Final 2011-2012 Winter Forecast

Hello everyone, this is the much-anticipated Final 2011-2012 Winter Forecast for the US. Before we even start, let me tell you that this will be a long outlook- there's just no way around it. We have to bring in final snowfall maps, storm tracks, precipitation, temperature, ice maps over this forecast, in addition to our reasoning behind it. So if you could care less about the reasoning and just want to see the forecast, go ahead and scroll down a ways.

Let's start off with the big point that will be influencing this winter: the La Nina.
First, what is a La Nina? A La Nina is when a specific section of the Pacific Ocean has sea surface temperatures (SST's) at or below -0.5 degrees below normal. That is the definition of the La Nina. However, there are also certain patterns that can be recognized and can strengthen evidence that a La Nina is present but not immediately visible. We will not delve into those and will just go with the SST's.
For those with skills in latitude and longitude, below are the regions monitored for a La Nina/El Nino.

Let's check out what's happened in the last several months in terms of monitoring and see if you can figure out where the La Nina's are. Image runs from Jan. 1st of this year to Oct. 23. Use the coordinates in the image above to find the temperatures below for a certain region.

Blue line is sea surface temperature. Pay no mind to the light blue line.

We can see last year's La Nina in effect in January, tapering off to warmer waters during the summer, and sinking back into a La Nina in the last couple months. It is crucial to analyze past conditions in order to make a proper forecast. However, it is also crucial to analyze current conditions.That said, let's take a look at current SST's and temperature anomalies for those areas at the time of writing (October 23).

Looking at this image, we can see clearly that the coldest sea surface temperatures are in the eastern portions of this monitoring area. However, when looking at the temperature anomalies (bottom image), we see a more basin-wide La Nina ongoing. We always trust anomalies when looking for a Nino or Nina, because SST's can look cold, but not be as cold as it seems. We can see anomalies well below -0.5 degrees in this monitoring region, clearly indicating a La Nina is in place.
The big question that comes with a La Nina is if it is 'east based' or 'west based'. A 'west based' La Nina is when the coldest anomalies are in the western portions of the monitoring region (top image), while an east based Nina involves the coldest anomalies at the eastern end of the monitoring area.  Below are the temperature effects from West and East Based La Ninas.

The East-Based Nina favors a cooler nation, while West Based La Ninas typically torch the East Coast westwards through into the Plains. Right now, I am expecting this East Based La Nina either to stay where it is, or more likely, spread slightly westward into the center of the ENSO area.

In the last couple days, the NOAA released their winter forecast which recognized the La Nina but also called out an index named the AO that may be the 'wild card' for temperature averages this winter. I've heard quite a few people ask what the AO is.
The AO is the 'Arctic Oscillation' index. It is a varying phenomenon that exists year-round but varies the most in the cold season. Here's an image to offer a better explanation:

Left side: Positive index.
Right side: Negative index.
Image courtesy of J. Wallace

If the Arctic Oscillation is positive, the US basically sees more moderate temperatures. However, when in the negative phase, the AO often brings down colder temperatures to the US. For more advanced weather folk, below is a 500 mb heights image showing a typical AO+, AON (AO Neutral) and AO- conditions during the DJF (December, January, February) time frame.

Colors are pressure anomalies. Blue= lower pressure= colder
Orange/red=higher pressure=warmer, sunnier

Notice the swath of blue over the eastern US when the AO index is negative (bottom image), and the opposite when positive (top image).

Another factor is the North Atlantic Oscillation (NAO). The NAO is based on pressure differences between the Icelandic Low (a permanent low pressure system stationed over Iceland) and the Azores High (a permanent high pressure stationed over the Azores). When the pressure differences are large, the NAO is considered positive. When the pressure differences are lower, the NAO is considered negative. Below is an image describing it.

The NAO has major variability and is something special to watch in the winter. Below is an image displaying the effects the NAO has on the US in the winter months.

When the NAO is positive, the Eastern US is warmer. However, when the NAO is negative, the East US experiences colder and snowier conditions as the jet stream dips southward, releasing colder air into the region.  Below is a general overview of the different NAO conditions and subsequent effects thanks to Ian Bell's website:

Positive NAO Index	Negative NAO Index
More and stronger winter storms crossing the Atlantic Ocean on a more northerly track	Fewer and weaker winter storms crossing on a more west-east pathway
Warm and wet winters in Europe	Moist air into the Mediterranean and cold air to northern Europe
Cold and dry winters in northern Canada and Greenland	Milder winter temperatures in Greenland
US east coast experiences mild and wet winter conditions	US east coast experiences more cold air outbreaks and hence snowy weather conditions

Did it seem cold last year? If you thought it did, it was. Last year had a negative NAO for much of the winter months. This year, we are getting some indication that the NAO may also be negative this winter, but the specifics remain to be seen.

If you have skipped down, STOP HERE.

Now we have arrived at our winter forecast. All of the above went into our forecast, and this is the best our forecast will get.

