Colorado: No El Niño, no La Niña – what’s driving the weather?

Spring outlook trends toward warm and dry conditions

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The Madden-Julian Oscillation has played a role in Colorado weather this winter.

By Summit Voice

FRISCO — With neither El Niño or a La Niña conditions in the Pacific Ocean, long-range weather forecasters have been struggling to develop confidence in their outlook for the coming spring season — a critical time for much of the West in terms of getting some relief from drought conditions.

A wet and cool spring could at least take the edge off the drought in some areas, helping to maintain stream flows and reduce the potential for massive and dangerous wildfires. Conversely, a return to last year’s very dry and warm spring pattern would spell trouble for places like Colorado.

So if the El Niño-La Niña cycle isn’t driving the weather, what is? What we do know is that conditions over the Pacific Ocean are the key to understanding exactly what path storms will take across the western United States, and that conditions in the North Atlantic can also be a factor.

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Precipitation patterns across Colorado have been a mixed bag this winter.

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A patchwork quilt of precipitation across Colorado.

So far this winter, meteorologists have pointed to a combination of a cooler-than-average conditions in the Pacific (similar to La Niña) and warmer-than-average ocean temps in the Atlantic as a factor in continuing dry conditions overall.

And in the latest three-month outlook from the National Weather Service in Boulder, meteorologist Mike Baker also discussed the influence of the Madden-Julian Oscillation (MJO) — basically a 30- to 60-cycle of moisture pulses moving around the globe from west to east.

Here’s the description from his slideshow:

The MJO (also the 30-60 Day  Tropical  Wave) is a combination of large-scale circulations associated with an oceanic Kelvin  Wave and atmospheric Rossby Wave. MJOs of sufficient strength will circle the globe along the equator ordinarily within a span  of 30 to 60 days. MJOs are characterized by an eastward propagating complex of enhanced and suppressed tropical convective  rainfall observed mainly over the Indian and Pacific Oceans. MJOs moving eastward across the central and eastern tropical  Pacific Ocean can have a significant influence on precipitation and circulation patterns in Hawaii and the continental United  States. Weather patterns and large-scale circulations attributed to MJOs in the eastern tropical Pacific can resemble similar  patterns associated with El Niño, but with a much shorter duration (from a few days to a couple weeks). MJOs occur most often  during weak La Niñas and ENSO-neutral conditions, and are weakest or absent during El  Niño cycles.

This year was no exception, as a moderate to strong MJO formed near Indonesia in early January. Slowly moving eastward, it helped fuel a wide area of enhanced precipitation from the west coast to the central and southern Rockies, and the farther east, through the southern tier of states.

But once the wave passed, sea surface temperatures once again cooled to values near those associated with a weak La Niña, fueling more concern that Colorado could see a dry spring.

The official outlook from NOAA’s Climate Prediction Center reflects those concerns, with better than average chances for above-normal temperatures and below-normal precipitation through May.

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