The NOAA 2016 Winter Seasonal Outlook for the months of December through February was released on October 20, 2016. La Nina is expected to one of the main drivers for weather pattern this winter. Thus, long range models indicate that the Southern US will overall have dryer and warmer conditions while the Northern US will see wetter, cooler conditions.
US Temperature Outlook
As indicated above in the areas of blue, the High Plains and the Northern Mississippi River Valley show a likelihood of being cooler than normal for the 3-month period of December, January and February. For much of the country as shown in the orange regions, from the Southwestern US through the Four Corners, Southern Plains and the Deep South, temperatures are expected to average above normal for that 3-month time frame. Another area of above normal is expected in the far Northeast US (mainly across Maine) For parts of Arizona, New Mexico and Texas, long range models show the potential of being much warmer than normal.
A key note about this temperature outlook, it evaluates the overall 3-month average. The north central US will have above normal temperatures during the winter months and in the same token the southern half will have below normal periods. But overall, the average for the 3-month period is expected to be above normal in areas of oranges and or below normal in areas of blue.
For areas with no shading, which is identified as “Equal Chances,” the long range models are not seeing a signal of either above or below normal. Thus these areas from the Pacific Northwest through the central Plains, Ohio River Valley, the Mid Atlantic and much of the Northeast have the same chance of seeing normal temperatures, above and/or below normal temperatures.
Implications of the warmer than normal temperatures across much of the country will likely mean lower than normal heating and energy needs/costs. But it also may have implications in agriculture for winter season crops and growing cycles, especially for winter wheat growers. It also may lead to early emergence of weeds as well as implications with pests and diseases. Many pests die off or decrease in numbers due to sustained cold periods, but if temperatures stay warm, some locations may not experience the traditional winter pest decline.
US Precipitation Outlook
As for precipitation, as indicated in the areas of blue in the graphic above, for parts of the Pacific Northwest into the northern Rockies, Northern Plains and then again in parts of the Great Lakes, the 3-month outlook indicates that conditions will be wetter than normal. For the southern half of the country, as shown in the oranges, from the Desert Southwest to the Southern Plains, the far Deep South and parts of the Southeast, conditions are expected to be dryer than normal. For parts of the Gulf Coast, there is a potential that conditions will be much drier than normal.
As with the temperatures, the precipitation outlook also evaluates the overall 3-month average. The Southern US will have storm systems while the areas highlighted as wetter than normal will have dry periods. But overall, the average for the 3-month period is expected to be above normal in areas of oranges and or below normal in areas of blue.
For areas with no shading, which is identified as “Equal Chances,” the long range models are not seeing a signal of either above or below normal. Thus these areas across the middle sections of the US have same chance of seeing normal precipitation, above and/or below normal precipitation.
For many farmers and ranchers, the drier than normal conditions are not welcome. The drought monitor issued October 18, 2016 shows that the drought remains solidly in place across parts of the Deep South and Lower Mississippi River Valley as well as much of the Southwest US. Abnormally dry conditions are also expanding in parts of the Southern Plains and the Lower Mississippi River Valley.
For farmers, ranchers and orchard growers that are in the areas of expected drier than normal conditions, if you can take precautions now to diminish the impact of less rainfall this winter that would be advised, especially if you are growing on non-irrigated lands. For dual purpose wheat farmers/ranchers in the Southern Plains, you may want to consider stocking rates this winter and ensure you have enough supplemental feed and hay available.
Main driver of this Winter Seasonal Forecast
As mentioned earlier, a significant driver for this forecast is the development of La Nina conditions. According to the NOAA, ENSO briefing provided on October 17, 2016, the most recent ONI value (July-September 2016) is -0.5ºC. So we are just at the start of a La Nina. The graphic below outlines the the forecasts for the ONI and highlights that La Nina is expected to sustain through the winter.
What is La Nina and El Nino?
La Nina is when the sea surface temperatures in a specific region in the Pacific Ocean are cooler than normal. The Oceanic Niño Index (ONI) is what NOAA uses as the primary indicator for monitoring El Niño (warmer than normal Pacific sea surface temperatures) and La Niña (cooler than normal Pacific Sea Temperatures). This overall climate pattern is called the El Niño-Southern Oscillation (ENSO).
There are several sections of the ocean that is monitored but the key region is the Nino 3.4 area, which is essentially in the middle of the Pacific Ocean along the Equator. The amount above or below normal of the sea surface temperatures for a 3-month running average is the index value. So when the index is -0.5 or lower, La Niña conditions exist. But when the index is 0.5 and higher, El Niño conditions exist.
For more information about La Nina and El Nino, Climate.gov has additional insight.
Other Factors that Influence the Weather Pattern
While the sea surface temperatures/ENSO pattern has a significant influence on the general weather pattern, there are other factors that play a role. They are the North Atlantic Oscillation (NAO) and the Artic Oscillation (AO). Note: in recent years many in the media have referred to the AO as the “Polar Vortex.” While the term “Polar Vortex” is a new term, the understanding of the Artic Oscillation by meteorologists is NOT new.
What is AO?
The Artic Oscillation index evaluates what is occurring with the wind and pressure patterns in the Artic. When the index is in a negative phase, the upper level winds are weaker, which allow cold artic air to push farther south than normal. So we tend to get cold outbreaks in the US. In addition, storm tracks tend to be farther south. When the AO is in a positive phase, the polar winds are stronger which keeps the cold air “locked” farther north and allows the storm track to remain north.
What is NAO?
The North Atlantic Oscillation (NAO) evaluates two atmospheric pressure areas in the North Atlantic. Changes in the pressure levels in these areas influence the path of the jet stream, especially for the eastern US. These shifts in jet stream impact the temperature and precipitation patterns. When we are in a positive NAO situation, the eastern U.S. typically sees stronger winter storms and overall is in a wetter period. When we have negative NAO, the eastern U.S. is generally colder and drier.
For more information about the NAO and AO, see the North Carolina State Climate office’s article on NAO and AO.
What does this mean for Winter Storms?
A key point about the outlooks is they are a 3-month average and they do not focus on the potential of individual storms. In addition, as mentioned above, the AO and NAO can significantly impact storms paths. Finally the complexities of ice and snow storms are more detailed than what the climate models are able to forecast.
The following statement in the NOAA Winter Weather outlook sums up the challenges and expectations one can have with the seasonal outlook.
“This seasonal outlook does not project where and when snowstorms may hit or provide total seasonal snowfall accumulations. Snow forecasts are dependent upon the strength and track of winter storms, which are generally not predictable more than a week in advance. However, La Nina winters tend to favor above average snowfall around the Great Lakes and in the northern Rockies and below average snowfall in the mid-Atlantic.”
For more information on the 2016 Winter Weather outlook, NOAA CPC also has a video
The team at WxIntegrations will continue to provide relevant information and resources to help you better understand and prepare by incorporating weather impacts into your planning and response.