bluewave

Record breaking rainfall with the impressive -IOD pattern. La Niña in the modern climate The Bureau of Meteorology has just changed the way it calculates sea surface temperature anomalies for monitoring La Niña (and El Niño). Traditionally, sea surface temperatures inside the Niño 3.4 region were compared to the long-term average of the 30-year period from 1991 to 2020. The difference between the current temperature and the long-term average temperature gave us the anomaly used for monitoring La Niña. However, rising global ocean temperatures caused by climate change have made this method ineffective. Put simply, Earth’s oceans are warming so quickly that the average ocean temperature of the past 30 years is cooler than the current global ocean temperature. This makes Niño 3.4 index values artificially warm when calculated using the traditional method. Instead of comparing the current state of the ocean to a baseline from the past climate, scientists have developed a new method that also incorporates the current average temperature of the global tropical oceans. This new method, with is called the relative Niño index, removes the climate change signal from the equation and makes it more useful in our rapidly warming climate.

Yesterday was the 4th day this month to reach 86° at SMQ. This has lead to the highs running +0.9 this month. Since it has been so dry, the minimums have been running -3.2°.

NYC has had many issues with tree growth on top of the equipment due to neglect when the NWS moved out to Upton back in 1993. So the new ASOS was installed in 1995 under a dense canopy leading to artificial cooling on sunny days. While this artificial cooling is exaggerated when the trees leaf out since 1995, they do get some artificial cooling in winter due to the taller trees and lower sun angle. So it’s no longer a reliable first order site for temperatures in our area last 30 years. I used JFK since its Liberty’s main station that he follows since it’s closer to his home station than the other sites are.

For JFK December was warm and wet finishing +0.9° with 4.44” of precipitation. January was near normal and dry at +0.2 and only 0.65” of precipitation. February was warm and wet finishing at +2.7 and 3.17” of precipitation.

Even JFK has a shot at 85-90° next Friday as the models have a warm downslope flow now.

It didn’t work out for the 2019-2020 winter since the rest of the Pacific was so warm with the record IOD reversal which supercharged the SPV during the fall when it was so positive.

The low volume is why it was so much easier to reach the North Pole this summer. Extent is only a one dimensional measurement of where the edge of the ice field is. But now there is so much open and thin ice behind that edge that it’s losing its relevance as a useful metric for describing the state of the sea ice. Since in the old days there was solid MYI older ice behind the edge of where the ice was. The Barents Observer ‪@thebarentsobserver.com‬ Follow "What struck me most: the ease of access through what used to be a far more ice-covered region", expedition leader Jochen Knies tells us, "We had been sailing through open water at 6–8 knots, something unthinkable three decades ago." See our report straight from the North Pole! #climatechange “I didn’t hear the usual grinding of ice” When a Norwegian vessel reached the North Pole this week, the scientific team made an alarming discovery. www.thebarentsobserver.com September 4, 2025 at 7:09

The volume is close to the lowest on record for this time of year since the ice is so thin due to the record MYI melt over the years. This allows the big disparity between extent and area. As the concentration is also near record lows. Zack Labe ‪@zacklabe.com‬ Follow ⚠️ While extent will not be setting any annual minimum records this year, the average thickness of #Arctic sea ice is actually at historic lows for this time of year (in the dataset by PIOMAS). Thinner ice is younger and usually more fragile. More graphics of volume: zacklabe.com/arctic-sea-i... ALT September 10, 2025 at 8:07 AM Everybody can

MPO made it down to 41° at the end of August which was the coldest since 2000. But not really that cold prior to 2000. The drier conditions allowed them to make it to the 11th coldest reading for August. The warmth back in June was more impressive. It was their first June 93° maximum temperature. Time Series Summary for Mount Pocono Area, PA (ThreadEx) - Month of Aug top 10 lowest temperatures Click column heading to sort ascending, click again to sort descending. 1 1986 31 0 2 1965 32 0 - 1907 32 0 3 1987 33 4 - 1941 33 0 - 1940 33 0 4 1982 34 0 - 1976 34 0 - 1942 34 0 - 1923 34 0 - 1910 34 0 - 1908 34 0 - 1904 34 0 5 1979 35 0 - 1921 35 0 - 1916 35 0 6 1972 36 0 - 1971 36 0 - 1968 36 0 - 1934 36 0 - 1927 36 0 - 1912 36 0 - 1911 36 0 7 1992 37 4 - 1989 37 6 - 1988 37 5 - 1963 37 0 - 1947 37 0 - 1946 37 0 - 1922 37 0 - 1915 37 0 - 1909 37 0 - 1905 37 0 - 1903 37 0 8 1981 38 0 - 1977 38 0 - 1930 38 0 - 1924 38 0 - 1919 38 0 9 1969 39 0 - 1964 39 0 - 1949 39 0 - 1944 39 0 - 1935 39 0 - 1906 39 0 - 1902 39 0 10 2000 40 0 - 1974 40 0 - 1966 40 0 - 1962 40 0 - 1952 40 0 - 1950 40 0 - 1936 40 0 - 1929 40 0 - 1917 40 0 11 2025 41 0 - 1984 41 0 - 1983 41 0 - 1958 41 1 - 1957 41 0 - 1954 41 2 Time Series Summary for Mount Pocono Area, PA (ThreadEx) - Month of Jun warmest maximum temperatures Click column heading to sort ascending, click again to sort descending. 1 2025 93 0 2 1952 92 0 - 1933 92 0 - 1914 92 0 3 2011 91 0 - 1911 91 0 4 2012 90 0 - 1964 90 0 - 1957 90 3 - 1956 90 0 - 1953 90 0 - 1908 90 0 5 2021 89 0 - 2008 89 0 - 1944 89 0 - 1943 89 0 - 1934 89 0 - 1925 89 0 6 2024 88 0 - 2023 88 0

