This will be long so grab a cup of joe, beer, or your favorite beverage and dive in.
Last year I provided a "first guess" on the fall and winter outlook on October 23rd. Today, six weeks earlier, I will attempt to do the same for this upcoming season. I really
providing an outlook so early and in fact I despise in doing so! Hopefully by the time you read through this post you will get a sense why.
Let me start by saying that there are numerous outlooks already out in internet land. I would bet that the majority are put together by weather hobbyists based on non-scientific reasoning. There are even a fair number, that I have come across, that are completely satirical (just to grab attention?).
Many outlooks will be based purely on the presence of "El Nino". I wish it was that simple. This warm event (El Nino), will have an impact on the weather, but to what extent? I will explain in this post.
But first, I want to briefly go over this next weeks weather. I wish everyone got rain during the past few days, but at least a few got some very beneficial water from the sky. There is one more chance coming up, mainly Thursday and Thursday night. In the satellite below....(click for a larger version)...green lines with arrows represent the winds at the jet stream level. There are several items to note. First, the wind pattern aloft is mirrored in both hemispheres, over the western Pacific along the equator and also across the eastern Pacific near the equator. The former is possibly from the beginning stages of a Madden Julian Osciallation (MJO) (I've discussed this many times in the blog) which will have an impact next week. The latter is helping pump moisture from Hurricane Linda up into the southwest part of the country.
In addition, there is a disturbance aloft (the X just north of Washington). This system will dive southeast and its associated cold front will move through the midwest and central U.S. later Thursday and Thursday night. That will bring thunderstorms to many areas, with the hardest hit probably the eastern 2/3 of Kansas, Iowa and Missouri but also at least scattered activity across many other areas.
The significant cool down will last through the weekend but then next week should be characterized by wide swings in temperatures. In addition, I'm seeing some signs that there might even be some severe weather across the central U.S. sometime next week and into the weekend (probably depends on the evolution of the developing MJO). Also, there might even be tropical activity in the Gulf Of Mexico later next week!
BTW, If I don't get a post done next Monday the 14th, the next opportunity will not be until about the 24th.
For much of the central U.S. (especially the high plains), the weather and climate is characterized by highly
variable conditions, both in short and long time periods. The proximity
to the Rocky Mountains and the Gulf of Mexico moisture source are just
two of the reasons for such variability. But it is much more
complicated than that. There are numerous intra-seasonal,
multi-seasonal, multi-year, multi-decade and even multi-century
ocean/atmosphere cycles that have influences on our weather.
Interactions
with land masses, oceans and the sun are what drives our weather.
Because of millions and millions of interactions across the
globe and the fluctuation of the suns energy, forecasts beyond just a
few days can suffer in accuracy. The
following are just a few of the tele-connection cycles and oscillations
that impact our weather (and feel free to Google these for an
explanation of each):
The Madden Julian Oscillation (MJO)
Global Wind Oscillation (GWO)
El Niño/La Niña - Southern Oscillation (ENSO)
North Atlantic Oscillation (NAO)
Arctic Oscillation (AO)
Pacific Decadal Oscillation (PDO)
Atlantic Multdecadal Oscillation (AMO)
Solar output
A
friend of mine, from back in my college days at the University of
Oklahoma, and I had numerous discussions about the weather and
apparent cycling of weather patterns. Through detailed observations, it was apparent
that even though weather systems moving around the globe were mostly
transitory but with often chaotic movement, there was a subtle observation that
weather patterns would repeat throughout the year. The
upper level atmospheric flow would show very similar behaviors on a specific time scale.
This cycle length appeared to vary from one year to the next and this cycle would start in early fall and dissipate during the last few days of summer.
During the northern
hemisphere Fall, the jet stream (band of westerly winds aloft) will
increase in velocity and traverse from a higher to lower latitude or
vice versa. The jet stream winds occasionally amplify into a
north/south fashion which is an unstable position for this wind energy
to be in. At some point the jet stream will "snap" back into place
(west to east) and thus starts a sinusoidal rhythm.
Once this first rhythm begins, it will eventually repeat and then
continues to do so until the velocity of the wind decreases during the
late northern hemispheric summer months. This cycling pattern of the
winds aloft and the behavior is similar from one cycle to the next. The
cycle length can vary considerably each year (on
the order of 25 to 60 days). The 2013-14 cycle was about 57 days. The current cycle (2014/2015), that is now dissipating, has been around 47 days.
The tele-connection
cycles and oscillations (MJO, GWO, ENSO, NAO, AO, PDO, AMO) that I
mentioned above can enhance or even work against this cycling pattern.
In my opinion, some of these tele-connection cycles may also help to get the cycling pattern started in the first place.
It's complicated!
So, the trick is trying to figure out the cycle length and how these other tele-connection
cycles and oscillations will impact the flow above us, and subsequently surface responses and sensible weather. Unfortunately,
this cycle length cannot be computed until the first full cycle is completed
and starts to repeat, at least I haven't figured out if it's possible to compute it earlier. It usually takes until late October or even as late as Thanksgiving to get a full grasp of the cycle length.
El Nino (the warm event)
Surely by now you have heard that the Godzilla of all El Ninos is coming, or at least that is what the media wants you to think. There are several empirical definitions of an El Nino event, but basically it means that the equatorial ocean across the Pacific has warmed to a certain degree above "normal" for an extended time period. Google ENSO for more information.
An El Nino has formed, there is no disputing that fact. But, will it become strong or very strong or even the strongest on record? There is some debate about that but certainly the global forecast models think it will mature as a strong one.
However, the cool season (October through April) weather pattern across North America, including the central part of the country, can be vastly different from one El Nino to the next, regardless of the strength. That is why I have extreme heart burn with vein popping reactions when I hear a forecast based strictly on El Nino.
