The cause of Sunday's fog

SPRINGFIELD, Mass. (WWLP) - Fog isn't uncommon here in western Massachusetts, but fog that lasts through noon is quite rare.

"It's very difficult to drive and normally the fog comes when there's a lot of snow on the ground. It's the first time it's really come like this and it's fairly cold," said Miguel Hollander of West Springfield.

While there wasn't much snow on the ground in the lower Pioneer Valley, snow did have a role in bringing us fog on Sunday.

The fog on Sunday morning wasn't your typical river valley fog, but fog generated by going from cold one day to warm the next, called "advection fog."

This graphic demonstrates how this advection fog came to western Massachusetts.

While there wasn't much snow on the ground from Saturday, the ground was still cold.

As warm, moist air moved over that colder surface, the temperature of the warm air mass dropped...saturating the air.

That moisture condensed to a saturation point and formed widespread fog.

The fog brought visibility down to less than a quarter of a mile in downtown Springfield.

Drivers had to adjust to the different driving conditions and act accordingly.

"Go slow and don't put on the high beams on when it's nighttime and just pay attention and keep your eyes about you," said Linda Costa of Agawam.