We had several inches of snow a few weeks ago and a couple of light dustings on top of it since. The last real snowfall was a week ago, only 3-4 inches and has stayed on the ground since...so our "white Christmas" was already in place. Christmas eve and Christmas day produced some amaxing "hoar frost" that coated the trees and other surfaces, so it "looked" like it had snowed again, even though it had not.
HOAR FROST
Radiation frost (also called hoar frost or hoarfrost or pruina) refers to the white ice crystals, loosely deposited on the ground or exposed objects, that form on cold clear nights when heat losses into the open skies cause objects to become colder than the surrounding air. A related effect is flood frost which occurs when air cooled by ground-level radiation losses travels downhill to form pockets of very cold air in depressions, valleys, and hollows. Hoar frost can form in these areas even when the air temperature a few feet above ground is well above freezing. Nonetheless the frost itself will be at or below the freezing temperature of water.
Here's what it looks like....beautiful "ice art"....
Feather-like hoarfrost on a deck rail....
Yesterday, the wind picked up and this delicate frost began to blow off the trees and it fell so thick for so long it was like a snowfall...but the sun was out and the sky was clear. It put about an inch of "frost - snow" on the ground by this morning. Amazing!
~~~~~~~~~~~~~
As mentioned above, the ground was covered this morning, from left over snowfall topped by falling Hoar Frost. Yet, a phenomenon called a "Chinook Wind" began to blow... in a matter of a couple of hours much of the ground and all of the trees were bare....
These areas were under 5-6 inches of white this morning....
CHINOOK WIND
The Chinook wind in southern Alberta and Montana is a well-known regional climatic phenomenon which amazes weather watchers and residents. It is a warm wind blowing off of the Rocky Mountains in the western Canadian province of Alberta and the state of Montana. First Nations people called it Snow Eater.
In the middle of winter, the air temperature might rise by 20 Farenheit degrees or more in the space of a day. It can be bitterly cold in the morning and balmy by afternoon. The snow can melt away leaving the ground dry in the space of a few hours.
The Chinook wind often moves at a high speed. It is most noticeable in winter, when its warm temperature contrasts so dramatically with the ambient cold air.
The Chinook is one of those winds from off the mountains, famous in legends around the world, but known by many names: Mistral, Foehn, Santa Ana wind are some of them. Not all of these winds are warm. The Mistral, for example, is a cold wind. However, like the Chinook it flows down off of the mountains.
A strong Chinook can make snow one foot deep almost vanish in one day. The snow partly melts and partly evaporates in the dry wind. Chinook winds have been observed to raise winter temperature, often from below −20°C (−4°F) to as high as 10°C to 20°C (50°F to 68°F) for a few hours or days, then temperatures plummet to their base levels. The greatest recorded temperature change in 24 hours was caused by Chinook winds on January 15, 1972, in Loma, Montana; the temperature rose from -48°C (-56°F) to 9°C (49°F).
The Chinook Arch
The Chinook almost always is accompanied by a band of flat cloud up high in the sky. Locals call this the Chinook arch. It can be a terrible tease to farmers hoping for a little more moisture on the fields, because these clouds drop no rain and the Chinook wind itself sucks the moisture off the fields and out of the soil.
For photographers and others who love the beauty of nature, the Chinook arch can be a stunning sight, particularly at sunset when the clouds take on shades of yellow, orange and red.
~~~~~~~~~~~~~~
Now by contrast ....here's what it looks like back home in Georgia! Photos sent by family and friends...
Whoodathunkit???? ;)
If you all want to get away from the snow, c'mon up to Montana!!!! LOL!
No comments:
Post a Comment