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Copyright 2012 Rocky Mountain Rider. ALL RIGHTS RESERVED. Reproduction of any editorial material, artwork and photos is strictly forbidden without express written permission of the publisher. For information about reprint rights, please contact the editor; editor@rockymountainrider.com.

 

The Weather Pattern Causing the Drought

By Matthew G. Fearon, Assistant Research Meteorologist,

Desert Research Institute, Division of Atmospheric Sciences, Reno , NV

 

October 2012 issue  

 

      The dry conditions over the western-central U.S. , the onset of which began during the winter season of 2011-2012, remain persistent.

      These conditions are inherently tied to an ongoing atmospheric blocking pattern, referred to as an “omega block” due to its structural resemblance to the Greek symbol omega (Ω).

      This “trough-ridge-trough” atmospheric wave structure, which initially centered itself over the central high Plains, has oriented the storm track in a south-to-north trajectory on its western and eastern sides (the troughs) leaving the center region (the ridge) disturbance free (see Figure 1).

 

 Figure 1. From Google Images on Omega Block.

      As a result, a large portion of the high Plains, including the northern Rockies , have seen limited amounts of moisture and precipitation and above normal temperatures over the past ten months. For the northern Rockies , limited moisture has lead to heat-based thunderstorms and dry lightning episodes during the summer months increasing wildland fire.

      More recently, this block-type weather pattern has gradually shifted westward and shrunk slightly in its extent, alleviating some of the drought over the eastern Plains (see Figure 2).

      And with the transition season upon us, which features a larger north-to-south temperature gradient, the potential for blocking-type patterns of this nature decay with time.

 

      The “omega block” is a recurring pattern that can last for days and or weeks, but not usually for months. It is a stagnating weather phenomenon that results when a large portion of the atmosphere’s energy [main sources are thermal gradients] has been used up. This goes on for a few days to a week typically until something significant, from upstream, disrupts the block.

            However, this latest case is extremely unusual, and appeared to self maintain and build on itself, particularly through late spring and summer, and significant disturbances were routed around it. The persistence of this particular case is not completely clear. Its duration might be one for the record books.

      Matthew G. Fearon is currently pursuing his Ph.D on the influence and entrainment of tropical moisture into Pacific weather systems through examination of the Trade Wind Inversion.

 

  

Copyright 2012 Rocky Mountain Rider. ALL RIGHTS RESERVED. Reproduction of any editorial material, artwork and photos is strictly forbidden without express written permission of the publisher. For information about reprint rights, please contact the editor; editor@rockymountainrider.com.

 

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