donsutherland1

A generally milder than normal pattern will likely continue through next Wednesday. However, exceptional warmth appears unlikely. The closing days of November will likely turn colder. There is potential for New York City's Central Park to experience its first freeze of 2025. The 1991-2020 normal first data is November 21. The 1961-1990 baseline was November 11. Last winter's first freeze occurred on November 30. The opening days of December will turn milder. However, colder conditions could begin to develop during the second half of that week and continue through the second week of December. Severe cold appears unlikely through at least the first 10 days of December. Afterward, the pattern evolution will depend, in part, on how the imminent stratospheric warming event propagates. Meanwhile, today will be Central Park's 1,393rd consecutive day without daily snowfall of 4" or more. The record of 1,394 days was set during February 22, 1929 through December 16, 1932. That stretch ended with 6.7" daily snowfall on December 17, 1932. The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -0.7°C for the week centered around November 12. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.16°C and the ENSO Region 3.4 anomaly has averaged -0.65°C. La Niña conditions will likely continue through at least mid-winter. The SOI was +31.56 today. The preliminary Arctic Oscillation (AO) was +1.436 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 86% probability that New York City will have a cooler than normal November (1991-2020 normal). November will likely finish with a mean temperature near 46.6° (1.4° below normal). Supplemental Information: The projected mean would be 1.1° below the 1981-2010 normal monthly value.

That’s true. Unfortunately, there’s no daily TNH index to quantify things.

Below is an illustration of an extreme forecast that is being pushed on Twitter/X despite the lack of evidence to actually support the idea (e.g., small pool of deep cold in the Northern Hemisphere) and the lack of skill in guidance from this far out: "Lower Rio Grande Valley" doesn't specify a specific point or location for purposes of verification, so it will be excluded. Here's the forecast coupled with December 2000-2024 statistics: This illustrative example will be verified at the end of December. Given the estimated probabilities for various outcomes, the odds are strongly against the extreme forecast verifying in more than one of the above locations.

Several things: 1) There remains a lot of uncertainty how the stratospheric warming will propagate. Propagation could be a big factor in prolonging/strengthening or bringing back Atlantic blocking. 2) Even as stratospheric warming often (not always) propagates favorably to build or prolong/strengthen Atlantic blocking, one should not immediately dismiss hints of evidence to the contrary. Confirmation bias is bad for forecasting. Such evidence exists e.g., here's the AO forecast from the EPS 46-day forecast: Although the below table talks about considering climate change-related impacts on forecasts, I highlighted the section that relates to how and why confirmation bias skews forecasts: A systematic forecasting framework allows one to acknowledge such evidence while avoiding rash decisions from model noise. As I don't have a crystal ball to have 100% confidence in whether or not the above AO forecast will verify, I have made a note to continue to monitor developments. Needless to say, there is more to it than such a framework. Each scenario has clusters of outcomes (not discussed above). It should be noted that such frameworks don't guarantee accuracy, but they do reduce the risks that can otherwise lead to bad forecasts, especially when one is dealing with timeframes over which model skill is limited or worse. Finally, the 11/22 12z guidance has reaffirmed the December 1-10 idea. Indeed, more than half of the 11/22 0z EPS ensembles suggested 1" or more snow in Detroit and Toronto (a good signal for measurable snow prospects from this far out). I expect those figures to hold up with the 12z cycle.

Yes. I used a full progression through Phase 2 for fuller insight. I plan to take a closer look at the MJO cases.

The teleconnection idea (predominant state during the periods) is based on the GEFS and EPS, including the weekly EPS ideas. That's why I noted that the probability for Scenario 3 has increased somewhat, as some of the guidance now moves toward a more robust AO+. The consensus remains a persistent PNA- (closer to neutral but not positive). Here's the latest GEFS forecast going into December (preponderance of ensemble members show a PNA<0):

And going beyond the lack of skill in MJO forecasts beyond 10 days, other factors can overwhelm it. Sometimes even high amplitude passages through Phase 8 during passage through Phases 7-2 don't generate a wintry response in North America. December 1-12, 1990 is one example. March 1-25, 2023 is another example, even as it was an off-the-scales passage through Phase 8.

Here's my thinking based on the latest guidance and some of the longer-range guidance. I focus on what I believe are the three biggest potential scenarios for much of December.

The 0z EPS rolls the cold forward pretty much as one would expect with a WPO-/EPO-/AO-/PNA- pattern evolution. One sees how the Great Lakes/Upper Midwest is the focus of the cold while warmth proves very persistent in the Southeast. 288 hours: 312 Hours: 336 Hours: 360 Hours: The usual caveats concerning skill apply that these timeframes. Moreover, how the stratospheric warming propagates will influence the pattern evolution for the second half of the month.

I wanted to illustrate that CPC isn’t panicking. This map at that timeframe is along the lines of what many of us are thinking. It’s very close to my baseline scenario.

The latest week 3-4 CPC outlook:

That's a great map.

A generally milder than normal pattern will likely continue through next Wednesday. However, exceptional warmth appears unlikely. The closing days of November will likely turn colder. Meanwhile, today will be Central Park's 1,392nd consecutive day without daily snowfall of 4" or more. The record of 1,394 days was set during February 22, 1929 through December 16, 1932. That stretch ended with 6.7" daily snowfall on December 17, 1932. The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -0.7°C for the week centered around November 12. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.16°C and the ENSO Region 3.4 anomaly has averaged -0.65°C. La Niña conditions will likely continue through at least mid-winter. The SOI was +26.47 today. The preliminary Arctic Oscillation (AO) was +0.707 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 83% probability that New York City will have a cooler than normal November (1991-2020 normal). November will likely finish with a mean temperature near 46.6° (1.4° below normal). Supplemental Information: The projected mean would be 1.1° below the 1981-2010 normal monthly value.

A number of boundary conditions e.g., SSTAs, and teleconnections this year differ from those in recent La Niña winters that saw extremely low snowfall. None of this guarantees a “big” winter, but it does mean the range of plausible outcomes is perhaps broader than what we’ve seen the last few years.