Although La Niña was our controlling weather pattern last year, the Climate Prediction Center (CPC) says it is back! The La Niña pattern started to subside late spring after impacting national weather all of winter 2010 to 2011. Earlier this month, CPC forecasters upgraded the La Niña Watch to a La Niña Advisory.
What is La Niña? It is a naturally occurring process in which the ocean waters off the Pacific Coast in South America becomes cooler than average. That cooler water influences a change in global pressure patterns, and increases the trade winds. This increase in trade winds causes a domino effect that leads to our polar jet stream (which helps move weather patterns in and out of the Pacific Northwest) dipping further south, bringing in cooler, unstable weather. That’s why transitional periods are more stormy, and winter periods are cooler and wetter. La Niña patterns occur every three to five years, but has a 50 percent chance of occurring back-to-back.
How is La Niña Tracked?
Buoys out to sea are monitored daily by NOAA scientists. When temperatures start to drop between 1 to 2 degrees above average on the surface, and 2 to 4 degrees above average they begin to watch for a La Niña pattern. If an extended period of time goes with cooler temperatures, watches or advisories may be issued. Once the NOAA scientists are sure that the temperatures are going to stay with the cooler pattern, the La Niña season is officially declared. Here is what one of the sea surface temperature maps looks like that is provided by the CPC.
La Niña Impacts:
It will be mid-October before the official winter outlook is issued, but by looking at past La Niña years, we can do a little preliminary forecasting. For instance, La Niña patterns generally mean a cooler and wetter than normal winter in the Northwest. Last year, we saw above average snow fall in the mountains, giving a quick boost to ski lodges that were struggling from the year before. We even caught a little snow on the Valley floor, however, it wasn’t a major snowfall and not that out of the average. We did, however, have some rough weather including the Aumsville tornado, caused by dramatic changes in conditions. We also had a few days where we had the lowest high temperatures on record.
Across the rest of the nation, the Northern Plains and the Ohio River Valley will also see wetter and cooler conditions, the southern states will see warmer conditions, and the drought-stricken states of Texas, Oklahoma, and New Mexico will continue to see a drought pattern. It is also possible that the Atlantic Hurricane Season will continue towards an above average season.