After a snowy and cold weekend, the atmosphere will take a break for us much of this week. We’ll see gradually warming temperatures overall and lots of sunshine. In this post, we also review the snowfall totals from over the weekend…Boulder’s biggest snowstorm in nearly two years.
Storm recap: Boulder’s biggest snowstorm in 21 months
This weekend’s snowstorm officially produced 8.9″ of snow in Boulder. This is the biggest single event snow total in Boulder since January 5, 2017. Denver reported just 2.7″ of snow.
The storm played out more or less as we expected, which isn’t surprising. Recall that we stressed how confident we were in our forecast. This isn’t just us being boastful! Trust me, there are plenty of times we let you know just the opposite…that we aren’t sure what exactly is going to happen and to take our prediction with a grain of salt.
The only deviation in the forecast was the arrival of the storm. The cold front and onset of the precipitation were delayed by about three hours from our thoughts the day before. We discussed this late-breaking adjustment with our Premium members Saturday morning. The timeline of weather observations from Saturday at BoulderCAST Station shows the initial cold front moved through around 7:30 PM, with a second strong surge of cold air just after 9:00 PM. After a high of 65 degrees in the afternoon, temperatures nose-dived into the 20’s before midnight with light rain quickly changing to heavy snow.
Weather history from BoulderCAST Station on Saturday showing the passage of the cold front.
If you recall from the forecast, the key players for this storm were very cold air, prolonged upslope from Saturday evening until Sunday afternoon, and a passing jet streak which was expected to produce scattered heavy snow bands during the storm. All players showed up and worked together for this event. As they say, teamwork makes the dream work! Notice the heavy green bands of snow in the radar animation of the storm below.
Radar animation from late Saturday night into Sunday morning.
Within these bands, snowfall rates were 1 to 1.5″ per hour. The heavier bands generally remained from Boulder northward Saturday night. However, additional bands did develop across the heart of Denver later Sunday morning. Light snow persisted across the area into early afternoon Sunday before winding down quickly.
Shown below is our original snowfall forecast map issued Friday morning (36 hours before snow started). Overlaid in boxes are actual snowfall reports. Green boxes indicate that the report was within 1″ of our forecast range. Red boxes indicate that the report was outside of our forecast by more than 1″.
Overall our forecast turned out well. The only problem area was around Longmont where those heavy snow bands delivered amounts just slightly higher than our forecast of 3-6″ there. By the way, 8″ of snow hasn’t fallen in Longmont since March of 2016, so this was rare occasion for northeastern Boulder County. Top this off with new record low temperatures being set Monday morning just about everywhere in the Metro area, and this truly was a great early season winter storm!
Morning lows on October 15, 2018. Record lows across the board.
Remnant system digs to our southwest today & tomorrow
The system which brought us the snowfall over the weekend has moved southwestward into California and Arizona. This is evident below. In its wake, a trough over the Great Lakes is helping to keep northerly flow over Colorado, noted by the blue arrow below. In a sense, Colorado will be between these two troughs for the next few days, ushering in calm and sunny conditions, a drastic change from this past weekend.
NAM 500 mb absolute vorticity today
On Tuesday, the system over Arizona becomes completely closed-off from the upper-level jet stream. This will lead to its persistence over the southwestern part of the country into Thursday. Once again, Colorado will be quiet and sunny, but still cool.
NAM 500 mb absolute vorticity on Tuesday
Clouds will be few and far between through the week (below). Much of the state will see full sunshine, thanks to dry air filtering in from the north. Clouds will be in on the (slight) increase though on Wednesday as the cutoff low pressure over Arizona moves northward into the southwest part of Colorado.
NAM cloud cover today (left) and Tuesday (tomorrow)
Highs Monday and Tuesday will largely be dictated by the snow cover. Today, with fresh snow on the ground, we can expect highs in the low to middle 40’s, with the lower end of the spectrum being near the Foothills and western portions of Denver. On Tuesday, while snow will likely still be around in spots, much will have melted – resulting in highs reaching the middle 50’s.
Warmth returns later this week
Much of the week will see gradually rising temperatures. On Wednesday, the low pressure system in Arizona moves slightly northward, with its northern fringes reaching southwestern Colorado. As evidenced below, the mid-level relative humidity increases, likely leading to a few mid and high-level clouds, especially over the western part of the state. Over the Denver Metro area, we’ll likely see sunshine transitioning into some clouds through the day and evening hours. Still, we expect mostly sunny skies.
GFS 700 mb relative humidity, wind, and heights on Wednesday
As for precipitation, the Front Range will stay dry due to high pressure over the Plains (below). However, a rain/snow mixture is possible across southwestern Colorado, potentially helping further with the ongoing drought conditions there.
GFS precipitation type and sea-level pressure on Wednesday
We discussed earlier about the warmer temperatures on the way. Our average highs are in the middle 60’s this time of year. We likely won’t reach this realm until Thursday afternoon. The figure below shows 800 mb temperatures for tomorrow, Wednesday, and Thursday during the mid-day. Northerly flow persists early in the week, with a gradual shift to southerly and westerly winds by Wednesday and Thursday. Middle to upper 50’s are a good bet on Wednesday. Thursday, thanks to a more downslope flow, 60’s should return.
GFS 800 mb temperature for Tuesday, Wednesday, and Thursday
Dry cold front ends the week
The week ends with a cold front, looking to approach late Thursday night out of the north once again. This is shown below, with another push of chilly air from the upper Midwest. Northeast winds on Friday will likely lead to temperatures only dropping a handful of degrees with no real chance for precipitation.
GFS 800 mb temperature for Friday
60’s and possibly low 70’s will stay in place through the upcoming weekend with essentially not even a chance of any rain or snow.
Forecast Specifics:
Monday: Sunny and much warmer than Sunday. Highs in the low to middle 40s on the Plains and in the middle 30’s in the Foothills.
Tuesday: Chilly to start, then sunny and mild with highs in the middle 50’s on the Plains and lower 40’s in the Foothills.
Wednesday: Sunshine early, then a few clouds in the afternoon. Otherwise, pleasant with highs in the mid to upper 50s for the Plains and middle 40’s in the Foothills.
Thursday: Mostly sunny with highs near average for this time of year in the low to middle 60’s on the Plains and upper 40’s in the Foothills.
Friday: Sunny and slightly cooler with high temperatures in the upper 50’s for the Plains and middle 40’s in the Foothills.
Weekend: Continued quiet conditions with generally sunny skies and 60’s to lower 70’s are expected for the Front Range.
High Country: Much of the week will be “quiet” for the High Country. Wednesday will see increasing clouds, with a chance of rain/snow over the southwestern part of the state. Check out our SummitCAST page for 6-day forecasts for more than 120 Colorado mountain destinations!
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, subscribe to BoulderCAST Premium.
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