Colorado Weather Forecast #188: May. 16, 2022 - May. 22, 2022

Increasing thunderstorm chances and moisture this week. Update on the potential for a wintry storm by the end of the week.

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Updated Mon May 16, 2022 3:00pm MST | Published Mon May 16, 2022

By Thomas Horner

Retrospective and Current Conditions

We called for dry conditions as we progressed into May and unfortunately that’s been the reality. The past seven days have featured almost no precipitation except for a few parts of the northern regions of Colorado:

Over the past 30 days, most of the desert southwest (Colorado, New Mexico, Arizona, and Utah) have seen less than half of their typical precipitation totals, and almost no areas have seen more than average:

This has not been a favorable pattern for our region…

…with the best impacts occurring in the northern Rockies and coastal ranges.

Snowpack

Overall there is quite a gradient in the state of the snowpack as you move from the Pacific Northwest to the desert southwest:

Still, ski mountaineering season in parts of central and northern Colorado is still well under way, even as the snowpack melts at a faster rate than usual.

The SNOTEL at Berthoud Pass reveals a below-average season and an earlier melt than usual:

At Schofield Pass (West Elks – central Colorado), an above-average season is also coming to a quicker end than what is typical:

In southern Colorado, an unfavorable storm track this spring plus widespread dust coverage has already brought things to an end for just about everywhere outside of the highest elevations of the western San Juans:

Severe Storms

It’s been pretty impressive just how little thunderstorm activity there has been this spring. This about when storm chasing season really starts to pick up steam, and the fact that many of us have yet to even hear a rumble of thunder is certainly outside of the norm.

Unfortunately, the Storm Prediction Center’s observations for the month aren’t currently available, so we have no hard data to do a comparison with besides the obvious fact that we’re well behind on precipitation totals for the season.

The lack of moisture did at least allow for good viewing of an impressive lunar eclipse last night. Here’s a photo that Thomas took:

(Thomas Horner)
(Thomas Horner)

Overall, hard to get any serious moisture and lift into the region with ridging so frequently overhead.

(via WeatherBell)
(via WeatherBell)

Forecast Discussion: Thunderstorm Chances This Week

We do have a slightly more favorable environment this morning. We have some low-level moisture in place, with a shortwave upstream of us advecting some mid-level moisture into the region:

(via WeatherBell)
(via WeatherBell)

…but so far this only looks to favor the eastern Plains for more significant thunderstorm chances. The approach of the shortwave should make for a better convective environment by tomorrow. The Storm Prediction Center has Tuesday’s severe storm threat as far west as I-25.

Thunderstorm chances into Wednesday are greatest along and east of the Divide, though much of northern Colorado has elevated thunderstorm risk thanks to a jet max nearby.

(via WeatherBell)
(via WeatherBell)

Wednesday features the best combination of moisture and dynamics ahead of another weak shortwave. Thunderstorms will generally be more widespread and get started earlier on, with some lighting threat in play by noon for some of Colorado’s peaks.

Overall, here’s the breakdown for each day’s thunderstorm threat for the 14ers:

…and for some climbing areas:

Note that 10-30% would mean isolated thunderstorm chances, and 30-50% meaning scattered, and >50% chance being quite considerable.

Thursday will feature some very warm temperatures ahead of a larger trough which will impact us by Friday (resulting in the thunderstorm chance uptick that day). In fact, we will likely see a decent cold front race down the Front Range and northern Colorado by Thursday evening, which could potentially limit high temperatures.

Friday’s trough is our much-touted potential storm. How’s it looking?

Forecast Discussion: Potential Winter-ish Storm, Thursday night to Saturday

First off, let’s go over what’s changed since our last forecast.

The good news is that blended guidance does better support the idea that Front Range will likely see some flakes and widespread precipitation, if only briefly. We’re also locking in the potential for a decent snow event along and east of the Divide. We’ll break that down in a second.

The biggest change since before last weekend was how various models were handling this storm. The ensembles of the GFS and Euro have largely swapped roles, with many recent runs of the Euro now showing a glancing blow and fairly minimal amounts of snow, and the GFS converging towards a more impactful storm. The Canadian ensemble still sits on the lower end.

We’d use this information to point to the fact that it’s likely this storm won’t be particularly exciting, but the very latest 12Z Euro run came out as we were writing this forecast, and has snapped right back to a more bullish forecast. This could merely be noise in its general trend towards a weaker storm, but highlights how much uncertainty remains across the board.

The other major change is that timings have generally been pushed forward by a day or so. Still plenty of disagreement here, but we would expect the largest impacts somewhere in the Thursday night to Saturday morning range.

With that in mind, here are the two burning questions:

Will we see an impactful snow event in the Front Range?

Despite the low-end snow impacts trending upwards, and the lingering presence of ensemble members showing historic amounts of snow in the Front Range (like a couple feet in Denver), we need to start paying credence to what the higher resolution deterministic runs are doing now that we’re getting a bit closer to the storm. These runs have been trending down (lower snow totals are a result of less precipitation and warmer temperatures, which tend to go hand-in-hand with a storm like this).

This is at least finally starting to substantially narrow the range of possibilities for this storm, as it becomes more likely that the Denver metro area will get a few sloppy inches of snow (which may mostly or entirely melt) but not a whole lot more. Still, the potential for a more serious storm isn’t entirely ruled out, though we do think chances have pretty much dried up by this point.

Looking at a blended snowfall exceedance chart for various population centers in Colorado presents a less exciting picture than just grabbing the latest runs from the GFS and Euro:

Biggest takeaway: the lower end probabilities have ticked up fairly substantially since our previous forecast.

Will we see some serious powder in central and northern Colorado?

We’d say the chance for powder hasn’t changed much since our last forecast. A lot of the higher-end scenarios have disappeared, but there remains a strong showing in the 5-10” range for a lot of higher elevation peaks across central and northern Colorado, with double digits still in the running especially near the Divide.

Probabilities from the Blend may not paint a particularly snowy picture, but these are actually fairly decent numbers considering the considerable lead time and level of uncertainty. Once we start aggressively dropping drier ensemble members over the next couple days (which is quite likely), these numbers should bump up quickly:

Let’s take a look at potential snow totals. Right now, we think it’s likely that totals will end up somewhere in the 75th to 90th percentile range since the driest scenarios may be too unrealistic. This is generally 5-13” near the Divide and 1-8” elsewhere, with totals dropping off quickly further west and south.

All of this is still mostly speculation as we wait for models to converge and run-to-run swings to become less drastic. We’ll keep you updated as model guidance really starts to become usable, but we’re excited by the increasing likelihood of some badly needed precipitation across at least the Front Range. Sorry, southern Colorado…

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