bluewave

It’s remarkable how dramatic a shift the pattern underwent from February 2015 to December 2015. Very deep Aleutian Low north of Hawaii with -EPO +PNA ridge and deep upper low near the Northeast. This was associated with a strong +PDO signature. Then the historic +13 December in the Northeast with strong +EPO-PNA and one of the strongest Southeast Ridges on record. We also began so see the ridge emerging NW of Hawaii where the deep trough had been. While it took several seasons, the atmospheric pattern eventually flipped the PDO to record low levels. The ridge NW of a Hawaii began to expand and become a potent Aleutian Ridge over time. So the pattern continues to this day with an historic 9 warmer to record warm winters in a row for the Northeast.

Not really surprising since we recently set a new 500mb height record over Ontario for this time of year. All the models have been back and forth from run to run. So no continuity. We will probably have to wait for this blocking over SE Canada and New England to weaken a bit and the tropics become more active. As we have seen here these brief dry soil moisture patterns eventually reverse with the heavy rains being more impressive than the preceding dry pattern.

If Aleutian Ridge results in a -PNA with trough axis potentially from the West Coast to Upper Plains then it pumps the Southeast Ridge. We want the Aleutian Ridge with a +PNA like January 22 and ridging building into the Rockies. But most of the time in recent years we had -PNA Aleutian Ridge amplifications which pumped the Southeast Ridge.

It could also be possible that this extreme mid-latitude SST warming is acting like a higher latitude version of an El Niño. So the past year we had a tropical and extra tropical El Niño at the same time. Perhaps the overlap between these two features is having an additive effect.

The warmer SSTs are the result of the record 500mb ridge east of Japan with light winds and more sunshine allowing the SSTs below to warm.

High to the north and low to the south with easterly flow to continue for at least the next 10 days. But some indication that low pressure becomes more dominant near early October as the high finally starts to weaken. We will also have to watch the tropics as the MJO becomes more favorable for development to our south.

Yeah, that’s what I meant by UHI is mostly evident at night. Notice how Phoenix didn’t really stand out with over 100 days this year as there were other Arizona stations with a similar number. But it was the leader in 80° minimums as the urban areas hold onto the heat that builds up during the day. So while climate change lead to urban and rural stations both having their top ranking for warmest summer, Phoenix had many more 80° minimums due to UHI. Phoenix had their warmest minimum average temperature of 87.5°. Casa Grande to the south with a population of only 56K had their warmest average minimum for the summer but it was cooler at 78.6. Care free also had their warmest average minimum temperature at 77.7 but with a population closer to onky 4K. So the differential is the UHI effect. The number 1 ranking is due to climate change. Climate perspectives site for comparison between rural, suburban, and urban sites with rankings, departures, and actual temperatures. https://sercc.com/climate-perspectives/ Data below from XMACIS Phoenix similar number of 100° days at 120. Data for January 1, 2024 through September 18, 2024 Click column heading to sort ascending, click again to sort descending. HAVASU ARIZONA RAWS 125 TACNA 3 NE COOP 124 ROBSON RANCH COOP 121 PHOENIX AIRPORT WBAN 120 Phoenix Area ThreadEx 120 BUCKEYE 5N COOP 119 BULLHEAD CITY COOP 116 EAST MESA COOP 116 LAKE HAVASU CITY COOP 115 Lake Havasu City Area ThreadEx 115 Phoenix lead in 80° minimums at 102. Data for January 1, 2024 through September 18, 2024 Click column heading to sort ascending, click again to sort descending. PHOENIX AIRPORT WBAN 102 Phoenix Area ThreadEx 102 MESA FALCON FIELD WBAN 91 BULLHEAD CITY COOP 86 SCOTTSDALE MUNICIPAL AP WBAN 84 SMITH PEAK ARIZONA RAWS 84 LAKE HAVASU CITY COOP 83 Lake Havasu City Area ThreadEx 83 YOUNGTOWN COOP 78 YUMA PROVING GROUND WBAN 77 YUMA MCAS WBAN 75 Yuma Area ThreadEx 75 BUCKEYE 5N COOP 72 AJO COOP 71 PHOENIX DEER VALLEY MUNICIPAL AP WBAN 70

This was actually the strongest +AO +NAO summer since 2018.

It’s been a while since we have seen a month start off like this.

Your area has been closer to the winter trough which has been focused over Western North America since 15-16 in the means.

Your Upper Midwest region which includes Michigan has been running colder relative to the means than the Northeast since 15-16. The 21-22 winter finished -2.1 relative to the new 91-20 normals. The 18-19 season was -1.5 relative to 81-10 and 17-18 finished -1.6. But 23-24 was your warmest winter since 1895 at +9.2 relative to 91-20. 16-17 was your 9th warmest winter at +4.6 above 81-10 with 15-16 at +5.4 and 6th warmest. https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/regional/time-series/102/tavg/3/2/1895-2024?base_prd=true&begbaseyear=1991&endbaseyear=2020

Yeah, this is a wider view of the situation.

While UHI is the reason for the urban areas like Phoenix running warmer than the rural locations especially at night, climate change is responsible for the whole region having their warmest summer on record including the low population Death Valley area.

Yeah, using 61-90 climo would be a challenge getting another cold winter in the Northeast if we don’t see some type of shift next 5 winters from last 9. The only parts of the U.S. to experience a cold winter relative 61-90 since 15-16 were the PAC NW and Upper Plains Rockies. As we have frequently seen the smaller geographic area Arctic Outbreaks focus in those areas.

