday=1027&eday=1231&var=min_dwpf&_r=t&dpi=100&_fmt=png

The continuous daily records in NYC go back to the late 1800s. A recent study based on tree rings found the driest period of the last 500 years was around the 1600s. And the recent 30 year period with the reliable instrument records was the wettest in the last 500 years. So my guess is during that drought around the 1600s there were probably months like this. Since a warmer atmosphere holds more moisture, the recent extreme rainfall events were to be expected and would have a much smaller chance of occurring in a much colder climate. As for temperatures, this recent period was the warmest since the end of the last ice age. But not nearly as warm as the prehistoric times when CO2 levels were actually higher than today. As we know CO2 can occur from natural sources like in the distant past. And we can cause the levels to change from emissions.

The inconsistency is the fact that we haven’t gotten such a strong La Niña signal before in October with the RONI, ONI, or any other La Niña metric as low as it is. Past La Niña years with such a strong -PDO were much more robust in the Nina SSTs. So we are getting multiple disconnects across the board including the early MJO indicator. December 2020 was the best for NYC snowfall in over a decade. Some would argue it was the best December since 2010 but not of that magnitude of greatness. The unusual south based block resulted in NYC finishing warmer than average at +1.7 even with a trough in the East. I can remember commenting in the NYC thread how the October MJO was acting more like we saw in 17-18 and 10-11 later in October. But then the historic November warmth arrived exceeding 2015. So many back in the NY thread were very concerned about the winter after seeing so much November warmth like we saw in the Niña background years like 2011 and 2001. Then the Euro started forecasting a great looking December pattern as we got closer to the start of December. This was pretty much the opposite of the seasonal model issued back on November 5th. So the early MJO indicator beat the Euro seasonal forecast. But that was a much stronger La Niña than this year as per the RONI and ONI metrics. The -PDO wasn’t as strong as we are seeing now. So perhaps the strong La Niña influence is being realized more in the -PDO index this time than at any other time in the past. The October Euro forecast for December doesn’t look so great. It’s got a coast to coast warm ridge across the U.S. We’ll wait to see what it comes up with on November 5th. If it continues along the same lines as October 5th, then we’ll need as big a miss as it had back in 2020 for the early MJO indicator to keep working as it has each La Niña year since 10-11. http://seasonal.meteo.fr/content/PS-previ-cartes?language=fr Current Euro 500 mb forecast for December 2020 forecast big miss to the delight of the winter fans around NYC Forecast Verification

With the dew points so low today, highs could beat guidance with low 60s possible in spots. This would result in lower RH values than forecast. So one of our driest days of the fall.

In order for the MJO relationship to work again this year, all the seasonal models are going to have to be way off for December. The last 2 years when the MJO 5 amplitude was closer to this strong in October were 2020 and 2017. Right now none of the forecasts models look similar to those two years in December. The key to those seasons was a snowy and at times colder December around NYC with a mismatch pattern going against the La Niña and -PDO. Then the whole winter still averaged warmer than normal, but not as warm as our recent warmer La Niña winters like 16-17, and 22-23. Snowfall was much better those years. The fact that the La Niña is so weak now like 16-17 instead of the stronger years like 17-18 and 20-21 also is different since our best La Niña winters since 10-11 have been stronger.And it was those stronger La Niña Octobers that had the stronger MJO activity. Not such a weak event having a stronger MJO October response this year. This a reversal from 95-96 to 08-09 when the weaker La Ninas have been the better winters. So while the seasonal models haven’t been the most reliable during recent winters, I am not ready to yet buy that there is going to be a big mismatch right out of the gate in December. Remember, the good La Niña winters start out with great frontloaded results in December and then revisit it again at some point later on. They don’t start out warm and snowless in December in NYC and then turn great later on. So I am going to view these October MJO results with caution and will need to see the the models as we get closer into December really diverge from the seasonal forecasts. Otherwise it will be a case of this winter following the weaker La Niña script with warmer and less snow December and the early October MJO indicator not working for the first time since 2010.

There is so much Pacific SST warmth west of the Dateline this fall that it’s driving the baseline much more than the meager ENSO region cooling.

The MJO activity in MJO 5 is unusually strong for weaker La Niña this month. The latest RMM index is closer to 2020, 2017, and 2010 than 2022, 2021, 2016, and 2011. Whether we use the ONI or RONI this fall so far is closer to the weaker La Niña years like 2016. But for some reason we are still getting the stronger October MJO response which preceded the better La Niña winters. These Decembers like 2020, 2017, and 2010, had more of a mismatch pattern where the December patterns were snowier and in some cases colder like 2017 and 2010. Since we are getting this divergence between the strength of the La Niña and early MJO response not really sure what to make of it yet. Since our best La Niña winters were actually the stronger ones of the groupings and not the weaker ones. Plus there is no guarantee that this indicator will continue to work as it did in the past. As always, we may just have to wait until December actually gets underway in order to know for sure. Especially since there are other indicators signaling the potential for above to potentially well above normal temperatures and below average snowfall in NYC. It’s based on the MJO RMM amplitude and VP anomalies in phase 5-6 during La Niña Octobers since 2010. The stronger October MJO responses had better winters in NYC relative to the other La Ninas in the multiyear event group. Those stronger MJO 5-6 Octobers also had the more robust peak La Niña ONIs from fall into winter of the multiyear groups. All the La Niña winters around NYC since 11-12 have averaged warmer than normal. But even the warmer than average 17-18 and 20-21 winters had better snowfall than the other years in the multiyear group. In addition, we haven’t had any cold neutral ENSOs in the -0.1 to -0.5 peak range with a strong -PDO since 2010. So not sure how the relationship would work for any year with the official CPC ONI not getting colder than -0.5. The other thing to consider is that we don’t know how long this relationship will continue to work it. http://www.bom.gov.au/clim_data/IDCKGEM000/rmm.74toRealtime.txt https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php Multiyear La Niña groupings below with peak MJO 5-6 strength and the peak ONI from the fall into winter…….Strongest October MJO 5-6 and La Niña ONI leading to best NYC winters of the multiyear group bolded http://www.bom.gov.au/clim_data/IDCKGEM000/rmm.74toRealtime.txt October 2024….Phase 5 peak +2.762…ONI….latest weekly only -0.3 October 2022…Phase 6 peak +2.177…..ONI….-1.0 October 2021….Phase 5 peak +2.087….ONI….-1.0 October 2020…Phase 5 peak +2.818….ONI…..-1.3 October 2017….Phase 6 peak +3.353….ONI….-1.0 October 2016….Phase 5 peak +1.800….ONI….-0.7 October 2011….Phase 6 peak +1.674….ONI….-1.1 October 2010….Phase 5 peak +2.880…ONI…..-1.6

