Monsoons finally arrived in Southwest Colorado this week after a couple of brief flirtations earlier this summer, promising more rain for a hot and dry Montezuma County.
There were two weak monsoon surges from late June through July, said Joe Ramey, a meteorologist at the National Weather Service office in Grand Junction. The stronger, third surge this week could hold the potential for flash flooding.
The weather forecast for Montezuma County reflects those trends.
The forecast for this week calls for thunderstorms through Friday, mainly after noon. According to the National Weather Service, there’s a 40 percent chance of showers and thunderstorms on Tuesday and Wednesday, and a 60 percent chance on Thursday.
High temperatures are forecast to be in the mid-80s through Wednesday, and in the upper 70s on Thursday and Friday. Sunny skies are forecast for Saturday and Sunday, with highs about 80 degrees. Overnight lows throughout the week are expected to be in the middle to upper 50s.
The rain may bring relief from the hot, dry July. In July, the average high temperature was 91.3 degrees; the normal high for Cortez is 88. Cortez received .97 inch of rain in July, compared with a normal of 1.28 inches, according to local weather watcher Jim Andrus.
The monsoon is a seasonal phenomenon in which winds start coming from the south instead of the west. Then, as high pressure sets up in the Southwest, winds help pull water into the region from the Mexican and Californian gulfs. And because of solar heating, a thermal low develops over the desert Southwest, which helps to pull even more rain into our area. As these two events interact, we get our familiar, seasonal pattern of almost daily thunderstorms.
This year’s weather also has been influenced by the El Niño phenomenon, which brought heavy snow to the Four Corners area this winter. The El Niño has ended, according to the weather service, but with a twist this year: El Niño’s opposite effect, La Niña, is unlikely to occur. The La Niña is often linked to drier winters.
“El Niño is over, but La Niña has not replaced it,” said Ramey.
El Niño occurs when temperatures in a patch of ocean off the Ecuador coast rise by about 1 degree (.5 degree Celsius) from three-month averages. The effect is that storms generally track in a more southerly direction across the U.S.
La Niña occurs when the patch of equatorial Pacific cools by about 1 degree from the average. It results in generally drier winters in the Four Corners as storms take a northerly track.
In June, weather service forecasters saw the ocean temperatures drop from El Niño, and reported the likelihood of a La Nina was 77 percent.
“It is now at 55 percent, so it is setting up for an ENSO (El Nino Southern Oscillation) neutral pattern,” which is neither El Niño or La Niña, Ramey said.
The neutral pattern isn’t necessarily bad news for the upcoming winter, he said, but it makes the long-term winter forecast more unpredictable.
“ENSO-neutral years do not have a favorite pattern, and the storm tracks vary widely,” Ramey said. “The climate record shows these years can be dry or wet, so it is kind of a wild card.”
Since 1950, there have been 19 El Niños. Of those, in the season that followed a La Nina occurred 11 times and an ENSO neutral occurred five times.
Journal reporter Jim Mimiaga contributed to this article
