Thursday, September 15, 2016

Weather changes are coming!

For those tired of this... changes are ahead!  We will have one last warm day on Friday, here are the forecast highs from the afternoon forecast issued today (9/15).

Most of the Inland Northwest has been drier than normal over the past couple months, with much needed rain on the way.  A strong jet stream will enter the region this weekend as the graphic below shows.
12z/15th GFS model depiction of 500mb height and 250mb wind speed 00z Sunday (5 PM PDT Saturday)

This system will tap into good moisture, see below.

00z GEFS Ensemble mean of Integrated Water Vapor Transport 00z Sunday (5 PM PDT Saturday)

See the yellow and brown shaded area off the Oregon and northern California coast?  This indicates a high amount of water vapor (moisture) with the winds transporting this moisture into the region.  This will produce rain on Saturday, and possibly into Sunday.  The westerly flow will result in enhanced lift along the Cascade crest and the Idaho Panhandle where the highest rain totals are expected.  Meanwhile downslope westerly winds off the Cascades into the Wenatchee area, Okanogan Valley, and Moses Lake area will produce much lighter totals.  

What are the models showing for rain totals?  Let's take a look.

12z/15th GFS, Canadian, NAM model 24 hour precipitation comparison ending 12z Sunday (5 AM PDT Sunday) 

The GFS (upper left), Canadian (upper right), and NAM (lower left) 24 hour rain totals ending 5 AM Sunday morning (9/18) are shown from the 12z model runs from September 15th.  The models suggest around 0.75-1.50" of rain near the Cascade crest, 0.25-0.50" with locally higher amounts for the Idaho Panhandle, with about 0.10-0.25" for most of eastern Washington.

After this models shows another opportunity for rain showers.  Here is what Monday looks like...

12z/15th GFS model depiction of 500mb height and 250mb wind speed 00z Tuesday (5 PM PDT Monday)

A low pressure system near the north tip of Vancouver Island with an enhanced jet stream still over the area.  Then for the middle of next week that low moves overhead for cool weather and a chance of showers.

12z/15th GFS model depiction of 500mb height and 250mb wind speed 18z Wednesday (11 AM PDT Wednesday)

The cool weather pattern may hang around through the end of next week.  Here are the 6-10 day temperature and precipitation outlooks issued by the Climate Prediction Center on September 15th.

Increased odds for cooler and wetter than normal September 21st through the 25th.
So enjoy Friday as weather changes are ahead.