Topic: Why do weather tracks change direction depending on radar??

[Daffypuck]

 This may be a dumb question, but why do storm tracks change direction when switching between radars? IOW, I look at one radar and it has the storm tracking due west. Then, when I switch to another radar that's 40 miles away, it has the same track tracking southwest. And I don't mean relative to the stations location, but literal direction.

[W3DRM]

Just a guess, but the angle of the beam used by the radars may be different so they are reporting returns from different parts of the storm. A radar further away but looking at the same angle will naturally get returns that are higher in altitude than one closer in. Within any given storm you will find many different air current directions.

[kcidwx]

This may be a dumb question, but why do storm tracks change direction when switching between radars? IOW, I look at one radar and it has the storm tracking due west. Then, when I switch to another radar that's 40 miles away, it has the same track tracking southwest. And I don't mean relative to the stations location, but literal direction.

Are you observing this looking at the actual radar reflectivity or are you looking at storm track information that's overlayed on the radar?

[Daffypuck]

The overlay. One radar will show the track going over my city, but then an adjacent radar shows it completely bypassing me.

[BigOkie]

The overlay. One radar will show the track going over my city, but then an adjacent radar shows it completely bypassing me.

It's mainly all about beam angles and time differences as to when the storm tracks are computed.  You can't expect radar signal returns from two different locations to actually return an exact duplicate track, especially given that each radar site averages a distance of 240 NM from each other (if my memory serves me correctly).

[kcidwx]

What's been mentioned above is correct. The most important point being the data from two different sites can't be expected to be the same.

The radar uses SCIT or Storm Cell Identification Tracking which is a centroid type algorithm. SCIT doesn't handle tracking very well when cells merge or split. Since SCIT is a centroid type algorithm, there can be errors in storm movement if the storm changes in coverage or shape rapidly. Here's my crude drawing of what happens. Pardon my MS Paint skills 



Although the cell movement is east, the centroid has shifted to the bottom part of the cell. The radar will compare the last scan to the new scan and think, based on the centroid, that movement is towards the SE.