Hints of the 2013-2014 Lezak Recurring Cycle Appearing

The new Lezak Recurring Cycle, a repetitive weather pattern that shows itself in the late fall and continues through the winter and spring, is beginning to reveal itself in bits and pieces on model forecasts.

This 500 millibar anomaly chart, valid for October 6, shows a very deep storm system pushing down through the Ohio Valley and Great Lakes into the Southeast. Current model forecasts have this storm system moving relatively close to the East Coast, and if the LRC catches on to this storm system, it's possible this would be a Nor'easter event. But that prospect is laced with 'if's' and other question marks, so I won't emphasize the the idea too much.

Just ~100 hours later, we see another very deep system across southern Canada and spreading its influence into the Midwest, Great Lakes and upper Plains. That solid red line crossing the border is the freezing line. If we see this system get caught up in the LRC too, don't be surprised to see very cold weather in the Midwest, Plains and southern Canada a few times throughout the winter. Additionally, take note of the stormy Bering Sea and lower heights along the waters west of Baja California. Both of these regions would provide potential storm systems for the United States. Model forecasts not shown on this blog post do portray storm opportunities for the Plains and Midwest due to the lower heights in and around the Bering Sea area. The Baja California energy source could help the potential for big snowstorms in the Great Lakes with the presence of a Southeast Ridge, or the chance of a Nor'easter if the ridge is not present. The last item to check out is extensive blocking high pressure across the upper latitudes. If the Lezak Recurring Cycle catches on to this blocking, don't be surprised to see colder weather for the winter. But again, all of this is educated speculation at this point.

Temperature anomalies for the October 5 through October 10 timeframe show cold conditions across the Central and East US. Again, this may come up again later in the winter if the LRC follows up on this colder than normal pattern. One thing I am concerned about is the spread of warmer than normal temperatures across Canada. Going into the fall, this could limit the cold air available to the US later in the winter season. However, it's only late September, and things could do a turn-around before we hit late fall and winter. Only time will tell.

Andrew

Final 2013-2014 Winter Forecast Release Date

The release date for the 2013-2014 Winter Forecast has been announced!

The final winter forecast will be released on SATURDAY, OCTOBER 26 at 12:00 PM Central Time. 

This will be the only forecast released on that date- due to time constraints, the European and Canadian forecasts are unable to be made and released. I will put in bits and pieces of information for each region in this final winter forecast, but it will not be a huge forecast.

Additionally, the format of my winter forecast will change. Rather than the long discussions I typically produce, the forecast will be laid out without this discussion. The reason? Most (if not all) of the information I would put in the discussion is contained in my daily posts.

Andrew 

Weather Ramblings: September 24, 2013

An interesting weather pattern will be evolving in the next few weeks, as we transition from summer weather to a fall-like pattern, especially in the medium and long range.

Model guidance for the 7 day forecast period shows deep troughing across the Gulf of Alaska, which helps to provoke some minimal high pressure development across the Central and Eastern United States. This high pressure is very weak when compared to typical high pressure anomalies when such deep negative height anomalies appear in the Gulf of Alaska. Such a pattern resembles a negative phase of the Pacific Decadal Oscillation, which Eric Webb of Weather Advance illustrated. The image below shows correlations of 500mb heights to the Pacific Decadal Oscillation. The image shows positive and negative colors- positive values mean the phase of the PDO would coincide with height anomalies in that area, while negative values mean the phase of the PDO would be opposite of height anomalies in any given area.

This image shows that the negative PDO produces a positive correlation with 500mb height anomalies in the Gulf Alaska- in this case, a negative PDO would provoke negative height anomalies in the Gulf of Alaska, which we see in the forecast above. That said, deep negative values are shown in the Central and East US, meaning a negative PDO would produce positive height anomalies in the aforementioned areas into Canada. The model forecast at the top of the page somewhat resembles this negative PDO pattern in the sense of deep troughing in the Gulf of Alaska, but we see no significant ridging in the east US and east Canada. The main cause of this seems to be positive height anomalies across the Arctic Circle and troughing across Europe and Asia- those two factors go against the typical -PDO pattern illustrated in the image above.

By the 264 hour mark, model guidance projects general high pressure formation across the Pacific Northwest and southwest Canada as troughing in the Gulf of Alaska shifts west to the waters south of the Bering Sea. This high pressure formation in the west coast of North America provokes the positive phase of the Pacific North American index, which helps cooler temperatures enter the central and east US. Ridging west of Greenland provides a basis for a colder weather pattern in the East US and Central US too, and thus it is no surprise that at the 360 hour mark of model guidance, deeper negative height anomalies (and colder temperatures) arise in the land east of the Rockies.

Teleconnection guidance confirms this idea of a turnaround to a positive PNA and persistent negative NAO throughout the forecast period. The bottom two panels show the West Pacific Oscillation forecast on the left and the East Pacific Oscillation on the right. Without going too in-depth with these two indexes, the negative phase helps cold weather prospects in the US, and the positive phase enhances warm weather across North America. With both oscillations projected to fall by the end of the forecast period, we could see some actual cold weather arrive in time for the second week of October.

