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I'm trying to understand why the summer (January) precipitations in Venezuela are so low in the central and southern parts of the country as well as in eastern Colombia. The most plausible explanation I could find was a rain-shadow effect but unless I'm wrong, the mountains are on the northern side while the winds are blowing from the ocean, east to west. This should not result in a dry season.

What have I missed?

My references are :

http://research.jisao.washington.edu/data_sets/ud/samerica/

http://kids.britannica.com/comptons/art-166714/The-map-at-left-shows-the-wind-belts-of-the

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  • $\begingroup$ The dryness in that map doesn't correlate with the drought severity in this map: indexmundi.com/blog/wp-content/uploads/2013/05/… $\endgroup$ – naught101 Sep 30 '15 at 12:48
  • $\begingroup$ Venezuela is entirely in the Northen hemisphere (as is most of Colombia) so January would normally be considered the "winter" (though such a definition is not particularly helpful in the tropics.) $\endgroup$ – Level River St Apr 16 '16 at 22:21
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In January the Intertropical Convergence Zone shifts to south of the equator. And the Subtropical High Pressure Belt moves into areas of Venezuela, which leaves it dry. I am guessing this from a study of principles of world geography and climatology; I don't live in Venezuela though.

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  • $\begingroup$ can you add some more detail to your answer ? What are the consequences of the ITCZ moving south of the equator ? How does it affect the climate ? $\endgroup$ – gansub Sep 29 '15 at 14:30
  • $\begingroup$ I think Saurabh is right. This has nothing to do with any rain shadow effect. It has everything to to with the inter-tropical convergence zone (ITCZ) which is directly over Venezuela in July, but migrates south to the north & central Amazon basin during January. The ITCZ brings strong convective rainfall whereas, when it moves south, it leaves behind bright sunny skies. Also, the low level airflow comes from the mid-Atlantic at the time of year when sea surface temperatures are lowest, and hence evaporation is at an annual minimum. $\endgroup$ – Gordon Stanger Oct 1 '15 at 12:57

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