Matt Makens

I should begin by saying, forecasts made in November struggle. Largely this is
due to the atmosphere which is working to change itself from its summer (~5 wave
pattern) to winter pattern (~3 wave pattern), and during that change, there are
some chaotic moments, especially during November.

When we deal with this, projections can suffer from this "outside noise," and
the relative stability of winter helps improve skill scores for forecasts. The
same can be said for April when we flip-back. With this in mind, the ultimate
transition out of La Niña into a neutral pattern remains to be seen but we have
had some really good consistency in the data for the past few months.

If you prefer a video presentation:

Here's the latest as I see it:

Last Thursday, NOAA/CPC issued their latest probability based forecast for La
Niña. 

As in past updates, we continue to see the trend toward a neutral pattern
something near/in the spring of 2023. This is within the sea surface temperature
projections. The atmosphere doesn't have to transition at the same rate and very
likely is delayed from switching from La Niña to neutral. 

Speaking of the atmosphere, its response to the current La Niña ocean conditions
is strong! October had the third highest SOI (Southern Oscillation Index) value
on record. 

We remain locked in a very strong atmospheric pattern and this likely doesn't
"change on a dime" even as ocean conditions are expected to change in the coming
months. A third consecutive La Niña winter is on the way, that has only happened
two other times. A fourth La Niña winter in a row has not been recorded.

As mentioned above, the atmosphere will take time to adjust, and we may stay in
a La Niña atmospheric pattern for months following the ocean’s transition. By
June, July, August a neutral pattern has the highest probability in both ocean
and atmosphere. For the remainder of the 2023, we have equal probability of
neutral to El Niño conditions (as projected in what modeling can stretch out
that far, as well as in the analog years I have selected); it is a slow
transition into that next phase.

Although not a perfect match, the most recent and most similar transition to
what we can expect may be what we observed from 2013 through 2015. That was a
long-duration transition into a robust El Niño. That was a lengthy process, and
we know the impacts of that El Niño period. I don't know that I would bet the
farm on that transition repeating itself, but it serves as a possible candidate
for comparison sake.

So, we have La Niña with us for awhile. That's one impact on the winter
(December through February) outlook.

Another impact has developed during the past month. A very active storm flow
over Alaska and the Gulf of Alaska has cooled the water in that area of ocean.
As a result, the storm flow is shifting south to follow along that contrast of
where the warm ocean meets the colder ocean. Alaska, as of right now, is going
to see ridging and a much quieter pattern emerge as the storm's and accumulation
of energy will be south of the state. 

The extent of the cooling in the Gulf of Alaska looks far less than last year
but there is still upwelling and potential pooling of more cold water than what
we have observed to date. This, as described, will shift the storm flow and
where we accumulate storm energy which ultimately can shift the Jetstream's
persistent pattern over the U.S. That obviously drives where the best moisture
and coldest of temperatures will be.

There's a third factor for our winter pattern. The extent of a blocking ridge
over the Eastern U.S. and Western Atlantic. The persistence of that ridging will
concentrate the coldest temperatures over the Central U.S. or the weakening of
that ridging will allow colder temperatures to reach the East Coast. In either
case, Colorado sits in the "split decision" zone, as is common with La Niñas. 

What do I mean by that? Well, northern Colorado, particularly the northwestern
mountains, can do well in La Niña winters in terms of snowfall. The southern
areas usually don't do well at all. The Front Range can come away with some
decent snows but the long-term average is drier than normal with La Niña driving
the pattern. Temperatures, sure we can get cold anywhere but we likely see a lot
more of the cold driving in from the northwest and impacting the northeastern
Plains more so than anywhere else.

With what we have observed through today, and ignoring any further changes to
the Gulf of Alaska and the Eastern U.S. blocking, the most likely scenario for
the winter is as follows - and it's a classic picture.

Again, December through February is winter, even if our snow season extends well
beyond that. 

We will need to revisit these conditions and forecasts going through the end of
2022. It'll be interesting to see the extent of the cold waters in the Gulf of
Alaska and how strong that potential blocking ridge will be to our east. A
change in one or the other could bring someone in the U.S. a much different
winter than expected.

La Niña's latest forecast and most likely weather pattern for the winter