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Climate:
Hot and dry summers with cool
evenings. The Jordan Valley below sea level is warm
during winter and extremely hot in summer. Rain falls
between November and March, while colder weather
conditions occur in December/January.
Required clothing: Lightweight
cottons and linens are advised between May and
September. Warmer clothes are necessary for winter and
cool summer evenings. Rainwear is needed from November
to April.
The major characteristic of the
climate is the contrast between a relatively rainy
season from November to April and very dry weather for
the rest of the year. With hot, dry, uniform summers and
cool, variable winters during which practically all of
the precipitation occurs, the country has a
Mediterranean-style climate. In general, the farther
inland from the Mediterranean Sea a given part of the
country lies, the greater are the seasonal contrasts in
temperature and the less rainfall. Atmospheric pressures
during the summer months are relatively uniform, whereas
the winter months bring a succession of marked low
pressure areas and accompanying cold fronts. These
cyclonic disturbances generally move eastward from over
the Mediterranean Sea several times a month and result
in sporadic precipitation.
Most of the East Bank receives less
than twelve centimeters of rain a year and may be
classified as a dry desert or steppe region. Where the
ground rises to form the highlands east of the Jordan
Valley, precipitation increases to around thirty
centimeters in the south and fifty or more centimeters
in the north. The Jordan Valley, lying in the lee of
high ground on the West Bank, forms a narrow climatic
zone that annually receives up to thirty centimeters of
rain in the northern reaches; rain dwindles to less than
twelve centimeters at the head of the Dead Sea.
The country's long summer reaches a
peak during August. January is usually the coolest
month. The fairly wide ranges of temperature during a
twenty-four-hour period are greatest during the summer
months and have a tendency to increase with higher
elevation and distance from the Mediterranean seacoast.
Daytime temperatures during the summer months frequently
exceed 36°C and average about 32°C. In contrast, the
winter months--November to April--bring moderately cool
and sometimes cold weather, averaging about 13°C. Except
in the rift depression, frost is fairly common during
the winter, and it occasionally snows in Amman.
For a month or so before and after
the summer dry season, hot, dry air from the desert,
drawn by low pressure, produces strong winds from the
south or southeast that sometimes reach gale force.
Known in the Middle East by various names, including the
khamsin, this dry, sirocco-style wind is usually
accompanied by great dust clouds. Its onset is heralded
by a hazy sky, a falling barometer, and a drop in
relative humidity to about 10 percent. Within a few
hours there may be a 10°C to 15°C rise in temperature.
These windstorms ordinarily last a day or so, cause much
discomfort, and destroy crops by desiccating them.
The shammal, another wind of some
significance, comes from the north or northwest,
generally at intervals between June and September.
Remarkably steady during daytime hours but becoming a
breeze at night, the shammal may blow for as long as
nine days out of ten and then repeat the process. It
originates as a dry continental mass of polar air that
is warmed as it passes over the Eurasian landmass. The
dryness allows intense heating of the earth's surface by
the sun, resulting in high daytime temperatures that
moderate after sunset. |