Well folks, after the spring like weather that we've been enjoying here in the Mile High City for the past few weeks, winter has returned in dramatic fashion.
The weather forecasters told us that Saturday would be the last warm day, so CatMan and I decided to go for a bike ride.
The thermometer at my house read a balmy 72 degrees (22C) when I left my house at around a quarter to 2 in the afternoon. The storm was supposed to arrive later that afternoon, so I was in a bit of a quandary as to which clothes to wear.
I thought about wearing my knickers... that would be these knickers...
... as opposed to these knickers...
But ultimately I decided to err on the side of more clothes rather than less, and I went for my full length insulated tights, with an insulated turtleneck and my warm bike jacket.
I was a little bit too warm at first, and felt a bit overdressed, as the paths were full of people dressed like this:
But about 15 miles out, the winds shifted, and the warm westerly wind suddenly became a bitterly cold northerly one. Holy Moly! It was like the temperature dropped by 20 degrees over the course of about 10 minutes!
So. This might be a good time to put on my weather geek wannabe hat and explain about the winds here in Denver. Denver sits on a high plain, just to the east of the Rocky Mountains. This geography creates a unique weather pattern for us known as the Chinook wind.
It basically works the same way as a heat pump or air conditioner does. When air is compressed, it warms up, and when it decompresses, it cools down. Have you ever felt the air coming out of a tire or an aerosol can? It's cold because it is decompressing... well, the opposite happens when the air pushes down off of the mountains. So upslope winds are cold and wet, and downslope winds are warm and dry - and this is one of the reasons that Denver has such a wonderful climate in the winter time.
Quite often - like the past few weeks - we'll have storms dropping snow by the feet in the mountains, but the temperatures here in town are almost spring-like. But... when conditions are right, the storm will push over the mountains and we'll get dramatic temperature shifts like we did on Saturday, when the westerly winds get cut off, and replaced by a wind blowing in from the north.
Anyhow, by the time I got home on Saturday just a few minutes after 5pm, my thermometer read 39 degrees (4C). Brrrr! My fingers (even with two pairs of gloves on) were so cold that I almost couldn't get my helmet off! I was pretty darned glad I'd opted for the warmer clothes because I would have been an ice cube if I'd been wearing fewer layers!
We had light snow off and on all day Sunday and Monday, but the big snow maker arrived last night.
Ready for more weather geekitude?
So, there are several ingredients required for us to get a really big storm here in Denver. If you look at the Chinook graphic above, you see that when the wind blows up against the mountains (which is called an upslope) it cools, and it leads to precipitation. So winds coming from the east are one ingredient, and the way we get those is when a low pressure system with it's counter-clockwise flow sets up to the south and east of us.
The second ingredient is moist air - generally this is moist air coming up from the gulf of Mexico. And finally, the position of the jet stream has to be right, with us sitting in a big trough, allowing cold air to come down from the north.
This graphic illustrates the phenomenon pretty well:
Here's another one from a different storm, but the same idea.
Anyhow, that's what happened last night, and I woke up to nearly a foot of fresh snow this morning!
Oh well... it was a nice little respite from winter, and I got in three good rides before the snow came back. I did get some good exercise shoveling though!
Well, at any rate. Happy Groundhog Day! At least Punxutawney Phil didn't see his shadow, and that's supposed to mean an early spring. Not holding my breath on that one, since I think his track record is around 40%, but hopefully, he's better at predicting the outcome of football games!
So tell me, how's the weather in your neck of the woods? Does the geography in your area create any unique weather patterns? Geeky minds want to know!