A Tie for the Driest Summer in Seattle History, While Texas Floods

Quite a precipitation contrast is occurring across the U.S.  

The Northwest is enjoying one of the driest summers on record, with Seattle destined to tie the all-time record low precipitation for July and August.

In contrast, an extraordinary precipitation event is about to occur in Texas, with Hurricane Harvey heading towards the Gulf Coast, bringing 15-25 inches in places over the next few days.

First, the situation here.   Since the rain event in mid-June, Seattle has had nearly no rain, with only .02 inches falling in July and August so far.

The plot of observed and normal precipitation at Sea-Tac Airport for the past 12 weeks shows the story (see below).  The observed rainfall (purple line) has been essentially flat-lined since mid-June.    Even with the heavy rain in June, we are now about 1.5 inches behind normal--not so much since the summers are so dry here.

The record low July-August precipitation was .02 inches in 1914 and .03 inches in 1967.  The latest model runs suggest no rain for the rest of the month.  Thus, it appears nearly certain that folks are now experiencing the driest summer (July-August) in over 100 years.

If one looks at the percentage of average precipitation for the last 60 days (below)...it looks really scary, with some locations getting less than 5% of normal in WA, OR, MT, ID, and CA.

Looking at the actual departure from normal in inches, the scare goes away--most of region is only down 1-2 inches, which is easily made up by slightly wetter month during fall and winter.

Fortunately, with a good snow pack last winter and lots of winter/spring rain, our water supplies are in good shape.

But if you REALLY want something scary, check out what is about to happen in Texas--perhaps the most damaging U.S. hurricane landfall in over a decade could happen later tomorrow....Hurricane Harvey.

Here is the latest precipitation forecast by the National Weather Service Weather Prediction Center.  Wow...over 20 inches in places.

Want to see an amazing contrast?    Here is the precipitation forecast from the NWS GFS model for the next 144 hr (6 days).  Over 25 inches in parts of Texas, with loads of folks getting more than 15  inches.  But nothing over most of Washington.  Next time a Texan jokes to you about the wet weather in Seattle, send them this image.

An interesting aspect of this storm is that the best NWS weather models don't agree on what will happen tomorrow and the next few days.

Here are some of the latest forecasts.  The left panel shows the tracks (purple is HWRF, the just replaced hurrican model and the green is HMON, the new NWS hurricane model).  Some other models are also shown like the Navy COAMPS (orange), and the operational GFS (blue line).   They all start the same, but some go left, some go right, and the some just hang around coastal Texas (which is very dangerous regarding flooding).

The lower right panel shows central pressure. HMON goes for 910 hPa, which is very low and would bring in a CAT 4 or 5 storm.  Catastrophic.  In contrast, HWRF is 940 hPa, 30 hPa weaker--perhaps a CAT 3 event.

Anyway, this is an extraordinarily serious hurricane that will bring a major storm surge along the coast, flooding, and wind damage.  No one should be on or near the Texas coast tomorrow.   The latest infrared satellite image is enough to put chills down the back of any coastal resident.  This will be a major test of the Trump administrator and his FEMA director--lets hope they are up to it.