The Large and Synoptic Scales of Atmospheric Patterns of Heavy Snow in Gilan Province

The heavy snow that occurred in the February of 2014 in Gilan province was an extreme individual phenomena that caused high economic losses and disrupted the daily life of people who were living there. In order to find large and synoptic scale structures of this phenomena, first the dates of heavy snow have been extracted in Gilan in the period of 1964-2014, using data produced by Rasht synoptic meteorological station and also reanalysis data from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR).
This climatological research has been conducted thorough two steps. First, averaged values of meteorological parameters have been computed during 1981-2010 years. Then the calculated anomalies have been analyzed. For this aim, two meteorological parameters including mean sea level pressure and geopotential heights at 10 and 500 hpa levels have been considered.
The results show that in recent years heavy snowfall over Gilan province has been intensified. Although there was not sudden stratospheric warming and weakness of polar vortex in the mentioned years. However, a blocking pattern in 500 hpa, especially with coupled type, have been detected for all of distinguished phenomena. In addition, sea level pressure patterns show a development of Siberian or Balkan high pressure. Also in some cases the combination of these two high pressures, has been extended to the Caspian Sea region and has caused instability and humidity transfer to the Northern coast of Iran.