donsutherland1

Temperatures will reach the lower and even middle 70s across the region tomorrow. It will turn slightly cooler for the weekend with highs mainly in the upper 60s and Lower 70s. In the Southwest and parts of California, near record and record heat is underway. The extreme heat will last through the coming weekend. Phoenix and Tucson will experience their highest temperatures so late in the season. Hurricane Helene will make landfall in Florida's Big Bend region tonight as a Category 4 hurricane with a devastating storm surge. Extreme rainfall could spread as far north as the southern Appalachians. Flooding rains will also affect such cities as Atlanta, Columbus, Macon, and Tallahassee. Already, as of 6:45 pm EDT, Asheville, NC has seen 4.72" of rain today. That is the highest daily amount on record for September. Its two-day total of 8.81" exceeds its prior 2-day, 3-day, and 4-day records. Helene's rainfall is unlikely to reach the New York City area. Continuing long-range guidance suggests that October could wind up warmer than normal across much of the U.S. The western U.S. could be particularly warm relative to normal. Widespread October warmth occurred during the last case where the AO fell to -2.000 or below while the PNA rose to +1.000 or above with a cool ENSO Region 3.4 anomaly in late September (2010), as was the case this year. The NAO fell to a preliminary -2.751 on September 24th (all-time September record: -2.371, September 12, 1971). That was the 9th lowest value on record. La Niña winters following September cases where the NAO fell to -1.900 or below featured a predominantly positive NAO. The most recent such winters were 2016-2017 and 2022-2023. The mean temperatures for those winters in New York City were 39.3° and 41.0° respectively. The 1991-2020 normal value is 36.2°. A warmer outcome is favored by the September run of the C3S multi-model forecast for Winter 2024-2025. The ENSO Region 1+2 anomaly was +0.2°C and the Region 3.4 anomaly was -0.5°C for the week centered around September 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.20°C and the ENSO Region 3.4 anomaly has averaged -0.18°C. Neutral ENSO conditions will likely evolve into a La Niña event during the fall. The SOI was -2.49 today. The preliminary Arctic Oscillation (AO) was -1.207 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 58% probability that New York City will have a cooler than normal September (1991-2020 normal). September will likely finish with a mean temperature near 69.1° (0.1° below normal).

From the NWS Greeville-Spartanburg Facebook Page: Already, as of 4:07 pm EDT, Asheville has picked up 4.44" of rain today. That breaks the daily mark of 1.71" from 1956 and the all-time September daily record of 4.40" from September 29, 1964. The 2-day total of 8.53" breaks both the 2- and 3-day rainfall records.

The initial reference was to the "modern period." Most datasets treat 1850-1900 as preindustrial for purposes of climate assessments. The chart only addresses that reference.

Technical details can be found here: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JD029867

Yes. That shows up well on the larger timeframe (1850-2023) available at Copernicus:

Phoenix is in the early stages of an unprecedented last week of September heatwave. This heatwave occurs as Phoenix is experiencing a warming climate. The second half of September has been warming rapidly (4.4F/2.4C from 1961-1990 to 1991-2020). The distribution of 100F (37.8C) and 105F (40.6C) or above readings has risen.

A generally pleasant temperature regime will continue through most or all of the week. it will turn warmer tomorrow. Showers are possible tomorrow, as well. In the Southwest and parts of California, near record and record heat is underway. Phoenix reached 113°, which smashed its daily mark of 108° from 1979 and 1989. It was also that city's latest 113° or above temperature on record by 15 days. The extreme heat will last through the coming weekend. Phoenix and Tucson will experience their highest temperatures so late in the season. Hurricane Helene will make landfall in Florida's Big Bend region tomorrow evening as a major hurricane. Extreme rainfall could spread as far north as the southern Appalachians. Flooding rains will also affect such cities as Atlanta, Columbus, Macon, and Tallahassee. Helene's rainfall is unlikely to reach the New York City area. Continuing long-range guidance suggests that October could wind up warmer than normal across much of the U.S. The western U.S. could be particularly warm relative to normal. Widespread October warmth occurred during the last case where the AO fell to -2.000 or below while the PNA rose to +1.000 or above with a cool ENSO Region 3.4 anomaly in late September (2010), as was the case this year. The NAO fell to a preliminary -2.751 on September 24th (all-time September record: -2.371, September 12, 1971). That was the 9th lowest value on record. La Niña winters following September cases where the NAO fell to -1.900 or below featured a predominantly positive NAO. The most recent such winters were 2016-2017 and 2022-2023. The mean temperatures for those winters in New York City were 39.3° and 41.0° respectively. The 1991-2020 normal value is 36.2°. A warmer outcome is favored by the September run of the C3S multi-model forecast for Winter 2024-2025. The ENSO Region 1+2 anomaly was +0.2°C and the Region 3.4 anomaly was -0.5°C for the week centered around September 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.20°C and the ENSO Region 3.4 anomaly has averaged -0.18°C. Neutral ENSO conditions will likely evolve into a La Niña event during the fall. The SOI was -4.87 today. The preliminary Arctic Oscillation (AO) was -1.207 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 52% probability that New York City will have a cooler than normal September (1991-2020 normal). September will likely finish with a mean temperature near 69.1° (0.1° below normal).

