My old starting problem has reoccurred a year later under the same conditions: car sat for a couple of days of thick fog and drizzle, then reluctantly started. Drove a couple of miles, shut down, then wouldn't restart. The lamba light is now on. I can't help but think that the high relative humidity has somehow condensed water and perhaps salt on the Mass Airflow Sensor and this has affected the starting process. MAS was replaced two years ago and car normally starts beautifully when in dryer conditions. As a Volvo owner for over 35 years I have never had a problem starting in a coastal maritime environment, except with the S70. I plan to take off the MAS and try to clean the inside with a Q-tip. Might also be a ground somewhere that's corroded and causes problems under exceptionally damp conditions. Any advice out there?

 

Try cleaning all connections.
Try to have the codes pulled and see where it leads you.

 

SOLUTION FOUND
I pulled the distributer cap and discovered burred edges on the contacts and the interior coated with a fine metallic dust. Obviously in such damp weather some moisture was infiltrating and causing shorting within the cap. With the burrs removed with the point of a slot screwdriver, the rotor sanded lightly and the interior cleaned the engine started fine. A temporary fix till I get a replacement.
Just a warning to those with similar problems: clean off the spark plug connectors and number them with a good indelible pen or tag them before removal - it won't start if you put the connectors back in the wrong order - and it's easy to do...