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Public Information Statement
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Public Information Statement
National Weather Service Seattle WA
230 PM PDT Tue Jun 20 2017

Summer Solstice 2017

Summer officially begins this evening, June 20th, at 9:24pm--when
the solstice occurs. In the Northern Hemisphere, the June Solstice
is that point in the Earths orbit when the 23 degree axial tilt of
the Earth leans the North Pole the most toward the sun.

At solar noon, the sun is directly overhead today along the Tropic
of Cancer (23.4 degrees north latitude). But here in Seattle (at
47.6 degrees north) the sun only gets up to about 66 degrees in the
sky at solar noon (90 degrees minus 47.6 degrees latitude plus the
23.4 degree solar declination). A plot of the position of the sun
shows that the height in the sky of the midday sun changes very
little for about a month around the solstice--this chart is called
an analemma (the chart looks like a figure eight).

In the Southern Hemisphere, the June Solstice marks the start of
winter. So it is no surprise that temperatures this afternoon in
Santiago and Buenos Aires are in the 50s, while Los Angeles will
have a high near 90 degrees. LA is around 34 degrees North, while
the two cities in South America are both close to 34 degrees South
latitude.

There is a seasonal lag of temperature and that means that the
warmest days of summer in Western Washington are probably still a
month away*. In general, the middle of July through August can be
considered Western Washington summerwith the driest and warmest
core of summer often being the last week of July and the first week
of August. The warmest temperature ever recorded at Sea-Tac was 103
degrees on July 29th, 2009but on average Seattle only gets a few
days in the 90s.

One key to summer weather in Western Washington is the strength and
position of the North Pacific Highwhich is centered between Seattle
and Hawaii. By mid-July, this high pressure system usually deflects
weather systems far to the north of Washington. The high wasnt yet
strong enough to keep a weak front out of the area today!

The cool cloudy weather today will give way to much warmer weather
for the end of the week. Highs in the 60s today are forecast to warm
well into the 80s for much of Western Washington for the weekend.

*A map of the U.S. that shows the warmest day of the year can be
found here:

www.ncdc.noaa.gov/sites/default/files/US-Warmest-Day-of-the-Year-
Map.jpg


$$
National Weather Service Weather Forecast Office
