On election night last year, there was an article published by the NY Times titled Don't be Fooled by Virginia which explained how the (unique) nature of Virginia reporting its results will inevitably result in the Republican candidate taking an early lead, only to be overtaken by the Democratic candidate near the end.
Nonetheless, if this trend persists, I would still avoid calling Virginia for the Democratic candidate until such time the Democratic candidate actually overtakes the Republican candidiate.
In the 2018 Senatorial race in Virginia, this normal pattern was broken, as Tim Kaine was projected as the winner as soon as the polls closed. Kaine won by 16%, so this isn't that surprising. However, if Biden wins Virginia by low double digits this year (and I think he has a strong chance of doing so), we could very well see the networks immediately calling the race for him when polls close.