No issue here. Just commenting on what you said. For agricultural and utility customers updating climo like the CPC does every 10 years makes sense. But it does minimize the warming trend when just looking at departures and not rankings.

Using the 61-90 baseline doesn’t fundamentally change the big picture. Whether we use 81-10 or 61-90, 14-15 was the last winter with a cold departure in the Northeast. The rankings are always exactly the same. By 81-10 climo 14-15 was -4.1. It was still a cold winter using the 61-90 baseline at -2.0.

Obviously, El Niños dominate the list. But there were some very warm La Ninas in there also for Canada .Part of the reason that our winters have been so warm in the U.S is a lack of cold in Canada relative to past winters. You will also notice how much the 97-98 super El Niño has been eclipsed by numerous weaker El Niños like 23-24 as the climate has continued to warm. Top 10 warmest winters in Canada and ENSO 2024….+5.2C….El Nino 2010….+4.1…….El Nino 2016….+4.0……El Nino 2006….+3.9……La Nina 2021…..+3.7……La Nina 2012……+3.6…..La Nina 1987……+3.1……El Nino 2007…..+3.1……El Nino 2017……+3.0……La Nina 1998…..+2.9……El Nino

The only colder than average winter in Canada since 14 was the 21-22 La Niña. They use a 61-90 baseline which does a better job at the long term temperature trends. Updating every 10 years like the U.S. does makes the warm departures smaller with each update. Even though the ranking of warmest to coldest winter stays the same. But a new warmest winter in 91-20 climate normals will have a smaller departure than if it occurred in previous decades. https://www.canada.ca/en/environment-climate-change/services/climate-change/science-research-data/climate-trends-variability/trends-variations/winter-2024-bulletin.html# Winter national temperature departures and long-term trend, 1948–2024 Long description The time series graph shows that averaged winter temperatures across the country have fluctuated from year to year over the 1948–2024 period. With the exceptions of 2014 and 2022, average winter temperatures have remained above the baseline average since 1996. The linear trend indicates that winter temperatures averaged across the nation have warmed by 3.6°C over the past 77 years, increased by 0.2°C compared to the last winter.

We are on track for one of the most easterly flow dominant Septembers on record. Nearly half the days this month so far at a station like JFK had their strongest gust of the day from an easterly component. The rest of the month should feature most of the days with easterly flow. Direction of strongest daily wind gust at JFK 9-16….NE…19 9-15….SE…25 9-14….S……15 9-13….S…..16 9-12….SE…17 9-11….SSE..18 9-10….N…..20 9-9…..S……27 9-8…..NW…32 9-7…..W…..34 9-6…..E…..20 9-5….E…..22 9-4….SE….23 9-3….N……29 9-2….NW….37 9-1…..SW….13 Forecast

Yeah, the last 9 winters had the strongest Pacific Jet east of Japan to the Aleutians on record back to 1950. It actually intensified more since 2019. These frequent jet extensions are a part of the reason why the winters have been so warm since 15-16 and less snowy back to 18-19 for places like NYC Metro.

Bradford was the most impressive warm record this summer in PA as it beat the previous warmest summer by nearly a full degree rather than the tenth of a degree at Reading. Time Series Summary for BRADFORD REGIONAL AIRPORT, PA Click column heading to sort ascending, click again to sort descending. 1 2024 68.2 0 2 2021 67.3 0 3 2022 67.0 0 - 2020 67.0 0 4 2016 66.5 0 5 2018 66.3 0 6 2012 66.1 1 7 2023 66.0 0 - 2005 66.0 0 - 1991 66.0 0 - 1975 66.0 0 8 1959 65.9 0 9 2011 65.8 0 - 1993 65.8 0 - 1987 65.8 0

I think this is why we have been getting the big model flips from run to run with the rainfall forecasts. Very strong blocking over SE Canada and New England. Cutoff lows underneath are notoriously difficult for models to forecast. This general pattern looks to continue for at least the next 10 days. Even day 11-15 there is some indication that it may try to continue with lows riding north but perhaps weaker high pressure over New England. Another example of the stuck weather patterns of recent years.

I thinks it's due to the higher heights near the Pacific Northwest and Vancouver in recent years compared to the older -PDO era. So we are getting a split -PNA vortex. One piece this week stays up in Alaska and another digs into California. The height rises in the middle register as a +PNA. In the older -PDO era we didn’t see this pattern much since the -PNA vortex was more consolidated. Could also be related to competing marine heatwaves changing the character of how we used to understand the teleconnections in the old days. As we have also seen changes in the North Atlantic with the AO and NAO not as in sync as they used to be. This was evident with the very strong winter -AOs during the 2020s and the NAO more neutral to even positive during those -AO intervals. As recently as 09-10 and 10-11 the -AO and -NAO were more evenly matched during stronger blocking intervals. Split -PNA vortex this week Weaker -PNA vortex in recent years with higher heights near PAC NW and Vancouver during La Ninas and -PDO Stronger and more consolidated -PNA vortex in older era during La Ninas and -PDO

At least 10 days of easterly flow with a big high to the north and low pressure to the south.

Newark actually tied for the most 89° days in a year. This recent era has seen much more onshore flow than from 2010 to 2013. It’s what happens with the strongest ridges setting up near or east of New England. Just enough high pressure to the east allows more SSE flow at Newark.