Interesting thing about Volcano shadows...

[epiceast]

 

 

Volcano Rain Shadows:   Another interesting revelation can now be found in this set of data, following its recent expansion to include many more data sites. That is, surprisingly, the rain shadows of the major isolated Cascade stratovolcanoes don't all extend in the same direction. The common belief is that Pacific Northwest rain shadows extend to the east and northeast of the blocking mountains, since the primary moist flows come from the west and southwest. For example, well-known precip data from lowland sites shows a strong rain shadow extending NE from the Olympic Mountains centered on the town of Sequim, and the high crest of the Cascade Range as a whole throughout WA and OR casts a strong rain shadow onto locations east of the crest in central WA and central OR (see the precip map below). But the volcanoes have some interesting quirks. 

    Only a few of the volcanoes actually have snowdepth and precip measurement sites on enough sides to determine the rain shadow direction, including Mount Baker, Rainier, Saint Helens, and Hood. On all of them, in general, the favored south and southwest slopes receive the most abundant precipitation and snowfall. On Baker, the rain shadow clearly extends to the north and maybe even the northwest (very strange), while the northeast and east sides receive huge snowfalls. See this data culled from the main spreadsheet, which shows snowdepths at six sites on Mount Baker along with a map of their locations around the volcano. On Rainier, the rain shadow extends strongly northeast, especially towards Crystal Mountain, while locations to the east near Chinook Pass have tremendous enhanced snowfall. There are no useful data sites to the north of Rainier, so it's unclear whether that direction is rain shadowed or not. On Saint Helens, the pattern appears to be similar to Baker, with a strong rain shadow to the north but very high snowfall to the northeast and east. On Mount Hood, the rain shadow extends to the northeast towards Cloud Cap and east towards High Prairie, while locations to the north like Red Hill have big snowfalls and similar precip to the south side and thus no rain shadowing. 

    Farther south, there are fewer truly isolated stratovolcanoes and also fewer useful data sites located on or near them. Mount Jefferson's rain shadow appears to extend eastwards, but information about the north and northeast is minimal. The Three Sisters have a strong eastward rain shadow towards Three Creek Lake, but the presence of three volcanoes clustered in a north-south line with the neighboring Broken Top just to the southeast complicates any analysis of the situation. Diamond Peak appears to have a strong rain shadow which extends east, and perhaps also somewhat northeast. On Mount McLoughlin, its rain shadow doesn't appear to extend east or northeast, but there are no data sites to check the north side. Also, the entire volcano in this case is somewhat rain shadowed by the Siskiyou Mountains to the southwest. As mentioned earlier, Mount Shasta also suffers somewhat from being in the rain shadow of the Klamath Mountains. Shasta has only a very few data sites in useful directions, but one of them shows that the east side towards Brewer Creek does not appear to be strongly rain shadowed. However, an amazing thing about Shasta is that during the spring, one can easily observe the effects of its rain shadow on the mountain itself and the numerous medium-sized volcanoes to its north and east while climbing high on the mountain. Ash Creek Butte to the east retains a deep snowpack, while the slightly taller Whaleback to the northeast is usually barren of snow, as are the shorter volcanoes extending north in a line. Shasta's rain shadow extends to the northeast and north. 

    Anyway, this all seems quite revealing and very interesting to me, and it's certainly useful for planning spring ski trips. Just because the south side of a volcano shows 100" of snow remaining at a measurement site, once can't expect to find a comparable snowpack on routes on the rain shadowed side. However, I don't have a good explanation as to why the volcanoes differ so much in their rain shadow directions. Similar isolated stratovolcanoes in seemingly comparable locations clearly have very different precipitation distribution patterns. The effects of regional topography on the direction of incoming moist storm flows must contribute significantly to the rain shadow direction. For example, this is certainly the key factor affecting Mount Shasta's snowfall as mentioned above, and also its rain shadow. 

http://www.skimountaineer.com/CascadeSki/CascadeSnow.html

 

They don't all face the same way, i've suspected this for a long time. Can the Mets provide some explanations?

[Jesse]

Interesting read. Although I think the higher snowfall totals in areas east of Mt. Baker, Mt. St. Helens and Mt. Rainier (Chinook Pass) may be due to cold air holding on longer on the east side of these peaks. The SW slopes may get more precip, but perhaps a greater percentage of it falls as snow east or northeast of the volcanoes mentioned. Topography is favorable for colder air to get trapped east of all three peaks mentioned.