Fcst
Mvmt
This column on the storm attribute table lists the forecasted movement
of each thunderstorm cell. On the radar image itself, a projected path
is displayed starting at the cell identification code, and extending
outward.
The forecasted movement of any given thunderstorm cell is separated
into two parts within the column. On the left, the first part is the
direction the movement is from, in degrees, which is inverse from where
the storm is headed. On the right, the second part consists of the
speed, in knots, at which the storm is moving. For an example, if the
output of one thunderstorm in the "Fcst Mvmt" column was 270/33, the
cell would be moving toward the east at 33 knots.
The movement is calculated from the centeroid of each storm cell, and
uses each cell's history. A centeroid can be determined from the
"Az/Ran" output, which is also plotted on the radar image, if desired
by the user, and is the base of the projected path.
In the event that a storm cell has just developed, and is identified by
radar, the word "New" may be displayed for the forecasted movement
because not enough data is present for the radar's algorithm to detect
where it is headed. Developing thunderstorms can often have unusual
paths since the radar's algorithm sometimes misinterprets cell
development as movement.
Squall lines may have several forecasted paths. With luck, they will
all be moving at around the same pace in the same general direction. If
not, take an average. It is a very good practice to take an
average of the various speeds and directions coming from the different
storm cells on radar. Thunderstorm cells that have been in existence
the longest tend to have the best projected paths. Try to rule out any
odd and abnormal paths if possible. Odd paths are often adjusted by the
radar between runs to be more accurate. Be careful though, as cells
moving in front of a squall line can often deviate from the movement of
the line. This situation, along with several others, makes the job of
radar operators difficult at times, especially when they are trying to
issue advanced storm warnings. Nonetheless, always heed National
Weather Service warnings, which are issued by experts, to seek shelter
immediately.
CLOSE
WINDOW
Jordan Gerth,
May 2007