Monday, July 28, 2014

Updated Thoughts on 2014-2015 Winter Outlook

This post will show my personal thoughts on the upcoming winter. In the past, I've put out posts focusing on one or two mechanisms that may influence the winter, but this article will show you what my personal thoughts are.

We're going to begin with a discussion focusing on sea surface temperature anomalies. We've gone over this quite a bit so far this summer, but I haven't really put my two cents into those posts.

Looking at this chart, I see a few things to keep an eye on. Primarily, the warm pool in the northeast Pacific must be watched closely. In the winter of 2013-2014, we saw persistent ridges of high pressure forming along the West Coast, leading to strong upper level lows dropping south into the Central and East US. This pattern allowed extreme cold to be pumped mercilessly into the United States. The warm pool has not dissipated from last winter to this winter, so my concern for another cold winter automatically rises.
I believe that mechanisms upstream (to the west) of the United States influence the weather pattern more than mechanisms more downstream (to the east), primarily because the upstream factors are almost guaranteed to affect our weather based on their location. A prime example is that ridging due to the warm pool in the northeast Pacific last winter. This allowed for a cold winter. However, the lack of persistent ridging over Greenland last winter would have typically argued for a warmer winter, especially in the East US. Did this happen? No, we still received record-breaking cold. You can point to the upstream location of that warm pool of water as a reason why we didn't see warmer weather prevail. All in all, my point is this winter has substantial potential to be cold once again. If those warm waters persist in the northeast Pacific into the winter months, it's probably a good bet you'll need those extra blankets to keep warm for December through February.

Something that has me concerned, however, is the large presence of warmer than normal water anomalies around Greenland and in the waters around northeast Canada, all the way to Europe. What could happen this winter is that we see persistent ridging in the northeast Pacific, but also in the northern Atlantic. From there, the question shifts to if we will see a persistent upper level low in North America, or not. The lack of an upper level low would likely place the US under predominantly zonal flow, something that would result in a warm winter. However, the presence of a strong upper level low could easily make for relentless cold in portions of central and eastern North America. This isn't subtracting from the overall likelihood of a cool winter based on the water anomalies in the northeast Pacific, but it is something to keep an eye on.

In a way, we haven't really seen last winter's pattern leave us. The image above shows 500mb wind speeds in the shaded regions, with wind barbs and pressure contours spread across the image. This graphic is valid for early this afternoon, on July 28, 2014. Even though it's July, you might notice some similarities to the upper air flow from January 2014. We still see strong ridging over the Western US, and an anomalous upper level low in Canada allowing cold air to dig into the North US. If this pattern continues into the fall months, the chances for a cold winter increase greatly. This is something that will have to be monitored closely.

Refresh this page if the animation stops looping.
The big discussion in the weather world revolves around the situation unfolding in the Pacific. Earlier this year, a record-breaking Kelvin Wave brought about the prediction of a moderate or strong El Nino event for this winter, with calls for Super El Nino-like conditions also being heard (admittedly, from me, too). The Kelvin Wave did hit the surface and brought about significant warming to the eastern Pacific waters. However, as we progressed into summer, these warm water anomalies seemed to evaporate overnight, the culprit seen as the band of below-normal waters about 100 meters down from the surface in the animation above. As of now, we are counting on the mass of slightly above-normal temperature waters in the western part of the animation to push east and hit the surface to make another push at an El Nino. It remains to be seen how this will all play out. One possibility is that the warm waters can hit the surface and induce a weak El Nino event. Another possibility is that the cold waters eat away at the warm waters and eliminate the chances for an El Nino this winter.

My current thoughts on the matter are that we are likely to see a weak El Nino this winter. The dissipation of the strong Kelvin Wave has left us with nothing to support a moderate or strong El Nino, so the most likely scenario is a weak El Nino, if we are to see one at all. I'm uncertain as to how those cold water anomalies will react to when/if the warm waters push east; it'll be something to monitor closely this fall. When all is set and done, however, I'm supporting a weak El Nino. A weak El Nino set-up would resemble something like this, as the image below shows.


To summarize:

I expect that we see a cooler than normal winter for many across the North US, primarily the Great Lakes, Upper Midwest, and Northeast. This comes as a result of the warm waters in the northeast Pacific, as well as the expectation for a weak El Nino. Temperatures should be warmer in the West US once again. I do think we see the drought in the Southwest US ease up at least a bit, but until we can nail down the presence (or lack thereof) of an El Nino, it's up in the air.
Precipitation looks to be on the above-average side around the Great Lakes again, thanks to lake effect snowfall, with the same outlook pegged for the Northeast. This comes from the warm waters off the East Coast likely interacting with cold air from Canada to produce the chance of precipitation. Conditions in the South Plains and Gulf Coast are likely to be slightly wetter than normal, with the opposite anomaly predicted for the North Plains. The Midwest and Ohio Valley ought to see around normal anomalies, as things look right now.

Bear in mind this is not my final forecast. It is merely an update with my personal thoughts, in advance of the 2014-2015 Official Winter Forecast to be issued in October.