Hello everyone, and welcome to the 2012-2013 Official Winter Forecast. Keep in mind this is not the final forecast, which will be issued later in the fall if it is necessary.
We will start out with an ENSO update and go from there.
The loop above displays sea surface temperature anomalies in recent months over the ENSO monitoring areas. For those less experienced, warm anomalies west of South America indicate an El Nino, while cool temperatures show a La Nina.
In recent months, we have seen a warming trend begin in the eastern and central portions of the ENSO monitoring area, also known as Nino 1+2 (eastern) and Nino 3.4. If we were in winter, this would have been a mainly east-based winter. However, as time progressed over the past few months, the trend of warming has been shifting westward into more central regions of the ENSO area, and even more recently, warm anomalies have been dangerously close to the 180 line, which, in my opinion, would clarify the presence of a west-based El Nino.
|Refresh page if animation stops.|
Underwater sea surface temperature anomalies can be used in coordination with the actual surface temperature anomalies, mainly to see if this is a widespread underwater warming/cooling or strictly a surface-based anomaly. In this case, we have seen a significant warming trend in the eastern ENSO region, with a very slight progression west with time on the surface.
Despite the slight progression west, I believe that we remain in a mainly central-based to possibly west-based El Nino at the time of publishing. However, I am closely watching that warmer than normal body of water in the western ENSO region to see if it will do anything.
Also able to detect if and where an El Nino may be is a graph of the SST anomalies across the ENSO regions. From top to bottom, they go from west to east in the ENSO regions. The charts above show distinct warming earlier in the year across eastern portions of the monitoring regions, but recently those have seen a drop off. However, the Nino 3.4 and Nino 4., both of which had had some trouble warming, have recently seen a period of sustained warming- a good sign for a central or west-based El Nino.
|Animation obtained from usmessageboard
Original graphics made by ESRL
Many of you may be wondering ‘What is the difference between west based, central, east based El Ninos?’ Well, as shown in the animation above, an East-Based El Nino will have a very warm majority of the nation, centered in the western half of the country. On the other hand, a west-based El Nino will bring a cooler than normal anomaly to the general Eastern US, intensifying on the East Coast. So, if you want to see some cold and snow, I suggest you start rooting for a west-based El Nino to get going.
Something else I look at to see how the El Nino is doing is an index called the OLR, or Outgoing Longwave Radiation. In a nutshell, OLR measures the anomaly of convection over the ENSO monitoring area. When there is more convection than usual in the ENSO regions (El Nino), the OLR will turn negative. When the regions are quieter than normal, we will see a positive OLR reading.
In the past few months, we have seen a drop-off from a positive OLR to a relatively neutral phase. This is to be expected, considering we are switching from a La Nina to an El Nino. However, in July, the OLR saw a pretty hefty drop of -0.7, which essentially indicates we have entered an El Nino. Considering a lot of warming did occur in July, as seen on the animations above, this is no surprise. The question is, can the OLR stay below normal?
I believe that we should see a below normal OLR (above normal convection) as long as we have that warm body of water circulating in the ENSO monitoring regions. And that is good, because that warm body of water looks to be ready to stay.
The stratosphere- as far above our heads it may be- provides significant help for winter forecasting. The stratosphere graphs, like the one shown above, run from 1mb to 70mb, with 70mb being closest to the surface. To be the most accurate, I have chosen the 70mb chart to help forecast the winter.
In recent months, the stratosphere has seen a period of below normal temperatures, followed most recently by a jump back to normal anomalies. This jump to normal can be thanked by the NAO, which will be discussed later.
Typically, a cold stratosphere in winter will mean a warm nation, and a warm stratosphere will allow cold air to flow south into our neck of the woods. Last year, we had a very cool stratosphere until mid-late winter, when something called a ‘Sudden Stratospheric Warming’ event, or SSW, occurred. These Sudden Stratospheric Warming events are supposed to happen in winter, which signals the atmosphere’s turn to being prepared for spring. It should be noted that SSW’s are supposed to occur every winter to make ready for spring. But last year, we just didn’t have a significant one.
Looking back at the summer conditions in 2011, we saw a somewhat below normal anomaly going into fall in the stratosphere, which could have been a tip-off to that winter. This summer, we have seen mainly normal anomalies, which puts me in a better place, mentally, as to this upcoming winter, as the stratosphere may not have as much trouble with warming as it did last winter.
