Pineapple Express Brings MoistureTo West Coast
Much Needed Rain Seen In California, Impacts Plains Too
It’s been in the news lately for bringing much needed rain to the west, especially to parts of California where most of the state is suffering some form of a drought. It’s called the Pineapple Express but you won’t see Seth Rogen or James Franco in it. So what is the Pineapple Express and how does it affect us in the Northern Plains?
The Pineapple Express is actually part of the polar jet, it’s a southern branch of it. A high pressure system that is located in the Gulf of Alaska blocks the polar jet but during the winter it weakens. As a result, the polar jet sometimes forms a southerly branch, which is better known as the Pineapple Express. This southerly branch typically is located just north of the Hawaiian Islands and brings moisture westward from as far as Asia. Much like how low pressure systems move across land, low pressure systems ride along the jet and bring heavy rain to the west coast. These heavy rains occur, typically, over the course of days but, sometimes, it can last for longer than a week.
Pineapple Express seen at 250mb
Systems riding along the Pineapple Express
The same high pressure that causes the Pineapple Express to form, when stronger, deflects most systems from bringing rain to the west coast. Acting like a force field, weaker low pressure systems ride along the edge of the high and impact central portions of the United States. That is, until the high weakens.
Going on for almost 4 years, California has been suffering one of the most severe droughts in its history. In short, it’s thanks to the driest January on record and the warmest year on record in 2014. Though the state would need 150% of its average rainfall to recover, the Pineapple Express has brought some much needed rain and will continue too as well… but the drought is far from over.
Drought Status of West Coast
Precipitation Amount Over Last 7 Days
While much of the moisture will impact the west coast, some will be brought over the Rockies and impact us, here in the Plains. It won’t be nearly as much as on the west coast, but the powerful winds in the jet stream will continue to move systems at the surface, which will carry the moisture northeast to the Northern Plains. Our next chance for rain will return on Tuesday.
Precipitable Water as of 3pm Sunday, Feb 8th
Precipitable Water Forecasted At 12pm, Feb 9th
So the next time you hear Pineapple Express on TV, you won’t be confused and think of Seth Rogen and James Franco. Instead, you’ll know that it’s a very important meteorological phenomenon that will help bring much needed rain to the west coast, with some making it as far north to us.