A report issued by the Met department says the country is "affected by an upper-level trough
of low pressure" which is centred over the northern Arabian Peninsula.
These turrets can develop when there is some strong lifting mechanism around the20,000-foott level, such as an approaching strong mid- and upper-level trough
. Winds with the upper trough bring in colder air aloft, and the lifting also cools the layer.
Wintertime upper-level maps often fall into one of three basic patterns for the United States, with an upper-level trough
in the west, in the center or the east.
5 (20 May) Strong upper-level trough
and jet over Upsondes: 18 New Mexico and Oklahoma.
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.
The presence of this upper-level trough
has caused a large portion of otherwise northwesterly moving hurricanes to swing away to the north before reaching the U.S.
The physical implications of tropical cyclone formation in an environment with a lowered tropopause stem from the fact that such a background is associated with the presence of a cold upper-level trough
. This feature may be of midlatitude origin (Davis and Bosart 2003), or it may have formed at lower latitudes within the tropical upper-tropospheric troughs (Sadler 1975).
"As an upper-level trough
swings through, the coldest upper air moves overhead and destabilizes the atmosphere," said Charles Dalton, a meteorologist serving with the National Weather Service in Portland.
The upper-level trough
located to the south of Sandy also contributed to the westward track of Sandy (e.g., Galarneau et al.
For example, a convective outlook discussion from the Storm Prediction Center may mention an upper-level trough
becoming negatively-tilted with time, which might cue you to go check out that 500-mb chart.