Much easier to get a strong -WPO with a relaxed Pacific Jet not constantly eroding the ridge.

The ridge axis was centered just off the West Coast during the 13-14 winter on the wettest storm days for NYC leading to that much snowier outcome than last winter. But the Pacific Jet was significantly weaker. So it allowed the 500mb ridge to remain in place and not get weakened and undercut by such a fast Pacific Jet. The lack of kickers coming into the West Coast during 13-14 with the weakened Pacific Jet allowed the colder storm track just southeast of NYC with numerous BM redevelopers. The Southeast ridge was much weaker and further east than recent years. 18 storm days for NYC DJF 13-14 with .20+ of precipitation

I have been discussing this for a while now. The rapid expansion of the mid-latitude ridging has been altering the way that the higher latitude teleconnections have been occurring relative to the past. We have also been seeing a much faster Pacific Jet with the record mid-latitude SSTs under these expanding ridges.

It was mostly that the +PNA was getting undercut by the very fast Pacific Jet. The composite below is for the heaviest precipitation days last winter from Philly to Boston. The energy diving into the trough to our west during the storms pumped the Southeast ridge allowing the wettest storms to cut to our west.

The recent dry pattern stretching back to last summer has mostly affected the soil moisture and vegetation. It was really only parts of NJ that had issues with the very low reservoirs last fall. As the NYC watershed upstate didn’t run into any low water supply issues. Long range precipitation forecasting is very low skill. We had a 500 year drought back in the 1960s followed by a steady increase in rainfall. While the drought from 1999-2002 did result in NYC watershed restrictions and low reservoir levels, it wasn’t as bad as the 1960s. We entered a much wetter pattern back in 2003. All our dry periods since then have been short and the rebound to wetter following them was more impressive. So we will need more time to see if the major drought covering Canada and parts of the CONUS is some type of new pattern the last few years. In the mean time the dry pattern has been influencing or daily temperature range. The low temperatures have been running significantly cooler than the highs. So this has lead to the great radiational cooling in places like Walpack, NJ. But the high temperatures have been beating guidance on the days with close to full sun and offshore flow.

Both the GFS and Euro have 850 mb temps which would support 90° highs by later next week at the usual warm spots if the flow becomes SW with full sun. But they have been wavering on whether we get SW or more onshore flow and amounts of clouds. So if the flow stays more onshore, then the warm spots will probably only top out in the mid 80s.

The EPS longer range was too cool for yesterday. It originally had mid 70s from its older forecasts. But the warm spots it to the low 80s yesterday. Data for September 11, 2025 through September 11, 2025 Click column heading to sort ascending, click again to sort descending. SOMERSET AIRPORT WBAN 83 NEWARK LIBERTY INTL AP WBAN 82 Newark Area ThreadEx 82 TRENTON-MERCER AIRPORT WBAN 81 Trenton Area ThreadEx 81 MILLVILLE MUNICIPAL AIRPORT WBAN 80 ATLANTIC CITY INTL AP WBAN 80 TETERBORO AIRPORT WBAN 80 CALDWELL ESSEX COUNTY AP WBAN 80 SOUTH JERSEY REGIONAL AIRPORT WBAN 80 Atlantic City Area ThreadEx 80 PENNSAUKEN 1N COOP 80

Models bring back the mid to perhaps upper 80s again going forward for the usual warm spots. Much drier pattern returns as the recent rains were just a blip in the expanding drought pattern. The cool departures will begin shrinking. If we get a warmer Sep 21 to 30, then the month could finish with a + departure.

It didn’t work out this past winter and we saw one of the strongest +PNA patterns from December into January since 1948. But you are correct that prior to this winter it was a good indicator. Even though the CPC registered ad a +PNA in February, the 500mb PNA had a more negative look. In any event, the winter PNA has been trending more positive since 1948.

