What Will Winter 2011-2012 Bring for Garrett County?
Last year this site predicted the probability of another colder and snowier than average winter in Garrett County (see here). This coming winter is showing signals pointing toward a similar winter.
Though I believe too much emphasis is placed on the ENSO cycle (i.e. El Nino vs. La Nina conditions in the southern Pacific Ocean), the apparent weak La Nina conditions, based on analogs, is generally supportive of a colder/snowier winter.
A second factor I believe should receive much more weighting is the prevailing weather pattern during the pre-winter months. For the past few months the overall pattern over the United States has consisted of a trough in the east or a closed upper low for a great majority of the time. This gives us an indicator of what the pattern might be during the winter months. Moreover, over the past several weeks there have been several significant east coast low pressure systems that took a track similar to a “Nor Easter” if it were winter. These systems may have been major snow producers if they had occurred a few months later, however the fact the pattern supports such systems now, again is indicative of what we might expect in December and January.
Though some forecasters place a heavy emphasis on snow cover (over the upper northern hemisphere), the extent of snow cover can be only a snapshot of the daily snow cover on the day a forecast is issued and can change dramatically just a few days later. Nonetheless on the date of this forecast, the snowcover over Canada is about the same as it was last year, though not nearly as widespread as it was on this date two years ago before the record winter of 2009-2010.
Finally, as was stated here last year, and perhaps the biggest driver of our winter weather in my opinion, is the multi-decadal cycle of negative North Atlantic Oscillation “NAO”. The NAO is a pressure oscillation between the Icelandic Low (a semi-permanent center of low pressure located near Iceland and southern Greenland during the winter) and the Azores High (a semi-permanent center of high pressure near the Azores in the Atlantic Ocean) over the North Atlantic Ocean. Generally speaking, a negative phase of the NAO results in more amplification of the jet stream and more frequent arctic intrusions into the eastern U.S. and a positive phase results in the prevailing jet stream shifting north and “bottling up” the cold air in Canada. See illustrated here:
And, as was referenced in last winter’s forecast, there appears to be a 20-30 cycle of the NAO, and as is illustrated in this chart, we appear to be in a period where more often than not the NAO is negative, and therefore correspondingly leading to colder eastern winters.
Based on the above, I believe Garrett County is in for a similar winter as last year with November and December potentially being particularly cold and snowy with an active southern jet stream as well as frequent lake effect/upslope snows. As far as total snowfall I believe we will see at least an average seasonal snowfall if not greater than average (the average annual snowfall in Garrett County being 138 inches since 1970).