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Location: East of Seattle since 1992, 615' Elevation, Zone 8b - originally from SF Bay Area
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Depends on where in the east and in the west, as there are many geographic features that affect climate. t's currently 36F at my house in Sammamish, Washington, 47°39′00.00″ North but 41F in Portland Maine 45.5152° N.
Even closer latitude to Portland Maine, oddly enough is Portland Oregon, where it's currently the same temperature as Portland Maine at 41F.
The role of the cordillera feels very exaggerated to me. There is no mountain chain to protect Western Europe from continental air. It isn’t needed, the predominant westerlies already do that.
Western Europe is much smaller and surrounded by water.
The western Cordillera is much wider and bigger than anything in Europe and runs the length of the entire continent.
In western North America it has a huge impact on the climate along the immediate coastline. Places like Seattle, PDX and Vancouver BC would be significantly snowier at sea level if the coastal ranges did not exist. Without the Coastal Ranges, Cascades, Rockies etc. the low coastal areas would get far more arctic intrusions from the interior. This is evidenced by gaps in the passes. Even low lying areas in those gaps are significantly snowier near sea level.
The interior of the inter mountain west would also be much wetter if there were no ranges. This has huge implications for the weather of North America.
Western Europe is much smaller and surrounded by water.
The western Cordillera is much wider and bigger than anything in Europe and runs the length of the entire continent.
In western North America it has a huge impact on the climate along the immediate coastline. Places like Seattle, PDX and Vancouver BC would be significantly snowier at sea level if the coastal ranges did not exist. Without the Coastal Ranges, Cascades, Rockies etc. the low coastal areas would get far more arctic intrusions from the interior. This is evidenced by gaps in the passes. Even low lying areas in those gaps are significantly snowier near sea level.
The interior of the inter mountain west would also be much wetter if there were no ranges. This has huge implications for the weather of North America.
Yeah I just don’t believe this. The reason Seattle and Vancouver aren’t cold and snowy is because prevailing atmospheric flow is west to east, off the mild Pacific Ocean. When that reverses, and it occasionally does, the mountains do nothing to prevent cold continental air from reaching the coast. This is why “arctic blasts” are a thing in the PNW, even more so than in Europe where there are NO mountains to block continental air. The difference of course is that Eurasia’s most potent source of Arctic air is far away to the east in Siberia. Other than that, both climates are moderated 99% of the time by oceanic air.
Western Europe has more water surrounding it though, since Europe's a peninsula, so Arctic air is moderated for them when they don't have westerlies. I used to read a weather forum for the Pacific Northwest and the people there were always complaining about how strong Arctic air masses have to be to not get shunted eastward by the Rockies and Cascades.
All it takes is a very modest pressure differential - lower pressure off the coast, higher pressure inland - to funnel continental air out to the coast at a rapid rate. The mountains do nothing to block this, they just direct the strongest easterly winds through narrow valleys like the Fraser River gap and Columbia Gorge. The reason this doesn’t happen often is that in the mid latitudes the flow is almost always westerly.
Yeah I just don’t believe this. The reason Seattle and Vancouver aren’t cold and snowy is because prevailing atmospheric flow is west to east, off the mild Pacific Ocean. When that reverses, and it occasionally does, the mountains do nothing to prevent cold continental air from reaching the coast. This is why “arctic blasts” are a thing in the PNW, even more so than in Europe where there are NO mountains to block continental air. The difference of course is that Eurasia’s most potent source of Arctic air is far away to the east in Siberia. Other than that, both climates are moderated 99% of the time by oceanic air.
You don't have to believe it. But it is scientific fact. There is quite a bit of literature out there you can find.
Of course the prevailing winds are west to east and proximity to the pacific obviously will moderate temps year around (both winter and summer).. But mountainous terrain has a huge impact on the ability of cold air masses during winter moving over the North American continent. Coldest air will always spill east of the Continental Divide.
When a cold air mass sets up and spills over the Rockies it compresses and warms up. The same process happens again as it crosses the Cascade and Coastal Range which mutes the air mass by the time it reaches the Pacific Coast.
You can see this clearly most winters on terrain maps showing temps at the 925mb and 850mb level. The Coldest air will always be held back behind the mountain ranges acting as a giant dam.
It is an observable fact. You only need to look at the low lying gaps in the Cascade/Coast range to see how much snowier certain locations are that have access to outflow of cold air. See for instance the Columbia river gorge and upper Fraser valley. They benefit from cold outflow from the interior when Arctic High Pressure sets up.
Immediate areas near the gaps in the Mountains relatively close to sea level have significantly higher average snow totals.
Last edited by Thealpinist; 04-06-2023 at 03:10 PM..
Perhaps one should review things like Japanese Current, Gulf Stream, AMO, PDO and Hadley Cell Circulation before speculating about weather patterns....and, for extra credit, try working this into your explanations https://www.sciencealert.com/our-atm...something-else
proximity to the pacific obviously will moderate temps year around (both winter and summer).. But mountainous terrain has a huge impact on the ability of cold air masses during winter moving over the North American continent. Coldest air will always spill east of the Continental Divide.
