First Preliminary Winter Outlook

This is my first winter outlook for the area, and other regions close to us. Most of the year's featured, a near neutral ENSO (discounting 2008, which had a weak La Nina), a negative PDO (discounting 1993-1994), and had teleconnection patterns that matched with this years.. I could not find a single year that even came close to matching with this year's teleconnections. In the past fifty years, there hasn't been a single instance where the NAO and AO fluctuated as much as it has. This is telling me that something is up with the observed wind patterns over the North Atlantic. For the teleconnections, the closest fits were 2008-2009, 1993-1994, and 1977-1978. As for precipitation patterns, the best fits were 2006-2007, 2008-2009, and 1977-1978.. I don't want to sound like I'm "wishcasting" (that's what happened last year), so I'll give you my first thoughts. These years were also checked for correlations in the AO and NAO, and there were only two years that corresponded, and those were 1993-1994 and 1977-1978. Some of you who are older, probably remember the winters of 93'-94' and 77'-78'. During the winter of '77-'78, the area saw temperatures about 10 degrees Fahrenheit below the normal average temperature. In the winter of 1993-1994, we saw temperatures about 4-6 degrees below average, mainly in the month of January. This may have biased my winter forecast, so don't expect it to be as cold as those years.

I'll start with storminess and precipitation. In actuality, this could go either way this year. In my personal opinion though, I believe that El Nino will be non-existent by the time December comes around. If this occurs, then I expect precipitation to be above normal in the Ohio Valley, all the way into the Eastern United States. Any place south of Indiana or west of Indiana will likely see below normal precipitation. The jet stream will likely be directed across the southern and central United States this year. The biggest storms will occur when the NAO dips to negative values, and the PNA also goes negative, forcing a large trough into the Midwest. For right now, I'm going to go out on a limb, and state that snowfall may be slightly above normal for the winter season.

I don't believe we will see another split flow jet stream, which will allow for a stronger jet stream, more dynamic storm systems, and colder weather for areas north of the jet stream. From Southern California into the Southeast, I expect above normal precipitation for the first part of the winter season, but near normal precipitation for the rest of the winter. In the east, coastal storms will be frequent so precipitation should be well above average. As for temperatures, the analogue years are nearly "black and white", meaning that some of the analogue years clearly show above normal temperatures across the Ohio Valley, Northeast, Upper Midwest, and other parts of the Northern United States, while the other half of the analogues show below normal temperatures across the Northern United States. When they were averaged, most of the United States should end up cooler than normal east of the Rockies. West of the Rockies, due to the strength of the western ridge, I expect above normal temperatures. In other words, there is a very good chance that we end up with below normal temperatures for the winter, but I will keep the original forecast at equal chances for above or below normal temperatures.

Rainy forecast for Today and Tonight

Some of the more important features on the weather map today will be the slowing cold front over the Ohio and Central Mississippi Valleys, the large and deepening upper level trough over and just to the north of the area, and a shortwave which will cause a wave to form along the frontal boundary. Currently, a very strong jet streak (145 knot wind speeds in the core over south central Canada to be precise) is rounding the western section of the trough. This will aid in the development of a open wave low pressure system later during the early afternoon and evening.

As the frontal system develops, increased cloud cover will overspread the region, especially during the afternoon hours. It may be sunny right now, but according to satellite imagery, thick, heavy cloud cover will move into the region during the next several hours. As the system develops, and lifting increases as the warm front strengthens, numerous rain showers will develop. Initially, it will take quite a while for the rain bands to get going due to the dry state of the atmosphere.. But once the storm system can draw in some moisture, rain will begin. For right now, I'm expecting the heaviest period of rain to be around 03z tonight or 11 p.m. as illustrated by the map below. The map below shows vertical motion. Where vertical motion is stronger, that's where the heavier rain will be at.

Rain showers will continue until the early morning hours, with only a few scattered showers left. By Saturday, yet another shortwave will approach the area, bringing an additional chance for showers.

This map is an isentropic map. A gradient in the red lines indicates a frontal boundary.

