La Niña to influence winter weather again

October 28, 2011

For the second winter in a row, La Niña will influence weather patterns across the country but instead of the near record snowpack that buried much of the Colorado mountains last winter, chances are we’ll be looking at only slightly above average precipitation this winter, says Klaus Wolter, a CU-Boulder and NOAA atmospheric scientist.

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Oct. 28, 2011

For the second winter in a row, La Niña will influence weather patterns across the country but instead of the near record snowpack that buried much of the Colorado mountains last winter, chances are we’ll be looking at only slightly above average precipitation this winter, says Klaus Wolter, a CU-Boulder and NOAA atmospheric scientist.

CUT 1 “Skiers shouldn’t get too excited about this coming winter. It will probably be OK. I’m expecting a near normal to slightly above normal winter but there’s definitely little chance of repeating what we had last year.” (:17)

 The “double-dip La Niña winter” as Wolter calls it, has a pattern to it in which the second year tends to produce less precipitation than the first, especially in regions that tend to be dry during La Niña winters.

CUT 2  “When you look historically at these cases eight out of ten go down after the first year. So it doesn’t matter if the first year is dry or wet, eight out often end up being drier in the second year than the first year. (:13) If you check the precipitation records we have in the west it holds up, too. From California through Colorado, Texas and into the Southeast, all these areas that tend to be dry with La Niña anyway, they tend to be even drier in the second year.” (:32)

Even though we most likely will not see as high snowpack as last winter, Wolter says there should be plenty of snow during the core winter months to satisfy skiers and borders.

CUT 3 “The nice thing about La Niña for the ski areas is that they tend to focus the snow season on the core winter months – Thanksgiving to early March are the best chances for good powder snow and frequent days with snowfall. (:18) A lot of the snow is orographic, which means that the higher you go the more snow you will get.” (:23)

 One drawback to another La Niña winter, says Wolter, is that folks on the Eastern Slope can expect a lot of windy days as an enhanced polar jet stream will keep storms moving quickly from west to east, typically dumping more snow on the western part of the state as the storms tracks over the continental divide.

CUT 4 “The drawback is that often there is wind. But most of the wind hits the east slope. So often with the more snow that you get on the west slope with this La Niña pattern, which comes in from the west, northwest, you get more wind on the east side.” (:13)

Another aspect of La Niña winters is that there tend to be wide temperature swings. Alternating warm Chinook winds and intense cold snaps are the signature of a Colorado La Niña winter, says Wolter.

CUT 5 “You might get a Chinook where it get’s really warm in-between storms or after a storm. And then you can get really deep Arctic outbreaks, too. Last winter, if you recall, in early February, we had the coldest cold snap since December 1990 - the coldest in 20 years. (:19) It was quite remarkable. There were cities like Crested Butte, Steamboat, Walden, Fraser - all hit minus 40. (:28) I’m not predicting that we are going to see a carbon copy of that but the risk of a cold snap is definitely increased.”(:34)

Last year, Wolter says, La Niña peaked in the fall season and was already weakening by late winter. This helped to offset dry spring expectations in 2011 that are typically associated with La Niña events that persist into spring.  But, he says, if we see La Niña conditions deep into next spring we may not be as lucky as last year and that’s because, in some cases, La Niña events that have lasted three years in a row have spawned severe drought conditions. The last time that happened was a decade ago, leading up to the record setting drought of 2002.

-CU-

 

 

 

 

 

 

 

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