A few weeks ago I was walking outside without a coat, but it has been -20F with the wind chill lately.
I looked at the 10 day weather forecast, starting next week temps will be back into the 20s and 30s again.
So why has the weather gone from maybe 20s/30s up until late december, then dropped about 30 degrees for 2 weeks, and then will go back up to the 20s/30s?
Is there an arctic vortex? Or did something else happen or is it just dumb luck? Any particular reason the temps would drop 30 some degrees for 2 weeks in late december and early January, then go back up again?
It’s weather, that’s what happened. The Jet Stream shifted south (as it sometimes does do to a variety of factors) allowing for cold arctic air to come south and cover the midwest and east.
Here’s a diagram of the polar front at the surface on the left … this is greatly exaggerated but we can see that it has a wave-like form … right now the eastern USA is in a trough … in a week or so it will move on and be in a ridge … every few years this arctic air mass pushes all the way down to the Gulf of Mexico coast, in other years it just barely crosses the US/Canadian border …
The Wikipedia article “Arctic Oscillation” appears to be incomplete, but it does have more information about this …
Johnny L.A., from your username and location I’m wondering whether you’re on the West Coast? The cold that Wesley Clark asks about is not just winter–it’s really cold right now in the Northeast, 15-20 degrees colder than average winter weather, and a few days ago it was more like 25-30 degrees colder. In fact, in Canada last week, this item about Ottawa being colder than the 3 average coldest world capitals was making the rounds:
There are record lows all over the Northeast and Midwest:
You take the good with the bad, we had a pretty mild fall here. The weather man likes to show that we are colder at noon than all of Alaska is at at 8:00 am this week. This is the kind of stuff weather pundits live for. Where’s global warming they cry!
It’s like a wave … when the eastern USA is super cold, us here on the West Coast are (typically) warm … the Rocky Mountains reach almost up to the halfway point in the atmosphere … all that cold polar air is just pour down the east side across all that flatland … here in the West we still have the oceanic air moving on-shore which moderates the temperatures by quite a bit … I’ve only seen two mornings at 32ºF this winter …
Hurricanes slamming the Gulf Coast brings us our best weather of the year …
My understanding is global warming will cause the polar cap to thaw and make Canada and USA colder for a decade or more. Is this correct?
I don’t believe this what’s happening now, btw. I think it is an Arctic blast, we get them occasionally.
There was a similar weather pattern just 3 years ago. Here’s a page on the weather then. Scroll down to the global map of Feb 2015 temperatures. Note that eastern North America was way colder than usual, while the rest of the world was warmer than usual, in many places, much warmer.
No … the “melting of ice” and “getting colder” are mutually incompatible … at best temperatures will remain the same during periods of ice loss … [see below] …
It looks like the period 1990 to 2010 saw very few of these Arctic blasts, the Arctic oscillation was positively indexed … now during the period 2010 to 2030 we may see the Arctic oscillation negatively indexed and see more Arctic blasts … much is still unknown about this phenomena …
The climatic sense of global warming does not change any of this, we take the average over the fifty year period to eliminate all the dynamic variations and oscillations … it was 10ºF overnight in Detroit, in 100 years, this exact same dynamic situation, the temperature will be 15ºF …
A fairly big chunk of the Canadian Arctic hasn’t seen direct sunlight in months … not even above the horizon …
It is the polar vortex. It is snowing now and there will be a warming for the next couple days, then back to the deep freeze. It is claimed (or conjectured anyway) that climate change is disrupting the usual weather patterns and this is one result.
Here in Montreal, we had an unusually cool and very wet summer (more like what we used to have 40-50 years ago) and an unusually long and mild fall. All unusual and perhaps indicative of a changed climate
The arctic ice is currently freezing, and yes it is cold in North America … wait six months, the ice will be melting and it will be warm in North America …
Average this out over the year and we see melting ice and warmer temperatures …
We don’t see heat energy drawn out of the air over North America and then applied to the polar ice to melt it … the polar front redirects that energy aloft and back towards the equator, which gets it above most of the CO[sub]2[/sub] so it can radiate out into space …
I read somewhere, quite possibly right here on the Dope, something to the effect (paraphrasing from memory) that the melting artic ice changes the…salinity?..or otherwise messes with the Gulf Stream currents, preventing them from bringing the warmer waters as far north as they have in years past.
This causes, temporarily at least, colder weather in the northern latitudes.
Usually the polar vortex circulates at the more northern latitudes (in the Northern Hemisphere). Sometimes it varies and dips southward, bringing large amounts of cold air southward, causing a cold snap. That’s normal variation.
There is some scientific opinion that global warming is weakening the vortex, making these periodic variations more intense. That may be why these episodes seem to be getting more intense and longer lasting. Naturally, global warming skeptics believe that this is not true.
This app (windy.com) helps to visualize the cold air masses streaming down from the Canadian Great Plains toward the US Midwest. I picked “5000 feet” winds, and colors showing temperature. Note the anti-cyclone (clockwise, high-pressure) over the Canadian Rockies, and the cyclone (counter-clockwise, low pressure) over the east shore of Hudson Bay. The winds stuck in between are pushing southward, including at the high-elevation “jet stream.”
To be a bit more precise, they reach a little over 14,000’. That’s above about 40% of the atmosphere measured by pressure, and (very roughly) 5% by height.
