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Tuesday, September 16, 2014 - 10:42am

Bring On The Westerly Winds!

Weather Talk

POSTED: Tuesday, January 7, 2014 - 12:04pm

UPDATED: Tuesday, January 7, 2014 - 12:14pm

The Impact Of Wind Depends On Many Factors, Such as The Origin, The Season And Area Mountains

       …you do not need a weatherman to tell you which way the wind blows. (Bob Dylan)

In my most recent “Weather Talk” I told you the characteristics of an air mass depend on where it originates. That could also be said about many people and it is definitely true about the wind.

When the winds shift out of the southerly and especially westerly directions they are usually carrying in warmer and drier air which tends to warm up our region. Except during our “monsoon” season where the mainly southeasterly low level winds carry in Gulf of Mexico humid air which helps power up our mid to late summer thunderstorms. Did you know that The word is derived from the Arabic term “mausim”, meaning season. In Meteorology
“Monsoon” is referred to as a “persistent wind”. We always think of the “monsoon” in India during their summer that carries in large amounts of moisture from the ocean, which in turn produces heavy rain fall for days that results in massive flooding. Did you know India also has a dry seasonal “monsoon” wind? This persistent wind blows from the land towards the sea and completely dries out their atmosphere.

Here in the Borderland we are in and we are surrounded by areas with desert climates. We are located in and to the south of us we have the Chihuahuan desert and to the southwest and west we have the Sonoran Desert. When winds carry in air from these areas it is by nature usually warmer and drier which tends to increase our temperatures.

The mountains also help warm and dry out the air as well. In an earlier “Weather Talk” I describe “Foehn Clouds”. http://www.ktsm.com/weather/weather-talk/foehn-clouds-over-franklins
This is associated the a wind we know as the “Foehn Wind”. The original Foehn, or Föhn Wind or Cloud in German, was the name of a warm southerly wind coming up and over the Swiss Alps. Now this term is used to describe similar meteorological effects on all mountains all over the world.
The generic name for this phenomena is Foehn wind, and "Chinooks" in the Rocky Mountain region are considered a regional type of Foehn, as are the "Santa Ana Winds" in the southwest associated with air forced across the Sierra Nevada range.

Chinook winds are large scale weather system driven winds over the central and northern Rockies that flow across the mountain ridge and then down the other side. Very often in the winter they replace an existing polar or arctic air mass that was already in place on the lee side of the mountains. In addition to being driven across the mountains by large scale pressure patterns, like high and low pressure centers, the air in a Chinook may have enough moisture on the windward side of the mountains to create clouds and precipitation as it flows up the windward slopes. By losing moisture in this way as the air ascends the slope on one side the air cools at something called the moist adiabatic rate, the air is set up to warm by compression on the other side of the slope at a faster rate referred to as the dry adiabatic. The combination of down slope flow, warming by compression and the replacement of a cold air mass can result in rapid warming on the downwind side of the mountain. This sometimes this results in a “mountain wave” which produces gusty winds on the lee side of the mountains for many miles. After all the moisture is removed from the air due to up slope rain/snow on the windward side of the mountain, the air on the down slope side usually is especially dry, causing rapid melting of area snow, or strong drying of natural fire fuels and thus an enhanced potential for wildfire. Chinook winds are often nicknamed “Snow Eaters” because of the down slope drying effect. We also all know about the critical fire danger and the fire spreading problem of the “Santa Ana Winds” in California.

Here in the Borderland during our cold season we do not welcome the cold northerly winds unless they bring us a rare treat of snowfall! We do celebrate are warmer drier southwest to westerly winds that do bring us some sometimes temperature relief. These same winds during the summer months help push the temperatures towards the triple digits. This proves that the pleasing effects depend on the direction and the “mausim” or season in which the wind blows.

Chuck DeBroder, Chief Meteorologist
KTSM, NewsChannel 9, NBC, El Paso, TX
cdebroder@ktsm.com
www.facebook.com/pages/Charles-DeBroder/
www.twitter.com/ Chuck DeBroder NC9 @wxchuckNC9

(Photo: Chuck DeBroder-KTSM))

 

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