August 24, 2017

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) 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.


  1. Live 30 miles NE of Houston now. First 'cane since moving here in 2012. Luckily, our neighborhood is situated somewhat high for this area. Did not flood during TS Allison, so should be fine for this one. Nonetheless, it'll be quite an experience.

  2. One aspect of this summer, which has been positive but will soon be negative, is being drier than normal is closely related to lack of thunderstorms and fire starts. The few isolated cells that formed under some weak instability 2 weeks ago, nearly every lightning strike started a fire in my region.

    And those fires are slowly burning in wilderness areas and will not be put out anytime soon. So the combination of heavier fuels due to a wetter spring, and an incredibly dry and hotter summer, is setting the stage for an extended fire season. Fortunately, no matter how people define it, it's been a relatively quiet fire season when it comes to "forest" fires.

    But a huge western ridge predicted in the models for the next couple weeks, keeping my eye open to any southerly different flow that might pop off some dry convection. We could be setting ourselves up.

  3. Looks like an extraordinary hot spell for the Northwest is possible for the first week of September, if the latest medium range models pan out.500 MB heights in the 590's for an extended period!

  4. I can't stand this hot sunny weather anymore, I'm moving to Juneau.

  5. Buddy - "diffluent flow" not "different flow". Why is dryer than normal a "positive"? Regarding high pressure in the west, can you explain what you mean by "setting ourselves up"?

  6. John k
    Our summer rains are small and insignificant anyway. However those disturbances produce lightning, which starts fires.

    By us having a dry dome of high pressure for most of the summer we have had less fire starting lightning.

    Yep, a rainy spring made for lots of dry fuel, and it takes lightning (associated to rain) to ignite that dry fuel. So if small disturbances come before the onset of significant fall rain we could be setting ourselves up for lots of lightning induced fires this summer yet.

    So calm and dry = lucky

  7. Cliff Buddy? You said nothing about the European (ECMWF) model?? I was counting on you as I can't access it. They hit Hurricane Sandy on the money. What's they're call on Harvey?

  8. I don't know that many people in the PNW are "enjoying" the driest summer in over a hundred years. I love warm (hot) weather, but a complete lack of rainfall for months on end, bookended by months of saturation, is less than ideal.

    ~ Colleen

  9. It's flooding down in Texas, all of the telephone lines are down

  10. colleen, I am enjoying the heck out of this summer. the rains will can bet on it. until then, let it shine!!

  11. Fire Season is a bit below normal. Except for Canada so far it hasnt been a mega season. So far

    NIFC data below


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