A convection-related index called the Madden-Julian Oscillation will be heading into Phase 6 (it has 8 total phases), so let's take a look at a 500mb composite chart for worldwide longitudes zoomed in on the 70-50 north latitude.

As you can see on this chart provided by Mike Ventrice, colors on here show anomalies for the 500mb level. In this case, cold colors indicate negative height anomalies (low pressure), while warm colors show positive height anomalies (high pressure). On the left side of the image, numbers in negative and positive values are shown. Basically, the numbers indicate how many days before (negative numbers) and after (positive numbers) the MJO enters Phase 6. Taking a look at this chart, there is a large signal of strong ridging over the 90W to 30W longitudes. When looking at the 70N-55N latitudes and 90W-30W longitudes, we find Canada and Greenland in that location. So, going by the image, it is plausible to expect strong ridging of high pressure from Central Canada (90W longitude line) to eastern Greenland (30W longitude line) approximately 15 to 30+ days after the MJO enters Phase 6. With model guidance predicting the MJO entering Phase 6 in just a few days. This means I am highlighting October 8 to October 23 (and possibly beyond) for increasing chances for cold weather in portions of the US due to this ridging over eastern Canada and Greenland.

Andrew

3 Reasons Why the Arctic Oscillation Will be Negative This Winter

As we approach winter, we begin to look at how certain atmospheric patterns will turn out for the season. I have found three reasons why the Arctic Oscillation should turn out negative this winter.

1. Positive Atlantic Multidecadal Oscillation (AMO)

Weekly sea temperature anomalies and monthly AMO data indicate we are in a moderate positive AMO. The AMO is shown by positive or negative sea temperature anomalies in the upper Atlantic and Arctic oceans. Taking a glance around the waters east of Canada and around Greenland, we find widespread positive temperature anomalies. While the strength of these anomalies varies, it is apparent that we are in a positive AMO scenario. Because it is called the Atlantic Multidecadal Oscillation, it would not be unreasonable to predict we see a positive AMO this winter. With the presence of warmer than normal waters around Greenland and in the Arctic, the polar vortex is weakened, leading to a negative Arctic Oscillation.

2. Warming Arctic Temperatures

Observed Arctic temperature across this year are shown above in red, with the average Arctic temperature pictured in green. The horizontal blue line depicts the freezing temperature, to identify times when ice coverage may grow or shrink, among other uses. Taking a look at the latest Arctic temperatures, we find that temperature anomalies have trended warmer since the below-normal temperatures experienced this past summer. The latest temperatures are on the drop from already-definitive above normal temperatures. The presence of warmer than normal Arctic temperatures, should they persist into the winter, will hamper development of the polar vortex and enable a negative Arctic Oscillation. Additionally, these warm Arctic temperatures may be able to enhance the positive AMO by warming up already-warm waters in the upper latitudes.

3. Low Solar Activity

This chart above shows observed sunspot values on a monthly basis, with the average trend line shown in blue. The forecast line is in red, but since it obviously has not verified and will not verify in the future, we will disregard the forecast. Notice how low we are in terms of sunspot activity now when compared to the beginning of this century, on the far left of this graph. Did you notice that the winter of 2011-2012 was warmer than normal? Take a look at the trend line for the area right above the number '12' and you can see a bump up in sunspot activity right as it crosses that '12' line. There's no coincidence here; the spike in sunspot activity did affect the winter of 2011-2012. Did you feel colder than normal for the winter of 2009-2010? The sunspot graph agrees- we saw a cold United States in that winter, as well as a minimum in the sunspot count. Now, as we progress towards the winter of 2013-2014, sunspot numbers will begin to fall off again. Chances are elevated that we see a cooler winter than those in the last few years due to, among other things, a weakening sun. With a weaker sun comes a weaker polar vortex and jet stream, helping lead to not only a negative AO, but a cooler winter.

Andrew

October SAI to Start Off Strong

The October SAI, which enables us to see how the Arctic Oscillation and winter temperatures will end up throughout the following winter, looks to start off strong when we actually enter the month of October.

The October Snow Advance Index uses Northern Hemisphere snow cover anomalies to predict the Arctic Oscillation and United States temperatures in the following winter months. If snowfall anomalies are above normal, a negative Arctic Oscillation and cooler than normal United States is favored. In the same sense, below normal snow cover anomalies across the upper latitudes result in a positive Arctic Oscillation, which helps to prevent cold air outbreaks in the US.

The image at the top of this post shows projected snow cover changes over the next 192 hours from the September 19th 0z GFS (this post was made on September 19th). On the bottom right, the percentage change in snow cover over the 192 hour period is shown as +2.73%. This is the highest increase I have seen in the last 4 or so weeks of tracking the GFS and its snow cover change forecasts.

The reason I'm excited about this high increase forecast is because of where we already are in the northern hemisphere snow cover department. This graph shows observed snow cover values (black) compared to normal (green) on the top image, with anomalies at each point on the bottom. After going through a below-normal spring and early half of summer, we find ourselves in above normal territory. With snow cover projected to shoot through the roof in the next 192 hours, it is likely we see a substantial increase in this positive snow cover anomaly by the time we get to October, when the SAI comes into effect.

Andrew