A new report recently released by NOAA details the possibility that we could again see a winter that is impacted by a phenomenon that occurs in the central Pacific Ocean known as La Niña. A La Niña occurs when the sea surface temperatures in this region fall below long-term averages for an extended period of time. This tends to impact the location of jet streams, most noticeably impacting temperatures and precipitation trends across North America in the winter months. As of right now, NOAA has a 50-60% chance of a La Niña pattern developing for the upcoming fall/winter seasons, leading to a La Niña WATCH being issued.
La Niña does NOT impact - Storm strength and intensity, first freeze date in the fall, last freeze date in the spring, the potential for ice storms/blizzards etc.
In a typical La Niña pattern, the Polar Jet Stream situates itself nearly overhead for much of the winter season keeping an active storm track in the region. This is usually where most of the precipitation producing storms will track with the biggest question being what is the strength/magnitude of the cold air that will be able to migrate southward in order to determine the whether we get rain or snow. Very rarely are two La Niña patterns ever alike, but a general consensus does lean towards a pattern where we see more precipitation compared to normal. Temperatures, on the other hand, can be more tricky.
Last year for the winter of 2016-2017 a weak La Niña was in place. You may recall it was a mild winter with several storm systems that brought more rain than snow. That's not to say we didn't have one or two good snow producing systems, however more often than not, especially towards the second half of the season these systems were able to tap a much warmer air mass causing us to experience above average rainfall for the first half of 2017. Our snow fell below average for the entire winter season due to this fact.
LOOKING AHEAD TO THIS WINTER:
TEMPERATURES: - DECEMBER 2018 THROUGH FEBRUARY 2017: Currently our area will see equal chances of below or above average temperatures. The strength of a possible upcoming La Niña pattern has yet to be determined which results in an equal chance forecast. Areas in the southern United States will likely experience warmer than normal temperatures. Last year's weak La Niña pattern gave us much warmer than normal temperatures in January and February, scaling back some by March.
PRECIPITATION: - DECEMBER 2017 THROUGH FEBRUARY 2018: Much of the second-half of the summer months have seen well below average precipitation, even though we still carry a surplus from the first-half of the year. Currently equal chances of above and below average precipitation are predicted for the long-term, however, if a La Niña pattern does establish itself for the fall/winter seasons, we typically will trend towards above average precipitation. As to whether it will be rain or snow, that will later be determined by temperature trends and it is too early to specify at this time.
SUMMARY OF WINTER 2016-2017
Last winter during our weak La Niña pattern we racked up significant snowfall deficits as our temperatures remained well above average, most notably in the typically colder month of February. Will we see a repeat again this year? While not all entirely likely, it isn't out of the realm of possibility.
BOTTOM LINE: This is just one piece of the puzzle when it comes to putting the winter 2017-2018 forecast together. Should a La Niña pattern establish itself by the fall, we'll likely see above-average precipitation, but as to whether it will be rain or snow, that remains unknown at this time. Further forecast model information over the next month or two will better clarify our temperature trends this winter.