The Driest Summer in Seattle's History

I am now entirely confident in this. We are going to break a major record in two days:

The driest summer in the history of observations at Seattle-Tacoma Airport.

And we are not simply going to beat the record, we are going to smash it.

Let me give you the numbers.   Logan Johnson, head of the NWS forecast office in Seattle, provided these number for the driest calendar summers (roughly June 21st-Sept 21st) at Seattle-Tacoma Airport:

1988 1.28"

1987 1.33"

2000 1.36"

1990 1.39"

Seattle-Tacoma Airport records go back to 1945-- so over 70 years!

As of noon today (Wednesday June 20th), Seattle-Tacoma Airport has received only .50 inches of rain. LESS THAN HALF of the previous summer record.  And most of the rain is over for a while.

According to the latest forecast model runs, it is possible that we could get a few sprinkles today, but nothing of any significance.   Here is the latest NWS SREF (short-range ensemble forecast) that show the cumulative precipitation prediction at Sea-Tac for a number of model runs starting 5 AM this morning.  No model run provides enough to threaten our record (most produce a few hundredths of an inch).

Folks--we have this in the bag....the driest calendar summer in Sea-Tac Airport history.  

Here is a plot of the observed (purple) and normal (blue line) precipitation at Sea-Tac.  We are about 3 inches behind for the summer!

Another way of appreciating our dry conditions is the following figure, showing the percent of average precipitation since June 21st.  Most of Washington State is below 25%, with some below 5% of normal.

Why have we have been so warm and dry this summer?  The same reason the eastern U.S. has been cool and wet:  an anomalous upper level wave pattern, with high pressure over the west and low pressure over the east.   This is illustrated by the upper level height anomalies (difference from normal) for 500 hPa (about 18,000 ft) for the past 90 days.

The yellow/orange colors indicate higher than normal pressures/heights. Blue the opposite.

Some folks will get upset with me for saying this, but there is no reason to believe that such a pattern has anything to do with global warming.

from Cliff Mass Weather and Climate Blog http://ift.tt/2jLMUcH