Coastal Dry, Inland Wet: The Western Seesaw Precipitation Anomaly Doesn't End

With all the talk of drought lately, a critical subtly is often missed by the media and others.

While the coastal regions, west of the Cascade and Sierra Crests have been far drier than normal, it has been moister than normal to the east.  

Let's go to the data to show what I mean.   The maps below will show you the difference from normal (the anomaly) of precipitation over the western U.S. for different periods;  these graphics are available from the Western Region Climate Center in Reno, NV.

For the past month (below), western Washington has been ground zero for dry conditions, with western Oregon being right behind.  But the situation changes radically over eastern Washington and Oregon, with many areas wetter than normal.  Head to Nevada, southern Idaho, and Utah:   it is downright moist. And east of the Rockies it is crazy wet.

But that is only  for the last 30 days you argue!  Fine.  How about the past 90 days?  (see below).  Very similar pattern with eastern WA with above normal precipitation.

Still not convinced that something is going on?  Let's check out the last 6 months...basically, the same, except that the California dryness is more severe.

One year?  Same thing.

So to properly understand our current water situationm the potential for wildfires this summer, and regional agricultural impacts, one must appreciate that the Cascade crest has separated two different regimes:  far dryer than normal over western Washington and Oregon, and wetter than normal to the east.  

Thus, it is important that folks in Seattle or Portland, mourning their desiccated gardens and browning grass, don't assume that the same is happened to the east.    And it is doubly important that our media and politicians don't make that assumption as well.

You can tell that mother nature knows the correct story in several ways.  Take wildfires.  We have been told by several media sources that wildfires would hit hard and early this year.  Some even said we were in a TINDERBOMB situation.  Well, we are well into June-- what has the wildfire season been like this year? Much worst than normal?

Well, let's look at the official U.S. government numbers from the National Interagency Fire Center (see below), which show the number of fires and the number of acres burned from January 1 until now (6/12/15 shown) for the entire country. The western U.S. dominates these statistics. This year 502, 254 acres have burned, the third lowest during the past 11 years, and 1/3 of the average for the previous ten years.  Only one fire is burning in the Northwest (a small fire of 103 acres that is not being extinguished--Thunder Creek in North Cascades National Park).  So much for a big, early start to the wildfire season.  It ain't happening.

We have had a huge amount of lightning and few fires during the last month.  Why?  Because the ground was too moist. And the moist conditions over eastern Washington have been very helpful to agriculture, reducing the need for irrigation from the rivers hit by the snowpack drought in the Cascades.

The question I am sure you are wondering about is: what about the future?   Will the west dry/east moist pattern continue?   We can turn to the NOAA/NWS Climate Forecast System model and check out the prediction for the next three months (see below, green and blue are wetter than normal, orange and red are drier).    The pattern is predicted to continue this summer.

Will there be new fires east of the Cascade crest?  There is little doubt the answer is yes.  There always are and warmer than normal conditions are predicted.  That will help dry things out, even if precipitation is normal.  And much of the precipitation east of the crest will be from thunderstorms, which often initiate wildfires.

The bottom line is that understanding the recent precipitation seesaw is very important, with large impacts on agriculture, wildfires, and other other major societal concerns.