donsutherland1

I screwed up on the last part. I had been looking at a lot of temperature charts and used the wrong scale when switching to winds.

The closest five analog PDO cases (based on RMSE) suggest that the PDO will likely rise during the winter, but remain negative. If one looked at the top 10 cases, just one (2010-11) showed the PDO rising above zero during the winter. That case ranked 10th in terms of RMSE. The October 2025 PDO value was -2.40.

I agree. The analog cases I used consider ENSO Region 1+2.

I see your point. The argument for RONI is that the overall warming of the Pacific is not temporary or cyclical. The use of traditional ENSO metrics i.e., R3.4 anomaly, ONI, etc., has beenb contaminated by the overall warming of the Pacific. In their present form, El Niño events are amplified while La Niña ones are shown as weaker. As the warming continues, La Niña events could even be obscured. Winter 2024-2025 is one such case. It showed up as neutral-cold on ONI, but was a La Niña case according to RONI. Some useful literature on the use of a relative index: https://iopscience.iop.org/article/10.1088/1748-9326/abe9ed https://journals.ametsoc.org/view/journals/clim/37/4/JCLI-D-23-0406.1.xml Australia's Bureau of Meteorology (BOM) has already made the switch to RONI. Here's a table from the article concerning the BOM's shift:

It could. That's the wild card so to speak. 2017-18 is in the analog mix. It saw 7.7" snow in December and 40.9" overall. 2016-17 had 3.2" in December and 30.2" overall.

When it comes to sudden stratospheric warming events (SSWEs) or major stratospheric warming events (MSWEs), these events can be a response to strong blocking (bottom-up), which often reinforces and extends the blocking. They can also be top-down events that lead to a downward-propagating tropospheric response. Typically, there is approximately a 10-20-day lag, where the NAO/AO move toward and into a negative state. This blocking can then persist for 30 days and longer, with some fluctuations. Tropospheric responses to vortex-splitting events are often stronger than those for displacement events. However, more often than not, the larger portion of the split vortex winds up in Eurasia and the smaller one moves into North America. So, if the sudden or major stratospheric warming event occurs in the closing days of this month, its impact on North America would probably start to be seen near mid-December +/- few days. Right now, a major event with a wind reversal isn't assured.

I agree. Hopefully, CPC will start using RONI as its official measure. In any case, the relationship holds true with ONI or RONI.

For another illustration of the importance of the PNA for parts of the East, the EPS is forecasting a WPO-/EPO-/AO-/PNA- pattern for the first 10 days of December. Setting aside skill issue at that range, here's how things have fared 1980-2024 when the only difference was a PNA- vs. a PNA+. I used NYC, but the same applies broadly to the Middle Atlantic Region.

Tomorrow through Friday will see highs mainly in the upper 40s to lower 50s. Another brief push of cold air could arrive to start the weekend. Overall, temperatures will likely remain generally below normal through Saturday. Sunday could turn briefly milder before another cool air mass moves into the region. Some showers are possible on Sunday. The ENSO Region 1+2 anomaly was -0.2°C and the Region 3.4 anomaly was -0.7°C for the week centered around November 5. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.07°C and the ENSO Region 3.4 anomaly has averaged -0.55°C. La Niña conditions will likely continue through at least mid-winter. The SOI was -7.13 today. The preliminary Arctic Oscillation (AO) was -1.861 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 November (1991-2020 normal). November will likely finish with a mean temperature near 47.4° (0.6° below normal). Supplemental Information: The projected mean would be 0.3° below the 1981-2010 normal monthly value.

COP30 is on track to become yet another farce in the process to address climate change. Its agenda contains no items on mitigation. It contains no discussion of a phase-out of fossil fuels. At the same time, it punts the discussion of the Paris climate goal and progress toward that goal to COP31. It is yet another ratification of a status quo that is the primary driver of climate change.

It does seem to become skillful within a week of the following month.

Here's the data for December vs. January-April snowfall for New York City for La Niña winters 1979-80 through 2024-2025. 2024-2025 is officially listed as cold neutral. December 2024 had 2.8" of snow.

Here's the evolution of the CFSv2 forecast for December. It should be noted that all the timeframes, the CFSv2 is not yet in its high skill area.

For Washington, DC to New York City, a PNA+ is far more common for days with 6" or more snowfall except during the second half of February and afterward when the wave lengths shorten. New York City statistics since 1950: For January, when wave lengths are at their longest, a PNA+ was present for 92.5% of days with 6" or more snowfall in New York City. For Boston, the PNA+ plays a smaller role.

A classic La Niña winter appears to be on the way. There will likely be some interesting developments, along the way, particularly if a sudden stratospheric warming event materializes in late November or early December. Then, the potential would exist for a cold end to December and possibly first half of January, if the polar vortex is displaced. Based on ENSO and the teleconnections, there is a signal for the coldest month relative to normal to be January in the Gulf Coast and Southeast. Perhaps the Arctic outbreak of November 10-11 that saw the coldest anomalies affect the Southeast offers a hint of how things might unfold in January. The C3S multi-model system appears to be quite aggressive with above normal temperatures. Last winter, there were some indications that it was too aggressive with the warmth, but I deferred to the guidance. That proved to be a bad mistake leading to an overly warm idea. This time, I am giving more weight to the analog cases for insight. The ECMWF seasonal forecast appears to be a better fit with the final cases I selected based on ENSO and the teleconnections. My selected comparison cases for Winter 2025-2026 are Winters 2016-2017, 2017-2018, 2021-2022, and 2024-2025. C3S Seasonal Forecasts: ECMWF: Analog Cases: ECMWF: December-February 500 mb Progression: Analog Cases: December-February 500 mb Progression: Select Snowfall Estimates: Albany: 45"-60" Baltimore: 10"-15" Binghamton: 80"-90" Boston: 35"-45" Buffalo: 85"-95" Burlington: 75"-85" Caribou: 110"-125" Chicago: 30"-40" Detroit: 40"-50" New York City: 15"-25" Newark: 15"-25" Philadelphia: 10"-20" St. Louis: 10"-15" Toronto: 100 cm - 125 cm Washington, DC: 8"-12"