The marathon North County heat wave started on June 27 and continued through July 4.
Paso Robles exceeded triple-digit readings eight days in a row. At its peak on Saturday, June 29, the Paso Robles airport hit 111 degrees, which broke the record for the day. The next day, another daily temperature record was smashed as Paso Robles hit 110 degrees.
On July 1, Paso Robles matched a 63-year daily record with a temperature of 107 degrees.
On Saturday, June 29, the temperature reached 119 degrees in Phoenix, making it the city’s fourth hottest day on record. The next day, Death Valley National Park hit 128 degrees, tying the record for the hottest June day anywhere in the country. The National Park Service thermometer, a short distance away, recorded a temperature of 129.9 degrees. The planet's highest recorded temperature occurred in Death Valley on July 10, 1913, when the mercury thermometer hit 134 degrees.
Along many of the beaches and coastal valleys of the Central Coast, it also sizzled. On Saturday, June 29, San Luis Obispo reached 103 degrees which broke a daily record. Avila Valley at the PG&E Energy Education Center hit 108 degrees.
However, the coastal areas did not see sustained and widespread offshore winds that could have made it a truly historic event. Back in June 20, 2008, the pinecones in Los Osos literally snapped, crackled and popped like Rice Krispies when Santa Lucia (offshore) winds drove the temperature to 110 degrees at Baywood Park. San Luis Obispo reached 113 degrees that day. During this heat wave, temperatures at the edge of Morro Bay never exceeded 70 degrees.
On June 30, tragedy struck north of Phoenix as 19 firefighters near the town of Yarnell, Ariz., were killed. They were fighting a wildfire that burned uncontrollably through bone-dry manzanita and chaparral. A line of thunderstorms moving southward caused the terribly hot winds to abruptly shift 180 degrees and suddenly increase in strength. In a moment, these firefighters who gave their all to save life and property were trapped and killed.
So what caused this heat wave?
A large and very strong area of high-pressure developed over Western United States. The thickness of the atmosphere reached near record levels. On average, half of the atmosphere’s weight lies between the Earth’s surface and an altitude of about 18,000 feet.
Meteorologists determine the thickness of the atmosphere by analyzing 500 millibar (mb) upper-level charts. In other words, this chart will tell you how high the pressure is 3 or 4 miles above the Earth's surface. Last weekend it reached 600 decameters (19,685 feet).
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That’s about as high as the 500 mb "heights" ever get. These 500 mb heights have a direct relationship to how hot it’s going to be it at the earth’s surface. The thicker the atmosphere, the greater amount of subsidence that occurs as the air sinks and warms on its way to the ground, kind of like a pressure cooker.
So what does the rest of summer season hold in store for us?
The U.S. Climate Prediction Center says that normal seasonal temperatures are predicted from July through September along the California coastline. However, temperatures farther inland are expected to be above normal.
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