La Niña is on the cusp of developing. Region 3.4 anomalies have fallen to -0.5°C in the most recent weekly average. A weak La Niña and potentially borderline moderate one still seems on course during the latter part of the fall and during the winter.

A generally pleasant temperature regime will continue through most or all of the week. Temperatures could top out in the upper 60s to lower 70s through the middle of the week before a slow warming trend commences afterward. Showers are possible on tomorrow and Thursday. Rainfall amounts should average 0.25"-0.50" in the New York City and Philadelphia Metro areas with some locally higher amounts. In the Southwest and parts of California, another round of excessive heat is now underway. Parts of the region will likely see near record to record high temperatures on several days during the week and weekend. Phoenix could see its highest temperatures so late in the season. In addition, a significant hurricane will likely make northwestern Florida landfall on Thursday. The storm will likely be a major hurricane on landfall given the ongoing marine heatwave in the region and relatively low shear. However, the hurricane's rainfall is unlikely to reach the New York City area. Continuing long-range guidance suggests that October could wind up warmer than normal across much of the U.S. Widespread October warmth occurred during the last case where the AO fell to -2.000 or below while the PNA rose to +1.000 or above with a cool ENSO Region 3.4 anomaly (2010), as was the case with the September 20th teleconnections. The NAO fell to a preliminary -2.751 today (all-time September record: -2.371, September 12, 1971). That would be the 9th lowest value on record. La Niña winters following September cases where the NAO fell to -1.900 or below featured a predominantly positive NAO. The most recent such winters were 2016-2017 and 2022-2023. The mean temperatures for those winters in New York City were 39.3° and 41.0° respectively. The 1991-2020 normal value is 36.2°. A warmer outcome is favored by the September run of the C3S multi-model forecast for Winter 2024-2025. The ENSO Region 1+2 anomaly was +0.2°C and the Region 3.4 anomaly was -0.5°C for the week centered around September 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.20°C and the ENSO Region 3.4 anomaly has averaged -0.18°C. Neutral ENSO conditions will likely evolve into a La Niña event during the fall. The SOI was -8.08 today. The preliminary Arctic Oscillation (AO) was -1.501 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 57% probability that New York City will have a cooler than normal September (1991-2020 normal). September will likely finish with a mean temperature near 69.0° (0.2° below normal).

Yes. Temperature correlation (2000-present):

I suspect that the low sea ice and resulting warming of the open waters is contributing to this increased volatility.

During La Niña winters, this would suggest a predominantly NAO+ winter. During El Niño winters, including 2002-03, it would suggest a predominantly NAO- winter. Still, the sample sizes are small, so such tendencies should be taken with a large dose of caution.

Today's preliminary NAO value is -2.751, which is well below the existing September record. It would also be the 9th lowest all-time. An even stronger NAO block occurred during October 18-22, 2002. Winter 2002-03 was an El Niño winter.

The latest guidance suggests that Phoenix will experience its hottest last week of September on record. Select record heat statistics for the last week of September are below.

A generally pleasant temperature regime will continue through most or all of the week. Temperatures could top out in the upper 60s to lower 70s through the middle of the week before a slow warming trend commences afterward. Showers are possible on Wednesday and Thursday. Rainfall amounts should generally be light. In the Southwest and parts of California, yet more excessive heat is now developing. Parts of the region could see near record to record high temperatures on one or more days during the week. Phoenix could even see its highest temperatures so late in the season. In addition, a significant hurricane will likely make northwestern Florida landfall on Thursday. The potential exists for the storm to be a major hurricane on landfall given the ongoing marine heatwave in the region and relatively low shear. However, the hurricane's rainfall is unlikely to reach the New York City area. Early long-range guidance suggests that October could wind up warmer than normal across much of the U.S. Widespread October warmth occurred during the last case where the AO fell to -2.000 or below while the PNA rose to +1.000 or above with a cool ENSO Region 3.4 anomaly (2010), as was the case with the September 20th teleconnections. The NAO fell to a preliminary -2.472 today (all-time September record: -2.371, September 12, 1971). La Niña winters following September cases where the NAO fell to -1.900 or below featured a predominantly positive NAO. The most recent such winters were 2016-2017 and 2022-2023. The mean temperatures for those winters in New York City were 39.3° and 41.0° respectively. The 1991-2020 normal value is 36.2°. A warmer outcome is favored by the September run of the C3S multi-model forecast for Winter 2024-2025. The ENSO Region 1+2 anomaly was +0.2°C and the Region 3.4 anomaly was -0.5°C for the week centered around September 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.20°C and the ENSO Region 3.4 anomaly has averaged -0.18°C. Neutral ENSO conditions will likely evolve into a La Niña event during the fall. The SOI was -3.98 today. The preliminary Arctic Oscillation (AO) was -1.948 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 51% probability that New York City will have a cooler than normal September (1991-2020 normal). September will likely finish with a mean temperature near 69.1° (0.1° below normal).

Today's preliminary NAO value is -2.472, which would break the September record.

