WATCH: Ominous storm cloud engulfs Vancouver Friday evening

VANCOUVER, Wash. (KOIN) -- Stormy skies quickly raced over downtown Portland and took aim at Vancouver Friday evening.

A dark and ominous storm cloud quickly raced north across the Willamette Valley before soaking Vancouver with beneficial rain. Portland has already surpassed its average monthly rainfall for August in part due to Friday's wet weather.

This dark storm cloud that moved over Vancouver is known as a 'shelf cloud'. That's when heavy rain pulls cool air from the higher levels of the atmosphere down to the surface. As the cold air hits the ground, it moves in all different directions. As that cold air is pushed out, it forces warm and moist air up into the atmosphere. As the warm air moves vertically it then cools. That's when the dark ominous clouds form out in front of the storm.

The chance of heavy rain showers remains through the overnight hours around western Oregon and southwest Washington through Friday night.

Stay with the KOIN 6 Weather Team as summer heat is expected to build over the next week.