Rain

June has been very dry across the region.  Only .23" in Portland so far this month, with just 6 days to go.   

Month Climate Rain Calendar Saturday Start

This is our 5th consecutive drier-than-average June and most of the Pacific Northwest has been dry.

precipanomaly

But I see some hefty showers Wednesday-Friday, especially west of and over the Cascades.  What's up?

A cool upper-level low is dropping down the Canadian coastline right now, and it arrives offshore by Wednesday morning. 

wrf_500_wed

A couple points.  First, this isn't quite as cold as the low that brought Timberline snow this past weekend.  The other is that as it approaches the upper-level flow turns southerly plus the airmass moistens up.  That begins tomorrow afternoon.  There are hints that some showers and/or thundershowers pop up across the region.  I think that's most likely over the Cascades but can't rule out a brief shower over the western valleys for your Tuesday afternoon.  Just keep an eye on the radar and sky tomorrow afternoon.

Far more likely is a three day period with widespread showers and embedded thunderstorms Wednesday through Friday.  By Thursday morning that upper-low is directly overhead = pretty good lifting. 

wrf_500_thu_pm

This pattern in June is typically a very good rain producer.   By the time it leaves the area Saturday, the "new and improved" GFS (American) model gives us a nice soaking.  Maybe 1/2" or more in the valleys and over an inch in the mountains.  Even a little in Eastern Oregon with thunderstorms.

gfs_totalprecip

The ECMWF is somewhat drier, sending less than 0.25" into most western valleys of Oregon.  

ecmwf_totalprecip

Both models shut off just about all the showers after Friday once the low moves to the north.  You can see it on the 24hr rainfall forecast from ECMWF ensembles.  Just about all the "rain action" is going to be Wednesday through early Saturday.  

ecmwf-KPDX-indiv_qpf_24-1377600

To summarize

  1. Expect a cool, wet, & breezy period Wednesday through Friday
  2. Water sports won't be pleasant Wednesday-Saturday...chilly!
  3. Thunderstorms are possible any of those days; could be a situation where you get 1/2" of rain at your home and 5 miles away it's sunny at the same time.  Think spring weather.
  4. At best we'll see up to 1" of rain in a few lowland locations by the time July rolls around a week from now.  At worst, just a quarter inch of rain to wet only the top of the soil.
  5. Regardless, this puts the beginning of fire season off for another week or two.  No major fire worries until the 1st or 2nd week of July.

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