Unseasonably cool temperatures will exist on Monday following a cold front and upslope flow. However, the heat and smoke return on Tuesday and will stay with us most of the week ahead. We’re also watching the potential for a much-needed wet conclusion to the week.
This week’s highlights include:
- June 2021 has thus far been one of the warmest on record
- Unseasonably cool and cloudy conditions start the week
- Temperatures rebound into the 90’s Tuesday through Thursday
- Smoke will be absent on Monday thanks to the wind shift, but will return the rest of the week as a slew of new wildfires have ignited to our west
- Tracking a potentially wet and cool end to the week
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.
Heatwave recap & smoke
Last week’s extreme heatwave was quite the event in the weather world. We knew it was going to be a long and hot stretch for the Denver Metro area, but no all-time record highs were observed such was the case in other states across the Desert Southwest. This facet for the Front Range was expected and well-discussed in last week’s outlook, with the comparatively “cooler” temperatures in our area owing to weak northwest flow and a surge of wildfire smoke aloft.
Denver hit triple digit temperatures three days in a row last week (Tuesday through Thursday), all of which were new daily record high temperatures. Boulder topped out at 99°F (twice)….again both of which were new daily record highs.
Boulder crushed the existing record high temperature on Wednesday hitting 99°F! 🌡️⛰️🌞
Another record-setting day is possible on Thursday, too. Our forecast calls for a high of 99°F. The record for June 17th is 97°F set back in 2012: https://t.co/zZW7PmtKY6#COwx #Boulderwx pic.twitter.com/jSjzuX6yH2
— BoulderCAST Weather (@BoulderCAST) June 17, 2021
For the second day in a row, Boulder set a new daily record high temperature at 99°F on Thursday. The prior record was 97°F from 2012. Cooler weather is expected Friday following a weak morning cold front! #COwx #Boulderwx #HeatWave pic.twitter.com/gfqWXAJTOT
— BoulderCAST Weather (@BoulderCAST) June 18, 2021
The month of June has been very hot and dry thus far in the Front Range where temperatures are running about 5 to 7°F above normal for the month through June 19th. This warm patch is clearly evident this month in the northern and western portions of the country.
Ironically, this temperature pattern looks eerily similar to the outlook we posted in our La Niña update last month (below right), with a cool southeast US and Pacific Northwest, and hot weather elsewhere. Of course our outlook covered the entire summer, but we’re right on-track as of now.
With the exception of the first few days of the month, June 2021 has been filled with unrelenting heat! There’s been nine 90+°F days in Boulder, including two new daily record highs mentioned earlier on the 16th and 17th. Low temperatures have also been well above normal cutting into the amount of heat recovery we have seen during the overnight hours.
For the period of June 1st to 20th, 2021 ranks 7th warmest all-time since 1900 in terms of mean temperature (below). Notably, 2021 is just behind 2012 which was brutally hot as well.
- 1952 – 75.3°F
- 1956 – 74.1°F
- 2006 – 73.1°F
- 1979 – 72.5°F
- 1910 – 72.5°F
- 2012 – 71.4°F
- 2021 – 71.0°F
- 1977 – 70.8°F
- 1933 – 70.7°F
- 1959 – 70.6°F
Fire weather concerns returned this weekend with winds picking back up across the drought-plagued Western Slope, Great Basin and Desert Southwest. Several new wildfires started on Sunday across western Colorado and conditions will be conducive to further starts and spreading early this week. If there was any hope for a reduction in smoke this week, that has certainly now gone up in flames with these new fire starts directly upstream of the Denver Metro area.
How many fires can you see? Satellite captured Sunday afternoon… #cowx #utwx pic.twitter.com/UWd26PmE0m
— NWS Grand Junction (@NWSGJT) June 20, 2021
Be sure to check our Colorado Smoke Forecast page for the latest on smoke reaching the Front Range.
Unseasonably cool to start the week
Unseasonably cool weather is in store for us on this Monday. A strong cold front located from the Great Lakes southwestward into the Midwest and northern Texas (below), has brought chillier air down from Canada. This has forced a retreat of the extreme heat well south of us into Mexico, Arizona and west Texas. The remnants of Tropical Storm Claudette are currently over eastern North Carolina and will be moving offshore by this afternoon and evening.
The overnight cold front ushered in upslope flow at the surface and produced some showers last night for most of the area. While the rainfall was widespread, it was generally light with less than 0.20″ everywhere (see below).
Radar estimated rainfall totals from Sunday night into early Monday
There could be a few isolated light rain showers lingering early this morning south and east of Denver, but overall the week begins dry with just widespread cloud cover under residual upslope.
