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. 

The Week in Review

Three winter storms rolled through RMNP over the last week.  Near the 9 – 10 kft level, a total of about 0.6 inches of liquid, in the form of snow, was added to the snowpack.  The first storm (last Fri.) contributed the greatest to the precipitation total, as the second two storms ended up tracking farther south than the model forecasts of last week.  As is often the case with many Front Range storms, positioning can make or break a forecast over very short geographical distances.  A classic example of this occurred with the third storm on Tues. Dec. 25th.  As seen in the plot below, a large north to south gradient occurred along the Front Range foothills, with most of RMNP (in Larimer County) receiving an inch or less of snow and upwards of a foot of snow fell in the foothills west of Denver.  As seen in the plot below, a large north to south gradient occurred along the Front Range foothills, with most of RMNP (in Larimer County) receiving an inch or less of snow and upwards of a foot of snow fell in the foothills west of Denver.

Also worth noting are the higher accumulations located at lower elevations (~5 – 8 kft) east of the Divide and the comparatively low snow accumulations west of the Divide.  These signatures are associated with relatively shallow (e.g, less than 10 kft) easterly-component upslope events that occur when cyclonic storms (horizontal counter-clockwise circulations) evolve and/or translate just south and east of our area.  In general, as the easterly-component flow deepens with stronger systems (e.g., up to 18 kft), the region of maximized orographic forcing (and highest snowfall accumulations) typically occurs closer to the Divide.  In addition, dynamical forcing, associated with the circulation physics, also contributes to snowfall formation.  When this contribution is weak, as was the case with the Dec. 25th storm, appreciable snow accumulations become limited to the terrain regions that are exposed to the orographic effect.  In the plot, notice how the Front Range foothills and the Palmer Divide are outlined quite well by the higher snowfall amounts.

The fresh blanket of snow that did cover the alpine regions during Friday’s storm (as visually observed from DIA while I was flying out of town) was once again scoured by the northwesterly winds which carried on at a moderate clip during the latter part of Sat. and most of Sun. (sustained near 30 mph and gusting frequently in the 50 mph range).  Temperatures were at their lowest on Sat., Wed., and today (single digits), and a moderating surge of warmth occurred on Mon., with mid 20’s throughout most of the day.

Currently (Thurs.), another storm system is affecting the area, with light snow and cold temperatures.  Accumulations have been light, with only an inch or two (0.1 inch of SWE) measured in the eastern locations of the Park.  Temperatures are currently the coldest of the week, and are currently near 0 F at 10 kft.  The more southern track of this storm, and its associated forcing, has been the main limiting factor for precipitation production.

The east side of the Continental Divide in Rocky Mountain National Park on 12/26/07  1. East Face of Flattop  (skiing) 2.  East face of Notchtop (alpine route) and 3. Gabletop Mtn (11,939')

The Upcoming Week

Today’s system (Thurs.) is on its way out of here, but will leave a chilled evening in its wake, with temperatures dropping into the single digits below zero near 10 kft.  The Wind machine will crank back up again on Friday, which when combined with the cold temperatures, will create wind chills as low as -25 F in exposed areas.  Travel above treeline will be for the bravest of souls.

A strong northwesterly flow pattern will become established over RMNP on Friday through Monday.  A series of small scale weather disturbances will stream into the northern mountains of Colorado from the Pacific Northwest.  The combination of a fast, moist air flow, a strong jet stream, and favorable orographic forcing will produce periods of snow on Sat. through Mon.  Upwards of 1.0 inch of SWE (1 – 1.5 feet of snow) is forecast to fall in areas with windward exposure to the northwesterly flow.  When all is said and done, new snowfall amounts may vary quite significantly throughout the Park.  The western ranges (e.g., Never Summer) are likely to receive the heaviest amounts of snowfall, while the eastern-most terrain will likely receive the least (due to less favorable terrain orientation, snow shadowing, and accelerating down-sloping winds - sound familiar?).  The strong down-sloping flow will also create large decreases in SWE eastward and down slope of the Divide.  Strong winds will persist throughout the period, which will continue to strip newly fallen snow from the alpine landscape and create new slabs in lee- and cross-oriented slopes and deposition zones.

A change in the storm track is forecast to begin on Tues. over the Eastern Pacific Ocean and western U.S.  The winds over RMNP will subside on Tues. and Wed., and temperatures will dramatically rebound, as a ridge of high pressure builds over Colorado.  This will provide a relatively tranquil weather window for accessing higher, more committing alpine routes.  A southwesterly storm track will become established along the west coast, allowing storminess to move into California, and possibly into western Colorado by the end of the week.

The east side of the Continental Divide of RMNP on 12/26/07  1. Sprague Pass (11,700') 2. Sprague Mtn. (12,713') and 3. Stones Peak (12,922')

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. 

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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.