Of additional significance is something called the Pacific Decadal Oscillation, or the PDO. The PDO can, and commonly does match up with different phases of the ENSO regime. That will de discussed later, however.
The image above shows 1 month changes in sea surface temperature anomalies across the globe, but we are focusing on the North Pacific. We are currently seeing what could be a cooling trend over the North Pacific. I am not sure yet, because there is a wide expanse of warm water over the North Pacific as well. However, look at the Gulf of Alaska’s coast. There is a sliver of warmer than normal temperature anomalies along the Alaskan and Canadian coasts. This could bode well for a positive PDO, which generally gives a cooler than normal touch to the Eastern US for the winter, and a warm and dry feel over the Northwest and Western US. But what is a positive (and negative) PDO characterized by?
In a positive PDO, we see warm waters along the Gulf of Alaska’s Alaskan and Canadian coasts, even down into the West Coast of the US. What the positive PDO is really composed of is the cooler than normal waters extended basin-wide over the North Pacific. These cooler waters are the component of the positive PDO. As paradoxical as it sounds, the cool waters show the warm PDO.
Notice the warm water anomalies over the Pacific Equatorial region. This is actually an El Nino, which leads one to seeing that an El Nino and Positive PDO seem to go hand-in-hand. That said, climatologically, it would be favored to have a positive PDO present with an El Nino. It’s not for sure, but is more prone to happen over a negative PDO.
In a negative PDO, we see a wide swath of warmer than normal temperature anomalies over the North Pacific, with a bit of cooling near the Alaskan and Canadian coasts, essentially opposite of a positive PDO. Note the cooler than normal waters in the Equatorial region, signifying the presence of a La Nina. Again, climatologically, a La Nina and Negative PDO will go together.
If a positive PDO were to develop this winter, it would essentially emphasize the effects of the El Nino- warm and dry in the Northwest, with cool and wet conditions being found in the Southeast. At this point in time, after looking at conditions in the Pacific in the Southern Hemisphere, as well as animations of the entire basin, it would appear that we may have a negative PDO on our hands this winter. Let’s take a closer look below at how that could happen.
The areas I have circled have seen a warming trend in the past 5 weeks of Sea surface temperature monitoring. This warming has encompassed the waters off eastern Asia, as well as almost the entire basin of the Southern Hemisphere portion of the Pacific. Some warming can also be seen to the south of the first mentioned warming area in East Asia.
If we look to the PDO phases listed above, we see that a cool phase, or Negative PDO, is defined by warm waters reaching across much of the Pacific from Eastern Asia. This warming continues moving south, and is reinforced in the Southern Hemisphere’s part of the Pacific. If we look at the map above, I can see that solution working out better at the moment, more-so than a Positive PDO. That arm of warm waters looks a bit too strong to be overcome by cooler anomalies in the Northern Pacific. Remember this section for later on.
One can also use recent precipitation trends to see where the most precipitation can be found. While these trends are likely to be more accurate in the fall, I think I can map out a few key points.
Notice the Gulf Coast and East Coast are both relatively OK in the midst of this horrible drought. This could very well be a sign of the El Nino that has taken hold, as El Nino’s tend to keep the mentioned regions on the wet side. However, recently the Great Lakes and Ohio Valley regions have been receiving precipitation, and this could be a sign in terms of what could be upcoming for this winter- a period of dry weather followed by a cool down and precipitation. However, I would not bank on any of this until the fall.
Getting a bit more regional, Notice the Great Lakes temperature anomalies in this image. The lakes are all 4 to 8 degrees above normal. Considering they are this warm and we haven’t even gotten to fall yet, I would see this as a very good sign for those who live in the lake effect snow regions. If favorable winds arise and cold air comes down from Canada, we could see more than a few major lake effect snow events, should the Lakes remain as warm as they are today.
And now, the moment you’ve all been waiting for… ANALOGS.
Remember that analogs are not my forecast, and are simply a tool to assist me in making my forecast.
This time around, I started out with all years that had a weak-mod El Nino, disregarding where it’s based or whether or not it came after a double-dip La Nina like we just had. That said, here are the analogs from all weak-moderate El Nino years.
