Analog-Based Forecasts Favorable for Cold, Stormy Winter

Two analog-based forecasts are favorable for a cold and stormy winter in the Central and East US.

The first forecast we look at is from the TropicalTidbits site. These images show the November (left) and December (right) Z500 height anomalies. Don't look at just the colors; look closer at the contour lines. We will look at the December forecast for now.

In the December forecast, we see a few favorable things:

I. Troughing off the Baja California Coast
On the right-side image, contour lines are shown dipping down to the east of Hawaii and west of Baja California. The depression of contour lines indicates increased storminess, and this is a feature we have seen on multiple forecast models for this winter. In this case, storminess off the coast of Baja California would most likely mean storm systems would move northeast into the Plains and southern Rockies. From there, they will most likely either shift northeast to hit the Midwest, or keep south and eventually run up the Appalachians due to the feature I will discuss next.

II. Ridging in the Southeast
In the Southeast in the December forecast, you can see an arching feature. This is commonly a signal of high pressure, and this is called the Southeast Ridge in the winter. The Southeast Ridge is able to push storms north and create the Panhandle Hook, Great Lakes Cutter and Colorado Low storms. If the ridge is weak enough, we could see storms become Nor'easters down the road, but based on this forecast, I would favor a stormier Plains, Midwest and Great Lakes.

III. Ridging in the Pacific Northwest
In another common feature we have seen in model forecasts for this winter, contour lines arch up across the Pacific Northwest and western Canada. This feature is actually a specific atmospheric index called the Pacific North American Index (PNA). This analog forecast shows a positive PNA, which is shown by ridging along the western coasts of the US and Canada. The positive PNA then enables a favorable storm track for the Midwest and Great Lakes by helping to create that Southeast Ridge, and also let cold air flow south into the Plains.

IV. Negative North Atlantic Oscillation
We see ridging along the waters close to Greenland, and that is a telltate sign of a negative North Atlantic Oscillation (NAO). The negative NAO enables the jet stream to buckle south and allow cold air to flow into the Great Lakes and Northeast, while also suppressing the Southeast Ridge. With ridging down south being suppressed, storm systems can shoot up the coast and become Nor'easters. This negative NAO is a reason why I am still eyeing the Northeast for a stormy winter, even though many signs point to the Midwest and Great Lakes getting the stormy part of winter.

The other analog-based forecast we can use is the Constructed Analog, or CA model from the Climate Prediction Center. In this forecast, we see the 500 millibar anomalies on top, with temperature anomalies on the bottom. I can't really decipher the 500mb forecast because there are no contour lines, but the temperature forecast pretty much echoes the temperature forecast from the TropicalTidbits site. We see a cold Midwest, Plains and East Coast, likely a result of ridging over Greenland (negative NAO) and maybe some slight ridging along the West Coast, but the lack of contour lines does not allow me to elaborate on that further.

These two analog-based forecasts are turning out favorable forecasts for the Central and East US in terms of a wintry winter season. Whether they actually verify is to be determined, but things are looking up.

Andrew

Long Range Lookout: Cool End of September, October Likely

It now appears the end of September and much of October will end up cooler than normal for multiple portions of the nation.

The European ensembles develop an Omega Block across much of Canada and far northern portions of the Plains. The Omega Block involves a body of high pressure being sandwiched between two areas of negative height anomalies. If you look closely at the height contours, you may be able to see what looks like the Greek letter Omega (Ω). The Omega Block pattern typically brings hot weather to those in the positive height anomaly region, and cool temperatures to those in the negative height anomalies. The Northeast, Ohio Valley and Plains will likely receive the negative height anomalies, while Canada and Greenland are inundated by positive height anomalies. Should this pattern stay in place for a prolonged period of time, it would not be impossible that we see a cooler than normal September over portions of the country that would be affected by this Omega Block. I do believe that it will be somewhat difficult to maintain this Omega Block, but I do not find it impossible that we see at least a form of a blocking pattern bring cool weather to parts of the United States.

This cool prognosis for September and October is supported further by CFS model projections of a negative North Atlantic Oscillation (bottom image) and negative Arctic Oscillation (top image). These two indexes are closely related, so it is no surprise to see these two going negative at the same time. It is epxected that the NAO and AO remain negative until at least October 10th, when the CFS starts to bring the two indexes to more neutral territory. But even in that situation, the CFS has lowered the projection from neutral to slightly negative in past model runs, which could mean we continue to see a negative AO and NAO past October 10th. Such a development would lead to a colder United States if the rest of the atmospheric pattern cooperates (indications are it would).

Andrew

What Are The Models Saying This Winter? - CMC1 Model

This model examination will focus on the long range CMC1 model.

The image above shows predicted 200 millibar contour lines and anomalies. We're going to focus on the contour lines for right now. We start in East Asia. Looking closely at the image, we see tightened contour lines in the area around Japan. Considering there is a 6-10 day gap between storm systems in the East Asian area and storm systems in the East US, a tightening of contour lines could suggest an increased number of storm systems. This, in turn, may suggest a stormy East US this winter. We see a large ridging pattern across the Alaska/western Canada. This ridging could then provoke a colder than normal pattern to evolve across the Midwest and East US, as cold air flows southeast along the ridge. If the ridge extends far enough into Alaska, a cross-polar flow situation could set up, which would transport Siberian air to the States. A cross-polar flow is one of the situations that brings the coldest air possible to the US- another situation would be the cold air displaced to the surface as a result of a stratospheric warming. Enhancing the probability of a stormy Midwest and East Coast is the presence of lower than normal heights offshore of the Southwest. This suggests a stormy subtropical jet stream, which could lead to some snowy events for portions of the Central and East US.

