There wasn’t a cloud in the skies over Wyoming on Tuesday. Literally.
For much of the day Tuesday, there was no cloud cover over the Cowboy State anywhere, prompting the National Weather Service office in Riverton to call out the “unusual” phenomenon and post a satellite photo showing a clear image of a completely cloudless Wyoming.
The only white showing were a couple of tiny dots in the northwest mountains from Monday’s first snow of the season
“It lasted most of the day yesterday,” meteorologist Jason Straub told Cowboy State Daily. “We had a high-pressure system in the area that was suppressing cloud cover, so we didn't have anything impacting us pretty much all day yesterday.”
The high-pressure system has since moved on, permitting cloudy skies Wednesday, but it might not be the last time this season where there’s nothing but blue skies over Wyoming.
Without any cloud cover to impede the view, the satellite image also clearly shows the scars left by large wildfires in northeast Wyoming.
Sweeping Brooms
The high-pressure system that crossed over Wyoming on Tuesday prevented the development of clouds, and Straub said it must have been a large system to keep Wyoming completely cloud-free.
“You need a pretty large area of high pressure holding the cloud cover down and pushing weather systems off to the east or holding them off to the north,” he said. “That’s what we had yesterday. This system shifted everything east.”
Cowboy State Daily meteorologist Don Day said the high-pressure system carried a surge of dry air from western Canada. The combination of high pressure and dry air descending on Wyoming pushed out the high humidity and cooler temperatures that caused the first snowfall of the season in the Wind River Range on Monday.
“The best analogy I can give is a broom,” he said. “The storm system that brought the mountain snow and cooler weather was like a broom that swept away a lot of the high humidity that’s generated the afternoon and evening thunderstorms. The air mass behind the storm was much drier, and it swept away that higher level of moisture.”
These seasonal “brooms” are typical at this time of year, a sign that summer’s strength is ebbing away and the seasonal transition is just around the corner. Day said Wyomingites should anticipate several more “brooms” over the next few weeks.
“That's why you get these periods of crystal-clear blue skies in September and October,” he said. “The same thing happens in spring. You get a nice warm-up and then get cold, wet weather. It’s the same things as we start to change seasons.”
Nothing But Blue Skies
With no clouds in the sky, one could assume it got warmer on the ground with nothing to block the sun’s rays. Straub said the cloudless sky might have made Wyoming a little warmer, but there probably weren’t any drastic temperature spikes because of it.
“Cloudless skies are a sign that there was no agitation of the atmosphere,” he said. “It allows more sunlight to reach the ground, so it does provide a little bit of heating, but not an excessive amount.”
Seeing nothing but blue skies during an active and ongoing fire season might raise alarm that Wyoming is too dry to extinguish its wildfires. However, Day said cloudless skies are nothing to worry about because a rebound is always on the horizon.
“After a frontal system like this, you're naturally going to have a rebound,” he said. “If you got these in mid to late July, that would be unusual. But this time of year, no, the brooms start. This broom will go through, and the weather pattern changes with the opportunity for some moisture to return.”
As for the weekly forecast, Day and Straub said Wyoming will stay dry for most of the week and into the weekend. The next broom, which should arrive early next week, will sweep in a change.
“Wyoming is going to stay dry for the rest of the week and through most of the weekend,” Straub said. “There will be a bit of cloud cover here and there, especially on the higher elevations of the Wind Rivers and the Bighorns, but no precipitation is expected through the weekend.”
“We’ll see some afternoon cloud build-up and a few afternoon showers and thunderstorms on Sunday and Monday,” Day added. “The next broom comes towards the middle of next week, which should bring some more moisture.”
A benefit of the “brooms” sweeping across Wyoming is that it clears the air of wildfire smoke. That’s good news for anyone with plans for the holiday weekend.
“This type of broom action means a really nice Labor Day weekend,” Day said. “It scoops away everything in the air.”
‘Gorgeous’
A cloudless day over Wyoming is a rare chance to take in the whole, unobstructed beauty of summer in the Cowboy State. Day said the National Weather Service’s satellite image is “gorgeous.”
“The broom action swept away the air pollution, so there's nothing there.,” he said. “You can see all that and everything on the ground, too. You can see where the fires have been and a little bit of snow in Wind River and Absaroka Ranges. You can see a lot of resolution there because of the clearing trend of these systems.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
