Hoarfrost creates sparkling scenery
The cold temperatures of recent mornings, in combination with saturated air, have made for some beautiful scenes across the area. Trees, street signs, bird feeders, etc. have been covered in a sparkling coat of hoarfrost.
You might not hear the term hoarfrost often, as the word “frost” means the same thing. It does differ, however, from the icy glaze objects may acquire from freezing rain or drizzle. It also differs from rime, which can occur with freezing fog.
Hoarfrost forms when water vapor in the air changes directly into a solid (skipping the liquid phase). This process is called deposition. Like dew, the ice crystals do not fall from the sky. Overnight, as temperatures cool and the air becomes saturated (relative humidity reaches 100 percent), the water vapor forms into ice crystals on nearby objects, giving trees their glistening, flocked appearance. The structure of the ice crystals can vary, like snowflakes, depending on the temperature at which they formed.
Speaking of chilly temperatures, it looks like January readings will go down in the record books as slightly below average. February sees average temperatures continue to climb, starting with highs in the upper 30s and rising into the mid-40s by the end of the month. An arctic blast is not out of the question, though, as record subzero temperatures occurred on this date back in 1950, when the mercury plunged to minus 21 degrees.
Overnight lows at the end of the month will still average below freezing at 29 degrees. Snowfall was on the positive side for January, with Coeur d’Alene receiving just over 28 inches in a month that averages about 21.2 inches. In February, average snowfall gets cut in half to around 11.5 inches, with total precipitation averaging 2.14 inches. You might remember February 2005, however, which was exceptionally warm and dry. It ended up being a “record” dry month with only .2 inches of snowfall and .17 inches of total precipitation.
Snowpack in the mountains is looking good, with most SNOTEL locations across North Idaho reporting snow water equivalents between 80 to 110 percent of normal. SNOTEL stands for Snopack Telemetry and it is a really neat system of sensors located in various mountain locations across the Western U.S.
The sensors take precipitation and temperature readings and can operate unattended for a whole year, which is necessary in rugged areas where taking frequent manual measurements is not possible. The data is transmitted by radio signal. The radio signal is actually sent skyward, where meteor “dust” reflects the signal back to Earth to two master stations located in Boise and Ogden, Utah. Those two stations then send their data to SNOTEL’s centralized forecasting system in Portland.
Why do we care about these data? This snow and temperature information augments the manual observations taken across the area. These data can then be used by a variety of government agencies responsible for monitoring things like stream flow, avalanche danger, flood potential, snowpack and other water management issues. Obtaining information about Idaho’s snowpack, or what’s been referred to as “frozen liquid gold,” is also useful for those involved in agriculture, hydropower generation, and even those who are planning recreational use of the “snow melt” in the spring for white-water rafting.
Outlook for February
The latest official monthly outlook issued by the Climate Prediction Center for February indicates above-normal temperatures are expected for the month. Precipitation trends were a tossup, however, with equal chances of above- or below-normal rain/snow totals.