General Weather/Earth Sciences Topics > Weather Conditions Discussion
Marked temperature variations over relatively short distances
DaleReid:
This morning while looking at my weather observations recorded by a couple stations and comparing to surrounding locations I noticed something weird, or what I thought was.
Some of the Univ of Utah MesoWest network stations are amateur, like mine. Some are official as can be found, such as Dept of Natural Resources stations or AWOS and other observations from government sponsored and maintained equipment (which in my mind should reflect pretty accurate readings).
None are, as far as I'm aware, a loose cannon wanting to have the lowest or highest readings for temperatures or rain or wind or snowfall.
Many of us here have high quality amateur stations like Davis, etc. Most of those auto report to CWOP and don't depend upon user entry of the values.
My stations are amateur, but four of them use (and agree within a part of a degree or so of one another) research/government/aviation quality sensors such as RM Young, Campbell Scientific, Vaisala and so on.
Here's what caught my attention this morning. I'm about 5 miles southwest of a moderate sized city and my temp was currently about zero. The seven or eight stations just north of me (including a full ILS commercial airport) were -11 to -14. A DNR Ranger station about 15 miles to my east was about -10. An airport and a few other stations 25 miles to the southeast was -8 or so.
Certainly during times of no wind and very cold temperatures and clear skies I've seen 'pockets' of noticably colder temps be reported. I had heard them described as cold air 'draining' down into valleys etc., although I'm not sure how that might work.
As the temps warmed up this morning my stations all came up together again following within a degree or so of each other. I got my long woolies on and checked a few Taylor mercury thermometers and they were in agreement with my automated stations, and comparing to the surrounding stations in the area and the airport, the readings were pretty well in agreement.
So what gives with 'pockets' of warmer or colder temps, enough to stand out when looking at the surrounding area readings (other than precip reports and all) are usually in good agreement?
I'm looking for some science if there is any.
Oh, one thing I do recall. Thirty years ago we had gotten a new Dodge Caravan which, for the time, was new to me to have a digital thermometer in the panel. We had driven down to my parent's place in central Wisconsin for Christmas eve and after we headed back and the kids were asleep, I amused myself by not old watching out for deer by watching the outdoor readings. It was brutally cold, -20s, and I noticed something that I'd not admit to earlier, which was that in the lower valley areas the temps were indeed several degrees colder and when we climbed onto ridges and traveled for a few miles the temps were higher. This was repeatable and a chance to see weather observations in action with my new toy of an outside temp gauge, which was moving.
Can colder air 'drain' into lower areas?
Dale
R.Sidetrack:
--- Quote from: DaleReid on January 24, 2025, 08:11:54 PM ---Can colder air 'drain' into lower areas?
--- End quote ---
Here is a 1975 Field Study with numbers:
Cold air drainage: a field experiment - UWM Digital Commons
DaleReid:
I had no idea such measurements were done and a nice paper published to distribute the findings.
I am not sure how you found the paper, but it was exactly what I was looking for.
Thank you. Dale
R.Sidetrack:
--- Quote from: DaleReid on January 24, 2025, 09:19:16 PM ---I am not sure how you found the paper, but it was exactly what I was looking for.
--- End quote ---
:D Actually, I used a 'quote' from your initial post as a Google search phrase. Here is what I gave Google: "Can colder air 'drain' into lower areas?"
Here is another interesting result from that same query: https://www.canr.msu.edu/news/analyzing_and_improving_your_farms_air_drainage
DaleReid:
The article on figuring out how to get air to flow seems odd at first, but makes good sense after reading it.
We have a lot of apple orchards here, and while on hilly areas, there are a couple which have set up big fans (think miniature are wind generators) about 50' tall and move air a bit which may be enough to prevent frost damage.
One think I just recalled. For a few years I was in a 4 story building on a steep bank next to the Chippewa River. In addition to watching for eagles, it was a nice place to have a perch to watch weather while sitting at my desk.
One very unusual thing I saw and wish that smartphone cameras or web cams were available back then, was looking up the river just before dusk one late late fall afternoon when the water wasn't frozen over yet. In very slow motion a completely obscuring fog bank slowly rolled down the river contained by relatively steep banks. This wasn't reflected along side the river on higher ground with any fog formation. It was if a slow progressive wave of say whipped cream came along the surface. It took perhaps 15 minutes to migrate slowly down a 1/2 mile or so.
The conditions must have been perfect, with little or no wind, near 100% humidity and cloudy conditions favoring fog formation, and something must have triggered it. Extremely fascinating and never saw such a thing again. I'm thinking that microclimate changes are more prevalent but just not easily visible.
I'm used to seeing smoke or dust be moved by wind. Air certainly can be moved by its change in density and weight on it's own part.
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