It’s been a brutally hot and dry month of July thus far. The monsoon is yet to materialize for the southwestern United States, but it won’t stop rain chances from increasing this week across the Front Range due to an influx of subtropical and even tropical moisture. Temperatures will remain rather warm, but not quite as hot as the last few weeks. Let’s take a “big picture” look at the week ahead.
This week’s highlights include:
- July has been very hot and dry so far, with only 0.01″ of rain in Boulder
- Despite the delayed monsoon, a slight pattern shift will lead to better storm chances this week
- Temperatures will remain near to slightly above normal through the week. No extreme heat expected
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, subscribe to BoulderCAST Premium.
Signs of a wetter pattern emerging
It has been a very dry and hot month of July so far for the Front Range with temperatures running about 5 degrees above average and well below normal precipitation having occurred in the aftermath of the delayed monsoon. It’s been particularly dry from Denver to Boulder, with rainfall totals for the month of only 0.29″ and 0.01″, respectively.
A look at the Tucson Dew Point Tracker shows the monsoon still has not begun in southern Arizona. In the graph below, the monsoon’s commencement will be confirmed when there are three consecutive days of 54°F average dew points. The threshold has not been reached yet in 2020.
The monsoon is now more than ten days late, and won’t start until at least Friday at the earliest if we’re lucky. It’s been quite a disappointing rainy season thus far across the Southwest. Little to no rainfall has fallen is most areas over the last 30 days.
Percent of normal precipitation over the last 30 days
While the monsoon is yet to officially start in the American Southwest, the long-standing weather pattern that has made July so brutal this year is beginning to change as we speak. It’s not a major shift by any means, but the strong high pressure center which has remained from Arizona into west Texas for several weeks will weaken and consolidate eastward in the coming days. Furthermore, an active easterly storm track is taking shape, undercutting the ridge. This track will bring several disturbances ashore from the Gulf of Mexico into Texas and northern Mexico. This storm trajectory is not very common, but it can happen when the pattern aligns like this. The last disturbance will move between Florida and Cuba over the next few days and pop out into the Gulf by Wednesday morning. The National Hurricane Center is currently monitoring this particular wave for potential tropical development. Odds seems fairly low however, but it will be something to watch given the eventual track towards Texas and Colorado thereafter.
With the monsoon on the brink of beginning and the influx of disturbances from the east underneath the ridge, we expect additional Gulf moisture to roll into the mix for Arizona. This moisture will ultimately recirculate around and get to Colorado mid to late-week leading to elevated storm chances each day, at least compared to what we have seen of late. Overall temperatures will remain warm through the week under persistent southwesterly flow, high pressure, and warm air advection, but not quite as hot as it has been in recent times. The daily development of thick clouds and some thunderstorms should help to take the edge off the heat.
On Monday and Tuesday, before the better moisture arrives from the south, our eyes are focused on a stalled cold front that is draped across eastern Colorado and southeast Wyoming. This is the front that took us from near 100°F on this past Saturday downwards to a cooler but “muggy” Sunday with highs near 90°F.
DOES IT FEEL STICKY? An overnight cold front brought in moisture to the area with dew points in the low to middle 60's. This is the highest they have been in our area in 2020 (when it wasn't actively raining). This will lead to scattered thunderstorms later today #COwx #Muggy pic.twitter.com/wzLQjNiKjW
— BoulderCAST Weather (@BoulderCAST) July 19, 2020
To the north and east of this front, dew points are in the 60’s. To the south and west, air is notably drier and more stable. This front will wander back and forth across our area in the coming days, shifting eastward during the day and sliding back westward as storms develop across northeast Colorado and push cool outflows our direction.
For Monday afternoon, it appears to be too dry for much storm activity across the Denver Metro area, but an evening outflow heading in from stronger storms to the east could supply the added moisture to see a few isolated storms pop during the evening hours. This facet is somewhat questionable, but we have the chance at 20% across the area.
A similar setup will be in-place Tuesday, but with the front located further west banked up against the Foothills. With more moisture to start the day (and possibly some low clouds), storms will develop earlier and be more numerous across the Front Range. Look for scattered storms and even a slight chance of a few strong or severe ones to spawn across the Front Range and northeast Colorado. Borderline severe hail and wind gusts will be possible Tuesday afternoon into evening, along with brief heavy rainfall. Tuesday’s temperatures will be a little cooler with the potential for morning cloud cover, cooler upslope flow, and developing storm clouds. We’re looking at mid to upper 80’s…the coolest day of the week!
SPC severe weather outlook for Tuesday
Moisture pump turns on Wednesday
By midweek, the flow of moisture into the southwestern United States really gets going as a result of the incoming disturbances mentioned earlier. Initially, however, it looks like the deepest moisture will remain across Utah and western Colorado, largely evading the Front Range. Moisture may be near or slightly below normal over Denver with only a meager chance of storms on Wednesday. Things will be rocking across the High Country, though, with scattered to widespread storms developing through the day, especially along and west of the Divide.
This deeper pulse of moisture will push eastward Thursday into Friday leading to a better of chance of storms in eastern Colorado as well, but nothing yet bordering on a certainty of rain or a total washout. The chance ramps up to 20% on Thursday, and possibly towards 40% on Friday. The wetter weather likely will continue into the weekend. The increased storm chances will cut into the heat, but not much. Highs Wednesday through Friday will be in the low to middle 90’s.
We stress that while we are hopeful for more productive rainfall this week across the area, this certainly isn’t a drought-busting pattern. Some (if not many) locations may see little in the way of liquid through the week. By and large, though, persistent low to moderate chances for storms should lead to everyone seeing something by the end of the week.
Forecast Specifics:
Monday: Morning sun, then partly to mostly cloudy skies developing through the afternoon with isolated thunderstorms from early evening into the late evening. Highs in the lower 90’s on the Plains and in the upper 70’s in the Foothills.
Tuesday: A sticky morning with low clouds possible following an overnight push of moisture. Expect a shift to scattered afternoon and evening thunderstorms across the area. One or two could be severe. Highs in the mid to upper 80’s on the Plains with middle 70’s in the Foothills.
Wednesday: Mostly sunny early, then hot and partly cloudy with isolated thunderstorms in the afternoon and evening. Highs in the lower to middle 90’s on the Plains and upper 70’s in the Foothills.
Thursday: Increasing clouds with widely scattered afternoon and evening thunderstorms. Hot with high temperatures in the low to middle 90’s across the Plains and upper 70’s in the Foothills.
Friday: Some morning sun, then mostly cloudy with scattered afternoon and evening thunderstorms. Storms could produce heavy rainfall. Highs near 90 degrees on the Plains and in the middle 70’s across the Foothills.
Weekend: Storm chances remain elevated heading into the weekend, but the supply of moisture is somewhat questionable at the moment. We don’t see any reason to expect widespread rainfall, but do look for the usual spotty afternoon/evening storm coverage to continue.
High Country: Moisture will be limited Monday and Tuesday this week with only isolated late day storms across the state. Things ramp up Wednesday through Friday with storm coverage becoming more numerous and intense. If you have to hike, get to the summit or peak before noon time to avoid the lightning threat. Check our SummitCAST page for daily updated forecasts for more than 120 mountain hiking destinations across Colorado. Here’s the early week forecast at the top of Quandary Peak:
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