Friday Update: Changes Arrive this Weekend, Snow Possible

In yesterday’s update we outlined in great detail everything that could go wrong with this approaching storm system. Somewhere around midnight last night it appeared as though the whole thing was falling apart. Today we’ve seen some rebounding from the models with regard to snow in Denver, and for reasons outlined below, we still think this storm deserves to be watched.

What we know
We know big changes are on the way beginning Saturday across the state. Highs Friday soared into the 60s for Denver, and while highs may climb back into the 50s Saturday, it looks like the real warmth is gone for awhile come Sunday. Sundays highs will be in the 30s.

Snow is probable for much of eastern Colorado late Saturday night through Sunday, though not everyone will see accumulating snowfall from this system. While models are all over the place with how much snow, mean forecast numbers for Denver would put us in the 0.5 - 3” range, with snow-favored locales doing slightly better. In other words, not a big storm at all. There are scenarios where this range could go up (or down), which I’ll address below.

This is a warm system for December, and with that, what precipitation may begin with or mix with rain at least initially. It also means snowfall ratios will be low for this time of year, likely 12:1 or lower, meaning light QPF can’t be made up for with fluffy snow for higher totals.

While models absolutely tanked last night with regard to QPF, the overall track of this storm remains favorable for snow in Denver, which is why we can’t dismiss this thing completely yet. If someone were to ask you to draw a picture of ideal 500 heights for a Denver snowstorm, you’d likely track an upper level low across the Four Corners, and come up with something that likely looks something like the forecast for Sunday from the GFS:

Unfortunately for snow lovers, in this case this may not tell the whole story.

Current model breakdown for snow at DEN looks like this:

12z GFS: 0” (though has 0.19” as rain, exactly 0.18” wetter than its previous four runs)
18z GFS: (appears slightly colder, but also down to 0.12” QPF)
18z NAM: 0.5 - 3” (highest south and west of Denver)
12z ECMWF (deterministic): 2.7”
12z ECMWF (ensemble): 3”
15z SREF (mean): 4”
18z GFS Upgrade: 2 - 6”
12z GEM: 4 - 8”

GEM is the clear outlier, though the ECM is close for southern/western Denver suburbs, and produces big time snowfall across extreme eastern Colorado into Kansas and Nebraska. The ECM ensemble forecast has also been pretty steady with 3 - 4” for Denver over last day or two. The operational GFS is finally producing moisture but not as snow, while the upgrade produces several inches for Denver. The NAM was snowless for all of eastern Colorado this morning, but now produces a bit for Denver metro at 18z. Mahem.

What we’re watching for
Better model agreement on snowfall.

The big thing we’ll be watching for over the next 24 hours is if models latch on to a higher snowfall forecast trend, or keep us somewhere between dry and a few inches. Was the slight uptick seen by some models today just a fluke? Or, are they starting to come around to a higher end solution?

If not, we’ll likely lock in a low end forecast for Denver tomorrow, with higher totals possible for the foothills, Palmer Divide, and portions of the eastern Plains into Kansas and Nebraska. While current NWP forecasts would mean a no-biggie storm for Denver, we think it’s prudent to watch this thing over the next 24 hours and see if anything changes.

More updates will follow as needed, so subscribe!

Oh, and if you’re holding out for next week’s storm, get ready for more of the crazy. Last night’s EURO dumped snow on Denver, today it’s moved the snow band about 400 miles south. The GFS? Virtually dry.

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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