The First Heavy Rain Event of the Season

Everything is going to change on Friday.

You know change is in the air when the National Weather Service starts warning of clogged drains and gutters, and localized debris flows.

Consider the European Center model forecast for accumulated rainfall through Sunday at 5 PM (see below).  

Mama Mia!  2-4 inches in the mountains and .5-1 inch in the lowlands of Oregon and Washington.  Even eastern Washington gets some decent rain.


The UW model precipitation is similar. Note how regional extensive the rain is, including east of the Cascade crest. This is the storm we have been waiting for.


The heavy rain will occur mainly on Friday and early Saturday.  If you were planning on putting in some plants or planting grass seed.....this is the time to do it!

This rain will mark the end of the wildfire season in the Northwest, the remaining fires will rapidly decline with the massive moisture, high relative humidity, and MUCH lower temperatures, with highs dropping into the lower 60s.

Snow, YES SNOW, above 6000 ft.

The reason for this change is the development of a strong trough of low pressure over the northeast Pacific, with a powerful jet stream of strong winds to its south.  

Here is the forecast for roughly 30,000 ft at 11 AM on Friday.  The yellow colors show you the strong jet stream winds.... coming right into the Northwest.  Some as strong as 150 mph.   The solid lines are heights (think of them as pressure).  The low center is due west of British Columbia. 

This is a very favorable pattern for heavy rain in our region.


This jet stream of strong winds is associated with a very moist plume of moisture that will drive into our region and rise over the mountains, releasing huge quantities of water. 

To illustrate, here is a graphic for 11 AM Thursday showing something called Integrated Water Vapor Transport (IVT), a measure of how much water vapor is being moved horizontally by the winds.  Blue indicates very high values.  Just drop a mention of IVT when talking to your friends...they will be impressed.


And the latest forecast model runs have a lot more coming after this.  If you were Noah, you would know what to do (see below).    Ironically, with all the talk of drought, our region could end up with near-normal summer and annual rainfall total before the month is over.  The water is well-timed for the upcoming salmon spawning season.




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