Autumnal Influence and No Rain In Sight

This is the kind of period that makes local meteorologists feel a bit like the famed Maytag repairman---ready to go, but little to worry about.

Could be a NW meteorologist

 Western Washington has had virtually no precipitation during the past two months, less than a tenth of an inch in total, with dry conditions extending east of the Cascades as well.   During the past few days, temperatures have been near normal as a persistent influx of marine air kept the high temperatures around 70F.

But the sun is weakening and nighttime is getting longer, and the impacts on temperature are being seen.  Nighttime has lengthened from 8 to 12 hours since June. Nighttime temperatures are now dropping consistently into the 40s over much of the region (particularly away from the water and where they are less clouds) and some cool locations, particularly in mountain valleys or east of the Cascades in low spots, are heading down into the 20s.   Frost has returned to the Northwest!  Note that some ridge-top locations are still staying in the 50s.

Let me illustrate.  Here are the minimum temperatures last evening (as of 6 AM).  Dark greens (40s), light greens (50s), aquamarine (30s), light blue (20s).

 The thirties are nearly all east of the Cascade crest...here is the same figure only showing locations of 35 and below:

Will rain return?  Not in the near future.  The latest forecast models suggest a very weak frontal passage, mainly north of Washington, on Friday...perhaps a sprinkle along the coast and over southern B.C.   But then ANOTHER major ridge builds over the region.  Great weekend and the early portion of next week.

Take a look at the upper-level forecast for next Tuesday at 5 PM.  The coloring shows the anomaly (difference from normal) at this level (500 hPa--around 18,000 ft). Major positive anomaly (this means ridging) just off our coast.   Folks...this is a dry pattern for us.

 Looking at the North American ensemble forecast for Seattle shows the story over the next few weeks.  The second panel shows precipitation and the bars indicate the range of the ensembles (running of many forecasts).  Although a few ensembles suggest some very light rain, the overwhelming majority are dry.  This suggests little if any rain through the first week of October. 

Ideal weather for taking that fall hike in the mountains.