The occurrence of western Iran heavy rain is related to existence STJ in based on upper-level trough
which is propagated to Western Iran located above surface cyclone with extending pressure trough to western Iran and North Arabia Saudi .
We're under the influence of an upper-level trough
pattern, and that's keeping the onshore flow and precipitation right here," said Metcalf.
After one of the warmest autumns on record in the Mojave Desert, a drastic shift in the upper air pattern took place in mid-December 2008 as a deep, upper-level trough
established itself across the western United States.