Thursday, May 20th, 2010

Rocky Mountain National Park Weather Forecast

A cold and snowy month of wintery weather gave a much needed boost to the RMNP springtime snowpack.

The Month in Review

The combination of additional snow added to the snowpack and the delayed onset of the high-elevation spring runoff has left the current snow water content at 100-125% of average levels for this time of the year.

The Never Summer Range was the big precipitation winner in RMNP, with around 8 inches of new snow water accumulating at 10,300’ over the past month.

This accounted for nearly 35% of the total annual average accumulation and brought the current seasonal accumulation up to the climatological peak value nearly a month later than average.

The sticky spring coating of new snow covered most alpine aspects around the Park, which has translated into a plentiful water supply for the formation of water ice, with the freeze-thaw temperature cycle serving as the catalyst.

All mountaineering eyes will continue to focus on the temperature and humidity data over the coming weeks to seek out the best climbing and skiing conditions, and the upcoming weekly forecasts will focus on this.

The presence of higher amplitude freeze-thaw cycles, controlled by local and large-scale humidity and temperature patterns, will be the key for the continued growth of water ice and the sintering and consolidation of the snowpack.

The Upcoming Week

Another bout of cool unsettled weather is currently producing a few inches of accumulating snow over the high terrain of the Park. As this system clears out on Thursday, temperatures will rise above freezing near treeline and the atmosphere will gradually dry out.

By Friday, another large wave of low pressure will develop and park itself over the western US and persist through the middle of next week.

Current forecasts indicate that RMNP will remain mostly in the warm sector airmass ahead of this wave through the period, with a brief cool down expected on Monday with the passage of a short wave moving through the long wave pattern.

Dry air will be transported over the region by deep and strong southwesterly flow. The drier airmass should allow for longwave radiational cooling of the higher elevation snowpack and water ice growth during the nighttime hours.

In addition, strong and dry southwesterly winds will cool the surface skin temperature of the snowpack owing to the sublimation process, which will aid the nocturnal sintering process and prevent rapid warming of the snow surface during the daytime hours.

However, the strong winds will also keep the lower atmosphere well mixed at night and will prevent deep freezes while in the warm sector airmass.

The end result of all of these competing factors should be an extended period of freeze-thaw cycles of shallow to moderate intensity.

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