Saturday, August 8, 2015

Roller Coaster Weather

You've probably heard the old adage "If you don't like the weather, just wait a little while and it will change."  While that saying is undoubtedly over-used, this week it will be true.  The cause of this roller-coaster weather will be a large low pressure system that's currently off the BC coast.  Here's the 500mb pressure map Saturday morning:

You can see the low just west of British Columbia.  During the first half of this week, the low will very slowly move down the coast, reaching Northern California by Wednesday:

This will do a couple of things.  First, it allows the very hot ridge of high pressure that's currently over Texas to amplify over the center of the U.S.  The Inland Northwest will be on the western edge of this ridge, but still close enough to feel its effects.  Our temperatures are going to jump up in a major way, and quickly.  After are mild weekend, temperatures will warm about 8 degrees on Monday, and then another 5 on Tuesday and Wednesday.  The result is a very hot middle of the week.  Here's the current forecast:

The other thing this pattern will bring is thunderstorms.  The area between the off-shore low and the mid-US high will see persistent flow from the south.  This brings moisture with it, which will bring the potential for thunderstorms.  Initially, these will be rather isolated and won't have much rain with them.  Any lightning from them will have the potential to start new wildfires.  

By Thursday, the low will stop moving south and begin to "eject" back into the jet stream to our north.  As it does so, it will track directly over the Pacific NW.  Here's the forecast for Thursday afternoon:

This scenario is nearly a "classic" pattern for strong thunderstorms in our area.  The ingredients we look for are: 

  • Instability: The 3-day hot spell will do a good job of destabilizing the atmosphere.
  • Moisture: The southerly flow will bring up moisture from the south.
  • Lift: The strong low will supply the lift as it moves over our area.
The exact details are still too far out to get into.  So as we get closer to the potential event, we'll likely update this blog.  Suffice to say, if everything comes together just right, we could be looking at a significant thunderstorm event on Thursday afternoon/evening.

In its wake, the low will bring much cooler temperatures.  Here's the forecast high temperatures for Friday:

So, enjoy the roller-coaster ride this week.

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