Rain Shadow Effect - Revisited

 

As recounted here and in other recent posts, the Rain Shadow Effect is the primary Regional "cause" of the four North American Deserts with the Mid-Latitude High-Pressure Zone being a secondary cause.

While the Rain Shadow Effect is a Regional Climate Effect in the case of the Western United States, on a smaller scale, it can be a temporary, local Weather Effect (paired with Orographic Lifting) in a direction "contrary" to the regional (Prevailing) trend.

In regard to the Organ Mountains in Southern New Mexico and the Franklin Mountains in extreme West Texas (part of the same Basin and Range Fault Block), the prevailing winds are generally from West to East.  But on rare occasions, Weather Fronts from the Northeast and East do happen in the region. 

Downtown El Paso is about 3,700 feet above Mean Sea Level and it often gets below freezing, but it is usually dry, so to get a rare "good snow", the moisture has to come from one direction, while the frigid air comes from another.

As with early 1985 (I think), a Cold Front arrived into the El Paso area from the Northeast and due to Orographic Lifting, the east side of the mountains received a coating of ice on the streets and 2 - 3 inches of snow.  Normally, that small amount of snow would not be much of a local travel impediment, but when it overlays a coating of ice, that's a different story.

While the eastern slopes were getting the ice and snow, downtown El Paso and the western slopes were just getting cold rain.  

Orographic Lifting and the Rain Shadow Effect can happen in wetter parts of the country where there is sufficient Topographic Relief.  The mountains of Rabun County, in the northeastern corner of the state, is the wettest part of Georgia, averaging about 70 inches of rain per year.  In contrast, the Augusta area, on the edge of the Coastal Plain gets about 40 inches of rain per year.