If these preliminary daily AO values hold, then this will be the first 7+ sigma AO swing outside of the December to April period in around a month or less. The lowest reading back on 10-7-24 was -2.445 rising to +4.795 on 10-23 for a +7.240 sigma swing. 4 out of the top 5 greatest AO swings occurred since 2005. So this goes to how amplified and volatile the AO index has become in recent years. Greatest AO swings on record in around a month or less since 1950 and the date on which the maximum difference from low to high or high to low occurred with the numerical value of the swing https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.daily.ao.nao.pna.aao.gdas.120days.csv https://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.ao.index.b500101.current.ascii #1……+10.790……3-11-21 #2…...+9.401…….1-16-16 #3……+9.256……3-2-56 #4……+9.039……4-21-13 #5……+8.522……1-25-05 #6…...+8.462…..1-15-77 #7…….+8.268….3-16-68 #8…….+7.793….2-25-01 #9…….+7.731….3-23-86 #10……+7.720…2-4-11 #11……+7.641…..3-5-70 #12…..+7.502…..1-19-85 #13……+7.387….3-20-78 #14……+7.240….10-23-24 #15……+7117……1-23-52 #16…..+7.066…1-24-08 #17……+7.043…3-19-15 #18……+7.038…2-10-76

Sunday looks like the lowest afternoon dew points of the season with some spots possibly approaching 10° or lower.

The actual +EPO 500 mb vortex near Alaska was pretty was pretty weak in 20-21. It was more of a +WPO Bering Sea low which cominbed with the +PNA at times and the -AO for a mild but snowy winter. 19-20 had a stronger +EPO vortex near Alaska which is why the winter was so mild and snowless combined with the +AO. Our last +EPO dominant 500 mb vortex winter during a La Niña was 2011-2012.

It’s funny that the snowfall climo has actually been better December 1st through 17th since 2011 in NYC than later in the month. NYC hasn’t had a decent late December snowstorm since the Boxing Day blizzard in 2010. My guess is this is related to the warm up we have been getting every year during the 2nd half of the month since 2011. High temperatures of 55+ have been very reliable from the December 17th through 25th. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending snowfall 12-01 to 12-17 2023-12-17 T 0 2022-12-17 T 0 2021-12-17 T 0 2020-12-17 10.5 0 2019-12-17 1.8 0 2018-12-17 T 0 2017-12-17 7.0 0 2016-12-17 3.2 0 2015-12-17 0.0 0 2014-12-17 1.0 0 2013-12-17 8.6 0 2012-12-17 0.0 0 2011-12-17 0.0 0 Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending snowfall 12-18 to 12-31 2023-12-31 0.0 0 2022-12-31 T 0 2021-12-31 0.2 0 2020-12-31 T 0 2019-12-31 0.7 0 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 Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending max temp December 17th through 25th 2023-12-25 62 0 2022-12-25 58 0 2021-12-25 60 0 2020-12-25 61 0 2019-12-25 57 0 2018-12-25 61 0 2017-12-25 55 0 2016-12-25 58 0 2015-12-25 72 0 2014-12-25 62 0 2013-12-25 71 0 2012-12-25 56 0 2011-12-25 62 0

60°+ Octobers have become much more common in recent years. In the old days Octobers were closer to 55°. Julys used to average around 75° and now closer to 80°. Decembers at Newark used to be closer 35° and now 40°. So a 5° rise in the 10 year running means since the 1930s. Time Series Summary for NEWARK LIBERTY INTL AP, NJ - Month of Oct Click column heading to sort ascending, click again to sort descending. 1 2021 64.4 0 2 2017 63.8 0 3 2007 63.5 0 4 1971 63.1 0 5 1990 62.4 0 6 2024 62.2 7 - 1984 62.2 0 7 2023 62.0 0 8 1949 61.6 0 9 1963 61.2 0 10 1995 61.0 0 - 1947 61.0 0 11 2019 60.4 0 - 1954 60.4 0 12 1973 60.3 0 13 1946 60.0 0

Those 850 mb temps should be near +20C early Tuesday for the 70° lows around Iowa. But they should modify quite a bit coming east. Looks similar to the other day when the warm spots went 80-85 in NJ. That should be good for more record high potential at around Halloween as the surface forecast highs have been beating forecasts with the record dry pattern.

The extreme +EPO pattern this month looks like a blend of influences. La Niña background forcing, marine heatwave east of Japan/-PDO, and some MJO. Notice how the MJO 6 composite is much weaker than the pattern we got. So the other influences are at work. Also notice how well defined the warm pool near Japan and the Cold SST pool near Alaska has become with the +EPO.

The unusual thing about the airmass next week will be how warm the minimums will be to our west. Models have been hinting at lows near 70° in Iowa. This could be a first for so late in the season as the departures are forecast to be off the charts.