2012-2013 Snowfall Forecast Part 3 – US Forecast

2012-2013 Snowfall Forecast Part 3 – US Forecast

As I stated in Part 1 of my winter forecast series, weather around the world can have a noticeable impact on the conditions in your small home town.  You can think butterfly flapping its wings in a sense, a chain reaction of events can cause something seemingly relatively minor (think 2 degrees difference in ocean temperature) to cause a rather large event.  With that in mind, I think it is important to know what to expect throughout the rest of the contiguous United States.

“Normal”

Rather than look at local records, I am choosing to look at what is “normal” for the US.  Below is the normal snowfall based on data from 1961-1991.

 This image just does not do it for me though, the snowfall scale is not precise enough.   Below is another image that I was able to find, but does not include a legend with the snowfall data.

During most years, even without a scale on the map, the snowfall throughout the US will look exactly like this map. Snow will fall heavily in the Rocky Mountains and Sierra Nevada’s, there will be areas around the Great Lakes with high snowfall due to the lake effect, and there will be a area of increased snowfall down the spine of the Appalachians into West Virginia.  Of course, this is not always the case though.

Looking back in history, there have been years where the lake effect engine just does not get going, and there are also years where Washington DC gets well above average snowfall and Boston is just left out in the cold, the winter of 2009-2010 comes to mind.

Temperatures throughout the nation typically take a North to South gradient  exceptions are made for areas of high elevation.  Below is what is expected during a normal January for the United States.  The map has huge bins for temperature but what can be taken away from the map is that anywhere in the lavender, light purple for the people who only had the crayola 8 pack, has average temperatures for the whole month that support snowfall.

Indices

As with the local forecast, tools such as large scale indices can be used to create a forecast for the country.  Unlike the Allentown and Philadelphia forecast, the ENSO cycle will be critical in creating the forecast. Below is the typical impacts of an El Nino Winter (Courtesy of this site)

In part 2 of the winter weather forecast, it is mentioned that the ENSO forecast for the coming winter is for a neutral to slightly El Nino status.  A slightly positive El Nino status would mean that, the southern tier of the US would experience a slightly cool and wet winter while the warm weather will be felt throughout the Pacific Northwest and even into Alaska.

Unfortunately for forecasters, the negative PDO cycle could off-set the ENSO trend due to the correlation of negative PDO to the temperatures in the Southern Tier.  Looking at the history of ENSO and PDO, I think a logical comparison period is the early and mid 1950’s.  Looking at just one of those years (1956-57), the nation as a whole was slightly above average temperature wise, while the precipitation was slightly below normal.

National/Regional Forecast

Click to enlarge.

I expect PDO to dominate the temperatures in most of the Western half of the Nation, while the slight El Nino will help to steer storms through the southern half of the country. This storm track, with some help from downstream blocking and warm SST off the east coast, could make for an interesting winter for folks along the East coast.  If you were to aggregate the nation as a whole, I expect that temperatures will trend slightly above normal and precipitation slightly below normal.

Northwest:  Due to the negative PDO, the Pacific Northwest will experience slightly below normal temperatures but there will not be much precipitation making its way across the area.  Snowfall will be down in many areas throughout Washington, Oregon, and possibly even into Idaho.

Southwest:  In the Southwest temperatures will trend near normal for the winter.  Assuming the normal El Nino Jet, precipitation will be normal through the region.  Las Vegas will be slightly cooler and wetter than normal.

Rocky Mountains: I expect it to be cooler than normal but snowfall to be near normal for the region.  As you get more south into Southern Colorado and New Mexico, snowfall should increase while the mountains of Wyoming could be below normal.

North Central: Dry and Warm conditions will dominate this area of the country.  Most storms will take the southern track, depriving this area of the moisture needed to keep snowfall up.

South Central:  A polar opposite of the North Central; conditions will be wetter and cooler than normal through the region.  Severe weather will likely be up for the year due to the number of systems moving through the region.

Great Lakes:  Forecasting lake effect snow is difficult this year, snowfalls should be normal with the warm lakes but will there be enough arctic fronts moving over the warm lakes to really get the lake effect engine going?  I’m not so sure.  With warmer than normal conditions throughout the northern tier of the country, I expect the lakes to produce slightly below normal this year.

Southeast: It will be cooler and wetter than normal for the southeast US.  The jet streaking across the region will bring moisture and decent dynamical forcing.

Northeast: Oh the Northeast, how I love and hate you at the same time.  With all the energy racing through the southern US, the NAO will be critical in determining whether the region experiences a heavy or weak snow pack this winter.  A negative NAO would set up a Ridge east of the region and cause the jet to pass over a large temperature gradient set up by the warmer than average ocean and the cool land areas.  Even if that scenario takes place, will it sync up with cool enough temperatures to produce snow?  The trendy forecast is for above average snowfall in the region…and I also expect above average for the region as a whole, but do not take that to mean that locations such as Baltimore, Philadelphia and New York will be above average.  I think that temperatures will trend above average for the region which could limit the number of cities impacted by snow.

1 Comment

  1. As of 12/17/13 in NM so far you are right on

    Reply

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