Sunday, October 30, 2011

2011-2012 Winter Outlook

With winter approaching, I thought I’d write a brief summary of the weather I am anticipating this winter.  My own unofficial outlook, if you will.    I’ll keep my reasoning brief, but with another La Nina winter seeming pretty likely, the overall national weather trend should follow what is usually observed on La Nina winters.   Listed below are some regional highlights and explanation.

As the graphic below depicts, during a La Nina winter, colder than normal sea surface temperatures near the equatorial Pacific Ocean have a response on the atmosphere to decrease the intensity of the subtropical jet, while increasing the intensity of the polar jet.  The end result is a more active northerly storm storm track. Often times, cold air moving south from Canada can interact with this polar jet resulting in occasionally colder storm systems bringing low elevation snows and major cold spells to parts of the country.

  My Outlook

Northwest U.S
La Nina winters in the Northwest tend to be cool and wet, and I see no reason to doubt that will be outcome of this year as well.  Despite last year being a La Nina winter, the season was not as wet and snowy in the northwest as you would usually expect to see.   I would expect this year to be closer to the typical La Nina winter.  Significant periods of rainfall will lead to an enhanced flood risk this winter.   I also wouldn’t be surprised to see a major cold spell or two with enhanced chances of low elevation snow events in the Pacific Northwest this year.
*Enhanced Flood Risk
*Possible cold snaps and low elevation snows

Southwest U.S
La Nina winters tend to favor drier conditions across the southwest, much like what was observed in the previous winter.  I don’t see a lot of hope for relief in the ongoing drought conditions in Texas, and some drought development is likely further west into New Mexico and Arizona.  I do think this winter will be very much like last winter, with near normal precipitation and snowfall observed across the northern half of AZ, with warmer and drier conditions further south.  Occasional northerly frontal systems passing through may result in brief but significant cold spells for the higher terrain of California, Arizona, and New Mexico.   Heavy snows will be possible in the Intermountain region once again this winter.
*Increasing dryness with southerly extent.
*A few brief cold spells, warmer than average temperatures overall.
*Heavy Intermountain Snows
*Continued extreme Texas drought

The climate prediction center calls for above normal precipitation and colder than normal temperatures for this region.  I believe however, that departures from normal may be muted in the overall warming trend observed for the past several winters in this area, so I anticipate near normal conditions overall for this region.

Looks like another snowy winter, and given a significant and wildly out of season snow event has just taken place in the Northeastern states (Never before has NYC recorded an inch or more of October snowfall, and yesterday Central Park measured nearly 3 inches), confidence is relatively high in this area.  A significant cold spell may also strike this region later this winter, complimented by heavy lake effect snow events.  While I doubt this winter will be as uncharacteristically snowy as last winter, I suspect amounts will generally be above normal for most of the region.

It will be interesting to review this outlook in March and see how I did! 

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