La Niña update

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From the Summit County Citizens Voice (Bob Berwyn):

In a three-month outlook covering April through June, National Weather Service forecasters say the weakening La Niña (cooler than average sea surface temperatures in the central and eastern Equatorial Pacific) will continue to influence Colorado’s weather, but to a continually lessening degree. Off the coast of Central America and northern South America, sea surface temperatures have actually climbed above average.

Through the first part of the three-month period, a west-to-east jet stream is expected to dominate the weather, with occasional dips (short-wave troughs) bringing spells of mountain snow on west-facing slopes favored under orographic conditions.

“The Pacific jet stream will likely continue to produce periods of moderate to heavy mountain snowfall on progressively higher west-facing mountain slopes as temperatures rise through at least the end of April,” forecaster Mike Baker said. ” … (A)t the same time, this prevailing zonal flow pattern will also continue to generate periods of abnormally warm and very dry weather, accompanied by potentially damaging downslope (Chinook) wind events in areas east of the Continental Divide.” This wind-flow pattern is also an important part of the Great Sand Dunes ecosystem in the San Luis Valley, helping to replenish the dunes,” he explained.

Later in May and into June, the pattern really starts to change. June is often one of the driest months in the high country, as increasingly warm temperatures in the desert southwest and across the Great Basin build a bubble of high pressure that pushes the jet stream farther north. Troughs in the jet stream will still dive southward across Wyoming and into Utah, but not as frequently. The same pattern can bring strong, gusty northwest winds to the Front Range and nearby plains, leading to a continued high fire hazard in that region. Currently, the eastern half of the state is rated as being in a moderate to severe drought, with little relief in sight in the next three months.

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