Mother's Day Snow? A Look at the Analogs and Latest Forecast

If you missed last night's update, you may want to take a quick look now as we won't revisit everything, but did want to get an update out tonight and talk a little about what the analogs are showing.

Remarkably, the models have been very consistent over the last several days with this next system. There remain some differences in track, speed, and eventually temperatures, but overall each individual model has been pretty solid run-to-run. While we continue to track this system and narrow in on its eventual impacts on Colorado, I thought I'd take a quick peek at what some of the analogs look like for this thing...

Snowfall Analogs
At face value, the snowfall analogs are downright impressive. Upon closer inspection, many of the closest matches overall and at 500mb are actually from April and March, with only 3 of the top 15 analogs coming in May. The overall top analog, and at least fairly close to May, is April 24, 1994 – a system which produced 2.2" of snow at Denver International Airport and 17.9" in Boulder. With that, the snowfall probabilities showing up in the analogs are likely overdone, like the percentage of top 15 analogs exceeding 4" of snow being 70% at the moment:

Percentage of top 15 analogs exceeding 4

Meanwhile, the three May analogs produce just 1", 2.7", and all rain for DIA, which is more realistic climatologically speaking. Of these analogs, the top match at 500mb is the 2.7".

Related: Denver's top 15 May snowstorms

Severe weather analogs
It continues to look like this system will produce quite a bit of severe weather this weekend as well, particularly across the heart of Tornado Alley: north Texas, Oklahoma, Kansas and Nebraska.

Analogs here show some potential for severe weather across northeast Colorado Saturday, but better chances for a more significant outbreak will be east.

Percentage of top analogs with at least 1 severe report with 110km of grid point | CIPS Analogs

Forecast update
When it comes to snow, this will no doubt be a very challenging forecast for lower elevations. While some operational runs continue to produce more than 15" of snow for Denver, other models are far more less bullish. Regarding the huge snowfall totals the EURO and Canadian are producing, these need to be taken with caution – it's coming up on mid-May, surface temps are warm, air temps will be marginal, sun angle is high... etc. THAT BEING SAID, crazier things have happened, so this of course continues to bear watching. Unfortunately, if there were any trends today it may be toward a colder solution.

The best chance of snow for lower elevations looks as though it'll come early Sunday as the main surface low works east/northeast of the state and cold air filters in behind.

The two images below are valid 12z Sunday (early Sunday morning). The top image shows QPF (and precip type), and the positioning of the surface low (southern Nebraska). Note the snow on the backside, with some the GFS trying to produce some snow across the I-25 urban corridor at this time. The second image shows wind speed and direction, with very strong winds forecast across southeast Wyoming and northeast Colorado which could mean blizzard conditions at times for those who see snow, including possibly the Palmer Divide if things set up right.

Weather5820 Models

Weather5280 Models

I meant to keep this short, but there's a lot to consider with a very complex setup for the next 3 - 5 days. Still lots of time to see how this eventually comes together, but for now here are a few summary points for what we're watching this weekend:

  • Moisture. More moisture headed for the state, possibly significant across northeast Colorado. For now would broad-brush 1 - 3" across northeast Colorado this weekend, but there's certainly the potential for more, especially across extreme northern Colorado.
  • Snow potential. It's there, needs to be tracked. For now the most significant snowfall totals are likely to be above ~7,000 feet, but it looks more and more likely that lower elevations (>5,000ft) will see some snow on the backside of this thing. For now we won't ignore the snow threat in Denver, but continue to place the greatest risk for a significant Spring snow across southeast Wyoming, and portions of western Nebraska. Greatest Mother's Day snowfall threat map | Weather5280 Models
  • Unseasonably cold. Cold temperatures by Sunday night? Unfortunately some models came in much colder for Sunday night after the heaviest precipitation pushes east, which is not great news for those with gardens. Currently the EURO is coldest (19° F Mon morning), but others too have dropped lows into the 20s for the metro area, so it seems probable that temperatures may drop (well?) below freezing by Monday morning.
  • Storm track. Probably the biggest thing giving us pause right now is some questions around the 500mb Low track and the amount of QPF/snow models are producing. There seems to a bit of a disconnect here with some tendency to throw this this thing north, which would not support some of the rain/snow totals the models are producing at this time. Seeing how this aspect evolves over the next 24 - 36 hours will almost certainly be key to boom or bust with this system.

You can bet we'll be all over this system as we know its impacts will be far reaching. For now still plenty of uncertainty around specifics, but it looks more and more that if you live in northeast Colorado you can plan on at least chilly wet weekend, especially from Saturday afternoon through Sunday. More updates to come, stay tuned!

Brendan Heberton

Brendan is founder of Weather5280. He is co-founder of FreshyMap, and develops software for geospatial data analysis and visualization.

Denver, Colorado
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