The seasons are changing! A series of temperature swings will be present this week, from potential record heat to more seasonal values for the beginning of Autumn. We’ll be mainly dry, but colder air will begin to knock on our door by the weekend. Read on for more details.
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.
Above average temperatures continue…
Following a pleasant weekend across the state with middle 70’s in the Denver Metro area both Saturday and Sunday, a warming trend will ensue into Tuesday. For an overview of this week’s weather, the mid-level absolute vorticity pattern at 500 mb (~ 15,000 feet up) is shown below. Over the Great Lakes, low pressure is present, continuing to move northeast. High pressure has moved off into the southeastern United States. Across our neck of the woods, low pressure is present in southern Nevada, tied to a trough axis in Canada and Montana. This system will not impact us directly. It will dive southward over the next couple of days, becoming decoupled from the main flow. This is what we call a “cut-off” low. Models have this system dipping into Arizona and Mexico, eventually moving back northward on Friday (but still staying to our south). The main impact today from the system will be clouds on the increase as moisture spreads in from the southwest. Highs will be near 80 Monday afternoon under increasing clouds, above average for our first official day of Autumn!
On Tuesday, the area will largely be in a split flow, with trough to our north in Montana, and the southern low pressure in Arizona/Mexico. Warmer air builds in further tomorrow with highs near the low to middle 80’s. This will be before a cold front advances late Tuesday night.
Cold front mid-week drops us back to 70’s…briefly
On Wednesday, the jet stream dips down into the state of Colorado. That will bring a decent cold front through the area starting late Tuesday night. The below figure shows the frontal position mid-day on Wednesday. This will help lower our highs to the mid to upper 70’s, a tad above where we should be this time of year. Our average highs this week are in the low to middle 70’s. You’ll notice again in the figure below below freezing temperatures (at ~10,000 feet up) over Montana, the Dakotas, Minnesota, and Wisconsin. While this cold air will not make it into Colorado, another surge is slated for the weekend and next week. Models continue to show that the brunt of the cold may stay north of us again but it’s a sure sign that colder air is building across Canada and the Arctic.
Record heat Thursday?
Come Thursday, the pattern will shift once again…this time to potential record heat. The jet stream noses back northward into Montana. In response, the low-levels will see southwest flow take over, pumping in dry heat from the Desert into Colorado (below). The temperature pattern indicated for Thursday is supporting highs near historical values for the Front Range. Our record high for Denver on Thursday is 90 degrees set in 2010, while for Boulder it is 88 degrees set in the year 2011. Right now, we see highs in the mid to upper 80’s possible, certainly infringing on these records.
Showery and chilly end to week
By Friday, we have yet another swing in temperatures expected! The colder air up north makes its way back south into northern Colorado (below). Upslope will likely be present on the Front Range through much of the day. Right now, the forecast models are keeping most of the cold air to our north, but we’ll likely see a sizable drop in temperatures with highs in the lower 70’s to end the week. This would be our coldest day since early June if it comes to fruition. Given the troughy pattern, clouds and shower activity will be possible as well, though chances aren’t looking too great on Friday.
The trough out west on Friday will be with us much of the upcoming weekend as well. Shown below is the 500 mb height anomaly pattern. Note the blue shading over much of the western United States signaling the southern dip in the jet stream out of Canada. This will likely keep the chilly air nearby, but details as to how far south it gets is uncertain at this point.
Along with the cold air and changing season, we also need to start thinking about snow! Cold air up north will also lower snow levels this weekend. Although not on the table for Boulder or Denver, light snow may occur in the High Country this weekend with snow levels dipping to around 10,000 feet. Up north in Wyoming and Montana, snow levels fall well below 5000 feet. Get excited folks…snow is not far away with October right around the corner!
Finally, don’t forget to submit your prediction for our 2019 First Snow Contest which closes on Wednesday, September 25th. HINT: Please don’t submit a prediction for a day in September…You will lose!
Forecast Specifics:
Monday: Partly to mostly cloudy skies with highs near 80 on the Plains and near 70 in the Foothills.
Tuesday: Mostly sunny and warmer with low to middle 80’s on the Plains and low to middle 70’s in the Foothills.
Wednesday: Cooler and slightly above average with highs with middle to upper 70’s on the Plains under partly cloudy skies. For the Foothills, upper 60’s are likely.
Thursday: Record highs possible under mostly sunny skies. Highs in the mid to upper 80’s on the Plains and middle 70’s in the Foothills.
Friday: Mostly cloudy skies with a chance of upslope showers in the afternoon and evening. Highs near seasonal averages on the Plains with lower 70’s, and lower 60’s in the Foothills.
High Country: Overall dry conditions will be present across the High Country this week except Friday, though a slight chance will exist in far southwest Colorado today. On Friday, a deep trough will lead to a chance of rain/snow showers for the higher terrain, along with cooler air coming southward. Visit our SummitCAST page for updated forecasts for more than 120 Colorado mountain destinations, including all of our state’s majestic 14ers.
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