Source:
World Meteorological Organization
News from the
Islamic Republic of Iran Meteorological Organization, 21 February 2008 -
During 18 days from 10 to 27 January 2008, the minimum temperature in
Tehran was continuously less than -5ēC; the lowest temperature recorded was
-11ēC, while the maximum temperature was below 0ēC for 12 days. The lowest
temperature recorded in Iran during this period was -32ēC.
Heavy snow in Tehran in January 2008
Flash floods,
avalanches, heavy snowfall, freezing rain, blowing snow, severe cold air and
frost led to blocked roads and extensive damage to crops.
Three similar
episodes were recorded in the winters of 1964, 1969 and 1972. A comparison shows
that the period 26 December 1963-29 January 1964 was the longest, with the
minimum temperature in Tehran being below -4ēC for 35 days and the lowest
temperature being -14ēC. The absolute minimum temperature of Tehran was -15ēC on
8January 1969 but the episode was shorter. The lowest absolute temperature of
Iran ever of -36°C was recorded in Saghez during the cold spell of 1969. The
last extremely cold weather event occurred in January 1972, when temperature in
Tehran dropped to -13ēC, but was of shorter duration.
Snow covered Qom, January 2008
Synopsis
In the beginning of
January 2008, the polar vortex moved southward and lay over the Aral Sea in
northern central Asia. A deep meridional trough frequently formed over western
Europe rather than over central Europe.
This trough caused
frequent lee cyclones to the south of the Atlas mountain range in north-west
Africa over Morocco and Algeria. Short westerly waves of these cyclones
periodically passed over North Africa, the Middle East and Iran. They caused
flash floods in southern provinces and heavy snowfall in central and northern
provinces.
Formation of a deep
trough over western Europe caused an elongated meridional ridge over the
Caucasus with a blocking high to the north. Southerly currents of this blocking
brought bitter polar cold air down to Afghanistan and Iran. A zonal polar front
jet moved southward and lay over 33ēN. The combination of the polar front jet
and the subtropical jet stream over central and southern parts of Iran increased
wind speed up to 370 km/h.
A positive North
Atlantic Oscillation associated with a marked La Niņa caused high pressure over
the Azores to intensify and extend east to eastern Europe.
Intensification of
cold high pressure in Siberia and its expansion toward the south-west and
integration with high pressure in Europe brought a very cold polar air mass to
Afghanistan and Iran, which lasted almost three weeks.
Hamedan, January 2008
Highlights
-
Displacement of
the tropospheric polar vortex towards central Asia
-
Deepening of the
trough over western Europe and formation of deep lee cyclones to
the south of the Atlas mountains
-
Expansion of the
Azores high from Europe towards the Caucasus and Caspian Sea and
integration with Siberian high
-
Advection of very
cold air from Siberia to Afghanistan and Iran
-
A positive North
Atlantic Oscillation and a marked La Niņa
-
Increasing
maximum wind speed of the polar front jet to 370 km/h as it moved south to
33ēN over Iran and the Middle East.
Islamic Republic of Iran Meteorological Organization
... Payvand News - 02/22/08 ... --
