Wednesday, April 29th, 2009

The Week in Review

Classic Rocky Mountain spring-time weather continued across the high country of RMNP, with periods of snow and warmth intertwined.

A strong Madden-Julian oscillation over the equatorial tropics has been a major contributor to the recently active weather patterns across the western US.

The water-equivalence in the snowpack above 9500 ft over eastern parts of the Park is now at 100 - 125% of the average annual peak, thanks to the big dumper two weeks ago. 

The combined monster storm and another smaller storm this past week added over 5 new inches of liquid equivalence (several feet of dense, high water-content snow) to the late season snowpack.

Between storms, an extended period of warm spring weather occurred, with several days of above-freezing temperatures below, near, and just above treeline. 

With free water developing in the new snow and limited or non-existent surface freezing, the instability characteristics in the new snow quickly transitioned from dry to wet, on aspects exposed to the sun.

(Click  chart  to enlarge)


We still haven’t shaken off the winter-style winds, as gusts once again topped 50 mph on several occasions this past week.  

However, with the mean north-south pressure gradient continuing to decrease with the change of seasons, calmer periods have been occurring more frequently amidst these gusty times.   Colder and higher elevation slopes are likely still developing dry wind slab instabilities during these gusty periods.

Eli Notes:  Remember that slab avalanche danger can be just as high this time of year as winter, so don't be fooled by conditions on warmer aspects, lower elevations, or by the warm weather in the Front Range.  I have had more slab avalanche troubles in April and May in RMNP then in the mid-winter snowpack months.  The lower danger corn season is not entirely here yet, so beware!

The Upcoming Week

An unsettled weather pattern over the western US will continue to produce a variety of spring-time weather over the region, including more new snow.

Keep in mind though, that the rapidly transitioning spring-time atmosphere poses great challenges for weather forecast models. 

The one-week numerical forecast skill has dropped off significantly since mid March.  At this time, any forecasts beyond three days into the future should be viewed with increased uncertainty.

With that caveat in mind, the models are converging on a solution that brings another weather system into the area on late Friday into Saturday.  With elevated spring-time levels of absolute moisture and frontal forcing, a modest precipitation event is shaping up for Saturday (several tenths of liquid equivalent).

The NWS numerical forecast for the mountains of RMNP over the upcoming weekend is as follows:

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