Monday, July 15, 2019

A wet week during the driest time of the year

We are now entering the climatologically driest time of the year for our region, a period when it is not unusual to get no precipitation for weeks.

But not this year.  It is now raining in parts of our region and that is just a preamble to the rainy period in front of us. 

To put it a different way, more JAWS (July Abnormally Wet Systems) will be making landfall on our coast.

Just to give you some perspective, here is the annual climatology of precipitation at Sea Tac Airport--specifically, the probability of getting .01 inches in a day.  During the next few days it will drop to around 10% ..or even a bit lower.  July 29th is typically  the driest day of the year, so if you are planning an outdoor activity (like a wedding or barbecue), THAT is best day to do so. (I know this is short notice if you were planning to tie the knot)

But our golden end of July won't be so golden this  year.    Rain moved in this morning, mainly south of Seattle, as evident from the weather radar, and some of it is heavy.

Weather radar image at 7:30AM Monday

And this is just the start.  Let me show you the predicted 24-h precipitation total during the next week.

The 24-h ending ending 5 PM today (Monday)-- rain over the coast, with light stuff from Seattle south.

The next 24h (ending 5 PM Tuesday) shows light stuff over western WA, but more  more over Idaho and Alberta.

Now you need the JAWS music.  Below is the 24-h ending 5 PM Wednesday, showing moderate rain hitting BC and northwest Washington.   Nice wetting over the Olympics and north Cascades.

And on Thursday, the heavier stuff moved down the Cascades to Portland.

And even more rain over BC and NW Washington on Friday.

 Now you really want to be impressed?  Here is the total accumulation through 5 PM Saturday. British Columbia will be soggy with substantial rainfall in the mountains, and western WA, particularly in the mountains, will get enough to wet things down.  Puget Sound will be a bit rainshadowed by the Olympics.

The implications of all this?   The wildfire threat in British Columbia has been low and will remain low.   There is a good chance we will escape the BC smoke this summer, which was the main source of our smoke last year.  The clouds and rain will make our wildfire season shorter and of less intensity.  It will reduce our water use and help bring up our streams, particularly in areas in which they have been low (like the Olympic Peninsula).   With this precipitation, our July totals will much higher than normal for virtually the whole region.

The latest extended forecasts (e.g., the NOAA/NWS CFSv2) do NOT indicate an unusually dry August (see below).  The bottom line:  after all the scary talk about a dry summer with catastrophic wildfires, it is becoming clear that such an apocalyptic scenario is becoming highly unlikely and you can enjoy the sunny days ahead without worry or concern.