The nation will have a pretty wild winter this year. The North US will experience much above average snowfall in the pink region, which is much of the Upper Midwest, some of the Midwest, and the Great Lakes regions across the board. The Pink area will also define frigid temperatures across the winter as the floodgates holding back the truly brutal Canadian air will spill over into the far Northern Plains/Upper Midwest. The likelihood of above average snowfall for the pink area is so due to this frigid air, which may direct moisture-starved Alberta Clippers southward. In the midst of the frigid air, snow ratios (an inch of water equals 'x' inches of snow) will rise as the colder air is in place. The snow ratios fall when warmer temperatures are in place. The blue area will likely generally be cooler than average, with the potential for above average snowfall, though less than the pink area. This blue area will extend into the Northeast. Despite the early season coastal storm the region experienced, we are unsure if this will be a pattern. This is why we are monitoring the LRC. The LRC is Lezak's Recurring Cycle. The LRC states that between October 1st and November 10th each year, storms that occur in this time frame have potential to re-occur in the next 40-50 days after the original storm happens. This coastal storm was in the time frame. That does indicate that the storm may re-occur, but that does remain to be seen. There is potential for a more icy winter right by the coast during this winter. This icy area extends through the light blue area, which is an area we believe may experience cool spells during the winter. Florida may get in on this, but if they do, it will be infrequent. Florida itself out westward will be very dry, especially into drought-stricken Texas. Texas westward will also be warm, and into the West Coast will be wet as systems move onshore in an attempt to strike the East Coast/Plains/Midwest later on.

Precipitation for the winter will be much under average counts yet again for the Southern US. We anticipate this drought to be even more prone to occurring, because dry air naturally sucks out moisture from any systems. In turn, droughts create their own high pressure systems that drive away systems that may produce rain in the area. The same precipitation anomalies cannot be forecasted for the Ohio Valley, where above average precipitation will once again be dominant, similar to last year's winter. We are also extending this above average precipitation westward into the Midwest, but with a chance portion added onto the gist.

Temperatures will nosedive in the Northern Plains and Upper Midwest as the Canadian Air is released into the region, almost as if too much cold air is built up in Canada and is overflowing the floodgates, so to say. This cooler weather will extend southeast throughout the Midwest and northwards back into the Ohio Valley. However, this cooler air will not be nearly as severe compared to the North Plains brutal cold temperatures. Warmer temperatures will be prevalent across the drought-stricken region from Texas westward and northward, forming more of a boundary between Arizona and California this winter. It is possible the warmer temperatures may extend westward. The same can be said for the light blue (cooler) temperatures.

Notes: Colors have nothing to do with strength, importance, etc. and are only meant to distinguish lines apart.
The storms will be very active this winter. We will be seeing classic Panhandle Hookers come from Oklahoma through the Midwest- a few of whom may even go into the Ohio Valley. A more intense track will take a low and dip it into the Gulf of Mexico, much like dipping a strawberry into chocolate, then shooting the system north. It is important to know that the 'chocolate' (moisture) of the Gulf of Mexico will remain on the 'strawberry' (storm system) as it moves north, therefore increasing precipitation totals. It is also important to realize that the Gulf of Mexico has had a very inactive hurricane season this year. Thus, warmer waters are still on the surface- waters that would usually be mixed in with cooler, deeper waters in the Gulf if a tropical system were to move across the region. Since that has not happened, it is very possible that more moisture than normal could be pulled up into these storms that dip into the Gulf of Mexico. This track will also occur with coastal storms, which are defined by the yellow line. These storms will tread across the Gulf of Mexico, then bolt northward and hug the coast as it 'bombs out' (rapidly strengthens in a short time period). Alberta Clippers (in green) will affect the usual areas in the North Plains but will sink southward in at least several points in time. When this happens, snow is likely to occur in the more southern Midwest regions.

This year’s snowfall will be different from last year, although the pattern may be somewhat similar. We will see above average snowfall through the North Plains into the southern Midwest as some far reaching clippers and/or stronger systems that draw colder air farther south may move through the region. This above average snowfall then extends eastward as we factor in the Nor’easters the northeast region will experience this year. This coastal storm that occurred several days ago we believe has a CHANCE of being in a pattern called the LRC. The LRC (Lezak Recurring Cycle) is a pattern that sets up with low pressure systems from the beginning days of October to November. In this time frame, any of the storms that pass through could happen again 40-50 days away from when that storm happens. That is the LRC in a nutshell. More northerly, we see the much above average snowfall area. We denoted this for several reasons. The first- and probably most important- is considering that temperatures will be downright frigid in the Northern Plains. These cold temperatures will raise snow ratios. Snow ratios is the number of inches of snow you would get out compared to 1 inch of water. An average snow ratio is 1:10, with 1 inch of water equal to 10 inches of snow. In colder environments, ratios will rise, with extreme cases above 1:20. In warmer climates, like the coastal storm we saw just before Halloween this year, snow ratios will fall, resulting in heavier snow. We will likely see these Alberta Clippers sink more southerly than usual, as the frigid air may divert the storms south. Thus, the Upper Midwest south would get the heavier snows. Another reason is for the Panhandle Hooker storms. Panhandle Hookers are storms that hook around the Oklahoma Panhandle and shoot north into the Midwest, usually bringing ample moisture, leaving behind fair amounts of snow. This also affects the Ohio Valley, which is why we have included them in this above average snowfall. Colorado Lows are similar, but curve around Colorado and go north. These typically affect the Plains more than anybody for snowfall.

The national ice threat will once again be similar to last year as temperature boundaries initiate a battle zone when systems move through the region. This ice threat will also occur with Nor'easters that may bring up some warmer air from the South.

Thank you very much for reading this. A lot of time and effort went into this, and we hope you liked it. The releases are not done yet...

Regional times are as follows:

Nationwide Winter Forecast Release: 12:00 PM CDT
Southwest Winter Forecast Release: 12:10 PM CDT
Southeast Winter Forecast Release: 12:20 PM CDT
Northeast Winter Forecast Release: 12:30 PM CDT
Midwest Winter Forecast Release: 12:40 PM CDT
Northwest Winter Forecast Release: 12:50 PM CDT
South Central Plains Winter Forecast Release: 1:00 PM CDT