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The weekly weather forecast for the high country of Rocky Mountain National Park, researched and written by professional meteorologist and mountaineer: Dan "the weather man" Gottas.
Issued Wednesday December 12, 2007
The Week in Review
After a week of unsettled winter weather, the snowpack in Colorado received a beneficial boost. Topping the new-snowfall chart were the San Juan Mountains, where about 10 inches of new snow-water equivalence (SWE) was measured at Wolf Creek Pass. Here, about 18 inches of SWE has accumulated over just the last two storm cycles (10 settled feet of snow), which represents nearly half of what is normally on the ground at the end of an entire winter season!
Here in the northern mountains of Colorado, we received mostly snowy leftovers, due to the precipitation-shadow effect that the regional-scale terrain creates during southwesterly flow regimes. Still, anywhere from 1 – 2 inches of new SWE was measured throughout the area, which resulted mostly from moist, warm-frontal and strong, jet-stream-level forcing.
In the eastern part of RMNP, about 1.5 inches of new SWE was measured at Bear Lake, but significantly more snow was observed at higher elevations closer to the Divide (see 12/10 Conditions Report for more info), where over 2 feet of new snow has fallen (~2.0 – 2.25 inches of SWE). Not too shabby for leftovers.
While most of the new snow fell with relatively little wind, the higher-elevation ‘breezes’ have returned, and have already begun to reshape the snowscape. Of particular note, a 24 hour period of moderate northwesterly winds (~25 mph gusting to 40 mph) occurred on Sunday just before the final snowfall event on Mon./Tues. Winds picked back up again early this morning (Wed.), and are moving along at a moderately healthy clip. Camera observations currently show vertically trapped stratus clouds (at near mountain-top elevations) diving down the east side of the Divide, from Glacier Gorge towards Milner Pass. This provides visual evidence of the local flow accelerations which are likely occurring just east of the Divide in association with a mountain wave. This process occurs quite frequently along the eastern-most oriented high terrain all along the Front Range, and significantly contributes to often dramatic decreases in precipitation, as one travels from east-side locations near the Divide to the lower elevations near the trailheads.
The temperatures have steadily decreased over the last week, and have recently bottomed out in the single digits and lower teens Fahrenheit (F), with the arrival of a Canadian continental airmass. In windier locations above treeline, the windchill temperatures are likely in the minus teens and twenties F.
Forecast Discussion
A west-northwesterly storm track will usher in another weather system this Thurs. evening, lasting through a good part of Fri. Snowfall amounts in RMNP are expected to be on the lighter side, as compared to recent storms. Model forecasted SWE is currently around a quarter to a third of an inch. Since temperatures are expected to be on the colder side with this system, higher snow-water-equivalence ratios of ~12:1 are possible (which translates to 3 – 5 inches of snow). The orientation of this system will also favor slightly higher precipitation amounts over the western ranges of the Park. Near-mountain-top winds are expected to be relatively light, when most of the precipitation falls. However, post frontal winds will increase on Sat. morning from the northwest, and will be strong enough to transport the new snow and form slabs.
Another system is forecast to move through the northern US Rockies on Sat. and Sun. The southern end of this system will affect the northern most mountains of Colorado with more westerly winds and some light snow. The moisture associated with the southern end of this system is somewhat limited, but orographic forcing and a relatively weak jet streak overhead should be enough to squeeze out some light snow over the higher terrain.
A higher-pressure ridge axis will move east of the mountains on Monday morning, and will be accompanied by a shift in wind direction from northwesterly to southwesterly over the higher terrain. During this time frame, a weather system is expected to deepen along the coast of California (sound familiar?). Energy and moisture associated with this system is forecast to begin moving into Colorado sometime around Tues./Wed. During this time and extending through the latter part of next week, the potential does exist for moister air to be transported into Colorado from lower latitudes – i.e., a higher likelihood for more significant snows.
Detailed 7-Day Forecast
The link above will take you to the National Weather Service forecast for the 12,000 foot level near Longs Peak. These forecasts are derived from computer-generated numerical forecasts, and are updated shortly after 3:30 am, 9:30 am, 3:30 pm, and 9:30 pm local time. In the lower right-hand corner of the page, one can view forecasts for other locations in the Park by clicking on the desired location in the terrain map.
Do-It-Yourself Weather Forecast Links
The link above provides a list of web links to various sites containing a variety of meteorological data and information. Collectively, these resources can be used to monitor and study current weather conditions, as well short-term, medium-range, and climate forecasts.
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