This Week in Colorado Weather: August 18, 2025

If you’ve been quietly rooting for a late-season monsoon comeback, it might be time to recalibrate. Boulder’s summer has been historically dry, and this week won’t offer much relief, at least initially. A persistent ridge of high pressure is set to lock in more heat and keep moisture at bay. But don’t tune out just yet—there’s a subtle pattern shift coming that could open the door to cooler temps and better storm chances by the weekend. Let’s take a closer look.

This week’s highlights include:

• Monsoon Letdown: Boulder has seen just 1.18″ of rain since June 13—its driest stretch in over 50 years, with the broader Southwest also missing out on typical monsoonal moisture.
• Western Drought & Fire Risk: The Mountains and Western Slope remain parched, with extreme drought and active wildfires persisting due to the monsoon’s near-total absence.
• High Pressure Dominance: A retrograding ridge of high pressure will park near the Four Corners this week, keeping the Front Range hot and dry with temps climbing into the upper 90s by Thursday.
• Late-Week Pattern Shift: A Canadian disturbance will flatten the ridge and push a cold front into eastern Colorado Thursday night or Friday, bringing cooler temps and increased moisture.
• Storm Chances Improve: Post-front, highs will dip into the low 80s or 70s and late-day thunderstorms should become more widespread and productive starting Friday.
• Tropical Activity Elsewhere: Hurricane Erin will skirt the East Coast without landfall but stir up dangerous surf; meanwhile, the eastern Pacific remains quiet, offering no moisture boost for Colorado.

DISCLAIMER: This weekly outlook forecast is created Monday morning and covers the entire upcoming week. Accuracy will decrease as the week progresses as this post is NOT updated. To receive daily updated forecasts from our team, among many other perks, subscribe to BoulderCAST Premium.

Monsoon has been M.I.A — Again

nother week, another letdown from the summer monsoon. At least expectations were low this time, so the lack of rain didn’t sting quite as much. Since June 13th, Boulder has picked up just 1.18″ of rainfall—making this the 7th driest such stretch on record and the driest in over half a century, even beating out the exceptionally dry summer we had last year.

Zooming out, most of Colorado has been bone dry, especially the Mountains and Western Slope. Extreme drought continues to grip the region, and wildfires remain active to our west. The monsoon has simply ghosted most of our state this summer.

Monsoon season has been particularly cruel to drought-stricken western Colorado this summer

What’s Going On?

It’s not just us. The entire Southwest has been stuck in one of the weakest monsoon seasons in years. Normally, a semi-permanent high-pressure system over the southern U.S. helps funnel moisture northward into the Four Corners. But this summer, that high has been stubbornly uncooperative—rarely setting up in the right spot to pull in the subtropical juice. And when moisture has made it in, it’s rarely led to anything significant or widespread.

The observed Standardized Precipitation Index (SPI) for the 60-day period ending August 16, 2025. SPI is used to compare precipitation as it relates to “average” over regions with vastly different climates

This Week: Hot, Dry, and Ridged

If you were hoping for a shift toward cooler, wetter weather—sorry, not this week. A strong ridge of high pressure is forecast to dominate Colorado and much of the Rockies through Friday. This particular ridge is retrograding, meaning it’s building in from the east rather than the west, which is a bit unusual.

While the Front Range sizzles under yet another prominent ridge this week, the East Coast is keeping a close eye on Hurricane Erin in the Atlantic.

With sustained winds around 130MPH as of Monday morning, Erin is a major Category 4 hurricane—but it’s taking a remarkably lucky track. Erin is expected to skirt past the Caribbean, Bahamas, U.S. coastline, Bermuda, and even eastern Canada without making landfall. Still, it’ll stir up dangerous surf, rip currents, massive open-ocean waves, and bring increased coastal erosion.

Slightly more relevant to our weather here in Colorado is the hurricane activity of the eastern Pacific Ocean, which can occasionally inject deep moisture into the Four Corners area with the right wind patterns. However, much like our summer monsoon season this year, the tropical eastern Pacific is as dead as a doornail right now.

Focusing back to our actual weather this week, the big ol’ ridge will quickly intensify in the coming days and set up shop near or just west of the Four Corners point through the week. This positioning will put our area under a hot and dry northwesterly flow pattern aloft from Tuesday onwards with temperatures bumping up a tad each day, culminating in the upper 90s by Thursday.

A disturbance sliding through southern Canada later this week will help flatten the ridge and send a cold front into eastern Colorado. That front should reach the Boulder–Denver area Thursday night or early Friday, bringing cooler temps and a bump in moisture.

Highs will drop back into the low 80s Friday with 70s favored through the weekend—below seasonal averages—and storm chances will increase. Late-day thunderstorms should be more widespread and productive starting Friday. The pattern moving in will be more favorable for severe storms, so that’ll be something to watch as we get closer.

Here’s a look at the full work-week. Our forecast temperature of 98°F on Thursday would tie Boulder’s daily record high for August 21st. Fortunately cooler temps will arrive on Friday.

Let’s hope (for once) the pattern shift this weekend actually delivers some moisture, not only to our area but to the broader Four Corners and western Colorado. Enjoy the weather!

Forecast Specifics:

Monday: Morning sun with widely scattered late-day storms developing, more numerous east and southeast of Denver. Highs around 90 degrees on the Plains with upper 70s in the Foothills.

Tuesday: Lots of sun with just a few afternoon clouds developing. A storm is two is possible, mainly over the Palmer Divide. Temperatures reach the lower 90s on the Plains with upper 70s in the Foothills.

Wednesday: Sunny skies, dry and hot. Highs in the low to middle 90s on the Plains with near 80 in the Foothills.

Thursday: Lots of sunshine and very hot with temperatures soaring toward record values in the upper 90s on the Plains and middle 80s in the Foothills. Depending on the timing of the front, a couple storms may form late Thursday evening, most likely northeast of Denver.

Friday: Cooler with a chance of scattered to numerous afternoon and evening storms. Highs cooler in the lower 80s for the Plains with lower to middle 70s in the Foothills.

Weekend: Highs stay cooler in the 70s to lower 80s with scattered late-day thunderstorms both days.

DISCLAIMER: This weekly outlook forecast is created Monday morning and covers the entire upcoming week. Accuracy will decrease as the week progresses as this post is NOT updated. To receive daily updated forecasts from our team, among many other perks, subscribe to BoulderCAST Premium.

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Ben Castellani

Ben grew up in southwestern Pennsylvania and holds both a bachelor's and a master's degree in Meteorology, the latter being from CU Boulder. His hometown received nearly three feet of snow from the Storm of the Century back in March of 1993, sparking his initial interest in impactful weather. Ben currently works on remote sensing and data analysis software at NV5 Geospatial Software in Boulder.

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