Official 2013-2014 Winter Forecast Comes Out Tomorrow

The Official 2013-2014 Winter Forecast comes out TOMORROW at 12:00 PM Central Time.

Also coming out tomorrow at noon are the 20 pre-selected cities' winter forecasts, and the winter forecasts for the North Atlantic Oscillation and Arctic Oscillation. 

Winter is quickly approaching!

Andrew

2013-2014 Winter Update: August 2013

With just 5 days left until the release of my Official 2013-2014 Winter Forecast PLUS 20 selected cities' winter forecasts at noon central time, I'll shed a little light on where we currently stand in the atmosphere, and what implications it could have for this winter.

Let's start off with sea surface temperatures over the world's oceans. Sea surface temperatures are significant indicators to high and low pressure formation over certain areas, so we want to be paying close attention to these SST charts as we move on through fall and into winter. There are a few areas I want to point out for this SST chart. The first region of interest is the body of above normal sea surface temperatures across the northeast Pacific. Per recent developments around the Pacific, the negative PDO regime that has been holding a grip over synoptic weather in North America for years now, dissipated. In its place, we have strong +SST anomalies. I'm feeling pretty good about the placement of those +SST anomalies, in the sense that such warm temperature anomalies could provoke persistent high pressure formation over the west coast of North America, which would go hand in hand with my analog set for this winter, which also shows high pressure straddling the west coast of North America. This persistent high pressure along the west coast of North America could very well then provoke a positive PNA pattern, which would add to cold weather prospects for the Central and East US. But of course, this is all educated speculation.
Moving on to the temperature anomalies along the Atlantic waters stretching from the Canadian Maritimes directly west to Europe, we see +SST anomalies in this area. Just like the Pacific, these +SST anomalies could provoke high pressure anomalies over the Atlantic, and this is something I have seen in another analog set I published on this blog, and do not discount the idea of such a scenario unfolding. If we look north into Greenland and the bodies of water in Canada, we see a continued trend of positive SST anomalies. If these positive SST anomalies continue into the winter, we could see the chances of a negative NAO increase, which could then lead to increased instances of coastal storms along the Eastern Seaboard. However, these coastal storms could go to the Midwest if that Atlantic ridging pattern I discussed earlier works out and expands into the East Coast. Again, it's all educated speculation.

Next, we will take a look at stratospheric temperature anomalies. The graph above comes from the Japan Meteorological Agency, and shows 30 millibar temperatures (black line) superimposed on the average 30mb temperatures for that time of year (gray line). The trend this summer has been above normal stratospheric temperatures, and the 30mb level is included in this trend. The upper stratosphere is not really included in this above normal temperature trend, but the mid and lower stratospheric levels are, and it is these two regions of the stratosphere that hold the strongest influence on the weather down here in the troposphere. This is all good news for winter weather lovers, especially if the warm stratosphere trend can continue through the fall and into winter.

This image shows zonal-averaged winds at the 30 millibar level- this is the same level we discussed in the temperature chart above. However, this zonal wind graphic has a much different bearing on winter weather. Take a look at the blue line stretching along the far left side of this chart. See those blue colors? That is a trademark sign of a westerly (positive) QBO. The QBO involves the stratospheric zonal wind pattern, and can have strong impacts on winter weather. The positive phase of the QBO means the stratosphere is less inclined to experience sudden stratospheric warming (SSW) events. If you recall from this past January, SSW events can lead to Arctic outbreaks of cold air, if the pattern is right. So, if you like winter weather, you don't want to see a +QBO for the winter. But let's look a little closer at this +QBO. As you can see, the blue strip of positive zonal wind anomalies signifying the positive QBO has been present since roughly May, and has strengthened since mid July. But look at the zonal wind chart since then. If you look closely, you can see the blue strip slowly narrowing along the 10S line on the bottom legend of this chart. Looking even closer along the EQ line right at the end of the left side of the graphic, you can see the darkest blue color is starting to become raggedy, and not as strong as it was earlier in June and July. If you didn't really see what I'm talking about, this is the point: there are small signs that the positive QBO is weakening. This would be great news for trying to break out of the positive QBO pattern and getting into at least a neutral QBO, which would enhance chances for sudden stratospheric warming events that would have otherwise been hampered by the +QBO.