As for temperatures, today, I expect highs in the upper 60's to lower 70's, with lows in the lower 50's tonight. Rainfall amounts won't be that high, with about a quarter to a half an inch expected, at a maximum. For Saturday, temperatures will drop into the lower 60's, due to a cold front passage. Lows Saturday night will dip into the lower 40's. As for Sunday, highs will make it to about 57, after a secondary cold frontal passage. For the rest of next week, temperatures will begin to moderate, but some models are indicating another blast of cooler air to affect the region around Wednesday.

Additional Features and Thoughts on the Winter Outlook

This will be yet another quite technical article on behalf of my discussion about what will happen during this winter season. While it is quite uncertain about what will happen.. There are several factors that can be used to determine a winter's temperature and precipitation relative to average.

WARNING: SKIP THIS PART IF YOU DO NOT WANT THE TECHNICAL DETAILS

In this article, I will specifically be discussing atmospheric blocking and the observed jet stream wind patterns. One of the defining factors of last winter's weather was the observed lack of high latitude atmospheric blocking across Greenland and the Arctic. This was caused by the fact that a Sudden Stratospheric Warming event never occurred until the latter part of the winter, by which time it was well too late for any significant change in the winter pattern. The first variable I will be discussing is the North Atlantic Oscillation.. I won't go into detail about this variable, as I have explained quite thoroughly in other blog posts from last winter. Last year, its tendency was mainly positive. When the NAO is positive, below normal upper level heights (or below normal upper level pressure) exist over Greenland, and above normal upper level heights exist over the Central Atlantic, usually near the Azores extending eastward to Bermuda. This causes a stronger than normal height gradient (and thus a higher pressure gradient), which causes a stronger jet stream. In this type of pattern, the weather across the U.S. is normally variable (though some meteorologists falsely claim that a positive NAO is associated with warmer weather across the United States, which is not always the case...), but favors a warmer, and stormier weather pattern across the Central Plains and Midwest. When it is negative, below normal heights occur over the Central North Atlantic Ocean, while above normal heights occur over Greenland and Northeastern Canada. This causes a more meridonal jet stream pattern, and more stagnant weather pattern. The strong, looping jet stream will force cold air out of the Arctic and into the Eastern and Southern United States, as a negative NAO favors a trough over the U.S. Over most of the past several months, the NAO has trended negative.. While this gives no indication as to what it will be during the winter months, its trends during the fall can be rather significant to the winter forecast. During the late summer and early Fall of 2011, the NAO had been trending slightly negative, but abruptly went into the positive territory... Many meteorologists were going on the boat that the index would fall again by November and December. THIS DID NOT HAPPEN. The reason was because of the Arctic sea ice extent across the Arctic Ocean. Arctic sea ice extent became the highest in the last 12 years in October of last year, right after it had hit record lows. When Arctic sea ice extent is higher, heat transfer to the atmosphere is rather minimal, and easily favors the development of upper level troughs and thus the reason for the "Polar lows". When Arctic sea ice extent is below normal, heat transfer into the atmosphere is above normal, and favors the development of upper level ridges.. And when this happens, the NAO plummets, as well as another variable, known as the Arctic Oscillation, which is a very similar index.  Just last week, it was recorded that Arctic Sea ice extent was at its lowest on record. Now, whether that will mean colder weather during the winter, no one knows.

This is a map of Sea surface temperatures relative to normal as measured by satellites and buoys.  According to the NCDC, the far North Atlantic and Arctic Ocean SST anomalies have increased since last year. This is another indication that atmospheric blocking may set up during the upcoming winter.

Other variables that are looked at include the PDO, PNA, and many others. In this post, I would like to focus on the PNA.. Basically, when the PNA is positive, A ridge is usually evident in the Western U.S... There is normally a stronger Aleutian low, and below normal heights across the Southeast United States. When it is negative, trough is located in the western United States, a ridge in the Gulf of Alaska and normally a southwest jet stream pattern over a good chunk of the United States (good for storminess in the Ohio Valley). A positive PNA favors very cold weather and a stagnant weather pattern across the East (unless of course conditions are ripe for coastal storms). A negative PNA favors stormy weather, especially in the West, Midwest and Central Plains. This could go either way, but, according to ESRL/PSD data, the PDO (Pacific Decadal Oscillation) tends to correlate well with the PNA... Normally, when the PDO is negative, the PNA also averages neutral to negative. Of course, since the PNA varies on weekly timescales and the PDO varies on yearly time scales, it's very hard to tell any kind of pattern.