Temperature anomalies for my set of analogs resulted in a much cooler than normal Southeast and cooler than normal Eastern US in general. Additionally, the Upper Midwest to the Northwest regions were warmer than normal. If you look closely at the loop above referencing the different bases of El Nino’s, you would see that this image looks a lot like what would be expected from a West Based El Nino. Coincidence, or a sign of what’s to come?
Precipitation anomalies for the same set of years were not too significant. You can point out the El Nino signatures, with above normal precipitation anomalies across the Southeast and portions of the East Coast, as well as a wet Gulf Coast. The El Nino also makes its mark in a wet Southwest and dry Northwest. However, the below normal anomalies that one would expect to see in the Ohio Valley have been shifted south. It’s not a huge shift and nothing to be concerned about, in my opinion.
We are still on the same set of years. This shows 500mb height anomalies for all weak-moderate El Nino years. We can see a very stormy pattern set up across the nation, specifically encompassing much of the East Coast. From this signature, one can determine the track of the jet stream as well. Also of note is the ridge up in Canada that is very close to Greenland. I find it possible that this influenced a negative NAO thanks to that ridge.
Now that we have examined all weak-moderate El Nino years, see where each one was ‘based’. Now, because cooler than normal anomalies are surfacing in the Nino 1+2 region this year, I am going to take out analog years that were east-based.
•1951-1952: East Based
•1957-1958: Central Based (DISCOUNTED- TOO STRONG)
•1963-1964: Central Based
•1965-1966: Central Based
•1968-1969: West-Central Based
•1976-1977: East-Central Based
•1977-1978: Central Based
•1991-1992: Central Based (DISCOUNTED- TOO STRONG)
•1994-1995: West Based
•2004-2005: West Based
•2006-2007: Basin-Wide (Mainly East Based)
•2009-2010: West-Central Based
Following ‘Round 1’ of eliminations, we now have 9 analog years.
Next, we’re going to eliminate years that started an El Nino before June. It should be noted that the site I use to determine this puts months into 3-month columns. Thus, I must determine the single month from that data.
•1963-1964: Began in May
•1965-1966: Began April-May
•1968-1969: Began in July
•1976-1977: Began in August
•1977-1978: Began in August
•1994-1995: Began in August
•2002-2003: Began in April
•2004-2005: Began in June-July
•2009-2010: Began in June
At this point, we now have 6 analog years. These 6 years are comprised of central or west-based weak-moderate El Nino’s that began in or after June. Let’s see what temperature and precipitation anomalies these bring up.
This time around, my analog years show a much cooler nation, hitting the Southeast and Ohio Valley especially hard. The Northern Plains and portions of the Northeast also get in on the coolness. Despite this, much of the Western US is warmer than normal, likely due to a ridge over the area as you will see below.
In precipitation anomalies for those same years, a wetter than normal Southwest is observed, due to the continuous barrage of low pressure systems across the region. At the same time, the Northwest is drier than normal due to the lack of the barrage of disturbances. Nothing too significant is found in the Eastern US, although by the spotty above normal precipitation anomalies, I would consider the Gulf Coast and East Coast slightly wetter than normal. There remains a drier than normal region, centered just north of the Gulf Coast that makes an attempt to stretch into the Ohio Valley. Whether that happens remains to be seen.
Next, for the same 6 years, this is the 500mb height anomalies. You can see a stormy pattern across the North Pacific into the West Coast, and a very stormy pattern in the East US. However, notice the large high pressure area over western Greenland into eastern Canada. This is a west-based negative NAO, the jackpot for Northeast snow lovers. The west-based negative NAO buckles the jet stream through the Northeast to provide abundant cold weather. Additionally, the storm track will shift in a position favorable for heavy snow throughout the East Coast, particularly the Northeast.
However, remember what I said about there being a better possibility for a Negative PDO this winter than a Positive PDO? Well, I was able to track down a website that sorts ENSO years into tables in correlation with that year’s respective PDO phase (click here). I have decided to find the years that are comprised of an El Nino and Negative PDO. This is the year I found in those tables that is included in my analogs already shown above.
Because it is also listed in those tables, I am going to double-weight (type it in twice) it when the final set of analogs are shown.
