May 20, 2021
Colorado Weather Forecast | May 20–26, 2021
Strong southwesterly and southerly flow into the weekend (quite gusty in the mountains), HEAVY snow/rain in the San Juans, thunderstorms.
Synopsis
- Heavy snow and rain begins in the San Juans late tonight / early Friday am, lasting into at least Saturday. Snow totals of 1–2 feet possible above 10,500ft.
- Gusty conditions (30–50mph) on Friday for most of Colorado’s peaks, less windy on Saturday (20–35mph), windier again on Sunday (30–40mph).
- Widespread thunderstorm chances on Friday and Saturday (30–50%!), particularly in southern Colorado. Much more isolated and weak on Sunday.
- Typical, fairly isolated thunderstorm activity from Monday to Wednesday next week. Warmer.
Discussion
Eastern Colorado has been slow to warm up and dry out as a closed low finally exited our region yesterday. This system brought a couple days of snow to the mountains, which certainly overperformed in spots.
On Monday, southeasterly flow targeted the southern Front Range, Mosquito Range, Tenmile Range, Kenosha Range, and parts of the Sawatch, with some 3–6" totals in spots (other areas, like A-Basin, only picked up 2").
As the storm pushed east over the Rockies, lee cyclogenesis really focused sustained, heavy snowfall in the Sangres and parts of the San Juans into Tuesday. Some areas have two to three feet of snow!
Eastern Colorado picked up a sizeable amount of water over the past few days, which generally fell as rain below 10,000ft.
4" of liquid precipitation in southern Colorado put a nice dent in their ongoing drought, and is a pretty incredible amount of water for our climate. This shows up as a precipitation anomaly of nearly +1000%!
The Western Slope has gotten almost nothing lately, exacerbating water and fire concerns as we get into the hotter months of the year.
Here’s a comparison of current drought conditions compared to last week:
The Front Range has continued to make gains, and almost all of the state north of the Palmer Divide and east of the Continental Divide is drought free.
In terms of snowpack, we see about the same distribution.
The northeastern Colorado mountains are finally starting to melt out…
…while, for instance, the San Juans are already well into early summer snowpack conditions.
Will the Western Slope get any respite? We do see a trough hanging out over Nevada and into the weekend:
This gets robust southwesterly flow going tonight, which transitions into southerly flow by Friday and through much of the weekend. This pulls quite a bit of moisture into the state:
Moisture and southwesterly/southerly flow is usually a good recipe for rain and snow in the San Juans. The Blend has 2.5" of water falling in the San Juans:
Even with our warm temperatures, that’s well over a foot of snow in the higher terrain. Correspondingly, the Blend shows totals of 12–24" throughout the high peaks of the San Juans by the end of the weekend:
Our website isn’t quite as optimistic, with high snow levels (10,500–11,000ft) and low snow-liquid ratios:
Regardless, a healthy amount of precipitation is on the table.
Elsewhere, the main story for this weekend are gusty conditions in the mountains and thunderstorm chances. Friday brings gusts of 50mph+over many of Colorado’s mountains as the jet stream moves overhead:
The winds settle down a little bit on Saturday (gusts of 30–40mph) before getting more firmly into the 40mph+ range again on Sunday.
With the heavy stream of moisture comes pretty serious thunderstorm chances on Friday and Saturday, before dry air moves in on Sunday and greatly reduces the threat to only weak, isolated storms. Look to the south — that will be the direction thunderstorms are coming from.
Note that in the southern Sangres, Sawatch, and San Juans, the lightning threat start a bit earlier on Saturday (10am-11am).
The system to our west falls apart on Sunday and lifts out of the area, bringing back mild ridging for next week and thus drier and warmer conditions west of the Divide:
East of the Divide (i.e. the High Plains, foothills, and urban corridor) wont feel the impacts from this system too much, but thunderstorm chances will be more widespread, with chances for very severe storms in far eastern Colorado or just east of the state. Parts of the plains will likely see some stratiform precipitation early in the morning on Saturday.
Forecast by
Thomas Horner (Twitter: @thomaschorner)
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https://highpointwx.com
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