Saturday, August 30, 2014

Below-Normal Lake Effect Snowfall Expected This Winter

Anomalously low lake effect snowfall is expected this winter.

The image above shows sea surface temperature anomalies across the Great Lakes, averaged out from August 11th to August 26th. In this image, we're able to get a view of SST anomalies across all five of the Great Lakes, something we can use to our advantage as we try to anticipate lake effect snow this winter. Let's go through each lake individually.

Lake Michigan
Lake Michigan is experiencing a generally below-normal summer, directly related to the extremely cold winter in 2013-2014. The middle section of the lake is experiencing anomalies a few degrees below normal, while the northern and southern fringes of the lake are observing generally above normal SST anomalies, though only by a few degrees. Lake effect snowfall for this winter in Lake Michigan is expected to be below normal.

Lake Superior
Lake Superior is seeing a well-below normal summer, again influenced by the very cold winter in 2013-2014. We see temperature anomalies approaching 6.5 degrees below normal in the eastern section of Lake Superior, though the western part is observing generally above normal SST anomalies. Because a strong fall low pressure system could easily eliminate those warm water anomalies, lake effect snow is expected to be below normal.

Lake Huron
Lake Huron is generally following the pattern of Lake Michigan, with the central portion of the basin seeing below normal temperatures. Above normal SST anomalies can be found on the outside fringes of the lake, but lake effect snow should be expected to be below normal this cold season.

Lake Erie
Lake Erie appears to be rather neutral across the board, with little to no noticeable anomalies to speak of in this body of water. As winter approaches and the air masses cool down, the lake should follow suit. Lake effect snowfall should be below normal this winter.

Lake Ontario
Lake Ontario is nearly completely below normal in SST anomalies as of mid August, so we can safely say at this point that lake effect snow should be below normal this winter.


Monday, August 25, 2014

2014-2015 Winter Forecast Update: First Maps & Outlooks Released

This is the latest update to the 2013-2014 Winter Forecast, likely the last one before the release of our Official 2014-2015 Winter Forecast. In this update, we will publish our first maps, to give you a feel of what we've been saying in recent weeks, now in the form of graphics.
This update will be organized into two sections: the Temperature Outlook section and the Precipitation Outlook section, with regional breakdowns for each section.

I. Temperature Outlook: Cold Winter Now Expected

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The temperature outlook for this coming winter can be significantly determined by the global sea surface temperature anomalies we are currently seeing. The image above shows the latest weekly SST anomalies across the globe. We're going to focus in on two major items here.

I. Persistent Warm Pool in Northeast Pacific
We've discussed this a lot this summer, and the enormity of its influence is still a concern for this winter. The large pool of warmer than normal waters is still present in the Northeast Pacific and into the Gulf of Alaska. Last winter, this body of warm waters allowed a very strong ridge of high pressure to form along the West Coast of North America, which then enabled the infamous polar vortex to slide south into Canada, making the winter of 2013-2014 as cold as it ended up being. This winter, it looks like that same warm pool will be back again, which could set up yet another dicey situation for the risk of a cold winter.

II. Warm Waters Offshore Greenland, Canada
Something we didn't see last year, but is now present, is a swath of above normal water temperatures from the area west of Greenland to the waters in northeast Canada. Typically, the presence of these warm waters in this part of the world can enable strong high pressure to form over Greenland, forcing the jet stream in the United States to buckle south and bring cold air flooding into the Central and East US. While this wasn't present last year, it is certainly available this year, and is something we'll need to watch often for an increased risk of a cold winter.

Something else we're using to watch for this winter is the perfect-scoring analog winter of 1958-1959, which we discussed earlier last week.

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The analog of winter of 1958-1959 was quite a cold one, as the image above shows. Temperature anomalies were well below normal across the Northern Plains and Upper Midwest, as well as the Northeast. Below-normal anomalies still extended into the Plains and Mid-Atlantic. From there, warmer than normal conditions were observed across the Western United States, as well as a fraction of the Southeast, in Florida.
The analog year of 1958-1959 matched up with all five of my parameters set forth that help determine the synoptic atmospheric conditions for a long-range outlook. I had success utilizing this method last winter, and current indications are that it could be successful again this winter. Whether or not that happens remains to be seen, but for now, it supports the growing theory that the upcoming winter will be a cold one.

Because this is just an update and not the actual Official 2014-2015 Winter Forecast, we won't go in-depth into my explanations just yet, but some other articles pertaining to my temperature outlook include Sea Ice Records, and the concept of a Modoki El Nino set-up.

That said, here's my first outlook for the upcoming winter.

