bluewave

After the lowest August 500mb heights on record for Iceland, Greenland is getting ready to experience some of its strongest 500mb blocking on record for the month of September. We have been seeing these big swings in the AO and NAO since just after 2010. So this makes extended forecasting of those indices very tricky at any interval beyond the 1 or 2 week range.

An unusual strom track is always possible when we get such extreme near record Greenland blocking.

Yeah, we want a more easterly track in order for a place like Newark to avoid the first under 1.00” month since May 2023 and July 2022. Monthly Total Precipitation for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. 2024 5.52 1.75 7.99 3.85 2.79 1.75 3.59 6.69 0.08 M M M 34.01 2023 4.31 1.41 3.32 8.07 0.89 2.66 6.26 4.27 8.31 4.02 2.91 7.55 53.98 2022 4.06 2.65 2.38 4.36 5.23 2.40 0.55

Yeah, the drier pattern here after the very wet summer is becoming evident now. Lawns have started turning brown with considerable leaf drop. Tough to get a happy medium these days between the brief dry patterns and big deluges.

Just pointing out the early September pattern. Very tough to get any year to play out exactly as a previous one especially with the evident amplitude differences going back the last several months. But I will say that some of the seasonal models lowest skill with La Nina’s in recent years seems to have been with the Western Trough details.It was one of the biggest surprises was with the 16-17 La Niña. It was as if the 15-16 super El Niño precipitation got delayed a year for California. So won’t try to pinpoint Western details this early in the game.

It was the first time that the summer 500mb ridge was this strong from east of Japan to south of the Aleutians .

After the historic flood in Suffolk last month September is off to the driest start on record at Islip. Time Series Summary for Islip Area, NY (ThreadEx) Click column heading to sort ascending, click again to sort descending. 1 2024-09-18 0.06 0 2 2019-09-18 0.33 0 - 1986-09-18 0.33 0 3 1985-09-18 0.36 0 4 1983-09-18 0.38 0 5 1979-09-18 0.49 0 6 1997-09-18 0.54 0 7 2001-09-18 0.64 0 8 1994-09-18 0.68 0 9 1965-09-18 0.69 0 10 1982-09-18 0.70 0

The September 500mb pattern so far is most similar to 2022. The 500 mb anomaly center locations are far are fairly close. But this time the Aleutian Ridge is stronger and the North Atlantic ridge east of Canada a little weaker. But its forecast to strengthen in the coming days.

We will probably need some help from the tropics next week to see a pickup in the rainfall. The best bet would be a system in the gulf with some type of inverted trough or PRE extending northward into the region. Then the rest of the forecast into early October would be contingent on development and track details.

This is another season which confirms that the big shift in the Arctic occurred with the record multiyear ice drop back in 2007. We have had over a decade now without the extended May to August dipole patterns from 2007 to 2012. But none of the years since have been able to recover back to the extent, area, or multiyear ice levels which were common before 2007. https://www.nature.com/articles/s41586-022-05686-x Manifestations of climate change are often shown as gradual changes in physical or biogeochemical properties1. Components of the climate system, however, can show stepwise shifts from one regime to another, as a nonlinear response of the system to a changing forcing2. Here we show that the Arctic sea ice regime shifted in 2007 from thicker and deformed to thinner and more uniform ice cover. Continuous sea ice monitoring in the Fram Strait over the last three decades revealed the shift. After the shift, the fraction of thick and deformed ice dropped by half and has not recovered to date. The timing of the shift was preceded by a two-step reduction in residence time of sea ice in the Arctic Basin, initiated first in 2005 and followed by 2007. We demonstrate that a simple model describing the stochastic process of dynamic sea ice thickening explains the observed ice thickness changes as a result of the reduced residence time. Our study highlights the long-lasting impact of climate change on the Arctic sea ice through reduced residence time and its connection to the coupled ocean–sea ice processes in the adjacent marginal seas and shelves of the Arctic Ocean.

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.