A low-pressure system spinning off from the northern jet stream may bring some much needed moisture to Southwest Colorado this week.
Cortez woke up to light rain Monday morning, a preview of a larger system hitting later this week, said Kris Sanders, meteorologist for the National Weather System.
A cold front from the Pacific Northwest is rotating south into the Southwest, while drawing in moisture from the Pacific Ocean.
“It is in a decent track, and will be slow to move through,” Sanders said. “There is a really good chance for precipitation Thursday and Friday” in the Four Corners.
Forecasters call for up to foot of new snow in the higher elevations of the San Juan Mountains, and areas with storm banding could produce more.
The lower valleys may see a mix of rain and snow. The storm will clear out by Sunday. After a warm-up into the 60s Monday and Tuesday, highs will drop into the 40s for the rest of the week as the storm moves through.
Warm days last week wicked away the snowpack of the Hesperus Ski area, which closed for the season Sunday.
For March, Cortez has seen 1.1 inches of snowfall, or 20% of the average March total of 5.4 inches, said Jim Andrus, observer for the National Weather Service.
Overall, snowfall for the winter season — October through April — is tracking at the average, he said.
Cortez has received 35 inches of total snowfall since October, 103% of the average 34.1 inches.
As of March 5, year-to-date precipitation for Cortez was 2.13 inches, or 74% of the normal 2.86 inches. Andrus credited a six-day snowstorm in February that put that month at 137% of normal for snowfall.
“The other 22 days in February were dry, so we got a much needed break when a storm broke through,” he said.
Mountain snowpack is below average for the Dolores River Basin, which feeds McPhee Reservoir. On March 8, the cumulative total for four Snotels in the mountains of the basin showed 71% of yearly average for snow-water equivalent.
The storm coming this week was attributed to a breakaway low-pressure system dropping in from the north, said Sanders, of the weather service.
The “cut-off low” happens when the northern low pressure is “so deep and wound up, part of it gets cut off from the main flow” and drops into the subtropical jet stream farther south.
“When it happens, they tend to meander over the desert Southwest, and can be a big weather maker this time of year,” Sanders said.
It may be short lived, however, as the 30-day forecast shows below normal precipitation and above normal temperatures, he said.
The dry pattern is in line with the current La Niña weather pattern, which has a tendency to decrease the chances of winter storms hitting the Four Corners.
The phenomenon is caused by the relative cooling of the Equatorial Pacific, and is opposite of El Niño pattern, the relative warming of the Pacific that increases chances for winter precipitation in the Four Corners.
