Page 82 - 2005 DT 12 Issues

The Fickle Wind The wind speed will depend on the pattern will overwhelm fl ows that nor-
pressure variation over that distance. mally occur as a result of topography,
f you spend any time in Southern The greater the pressure gradient, the but not in the Las Vegas Valley. Here
Nevada you’ll notice that next to higher the wind speed. The relationship the local topography rules and it has

Iperpetually sunny skies, wind is a is linear: quadruple the pressure gradi- the most pronounced influence on our
major component of our weather. There ent and the wind speed will increase by afternoon winds, pushing up-valley in

is either too much or too little of it. A a factor of four. a southeasterly flow. As the afternoon
few miles, or just a few minutes, make Other forces also act on wind—the wanes and evening comes on, tempera-
all the difference. The morning calm can Coriolis force associated with the earth’s ture differences between the mountains
be replaced by a hat-grabbing 30 mph rotation will defl ect the direction of the and low lying areas cause forced down-
afternoon wind that appears without wind to the right of its path (clockwise) slope fl ows from the east and southwest
a clue from some other dimension of in our hemisphere, and high wind that converge into Las Vegas, continuing
the Twilight Zone. If it’s garbage day, speed will increase the Coriolis force. the southeasterly up-valley flow. The

you’ll hope the address you marked However, large scale systems rotate confl icting southwesterly winds meet
on the can and lid haven’t faded into counter-clockwise because centripetal head-on with the southeasterly winds
oblivion. Otherwise, how will you claim force is directed at right angles to the in the lowland regions north of the
your wayward receptacle among all the fl ow of the wind and inwards towards Spring Mountains.

look-alikes that sailed with it into the the centers of rotation (high-to-low pres- Most of these wind flows gradually
next neighborhood? sure centers) overpowering the weaker drain away as night approaches, but pre-
Wind conditions vary in response Coriolis force—think cyclones and hur- vailing winds in the Las Vegas Valley are
to variations in atmospheric pressure. ricanes. Frictional deceleration, which the very last to calm down, succumbing
These variations are far greater when creates drag opposite to the path of only after the sun is well set.
measured from the surface to the upper motion, will cause the air to slow down. Perhaps this is one reason why the
atmosphere, but it is the horizontal varia- Most of these effects are only noticed in temperature doesn’t fall that much in the
tion at the surface that produces wind. large, regional patterns. evening in Las Vegas. Or perhaps it’s the
Temperature has a lot to do with air In Southern Nevada, our wind pat- summer wind that keeps blowin’ in from
movement. Cold air is heavy and dense terns are determined to a great degree by the Strip, carrying the bright lights and
and likes to lie around on your bedroom topography. We live in a valley with an el- high voltage with it. ❏

floor in the winter. You need your ceil- evation at its lowest point of about 2,200
ing fans to force the lazy cold air up and ft above sea level. The southwest Valley October Board Notes:
push down the lighter warm air hovering rises approximately another 1,600 ft. to
above you. In a climate that is hot for the foothills of the Spring Mountains, • No motions were offered at
most of the year, air conditioning/heat- which range up to the 11, 918 ft peak of this meeting.
ing vents are placed near the ceiling, Mt. Charleston. Wind is, at its simplest, • Standing Rules have been
because the density of the cold air will a form of solar energy. We experience revised and will be submitted to the
naturally cause it to fall downward, both the larger patterns of thermally membership at the first quarter general

displacing warm air. driven regional winds (monsoonal or meeting for a vote. A copy will appear

Spatial differences in atmospheric southwesterly plain-to-mountain flows) in the December Desert Trumpet.
pressure are generated by the uneven and the thermally driven local wind pat- • A trail building seminar with

absorption of solar radiation at the terns (down-slope flows). field work by the Great Basin Institute

Earth’s surface. Some areas will warm As morning dawns, wide-spread was presented on October 7-9, at the
faster than others depending on ground wind patterns throughout most of Visitor Center. A new 840 ft trail from
cover, terrain, reflecting or absorbing Southern Nevada generate a southerly the Red Springs parking lot to the boul-

surfaces, or cloud distribution. High to southeasterly fl ow. As the day pro- dering route was completed by partici-
pressure is associated with colder air gresses, the southwesterly monsoonal pants from GBI, Friends, REI, NPS and
masses, low pressure with warmer air. winds dominate. RRCIA. Pat Williams suggested that this
At the earth’s surface, large-scale winds Then, something strange happens. training be included in the annual fall
always blow from high to low pressure. At many locations, the monsoonal fl ow training schedule.

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