Incessant heavy rain will pile into the Pacific Northwest, USA 🇺🇸 & British Columbia, Canada 🇨🇦 in the next 72 hours due to a significant atmospheric river event.
Flooding & landslides are highly likely. The atmospheric warmth & moisture can be traced all the way to the tropics.
A strong meander in the jet stream allows Alaska to cool under Arctic air but also helps lift Tropical warmth & moisture into British Columbia & the Pacific Northwest.
Notice how the atmospheric moisture aligns and focuses on the same area. This is like nature's firehose. Extreme rain and locally very high freezing levels expected. Meteorologists call this an atmospheric river.
Some refer to this atmospheric river as 'the Pineapple Express'.
A warmer atmosphere can hold more moisture. As the tropical air crashes into the terrain of North America, air is forced upwards and enhances rainfall amounts further.
This is called orographic lift.
Speaking of temperature...
The thermal contrast between Alaska and California is extremely impressive for November.
You can see the thunderstorms piling into the east coast of Sicily all day, wrapped around a broader circulation from a developing cyclone to the south.
Catania (home to over 500,000 people) was in the bullseye for near constant thunderstorms today.
Explosive cyclogenesis under a rip-roaring jet stream in the Pacific is about to bring extreme weather down the west coast of North America.
Nerd bit: I have contoured mean sea level pressure under the jet to show the text book interactions of the left-exit. Poetry in motion.
This is how the wind gusts look as the low pressure rapidly develops. The storm is likely to reach hurricane force out at sea with waves of 30-50 feet.
Nasty.
Large rainfall totals incoming as tropical moisture blasts along atmospheric river like a firehose.
Some relief for the extreme drought covering much of western USA.