question about upper air analysis charts

[Tim]

anyone know what the stations with the dotted circles around them mean?

[Matthew]

I was told that they are positions of reporting stations whose information has been excluded from the making of that particular chart.

In other words....just there to throw you off

Matt.

[FREEFALL]

I was told that they are positions of reporting stations whose information has been excluded from the making of that particular chart.

In other words....just there to throw you off

Matt.

To add a little more....the station's data that is circled was not used in the creation of the chart because it's data was way off of what was expected to be reported by said staion relative to surrounding stations.

[Tim]

any idea why the data would be so far off?

edited for clarity

[Changes in Latitudes]

There's a fair bit of reasons for erroneous upper air data. Poor soundings, equipment malfunctions both in the air and on the ground (radiosonde sensor failure, ground receiver failure), human error...etc. Sometimes the computer algorithms designed to filter out garbage data misinterpret certain parameters and toss out good data as well. The onus lies on both the observer and organizations like NCEP or Environment Canada to subjectively AND objectively filter out poor data. To be brief, it's quite a task.