Meteorological
winter is just around the corner, officially beginning Sunday, December 1st. So, it’s
time to start talking about what may be. The season will have ups and downs,
alternating between warm and cold. At times we could see a few bouts of
bitterly cold air. There will be a chance for a few significant snow events as
well.
What is a
seasonal outlook?
A seasonal outlook is different from short and medium range forecast. Instead,
it tries to predict the overall pattern when it comes to temperature and
precipitation pattern that could occur during the entire season. It attempts to
place some light on the three possible outcomes, above average, average, and
below average. A seasonal outlook deals
with the overall global climate pattern that looks to be prevalent. It is more of an overall snapshot of what to
expect, instead of the a more accurate shorter-term forecast.
The 2024-2025
winter outlook will be divided into two parts. Part one will be based on early
analysis. If I see more interest or the pattern looks to make a big change, I
would issue a part three.
Okay, let’s
take a look at how things might unfold.
Sea
Surface Temperatures:
Last October
This
October.
Comparing last
October to this October we can see some difference and a lot of things that
look similar.
In the
Pacific we can see warm SST in the northwestern Pacific, with more cooling in
the northeast Pacific. The SST in the
equatorial Pacific look much different than last year. Last October we had an
El Nino that was transitioning to ENSO neutral. This year we’re transitioning
from ENSO neutral to what looks like a La Nina. The current SST anomalies in
the western Atlantic are even warmer than last Octobers’.
Teleconnections:
The Atlantic
Oscillation (AO)…
The AO deals
with the strength of the Polar Vortex (PV) and determines whether or not there
will be a supply of Arctic air available to fuel winter weather. I will explain
more about the PV when I discuss the current snow cover. A positive AO
indicates that the PV will be strong and Arctic air will have a greater chance
of cold arctic air staying locked up near the pole while a negative AO
indicates the potential for a weaker PV leading to a greater chance for arctic
air to escape southward. The AO can flip phases on a weekly basis.
The North
Atlantic Oscillation (NAO)…
The NAO, in
its negative state, indicates high-latitude blocking over Greenland. This
lingering area of high pressure causes the flow to stagnate. The storm track is
often underneath it and can result in persistent storminess for the Eastern US.
On the contrary, a positive NAO has no such block and the storm track moves
quickly across the CONUS and out into the Atlantic. Like the AO, the NAO can
switch Phases often.
Can the
eastern US still get winter weather with a positive NAO? Yes, but they’re often
quick-hitters and rarely significant events.
The Pacific
Decadal Oscillation (PDO)…
The PDO
deals with sea surface temperature anomalies over the Northern Pacific (north
of 20° north latitude), as with all teleconnections it has a positive and
negative phase. These phases typically last for decades. The PDO represents the
oceans response to the atmosphere. In
this way it is a prime driver for low pressure systems in the north Pacific,
for example the Aleutian low-pressure system in the Gulf of Alaska. Depending
on how strong this low is, it will have a different impact on wind flow, and the
pressure gradient. If the Aleutian Low is very strong, we tend to see a
stronger southernly flow along the immediate West Coast.
The positive
phase is characterized by cool SSTs north of Hawaii and warmer than average
SSTs in the Gulf of Alaska and along the West Coast of North America. The
negative phase we see the opposite, warmer than average SSTs north of Hawaii
and cooler than average SSTs in the Gulf of Alaska and along the West Coast of
North America.
During the
positive phase the Mid-Atlantic and Northeast is more likely to experience
overall below average temperatures for December, January and February. During
the negative phase the opposite is true, with the Mid-Atlantic and Northeast
likely to experience overall above average temperatures for December, January
and February.
Pacific
North American Pattern (PNA)…
The PNA involves
the flow pattern over the Northeast Pacific. As a result, it is a major player
in the weather pattern over North America. The PNA is very variable, changing
between positive and negative every few weeks.
The PDO and
the PNA are closely linked to each other…
There is a
direct correlation link between the PDO and the PNA. During the winter the
correlation is greater than 0.80.
The PNA is
closely related to the strength of the Aleutian Low and the strength of the PDO
The PNA for
our purposes here, is the PNA is the main driver of the trough ridge pattern
over North America
During a
negative PNA there typically is more overall upper level troughing over the
western U.S leading to cooler and wetter conditions, while the eastern U.S. is
more likely to see overall ridging leading to drier and warmer conditions.
During a positive PNA the eastern U.S. sees more in the way of troughing while
the western U.S. sees more in the way of ridging.
Quasi-Biennial
Oscillation (QBO)…
The QBO is
another prime teleconnection driver of climate. The QBO deals with
stratospheric winds. The negative phase leads to the winds blowing in an
easterly direction, with the positive phase having winds in the westerly
direction. The QBO is a major driver of the strength of the Polar Vortex. When
the QBO is positive the polar vortex tends to be stronger overall. A negative
QBO tends to see a higher likelihood of a weaker polar vortex.
EL Nino Southern
Oscillation (ENSO)...
The ENSO
involves Sea Surface Temperature anomalies across the equatorial Pacific. It has
a warm phase called El Nino, a cool phase called La Nina, when neither is in
place, the ENSO is considered neutral.
Like I said
above last winter was an El Nino, typically that means cooler temperature
anomalies for southern half of the U.S. with a warmer temperature anomaly over
the northern tier. Precipitation during a El Nino typically sees the northern
tier anomalies drier in the northern tier, and wetter in the southern tier. During La Nina we see the opposite occur with
temperature and precipitation anomalies.
The
temperature and precipitation correlation anomalies during La Nina can be seen
in these two graphics.