These clouds will be somewhat slow to move out on Monday, but mostly sunny skies will start to take over by the late morning into the afternoon hours. Highs should reach the upper 60’s to lower 70’s. Our average high for June 21st is right around 81 degrees so all in all, not a bad day to be outside with the pleasantly cool conditions.
The one-day push of deeper upslope from the northeast will keep the wildfire smoke away from the Front Range on Monday as well. Seriously, get outside and enjoy the beautifully cool and cleaner air on Monday. The heat and smoke will return quickly in the coming days….
Heat returns Tuesday
That cool and comfortable weather does not last long, unfortunately. By Tuesday, the ridge of extreme heat builds back northward into the Four Corners area, while the trough which brought us the cooler weather moves into the eastern United States.
As winds shift back to westerly, hot temperatures take over again on Tuesday and we should easily push into the middle 90’s. Record highs for Boulder on Tuesday are in the upper 90’s so these will likely remain intact. This heat will continue into Wednesday as well, slowly backing off a little come Thursday. There is a very slim chance that some storms could develop around the periphery of the ridge Tuesday, but most of us will remain dry with moisture severely lacking.
As flow turns westerly again, smoke will return to the Front Range by Tuesday morning and will then linger through most of the week ahead. This forecast is based on fires that are actively burning as of Monday morning. Any new fires that spawn this week will only exacerbate the situation.
Cooling down and turning unsettled by late week
Come Wednesday, Thursday, and Friday, a trough of low pressure off the West Coast will slowly track eastward into the northern Rockies and combine with another trough moving south from Canada into Montana and Wyoming. The interaction of these two trough axes is quite uncertain at this point. The GFS, for example, digs the trough from Canada further south than the Euro model, which would point toward a more unsettled pattern. The real solution is likely somewhere in between.
All that said, Wednesday and Thursday will still be very warm, in the middle 90’s Wednesday and lower 90’s Thursday. Moisture from these two troughs will increase from both the south and the north, bumping up our chance of scattered afternoon showers and storms.
Along with the moisture there will be an uptick in instability, especially Thursday and Friday (below). If the trough on Friday from Montana moves as far south as the GFS suggests, a cold front would push through the Front Range, resulting in temperatures back into the 70’s. There will also be the potential for severe weather somewhere across eastern Colorado to close out the week.
All these points taken as a whole, a 10% chance of storms exists on Wednesday, jumping up to 30-60% by Thursday and Friday with the moisture, instability and forcing for ascent increasing. 90-degree temperatures will fall flat on their face late this week, probably back into the 70’s come Friday!
Uncertainty for the weekend
In addition to the tail-end of the week ahead being wet and uncertain, the weather for the upcoming weekend will be highly dependent on the trough/ridge location and pattern. The GEFS ensemble spaghetti diagram for Saturday highlights this uncertainty (below). Notice how the GEFS shows a ridge across the Pacific Northwest, along with a trough over the Dakotas to Wyoming. However, there is large spread in the placement of these two features. A broad brush outlook for the weekend would favor warming temperatures, along with minor chances of afternoon/evening showers and storms.
Stay up to date with Colorado weather and get notified of our latest forecasts and storm updates:
We respect your privacy. You can unsubscribe at any time.
.
Forecast Specifics:
Monday: Mostly cloudy early becoming sunny by afternoon. Highs much cooler and below normal in the lower 70’s on the Plains and middle 60’s in the Foothills.
Tuesday: Mostly sunny, dry and hot with middle 90’s on the Plains and upper 70’s in the Foothills.
Wednesday: Partly cloudy skies with isolated showers and weak storms. Highs remain hot in the middle 90’s on the Plains and near 80 in the Foothills.
Thursday: Increasing clouds with scattered thunderstorms and highs in the lower 90’s on the Plains and upper 70’s in the Foothills.
Friday: Increasing clouds with scattered to widespread late-day showers and thunderstorms, along with cooler temperatures in the middle 70’s for the Plains and middle 60’s in the Foothills.
Mountains: Dry conditions will start the week in the higher terrain. Unsettled weather and increasing chances for afternoon showers/storms will return Wednesday, Thursday, Friday, and the upcoming weekend. As always, plan any Mountain activities with dangerous late-day lightning in mind!
Help support our team of Front Range weather bloggers by joining BoulderCAST Premium. We talk Boulder and Denver weather every single day. Sign up now to get access to our daily forecast discussions each morning, complete six-day skiing and hiking forecasts powered by machine learning, first-class access to all our Colorado-centric high-resolution weather graphics, bonus storm updates and much more! Or not, we just appreciate your readership!
.
Spread the word, share the BoulderCAST forecast!
.
You must be logged in to post a comment.