A “perfect storm” of ingredients are coming together across Colorado to produce gusty winds for the Front Range on Wednesday. When will the winds arrive and how strong will they be? Read on to find out. We also discuss snow amounts in the Mountains and our latest thoughts on the potential for a White Christmas in Denver.
A windy Wednesday
Hooray! The oh-so-common “windy day” for the week which we have been advertising has arrived. The upper-level set-up is such that a strong 165 MPH jet will be overhead on Wednesday across Colorado…
GFS 250 mb wind forecast for Wednesday. The nose of a 165 MPH jet streak will be overhead.
There is also an embedded trough axis passing through later Wednesday morning.
GFS 500 mb vorticity map for Wednesday. A trough will be passing by during the morning with strong winds at the base.
The atmospheric recipe coming together is really a “perfect storm” scenario for gusty winds:
- Jet stream overhead with strong winds present (165 MPH). These winds also extend down to 700 mb (80 MPH).
- Cold air aloft but relatively warm air in the lower levels. This will lead to steep lapse rates…that is, a sharp decrease in temperature with altitude. This will make the atmosphere unstable which increases mixing to help funnel the stronger winds aloft down to the surface.
- Deep atmospheric subsidence resulting from the mixing down of strong winds and the wake of the trough axis.
Ingredients #2 and #3 are shown below in the forecast sounding from the HRRR model valid at 2:00 PM Wednesday. Essentially the setup is displacing the strong winds that ordinarily would be high-up in the atmosphere downwards. Unlike most of our wind events in the Front Range, the driving force for this one isn’t directly related to the Mountains.
Atmospheric forecast sounding for this afternoon from the HRRR model for the area around Fort Morgan northeast of Denver.
Of course, the HRRR model is actually showing an amplified mountain wave on Wednesday producing extremely strong winds for the Foothills (see below). Gusts of 75+ MPH are evident, but this doesn’t seem to jive with the pattern indicated by the global models. The synoptic winds are too northwesterly we think for this downslope windstorm to ultimately verify. At this time, confidence is low that Foothills’ locations will see gusts anywhere near this strong. As for the rest of northeast Colorado, confidence is higher in strong winds impacting areas northeast of Denver towards Sterling where the subsidence will bring the winds down with the greatest intensity. In these areas, 45 to 55 MPH gusts will be widespread with the potential for blowing dust. For the immediate Boulder and Denver area, though, winds won’t be as bad. Ironically, in this atmospheric setup, the Mountains act somewhat as protection. Just 30 to 40 MPH gusts will be common through the day Wednesday.
HRRR model forecast near-surface wind gusts for 2 PM Wednesday afternoon.
We’re still expecting highs to reach into the low to middle 50’s across the lower elevations on Wednesday, well above normal again for this time of year. Skies will generally be sunny as well. Thus, the main take-away is that it will be windy, but overall, not a bad day for mid-December in Denver!
Mountain snow
Light to moderate snow will began in the Mountains after midnight Tuesday night and will continue into the afternoon hours Wednesday. This is associated with a brief pulse of moisture embedded in the northwest flow and the passing trough. Drier air will then filter in with gusty winds remaining through the evening in the Mountains. The NWS has raised Winter Weather Advisories for most areas above 10,000 feet. While snowfall totals will be just 2 to 6″, wind gusts of up to 60 MPH will create dangerous travel in spots. PowderCAST is showing only 2 to 5″ for most of the ski resorts.
Christmas is not looking very white
We hate to be the bearer of bad news, but clarity is starting to take shape for the forecast period leading up to the Christmas holiday. While we can’t 100% rule out snow for the lower elevations on Christmas, it appears that little change in the weather pattern will take place through early next week. That means more sunshine and more above normal temperatures, though there will be a cooling trend. Frequent but weak atmospheric waves will move through with only meager moisture chances for Colorado. We’re not expecting precipitation in Boulder or Denver in the next several days.
Look for highs in the 50’s to close out the week, with possibly even lower 60’s on Friday. A cold front is currently slated to move in Friday night, but that very well could change. If this front does materialize, it will make for a cooler weekend….far from what we should consider cold, though. Some models are showing hints of light snow for the region Saturday afternoon into Saturday night. This will be something we watch in the next few days.
As we discussed in our outlook yesterday, there are hints of a more favorable pattern developing next week capable of producing snow east of the Mountains. This change looks to take shape in the days FOLLOWING Christmas. That unfortunately means that unlike last year, we probably won’t be seeing a white Christmas this year. We’re hesitant to say more as models are wavering considerably at this time. Let’s just cross our fingers that we can play a little catch-up on snow…sooner rather than later.
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