I'll repeat what I said earlier. If it was a 1st solo nav, it wasn't the day for it. Can I respectfully suggest that the best way to mitigate the risk would have been to wait for a better day? There's plenty of opportunity to fly in more marginal conditions both dual & solo later on. If I don't see a cloud base of 3,500', good vis and no sign of deteriorating weather, I won't send them 1st solo. Too conservative..? Maybe, maybe not.
Anywhere you can dig up a historical TAF/ARFOR?