Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
What accounts for this. Is it a shift from frontal precipitation being the dominant type in fall/winter/spring to more and more summer convection further east and inland? In the Southwest, I'm guessing the monsoon also comes into play?
The Rockies block most moisture from the Gulf of Mexico (mainly a summer source) from reaching west, while it drains the last remaining Pacific Ocean moisture (mainly a winter source) which has already lost moisture several times from passing through a number of mountain ranges to the west.
Boise is also relatively mild winter-wise compared to east of the Rockies.
this map shows the extent of the winter precipitation max, with the Rockies roughly the boundary of 50% in Oct-Mar. California and western Oregon stand out in having an almost winter only precipitation season.
Doesn't an area of high pressure position itself in the SW United States during the summer?
Bingo! The air to the east is more humid and unstable in the summer, and thus gets a lot more convective precipitation in the warm months. These thunder storms spin in a counter-clockwise direction, which means the rain can be coming from any direction.
In the cold months the precipitation comes from storms moving in off the Pacific Ocean (the west). As a result, rain shadows develop with each successive mountain range blocking what remains of the moisture from the previous range.
BTW, where I live just north of the eastern side of Washington State, we get even amounts of precipitation in the cold and warm months. Places to the west (like Vancouver on the wet side of the mountains) get most of their precipitation in the cold months, and locations to the east (like Calgary) get most of their precipitation in the warm months.
Location: Live:Downtown Phoenix, AZ/Work:Greater Los Angeles, CA
27,606 posts, read 14,590,333 times
Reputation: 9169
In the distance between Phoenix and Riverside, CA; summer gets noticeably drier by Blythe, CA; even drier by Indio/Palm Springs, then on the west side of San Gorgonio Pass/Banning Pass, generally rainless summers
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.
Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
