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 Thursday February 7, 2007

The Week in Review

Under a swift northwesterly storm track, the unsettled weather pattern over the past week reinforced the cold conditions that have continuously engulfed the mountains of RMNP this winter.  Periodic snows added between 0.75 – 1.25 inches of water equivalence to the snowpack in the subalpine regions throughout the park.  However, periods of moderate winds (25-35 mph gusting to 50 mph) over the past week and strong winds (40-50 mph gusting to 75 mph) over the past couple of days have continued to reshape the snowscape.   With temperatures mostly in the single digits and teens F, the existing snow has also remained cold and ‘dry’ (i.e., liquid water free).

As a result of the moderate to strong winds, snowpack and snow-surface conditions vary considerably with elevation and location (as independently observed by Eli and me).  In the eastern alpine regions, considerable wind scouring has removed most of the snow through transport and sublimation processes.  Losses resulting from the latter process are accelerated when the overlying atmospheric conditions are warm, dry, and windy.  Although it’s been far from warm, the dry and windy components have been frequently occurring between storms, and are visually characterized by near-mountain-top plumes of ice crystal haze/cloud backdropped by clear skies (see image below).  Here, the airborne ice crystals (originating from blown surface snow) are efficiently sublimated (from ice to vapor) as the turbulent nature of the wind continuously mixes down drier air from higher altitudes.

As for transport, a significant amount of blowing snow (from the alpine regions) and falling snow have converged in the subalpine regions just below treeline.  This is particularly the case in places where the upwind alpine terrain gradient is slowly varying (e.g., slopes like the eastern flanks of Mt. Lady Washington, or high alpine valleys such as Loch Vale).  Downwind from these features, the treeline region ‘trips’ the flow and allows the transported snow to settle in the turbulent air flow on the down-slope side below treeline.  Due to the resulting deep accumulations and locally lower wind speeds, these zones provide some of the best powder stashes for skiing in the park (see Feb 6th conditions report for a hands-on example).

The Upcoming Week

For the upcoming week, three weather systems are forecast to affect the mountains of RMNP (see forecast graphic below).  The first, second, and third system will move into the area this evening (Thurs.), next Tues., and next Thurs. respectively.  All three systems will track into the area from the west-northwest, and will have west-northwest winds associated with each period of precipitation.  East-side fronts/snows are currently not expected with the first two systems (i.e., expect down-sloping winds east of the Divide, in the eastern foothills, and on the plains), but is still a possibility with next Thurs. system.

For the first system, the combination of strong jet-stream forcing, weak thermodynamic stability and strong orographic forcing will produce moderate snowfall totals (6-12 inches) over the higher terrain.  This combined with strong winds (sustained > 50 mph) above treeline on Fri. and Sat. will increase the avalanche danger near terrain features that form lee- and cross-loaded slabs under northwesterly flow.  Also, expect considerable drifting in the subalpine zones just below treeline east of the Divide.  Another brief shot of cold temperatures (single digits F above treeline) will move into the area Thurs. night and Fri.

A warming trend will begin on Sat., and will be in full force on Sun. and Mon.  With the winds slacking off by Sun. (forecast to drop down to 10 – 20 mph near treeline) and temperatures approaching the freezing mark near 10 kft,, it will feel downright balmy compared to recent memory.  At the current time, the Sun. / Mon. appear to be the best time window for attempting more committing alpine adventures.

Due to limited moisture and a fast pace, Tues. system is expected to produce only light amounts of precipitation, a brief period of moderate northwesterly winds (sustained near 30 mph near treeline), and single digits F above treeline.  A quick recovery is forecast to occur on Wed. before the next system affects the area on Thurs.

Detailed 7-Day Forecast

NWS Forecast for the 12,000 foot level near Longs Peak 

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

Weather Observations and Forecasts

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.