That’s why during the fall of 2023 I was pointing out the WPAC to IO would have more influence than we typically get with such strong El Niños. It lead to me doubting the Euro seasonal forecast of the typical Nino trough with colder conditions in the Mid-Atlantic and Southeast. The ridging in Canada was also stronger and more extensive than we typically see with El Niño events building down into the East which we usually see with La Ninas. So effectively a hybrid pattern with the warmest features of an El Niño and La Ninas merged together. We got early hints this would be the case back in May 2023 when the historic ridge developed over Canada leading to the record wildfire season. So there are clearly multiple areas of record SST warmth contributing to the overall pattern. In the old days we could just look at Nino 3.4 and have a reasonable assumption of what the pattern would look like. Now as I have been saying we have to deal with competing influences from these numerous areas of record SST warmth. This has been one of the reasons these seasonal models have been having so much of a challenge with the recent winter forecasts. The stock El Niño and La Ninas composites from the colder climate era are not manifesting in the same ways anymore. We first got a sample of this when the El Niño forecasts in 2018-2019 and 2019-2020 failed to couple due to the record SST warmth from the IO into the WPAC.

Yeah, the last cold and snowy month around our area in January 2022 actually had a strong +NAO pattern. We were able to get that great MJO 8 and have one cold snowy winter month. But the ridge axis over the Rockies was a little too far east so this favored coastal areas for the heavy snows instead of areas south and west of NYC.

The JMA seasonal just updated for the winter. It was the only model that got the 2013-2014 winter correct with its fall forecasts. This time it has a much different look. It has a more +PNA pattern than we typically get with a La Niña. So it has a Baja ridge instead of the deep trough we had there in 2022-2023. My guess is that this is a continuation of the ridging and warm water we have been seeing near the West Coast this summer. In the East we have the familiar -AO Greenland block linking up with the Southeast ridge. So a milder winter in the East than last winter. As always these extended forecasts much of the time are low skill. So I just include here for informational purposes. https://ds.data.jma.go.jp/wmc/products/model/map/7mE/map1/zpcmap.php Famous forecast from September 2013 showing the record TNH winter

The Euro lost the cutoff low for early next week. It’s replaced by a 591 dm ridge to our west. So it has mid 80s from Sunday right into next week. New run Old run

This is where we get into non-linear climate shifts as opposed to the more generic and bland sounding CC term. From around 1880 to 1982 we were more or less in a common climate era as the temperature didn’t change that much. Then once emissions began to accelerate after 1980 temperatures began to rise at faster rate. The 1970s were the last time the CONUS had top 10 coldest winters. The next era was from 1982 to 1997 when be began to notice a faster rate of warming than before 1982. Regionally we were still getting very cold winters during this period. But the cold wasn’t as widespread as back in the 1970s. The first real jump in global and national temperatures occurred in 1998. So the next era with similar temperatures occurred from 1998 to early 2015. Some regions like the Midwest and Great Lakes were able to have a very impressive cold and snow in 2013-2014. But this cold couldn’t reach the magnitude across the CONUS that it did during the 1970s. So it was more focused into your area. 2015-2016 was the greatest shift or jump in temperatures that we have ever seen. This marks the beginning of a much warmer era where none of the winters since then have been able to rival any of the snow and cold records experienced as recently as 2009-2010 to 2014-2015. This last decade was the warmest on record during the winters for the CONUS by a significant margin. So we went from CONUS widespread cold in the 1970s to more narrowly focused regional cold prior to 2015-2016. The cold outbreaks since then have been regionally focused more around 30-45 days rather than the 90 day + regional cold of 13-14 and 14-15. The geographic footprint and duration of the cold has been getting shorter. Following the 2015-2016 baseline temperature shift or jump, the cold outbreaks between have been more narrowly focused and of shorter duration. The area around Rockford, IL set a new all-time low in January 2019 but the duration of the extreme cold wasn’t that long. My area in the Northeast had a great 2 week cold period from late December 2017 into early January 2018. But this didn’t last and was followed up by our first 80° February warmth ever. Fast forward to February 2021 for the record cold focused in the Plains for around a month. But the magnitude of the warmth in December 2021 around DFW was greater than that of the cold in February 2021. Next we experienced another global and national baseline temperature shift or jump to higher during 2023-2024. So the core cold this winter was again more narrowly focused and didn’t rank very high as it followed the 4th warmest December on record for the CONUS. The common theme since 2015-2016 has been shorter and more regionally focused cold events surrounded by periods of higher ranking record warmth.

Yeah, hoping the Euro is correct about the heavy rain potential with the omega block and cutoff low next week.

The seasonal models at this very early stage seem to like the idea of a very amplified Aleutians ridge. I am not looking at these long range forecasts for the exact locations of the ridge-trough axis yet. But several solutions both keep the trough axis to our west. Would match recent years where we get a Southeast Ridge or WAR influence for the Northeast. I want to see what the MJO activity and the rest of the October pattern looks like before refining the outlook more than these generalities.