Weather West: Coast Spared Again from Heatwave

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The following is an excerpt from a recent article on the Weather West Blog. 


By Daniel Swain of Weather West

June 2021 hottest on record for interior CA (but not coast)

June 2021 was the hottest on record across a large portion of the interior West–including eastern California.

June 2021 was a month to remember in California…if you happen to live outside the densely populated coastal cities from the Bay Area south to Los Angeles. In marine-influenced zones, June was a relatively unremarkable month–with a robust marine layer bringing periods of cool temperatures and coastal drizzle. But in dramatic contrast with these near-average coastal temperatures, inland portions of California (including the Sierra Nevada & foothills as well as the SE deserts) suffered through what turned out to be the singularly hottest June in over 100 years of record keeping. In fact, a very large fraction of the interior West experienced its hottest June on record–mainly the result of all-time record breaking heat during the first part of the month in the Southwest, then the all time record-shattering heat in the Pacific NW later in the month. Throughout 80-90% of the land area of the American West, June 2021 will be remembered for quite some time for its extreme heat, unless you (like most people in California) live near the coast. This is a pattern we’ve seen occur somewhat frequently in recent years, with searing heat inland yet quite mild conditions where the marine influence hangs on, and which also makes for a rather strange reality where CA may have experienced its hottest June on record overall (see NOAA’s official numbers out tomorrow) despite most *people* in California experiencing a relatively comfortable month. This pattern may protect the immediate coast yet again during the upcoming heatwave, though this protective influence may be slight weaker than earlier in the summer due to warming coastal SSTs (and often disappears by early autumn, in any case, when coastal CA tends to see its hottest annual maximum temperatures in most years).

Yet another major heatwave will affect most of interior CA, but will largely skirt coast

Yet another strong ridge will bring yet another major heatwave across the West later this week.

As noted above, the recent pattern seems likely to continue: record heat inland, but remarkably unremarkable temperatures along and near the coast. Another strong ridge will build in later this week across eastern California and Nevada–bringing hotter than average July temperatures once again to a broad region stretching from the Pacific NW to Arizona. Unlike the last event, which baked the Pacific Northwest with almost inconceivably hot temperatures, this event will be somewhat weaker and primarily focused on California. But many places in the Central Valley (especially the far northern and far southern portions) as well as the Sierra Nevada and western Nevada will nonetheless experience heat that will likely meet or break daily records, and could even approach monthly/all-time records yet again in a few spots.

It is worth noting that the surface temperatures currently being projected by both the GFS and ECMWF operational runs still appear to be biased too high in places like the Central Valley (they are currently showing all-time records for most Central Valley cities this weekend, despite a large-scale pattern that does not really appear to support them). That adds some additional uncertainty to the forecast for this weekend, but at this time I don’t expect widespread 115+ temps in the Central Valley as is currently being depicted by explicit model output (though a few places could get that high, and daily records are still likely). The NWS has already issued Excessive Heat Watches for the entire Central Valley and much of the higher elevation CA and NV interior for the coming event.

The coming heatwave will affect a majority of the American West, but will be focused on Central/Northern California.

This type of heatwave, with a strong “heat dome” aloft associated with a hot mid-level airmass building in from the southeast, tends not to be conducive to extreme coastal temperatures in CA–and this event is unlikely to be an exception. It may get a bit warmer at the beaches than usual this weekend, but much of the SF Bay Area and the more coastal portions of the LA/San Diego metros (i.e., where most Californians live) will be warm to hot, but nothing too extreme. This is because there just isn’t enough offshore flow to overcome the strong marine influence this time of year and to fully suppress the marine layer.

Read the rest of the weather report here.

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MarcelK Jul 08, 2021 09:08 AM
Weather West: Coast Spared Again from Heatwave

Global warming/heating--which causes rapid climate change--is real. Greenhouse gases in the atmosphere are transparent to incoming solar radiation but that solar radiation is transformed to the infrared range before being reflected out to space, and greenhouse gases scatter infrared radiation, slowing its escape, . Some of that is a good thing--without it the Earth would be frozen solid. But the amount of greenhouse gases in the atmosphere is climbing rapidly; 350 ppm is considered the highest "safe" level but we are now at 419 ppm, up 2 from last year. As a result, there is slightly more incoming radiation than outgoing radiation, raising the temperature at the surface over time. Most of that energy has gone into the oceans, which sometimes release it in large bursts. Warmer oceans change airstream patterns and increase the intensity of hurricanes and tornadoes. Warmer air holds more moisture, changing humidity, rain and snowfall patterns. There are many undesirable effects (NASA lists 26,000 of them) such as changing when plants flower that throw off the balance between plants, insects and birds that most people don't notice ... they only notice when there are huge effects on humans, like the recent massive fires in Australia and California and these heat domes. It's still not quite too late to turn this back, but close. (That's what the "10 years" we heard from Greta Thunberg and AOC was about--not that we will all die in 10 years, but that we will reach levels with severe consequences.)

MarcelK Jul 08, 2021 09:43 AM
Weather West: Coast Spared Again from Heatwave

Here is one of those undesirable effects of global heating that most people aren't aware of: https://www.theguardian.com/environment/2021/jul/08/heat-dome-canada-pacific-northwest-animal-deaths

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