Hot or Cold? Wet or Dry? 2017-2018 Winter Outlook
Every year the National Oceanic and Atmospheric Administration publishes their three month winter outlook for December, January and February. They began their winter outlook forecasts in October and are ever changing just like weather patterns.
But when a specific weather pattern began to take shape this October, NOAA and the Climate Prediction Center started to understand that this winter is a weak La Nina winter.
La Nina is the periodic cooling of the Eastern Pacific Ocean near the equator combined with cooling over the Central Pacific Ocean. Sea-surface temperatures need to be at least half a degree Celsius cooler than normal for a La Nina pattern to be considered. If the La Nina conditions hold it will be the second consecutive winter with one.
The typical La Nina winter weather pattern brings the polar jet stream into Alaska, then plunging into the central and eastern states. This path can bring below-normal temperatures into the northern U.S., especially the northern Rockies across the northern Plains and into the Great Lakes. Meanwhile, the southern Plains often are left warm and dry. The Pacific jet stream tends to track close to the Pacific Northwest, bringing increased chances for moisture there. Finally, odds increase slightly for wetter-than-normal conditions in the Ohio River Valley
No La Nina is exactly alike and it’s also not the only influencing condition for winter. Besides La Nina, this winter will also be affected by the Arctic Oscillation and North Atlantic Oscillation which can influence the number of Polar air masses that dive into the Southern United States and nor’easters on the East Coast. The Eastern Pacific Oscillation can impact the location of where the cold air will be located in the northern United States. Lastly, the Madden-Julian Oscillation can impact both temperatures and precipitation on a weekly time scale. Since 1950, twelve other winters have been classified as having a weak La Nina condition, the temperatures and precipitation outlooks have never been exactly the same.
When it comes to the Southern U.S. NOAA forecasts above-average temperatures for the area and below-average precipitation through the three-month outlook. The Northern U.S on the other hand is forecasted as seeing below-average temperature and above-average precipitation.
These forecasts must be taken with a grain of salt as last winter’s weak La Nina pattern had the West and upper Midwest recording some of the wettest winters to date. While large areas of the East, South and Midwest had one of the warmest winters on record. When the outlook says wetter than normal that does not always mean a winter is going to be snowier.
Forecasting specifically for the Heartland, NOAA has both Northeast Missouri and Southeast Iowa within the probability of seeing above normal precipitation while temperatures for both areas fall within the equal chances of above or below normal category. But a startling trend across the Heartland is each of the La Nina winters prior to 2000 showed below normal temperatures with each set up. Now every winter after the year 2000 with a weak La Nina showing at least temperatures 4 degrees above normal.
For more information on the La Nina trends, click here.
If you would like to find more information on the upcoming winter, click here.
To find the National Oceanic and Atmospheric Administration page, click here.