Darkest Before the Dawn

The fourth of July should be a decent day across the Northwest...and the trendline is positive towards dry conditions and normal or above-normal temperatures.  This morning's visible satellite image (below) shows clear skies over Oregon and eastern WA, with some broken clouds over the west.  The radar is clear.

Yesterday was pretty exciting for July, with winds gusting to 20-40 mph and some power outages  (including my house in north Seattle).   For example, here are the winds at West Point (admittedly a well exposed site).  Gusts to 33 knots (38 mph).  Admittedly, not as strong as the East Coast derecho a few days ago (where winds gusted to 70-80 mph), but very strong for this season.

 And yesterday's precipitation totals were highly variable and in places quite respectable, particularly in the Puget Sound convergence zone area.  A few locations over the eastern foothills of the Cascades got an inch or more, while south of the convergence line (Seattle south) and over the Sound it was dry.

 Now that the worst is past, it is safe to tell you how bad it was:

(1) The -25.7 C 500 hPa  (roughly 18,000 ft) temperature at Quillayute WA yesterday morning, was the coldest in North America.  AND the coldest July 500 hPa temperature at Quillayute since -26.1 deg C was reported on 2 July 2000.

(2) A number of Washington locations experienced daily record precipitation records (record for that day) and several (particularly over northeastern WA) had MONTHLY record totals (e.g, Republic,
Colville, Boundary Dam, and Newport).  Several  locations had top 10 monthly totals.  Here is a summary from the Office of the WA State Climatologist (OWSC):

Here is the % of normal precipitation for the past 30 days.  Much of eastern Washington, northern Idaho, and the northern Willamette Valley had more than 200% of normal rainfall, and the rest of the region was at 100-200%.  Amazingly, parts of the Southwest U.S. and the intermountain west has received less than 5% of normal rainfall--extraordinary contrasts in such close proximity. 

An important issue with the precipitation and temperature pattern we have had the past few months is the impact it has had on soil moisture.   Take a look at the last soil moisture anomaly map (difference from climatology).  

Much wetter than normal over the NW (surprise!), but huge negative (dry) anomalies over the southwest and the central U.S.   Such dry anomalies have many bad implications:

 (1) enhanced change of wildfires over the southwest

 (2) damage to crop productivity in the U.S. grain belt

 (3) more severe heat waves in the dry areas.

Why do dry soils make the temperatures warm?   It turns out that a lot of the heat of the sun goes into evaporating water (going into latent heating) rather than warming the surface (sensible heating).   Thus, over a moist surface the surface temperatures don't warm as much, since a lot of the sun's energy is going into evaporating water.   Also moist surfaces and moisture evaporating from them promote clouds, which reflect solar radiation to space.  Thus, we can get into a positive feedback loop where heat produces dry conditions, which promotes more heat, etc.

But no such worries in the moist Pacific Northwest where our forlorn tomatoes finally will get the weather they deserve.