Near record heat will transition to cooler temperatures through the week. Read on to find out when a cold front will arrive and which day holds our best chance of rain.
Early in the week, we’ll see the continuation of a double-lobed ridge of high pressure to our south and west (below).
GFS 500 mb height anomaly forecast for Tuesday
Thanks in large part to this ridge starving out the monsoon, Boulder has seen no measurable rainfall in the last ten days. Strikingly, our monthly rainfall total so far is just 0.08″. In the unlikely event that the month concludes rain-free, this would be our driest August ever. The grass in downtown Boulder is clearly struggling with the persistent hot and dry conditions…
The airmass in-place over Colorado this past weekend and continuing into early this week is extremely dry. I did some alpine hiking over the weekend and there were no storm clouds to be found. Would you believe that the picture below was the view from La Plata Peak yesterday around 3:00 PM? Only a couple tiny cumulus clouds filled the sky. In fact, I didn’t even BEGIN this hike until mid-day….something only a crazy person (or confident meteorologist) would attempt in mid-August. I’ll let you decide which was the case here…
The view from La Plata Peak on August 18, 2019. Extremely dry air for mid-August led to ideal hiking conditions.
Dry and hot weather will hold across the Front Range through Tuesday before a cold front brings cooler temperatures and storms back into our forecast. On Monday we will be flirting with record high temperatures across the Metro area with highs climbing into the middle to in some cases, upper 90’s. For August 19th, the current record highs for Boulder and Denver are 96 and 97 degrees, respectively. Tuesday will be slightly cooler thanks to increasing cloud cover, but we’re still talking lower to middle 90’s again.
HRRR forecast surface temperatures for Monday afternoon. Middle 90’s are widespread across the Denver Metro area
Relief from the heat will arrive Tuesday evening or night in the form of a cold front from the northeast. Global weather models are not in great agreement right now on the timing of this front, but either way, it should pave the way to a cooler rest of the week with highs dropping back into the 80’s Wednesday and beyond. The moisture from the front may develop low clouds and/or fog across the Denver and Boulder areas late Tuesday night into Wednesday morning. This should burn off rather quickly Wednesday morning, though.
Our best chance of rainfall this week will be Wednesday when the post-frontal easterly flow will help to hold in more moisture across the area. We’re expecting only scattered to widespread coverage, and with upper-level winds westerly at only ~15 MPH and precipitable water cresting just above one inch, heavy downpours and localized flooding could be a concern for portions of northeast Colorado.
NAM forecast 800 mb temperatures (left) and precipitable water (right) for Wednesday evening. Cooler and moister air takes hold behind a cold front.
While shear won’t be that impressive, some of the higher-resolution models are showing CAPE along the stalled front exceeding 2000 J/kg. Thus, we cannot rule out the potential for severe weather as well on Wednesday, with hail up to 1″ in diameter. The target for this should be locations in and near the Foothills where instability will be the greatest.
NAM CAPE forecast for Wednesday afternoon and evening. Watch out areas in and near the Foothills!
With the monsoon plume suppressed and low-level easterly flow relaxing late in the week, our area will once again dry out with only isolated chances for thunderstorms on Thursday and Friday. This is true for both the Denver Metro area and statewide.
Forecast Specifics:
Monday: Mostly sunny and dry with near-record heat. Highs in the mid to upper 90’s across the Plains and in the middle 80’s in the Foothills.
Tuesday: Morning sunshine and then partly cloudy. A few isolated storms are possible, mainly east of Denver. High temperatures in the middle 90’s across the Plains with lower 80’s in the Foothills.
Wednesday: Low clouds and patchy fog in the morning, then partly cloudy with increasing clouds and scattered afternoon and evening thunderstorms. Storms could produce 1″ diameter hail and localized flooding. Highs in the lower to middle 80’s on the Plains and near 70 in the Foothills.
Thursday: A mix of clouds and sunshine with isolated late-day storms. Look for highs in the middle to upper 80’s on the Plains and lower 70’s in the Foothills.
Friday: Mostly sunny with slight chances for afternoon and evening high-base storms. Highs in the mid to upper 80’s on the Plains and in the middle 70’s in the Foothills.
High Country: Very dry air across the state will lead to completely dry conditions statewide on Monday. Tuesday through Friday will be fairly dry as well, but isolated storms will be possible in some mountain ranges thanks to a slight increase in moisture. Overall, though, this week will offer excellent hiking conditions. Visit our SummitCAST page for updated forecasts for more than 120 Colorado mountain destinations, including all of our state’s majestic 14ers.
DISCLAIMER: This weekly outlook forecast was 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.
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