Weather prediction: Monsoons may be on the way later this month

But new ‘La Nina Watch’ indicates upcoming winter could be drier and warmer than average

A family plays in the water at John Denver Sanctuary to cool down during a hot summer day in Aspen on Friday, July 9, 2021. (Kelsey Brunner/The Aspen Times)

While higher than normal temperatures are likely to continue in Aspen and the Roaring Fork Valley through the summer, monsoonal moisture is predicted toward the end of the month and into August.

That’s according to the latest climate models for the next month from National Weather Service forecasters at the Climate Prediction Center in Maryland. The CPC’s online site also features long-range forecasts for the fall and winter — it issued a “La Nina Watch” on Thursday — and if you’re a skier or snowboarder, you’re probably not going to love them.

But getting back to this summer and the prospects for rain and diminished wildfire danger, things are looking up, according to the latest CPC models.

The CPC posts several different temperature and precipitation outlooks on the main page of its site, including a 6-10 day outlook, 8-14 days, 3-4 weeks, one month and three months. A look at the maps for the two soonest outlooks shows the likely continuance of above average temperatures and below average precipitation in Colorado and most of the West.

However, the same maps show below average temperatures and above average precipitation likely to occur in Southern Arizona, Southern New Mexico and most of Texas, which would indicate possible monsoonal moisture forming, said Norv Larson, an NWS meteorologist in Grand Junction.

Then comes the 3-4 week forecast, which is valid July 24 to Aug. 6. Temperatures in Aspen and Western Colorado are predicted to have a 55% chance of being “above normal” at that time, but the monsoon precipitation bubble — which predicts a 55% chance of above average rainfall — has now expanded to include most of Western Colorado, all of Utah, all of Arizona and a sliver of Western New Mexico.

“(The models) would seem to indicate (the possibility) of sub-tropical moisture to come into our area,” Larson said.

The three-month outlook shows temperatures likely to have 50% to 60% chances of higher than normal, with precipitation back down to 33% to 50% below normal.

And that appears to be the beginning of a possible drying trend that might flow into at least the early part of the 2021-22 winter, according to the long-range forecasts.

The La Nina Watch issued Thursday by the CPC says the weather phenomenon could potentially emerge “during the September-November season and (last) through the 2021-22 winter (66% chance during November-January).” La Nina is affected by temperatures in the Pacific Ocean and causes the jet stream to push storms to the northern part of the country. El Nino, conversely, causes the jet stream to push storms toward the southern part of the country.

The CPC’s long range forecasts for the upcoming winter suggest higher than normal temperatures throughout the winter and below normal precipitation for at least the first half of the winter. During the second half of the winter, precipitation is currently predicted to return to normal levels, according to the forecasts.

Larson emphasized that long-range weather forecasts can and likely will change.

The longest forecast issued by the NWS in Grand Junction is seven days, he said. And that indicates that moisture is likely to weaken the warm high pressure system next week that hovered over the Roaring Fork Valley this week, bringing cooler temperatures and the possibility of scattered thunderstorms, Larson said.

Grand Junction, by the way, reached an all-time high of 106 degrees Friday afternoon.


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