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New study shows link between Pacific sea surface temperatures and tornado patterns in the Midwestern U.S.

Cooler Pacific Ocean temps may drive tornado activity into southern U.S.

A tornado near Lakeview, Texas. Photo courtesy NOAA.

A tornado near Lakeview, Texas. Photo courtesy NOAA.

By Summit Voice

FRISCO — After studying more than 56,000 tornados, researchers at the University of Missouri say they’ve found a clear link between Pacific Ocean sea surface temperatures and the patterns of storms that spawn the violent twisters. The findings could help scientists predict the type and location of tornado activity in the U.S.

When surface sea temperatures were warmer than average, the U.S. experienced 20.3 percent more tornadoes that were rated EF-2 to EF-5 on the Enhanced Fuijta (EF) scale. (The EF scale rates the strength of tornados based on the damage they cause. The scale has six category rankings from zero to five.)

“Differences in sea temperatures influence the route of the jet stream as it passes over the Pacific and, eventually, to the United States,” said Laurel McCoy, an atmospheric science graduate student at the MU School of Natural Resources. “Tornado-producing storms usually are triggered by, and will follow, the jet stream. This helps explain why we found a rise in the number of tornadoes and a change in their location when sea temperatures fluctuated.” Continue reading

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Climate: Study looks at changing monsoon patterns

Natural climate variables so far outweigh global warming impacts

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The North American monsoon is an important climate factor in the Rocky Mountains.

By Summit Voice

SUMMIT COUNTY — The timing and amount of monsoon rains in the northern hemisphere have important economic and environmental ramifications, for example for farmers in Asia and the wildfire season in the southwestern U.S.

As a result, climate researchers have been trying to determine how the Earth’s steady warming will affect those seasonal rainfall patterns, and so far, the jury is still out. Some recent research has suggested that the timing of the North American monsoon might be delayed, while other studies have indicated that there could be an overall increase in monsoon precipitation.

In one of the latest studies, scientists with the International Pacific Research Center, University of Hawaii at Manoa, say that monsoon rainfall patterns appear to more influenced by natural long-term swings in ocean surface temperatures. The Interdecadal Pacific Oscillation or mega-El Niño-Southern Oscillation, which has lately been in a mega-La Niña or cool phase is one key factor, and shifts in the Atlantic Multidecadal Oscillation, also contributes to the intensification of monsoon rainfall. Continue reading

Colorado: A warmup, but no snow in sight

Drought expected to persist; water supply outlook grim

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Colorado’s snowpack hasn’t been above average since the big winter of 2010-2011.

By Bob Berwyn

FRISCO — Temperatures will begin to moderate across the Colorado high country the next few days, with highs climbing back to near seasonal norms, which is only in the lower 30s, but that should feel downright balmy after enduring an Arctic air mass the past few days.

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Dry conditions persisted across Colorado in the autumn of 2012, especially in the plains.

The nicest weather will be up on the mountain slopes, because warmer air aloft will trap cold air on the valley floors, and with no incoming weather systems to stir up the atmosphere, those inversions are likely to persist for the foreseeable future. That also means there’s no snow in the forecast for the next 10 days unless there’s a dramatic shift in the jet stream, which will stay far to the north for the next week at least. Continue reading

Colorado: Mostly dry into December

Is Colorado facing more drought?

So far, the pattern of storms across the Pacific Northwest and northern Rockies shows little signs of changing, with most of the weather action far north of Colorado.

By Bob Berwyn

FRISCO — Ullr, why has thou forsaken us?

If you’re holding out for more snow before heading out to make turns on the hill, you may want to reconsider. The outlook for the next 10 days is mostly dry and warm, with perhaps a chance of snow brushing the northern mountains Sunday night into Monday morning. Beyond that, another ridge will build into the Southwest, bringing more dry weather and a return to above normal temps for much of next week. Continue reading

Climate: NOAA drops El Niño watch

Forecasters call for neutral conditions, but say a La Niña is not out of the question

n El Niño never managed to establish itself in the equatorial Pacific this year.

The three-month precipitation outlook from NOAA’s Climate Prediction Center.

By Summit Voice

FRISCO — With sea surface temps cooling to near average in much of the equatorial Pacific, NOAA’s Climate Prediction Center has dropped an El Niño watch that’s been in effect for the past several months.

El Niño is part of a cyclical pattern of sea surface temperature variations that affects global weather patterns. The emerging El Niño forecast last spring and summer offered some hope for drought relief in the parched Southwest and the southern tier of states, where warmer than average Pacific Ocean temps can help boost winter and spring precipitation.

During La Niña years, when cooler-than-average sea surface temperatures prevail in the same region, the storm track often shifts northward, driving storms into the Pacific Northwest and then down across the northern Rockies and northwest Colorado. Continue reading

Colorado: Forecasters still grappling with winter outlook

An El Niño often brings decent October precipitation to the high country, but signals are mixed this year.

No clear signal means water managers will be biting their nails for a few months

By Bob Berwyn

FRISCO — Without a strong El Niño or La Niña signal, Colorado weather watchers are struggling even more than usual to get a sense of how much snow to expect this coming winter, critical information for water managers who have seen reservoir storage dwindle to below 70 percent of average for this time of year.

Even if winter snowfall is close to normal, some reservoirs are unlikely to refill completely next spring, leaving utilities in the position of hoping for an above average winter.

“We’re far from through this. The story has yet to unfold,” Blue River Basin water commissioner Troy Wineland said after participating in a weekly statewide water webinar, explaining that many local streams are flowing well below seasonal averages. A few others are close to average due to upstream releases of stored water, he said. Continue reading

Weather: El Niño, or La Niña’s ghost?

El Niño still struggling to develop

Will a negative Pacific Decadal Oscillation influence Colorado’s winter weather? Graphic courtesy NASA.

The three-month precipitation outlook from the Climate Prediction Center.

By Bob Berwyn

SUMMIT COUNTY — Climate experts are still hedging their bets when it comes to an outlook for the coming winter, with the official outlook from NOAA’s Climate Prediction Center showing no strong trend toward above- or below-average precipitation.

A somewhat murky El Niño outlook is clouding the picture, with sea surface temperatures in the equatorial Pacific ranging above average, but cooling down from just a month ago.

“It’s vexing … the models are just not up to the task,” Wolter said. Overall, he said he’s “guardedly optimistic” that Colorado will see at least close to an average snowfall year, which would would be critical to maintaining water supplies in the state’s depleted reservoirs. Continue reading

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