Extreme Temperature Diary- Tuesday June 15th, 2021/ Main Topic: Detailing Heatwave Alpha (Day 2)

The main purpose of this ongoing blog will be to track planetary extreme or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials).😉

Main Topic: Detailing Heatwave Alpha (Day 2)

Dear Diary. Now that we have a major heatwave affecting a portion of the United States, as usual it’s time to go into detail mode on this blog and site. Since Alpha is a western heatwave, I’ll turn to my West weather expert, Daniel Swain, for those details.

Here is an excerpt from his latest blog:


Severe heatwave across California interior and broader Southwest this week

Filed in Weather/Climate Discussion by Daniel Swain on June 14, 2021 

Severe to locally extreme heatwave likely across interior CA this week

A very strong early-season “heat dome” will shift westward toward CA and the West Coast.

I’ll cut to the chase: it’s going to be very hot across the inland 3/4 of California beginning Wednesday or Thursday and continuing through at least Saturday–and perhaps into the early portion of next week. Many areas are likely to experience record temperatures during this relatively early-season heatwave–especially across the Central Valley and the deserts of SE CA, though possibly elsewhere. All-time June monthly records may plausibly fall in these places, and there’s even a chance that a few spots could approach all-time record high temperatures (again, most likely in the southern Sacramento/San Joaquin Valleys and in the SE desert counties).

This heatwave will be caused by a record-strength mid-June high pressure system over the Four Corners region of the Southwest that will slowly retrogress (move westward) toward CA by Thursday. All-time record high temperatures are possible in other interior SW areas already accustomed to extreme heat–including both southern Nevada and western Arizona (Las Vegas and Lake Havasu City may see their highest temperatures in recorded history). The blistering heat across these regions (well above 120F in some lower desert spots) will last for many consecutive days in these areas, and will pose major risks to public health. Given the rapid expansion in wildfire activity across Arizona, Utah, and western Colorado in recent days, I would expect that many consecutive days of record-breaking temperatures will just exacerbate the situation.

It’s worth noting that the region of maximal extreme heat during this event–which will likely break some all-time records–is broadly co-located with the epicenter of the still-worsening extreme to exceptional drought conditions across the Southwest. This is probably not coincidental, as the record low soil moisture will allow a much greater than usual fraction of the sun’s energy to go toward heating the atmosphere (rather than evaporating water from the soil). The notion that extreme dryness can beget extreme heat, which further exacerbates the dryness, is a classic “positive” (self-reinforcing) feedback in the climate system.

Most extreme temps Central Valley and SE deserts, but hot elsewhere too

The ECMWF and GFS models have been recently spitting out some eye-popping high temperature numbers for the Thurs-Sat peak of the heatwave across the Central Valley (widespread 112+, locally 115+) and the SE desert regions (locally above 120F). In the near-coastal transition zones (i.e., SF and LA area inland valleys), numbers are less exceptional but still quite impressive for mid-June (105-110+). The immediate coast will be very warm, but temperatures will probably not be record breaking in most spots due to lack of offshore flow.

500mb heights–a measure of the strength of the mid-atmospheric ridging–will reach record levels over the Four Corners region before shifting westward. (NOAA)

I’ll be honest: I’m not sure whether to believe the all-time record high temperatures currently being spit out by the operational model surface schemes for the Central Valley (though the SE desert numbers are more believable). On the one hand, these models do have a track record of historically generating heat wave extremes that are just a bit too hot. But on the other hand, the soil column across much of NorCal is presently drier than it has been in recorded history–and that might be enough to add a couple of degrees to what otherwise might have been slightly less extreme values. For now, I would expect actual highs to come in a few degrees cooler than the absurdly hot temperatures currently being predicted by the ECMWF for the Hwy 99 corridor in the Central Valley (widespread 115-117F). But even then, that’s still a widespread 110-112F+ heatwave–and given the above caveat there’s at least a chance that the models are right.

Coastal areas may see only a couple of warm to hot days later this week, but inland areas will likely be very hot (well over 100F) on each day from Wed through at least Sunday, and perhaps as late as next Tuesday. Thus, human health and agricultural impacts from this event have the potential to be extreme in these areas–especially against the backdrop of already exceptional drought in many areas. Additionally, I would expect to see a major uptick in wildfire activity this weekend virtually everywhere as vegetation dries even further beyond its currently record-dry levels (for the calendar date) and people spend time outside to try to escape the heat.

Just to reiterate: this will not be a typical June heatwave across inland areas, and could rival (or even surpass, in some areas) the extreme and record breaking heat experienced last Aug/Sep in those areas (though not at/near the coast). Prepare accordingly.

Today I will be adding notes about this heat wave in the space below:

Here are some of Tuesday’s “ET’s:”

Here is some more May climatology:

Here is more climate and weather news from Tuesday:

(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity. In most instances click on the pictures of each tweet to see each article. The most noteworthy items will be listed first.)

Now here are some of today’s articles and notes on the horrid COVID-19 pandemic:

(If you like these posts and my work please contribute via the PayPal widget, which has recently been added to this site. Thanks in advance for any support.) 

Guy Walton “The Climate Guy”

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