Cooler weather returns to the state starting tomorrow, followed by a gradual warming trend by week’s end. We detail the week ahead and the return of wildfire smoke. Read on for more details.
Monday a transition day
On this Monday, we will be in a state of transition. Below shows the mid-level pattern across the CONUS. Note the trough of low pressure across eastern Montana. This dip in the flow will allow the jet stream to sag southward and bring in another round of “autumn” weather starting overnight tonight and tomorrow. A cold front will advance through tonight. But before that happens, we can expect another mild day today, albeit cooler than yesterday – we’re expecting upper 70’s to lower 80’s under abundant sunshine.
GFS 500 mb absolute vorticity today
Clouds will be on the increase later this afternoon and evening with the trough digging south and the approach of the cold front. While most of should us will remain dry ahead of the front, a few widely scattered showers are possible this evening and overnight. The best chance appears to be in the High Country where better forcing is indicated. A few snow showers may result in the mountains but no accumulation is expected. You may have noticed smoke that returned to the area yesterday. This is thanks to a few fires in western and northern Colorado. The HRRR model (below) indicates that this smoke will remain across the area into Tuesday. A gradual improvement in visibility is expected as the week progresses.
HRRR model smoke outlook today
Cold front pushes in for Tuesday
As mentioned earlier, a strong cold front will push through overnight tonight and usher in some chilly air for Tuesday, the coolest air so far this autumn season. Below is the near-surface temperature map showing the frontal position Tuesday morning. The airmass will drop some 10 degC compared Sunday and we’ll likely have middle 60’s for highs as a result. It will also be a nippy evening tomorrow with lows dipping into the 40’s in most areas. It’s still a little too early to be worrying about frost potential, but its getting closer for sure with each passing day!
NAM 800 mb temperature and wind on Tuesday
The airmass is quite cold, shown below. Connected with the trough are below normal temperatures across Colorado and the Northern Plains. Outside of this region, much of the nation is near or slightly above average.
NAM 700 mb temperature anomaly for Tuesday
Gradual warming trend Wednesday through Friday
As we move into the middle of the week, we’ll continue to experience the crisp and cool airmass, albeit highs should reach the lower 70’s on Wednesday. Of note is a weak shortwave trough embedded in the northwest flow Tuesday night and Wednesday that will primarily impact the High Country in terms of clouds and some light precipitation. The Plains will stay dry, as noted by the very dry air in place across the state. Precipitable water values are less than 0.2″. We’ll likely see an increase in clouds for the early part of Wednesday, then gradual sunshine.
NAM precipitable water on Wednesday
Thursday and Friday will continue to see gorgeous weather and tranquil conditions. This is one of those weeks where we will see cool to mild days, and crisp/cool nights, typical for fall weather. The pattern will shift Thursday and Friday, as the trough moves out, and behind it, westerly flow to weak ridging takes over (see below). This pattern will remain in place through Friday. Whereas we’ll start the week in the 70’s, we’ll end the week likely in the upper 70’s to low 80’s.
GFS 500 mb vorticity map for Friday
Some recent model runs are showing the potential for another dry cold front to impact the Front Range early Friday. We’d like to see a little more consistency before we totally buy-in. Just know that there is the potential that Friday could come in several degrees cooler than our forecast.
Finally, don’t forget today is your last chance to enter our 2018 First Snow Contest. Based on our weekly outlook, we would NOT advise forecasting snow in the month of September!
Forecast Specifics:
Monday: Mostly sunny skies then increasing clouds by evening. A slight chance of a brief thundershower or two this afternoon and evening, but dry overall. High temperatures near 80 on the Plains and upper 60’s in the Foothills.
Tuesday: Much cooler under mostly sunny skies. Highs in the middle 60’s on the Plains and middle 50’s in the Foothills.
Wednesday: Morning clouds, followed by afternoon sunshine and highs in the low 70’s on the Plains and lower 60’s in the Foothills.
Thursday: Sunny and tranquil with highs in the mid to upper 70’s for the Plains and middle 60’s in the Foothills.
Friday: Partly cloudy with highs in the upper 60’s to lower 80’s, depending if a cold front moves through or not. Either way, it will be dry.
Weekend: The upcoming weekend appears to show a continued warming trend, however there are signs a system may move in for Sunday for the potential of unsettled weather.
High Country: There will be a chance of showers and a few snow flurries across the higher terrain today and tomorrow. Drier weather is in store for the remainder of the week with gusty winds possible each day thanks to the jet stream overhead. Check out our SummitCAST page for 6-day forecasts for more than 120 Colorado mountain destinations!
DISCLAIMER: This weekly outlook forecast was created Tuesday 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, subscribe to BoulderCAST Premium.
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