I'll explain why I think total migration is more important than net migration. From Chris Briem via Twitter:
Biggest Pgh migration population loss is still to DC Metro. What about in the future? From Governing on DC economy: http://bit.ly/rBsOUf
There are some dark clouds on the DC metro area's horizon. By comparison, Pittsburgh looks great. People move from places of higher unemployment to places of lower unemployment. Massive job losses in NOVA could fuel an exodus to Pittsburgh.
The spread in unemployment rate is only part of the story. The employment picture is great in North Dakota, better than in Pennsylvania. Why won't the economically displaced go to Fargo instead of Pittsburgh? Chain migration. We go where we know.
Inmigration plus outmigration is a measure of the connectivity between two metros. If there is a reversal of fortune, you can predict where the new residents will come from by looking at the total migration picture. Net migration isn't predictive. It is a past performance metric. Furthermore, net migration is a lagging indicator (see mesofacts). I'd rather look at employment data.