2011-2012 NOAA winter outlook

The National Oceanic and Atmospheric Administration (NOAA) released its 2011-2012 winter outlook for the United States on October 20, 2011. NOAA’s winter outlook shows warmer and drier conditions for the southern portions of the United States, including Texas. Cooler and wetter conditions are possible for the northern parts of the United States, stretching from Seattle, Washington to the Great Lakes region.

NOAA takes into account many variables in the atmosphere and oceans and uses analogs of previous winters to make an overall forecast for the coming two to three months. In this post, I will explain the factors in determining the winter outlook, and show why these variables can cause significant impacts in the United States in the winter of 2011-2012.  

Below is NOAA’s temperature outlook for the United States 2011-2012 winter:

Image Credit: NOAA

NOAA’s precipitation forecast for the United States 2011-2012 winter:

Image Credit: NOAA

When meteorologists gather information for the winter outlook, they look at various pattern changes.  For example, when making winter outlooks, meteorologists look at areas including EL Niño/Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO) and the North Atlantic Oscillation (NAO). Plus they look at large-scale weather patterns in the months of October and November. What do these patterns mean? How do they affect our weather?

The ENSO practically looks at whether we are in a La Niña ,El Niño, or neutral state.  In an La Niña pattern, the tropical ocean waters of the eastern Pacific around South America are cooler than average and pressure levels across the western Pacific lower.  In an El Niño event, the opposite pattern occurs with warmer tropical ocean waters off the eastern Pacific around South America.  ENSO can also be neutral, which shows neither La Niña or El Niño conditions in the Pacific.  The ENSO phases are all different, and have variations each year.  Meteorologists gather all of these phases over the years and are able to find a particular recognition of weather across the world for each pattern. For instance, El Niños provide fewer tropical cyclones in the Atlantic Ocean due to higher shear in the atmosphere that prevents tropical development.  

For 2011, La Niña has returned, but the signal is fairly weak to moderate. La Niña is not expected to be considered strong this year, which is very important to recognize when it comes to the winter outlook. Once again, El Niño’s and La Niña’s vary from year to year, and they all yield to different results.

Here is the basic pattern recognition for a moderate to strong El Niño and La Niña phase:

In La Niña phases, dry conditions are possible for the southern portions of the United States. Image Credit: NOAA

The Pacific Decadal Oscillation, or PDO, focuses on the shift of temperature patterns across the north Pacific ocean and has a warm and cool phase which can impact the United States weather.  The PDO looks more into climate variability, and phases can extend for 20 to 30 years. A positive or warm phase of the PDO shows cold water in the north-central Pacific ocean with warm water over the west coast of the United States, which typically sets up a ridge, or extended area of high pressure of sunny weather across the western coast of North America. In a negative or cold phase of the PDO, warm water in the north-central Pacific helps create a ridge over the central Pacific and a strong Pacific jet stream which can steer stormy weather.

We are currently in the negative phase of the PDO. Image Credit: University of Washington

As of now, we are currently in a negative phase of the PDO, which meteorologists use as a factor in figuring out winter outlooks. What does this mean?  It means drier and slightly warmer conditions along the southern portions of the United States with increase stormy weather across the Great Lakes into New England.  

Here is an image of the current sea surface temperature anomaly:

Sea surface anomaly as of October 24, 2011. It shows warmer water across the central Pacific and cooler water off the western coast of the United States. (Negative PDO) Image Credit: NOAA

The North Atlantic Oscillation, or NAO, is slightly more complicated because it is temporary and can only be predicted in a couple of weeks. The NAO can be the biggest game changer in forecasting this upcoming winter. The NAO focuses on the strength and positions of pressure systems along Iceland and the Azores.   If the NAO becomes negative, the United States could experience more troughs digging into the southeast.  When this happens, stormy weather and cold air could be associated with it.  Last year, we saw a lot of phases, especially earlier in the season, where the NAO became negative.  Whenever you see the NAO turn negative during the winter months, you must pay attention to it!

Blue represents the negative NAO phases, while the red shows positive phases. Image Credit: NOAA

In the image above, you can see when the NAO became negative or positive. The blue colors represent the NAO becoming negative.  If you look closely at the chart, the extreme dips in the NAO correspond to the nasty winter weather across the eastern United States. For instance, there was a  huge drop in the NAO during 2010 and 2011.  During this time, we saw extreme winter weather which produced record amounts of snow across the Ohio Valley and Northeast.

Soil temperatures, snowfall across Eurasia, and recognizing weather patterns across the country during the months leading into winter are also important factors NOAA takes into consideration when it comes to making winter outlooks.  

What is the bottom line here? If you are in the northern third of the United States, from Washington east into New England, expect a colder and wetter winter.  If you are living along the south from New Mexico east into the Gulf coast states, expect a drier and warmer winter.  

Just because there’s an outlook calling for warmer or drier conditions does not mean you will not see cold and wet periods along the way. I expect the southeast to see waves of cold air and possibly wintry precipitation, especially if the NAO becomes negative. If you live around Chicago east into Philadelphia and New York City, be ready for what could be another nasty winter.  Are you ready? If not, enjoy the warm weather while you can!

October 24, 2011

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