Here is the latest Sea Surface Temperature anomaly map. (click for a larger version if you want).
The water temperatures along the equator across the Pacific Ocean are running 2 to 4 degrees C above normal. There are some indices, that can be calculated using different methods, that can be used to determine if an El Nino (or the cool event - La Nina) exists. Those are the Multivariate ENSO Index (MEI), the Southern Oscillation Index (SOI), and the Oceanic Nino Index (ONI). All three show a variant strength to this El Nino.
The MEI chart
The SOI chart
The ONI chart
On the MEI and ONI, I highlighted the "strong" or "very strong" El Nino events that occurred in the past. The graphs are a little blurry for some reason.
Very Strong El Nino:
1982-1983
1997-1998
Strong El Nino:
1957-1958
1965-1966
1972-1973
Other notable ones:
1987-1988
1992-1993
There is another thing to consider and that is just where across the Pacific Ocean are the warmest waters located. To represent those locations, the following map of Nino regions is used:
For instance, if the waters are the warmest in the Nino 4 region, the sensible weather across the U.S. is different, in general, than if the warmest waters were located in Nino 3.4 or even Nino 3 or Nino 1+2. But, the location of these warm waters ONLY accounts for a percentage of what controls the weather pattern, or what I like to say "call the shots".
A very simplistic and composite of what the jet stream does during the January through March time frame is shown in the following map:
But this is just a composite and DOES NOT take into account considerations for the various Nino regions or any other forcing.
In addition for this year, there is a HUGE wildcard in this El Nino. That is the warm waters that have developed off the California coast and the relatively warm waters across the northeast Pacific. In addition, the rapidly cooling waters across the north Atlantic basin may also play a role this year.
The above normal water temperatures across the northeast Pacific Ocean is part of what is called the Pacific Decadal Osciallation (PDO). The change in phase from warm to cold and back to cold can take 15 to 30 years! Depending on the location (from east to west), the presence of warm or cold waters here can have a definite impact on the weather across the U.S.. The past two winters the location of the warmer waters helped feed brutal Arctic air into the country during the winter and is partially responsible for the 3+ year long drought across the northwest part of the country.
Here is a chart of the PDO
The five red boxes (from left to right) represent the 5 strongest El Nino events on record. Something that pops out for me is that the PDO index was different during the 1965/66 event and certainly the 1972/73 El Nino event. Notice on the far right that in the current El Nino, the PDO is somewhat similar to the 1957/58 El Nino event. Does this mean anything? Perhaps. The biggest difference is that the 1958-58 El Nino followed a very strong La Nina and was coming out of a very extreme and spatially large drought.
As far as the current warm event, the following graph shows the predicted strength from various computer models.
The black line represents the average from all the solutions. You might note that there is quite a spread, so it's still not 100 percent certain that this will be a strong or very strong event. In the same breath though there are some solutions that are off the charts! WOW!
But, lets just assume that it will end up being strong or very strong. The following charts and maps represent the weather that occurred during those past El Nino events. (and keep in mind there have only been five of those to chose from!).
Starting with the strongest El Nino, the 1982_1983 event:
The red line = daily high temperatures
The blue line = daily low temperatures
The green line = the "normal" daily high
The purple line = the "normal daily low
DJF = December, January, February or the winter months
For Dodge City
For the United States departure from normal (temperature on the left, precipitation on the right)
For the 1997_1998 event
For the 1957_1958 event
For the 1965_1966 event
and finally for the 1972_1973 event
Hopefully you can see that of the five strongest El Ninos, the average temperatures and precipitation are not all the same. The Climate Prediction Center likes to take a composite of events. But really, all they are doing is taking an average of extremes.
Taking a composite of the five events mentioned, the following is what I come up with:
Averaging the 3 month period of December, January and February only...
Averaging the period from October through April...
The Outlook
The following is the current outlook from the Climate Prediction Center:
The average for the period September through November...
The average for the period of December, January and February...
My take on this...
Going back to the cycling pattern I mentioned above... Again, it doesn't even start until later in the fall (mainly after October 1st). Once the cycling pattern is established, the warm event (El Nino) will mostly likely have an impact on that pattern but to what extent is highly uncertain. I should have a much better idea of what to expect later in October or early November.
All I can go on for now is looking at the contributions from ENSO, including what the PDO and AMO do based on current water temperatures. You may recall from the sea surface temperature map above that there is a large warm pool across the northeast Pacific Ocean basin. That is likely to have an impact, IF it stays that warm and in that area. Because, if the warm pool shifts west and stays there, the result will be a much warmer than average winter across the central U.S.. I'm not going with that idea at this time.
There is also rapidly cooling waters across the north Atlantic Ocean basin which may cause changes in the NAO (North Atlantic Oscillation) which could have impacts on the jet stream across North America.
Looking at the top five El Nino events and comparing the phases in the PDO, I'm leaning towards a weather regime similar to what occurred during the 1957/1958 El Nino. That is NOT to say the weather will be identical to what occurred back then. I'm only shifting the probabilities in that direction.
For the high plains and some of the adjacent central plains...
At this point I would go with a wetter than average fall with near normal temperatures (maybe shifting towards above). The first part of the winter may have below normal precipitation (but that is NOT to say there won't be a storm) with near normal to slightly above normal temperatures. For the second part of the winter (say mid January through February) the odds should shift in the direction of below normal temperatures and above average precipitation. Late winter into early spring could get rather active with odds favoring above normal precipitation.
Looking even farther into the future, the spring months may be wet with below normal temperatures.
I no doubt will be updating this outlook once the pattern is established and starts to cycle.
