ForecastWednesday/Thursday Storm Looks Weak; More Active Pattern Next WeekA winter storm around Thanksgiving wont bring much snow, but next week looks much snowier.
- Storm from Wednesday to Thursday morning will bring up to a few inches of snow to much of Colorado's mountains (favoring the northern mountains) and parts of the Front Range.
- Warmer on Friday and Saturday, potential disturbance on Sunday.
- Stormier next week, with heavier snow expected by Tuesday and Wednesday.
We did a post-mortem on last week's storm on social media, but in case you missed it...
Storm was a boom almost across the board -- came in a little deeper than expected and with a bit more moisture. Frontogenesis was also underestimated a bit.
With the impressive snow-liquid ratios (20-30:1) only a tiny bit more liquid = several more inches of snow. So actually some models had a pretty good handle on the overall impacts, but even relatively minute differences in liquid precipitation had outsized effects on snow totals.
Perhaps the biggest boom was the base of the foothills from Boulder to Golden. A shallow upslope was aligned perfectly to bring consistent snowfall with fluffy snow-liquid ratios. Ask us how we know... We measured 12" in Golden.
This upslope was too shallow to bring more consistent snowfall over to I-25, or too far up the foothills -- so the base of the foothills was the sweet spot.
Another impressive boom was Steamboat and the Park Range, which looked like they might actually bust after an uneventful Thursday morning. We ended up in a good spot in the jet right entrance region and the strong mid and upper level dynamics were able to wring out the fairly dry atmosphere. Double digit totals up there.
Winter Park also got a piece of the action after a very slow start.
For us, this was perhaps the biggest issue with our forecast -- we were expecting the storm to be rather frontloaded, but it ended up being backloaded.
Overall, we to set up our forecasts where booms are more likely than busts, and we definitely succeeded there (if we were in charge of dispatching snowplows, we probably wouldn't take that strategy).
The deeper low-level front also meant Colorado Springs got way more action than we were expecting. Oops.
Otherwise though, a modest to uneventful storm for most mountain ranges.
Colorado's statewide snowpack has slumped to about average after a strong start to the season.
Next Storm: Wednesday to Thursday
Weak upper level ridging has developed over our region which has warmed us up to near average temperatures.
On Wednesday, a weak shortwave is forecasted to dig into the central Rockies, pass over Colorado on Thursday, and develop into a closed low over Texas.
This will provide another cooldown and a quick hit of snow for Colorado, but totals look to be rather meager across the board. The latest runs of the Euro and GFS paint fairly different pictures -- the Euro actually has a halfway-decent event for some mountains (3-7" in Summit County) while the GFS is forecasting more of a 0-3" event.
When taking a look at the Blend (which accounts for all ensemble members and various other models), it seems that most guidance is more inline with the latest GFS run -- only a few inches in spots.
For comparison, here is the Euro's guidance. You can multiply the snow totals on here by about 2x to account for higher snow liquid ratios:
Like we said, this looks to be a bit of an outlier. We would look for support from the short-range ensemble forecast, and it simply isn't there:
Despite the general agreement on a lack of snowfall accumulation, models actually continue to have a pretty poor handle on this storm with some significant differences in the setup, even if those differences aren't a game-changer for snow totals. Thus, we could see some surprises in a few spots, which are clear when looking at a probability map.
Generally, most models are expecting us to not really get good jet dynamics, nor much available atmospheric moisture.
With all that in mind, we'd forecast about Trace to 4" for mountains along and north of I-70, and 0-3" for mountains further south.
We'd also expect Trace to 2" for the Denver metro area, with up to 3-4" for parts of the foothills and on the Palmer Divide. Further north (Longmont to Fort Collins), nothing much. Also maybe only 0-1" from Colorado Springs to Pueblo.
Snow is expected to start by noon on Wednesday in northern Colorado, and spread throughout the mountains by the evening, tapering off by around noon on Thanksgiving.
In the Front Range, expect a cold front by the early afternoon on Wednesday. Winds wont turn sufficiently easterly until Wednesday night or Thursday morning, which could set up an upslope and deliver a couple inches of snow.
There looks to be a chance that surface moisture on Wednesday night could be halfway decent, so we're keeping an eye out for slight boom potential in the Front Range.
A larger impact from Wednesday's storm will likely be winds as the jet stream moves overhead, with gusts of 30-60mph possible along the Divide during the day on Wednesday.
Next Week: More Active
This Friday through Saturday will be warmer behind Wednesday/Thursday's system. Sunday could feature some strong gusts along the Divide (70+mph) as flow becomes more zonal, heralding a more active pattern next week.
In fact, some models have a weak disturbance hitting Colorado on Sunday (up to 4" of snow) though model consensus is all over the board (some models have a pretty pleasant Sunday in store).
Better consensus exists around a larger wave on Tuesday/Wednesday -- this looks to have decent chances of being a significant snow storm.
After that there is far too much uncertainty to talk specifics, but a weak signal for another storm by Friday/Saturday that week.
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