This is a chart of how the PNA index has varied over the past fifty years. So far, no pattern has been recorded by this particular index, unlike other atmospheric variables.

This is a chart showing both the variations of PDO and the PNA in comparison to each other. There is somewhat of a correlation between them, the actual calculated value of correlation is 0.250 for the past 10 years, which is quite a bit better than most variables correlations.

STOP!

In conclusion, I believe that all of this will influence the winter's weather patterns. In fact, I have come to believe that the PNA will average near neutral for the winter, which would favor a jet stream pattern through the lower Ohio Valley (depending on the development of the El Nino of course). Now, this is not my official forecast. This is only one of the many possibilities. I believe that with the recent development of record breaking low ice extent, a tendency for the NAO to trend negative over the past few months, the PDO index dropping, and SST anomalies, that the winter will feature near to slightly above normal precipitation in the Ohio Valley, in fact, mainly areas east of the Mississippi. For right now, with so much uncertainty, temperatures will be a "wild card"... Even though I believe that we have a better chance of seeing below normal temperatures across the area, historical data suggests otherwise. Only a few analogues that match up with the current year actually show below normal temperatures during the winter months. The ironic thing is that each of those respective winters featured particularly brutal cold outbreaks, mainly the winter of 1993-1994. My first official forecast will be released over the weekend, so expect it then. I will reveal my preliminary thoughts on storminess, temperatures, precipitation, and other things.

Another look at the Possibilities...

As I have stated in the previous post, my findings and conclusions were this yesterday: One; That the best matches for the year's forecast were the years of 2006, 1993, 1981, 1976, 1969, and 1966... There are a few other years, and I'm changing them.. Even those these years are the closest in the weather patterns, they are actually quite far from what we are experiencing.. This is the first year that I have made a winter forecast (this is my third year) where the year in question did not have even a close match... So, this one may go on intuition. One of things I would like to emphasize in this update is the ENSO pattern (tomorrow's update will feature atmospheric blocking and SSW's).. Across the Equatorial Pacific, the current El Nino is dying.. According to Climate Prediction Center charts, the above normal SST anomalies have been fading away over the past several months, and shifted westward, as the thermocline in the equator region moves upward (the dividing line of colder waters located about 200 meters below the surface of the ocean.)... This is associated with an increase in upwelling and thus a closer La Nina pattern. I would not be surprised to see a neutral pattern come in for the winter period, or even a weak La Nina. On average, most neutral ENSO winters feature above normal snowfall across the region, but colder than normal temperatures. But that all depends on other factors such as atmospheric blocking across the North Atlantic (which I will explain in tomorrow's post). Another factor that is contributing to the weakening of the El Nino is the fact that atmospheric wind and precipitation patterns are not responding. First of all, the trade winds have not really backed off (while they are weaker than last winter's trade winds, but that was brought on because of the original intensification of the short-lived El Nino back in July), and this is the reason for the westward advancement of the above normal sea surface temperatures.. For an El Nino to strengthen it needs to stay in the eastern ENSO zones. Other factors, such as a very strong negative PDO regime is likely affecting the development of the El Nino.

What this means is that this winter will likely not reflect El Nino weather patterns, which on average would usually mean above normal temperatures across this region, but with drier than normal weather. I expect with a farther north southern jet stream, that precipitation will likely be above normal. Right now, temperatures look to be the wild card. I will have this resolved by the time I have next week's article published. Until then, here are my current thoughts. If the ENSO event does turn into a weak La Nina or even stay neutral, I expect temperatures to be slightly below normal across the region. If the ENSO strengthens into a stronger El Nino, then I would expect near or slightly above normal temperatures for the region.

