We sure sound like a broken record, but the week will begin hot and smoky across the Front Range. As we head into midweek and especially beyond, we’re expecting a big drop temperatures, as well as increasing chances for wet weather. Thick, elevated smoke will likely linger through the week as massive upstream fires continue to rage across the Pacific Northwest and parts of Canada.
This week’s highlights include:
- Elevated wildfire smoke likely to linger most of the week with milky skies and reduced visibilities
- Hot temperatures to start the week, then a welcomed cool down
- Increasingly unsettled weather Wednesday through Friday as a strong August trough moves in
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.
Hot & smoky to start
Lots of weather to speak of on this Monday! Across the nation, Tropical Storm Fred is making landfall along the panhandle of Florida. High pressure exists over Nevada today. Low pressure exists over southwest Colorado. This low pressure will touch off afternoon showers and storms over the higher terrain in the western part of our state.
Infrared satellite animation from Monday morning as TS Fred bears down on Florida
The wildfire smoke has built back in across much of our state and over a large portion of the western United States in fact! Note below the HRRR model total column smoke forecast for this early this afternoon. This resurgence of smoke across Colorado this week is due to northwesterly flow transporting the smoke into the area from the west and northwest. High temperatures Monday afternoon should top out in the lower 90’s, despite the smoky conditions. Temperatures warm aloft as high pressure settles in. Only a slight chance of a few afternoon storms are forecast across the Mountains with the Denver Metro remaining dry.
The 90+ degree weather will continue on Tuesday. However, by Tuesday evening, a large trough of low pressure is poised to dig across the Pacific Northwest. As for our sensible weather on Tuesday, that should allow a more southerly flow to develop in the low-levels, with highs warming a few more degrees from Monday. This trough will be our weather-maker come late Wednesday through Friday, finally bringing a major cooldown to the Front Range!
The enhanced southerly flow is evident in the NAM near-surface temperature pattern on Tuesday (below). Note the very warm air ahead of of the aforementioned trough. The trough is accompanied by a strong cold front digging across eastern Montana, Wyoming, and northern Nevada tomorrow night.
Highs should reach the low to middle 90’s on Tuesday, with well above average temperatures expected ahead of that front (below). This heat will be with us at least into midday Wednesday as well. However, expect a sharp change late Wednesday into Thursday behind the cold front. While we might see minor reprieve from the smoke on Tuesday and early Wednesday with the southerly flow, a return or heavier smoke appears possible late in the week as northwest flow builds back in.
Looking for the latest smoke forecast for Colorado and the western United States? 🌲🔥💨🏭
Head over to our Smoke Forecast suite for up-to-date 48-hour smoke predictions from two weather models across four regions: https://t.co/gcXXztAvZa#COwx #Smoke #COFire #CAwx #DixieFire pic.twitter.com/2EEPGvuPIE
— BoulderCAST Weather (@BoulderCAST) August 12, 2021
Turning cooler & unsettled mid to late week
Our late-week weather all hinges on the position and speed of that surface cold front and mid-level trough digging into the area. The cold front is forecast to reach the Front Range sometime between late Wednesday afternoon to late Wednesday night. The timing differences are due to model discrepancies at this point, which we will get to later. All in all, temperatures should top out near 90° on Wednesday, but drop into the 80’s come Thursday and Friday.
Our chance of rain showers and embedded storms will increase mid to late day on Wednesday, as well as through Thursday and possibly part of Friday. Ahead of this large trough to our west, enhanced moisture will be surging into the region. That, along with deep lift and the front, should focus more unsettled conditions across the area.
However, the devil will be in the details. The global ECMWF and GFS models are not in complete agreement on the actual forecast track of the trough, particularly when it comes to its position and timing. The GEFS ensemble depicts the unsettled pattern toward the latter part of the week, with the potential for 0.25 to 1.0 inches of rain in our area, which gives us confidence. Nonetheless, exactly how the trough will evolve is highly uncertain at this point of writing Monday morning.
The ECMWF and GFS are in broad agreement on Wednesday, with the trough near central Idaho (see below, left panels). This would favor our last warm day on Wednesday. The models diverge on Thursday and Friday, with the ECMWF bringing the system over southern Idaho and the GFS placing it over northwest Wyoming. These differences maximize on Friday, with the ECMWF more south than the GFS. These large differences will have a big player on forecast high temperatures and overall rain chances. The good news: the general theme is the same — expect a downward trend in temperatures after Wednesday, along with wetter days.
It’s also worth mentioning that the worst of the smoke this week will bypass Colorado to the north through Wyoming and Montana. The smoke that we do see here in the Front Range will be thick, but will largely be higher up in the atmosphere. This will create milky skies and reduced visibilities, but air quality should remain bearable for most. Don’t worry, this week will be nothing like what unfolded ten days ago!
HRRR total smoke forecast animation spanning through Tuesday night
Enjoy the week and let’s hope the late-week cooldown arrives on schedule!
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Forecast Specifics:
Monday: Mostly sunny, smoky and hazy with highs in the lower 90’s on the Plains and upper 70’s in the Foothills.
Tuesday: Mostly sunny, smoky and hot with isolated afternoon and evening high-based storms. Little to no rainfall, but watch for gusty outflow winds. Highs in the low to middle 90’s on the Plains and near 80 in the Foothills.
Wednesday: Increasing clouds with widely scattered late day rain/storms. Highs near the low 90’s on the Plains and upper 70’s in the Foothills.
Thursday: Partly to mostly cloudy with rain showers or storms likely . Highs in the low 80’s on the Plains and low 70’s in the Foothills.
Friday: Partly to mostly sunny with showers or storms possible and highs near 80 in the Denver Metro and upper 60’s in the Foothills.
Mountains: Scattered showers and storms will be prevalent over the southwestern mountains today and tonight. Slightly drier weather ensues on Tuesday. Scattered storms return Wednesday through Friday, along with breezy conditions. Some high elevation snow showers are possible Thursday.
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