Friday, September 18, 2015

Special Post: 2015-2016 Winter Pattern Beginning to Form?

In today's special post, we're looking at how the upcoming winter pattern may be giving a sneak peak at what it will do this cold season.

The above two-panel image shows daily sea surface temperature anomalies for September 16th on the left, with the 500-millibar height anomalies for September 17th shown on the right. I've discussed the importance of realizing an ocean-atmosphere relationship for some time, and this latest evidence is only adding credibility to that relationship.

I've highlighted two areas of interest on the right-most panel. From Alaska, south into the British Columbia and Pacific Northwest regions, negative height anomalies were observed on September 17th. In the other highlighted region, positive height anomalies were extending from the Bering Sea into the waters north of Hawaii. Although not shown, we also saw a closed upper level low placed due south of that ridge in the Bering Sea, forming a Rex Block pattern.

It is no coincidence that sea surface temperature anomalies reflect this atmospheric pattern. We see a swath of above-normal to well-above-normal water temperatures across the North Pacific, with a body of below-normal SST anomalies just south of the Aleutian Islands, extending back towards Japan. In addition, we also see a cooling of water temperatures over the last month in the Gulf of Alaska / Northeast Pacific, as the graphic below shows.

Change in water temperatures over the last calendar month
In addition to this pattern showing up in the past, model guidance insists it is here to stay, at least for the next 10 days.

The GFS ensemble mean 500-millibar height anomaly forecast for 132 hours out is shown above on the left panel. We see a set-up very similar to what we have been seeing, with a Rex Block orientation in the North Pacific, a deep trough in the Gulf of Alaska, and a stagnant ridge in the Central and East US.

Even in the very long range, over 10 days out, the GFS ensembles still show a signal for ridging in the Bering Sea, a trough in the Pacific Northwest, and a ridge in the Central US. While accuracy at this long range timeframe is quite low, the pattern has a decent chance of locking up like this if it verifies 5 days down the road.

While we may see sea surface temperatures change drastically over the next few months, I'm getting the feeling that we're closing in on our winter pattern, and it could resemble something like the pattern shown above.
This current pattern, and the one forecasted over the next two weeks, is not unlike a modified strong El Nino, as shown in this link (click here), which I've been discussing as a favored set-up for the winter (a modified textbook El Nino pattern). Whether it sticks around and/or returns during the winter remains to be seen, but I find it plausible we enter into this pattern for the winter. This would bring about a warm winter for much of the Central and East US.

To Summarize:

- The current weather pattern is forecasted to continue over at least the next two weeks.
- This pattern is following sea surface temperature anomalies over the Pacific, making it more likely to maintain.
- This pattern resembles a modified Strong El Nino pattern, and could stick around for the winter months.



Anonymous said...

Currently that looks like a dreadful 97-98 pattern, but I believe it's premature to forecast widespread warmth all winter. December may look like this and be warm but often the trough in the West retrogrades by late winter and opens the door for colder weather in the East.

Anonymous said...


Anonymous said...

The only thing we can do is wait till November. Any one making a winter forecast at this time is way off base. To the above statement about 1997 98 the waters off the pacific northwest are way warmer this year then in 1997 98. this will not be a 1997-98 el nino type winter. I truly believe we will have a negative NAO at times this year. Tim Dantoni

Tim G said...

Bummer, I was hoping for a cold, snowy winter in Chicago Land. Oh well. Of course, I know that can still happen, but the west REALLY needs the moisture so I guess I can't begrudge them getting more snow/rain this coming winter. Especially California.

Christopher Ebie said...

Glad to see you are more active again. You posts are always interesting and I like your presentation and style.

Frank-o said...

The main influence on our mild and low-snowfall winter's here in North Carolina has been a positive North Atlantic Oscillation (NAO), which data would point to being more positive then negative, which means....Warm.....

Elizabeth said...

SO glad to have you back ,Andrew! I always came here to read your winter information-especially because of the EXTREME warm weather bias in the common weather media-and
I mean COMMON in every sense of the word....You know what I mean: the silly apology that always precedes the average snow forecast on the evening news," Sorry but there is bad news in the forecast-we have some snow moving in!" Or in reverse,when there is a SLIGHT rise in temperature in the middle of February they trumpet "a WARMING TREND this week!" Ugh ! They don't seem to realize that a portion of the public actually LIKES cloudy, snowy and rainy weather...My message to the TV meteorologists : Don't give your opinion please just tell the weather! :) Fortunately you have no such bias and it is very refreshing !!!! Perhaps it will rub off onto some of the others - LOVE your site.