Looking Forward to Winter

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No season is the subject of speculation quite the way winter is.  Sure, people anticipate all four seasons, planning activities such as vacations, sporting events, and outdoor activities around each one.  But, there is something about the way winter is anticipated, as experiences can vary year to year in winter more than in any other season.  Every October, speculation begins to intensify.  Fear and dread clearly radiate from the voices of some, while excitement and anticipation come from others.  Most likely, this depends on one’s location, as well as preferred activities.

I spent a lot of years in the Midwest, and completely sympathize with those who dread winter, and hope for nothing more than to have their pain be as minimal as possible for the season.  Here in Colorado, on the other hand, enthusiasts of outdoor snow sports, mostly skiing and snowboarding, anticipate winter with great excitement, typically hoping that the coming season’s snowfall and snowpacks will be at least in line with seasonal averages, if not more.

As an Epic Pass skier who lives in Denver, my ideal winter would be one with plenty of snow in the mountains, particularly the resorts I ski near the I-70 corridor, but generally milder east of the mountains, where Denver is.  And, given this year’s setup, I may actually get this kind of winter that I want!

I have received quite a few questions, both from people local to Colorado, and those considering traveling here to ski in the mountains, regarding what kind of winter to expect.  Now that the National Oceanic and Atmospheric Association (NOAA) has released its outlook for the season, there is no better time to give my own take on how winter 2016-17 is looking.

First, I should note that, the NOAA forecast, as well as other forecasts already made for the winter season primarily focus on one phenomenon: La Nina.  This, of course is the inverse of El Nino.  So, while El Nino winters tend to be wet to the south and dry to the north, La Nina winters will tend to be the opposite.

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This is reflected in NOAA’s graphical precipitation outlook for the winter.

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However, this year’s La Nina is likely to be a weak one.  Both El Nino and La Nina can be strong, moderate, or weak, and the predictive power of the phenomenon is limited in cases when the anomalies are weak.  In these cases, I find it useful to look at other patterns that are beginning to emerge when speculating about long-range weather patterns.

Anomalies in Sea Surface Temperatures are the most commonly used data point when predicting weather long term.  This is because the ocean retains much more heat than land or air, making it more likely that the current pattern will persist for longer.  Ocean temperatures can also have a major impact on atmospheric circulation, as is evidenced by the El Nino phenomenon itself.

When looking at current SST anomalies, three patterns emerge as having the potential to impact the weather Colorado and the rest of Western North America will experience this winter.

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First is the weak La Nina, whose impact would be more precipitation for the Northwest, but less for the Southwest.

Second is the abnormal warmth off the East Coast of North America.  This pattern emerged at the end of a summer that was hotter and drier than normal across much of the Northeast, a pattern that generally has continued, although they are currently experiencing a cold snap.  This warm anomaly, if it persists, would mostly likely lead to frequent northwesterly flow over Western North America, as the predominant pattern in winter is one called a wave #3 pattern.  This means three ridges and three troughs over the globe, a ridge to our west and a trough to our east.

The final temperature anomaly that appears to be in a crucial area are the warm anomalies off the coast of Alaska.  These warm temperatures could strengthen a phenomenon known as the “Aleutian Low”, which would act to steer wet weather into the Pacific Northwest.  Under this scenario, Colorado and the interior west will likely be drier.

All three phenomenon point to, although not with too much confidence, more frequent northwesterly flow across the state.  This pattern tends to be dry in Colorado overall, but, as pointed out by Joel Gratz, is a favorable wind direction for upslope storms at ski resorts along the I-70 corridor, including Vail, Copper Mountain, and Breckenridge.

With La Nina being weak, and the other two SST warm anomalies (see map above) being in close proximity to areas of cool anomalies, there is low predictive power to this seasonal forecast.  Any scenario is still possible.  However, signs are pointing, generally, towards a dry winter for much of the west, particularly the Southwest, and a wet winter in the Northwest.  Locally, in Colorado, the most likely scenario is a mixed bag for the ski resorts, with the storms that do occur favoring the corridor of popular resorts near I-70 1-2 hours west of Denver.

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And a warm and dry winter on the East side of the Continental Divide.

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(Note: the two photos above are from the previous winter season)

 

 

 

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