Winter 2014-15 Forecast

Winter 2014-15 Forecast

Nov. 11, 2014

As a significant intrusion of Polar air is set to invade the eastern half of the United States this week, it's a good time to look at what Mother Nature has in store for Nebraska this winter. It appears likely that most of Nebraska will see snowflakes this week, however, the over-riding question is whether we are transitioning into a repeat performance of last winter's bitter temperatures and sparse precipitation.

I doubt anyone will forget the endless string of Arctic intrusions across the eastern half of the United States as an exceptional strong upper air trough locked into place across eastern North America.  This upper air trough was counter-balanced by a west coast upper air ridge that extended northward into the Gulf of Alaska.  That ridge was supported by unusually warm sea surface temperatures in the northeastern Pacific Ocean.

The ocean currents along the western United States flow from the Gulf of Alaska southward to the eastern Equatorial Pacific region.  This anomalous warm water continuously moved southward and helped reinforce above-normal sea surface temperatures in the eastern Equatorial Pacific, which led in part to the Climate Prediction Center's forecast for a weak to moderate El Nino event this winter.

This warm pool of water has helped support a very active eastern Pacific Ocean hurricane season and the storm tracks of these tropical systems have been much further north than normal.  The last five systems have moved northward into the Baja Peninsula, before lifting into the southwestern US and enhancing upper air troughs moving across the central Rockies.

Our wet spell from late August through early October developed when surface fronts moving across the central US pulled in moisture.  Fortunately, the last couple of systems have dropped significant moisture south of Nebraska and allowed for an extended period of drying the past three weeks that supported good harvest weather.

During the last eight weeks the Gulf of Alaska sea surface temperature anomalies began to cool, a trend that shows no signs of ending.  Therefore, it is unlikely that the western United States ridge will be as strong or displaced as far north as last winter. Since the Polar Vortex that made the news last winter is dependent on a strong ridge from California to the Gulf of Alaska, I believe that we will not see long-lived Arctic outbreaks this winter across the eastern US.

Since the western US upper air ridge is not as strong as last winter, upper air troughs will be able to work their way into the west coast on a more frequent basis.  We are already seeing this in the Pacific Northwest as heavy rain events have dramatically increased during the past month.  Even the northern quarter of California has begun to benefit from this trend and drought conditions have slightly improved from exceptional to extreme drought.

As these troughs entered the Pacific Northwest, pieces of energy split off the main trough and dove southeastward into the southern Great Basin region, then moved eastward across the southern Great Plains. The remaining energy has moved across the U.S.-Canada border then deepened in a mean position extending from the Hudson Bay region southward into the southeastern US.  This pattern has repeated every seven to 10 days, bringing a consistent period of cold, wet weather followed by warm dry weather.

I expect this trend to continue through the first half of the winter across the lower 48 states.  If El Nino impacts are a bust this winter, this trend will likely continue all winter with distinct periods of well above normal temperatures followed by distinct periods of cold and stormy conditions.

If typical El Nino conditions do develop, strong winter storms will likely move across the southern half of the United States, then up the eastern US coastal region.  Artic air intrusions will be more prevalent across the northeastern US with only glancing blows for the Central Plains that last only a couple of days as the northern jet weakens and cold air remains bottled up across the eastern half of Canada.

This type of pattern generally supports above normal winter temperatures and below normal precipitation across the northern Plains, including the northern half of Nebraska.  Southern Nebraska would have a slightly elevated risk for above normal moisture and above normal temperatures as winter storms move eastward across the southern Plains.

If an El Nino is going to fully develop, we should begin to see the impacts in December.  Although California will not likely see a complete drought recovery, conditions should improve dramatically compared to the past two years.  Furthermore, the southern Plains would also see major drought recovery and above normal wheat prospects for 2015.

As a significant intrusion of Polar air is set to invade the eastern half of the United States this week, it's a good time to look at what Mother Nature has in store for Nebraska this winter. It appears likely that most of Nebraska will see snowflakes this week, however, the over-riding question is whether we are transitioning into a repeat performance of last winter's bitter temperatures and sparse precipitation.

I doubt anyone will forget the string of Arctic intrusions across the eastern US last winter as an exceptional strong upper air trough locked into place. This upper air trough was counter-balanced by a west coast upper air ridge that extended northward into the Gulf of Alaska.  That ridge was supported by unusually warm sea surface temperatures in the northeastern Pacific Ocean.

The ocean currents along the western United States flow from the Gulf of Alaska southward to the eastern Equatorial Pacific region.  This anomalous warm water continuously moved southward and helped reinforce above-normal sea surface temperatures in the eastern Equatorial Pacific, which led in part to the Climate Prediction Center's forecast for a weak to moderate El Nino event this winter.
This warm pool of water has helped support a very active eastern Pacific Ocean hurricane season and the storm tracks of these tropical systems have been much further north than normal.  The last five systems have moved northward into the Baja Peninsula, before lifting into the southwestern US and enhancing upper air troughs moving across the central Rockies.

Our wet spell from late August through early October was the result of moisture from several of these systems getting pulled into surface fronts moving across the central US and dropping widespread heavy rainfall.  Fortunately, the last couple of systems have dropped significant moisture south of Nebraska and allowed for an extended period of drying the past three weeks that supported good harvest weather.

During the last eight weeks the Gulf of Alaska sea surface temperature anomalies began to cool, a trend that shows no signs of ending.  Therefore, it is unlikely that the western United States ridge will be as strong or displaced as far north as last winter. Since the Polar Vortex that made the news last winter is dependent on a strong ridge from California to the Gulf of Alaska, I believe that we will not see long-lived Arctic outbreaks this winter across the eastern US.

Since the western US upper air ridge is not as strong as last winter, upper air troughs will be able to work their way into the west coast on a more frequent basis.  We are already seeing this in the Pacific Northwest as heavy rain events have dramatically increased during the past month.  Even the northern quarter of California has begun to benefit from this trend and drought conditions have slightly improved from exceptional to extreme drought.

As these troughs entered the Pacific Northwest, pieces of energy split off the main trough and dove southeastward into the southern Great Basin region, then moved eastward across the southern Great Plains. The remaining energy has moved across the U.S.-Canada border then deepened in a mean position extending from the Hudson Bay region southward into the southeastern US.  This pattern has repeated every seven to 10 days, bringing a consistent period of cold, wet weather followed by warm dry weather.

I expect this trend to continue through the first half of the winter across the lower 48 states.  If El Nino impacts are a bust this winter, this trend will likely continue all winter with distinct periods of well above normal temperatures followed by distinct periods of cold and stormy conditions.

If typical El Nino conditions do develop, strong winter storms will likely move across the southern half of the United States, then up the eastern US coastal region.  Artic air intrusions will be more prevalent across the northeastern US with only glancing blows for the Central Plains that last only a couple of days as the northern jet weakens and cold air remains bottled up across the eastern half of Canada.

This type of pattern generally supports above normal winter temperatures and below normal precipitation across the northern Plains, including the northern half of Nebraska.  Southern Nebraska would have a slightly elevated risk for above normal moisture and above normal temperatures as winter storms move eastward across the southern Plains.

If an El Nino is going to fully develop, we should begin to see the impacts in December.  Although California will not likely see a complete drought recovery, conditions should improve dramatically compared to the past two years.  Furthermore, the southern Plains would also see major drought recovery and above normal wheat prospects for 2015.

Al Dutcher
State Climatologist