Physical
Sciences Laboratory
Physical
Sciences Laboratory
We’re in the
process of transitioning from El Nino to La Nina
La Nina:
A La Nina
would affect the weather this winter in the US, he said. The north may
experience colder-than-average conditions while it would be warmer to the
south.
This La Nina
should be weak to moderate, but a weak one is much more likely.
Weak
La-Nina’s tend to be fickle with a lot of variability.
So, teleconnections like the MJO, PNA, NAO and AO will play a huge role in how
things play out week to week as we go through the winter season.
The call for
a colder wetter winter is based on a La Nina forming out West and impacting the
jet stream
I expect the
northern polar jet will be very variable, with the southern subtropical jet
being weaker. This would generally correlate
to seeing wetter anomalies in the north and drier anomalies in the south.
Models:
National
Multi Model Ensemble (NMME)
Precipitation
November –
January
January -
March
Temperature
Nov to Jan
Some
possible analogue winters:
Weak La Nina years
1950-1951,
1954-1955, 1964-1965, 1967-1968, 1971-1972, 1974-1975, 2000-2001, 2005-2006,
2008-2009, 2016,2017, 20017-2018, 2022-2023
Closest match
for Weak La Nina years
2016-2017
ENSO Neutral
Winters
2017-2018
2022-2023
Primary
storm track:
Storm tracks
will be a result of a weak La Nina and strong influence from the NAO and AO. The pattern setting up supports the idea of
Clippers
Lake Cutters
Appalachian
runners
Inland
runners (Miller B nor’easters) that transfer to the coast.
The classic
Miller A nor’easter will be very hard to come by.
Putting
it all together:
Based on the
current look of the teleconnection and the analogue package I’m using for now.
With the
Idea of the polar jet stream being amplified and the subtropical jet being
weaker; we will have a pattern that could support a strong ridge in the west
that would increase the odds of polar air masses into the eastern U.S.
Much of the
winter will be driven by the slowly developing weak La Nina and a positive QBO.
This would mean they will fight each other at times during the upcoming winter.
A positive
QBO will tend to decrease the odds for high latitude blocking, which means we
will see stretches of zonal (west to east) flow. This combination would lead to
a higher likelihood of less cold air outbreaks during the winter. So, while
polar air entering the pattern is there, arctic outbreaks might be more
difficult to happen.
Based on
this we could see winter start out a little more hard-hitting during the 2nd
half of November. With the heart of winter being variable. Then Spring arriving
a bit sooner than we’ve seen the last few years.
I’m going to
break the region into zones. I think this will make it easier to understand
what I’m generally expecting. This will be biased on the 30-year average.
.
Zone one…
Those of
y’all in zone one, will see overall slightly below average temperatures during
December to end of February. As far as general precipitation it should end up
being wetter than average. With the cooler temperatures snowfall should end up slightly
above average to above average as well. I expect those near the Great Lakes
will experience several lake effect snow events. So, the typical snowbelts
should end up with overall above average to well above average snowfall for the
season.
This doesn’t
mean there won’t be warm periods. As I said above, La Nina tends to bring
highly variable conditions so every storm will depend on how the pendulum is
sitting.
Winter while
not the old fashion winters from decades pass, it shouldn’t be all that bad.
Zone two…
This zone looks to see overall near average temperatures,
along with average general precipitation. There will be an issue with mix
events during the winter. As far as snowfall that looks to be overall average
to slightly above average.
Winter will end up being a bit of a
roller coaster, but there should be some snow events.
Zone three…
This zone
looks to see overall average temperatures to slightly above average, along with
average general precipitation. There will be an issue with mix events during
the winter. So, expect to see many events start out as a mix then switch over
to snow, or starting out as snow and changing to a mix. But there will be a
chance for pure snow events. As far as
snowfall that looks to be overall average to slightly below average.
Winter will
end up being very hit and miss.
Zone four…
This zone
looks to see overall Temperatures above average with precipitation near average. Snowfall accumulations will be below to well
below average, when everything is said and done. Unless a storm tracks just
right, I don’t except to see much in the way of snow. some of your storms will
be a mix. But generally, many of them could be all-rain events. It is possible
some places in zone four, won’t see any snow this winter.
Winter will
end up being lack-luster
That very
warm Atlantic..
Above I
mentioned the super warm SST in the North Atlantic. As I’ve said before, there
is no doubt that the oceans and atmosphere are becoming warmer. This is impacting
weather patterns and storm tracks. The
warm water temperatures mean more water is evaporating, while the warmer air
temperatures mean the atmosphere can hold more water vapor.
I have to
try and factor this idea into my outlook. As the ocean/atmosphere dynamics will
lead to a greater chance for above average amounts of heat. This won’t only effect
storm tracks it could also impact storm intensity.
Over the summer, the entire
Northeast saw the effects of this idea; there were several very significant
rain events, that lead to major flooding. This idea will likely impact winter storms,
with more available moisture for storms to drop snow on parts of the region.
Coastal
storms like nor’easters strengthen over warm ocean waters. The interaction of
the warm water and colder polar/arctic air can create monster storms. A La Nina
pattern impacts the jet stream, which reduces the odds for coastal nor’easters.
But depending on what the other teleconnections are doing at the time. Those
warm waters could produce a massive storm.
So northern parts
of the region should see some cold and snow, while the Middle Atlantic and I-95
could see a warmer winter and maybe little in the way of snow. It will depend
on how the AO and NAO behave. The last few winters have had many setups that
resulted in close calls with snowstorms, but one thing or another didn’t line
up, leading to storms being suppressed to the south and east, resulting in a
lack of real winter weather.
Well, that’s
it for part one.
I hope you
found this interesting and educational. As always, I can’t answer questions
about the outlooks from other outlets. But I will always answer all y’all’s
questions in regards to my outlooks and forecast.
Link to part two.
.
