Climate Talk

Located squarely in the mid-continent, hundreds upon hundreds of miles away from wet maritime air masses, South Valley Park’s landlocked position very much determines its climate and the varieties of its weather, notably its large diurnal and seasonal differences in temperature, its persistent aridity, its sunshine and lack of clouds.

 Three maritime sources and two continental sources influence our mid-continental climate: the maritime polar (the wet and cool Pacific Northwest); maritime tropical (the warm Pacific from the Baja area of Southern California); maritime tropical (the Gulf of Mexico); the continental tropical (Mexico); and the polar continental (north-central Canada).

                The driving force behind the movement is air is a term called atmospheric convection.  When air is heated, it increases in volume and then rises because of its greater buoyancy.  These vertical air currents deplete the surface of some its air, thus creating regions of slightly lower pressure at the bottom of the rising air column.  As air is forced to move from areas of higher pressure toward the newly created low-pressure area, a horizontal pressure gradient develops.  These air movements vary in size and in their significance for the climate, ranging from local winds, such as dust devils and warm southerly chinook winds, to large-scale air currents in the upper levels of the atmosphere.

 The largest-scale wind patterns are sometimes called “the winds aloft."  These are initiated by pressure systems set up by latitudinal variations in insolation (incoming solar radiation).  In the Northern Hemisphere, the winds aloft are deflected to the right by the Earth’s rotation, spiraling counterclockwise around the lows and clockwise around the highs.  Centers of low pressure are called cyclones; centers of high pressure are called anticyclones.  As a result of the Coriolis effect, large-scale air motions move perpendicular to the pressure of gradient, that is, around regions of low and high pressure, but not directly to or from them. 

The sharp north-to-south temperature gradient that exists in the Northern Hemisphere during the winter months causes the upper-air westerlies to intensify seasonally and with increasing altitude.  Consequently, winds in the southern Rockies are nearly twice as strong in the winter as in summer.  During the summer, when westerly airflow is weak, the main air current and its associated polar front jet stream stray far to the north, typically over Canada.  By winter, the westerlies and the main axis of the polar front jet tend to be positioned over the Southern Rockies, guiding Pacific storm systems through the region fairly regularly. However, during those winters when a large ridge in the upper atmosphere keeps the polar front jet along or to the north of the Canadian border, the southern Rockies experience a lack of snow, severe drought, and unseasonably warm weather.