A Bomb Cyclone Will Hit the Southern Oregon Coast

An explosively developing bomb-cyclone will hit the southern Oregon coast tomorrow, with hurricane-force wind gusts, towering waves, and lots of precipitation.

The term "meteorological bomb" is given to a midlatitude cyclone whose central pressure declines by more than 24 millibars (or 24 hPa) in 24 hours (there is a latitude dependence of the criterion, but this is close enough).  This storm is going to blow that criterion away.

Virtually all the models agree on this extraordinary strengthening, so confidence it quite high.  And there are some aspects of this storm that are very unusual. Let me show you the details.

The initial step in the development of the storm, a process called cyclogenesis, is occurring as I write this blog. The latest forecast for 4 PM today (below) shows an extremely weak initial development on a preexisting warm front, with the low pressure center being a very modest 1022 hPa (I put a blue oval around the developing storm in the weather map below, which shows pressure (solid lines), temperature (shading) and surface winds).

Fast forwarding to 3 AM, the low center pressure had deepened to 1009 hPa (13 hPa in 11 hours).

But now the storm is ready to explode.  By 10 AM Tuesday, the storm's central pressure had plummeted to 983 hPa (39 hPa in 18 hour!).   Well exceeding the requirements to become a bomb cyclone.

And as the storm makes landfall around 6 PM Tuesday, the storm is predicted to be around 980 hPa.  In fact, I am only showing you the medium resolution simulation (12-km grid spacing).  The higher resolution domains drop the pressure to around 978 hPa at landfall.   

Notice the HUGE pressure gradients (pressure differences) associated with the storm.  These will produce tremendous winds in the coastal zone and immediately offshore.  You see the blue colors?  That is cold air that will be streaming from the northwest at the same time, sucked to the southwest by the low pressure center.  In fact, the high pressure associated with the cold air is contributing to the strong pressure gradients and strong winds.

Talking about the winds, here is the wind gust forecast for 5 PM tomorrow (Tuesday).  Gusts to 70 knots (81 mph) to the west/southwest low center.  In the field, this is known as the "poisonous tale of the bent-back occlusion."   Repeat that to your friends...they will be impressed.

The strong winds will rev up substantial wave activity, reaching 11 meters (36 feet) along the coast.  Particularly impressive, considering short-duration of the winds from this fast moving storm.

And there is more, much more.  The storm will bring substantial precipitation from southern Oregon into northern California (see below), reaching 2-5 inches in the Sierra Nevada.  Not much in Washington.

And with cold air streaming in from the northeast, large amounts of snow will fall in the Oregon Cascades, the Siskiyou Mountains, and the Sierra Nevada.  In some places, several feet (see forecast of the total snowfall through noon Wednesday).  If you are planning on driving south from Oregon into California or across the Sierra Nevada, bring your chains.

The National Weather Service forecast summary for the region has almost every  type of warning imaginable, from high wind warnings, storm warnings, and winter weather warnings, to high surface warnings and more.

An unusual aspect of this storm is its track--from the west/northwest.  Most major cyclones this time of the years comes from the southwest.

Anyway, a major event--but what should we call it?  A day later, it could be the Thanksgiving Eve storm.  Will have to think about it....