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.


Jordan Gerth, May 2007