Sam Argier's Weather Blog

Posted: 9:34 a.m. Thursday, July 19, 2012

The cutoff low is the weatherman's woe 

Cutoff low on the water vapor satellite image.
Cutoff low on the water vapor satellite image.

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Low finally moves over Western Washington on Friday photo
Low finally moves over Western Washington on Friday

By Sam Argier

If you have been watching the weather forecast this week, you may have noticed a very persistent low pressure system that has been spinning to our south.  This water vapor satellite image shows the swirl off the Northern California coast this morning; that is the area of low pressure spinning in the upper levels of the atmosphere.     

Sure, we see our fair share of low pressure systems moving across the Pacific Northwest, but this one is different.  Is has been hanging out around Oregon and far Northern California since Monday!  Yes, it’s the infamous “cutoff low.” 

You may have heard of the cutoff low.  There is actually a saying that “the cutoff low is the weatherman’s woe.”  The woe comes from the fact that these systems can be unpredictable and are often difficult to forecast. 

This low pressure system is cutoff (hence the name) from the upper level winds of the jet stream.  The west to east winds of the jet stream are often referred to as the storm track because they guide disturbances our way.  They push a storm in from the west and eventually off to the east.  In the case of the cutoff low, those westerly winds are not in play.  A system can stall out with very little movement for several days, often bringing a prolonged cloudy and wet period around a region.  In our case, this low brought us some showers and a few thunderstorms on Tuesday.  We have not heard the last from it yet, it will pay us a closer visit over the next 24 hours.  

Low Moving Northeast

Even for a sluggish cutoff low, there comes a time when it will eventually leave.  For the past several days, there has been nothing coming through to push this system out.  Weather works on the bully system, meaning that whatever force is biggest and strongest will win out.  In the case of the weather pattern setting up over the coming days, a stronger trough is moving in off the Pacific Ocean.  This will give the relatively weaker cutoff low a kick in the pants, pushing it to the northeast over the next 24 hours.  The image above shows its track. 

It will make a pass over Western Washington on Friday, bringing scattered showers with the chance of thunderstorms tomorrow.  Temperatures will be dropping back into the upper 60s and low 70s.  That stronger low will be moving through this weekend, keeping us on the cool and cloudy side for mid-July standards.  Saturday brings morning clouds with partial afternoon clearing.  A few showers are expected along the coast.  Sunday will stay mainly cloudy with some showers looking to move in during the afternoon and evening.  Temperatures hold in the upper 60s and low 70s; well below the average high of 77 for this time of year.   

Have a great day! 

-Sam Argier, KIRO 7 Morning Meteorologist  

Sam Argier

About Sam Argier

Sam Argier is Chief Meteorologist at KIRO 7 Eyewitness News. You can catch his weather forecasts Monday through Friday from 5:00 p.

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