The temperature forecast for the winter from the CMC1 model shows a very warm nation. We see consistently above normal temperature anomalies stretching from the West to the East. Much warmer anomalies are found in northern Canada towards Greenland, and this could be suggestive of upper latitude blocking. However, whether than actually happens remains to be seen, as temperature anomalies can be deceiving. Negative temperature anomalies are found in western Alaska, which may or may not suggest troughing in that area. Again, temperature anomalies can be deceptive, and I'm not willing to speculate beyond that.

Precipitation anomalies suggest a very wet Midwest and Northeast for this winter, with a dry Southeast. Considering the prospect of a Southeast Ridge, storms would tend to be directed north into the Midwest and Great Lakes. I would not be too surprised to see the precipitation pattern along the eastern half of the nation verify- it is in line with my current thinking for this winter. As far as the West, I would expect to see dry precipitation anomalies further to the north due to the idea of some ridging closer to the Pacific Northwest and western Canada. But this is only one model's take, and we are still months away from winter.

Andrew

Persistent Stratospheric Warming Setting Stage for Winter

Stratospheric warming currently ongoing throughout this past summer and now is beginning to set the stage for this winter.

This graph shows observed temperatures in the 70 millibar region of the stratosphere from the latitudes of 65N to 90N. The red line illustrates the actual observed temperatures, while the green line shows average temperatures for that time of year. The light gray lines depict the minimum and maximum temperatures observed to this date for any certain time of year. Looking at this past summer, where the red line begins to arch up, we see the observed temperatures were consistently above the green line, meaning the stratosphere has been above normal for a while. It then tapered off for a little while, but as the zoomed-in portion on the bottom right shows, stratospheric temperatures have been on the rise for a bit, to the point where they are above normal.

The temperatures have been above normal for good chunks of the last few months, but the question now is: What is causing these above normal stratospheric temperatures?

An examination around the solar activity reveals daily sunspot trends may be at fault. This chart shows many things at once, but we want to focus on the red line, which shows daily sunspot values. Take a look at the red line after the big spike in the middle of the chart. After that spike, sunspot values take a dive, and stay in slightly below normal territory for a while. This big drop-off happens in the month of June and into early July. Taking a second glance at the stratospheric temperatures, the 70 millibar level was constantly above normal throughout this period of low sunspot numbers. A second example can be found in the time during and right before the big spike on the sunspot graph. These above normal sunspot numbers happened between April and late May. Examination of the temperature chart shows consistently below normal values in this same time frame, meaning there may be a negative correlation between daily sunspot numbers and stratospheric temperatures.

All of that said, if we continue to see the current sunspot numbers stay at unusually low values (circled in blue), the stratosphere should continue to warm. Further warming may set the stage for a warmer than normal stratosphere this winter, which would then encourage a cooler than normal winter.

Andrew

Preliminary 2013-2014 Winter Storm Tracks

This is my preliminary 2013-2014 winter forecast. Bear in mind this is all VERY preliminary, and certainly not set in stone. There are four storm tracks we will analyze here- from the top of the image to the bottom, we will analyze the Alberta Clipper, the Colorado Low, the Panhandle Hook, and the Nor'easter.

Alberta Clipper
The Alberta clipper involves a relatively low-amount snow system that originates in the Canadian province of Alberta and swings down into the US, leaving howling winds and biting cold in its wake. The clipper system is moisture-starved, leading to its usual 2-5'' snowfalls it puts down. This winter, I anticipate the Alberta Clipper to be a little less prevalent than usual, but due to a still-unknown pattern just offshore of Canada, confidence in that outlook is low.

Colorado Low
The Colorado Low is a storm system that originates from the West US and passes in or close to Colorado, depending on its eventual track downstream. The Colorado Low then moves northeast, and can bring rather significant snows to the Plains, Midwest, Great Lakes and even the Ohio Valley. This winter, I expect we will see more Colorado Lows than usual, as ridging in the West and a stormy pattern offshore the Southwest should lead to a more active storm track.

Panhandle Hook
The Panhandle Hook is essentially the motherlode storm system for the Midwest and Plains. It comes from the West US and does a hook around Oklahoma (hence the PANHANDLE Hook) before coming north and east. The Panhandle Hook is relatively rare, but when it happens, under the right conditions, over a foot of snow can hit areas affected by this system. I anticipate an above normal number of Panhandle Hook systems, as stormy conditions are expected in the region where Panhandle Hook systems originate.

Nor'easter
The Nor'easter is quite possibly the most intense winter storm that can hit the United States. Its cousin, the Panhandle Hook, will be rather active this winter, and it's no surprise that the Nor'easter should be either normal or slightly above normal for this winter as well. It will depend on the presence (or lack) of ridging in the Southeast, which, if it were to be present, would discourage Nor'easters. I'm not sure which way I'll lean as far as if these storms will be normal or above normal. That should become clearer by October.

Andrew