Guest essay by Eric Worrall
As late as last October NOAA’s climate models were predicting a milder than normal winter.
Another mild winter? NOAA’s 2018-19 winter outlook
Author: Mike Halpert
October 22, 2018
The air is starting to feel crisp, the leaves are changing, and the aroma of pumpkin spice lattes are filling your favorite coffee shops. This can only mean one thing – it’s time for my annual post on NOAA’s expectations for the upcoming winter! And once again, one of the key players is found in the tropical Pacific. In contrast with the last two years, when we were looking at potential La Niña development, this year we’re waiting to see if El Niño will arrive in time to impact winter. Without further ado, let’s take a look at NOAA’s 2018-19 Winter Temperature and Precipitation Outlook and see how ENSO has affected this forecast.
As usual: Outlooks are probabilistic, so no guarantees
Wait, just one more thing before jumping to the outlooks. I again remind readers (if this seems repetitive, well, it is) that these forecasts are provided in terms of probabilities (% chance) for below, near, or above average outcomes with the maps showing only the most likely outcome (1). Because the probabilities on these and all CPC outlook maps are less than 100%, there is no guarantee you will see temperature or precipitation departures from normal that match the color on the map. As we’ve explained in earlier blog posts, even when one outcome is more likely than another, there is still always a chance that a less favored outcome will occur. And in fact, for the forecasts to be reliable (a critical part of a probabilistic forecast), less likely outcomes MUST happen from time to time.
Outlook for 2018/19 winter
Finally, the outlooks! Both the temperature and precipitation outlooks depend to a certain extent on typical El Niño impacts, but forecasters think a weak El Niño event is most likely. This means that despite the potential for El Niño, confidence in this outlook is less than we had than during recent strong events like in the winter of 2015/16 (more on confidence below).
This lower confidence is reflected in fairly modest probabilities for the temperature outlook, with the largest probabilities only between 50-60% for above normal temperatures in Hawaii, Alaska, and parts of the Pacific Northwest and northern Rockies. The other shaded regions on the map indicate probabilities between 33-50%, meaning that the forecast only tilts modestly towards above normal temperatures. And while no areas of the country are favored to have below normal temperatures, it certainly wouldn’t be surprising for some areas to experience below normal temperatures this winter. This would be most likely in the white areas labeled EC (more on that later).
Now that the observed conditions are a little colder than their October mild winter forecast, NOAA seem to be blaming global warming and warmer oceans for the deep freeze.