La Niña Impact on U.S. Winter 2016-2017 Snowfall

Milwaukee – The original weak La Niña forecast earlier this summer was reinforced by the monthly ENSO outlook released Thursday, October 13th.  The latest forecast reversed the September Neutral outlook.  The September forecast was a low confidence 55 to 60% Neutral outlook.  It has now been replaced by a 70% confidence La Niña outlook.  A flip flop in the forecast was not a surprise and we discussed that in an earlier video blog.

Fig. 1 October ENSO Probability Forecast
Fig. 1 October ENSO Probability Forecast

So, the official NOAA outlook is back to expecting a weak La Niña this winter transitioning to neutral by late winter or spring.  We have maintained that outlook all along at Snowplownews.com.

How does that impact snowfall and who can expect more snow than average?  Great questions and let us first answer that by looking at snowfall and temperatures for the United States in La Niña winters. Then compare that historical data to the NOAA current outlook for winter 2016/2017.


La Niña Snow and Temps

In these next images, historical weather data is plotted for La Niña.  I focus on November through April in 3 month increments.  The anomalies (deviations from normal) for snow and temperature are plotted.  We start with temperatures.  Blue is below average temperatures and yellow above average.

Click Maps to Enlarge

Starting with Fig. 2, temperatures are below average in the northern plains in November and continue below average through Fig. 5, February, March and April.  Texas and points east look mild with slightly above average temperatures.  Certainly it looks colder than the very mild winter of 2015/ 2016.

Now, we can focus on snowfall during the same time period.  Blue areas on the map represent above average snowfall with brown, yellow and red below average snowfall.

Click Maps to Enlarge

Snowfall is above average from November through April, figures 6 through 9, especially in the central California Sierras north through the Cascades and into the northern and central Rockies.  This includes Oregon, Washington, Idaho, Montana and Colorado.  Also, look how the area of blue, above average snow, grows during the winter in the Midwest and New England.  This includes Minnesota, Wisconsin, Michigan, Ohio, Indiana, New York, Vermont, New Hampshire and Maine.  Recently, significant rain and snow has fallen in the Pacific Northwest.  This is not surprising when you look at these maps.  In fact, here is a 30 day rainfall plot of Washington.

Fig. 10 Washington Rainfall
Fig. 10 Washington Rainfall

In figure 10, note how the rain has really increased since October 5th.  The area of green, above average rainfall, is currently over 200% above normal.  During the same time period, the highest peaks of the Northwest  – from Mount Shasta to Mount Baker – saw over 10 feet of snow.  With La Niña forecast, it would not be a surprise to see above average rainfall and snow continue through spring.

So, historical data shows that the northern United States, especially the Pacific Northwest experience below average temperatures and above average snowfall during La Niña winters.  In the last two weeks, the rainy season in the Pacific Northwest has begun and the impact is significant and in line with the November, December and January La Niña historical data.

NOAA CPC Winter Forecast

This now brings us to the Climate Prediction Center forecast for winter 2016 and 2017.  How does it compare to the La Niña historical data and the forecast of La Niña weakening by February 2017?  Again, we start with a look at the temperature forecast.  Red denotes areas with expected above average temperatures and blue represents areas more likely to experience below average temperatures.

Click Maps to Enlarge

NOAA forecasts well above average temperatures for the Southwestern United States from November through April in figures 11 through 14.  The chances for above average temperatures, extends east along the Southern United States, but the odds are not as strong.  Below average temperatures only appear in the North Central United States from December through April figures 11 through 13.

Here are the NOAA precipitation forecasts for the same time period.  The brown shade denotes below average precipitation and green above average.

Click Maps to Enlarge

The NOAA forecast favors below average precipitation for the Gulf Coast and Southeast United States from late fall through early spring in figure 15.  An area of above average precipitation resides over the Northern Rockies and smaller area over the Great Lakes in figures 16, 17 and 18.

The NOAA forecast highlights a dryer and warmer winter for the southern United States.  The NOAA forecast for the northern United States calls for average to slightly below average temperatures and average to above average precipitation.  The NOAA forecast compares very favorably with La Niña historical temperatures in figures 2 through 5.  Precipitation and snowfall are not the same; however, the NOAA forecast of above average precipitation does align with La Niña historical bountiful snowfall in the Cascades and Northern Rockies.

Summary

After looking at all of the figures and forecasts, what can we expect this winter?  Most locations in the northern United States will experience colder temperatures than last winter’s very mild El Niño.  For many northern locations, temperatures return to long term averages.  Some locations will see below average temperatures, especially in the Northern Plains and Great Lakes.  Snowfall across the Northern United States also rebounds from last winter to long term averages.  Above average seasonal snow is most likely in the Pacific Northwest, Northern Rockies, Great Lakes and New England.

One final point, as La Niña weakens in February and March, the temperature and snowfall in figures 5 and 8 are unlikely to verify as the influence of La Niña on our weather patterns retreats.  For snow hounds and people in a snow-reliant industry, this winter will resemble a more normal winter season than last winter.

Meteorologist Mark McGinnis can be found on Facebook and on Twitter @fairskiesconsul