I was able to participate in a conference call with Mike Halpert, Deputy Director of NOAA Climate Prediction Center, and Deke Arndt, Chief of Climate Monitoring at NOAA's NCDC, this morning and we had an interesting discussion on this upcoming winter. With the exception of last year the previous winters have been fairly snowy and cold. Going into this winter season and trying to predict what will happen during that three month time period has been a little more challenging for forecasters.
Earlier this year it appeared as if the La Nina pattern we were in was going to weaken and ENSO neutral or even weak El Nino conditions were going to develop; meaning sea surface temperatures were beginning to warm. A few months ago it looked as if that pattern was beginning to pan out. Sea surface temperatures along the equitorial Pacific were beginning to warm signaling a shift into an El Nino pattern. However, earlier this month the development of El Nino came to a halt resulting in a very unique situation because something like that hasn't really happened over the 60 year climate period forecasters had been looking at. This in itself poses a challenge when trying to predict what will occur during the winter months because there are no real past cases to rely on. A theory as to why this may have occured is there was possibly no true interaction with the atmosphere and sea surface temperatures. Another challenge for forecasters has been the shift from the 1971-2000 climate period to the 1981-2010 climate period. We've lost our 'base period', so to speak, with trying to forecast seasonal outlooks causing the trend signals to be lost. There have been, however, some signals pointing to a possible redevelopment of those conditions based upon the forecasting outlook models and earth system models.
So, what does this mean for temperature and precipitation across the U.S? The persistent warmer than normal conditions will likely continue across the Plains and further west with cooler than normal temperatures in Florida. Closer to home there is about a 50/50 chance that we may end up either warmer or colder than average. For precipitation, there is a 33% chance that extreme northwest Illinois and the Midwest will end up drier than average along with the Pacific Northwest. It's important to realize when forecasting these outlooks they are probabilistic and not guaranteed. Just take last year for example. The winter was forecast to be a cold and snowy winter but ended up being fairly warm and dry. There are other teleconnections we have to look at that will also play a role in what this winter has in store. For example, the Arctic Oscillation. Unfortunately the skill level in predicting that months in advance just isn't there and this is a phenomenon that we can usually forecast only a few weeks in advance.
An interesting feature that was pointed out by someone from USA Today was the high confidence in above average temperatures for the north slope of Alaska. Sea ice is at its record low and it's possible this may have a small impact on the weather for the lower 48. It will be critical to see how that will interact with the Arctic Oscillation this year.
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