Drought is again expanding over the US West. Oregon, after a very rapid April and May snowmelt, is being advised to conserve water. And with high pressure building in over the Southwest, weather models are predicting the emergence of an extreme heatwave by late this weekend. One that current guidance is indicating will bring 100 to 120 degree (F) temperatures to a wide region stretching from California’s Central Valley, through Southern California, Northwestern Mexico, Arizona, Nevada and into Southern Utah.

(The US is expected to swelter under a heat dome that is predicted to form this weekend and expand on into next week. Record heat is predicted to first impact the US Southwest before building into the Central US by late next week. Image source: NCEP/NOAA.)

The trigger for what may become a record-shattering heatwave is the predicted development of a powerful atmospheric ridge. Model guidance now shows a strong high pressure system currently over the Northeastern Pacific extending its influence eastward over the coming days. By the middle of next week, most of the US is predicted to fall under the atmospheric sway of a big bully of a high pressure system centered over the Southwestern States. Spiking atmospheric pressures and clear skies are expected to then usher in record temperatures for much of the US Southwest.

For parts of California’s Central Valley near Fresno, temperatures could rise as high as 116 F by Wednesday of next week (June 21). That’s about 23 degrees (F) above average for this time of year and would beat the hottest reading ever recorded in any month for the city. The same day prediction for Sacramento is in the range of 110 F — a little shy of the all-time record, but a reading that would shatter the June 21 daily record by a good margin.

110 degree + readings are expected to blanket Southeastern California, Sections of Northwestern Mexico, Southwestern Arizona, and Southeastern Nevada. Near 100 degree readings are expected to extend as far north as Redding, California. In other words, a huge section of the Southwestern US is expected to experience Death Valley like weather conditions.

(Record heat is predicted to blanket most of the Southwest US by next week. This graphic shows predicted peak daily temperatures on Wednesday, June 21. Image source: Pivotal Weather.)

This kind of record heatwave is something one might have expected during an extreme year of the 20th Century in July. But what we’re seeing is its potential to emerge now in mid-to-late June. An indication that record global atmospheric temperatures are starting to have some rather serious regional impacts along the lines predicted by various Global Circulation Models. These models indicated a particular vulnerability of the US Southwest to extreme heat and drying under the atmospheric forces set off by human fossil fuel burning. And this predicted heatwave is building up in an atmospheric context in which global temperatures will likely be around 1.2 C hotter than 1880s averages during 2016.

In this context, the potentially building record heatwave threatens to greatly expand and reassert drought conditions in the US Southwest this Summer. Should it emerge as models are currently predicting, it will greatly increase soil moisture evaporation and remaining snowpack melt across the region — amplifying drought conditions in over a region where many had hoped a strong El Nino would stave off these kinds of climate change related impacts for at least another few years. And for these reasons along with the direct risks of heat injury to human beings, interests should closely monitor its development.

Links:

US Drought Monitor

Quick Oregon Snowmelt Dampens Water Outlook

US Climate Data

Pivotal Weather

NCEP/NOAA

Hat tip to Zack Labe

Hat tip to DT Lange

Hat tip to Colorado Bob