January 31, 2021

The Extreme Protection of the Rocky Mountains

The Rocky Mountains,  a few hundred miles to our east, offer profound protection for our region from the bitter winter cold of the interior of North America.

During the next week, this protective shield will be put to a severe test and will not be found wanting.  Let me show you.

The terrain map below show the double terrain protection our region enjoys.  To the east are the Rockies, with plenty of terrain rising to 8000 to 10,000 ft.  To the east of the Rockies are the Great Plains of the interior of our continent, which provides a flat, low-elevation conduit from the frigid, snow covered Arctic directly into the middle of the continent.


The Arctic is a particularly good place to generate cold air.   Covered with snow, which is a very effective emitter of infrared radiation to space.  Little solar radiation in winter.  Generally light winds and high pressure dominating.  

 Think of the Canadian Arctic and the nearby ice-covered ocean as the refrigerator for North America.

But to drive the air southward effectively you also need the right large scale wind flow, one that produces strong northerly (from the north) flow over the interior of the continent.

And we will have that in spades!

Take a look at the forecast upper-level (500-hPa pressure level, about 18,000 ft)  weather map for 4 PM PDT on Friday.  

Wow.  HUGE ridge (high pressure) over the West Coast, with a deep trough to the east of the Rockies.  The result of this highly disturbed upper level flow pattern is strong northerly flow pushing southward over the Great Plains


Now, let me show you a sequence of surface air temperature forecasts this week, which will allow you to view the invasion of cold into the hinterlands of North America.

Start with today at 1 PM.      The coldest air is found in the northern Canadian Arctic.


By Wednesday afternoon at 4 PM, the cold air is moving southward, with a notable extension into Alberta.  Note how the Rockies keep the cold air to the east!
By 4 AM Sunday, frigid air has plummeted through the Canadian plains into the northern plains of the U.S., with the Rockies providing protection for the western U.S.   Huge north-south extend of the cold air, with the source region in northern Canada. 

And by 4 AM Wednesday of next week the cold air moves eastward, into the upper mid-West and the northeast U.S. But we in the Northwest remain untouched!

Finally, to impress you with the temperature contrasts, here are the forecast temperatures for 10 PM Saturday.   36F in Seattle...which is cold for us, but -25 to -30 over Albert and as low as -11 in Montana. A four hours drive from Spokane (28F) to Great Falls, Montana (-10F) would be quite a shocker.


So if you don't get the cold air you grave during winter, you know one source of this warm affliction...the Rocky Mountains.





17 comments:

  1. Hi Cliff, just in case you're interested in a bit of Canadian geographical pedantry, the area above your US plains we would call the prairie (or prairies). Canadian plains is never a term one would say or hear and without context we wouldn't understand what you meant. Mark

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  2. So interesting!...I am guessing, that, on a smaller scale, our Cascade Range protects us, in both winter and summer, from the more extreme temps found in Eastern Washington...of course, being closer to the Ocean also has it's effect on Western Washington..all in all, our supposed "Mediterranean" climate has some merit.

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    1. Not just some merit - it's everything really. At our latitude, the Prevailing Westerlies is the primary circulation pattern that moves weather in from the west off of the Pacific. This movement of marine air and associated weather over us goes on all year long, and is responsible for our climate. Cold continental air moving over us from the east does happen occasionally, but is really just a weather "outlier", soon gone thanks to the Westerlies.

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  3. I often dream of what our winter climate would be like without the Canadian rockies and Northern cascades to block Arctic intrusions. Can you imagine the snowstorm potential being so close to the Pacific??? 😁

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  4. It's a 6 hour drive in good weather from Spokane to Great Falls

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  5. For those who were looking forward to snow in the lowlands, I'm thoroughly unimpressed by the "saving grace" of the Rockies, shielding us from that nasty old cold and snow.

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  6. So are we gonna get shut out on snow and cold this year....if they say it will be colder this month...that's kinda a relative thing...cold could mean in their eyes...42 for highs and 33 for lows...both would be colder but not snow cold...anywho I'm no longer on the snow anymore...bring on spring and put this lame winter for the lowlands behind us...

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    1. Yeah, probably one of the most boring winters.. It never got below like 28 degrees

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  7. It is predictable during this month for the hardware stores to start selling spring flowers. Unknowingly people buy and plant them only to have them crushed by 7-10 days of freezing temperatures later in the month. Sad but too funny.

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  8. Looks like the cold pattern that Weather.com was hinting at has moderated a bit in the past few days. It seems like "pre-spring" has already begun and I'd hate for a shot of Arctic air in February to sidetrack progress. At this point in February, I'm done with winter regardless of what it's been like.

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  9. The extended forecasting has been absolutely awful this winter. It goes from calling for 20's and snow 7-10 days out and then 12 hours later says upper 50's and rain. I've never seen the forecast jump around so much. Even the 3-4 day forecast is constantly changing with every run by a ton.

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  10. We haven't had the primo cold in over a decade. We haven't had a great windstorm since the Hannukah storm. We missed out on the recent storm that dumped massive snow and rain on California. Cliff, what the hell is going on? If this is due to global warming does this mean we'll never get extreme weather again? I'm longing for the colossal blizzard that jackknifes metro buses and paralyzes the city.

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    1. Was it the 2009-2010 winter that did in Mayor Nickels? Around that time I put chains on my vehicle for the first time since we moved to Seattle in 1975. I had fun driving co-workers home when Metro threw in the towel.

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    2. I agree!...the term "jackknifed semi" has a NW winter ring to it!...I miss it!lol

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  11. This is quite typical in the winter, isn't it? Virtually every year a cold snap hits the midwest where temperatures drop below 0F. I'm from Indiana. Winter time temps would bottom out typically in the range 0 to -15F. Once it was about -30F. Same pattern next week I presume. While rare, what if the winds were north east rather than north west? What conditions would drop western Washington temps into the 10s and 20s?

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  12. I think you give the mountains way too much credit in keeping us warm, its mainly the ocean. If there was land to our northwest we would be way colder. England is at a very similar location to Seattle, they have no mountains to their east, and they have nearly the same climate. Its not like its very common for flow to come from the east.

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