All in all, there's still a lot of time until winter comes around, but current trends are rather favorable for this winter in terms of cold weather for the Plains, Midwest and portions of the East US.

Remember: The Official 2013-2014 Winter Forecast comes out at 12:00 PM Central Time this Saturday, August 31.

Andrew

Tropical Activity About to Spike; Landfall Threat Low

Tropical activity across the Atlantic basin is about to spike, with the GFS model predicting the development of two tropical cyclones in just over a week's time.

This spike in tropical cyclone development comes as a Madden-Julian Oscillation pulse creates a favorable tropical cyclone development environment for the Atlantic. Those more familiar with the MJO may recognize this as Phase 8 and 1. As the MJO pulse pushes over the Atlantic, it is expected tropical waves shifting west from Africa will have a favorable environment to develop. When they move out to sea, it appears probable that the northern Caribbean may be scraped by the first tropical cyclone, as the GFS forecast above shows. Beyond that, the dome of high pressure stretched across the Atlantic should erode to a point where both cyclones would be able to curve north and east, away from the US Mainland.

Beyond this first spike in activity, ridging in the north Atlantic should rebuild, and any tropical cyclones that develop in the next 14+ days after these two cyclones could move west enough to threaten the Gulf and western Caribbean. Of course, this is all speculation, but we are rapidly approaching peak hurricane season, and these spikes of tropical cyclone development are to be expected as we move through the rest of August, September and even into a bit of October.

Andrew

Significant Heat Wave Next Week May Become Prolonged

The anticipated heat wave that will begin to push east over much of the nation over the coming workweek will eventually draw back west, but will be able to sustain itself in that position.

The GFS model forecast above projects a very strong dome of high pressure over the Plains, extending its influence across much of the nation and into the Eastern Seaboard. The entrance of lower heights into the West Coast provides reason as to why the ridge of high pressure has decided to pulse east, but as soon as those lower heights shift east, it is likely portions of the East US will see a reprieve from the expected hot temperatures.

This shift of hot weather into the east US coincides with the development of a moderate to strong MJO wave that will be entering Phase 8 or 1 in coming days. Temperature composites on the left-hand side of the graphic show that Phase 1 of the MJO sees warm temperatures across much of the nation, and this will certainly be shown by this ridge of high pressure that will encompass much of the nation to kick off the workweek. Models then diverge, but the European and American ensemble suites seem to be insistent on keeping the MJO wave around Phase 1 territory. This could easily pressure the dome of high pressure into shifting east again at any time after it retreats west towards the end of the upcoming week. Basically, this could be a prolonged warm weather event. This does all depend on if model projections are correct, and we all know that high confidence in medium/long range models is playing with fire. Very long range forecasts from the European weather offices see the MJO shifting towards Phase 2, which would likely alter the weather pattern into one that sees portions of the East and Central US getting a break from the warm weather. But if the MJO stays in Phase 1, millions of people in the United States may be dealing with several days of anomalously hot temperatures.

Andrew

New Long Range Models Support Theory of Cool Winter

A new suite of long range models has come in, and continues to support the idea of a cold winter for the Central and Eastern US.

The image above is just one of many long range models showing a favorable atmospheric set up for the winter of 2013-2014. You may remember the following five points from a winter post I made a little while ago. While you may frown upon how this information is not 'new', the reason I do not update it is because the information here is still valid, and that's something winter weather lovers should be happy about.
These are the five things I have seen in new long range forecasts over the past week or so.

