2024-2025 La Nina

[Terpeast]

1 hour ago, PhiEaglesfan712 said:

I don't think we'll get a 89-90 scenario.

I don’t either, but to me that’s now the worst case scenario.

[bluewave]

1 hour ago, PhiEaglesfan712 said:

I don't think we'll get a 89-90 scenario. November 1989 was cold, and it was already snowing by Thanksgiving. I think we'll more likely get another 2005-06 or maybe a 2020-21. Both were warm Novembers that turned cold at the beginning of December. Both years had a warm period in the middle of the winter, but reverted back to being colder and more snowy in February.

It will be fun to see if we can actually sustain this 500mb pattern long enough to bring the PDO back to neutral by Christmas. While the the trough will be further south than normal for the +PDO, it should reduce the -PDO level the longer it continues. We’ll find out if this is just a temporary shift of the North Pacific circulation. Or the recent -PDO peak is already behind us and we move to a more neutral to positive regime.

 

[donsutherland1]

Five  thoughts on the upcoming colder pattern triggered by a developing EPO block and forecast AO-/PNA+ pattern:

1. The first half of December looks cold in much of the East. A one-week period with a temperature anomaly of 6°-10° below normal is plausible.

2. Initially snowfall options could be limited due to the source region of the air masses.  It remains to be seen whether the recent rainfall in the East and the upcoming storm to the Great Lakes region later this week were exceptions rather than the beginning of the end of the ongoing drought in the Northeast. Until a persistently wetter pattern emerges, my operating assumption remains that the drought will persist. That raises the bar for big snowfall events even as cold should be sufficient to allow for opportunities through at least the first half of December. The Great Lakes region and LES belts should be in good shape. For snowfall, I'd rather be in such cities as Chicago, Detroit, Buffalo and Toronto than Philadelphia, New York City, or Boston.

3. In most cases following exceptional November warmth and a colder first half of December, the second half of the month was not much warmer than normal. Therefore, the odds are now tilted toward a cooler than normal December in the eastern third of the U.S. including such cities as Philadelphia, New York City, Buffalo, Chicago, Detroit, and Indianapolis, among others. Toronto could also wind up colder than normal.

4. The long-range guidance might rush the break in the colder pattern. I suspect that timing closer to the winter solstice than mid-month might be more realistic for the onset of any pattern change.

5. These developments do not necessarily mean that winter won't be warmer than normal as per the seasonal guidance (the seasonal guidance usually does better with three month assessments than month-to-month ones). They do reinforce the idea that the coming winter won't be as abnormally warm as the last two winters have been.

A potential wildcard remains ENSO. The probability of a full-fledged La Niña event (tri-monthly average) has decreased. A neutral-cold outcome remains possible. The relative ENSO Index (RONI) will be consistent with La Niña.

[bluewave]

1 hour ago, donsutherland1 said:

5. These developments do not necessarily mean that winter won't be warmer than normal as per the seasonal guidance (the seasonal guidance usually does better with three month assessments than month-to-month ones). They do reinforce the idea that the coming winter won't be as abnormally warm as the last two winters have been.

Great post. If NYC can finish December at or below 36.0° which would be -3.1 or lower, then my guess is that they will at least have shot at the first colder than average winter in 10 years. While this won’t be a guarantee, 5 out of 7 winters since 1991 with a December at or below 36.0° went on to a colder winter using our new warmer 91-20 climate normals. So the departures below are set to the 91-20 normals where the NYC December average is 39.1° and the winter average is 36.2°

https://www.weather.gov/media/okx/Climate/CentralPark/nycnormals.pdf

All Decembers since 1991 in NYC at or below 36° since 1991 and the DJF average temperature set to the 91-10 departures 

2000……31.1°……DJF departure using 91-10 normals..-2.7

1995…….32.2°….DJF….-4.0

2010…….32.8°…DJF…..-3.4

2017….….35.0°…DJF…...0.0

2005….…35.3°…DJF….+1.1

2009…….35.9°…DJF….-2.4

2002….…36.0°…DJF….-5.0