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6/12/08 Weather Forecast for RMNP |
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 June 12, 2008
2008 Spring Recap
It’s been a cool spring season in the mountains of RMNP, as abnormally strong winter-like storms have continued to develop over the western US. The continued presence of La-Nina and the recent occurrence the Madden-Julian Oscillation (MJO) have greatly contributed to this stormy weather-climate pattern.
The recent shift of MJO activity from the Western Hemisphere / Africa region to the Indian Ocean region forced an eastward shift in circulation anomalies over the eastern Pacific Ocean and western US. In the plot below, this shift is represented by the upper-left to lower-right tilt of highs and lows during the month of June, which has recently placed Colorado just east of the lows (i.e., the sweet spot for storminess).
Experts in this field of study are suggesting that additional MJO activity may force another anomalously strong storm system over the western US within the next couple of weeks. Working against this scenario is the strong summer heating of the intermountain west, which is ever increasing day by day. Since weather forecast models do a poor job predicting the longer-range effects (1-2 weeks) of this type of tropical variability, daily monitoring of observations and short-term forecast trends often serve as better predicting tools.
The Week in Review
Three storms affected the northern mountains of Colorado over the past week. Each storm brought a period of sub-freezing temperatures, new snow, and wind to the alpine regions.
In the plot above, each storm (see vertical lines labeled with ‘L’) is associated with a minimum in pressure. With these winter-like systems, the coldest air exists west of the pressure minimums near the surface (to the right of each ‘L’, or later in time after the pressure min passes). After each low passes, fast and strong pressure increases, (associated with colder, subsiding air) create strong east-west pressure gradients.
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These pressure behaviors, in the presence of mountains, force rapidly developing winds (see rising spikes in the wind gusts following the L’s in the lower panel). The vertical thermodynamic stability of colder airmasses (which are highly resistant to being lifted over the mountains) combined with a pressure gradient that forces cross-barrier wind flow (from the west-northwest) further accelerates the wind.
In the tangible world, these post-low meteorological periods can produce challenging conditions for alpine climbers, with the formation of reactive wind slab (when new snow falls) and erratic knockdown wind gusts. The post frontal environment following the June 5th storm created such conditions, with 6-12 inches of new snow and wind gusts to 70 mph.
As these colder storm airmasses are quickly moderated to above freezing temperatures by the strong heating of the late spring sun, other processes like surface radiational cooling become important for refreezing the surface snow and producing favorable climbing conditions (see last weeks weather discussion). More examples of this during the past week are shown below.
The Upcoming Week
Since a large degree of climbing activity has been occurring in the higher alpine environments, the forecast for the upcoming week will focus on the higher terrain. Shown below is a detailed forecast for the 13,000 foot level near Longs Peak through Sat. morning.
There are three weather features worth noting for climbing trip planning purposes. First, on Fri. and Sat. there is no risk of thunderstorms or precipitation in the area. Second, the winds are forecast to remain at moderate levels, with westerly gusts up to 40 mph. And, third, temperature will moderate to above freezing levels. With this, the near surface snow will become less bonded.
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However, with the atmosphere drying out significantly (see low relative humidity and sky cover), radiation losses during the nighttime hours will allow the snow surface to firm up for morning ascents. In addition, the persistent winds will effectively act to keep the snow surface cool and slow to warm.
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The forecast the rest of Sat., Sun., and the first part of Mon. is as follows:
Here, the warmest day will occur on Sat., with a cooling trend on Sun. and Mon. The winds will pick up on Sun., as a weather disturbance passes over MT and WY. With the favorable northwesterly wind direction and weak post-frontal conditions, wind gusts could be higher than forecast, if a mountain wave develops. Atmospheric moisture will remain low for good nocturnal radiational cooling of the snow surface, and there is no threat of thunderstorms or precipitation.
For the rest of the week, a ridge of high pressure is forecast to build over Colorado. With this, the atmosphere will warm, and dry air will be reinforced over the western mountains. However, there are preliminary indications that moisture may be on the increase east of the Divide, which may be enough to fuel a few isolated afternoon thunderstorms over the eastern terrain. Since forecasting convection details that far out is nothing short of gambling, keep an eye on the sky and the short term forecast during these later days.
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Detailed 7-Day Forecast
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
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.
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