Next, I looked at years that had an El Nino following a double-dip La Nina. The year(s) that fit into this category as well as my analogues I already have included:
Technically, 2009-2010 was not a double-dip La Nina, but a closer examination of the ONI index reveals that it truthfully was a continuous double-dip La Nina. Like before, both of these years will be double-weighted in the final analogues.
Now that we have our final analogues, here is what they look like:
For temperatures, my analog years show a very cool Eastern US, hitting the Southeast particularly hard, where temperature anomalies bottomed out at nearly 4 degrees below normal. These cool temperatures extended back to the Ohio Valley as well as the Midwest and Northeast. Also hit by the cool down were the Northern Plains and Great Lakes.
On the warm side was much of the Western US, and maybe the very tip of the New England area.
Because this is an El Nino, I don’t trust the cool anomalies in the Northern Plains too much, but the whole scenario is based on history, so I can’t argue with that.
Precipitation anomalies were not all that exciting, with a fairly wide expanse of slightly below normal precipitation across portions of the Southeast into the Ohio Valley. Wetter conditions were found in the Southwest, thanks to the train of storm systems, and these wet anomalies were reciprocated on the Gulf Coast. While it is not shown, I believe the Northeast will have a stormy winter, as is typical in an El Nino.
The Northwest ended up much below average in precipitation, as the lack of storm systems in that area hit precipitation totals hard.
Lastly, 500mb height anomalies for these years in the winter time were overall pretty stormy. A swath of below normal heights covered the entire nation, with much below normal heights registering in over the Eastern US, especially the Mid-Atlantic.
Notice the very strong high pressure ridge over southwest Greenland. This is indeed a negative NAO, as I had described in the last set of analogs. However, notice how it is west-based and strong. Too strong of a negative NAO can be harmful to snowfall totals for the Northeast. However, I took a look at other precipitation variables for these years and discovered that the storm track still curved into the Northeast and gave a big-time hammering to the East Coast.
After all of the above is set and done, I present to you The Weather Centre’s Official 2012-2013 Winter Forecast.
I believe the winter will end up mainly cooler than normal over the Northeast and Southeast, as a consistent storm track brings storms up the coast that may be able to bring down arctic Canadian air. There is wiggle room in the Great Lakes, which may be influenced by the El Nino and end up going either warmer or cooler than normal. The Northwest and Northern Plains will likely be warmer than normal as a ridge takes hold over the region. I do not doubt the potential for a few arctic blasts in the Plains, but overall a warm pattern appears to be evolving.
Precipitation-wise, one can expect a wet winter across the Gulf coast and Southwest, as the sub-tropical jet stream heralds in storms over and over again. It should be noted that there is an increased severe weather risk in the Southeast/Gulf Coast region this winter, as the jet stream combines with storm systems and Gulf air to produce strong thunderstorms, potentially on numerous occasions. Using analogs shown above, I did put a ‘possible dry conditions’ over the southern Ohio Valley, but I’m not confident in that just yet. The Northwest should remain dry due to a lack of incoming storm systems that have been displaced south. The Northeast and Mid-Atlantic will get their more-than-fair share of snow this winter, as countless storm systems barrel through the region and dump more and more snow. Should we see a pouring out of arctic air from Canada, the Great Lakes should end up snowy, thanks to lake-effect snowfall.
The snowfall forecast calls for a snowy time across the Great Lakes if Canadian arctic air is able to push down south and ignite the lake effect snowfall machines. The Northeast will be the hotspot this winter, as many Nor’easters push up the coast and create a chaotic scene in the worst storms. Due to the storm track entering the Southwest, skiing conditions should be better than normal in those areas, while the Northwest stays high and dry due to the lack of a storm track in the vicinity.
I find it possible/likely that the Southeast, Southern Plains, southern Ohio Valley, and Mid-Atlantic regions will share in a good ice storm this winter. While the risk may have to be adjusted a bit farther inland, the areas marked now stand a fair chance of seeing some ice during the wintertime. Nor’easters that begin to rapidly strengthen while still within the warm air holds of the Southern US may be able to pull some cool air into the system and produce a good ice storm in the region delineated above.
Here is the Overall Graphic for the winter forecast.
Thank you for reading the official 2012-2013 winter forecast. If you have any feedback or questions, do not hesitate to ask them below. They will be answered fairly quickly.
Keep in mind this is not the final winter forecast, which will be published in October.
Thanks again for reading!