Subject to potentially drastic change
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My first outlook places the Pacific Northwest in slightly warmer than normal conditions due to the aforementioned warm pool in the Pacific Northeast and Gulf of Alaska, where a sustained ridge may form. The majority of the Rockies and the Southwest may observe around normal conditions, though a bump up to warmer than normal could be in the cards for the 2014-2015 Official Winter Forecast. I expect the majority of the Central and East US to see below normal temperatures for the upcoming winter at this time, with the Gulf Coast around neutral. New England may have to watch for bouts of warmth due to the proximity of warm waters near Greenland, which could spread ridging into the Northeast.

II. Precipitation Outlook Still Cloudy

We're going to start out this section by going back to our analog year of 1958-1959 and seeing what it says.

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During the winter of 1958-1959, the majority of the nation saw quite a dry season. The southern Midwest and Ohio Valley regions were hit by a strong drought-esque episode, which saw precipitation anomalies running more than 5 inches below normal. This episode was observed in the Gulf Coast, Plains, Mid-Atlantic and Northeast, in addition to the aforementioned two regions. Some dryness was observed in the Rockies and along the West Coast, but anomalies are too variable to determine a specific trend. Some above normal precipitation was seen in the northern Ohio Valley, as well as the deep Southeast, but the majority of the nation was dry.

Because some of the other variables are still too uncertain to definitively forecast on, I made this outlook based predominantly off of the analog year of 1958-1959, typical precipitation patterns with ridging in the northeast Pacific, as well as a couple other factors that are expected to play into this winter.

Subject to potentially drastic change.
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As of now, I'm expecting precipitation anomalies to be mainly below normal across the southern Midwest and Ohio Valley into the Mid-Atlantic and parts of the Southeast. Wetter than normal conditions should persist along the Gulf Coast, primarily in Florida, while slightly above normal conditions can be expected in the Southwest. Normal to slightly above normal precipitation anomalies may be observed in the Great Lakes and northern Ohio Valley, while average conditions are currently favored in the Rockies and New England.

These graphics are expected to change, potentially significantly, by the time the 2014-2015 Official Winter Forecast is released. However, this should give you an idea of where my thoughts are right now, even though they certainly are not set in stone.


Sunday, August 24, 2014

Recent Arctic Sea Ice Records Suggest Another Frigid Winter Ahead

This is a follow-up post to the sea ice publication yesterday.

An examination of recent sea ice levels and their corresponding winter temperature anomalies indicates the winter of 2014-2015 may very well be heading down a colder than normal path this season.

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The image above shows observations of sea ice areal coverage from the year of 2007 to the present year. 2014's sea ice coverage is seen in red, with other years defined by the color legend on the bottom-left corner of this graphic. Taking a glance over this image, we find that this year's sea ice coverage is running in the upper percentile of coverage compared to previous years, as the red line is well above the record-setting years of 2007 and 2012. The red line is located very close to the years of 2013 (black line), 2009 (neon green line), and 2010 (yellow-ish green line). To try and see if we can pull any useful data from here for the upcoming winter, I took a look at winter temperature anomalies for years with sea ice coverage similar to this year, in this case the three aforementioned years.

The results are quite ominous.

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The first year we'll examine is the winter of 2009-2010. The sea ice coverage was remarkably similar to what we've experienced thus far in 2014, and is similar to what we're expected to see later on this year. Temperature anomalies during the winter of 2009-2010 were predominantly below-normal across the country. The cold was maximized in the Central Plains and Gulf Coast, while persisting across the Midwest, Plains, Ohio Valley, and Mid-Atlantic. The Upper Midwest, New England, and West Coast regions experienced above normal temperatures this winter. Overall, this winter brought about a significant cold trend to most of the nation, something we may have to watch for if this sea ice similarity stands.

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The following winter, the winter of 2010-2011, also saw a remarkable similarity in sea ice between the year of 2010 and the present year of 2014, even more so than the year of 2009. The winter of 2010-2011 was yet another cold one, with the below-normal temperatures entrenched best in the Northern Plains and Southeast. Below-normal conditions were spread across the Midwest and Central Plains, all the way into the Northeast and Mid-Atlantic. The Southwest observed predominantly above-normal temperature anomalies, as did a portion of the South Plains. Small fractions of the Upper Midwest and New England regions also saw relatively warm winters, though the overall nation was gripped by below-normal temperatures. The trend of below-normal temperatures with similar sea ice coverage is quickly becoming better defined.

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Lastly, the sea ice graph tells us that this past year, the year of 2013, is matching up quite well with sea ice coverage in 2014. So, as rough as it may be to do so, we must re-analyze the winter of 2013-2014. As most of us may remember, this past winter was not a good one, and temperature anomalies reflect this. Anomalies across the country ranged from several degrees above normal, to nearly ten degrees below normal. The core of the cold was placed in the Midwest and Upper Midwest, though below-normal temperatures enveloped a wide swath of the Lower 48. Only the Southwest and Southeast regions saw above-normal temperatures.

