Saturday, February 25, 2012
During our recent bout of warmish weather, the family decided that they'd had enough of the indoors. We took the whole gang out for a ski on a large, local lake. The windblown surface of the lake provided an ideal surface for a recreational ski- flat, hard, obstruction less...perfect.
Given that so many of our family live in locales where the local bodies of water don't freeze solid for months on end, we get many questions about the safety of the ice thickness.
Given that the average temperature has been below 0F for months at this point the ice is pretty thick. A quick check with a local ice fisherman showed it was only about 5 feet thick.
How strong is 5' of lake ice? In tests a few years back- enough to land a loaded 747 on. The skiing family should present no issues...
What about those cracks? The savvy winter traveller would look at this photo and be well comfortable with these deep fractures. As the ice thickens and temperature variations cause expansion and contraction these long cracks form in the ice. Bottom line- only substantially thick ice, formed over months will have enough rigidity to form these cracks.
Early season ice would be clear as a lens...and about as fragile. The seasoned winter traveller would avoid it at all cost.
Saturday, February 4, 2012
Sorry for the dearth of posting lately- winter is in full force here and I've been quite busy with work projects, taking a couple of classes and teaching a couple of classes as well. Winter has been a little easier without hours of idle time to contemplate on things but my blogging has suffered.
About a week ago, a relentless high pressure system moved into the Interior region and the millibar chart went off the charts. One thing happens here during such high pressures- the atmosphere thins and all the latent heat radiates directly into outer space. On those cold nights, a well dressed North dweller can go outside and stare heavenward and seemingly look all the way into Creation. Most folks who live in the Lower 48- places with pollution, light wash, and mere thick atmosphere have no idea what kind of view can be had over their heads when the contents of the atmosphere peel back.
The downside of this startling and miraculous view is cold....bone chilling, dangerous, life threatening cold. During this particular episode, the official temperature for my small town hit -50F and many folks in the low lying river bottoms hit -60F. At those temperatures, exposed flesh freezes in seconds and machinery often just fails for little apparent reason. Travel is not recommended and survival gear is a must when one does. The other upside is such cold primes the body's mechanisms and after a stint at -40F or below; temperatures of 0F feel downright balmy.
The extreme high pressure system also did something else- as it moved off to the east and our Canadian friends it left a vacuum that the next low pressure system rushed to fill. Those low pressure systems carry lots of moisture from the Gulf of Alaska and warmer air masses from the Pacific. In coastal Alaska, those systems dump mountains of snow when they contact the coastal mountains with the cold Arctic air masses spilling over; but when they build enough force to cross into the Interior regions they create what is known as a Chinook.
The Chinooks here pack unbelievably warm temperatures and gale force winds and its not unusual for these winds to hit, raise temperatures dramatically and then vanish as quickly as they came. The chart below shows just how quickly it happens- on January 28 and 29 the temperature was -50F (often -60F in low spots) and by the evening of February 2nd the winds were in excess of 60mph and the weather had warmed to 40F! 100 degrees Fahrenheit delta in 100 hours. In the early morning hours of the 3rd the winds vanish and the temperatures plummet to below 0 again. Returning the North to its frozen state.
The brief respite was welcome from such a cold January and it was nice to go outside in a light shirt and not feel immediate pain and worry about losing appendages. Just a couple more months until winter's grip is broken we return to warmer weather and more adventures.
Chart sourced from Weather Underground