The National Oceanic and Atmostpheric Administration (“NOAA”) recently released their 2010-11 winter outlook: (http://www.noaanews.noaa.gov/stories2010/20101021_winteroutlook.html ). Their official forecast for the Mid Atlantic is for “equal chances for above-, near-, or below-normal temperatures and precipitation.”
Their forecast utilizes several climatological factors, most notably the current “La Nina” phase, discussed below, to predict the predominant winter pattern.
While long range forecasting in the meteorological community has become somewhat more accurate in recent years, overall, because we do not yet completely understand the various climatological phenomena and the extent to which they influence our weather, we are still not able to accurately forecast the weather months ahead of time with any real consistency. As time goes by however, and more and more research is examined, we are slowly getting closer to more accurate longer range forecasting.
Specifically, over the past 20 years of meteorological research, several large climatological phenomena or “teleconnections” have been identified as having an effect on the Eastern United States’ winter weather.
The El Nino/La Nina Southern Oscillation (“ENSO”) which involves variations in the temperature of the surface of the tropical eastern Pacific Ocean, warming or cooling, known as El Nino and La Nina respectively. See the map below from NOAA for a description on how ENSO phases affect eastern U.S. winters.
The Pacific decadal oscillation (“PDO”), a pattern of Pacific climate variability that is detected as warm or cool surface waters in the Pacific Ocean north of 20 degrees North (as opposed to ENSO which takes place in the tropical regions of the Pacific). A “cool” phase of the PDO is associated with cool sea surface temperatures along the Pacific coast of North America, and visa versa a “warm” phase is associated with warmer sea surface temps. It is an oversimplification but a warm phase is generally correlated to below normal winter temperatures in the eastern U.S. and a cool phase to above normal winter temps.
The Quasi Biennial Oscillation (“QBO”), s a quasi-periodic oscillation of the equatorial zonal wind between easterlies and westerlies in the tropical stratosphere. Generally stronger easterlies favor a more “blocky” weather pattern and associated colder/stormier weather in the east.
The Arctic oscillation (“AO”) an atmospheric circulation pattern in which the atmospheric pressure over the polar regions varies in opposition with that over middle latitudes.
The North Atlantic Oscillation (or “NAO”), closely related to the AO, 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 diagram below from Intellicast.com).
(Note that there are various additional indicators that meteorologists believe play a role in establishing our winter pattern such as, but not limited to, solar cycles, snow cover (both over North America, as well as Europe and Asia), soil moisture, global warming and volcano eruptions (particularly noteworthy this year), but for purposes of simplicity I will save their discussion for future posts.)
Among the aforementioned teleconnections, meteorologists still are not sure what factors are the “chicken” or the “egg.” Many meteorologists place a very heavy emphases on the ENSO phase. For example, many meteorologists have associated last year’s record breaking winter with the weak El Nino that was present during the most of the winter.
I personally believe, of the teleconnections discussed above, that the North Atlantic Oscillation (NAO) is the most predominant and consistent predictor of our winter weather in the eastern U.S.
For example, generally speaking, whether or not the ENSO is La Nina or El Nino, the phase of the NAO seems to bare a stronger correlation to the outcome of eastern U.S. winters. Take for example that while a moderate El Nino and negative NAO might combine (such as was the case in 2009-2010) to produce a very extreme (i.e. below average temps and above average snow) eastern U.S. Winter, even a strong La Nina event can produce an extreme winter when combined with a strongly negative NAO (as was the case in the record-breaking winter of 1995-96).
The problem from a forecasting perspective is that it is difficult to determine the phase of the NAO at any point in time in advance, and therefore difficult to extrapolate into a winter forecast. However, note that on the NAO index below, there appears to be a 20-30 year cycle wherein the predominant phase of the NAO is more often than not negative (i.e. colder eastern U.S. winters) during late 1950’s until the late 1970’s (see also http://www.cpc.noaa.gov/data/teledoc/nao.shtml), then more often than not positive (i.e. warmer eastern U.S. winters) during the early 1980’s until the late 2000’s.
My own feeling is that we are now entering into a new 20-30 cycle where the NAO is more often than not negative and thus will see generally more often than not colder winters in the eastern U.S. during this period.
My own belief is that the winter of 2009-2010 represented the early stages of this cycle. While surely there will be some warmer winter anomalies (as was the case every so often during the 1950s through the 1970s), I believe, on average, we will see predominately colder/snowier winters for the next 20-30 years. While I do not expect this winter to produce anywhere near the amount of snow we received in the record setting winter of 2009-2010 (a seemingly “once in a lifetime” winter), my suspicion is that this winter will produce above-average snowfall for the Garrett County region. Time will only tell…