27 Jun 2013

Dangerous heatwave expected for south west US

South western parts of the US are about to be gripped by an intense heatwave that could bring record-breaking temperatures to some parts of Nevada, Arizona and California.

The US National Weather Service (NWS) has issued excessive heat warnings across all three states, which make it clear that temperatures will reach dangerous levels capable of stressing the body if precautions are not taken.

As the jet stream heads sharply north towards the Pacific west’s US-Canadian border, it will allow a strong area of high pressure to build over the south west of the US.

This will bring cloudless skies, light winds and rapidly building heat. With days longer than the nights at this time of year, the air is heated for longer than it is able to cool – resulting in temperatures rising day after day.

Another contributing factor is that much of the area to be affected is desert. Dry air heats up more quickly than moist air because all of the energy goes into lifting the temperature, rather than being shared with the process of evaporating moisture.

This is the reason that desert environments have some of the greatest daily range of temperatures on the planet. Moister, tropical environments have smaller ranges of temperature and more constant warmth.

Latest forecasts suggest that the highest temperatures will be recorded from Friday to Monday, with a large area recording triple digit heat – when the temperature hits 100F or more.

According to NWS, the temperature at Death Valley in the Californian desert could soar as high as 53.9C (129F) this weekend. Death Valley currently holds the record for the highest temperature ever recorded on earth, 56.7C (134F), reached on 10 July 1913.

Las Vegas will also see intense heat, with temperatures predicted to hit 47C (117F) this weekend at the city’s McCarran international airport.

Aside from the very high temperatures, there are worries that tinder-dry vegetation may catch fire due to lightning strikes, sparking off wildfires that could quickly spread under the intense heat.

Another concern is the risk to illegal immigrants trekking up from Mexico on foot across the remote deserts of southern Arizona, where shade is scarce and heat is expected to reach 115F to 121F (46C to 49C) over the weekend.

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