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FXUS65 KBOU 102147 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 247 PM MST Sun Dec 10 2023

KEY MESSAGES

- High winds up to 75 mph in the higher mountains and Front Range Foothills until 5 pm this afternoon.

- Light snow in the mountains through Monday, possibly spilling onto northern plains Monday night with a little freezing drizzle as well.

- Still uncertainty around cutoff low through the Southern Rockies Wednesday - Wednesday night, but most impacts should stay south.

SHORT TERM
(This evening through Monday)
Issued at 246 PM MST Sun Dec 10 2023

As far as the High Wind Warning is concerned, we will keep it going through 5 pm. Peak wind gusts 70-75 mph still possible, but with some decrease in the GJT-DEN 1500m pressure gradient in the last two hours. The gradient should continue to slowly decrease this afternoon. The models still show an increase in snow coverage tonight into Monday morning, as the right entrance region of the jet slides south across the forecast area. Some weak showers generated across the plains this evening, but not enough to warrant pops out there. Snowfall totals in the mountains north of I-70, could pick up to 4 inches overnight, and another 2 inches on Monday. Spatial cross- section shows some decrease in the moisture by midday Monday, but still some residual light snow in the mountains in the afternoon. Across the plains, variable mid and high level clouds expected. High temperatures similar to today but minus the wind.


LONG TERM
(Monday night through Sunday)
Issued at 246 PM MST Sun Dec 10 2023

For Monday night, a backdoor cold front will slip across the plains. At the same time, weak frontogenesis and QG lift occur across the northern border area. The combination of these should be enough to support light snow across the northern sections of the mountains, foothills, and plains, roughly along and north of a line from Boulder County east/northeast to the I-76 Corridor. Most of this will be quite light, and maybe even start as some light rain in the lower elevations. Can't totally rule out an inch or so along the far northern border where there's a stronger F-gen signature.

Later in the evening and overnight Monday night, we'll lose our forcing but we'll still have shallow upslope in place. Cross sections show a profile favorable for light freezing drizzle with temps in the moist layer warmer than -10C. Thus, supercooled liquid water is likely, and thus freezing drizzle will be a threat as long as we develop sufficient moisture in the boundary layer.
Some of that could even sneak as far south as metro Denver, especially when considering location of the surface cyclone.

By Tuesday afternoon, it appears any precipitation should have ended with lack of any forcing features. Temperatures will likely end up on the colder side of guidance (upper 30s) though with fairly widespread cloud cover expected and colder high pressure east of the Rockies and no lee troughing.

For Wednesday and Thursday, we're still eyeing the closed low moving from the Desert Southwest eastward across the Southern Rockies. Just a couple of the runs were farther north yet, including the operational ECMWF. However, most ensembles were farther south which would keep most precipitation limited to areas from roughly Park County eastward across the Palmer Divide.
Lincoln County would have the best chance of seeing any accumulation, and from ensemble guidance that would generally be a couple inches or less. Only a small chance (10%) of anything more than that. Wednesday night would be the most likely time frame for that snow.

For the latter part of the week, there is generally ridging with only a couple weak shortwaves possibly shearing across the area.
That would bring dry weather and allow for warming temperatures.
We should reach above normal temperatures by Friday or Saturday, and then likely remain above normal with dry conditions through early next week.

AVIATION
(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1038 AM MST Sun Dec 10 2023

VFR conditions to prevail through tonight with mid and highs clouds. West northwest winds with gusts to 25 kts will persist at DEN/APA until 21z or so, then taper off a bit. Stronger winds will linger a bit longer at BJC. The trend in the models is for the wind to decrease a little sooner so had adjusted to timing in the terminals to match that. Decreasing winds late this afternoon/ evening with a transition to drainage.

BOU WATCHES/WARNINGS/ADVISORIES
High Wind Warning until 5 PM MST this afternoon for COZ033>036.

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