The Hawaiian Special: All Aboard The Pineapple Express

Moderate rain on tap for tonight, with this HRRR radar simulation. You'll hear the rain pounding outside by 8 or 9 pm 

Moderate rain on tap for tonight, with this HRRR radar simulation. You'll hear the rain pounding outside by 8 or 9 pm 

Tonight, will be rainy I'll admit, but it's nothing like what's going to transpire this weekend.

Later this evening, a potent warm front will make it's way onshore from the SW, and it does have a little sub-tropical moisture contained in the system, so look for some moderate rainfall later this evening (nothing our storm drains can't handle). Just to our south, Seattle has accumulated over 60 mm of rain so far today, just shy of a daily record, as of now.

The next event is looking very interesting for this weekend, and it's worth mentioning now. I won't discuss freezing levels much as of yet, but 2000 + metres for at least 24 hours this weekend is a good estimate for now.

First, a definition is an excellent starting point.

Wikipedia Definition:

Pineapple Express is a non-technical term for a meteorological phenomenon characterized by a strong and persistent flow of atmospheric moisture and associated with heavy precipitation from the waters adjacent to the Hawaiian Islands and extending to any location along the Pacific coast of North America. A Pineapple Express is an example of an atmospheric river, which is a more general term for such narrow corridors of enhanced water vapor transport at mid-latitudes around the world.

For Precipitable water values anything over 1-1.5 inches is significant. You can think of precipitable water as taking a column of the atmosphere and 'wringing it out' and all the moisture that falls to the surface is 'precipitable water"

For Precipitable water values anything over 1-1.5 inches is significant. You can think of precipitable water as taking a column of the atmosphere and 'wringing it out' and all the moisture that falls to the surface is 'precipitable water"

A quick little edit might make the concept a little easier to understand:

Pineapple Express.png

ll kidding aside, these type of atmospheric river events can bring heavy rains and high snow levels, and ultimately increase the risk of slope failure. 

Anyone who lived in Vancouver in November 2006 can tell you about the consequences of having an immense amount of rain in such a short amount of time. 

How abnormal are atmospheric rivers in March?

Abnormal, yes, but they can and do happen in late winter. 

Our friend climatology can help us out to find out how atypical this weekend will be.

See the purple shades? Huge anomaly compared to CFSR 1981-2010 reanalysis: or about 130 mm more than you would expect in an 'average March 5-11th time period

See the purple shades? Huge anomaly compared to CFSR 1981-2010 reanalysis: or about 130 mm more than you would expect in an 'average March 5-11th time period

#50ShadesofVan