After a warm and breezy start to the week, the weather turns colder and very active as a series of cut-off low pressure systems merge over the western United States. This will bring the threat of rain and snow to the Front Range Wednesday through Friday. Read on for more details.
Calm and warm to start
Our nation is experiencing a variety of weather as we begin the week, evident in the below 500 mb absolute vorticity plot. Over the eastern part of the country, a deep trough of low pressure is bringing unsettled and colder weather. High pressure is present over California, spelling out gorgeous conditions for us. For the weather by mid-week, we are watching a system off the coast of Washington, as well as one in the eastern Pacific Ocean. Both of these disturbances may merge over the Four Corners region bringing the potential for rain/snow in Colorado later this week.
GFS 500 mb vorticity map for Monday showing a complex pattern across the United States
Let’s not get ahead of ourselves, however! All will be quiet across Colorado today and tomorrow. The ridge over our area will facilitate a downslope warming period with above average temperatures expected both days (see below). A nice lee trough axis will be present on Tuesday, a sure sign of the warmer weather in-store (and possibly a big wave cloud as well). For Monday, expect middle 60’s with lots of sunshine. Tuesday, high temperatures may approach the lower 70’s, dependent on just how extensive the wave cloud coverage is.
GFS 800 mb temperature and wind forecast for Tuesday morning
Unsettled Wednesday through Friday…how much snow?
By mid-week, the pattern begins to turn quite active and unsettled. The offshore trough will move into Oregon and California on Tuesday (see below). High pressure remains over Colorado. At the same time, the long-standing cut-off low near Baja California progresses further northward. We will need to watch these systems closely as they come together and interact with cold air diving down from Montana.
The pattern we are about to see unfold this week across Colorado is a rather complex and notoriously difficult one to predict, mainly because the systems will largely reside south of the polar jet stream and become cut-off from the main upper-level flow. The finer details of how the merger progresses from Wednesday into Friday will be key to determining the amount of rain/snow we receive. Below shows the upper-level jet stream for Wednesday and Thursday (top panels) and the mid-level 500 mb vorticity (bottom panels). Something we will have to watch for will be potential interaction with the right-entrance and left-exit regions of the jet (yellow-shaded areas below) which could enhance snow chances Wednesday night and Thursday. In addition, the potential merging of the southern system with the northern one in Idaho and California (bottom panels) will ultimately determine when and where the precipitation occurs. Furthermore, sub-tropical moisture will be plentiful on the southeastern quadrant of the eventual conglomeration.
On top: GFS 250 mb wind forecast maps for Wednesday morning (left) and Thursday morning (right). On bottom: GFS 500 mb vorticity maps for Wednesday morning (left) and Thursday morning (right)
The models are consistent in showing that the initial influx of colder air arrives Wednesday morning. The cold air becomes further entrenched Wednesday night and Thursday and stays with us into Friday. At the same time, snow levels likely will fall below 5000 feet sometime Wednesday afternoon or evening. Precipitation could start as early as midday Wednesday as a rain/snow mix, with a gradual change to snow by Wednesday evening. After this, any precipitation that spreads across the Front Range will be all snow the rest of the week.
We can’t stress enough, we’re still two to three days out and uncertainty from Wednesday onward is high. Our Snow Probability Charts do give us an idea on potential snow amounts in Denver and Boulder with several inches of accumulation on the table. The operational GFS is showing between 3 and 8″ by Friday morning for the Front Range. As we mentioned earlier, however, due to the tricky pattern this week, we do not yet have a good handle on exact amoutns. Narrowing down the track of the storm and the jet stream location will be key players and part of the evolving forecast in the coming days. It’s fairly likely, though, that the San Juans will see their first big powder dump of the year…a much-needed one considering the disappointing start to the snow season they’ve had.
In summary, expect a warm early-week with 60’s to lower 70’s. Clouds will increase late Tuesday and Wednesday, with rain/snow Wednesday transitioning to all snow Wednesday night and Thursday alongside much colder temperatures. Join our email list for updates on the evolving winter storm. On the upside, a nice warm-up will ensue Friday into the upcoming weekend!
Forecast Specifics:
Monday: Mostly sunny, warm and breezy with increasing upper-level clouds. Highs in the middle 60’s for the Plains and middle 50’s in the Foothills.
Tuesday: Partly to mostly cloudy skies under a large wave cloud, but very warm. Highs upper 60’s to lower 70’s on the Plains and upper 50’s in the Foothills.
Wednesday: Cloudy skies with a chance of rain/snow showers turning to all snow by evening. Snow could mix with freezing drizzle overnight. Highs cooler in the middle to upper 40’s in the morning, dropping throughout the day behind a cold front.
Thursday: Overcast with light snow possible and highs in the lower 30’s for the Plains and middle 20’s in the Foothills.
Friday: A few morning clouds and possibly flurries, then mostly sunny with highs in the 40’s for the Plains and 30’s in the Foothills.
High Country: Expect a nice start to the week today and tomorrow under mild and dry conditions. The weather becomes quite active with periods of snow Wednesday into Friday. Several inches of snow are likely, with southwest Colorado most favored. Quieter weather takes hold for the upcoming weekend. Check our PowderCAST page for always-updated weather forecasts for all of Colorado ski resorts.
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.
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