Much of the region dropped below freezing this morning, with the main exceptions being locations close to large bodies of water.
Even my neighborhood in Seattle, not far from the water, awoke to glazed cars and icy roofs (see below).
So how cold did it get? The map below shows the low temperatures this morning. Below freezing over much of western Washington, while eastern Washington was in the teens or low 20s, with a few single-digit temperatures over northeast Washington.
If you like cold, the Methow Valley did not disappoint, with most stations in the teens.
Keep in mind that the above temperatures are NOT at ground level, but at 2 meters (about 6 feet) above the surface, which is the standard height for surface air temperature.
On cold, nearly clear nights, like last night, the ground temperatures are considerably cooler than at 6 feet.
I checked that out this morning with a research-quality thermometer over a grassy area.
Frost was evident, and the ground temperature was 29.4°F.
At 6 feet, the temperature was 33°F. An inversion (temperature increasing with height) was evident.
Tomorrow morning should be icy as well....so be careful...
What is the cause of the temperature inversion? Since it's the beginning of the cold season I'd expect the historic warmth of the soil to cause the temperature to be warmer as you get closer to the ground.
ReplyDeleteI'm not an expert, but the idea isn't that complicated and also is fascinating:
DeleteOn clear calm nights, radiative cooling happens leaving surfaces colder than the surrounding air, emission of thermal black body radiation cools surfaces (cars, streets, etc). If there's not a lot of moisture in the air, then the radiation doesn't reflect back to earth and you get a net cooling at these solid surfaces.
As these objects cool, if the air is calm, then near by air parcels also cool, causing an inversion, where the ground is cooled, and the air nearest to the ground is cooled, relative to the air above (10 feet even)
Not sure what the temperature gradient is in the soil, but I think, the surface can cool appreciably this time of year..
Read his previous blog post. Explains it well
DeleteHad some frost on my car I think last Tuesday in Tacoma (car is parked on the street in front of my house). It was not a solid ice, but did have to scrape the windshield though.
ReplyDeleteOver the weekend, saw frost on the grass so now the real frost looms.
Seems it's a tad late to the game but some years we get several instances of frost, beginning around the middle of Nov. and by mid Dec, several instances of hard frosts have been experienced. Still too early to know for certain.
Currently, my car is in the shop for repairs, should get it back today (Monday). At 9:15AM, it's still only 38F out there.
Did you get your car back from the shop? Is your car running alright?
DeleteJust curious, are we tracking date of first frost for a given location? If so, are we seeing any change over the years? That is, is the first frost date coming later over the years?
ReplyDeleteOn Sunday afternoon, there were still a couple of areas of visible frost alongside the Centennial trail. Yet, as I was riding south, the sun was at just the right angle to cause certain surfaces to reflect a blinding light. All I could think about was "one bad month down, three more to go!"
ReplyDeleteA really cold morning indeed
ReplyDeleteThe hard freeze only lasted long enough for me to rake up another heaping of fallen leaves, before rain turned the yard back into quagmire worthy of ww1 trench foot remake.
ReplyDelete