I do believe we are in luck for tomorrow's tour. Approaching frontal conditions with light drizzle, moving into a southerly airflow could well create fall conditions.
In other words, migrants flying tonight will set off in nice warm air and clear skies hoping to make it as far north as possible. By mid-night they will start moving into cloud and rain, won't be too happy about that and will give up migrating- they will look for a suitable resting place and will wait for the rain to pass.
So the birding forecast tomorrow is: hopefully an interesting tern or gull, a scattering of common migrant land birds, an influx of hirundines and maybe an interesting wader or two.