On Sunday, a powerful trough of low pressure swept across Colorado, bringing a round of strong thunderstorms to the I-25 corridor and Eastern Colorado, along with much cooler temperatures. Thunderstorm development occurred early in the day, which sent early afternoon temperatures down into the low 50s. The high for the day only topped out around 70 in Denver.
Today, the low pressure system has shifted well east of Colorado, bringing more active weather to the Midwestern states where portions of Iowa and Missouri are under an elevated threat for severe thunderstorms. The satellite image below (courtesy of the College of DuPage) depicts this system very well. You can also see some moisture over the Pacific Northwest, associated with another trough of low pressure over this region. This feature is expected to result in some stronger thunderstorms across western and central Montana this afternoon.
Colorado and the southern and central Rockies are experiencing beautiful weather today as the atmosphere has dried out behind the weekend system. The average high for Denver today is 86, and temperatures should be right around this mark across the I-25 corridor this afternoon. Unfortunately, the comfortable temperatures will be short-lived as high pressure strengthens over the Southern Rockies heading into the middle part of the week. This will result in a heat wave across the Four Corners states, with temperatures soaring into the mid to upper 90s in Denver on Tuesday. The image below depicts the GFS model-projected ridge of high pressure over the Southern Rockies on Tuesday (image courtesy of Tropical Tidbits).
The heat wave will continue on Wednesday and Thursday with even hotter temperatures expected. In fact, forecasted highs for Denver on Wednesday and Thursday are right around 100 degrees. Other “usual” hot spots in the region could see temperatures approach or exceed triple digits as well, such as Pueblo, Grand Junction, and Salt Lake City. Moisture will be sparse through the middle of the week as well, resulting in an increasing wildfire threat as the week progresses. Thursday will likely see the highest fire danger across the Southern Rockies as winds increase ahead of the next approaching trough from the Pacific Northwest.
The good news is that a break from the heat is expected this weekend as the previously mentioned trough of low pressure swings across the Central Rockies. Friday will likely feature another day (though not as hot as Thursday) across Colorado, while temperatures farther west in Utah and Idaho begin to cool off. By Saturday, the cooler air will spread into Colorado as well with highs in Denver projected in the low 80s on both Saturday and Sunday. Thunderstorm chances will also increase over the weekend as well. Northern and eastern Colorado look to be favored for moisture once again with the weekend system. It’s still a good ways out, but anytime you have a strong upper level trough crossing the Central Rockies at this time of year, the threat for severe weather is probably going to be elevated across Eastern Colorado. The image below depicts the GFS model projected trough of low pressure on Saturday (courtesy of Tropical Tidbits).
Now that we’re getting toward the end of June, many people are starting to wonder when the North American Monsoon will get going. This is especially true this year, given the widespread severe drought conditions across the Four Corners region, along with ongoing wildfires across portions of Utah and Western Colorado. The start of the monsoon varies every summer, but on average it usually begins during the first or second week of July as moisture from the higher terrain in Mexico spreads northward into Arizona and New Mexico, and then into Utah and Colorado.
There are no real signs of the monsoon at the moment, likely due to the active jet stream over the Western U.S. with frequent troughs crossing the Northern and Central Rockies. This is suppressing the persistence of a subtropical ridge that allows for moisture to spread northward into the Southwest U.S. However, longer range models do show an upper level pattern reminiscent of the seasonal monsoon taking hold in the July 5-10 timeframe. A rough estimate of the second week of July for the start of the monsoon seems like a good call for now.