Winter Weather Advisory Posted for Denver; Bumping Up Snow Totals a Bit

A banded snowfall event is more likely, meaning some of you will overperform on this storm by measuring quite a bit more snowfall than others.

It's been interesting watching data come in today. The typical bottom-falls-out with regard to QPF numbers hasn't happened –– in fact, the opposite in some cases. It's still hard to get overly excited about this system after what happened this week, but could we see it over-perform in some areas? Absolutely. Cold temperatures, long duration, decent jet action (banded snowfall), and modeled moisture continuing to increase would suggest maybe so.

That said, dynamically we don't see all that much of a change from yesterday, yet models have increased snow quite a bit today? It's hard to say why that is outside of them having a hard time with heavier banded snowfall. So is the tendency to increase QPF across the board today by the models a red herring and really our totals laid out this morning are the better forecast? Perhaps. The most realistic outcome is likely low-end totals for most, with a handful of areas busting high under banded snowfall.

The National Weather Service has issued a Winter Weather Advisory for Denver and the western and southern surrounding counties. This seems prudent even in the case of lower snowfall totals. Some tough winter travel conditions are likely from tonight through Sunday night along the Front Range of Colorado and adjacent plains.

The NWS is calling for 3 - 6" in Denver, with heaviest totals west of I-25. If many of the QPF forecasts modeled this afternoon are correct, this is entirely possible. The latest ensemble mean forecast from the EURO has 0.3" of liquid for Denver, which would be 3" of snow at 10:1, 4.5" at 15:1, and 6" at 20:1. We'll likely be in the 15:1 to 18:1 ratios for much of this event. So, if a good forecast... we may bust low with our forecast in Denver, even with our updated totals.

EURO precipitation forecast

For those of you that have followed us over the years you know it's rare that we adjust a forecast as we head into an event. Today feels like a day we need to do so if only slightly in some cases. The main adjustment was to up areas right along the foothills and south/southwest suburbs of Denver.

Boulder, Castle Rock, Golden... all look to have a pretty good shot at 3 - 6" (with perhaps even some number-padding snow showers Sunday night to boot). As we said above, for this area it may be boom or bust: end up under a band, could we see some 6"+ totals? Probably. Not end up under one, look for much lower end totals. The 3 - 6" is a broad-brush. For downtown Denver we'll nudge up to 1 - 4" instead of 1 - 3", with some skepticism around duration shown in some modeling and perhaps overdone moisture. Might the entire city see 3 - 6" absolutely, but we think the odds downtown and east/northeast are on the low side despite models getting excited today.

To that end, it's worth noting again that even while overall numbers have ticked up today, probabilities continue to show a drop off for higher-end totals. The latest gambler charts based on 15:1 ratios have improved from this morning... but still show Denver's odds at more than 3" of snow at under 40%, but better than 50% odds for Boulder. The question is, do these have a better handle with what will be reality or are latest models picking up on something?

Again, the difference maker in the end may come down to a few heavier bands of snow. i.e. most of our earlier forecast pans out, but a few areas bust high. With jet overhead models have a notoriously hard time handling these setups... Good chance in the end if you ended up under a heavier band of snow you'll think this was a great storm, and if not, you'll be disappointed.

It still looks like Denver's best chance for accumulating snow comes between say midnight tonight and noon Sunday. In fact, the latest HRRR doesn't really have snow developing along the northern urban corridor until after about 3am tonight, moving the snow into Denver around 4am. It might be a bit slow... but I think the right idea that snow holds off in town until midnight, or perhaps after.

A trailing shortwave may keep those snow showers going from time to time through Sunday night, and if so may pad the numbers above just a touch in a few locales. Would expect mostly a Trace to 1" of additional accumulation Sunday night, but we'll see if that too needs adjustment tomorrow.

Exciting times! We'll see how this goes. Bottom line is it'll be cold and snowy Sunday, boom or bust, and likely a slow morning commute for some on Monday. Please keep us posted with conditions at your house, and stay warm!

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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