The weekly weather forecast for the high country of Rocky Mountain National Park, Colorado;  researched and written by professional meteorologist and avid mountaineer:  Dan "the weather man" Gottas. 

Issued Thursday May 1, 2008

The Week in Review

Over the last week, the mountains of RMNP received a strong dose of both winter and spring.  The water content in the snowpack has increased to its healthiest levels for the year, which is currently close to average in the eastern sections of the park.  Climatologically speaking, the end of April corresponds to the time of maximum snowpack water content near and above treeline, with steep melting rates occurring during May and the first part of June.

Last weekend’s storm brought new snow, cold temperatures, and wind to the high peaks of the Front Range.  Snow accumulations were 3-6 inches, with drifts up to a foot.  Moderate winds (sustained 20 – 40 mph; gusting up to but less than 50 mph) created a variety of surface conditions, from hard slab, to scoured patches exposing the underlying frozen cement, to fields of very shallow soft sastrugi, to smaller wind-protected patches of powder.

A warming trend, as advertised by the models, occurred during the first part of this week, with temperatures above treeline reaching the mid 40’s F by Wed.  Overnight temperatures remained near or above freezing on Mon. and Tues. nights.

During this warm period, both the persistent winds and a fair amount of blocked solar radiation by mountain-wave cloudiness prevented rapid warming of the near-surface snow and neighboring exposed terrain, thereby reducing the occurrence of wet point release slide activity for the given warm-up.

The Upcoming Week

Another cold weather system is impacting northern Colorado this morning (Thurs.).  Moderate to heavy snowfall was falling along the lower Front Range foothills (25 – 35 dBZ in the radar image below), and some observations and web cams are indicating 3-6 inches of new accumulation near the higher terrain below treeline.

The blotchy nature of the radar echoes indicates regions of enhanced precipitation associated with convection and a thermodynamically unstable atmosphere.  The reflectivity, as expressed in dBZ, is strongly dependent on the size of the snowflakes or raindrops and is also dependent on the population of snowflakes/raindrops present.  In general, heavier precipitation rates are associated with higher values of reflectivity.

While most of the storm dynamics and associated heavier precipitation echoes have moved and developed east of RMNP, some additional accumulations can be expected for the remainder of Thurs. with lingering orographic forcing and some weaker storm dynamics.  With the large scale storm system forecast to deepen over western Nebraska, strong winds will develop on the western side of the circulation over northeastern Colorado.  With this, sustained northwesterly winds near 40 mph (with higher gusts) are expected to develop later Thurs. into Fri. over the higher terrain.  This will once again act to redistribute the newly fallen snow, and form deeper hard slabs in areas.

For the weekend, the storm system is forecast to move east, and with this the winds will slacken and the temperatures will slowly moderate.  By Sat. afternoon, the wind direction will shift to the southwest, as a weak but persistent through of low pressure re-establishes itself over the western US.  With this, mid and high level moisture will move into the mountains, which will increase cloudiness and produce scattered precipitation during the afternoon on Sat. and Sun.

For the following week, indications are that a couple of weaker weather disturbances associated with the western states trough will affect Colorado.  Since the recent improvements in one-week forecast skill (during last weeks warming trend), a downward trend in correlation has commenced over the past three days (verification for the current storm system) to lower levels of statistical significance.  Reliable forecasts for next week’s pattern will be much better served by shorter-term (1-3 day) forecast models.

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.