1. Active East Asian Jet Stream 
You will see a tightening of the contour lines in eastern Asia on the image above. This symbolizes the jet stream is under stress, thus increasing its strength in that area. From looking solely at the image above, it would appear pressure anomalies are below normal in East Asia, meaning more storms in that region. If you have been with this blog for a while now, you may recall the times I have brought up a correlation between storms in East Asia and storms in the East US 6-10 days later. If the tightening of the jet stream in E. Asia is due to a stormier pattern in that area, it is entirely possible we see a stormier East US.

2. Ridging Pattern in Northern Pacific 
It is well established that the Bering Sea is a favorite place for the origination of sudden stratospheric warmings (SSW's), a phenomenon that involves rapid warming in the stratosphere that then allows unusually cold air to reach the surface and lower latitudes just a couple of weeks later. Last winter, we saw a magnificent SSW originate from the Bering Sea, and other warmings attempt to take place in that same vicinity. With positive height anomalies stationed over the Bering Sea, intrusions of warm air by these positive height anomalies into the Arctic are more easily accomplished, thus increasing the likelihood of SSW events. Once again, this feature has been displayed on multiple forecasts for multiple months now. Additionally, bear in mind that these features were in the forecast when the CFS model was projecting a very cold winter. In my opinion, it could very well be that the CFS is flopping around with its temperature forecast, as is customary of long range models, while the upper level atmospheric flow really tells the story (i.e. the pattern really is favorable for cold weather, even though temperature forecasts do not reflect it). This issue may occur with other models as well, though I have yet to document such an issue in-depth.

3. Ridging Pattern in Western North America 
The image at the top of this post displays a widening of contour lines in western North America. When you get the expansion of these lines, it is typically demonstrative of high pressure anomalies present in the area. The presence of high pressure anomalies in Western Nor. America is defined as a positive Pacific-North American index (PNA) pattern. In response to high pressure in the West US, low pressure (and thus cold air) is favored in the Central and East US. It is also known that a positive PNA results in winter storms taking a track favorable for the Midwest/Ohio Valley to receive snowfall. Yet again, the June CFS forecast identified the +PNA pattern for this winter, just as the current forecast shows.

4. Low Pressure in Eastern North America
 This is kind of an extension of Number 3, in the sense of a low pressure response to positive height anomalies across the West US due to the positive PNA pattern. The new long range models are picking up on those low pressure anomalies, though some are reluctant to allow the anomalies to stretch into the United States. I believe the low pressure anomalies do actually stretch into the US, but because the forecasts are averaged out over time periods of months at a time, the anomalies are not shown correctly.  The reason why the models may be reluctant to do that on the image above is because we could see high pressure in the Bering Sea work against development of the +PNA pattern, thus preventing low pressure anomalies from reaching the US. However, we could also see the Bering Sea positive height anomalies combine with the +PNA in a favorable winter pattern.

5. High-Latitude Blocking Pattern in Greenland
 The image above shows an expansion of contour lines towards Greenland, an indicator that high pressure anomalies are favored in that area. Positive height anomalies in/near Greenland results in the negative phase of the North Atlantic Oscillation. The North Atlantic Oscillation (NAO) is a phenomenon that involves height anomalies across Greenland. In the negative NAO, high pressure is stationed over the land mass in a move that permits cold air and Nor'easter's to affect the Eastern US. On the other hand, a wintertime positive NAO results in a warmer United States with lower probabilities of big snowstorms for the nation as a whole. I brought about the theory that averaging out one to three months in a forecast may not project the real picture, and that theory also applies here. It applies here in the sense that the NAO may be very negative at times, but may also be less negative during some times. The tendency for a more negative NAO over a less negative/more positive NAO for this three month period in winter may then lead to pressure anomalies averaging out positive over Greenland (a sign of the negative NAO), thus showing an expansion of contour lines towards that region.

With many global models continuing to support the five points above, the case continues to build in favor of a cooler than normal winter in the Central and East US. It will be critical to this cold winter theory that we see these five points continue to show up in future model forecasts through September and October. If we can still find these five items in long range forecasts by October, there would be little opposition for these five points to actually verify, and this little opposition for a cooler winter.

Andrew