A generally pleasant temperature regime will continue through most or all of the week. Temperatures could top out in the upper 60s to lower 70s through the middle of the week before a slow warming trend commences afterward. Showers are likely on Wednesday and Thursday. Some uncertainty still exists concerning rainfall amounts. In the Southwest and parts of California, yet more excessive heat will develop early this week. Parts of the region could see near record to record high temperatures on one or more days during the week. Phoenix could even see its highest temperatures so late in the season. Early long-range guidance suggests that October could wind up warmer than normal across much of the U.S. Widespread October warmth occurred during the last case where the AO fell to -2.000 or below while the PNA rose to +1.000 or above with a cool ENSO Region 3.4 anomaly (2010), as was the case with the September 20th teleconnections. The NAO fell to a preliminary -1.909 today. La Niña winters following September cases where the NAO fell to -1.900 or below featured a predominantly positive NAO. The most recent such winters were 2016-2017 and 2022-2023. The mean temperatures for those winters in New York City were 39.3° and 41.0° respectively. The 1991-2020 normal value is 36.2°. A warmer outcome is favored by the September run of the C3S multi-model forecast for Winter 2024-2025. The ENSO Region 1+2 anomaly was -0.2°C and the Region 3.4 anomaly was -0.2°C for the week centered around September 11. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.27°C and the ENSO Region 3.4 anomaly has averaged -0.10°C. Neutral ENSO conditions will likely evolve into a La Niña event during the fall. The SOI was -1.07 today. The preliminary Arctic Oscillation (AO) was -2.493 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 53% probability that New York City will have a cooler than normal September (1991-2020 normal). September will likely finish with a mean temperature near 69.0° (0.2° below normal).

Today, the NAO fell to -1.900, which is very unusual for September. Since 1950, there have been three La Niña winters that followed such outcomes (1971-72, 2016-17, and 2022-23). All three favored a predominantly positive NAO during the winter. All three winters also favored warmer than normal winters in the eastern third to half of the CONUS. 2022-23 had solar activity that is most consistent with what is likely during the upcoming winter. Winter 2016-17 followed a strong El Niño winter, but the PDO was positive (very unlikely this time around). The composite for the two most recent winters (selected because they fall in the contemporary climate regime): For comparison, the latest C3S multi-model and CPC outlooks follow: C3S: CPC: It's early, so the C3S, which did well last winter from this timeframe (but hasn't always fared as well, might be aggressive and overly expansive with the warmth. For example, the Great Lakes Region (Chicago to Toronto) might wind up milder than normal, but not excessively so, with normal to somewhat above normal snowfall. Overall, the latest NMME (9/8 0z initialization) has an outlook that closely resembles the anomaly patter (but not necessarily the values) shown on the C3S. The CFSv2 offers a sort of compromise between the CPC outlook and the C3S.

I suspect 2021-22 will probably offer better insight, but it's still early.

It's a factor to watch. However, at this time, I suspect that the very strongly negative PDO will have a larger impact on the pattern, which would impede a deep or sustained EPO-.

Not all, but some seasonal forecast methodologies are failing. On Social Media, there were several winter forecasts that assumed, for example, that the East would be cold and snowy (it was again much warmer than normal with much lower than normal snowfall). CPC did well. The North Pacific marine heatwave is impacting PDO. That marine heatwave wasn't around in the 1980s or 1990s. Moreover, the likelihood of such a heatwave is much greater today than it was then.

Cooler air will arrive overnight. Temperatures could top out in the upper 60s to lower 70s through most of next week before a slow warming trend commences. Showers are also possible during the second half of next week. In the Southwest and parts of California, yet more excessive heat could develop early next week. Parts of the region could see near record to record high temperatures on one or more days next week. Early long-range guidance suggests that October could wind up warmer than normal across much of the U.S. Widespread October warmth occurred during the last case where the AO fell to -2.000 or below while the PNA rose to +1.000 or above with a cool ENSO Region 3.4 anomaly (2010), as was the case with the September 20th teleconnections. The ENSO Region 1+2 anomaly was -0.2°C and the Region 3.4 anomaly was -0.2°C for the week centered around September 11. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.27°C and the ENSO Region 3.4 anomaly has averaged -0.10°C. Neutral ENSO conditions will likely evolve into a La Niña event during the fall. The SOI was +1.31 today. The preliminary Arctic Oscillation (AO) was -2.603 today. That is the second lowest value for September 21. Only September 21, 2010 (-2.675) had a lower value. That is also the fifth lowest value for any September day. Based on sensitivity analysis applied to the latest guidance, there is an implied 57% probability that New York City will have a cooler than normal September (1991-2020 normal). September will likely finish with a mean temperature near 68.9° (0.3° below normal).

It just missed, as I posted above (4.073 million square kilometers, 6th lowest figure).

I'm not sure whether the 1950s era temperatures preceding the break were from a somewhat different location. Here are the Del Rio Area threaded summer means:

Climate change is influencing patterns, particularly from large-scale marine heatwaves. The current PDO- is one example. The increased frequency of the MJO's residing in the Marine Continent phases is another. That's why some seasonal forecasting methodologies based largely on analogs (even when the variables closely fit) now consistently perform poorly.