With changes in temperature and weather patterns bring changes in recreational opportunities. Every late fall on the approaching winter solstice there is the potential for good natural ice for ice skating. The winter solstice with low sun angles and long nights often brings cold temperatures to high elevations. This can be augmented with favorable weather conditions. When snow does not prevail for snow sports, ice can be great if a persistent polar jet sets up with only early fall snows to chill down the water.
Skating Bridgeport Lake
Ice Safety
Testing the ice is curucial for safety. A drill is usful for verifying thickness. In good water ice, cracks can give an estimate of thickness from the thickness of the shearplane. Also, small bubbles can indicate depth. Over 3" of good water ice is adequate for supporting a skater; 5-6" provides good margins. A portable electric drill with a 1/2-3/4" diam. 6" long bit works well for determining thickness (keep battery from cold soaking prior to use).
The Kiwis have been making good use of ice on the South Island of New Zealand have an excellent site with good eneral information (I'm going to have to go skate there sometime; the east side is much like the Eastern Sierra). http://iceblock.org.nz/safety/Here are additional sites with useful information on ice formation and safety:
http://www.blueiceonline.com/howsite/lakeice_about.htmlhttp://lakeice.squarespace.com/thickness/
http://www2.gi.alaska.edu/alison/ALISON_SCIENCE_BConcepts.html
It is important to recognize ice variabiilty inherent with water bodies.based upon subsuface flow, artesians, springs, inlets/outlets. Surveying ice from aircraft can help identifying good ice areas.
The weather is of course crucial for not just forming thick enough ice but also the quality. Late November 2011 has provided a string of dry cold days due to a stationary high pressure and a low to the south with the polar jet providing the chilldown. The condition is somewhat characteristic of a Rex Block which is the reverse "S" pattern of the high pressure which prevents eastward migration of the high pressure from the the complimentary cyclonic and anti-cyclonic flow around the low and high. A key is a persistent high pressure over the west coast blocking storm systems with the anti-cyclonic cold northerly flow around the high providing the low temperatures needed. These persistent cold dry condition can be favorable for good ice formation. Monitoring the weather conditions can help identify periods favorable to ice formation.Weather is particularily important in the Sierras for determining good safe ice due to the relatively mild conditions that can prevail in fall. It is the trends and duration of cold that provide good sheeting. Although ice can thicken into January and February at higher elevations where freezing condiotns are more persistent, the best quality ice often occurs early season before much snow has fallen and ruined surface conditions. The short days of late fall provide the advantage of duration or cold nights and low sun angles to provide net freezing.
The following graph illustrates typical trends ice sheet formation thickness versus time for various temperatures:
December 2011-Exceptional Season of Ice Skating in the Sierras
The month of December resulted in no significant precipitation to cover the ice that had been formed. Conditions remained cold with polar air streaming around the stationary ridge that was blocking the storm systems. The high pressure was promoting subsidence inversions that was capping the cold air in the valleys. Some low lying areas were much colder than higher elevations. Temperatures dropped into the single digits and even subzero temperatures the week before the winter solstice. Without any snow, ice skating became prevalent in the Lake Tahoe area and all along the Eastern Sierras. With it this good, it even made the main stream news.
Bridgeport Reservoir
Virginia Lake
Tioga Lake
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