The Ridge from Hell

If we were to name ridges like we name Hurricanes, surely the one that has gripped the western U.S. in recent days would be called Satan or Lucifer because it is straight from hell.

You are already aware of the heat records.  130˚F in Death Valley, the 3rd highest temperature every recorded on this planet (and possibly the highest).  Five record highs at Salt Lake City so far this month, including two consecutive days of 105˚F on the 1st and 2nd and three straight above 100˚F this week.  Below average precipitation across much of the interior western United States, but lightning sparked fires in California.  Indeed, the Devil would be proud.

Now we add poor air quality to the mix in Salt Lake City, with PM2.5 concentrations rising overnight due to smoke with values peaking at 86.1 ug/m3 (unhealthy) and remaining high at 44.3 ug/m3 (unhealthy for sensitive groups) at 6 am this morning.  

Source: Utah Division of Air Quality

That was high enough to cause me to skip my morning hike. 

It's worth a quick look at the past few days to show how the large-scale evolution of the ridge brought us to where we are today.  

On Saturday, August 15, clear skies prevailed across much of the southwest United States, with localized smoke evident from fires in northern California and Colorado.  At this time, the ridge was relatively low amplitude and northern Utah was actually in northwesterly flow

Source: NASA

By Sunday, August 16, the ridge amplified, with temperatures increasing across much of the west.  Death Valley reached 130˚F that afternoon.  However, moisture was streaming northward around the western periphery of the ridge and into northern California, producing thunderstorms.  

Source: NASA

Ditto Monday, with some evidence of smoke from fires in the Sierra Nevada.

Source: NASA

On Tuesday, smoke emissions and spread increased.  A complex flow pattern led to smoke being transported both southward by the northerly low-level flow associated with low-level high pressure off the California coast and northward around the periphery of the mid- and upper-level ridge over the western interior.  

Source: NASA

This continued on Wednesday, but in addition to the now growing fires in California, emissions in Colorado increased as well.  

Source: NASA

And by yesterday, smoke permeated much of the western Great Basin from California and, with contributions from Colorado (and lesser contributions from a few other spots), had largely encircled the upper Colorado river basin.  

Source: NASA

Meanwhile in northern Utah, some weakening of the ridge and the passage of a weak trough allowed smoke that had encircled the ridge from California to gradually move in yesterday and finally permeate the Salt Lake Valley overnight.  As I write this, it's a little early for a good visible satellite image, so I'll use the HRRR-smoke vertically integrated smoke analysis to illustrate the situation as of 1200 UTC (0600 MDT).  Very high concentrations stream northward through northern California and then northeastward through northwest Nevada and southeast Oregon and over the southwest Snake River Plain.  High concentrations are draped across northwest Utah, with a sharp gradient to our south.  

Source: NOAA/ESRL

There is a tendency to assume that high-pressure, or ridges, are relatively benign, but the events of the last several days provide a clear example of the severe impacts that these systems can produce.  Extreme heat, lightning-caused wildfires, and poor air quality associated with smoke emissions and transport are examples of the "severe" weather and related hazards associated with this ridge.  We could add extreme wildfire behavior to the mix if we wanted too (see Fire Tornadoes Reported in Northern California Wildfire from the New York Times).  Additionally, this event is an amplifier of drought conditions that plague the region.  

Indeed, this is the ridge from hell.  Sadly, weather and related extremes associated with high-amplitude ridges during the warm season are going to become more common and severe in the coming decades.