After another relatively tranquil week of weather in RMNP, a winter storm developed over the area on Tuesday evening.  By early Wednesday morning, this system ushered in colder air and much needed moisture.  As of this morning, snowfall observations indicated 3- 4 inches in Estes Valley, and about 5-6 inches at Bear Lake (with 0.3 – 0.4 inches of water equivalent).  Although we have not yet received any snowfall reports from the higher elevations in the Park, other high-elevation reports in Boulder, Grand, and Larimer counties were indicating water equivalencies around 0.6 inches.  With the light winds (< 10 mph) and cold temperatures (single digits F) that occurred with the precipitation at these higher elevations, up to 10 inches of snow likely fell. 

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Only light snowfall, with minimal accumulations, is expected for the remainder of the day on Wednesday.  In many areas in the Park, where exposed ground existed prior to this recent snowfall, expect significant settlement in the new snow, as a flux of heat occurs from the ground to the snow.  In higher and more north-facing locations, where the new snow accumulated on existing ice/snow, powder conditions will persist for several days, as temperatures are expected to remain cold for the rest of this week, and then slowly moderate starting this weekend.  At the time of this writing, very little wind loading has occurred with the new snow. 

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However, northwest winds are expected to develop today and tomorrow over the higher elevations, with sustained speeds of 15-20 mph and gusts to 25-30 mph.  Where these conditions exist, expect some blowing snow, lee-slope/cross-slope loading, and slab formation.

Climate-diagnostic analyses now indicate that the anomalous mid-latitude circulations patterns over the Pacific Ocean are in response to recent tropical-convection anomalies forced by La-Nina.  The current large-amplitude ridge pattern along the west coast of North America, which has allowed colder air and storminess to move into the central US, will continue through the end of this week.  This will allow another upper-level disturbance to move through Colorado on Friday.  Most of the forcing associated with this wave is currently forecast to remain south of RMNP, however some light snow showers over the higher terrain are possible. 

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The main effect of this system will be to reinforce the colder airmass that is already in place over our area.  By Saturday, the airmass will begin to moderate, with a gradual drying and warming trend continuing through Monday.  Winds are expected to be relatively light during this period.  The next upper-level disturbance is currently forecast to develop along the California coast on Tuesday.  During this time, south-southwesterly flow will develop over Colorado, which will be accompanied by an increase in cloudiness and the possibly mountain snow showers – however, most of this activity should be confined to the southern mountains of Colorado. 

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Beyond Tuesday, computer-model guidance is suggesting retrogression (westward movement) of the west-coast ridge, and the reestablishment of an active northwesterly storm track into the western states.  This type of shift in the large-scale pattern would be consistent with a westward shift in tropical convection over the western Pacific- a trend which is also currently suggested by other climate-diagnostic monitoring tools.  Such a pattern would allow cold air to infiltrate the western US states, and possibly phase with a northward-moving, moist airmass from the south-central states in the proximity of the Rocky Mountains.  It’s a long ways out, but this potentially snowy configuration bares watching.

Do-It-Yourself Weather Forecast Links

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.