Mesa, Arizona

... Excessive heat watch in effect from Saturday morning through
Sunday evening...

The National Weather Service in Phoenix has issued an excessive heat
watch... which is in effect from 10 am Saturday morning through 8 PM
Sunday evening.

Strong high pressure aloft centered over West Texas will expand and
strengthen over the southwest United States during the next couple of
days... bringing the hottest temperatures so far this year. Forecast
highs over the Lower Desert will range from 109 to 115 degrees
Saturday... and from 110 to 117 degrees Sunday. The heat index is
forecast to reach or exceed 105 degrees for at least several hours
each afternoon. The forecast high temperature at Phoenix Sky Harbor
Airport is 112 degrees on Saturday and 113 degrees on Sunday... with
an overnight low of 89 degrees Saturday night.

Precautionary/preparedness actions...

It would be wise to complete as much outdoor activity as possible in
the early morning when the sun and heat are less intense. During
periods of excessive heat... individuals can suffer heat-related
illness when the body can no longer cool itself. If you plan to be
outside for an extended period of time in the afternoon or early
evening... stay in the shade as much as possible and drink abundant
amounts of water. Wear light-colored and loose-fitting clothing. If
you wear a wide-brimmed hat... your head and body will be much cooler.
Stop outdoor activities... drink lots of water or other non-alcoholic
beverages... and if possible... spend more time in air-conditioned or
well-ventilated places.



National Weather Service Phoenix is on the internet at

An excessive heat warning/watch is issued when extreme heat or
the combination of extreme heat and very low or very high humidity...
will compromise the health of an average adult person if avoidance
of direct exposure is not taken to preclude the onset of heat stroke.
The warning is issued when the threat is imminent... and the watch is
issued when notification precedes the event by 12 to 72 hours.

Summertime in the lower Arizona and southeastern California deserts
has occasional extremely hot days. People who live in the desert
areas... or those who visit... are vulnerable to significant health
problems that may lead to death if protective action is not
immediately taken. Drinking abundant amounts of water is not enough
to protect against dire health conditions due to the exposure to
excessive heat and very low or very high humidity. The average
adult person must take action to reduce direct exposure to the sun
by staying inside cool sheltered accommodations. The goal is to
keep the body core temperature near normal... or the condition of
hyperthermia may occur... followed by heat exhaustion or worse...
heat stroke.

The National Weather Service forecasters use many factors to
determine when extreme heat conditions are about to occur in the
lower deserts. The rarity of an excessive heat episode is a leading
factor in determining the issuance of a warning and watch. Air mass
analysis schemes developed by the University of Delaware compare
daily meteorological parameters with known health statistics of the
region. Subtle changes in wind... sky coverage... temperature...
humidity and the calendar date of the episode contribute to the
determination of issuance necessity. Thus... a temperature of 112
degrees in a very dry air mass will trigger the issuance of an
excessive heat warning... but the 112 degree temperature in July
may not. Similarly... that same 112 degree temperature may trigger an
excessive heat warning for one location but not at a different
location.