While the sample size is rather small, it is no secret now that years with similar ice coverage as the current one saw below-normal to well-below-normal temperatures in the following winter. It'll take a few more months to determine how valid this correlation may be, but this is yet another ominous sign of many that are telling of a cold winter ahead this season.


Saturday, August 23, 2014

Arctic Circle Observations Indicate Immense Cold Air Available

Observations of Arctic temperatures and sea ice indicate quite a plethora of very cold air in the region.

The image above shows a history of sea ice coverage by millions of square miles, recording coverage from present day (black line) to 2005. As the chart shows, we are currently near the upper envelope of sea ice coverage, when compared to the last ten years of sea ice records. The black line even seems to resemble the sea ice coverage from this time in 2013, as the dandelion-yellow line shows. The availability of this sea ice is beneficial to those of us hoping for a cold winter ahead. Such a swath of sea ice enables cold air to sustain itself in near the North Pole for a longer period of time. After all, you can't have a cold winter if there's no cold air up north to begin with.

The chart above shows a record of temperatures in the far north Arctic since January 1st of this year, with benchmark days on the bottom legend. The red line on this graphic depicts observed Arctic temperatures, while the green line indicates average temperatures for a given time of year. The constant blue demarcation is the temperature of 273 degrees Kelvin, the equivalent of 32 degrees Fahrenheit, or 0 degrees Celsius; the freezing temperature. Just eyeballing this chart, we find that temperatures have only risen above average twice this entire summer, with the first occurrence only lasting one or two days. The ongoing above-average anomaly appears a bit stronger, but does not outweigh the general below-normal trend in temperatures for the summer, reflected well in the above normal sea ice anomalies.

Similar to last year, Arctic sea ice is running above normal, while temperatures are running below normal. These two factors are likely to play some role this winter, though to what degree is unknown. What we can gather at this moment, however, is that there is a vast reservoir of cold air available up north; a positive sign for those wishing for a repeat of this past winter.


Tuesday, August 19, 2014

Perfect-Scoring Winter Analog Paints Ominous Picture for Upcoming Season

For the first time, an analog year has matched all five of my parameters for the upcoming winter season, and is now indicating that the upcoming winter could be another rough one.

The analog year that matched all five parameters was the winter of 1958-1959.  The image above shows 500mb height anomalies during the December-January-February period of that winter season. In this graphic, blues and purples depict stormy and cold weather, while yellows and reds indicate warm and quiet weather. The winter of 1958-1959 saw strong ridging/high pressure positioned over the north-central and northwest Pacific regions, with some stormier weather observed near the Gulf of Alaska. This Pacific ridging extended well into the Arctic, helping to dismantle the mid-level polar vortex, sending it to lower latitudes like we saw last winter.
In North America, we observed what appears to be the polar vortex centered in the Canadian Maritimes, spreading its influence across Canada and into the North US. Some slight ridging was recorded in the West US, especially into the Southwest, as well as the Southeast.

Let's push on to the temperature composite for the winter of 1958-1959.

During the winter of 1958-1959, much of the nation was locked into a rather brutal winter, with temperature anomalies in the North US dropping below -6.0 degrees Fahrenheit, anomalies not too far off from what we saw this past winter, in 2013-2014. The core of the cold was placed from the Upper Midwest into the Great Lakes, but below-normal temperatures snaked their way through the entirety of the Central and East US, save for Florida, which saw weak ridging. The West US saw a very warm winter in December-January-February of 1958-1959, again a similar story to what was seen in 2013-2014.

Lastly, let's go ahead and check out precipitation anomalies from this analog.

During the winter of 1958-1959, very dry conditions plagued the Southern Plains, Gulf Coast, and southern Ohio Valley all the way into the Northeast and Mid-Atlantic regions. Precipitation anomalies below -5.0 inches were recorded in Mississippi, Alabama, Louisiana and Oklahoma, just to name a few. The dry conditions extended north into the Midwest and Upper Midwest, but wetter than average conditions prevailed in the upper Ohio Valley, along the eastern Great Lakes. This was also the scene in Florida, and coastal Texas. The Pacific Northwest experienced a rather wet winter in 1958-1959, while some parts of the Southwest dealt with dry conditions.

Let's break this all down.

The winter of 1958-1959 matched five out of five parameters I set forth that indicate what this winter will look like. For instance, it is expected that the winter of 2014-2015 will see a positive PDO, and the winter of 1958-1959 had that as well. Such a comparison happened, successfully, four other times. It's quite rare to find an analog as similar to projected conditions as this one, and we can only hope that the similarities stick as we head into fall.

Analog forecasting gives us a general idea of what the upcoming winter may be like. It's not a set-in-stone picture of what we will experience. While I cannot confirm that we will see a very dry or cold winter, the chances of both are considered to be elevated, if this analog year is to be believed.