Thursday,  December 10th, 2009

Rocky Mountain National Park Weather Forecast
 

The mountains of RMNP remained in a deep freeze over the past week.

The Week in Review

Over the past two weeks, the Madden Julian Oscillation and El-Nino conspired over the central tropical Pacific Ocean to produce a strong widespread region of deep tropical convection.

Energy dispersed northeastward in a great-circle arc, which formed and amplified a series of quasi-stationary high and low pressure waves stretching from the mid latitudes of the eastern Pacific to the US. 

The position of this wave train allowed cold continental arctic air to surge southward from Canada into the west-central US states including CO. 

Temperatures near treeline ranged between -14 and 19 F throughout the week.  The cold temperatures produced low density snow (of the fluffy variety) over a four day period, with 0.8 inches of new snow-water-equivalence measured by the snow pillow at Bear Lake.  With some settling, the snowpack depth increased by about 10 inches over the period near the lake.

With the arctic surge displacing the jet-stream position south of the state, most of the new snow fell under light-wind conditions. 

These arctic patterns often offer virtually windless periods of opportunity to sample freshly fallen snow, before the inevitable windy freight train transforms the snowscape.

Very strong winds returned on late Tue., as the mid- and high-altitude cold pool began its northeastward retreat. 

The strong west-northwest winds have worked the new snow into sensitive hard wind slabs and drifts, which are lying on top of weak, faceted snow layers; sketchy ingredients for avalanches.

The Upcoming Week

The arctic air will continue to erode and retreat northeastward, as a much milder airmass moves in from the Pacific Ocean over the next few days.  During this time, temperatures will rebound as much as ~15 degrees C (25 F) in places through Sat.  We will still be contending with moderate to strong winds for most of the week.

A Pacific storm system will move across CO on Sun., bringing another round of snow with it.  Current precipitation forecasts indicate the potential for 0.5 inches of liquid, or about 8 inches of snow.  Orographic forcing will be more favorable with this storm, with moderate westerly component flow near and above mountain top.  If these verify, new snow totals could be greater than the current forecast.

Another storm system is forecast the brush by the northeastern part of the state on Wed.  Only light orographic snows are forecast with this system, and successive model runs have reduced its impact on CO.

A peek into the distant weather future (two weeks out) shows another possible high-amplitude pattern setting up.  Strong tropical forcing is again expected to occur during this time over the central tropical Pacific and will influence the weather pattern over the western US.

The probabilities are high that a high-amplitude ridge will form along the west coast.  However, what will evolve downstream over the Rockies is still a fuzzy unknown, with equal probabilities for cold/snowy and dry/warm conditions over CO.

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