Some thoughts....

Some additional thoughts on this winter's outlook... Last winter as most of us recall, featured rather warm temperatures. This was in part due to the lack of cold air in Canada (it was also a rather warm year in western and Central Canada), and the fact that there was virtually no atmospheric blocking across the North Atlantic. Towards the latter half of the winter season, an SSW occurred over the Arctic regions. An SSW stands for Sudden Stratospheric Warming event. In theory, an SSW should lead to increased atmospheric blocking over the North Atlantic or the Arctic, approximately 2-4 weeks after the SSW has occurred. Last winter, it came too late, as very little extremely cold air had built up over western and central Canada. When conditions were favorable over Alaska for the build-up of a record breaking cold air mass, the jet stream patterns became unfavorable for the movement of this arctic air mass into the Eastern United States. This year, over the course of the spring and summer months, strong atmospheric blocking has set up across the North Atlantic. In fact, we just recorded the lowest NAO value on record back in June (Climate Prediction Center).. Right now, positive stratospheric temperature anomalies have been building across the North Pacific and Arctic regions, possibly in correlation with the strengthening negative PDO regime. This has lead to a drastic drop in NAO values over the past week or so, and the reason for the cooler weather. IF this pattern can stay in place for the next couple of months, it could possibly become the main winter weather pattern. This kind of a pattern would be very favorable for extremely cold winter weather, but drier conditions across the Northern U.S. Another signal I'm looking at is the ENSO conditions. If the CFSv2 long range forecast is correct (the first set of ensemble members), then the El Nino will weaken considerably by December, and become neutral. This remains consistent with the fact that El Nino's usually struggle to develop in the negative episode of the PDO. Of course I am still investigating this winter, and I will provide more updates as the week goes on, but at this point, there are three possible weather patterns that this winter COULD feature: One, a rather warm, and possibly wet winter associated with the El Nino (similar to 2006-2007). Two, a rather cold and dry winter, similar to the winter of 93-94. And three, a winter similar to 2010-2011 where the negative PDO, intense atmospheric blocking, and positive PNA patterns dominated and caused a rather cold and snowy winter. The most likely winter weather pattern at this point is number one, mainly based on historical analogues. After reviewing the data, this year is very unique in the fact that virtually no years in the historical record from 1951 onward even come close to having similar weather conditions to this summer and fall. This may be a rather unique winter season, and quite a bit different from the last winter season. I will discuss this in a related post tomorrow.

All in all, the most likely scenario for the winter is one that features near or slightly above normal temperatures, and likely above normal precipitation (given a strong southern jet stream, which will average farther north than normal).. 

Winter Outlook Release Date

I will have to review more data for the upcoming winter.. But I should be finished by next weekend. I will also publish the forecast in the paper.

As for what my preliminary thoughts are.. Based on the past winters, I expect that December could end up rather warm or just slightly above normal temperature wise, with near or slightly above normal precipitation (given an active southern jet stream that could be slightly farther north than on average.).. By January, the NAO (North Atlantic Oscillation), could drastically change after taking a brief dip into positive territory, and taking a sharp dip into the negative index values. I'm basing this off of the fact that in recent years, the NAO has been drastically changing and to near opposite ends of the spectrum over a time period of a few months... Take for instance this past summer and spring, we had one of the lowest values of the NAO on record. I believe this to be in part influenced by one of the lowest solar activity periods in the records. What could happen is that it will likely drop again this winter, leading to a much colder end to the winter season. By February, temperatures will likely remain cold...

This is only preliminary, and if El Nino decides to strengthen rapidly, all of these ideas will be null and void. I expect several updates on the winter forecast this fall.

First "Sneak Peek" Into the Winter Outlook

This is a map that I have compiled of my analogue years for the winter... The winter's used are 2006-2007, 1993-1994, 1969-1970, 1966-1967...

This would indicate a colder than normal winter for the region, but with precipitation near normal with snowfall above normal... I'm not sure if this is going to pan out, but this is the best I can do based on history.