This is the prevailing common wisdom but it is incorrect. Proximity to the Pacific is not the primary cause of the west coast’s mild weather. If proximity to warm water were sufficient, then the east coast of North America wouldn’t have continental winters. But it does, because the primary determinant is not proximity to water but rather the direction of atmospheric flow. Air masses in the midlatitudes move from west to east. This is why cold air spills eastward, not because it can’t get past mountains. It can easily get past mountains, as the Fraser River and Columbia Gorge gaps illustrate. But when arctic air sinks south, it inevitably is swept east by the prevailing westerlies.
When the flow reverses and becomes east to west, arctic air can quickly settle in over the Pacific Coast. But the flow only reverses for short periods a handful of times per season, and then the usual west to east flow resumes. Let’s imagine for a moment that the predominant westerlies of the midlatitudes were changed into predominant easterlies (this wouldn’t happen, but just imagine): the west coast of North America would have a continental climate, and the east coast would be much milder than it is now. Mountains wouldn’t change this substantially. The main effect of the mountains in that case, I guess, would be to make the hypothetical continental climate of the west coast much drier than the present continental climate of the east coast, and hotter/less humid in the summer.
This is the prevailing common wisdom but it is incorrect. Proximity to the Pacific is not the primary cause of the west coast’s mild weather. If proximity to warm water were sufficient, then the east coast of North America wouldn’t have continental winters. But it does, because the primary determinant is not proximity to water but rather the direction of atmospheric flow. Air masses in the midlatitudes move from west to east. This is why cold air spills eastward, not because it can’t get past mountains. It can easily get past mountains, as the Fraser River and Columbia Gorge gaps illustrate. But when arctic air sinks south, it inevitably is swept east by the prevailing westerlies.
When the flow reverses and becomes east to west, arctic air can quickly settle in over the Pacific Coast. But the flow only reverses for short periods a handful of times per season, and then the usual west to east flow resumes. Let’s imagine for a moment that the predominant westerlies of the midlatitudes were changed into predominant easterlies (this wouldn’t happen, but just imagine): the west coast of North America would have a continental climate, and the east coast would be much milder than it is now. Mountains wouldn’t change this substantially. The main effect of the mountains in that case, I guess, would be to make the hypothetical continental climate of the west coast much drier than the present continental climate of the east coast, and hotter/less humid in the summer.
No one is disagreeing with you regarding the direction of the atmospheric flow having the largest impact.
You are however massively underestimating the additional impact that large mountain ranges have on the ability of arctic air to penetrate west of the continental divide during the winter months. If there were no mountain ranges on the west coast you would see much larger and more sustained arctic outbreaks. Of course it would be somewhat muted based on where you are located on the continent.
Your comment regarding the gaps in the mountains doesn’t make sense. The atmosphere is a fluid. Cold air is dense and shallow. The gaps are the obvious low points for dense cold air to penetrate into lower elevations along the coast. If the Fraser gap and Columbia gorge didn’t exist. Fewer arctic outbreaks would reach the coastal Pacific Northwest.
Fraser outflow is the primary way Vancouver BC and the lower mainland coast gets the most cold arctic air in the winter. This is well known fact. Of course the climate will always be dominated by the direction of the atmospheric flow. But it is fairly obvious and well known that the large ranges have a profound impact.
Last edited by Thealpinist; 04-07-2023 at 09:21 AM..
Yeah I just don’t believe this. The reason Seattle and Vancouver aren’t cold and snowy is because prevailing atmospheric flow is west to east, off the mild Pacific Ocean. When that reverses, and it occasionally does, the mountains do nothing to prevent cold continental air from reaching the coast. This is why “arctic blasts” are a thing in the PNW, even more so than in Europe where there are NO mountains to block continental air. The difference of course is that Eurasia’s most potent source of Arctic air is far away to the east in Siberia. Other than that, both climates are moderated 99% of the time by oceanic air.
Those arctic blasts are still heavily moderated though because as Thealpinist commented, they get compressed by downslope heating as they cross first the Rockies, then the Cascades. That's why record lows are so much higher for cities in Western Oregon and Washington than the eastern halves of those states, and even moreso when compared to, say, Montana. On the East Coast record lows are still higher closer to the water, but not as dramatically as the West Coast because the Appalachians have so much less relief.
Your comment regarding the gaps in the mountains doesn’t make sense. The atmosphere is a fluid. Cold air is dense and shallow. The gaps are the obvious low points for dense cold air to penetrate into lower elevations along the coast. If the Fraser gap and Columbia gorge didn’t exist. Fewer arctic outbreaks would reach the coastal Pacific Northwest.
But the gaps do exist, not just the Fraser and Columbia but all up and down the coast. The Central Coast of BC is a series of fjords and gaps where cold air comes streaming out. All mountain chains have such gaps and so cold air has no trouble crossing the mountains. It may be a factor that reduces the amount of arctic air reaching the coast but I think it’s a minor factor. Whenever the flow reverses, the coast gets arctic air. I’ve never seen a case where offshore flow stops at the mountains. It’s just that offshore flow is not all that frequent.
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