If you caught last week’s State of the Atmosphere you’ll recall we talked about the potential for at least one system impacting the state during the first week of November, and in general the potential for a cooler week. We also talked about how models are having a difficult time with medium range outlooks, which continues to be the case. That said, confidence has grown in that we will see at least some rain and possibly snow across portions of eastern Colorado come late Sunday and Monday.

Synopsis
A large upper level disturbance will begin impacting the state Saturday and on into Sunday with a chance for mountain snow across western Colorado. Depending on the eventual track of the upper level low, we could see our first accumulating snow in Denver, or walk away with another brief bout of rain showers and cooler temperatures. The best chance for rain or snow in Denver will come in the late Sunday into Monday time frame, with mountain snows developing already on Saturday.

California rain and snow
Before this next system begins to impact Colorado, it’s forecast to bring beneficial moisture to drought-stricken California. The Canadian and Euro models both produce between 1 and 2 inches of precipitation, and upwards of 10 inches of snow through Tuesday night for the higher elevations of central and northern California; this is great news!

Don’t live and die by the GFS
Many already completely discounted any threat of snow for Denver with this system in recent days. While it’s true, this system once looked more impressive on the GFS before a handful of miserable runs (if you’re hoping for snow), I continue to not understand why some hang their entire forecasts on its operational run, especially greater than five days out. Doing this will lead to a great number of conflicting forecasts -- i.e. yesterday’s 12z GFS produced nearly 0.5” QPF, while its 18z run produced <0.1”. The fact of the matter is, models (today) are generally unimpressive with this storm for Denver, but:

• There’s very little run-to-run consistency.
• There’s little consensus between models on eventual track.
• This morning’s 12z suite is still almost 4 days out from any potential impacts in Denver.
• This is (like it or not) likely our best chance of snow so far this season in Denver.

Taken at face value, today’s 12z model run largely suggests Denver would escape with a period of unsettled, cool weather but very little rain, and likely not much of any snow. Both the 12z GFS and EURO models came in considerably drier for Denver, and neither had a temperature profile that would support snowfall.

That said, the Canadian model continues to bring accumulating snowfall to Denver. It’s also worth considering what time of year we’re in, and with any precipitation the GFS/EURO produce there’s likely to be good evaporational cooling that may better support a changeover to snow -- although not depicted very well in the models. Additionally, the EURO ensembles actually came in wetter for KDEN than its deterministic, suggesting the possibility of some light snow.

Bottom line? A lot to watch here.

Any way you cut it, it looks like an unsettled weekend for the high country, and eventual out east for late Sunday and Monday. Here’s the 12z GFS 6hr QPF + precip type valid late Monday afternoon:

Lots of time, watching track carefully
There’s still a lot of time to track this system and get a better idea of how things will shape up across eastern Colorado. The eventual track of the upper level low will greatly determine what kind of storm this will be for us.

Here is the latest 12z snowfall forecast. Its coverage is far more sparse than EURO/GEM for mountain snowfall, but it’s certainly nice to see some snow forecast after a slow start in the high country.

Stay tuned as we head into the weekend as we’ll be sure to post updates as this system continues to evolve. If you have not already, now would be a great time to subscribe to Weather5280 and be assured we’ll keep you ahead of the storm!