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Sunshine Analysis – Olympic Rain Shadow vs. Downtown Seattle
Our second study examines the month of November,
2010 and sunshine data from three different weather stations, one located in
Sequim, one in Port Angeles, and one in Seattle. As is common in the Pacific
Northwest, November was wet, cold, and stormy. Overall sunny days in Sequim were
down from 11 in October to 7
in November, and total recorded sunlight in Sequim was only 50% of the month of
October. Seattle fared even worse, recording only 41% of the sunlight recorded
in October. The complete
October report is also available.
Sequim was 1.27 times as
bright as Seattle; Port Angeles was 1.08 times as bright as Seattle.
Sequim recorded an
average of 1.02 hours of bright sun per day, compared to only .52 hours/day
in Seattle, and .68/day in Port Angeles.
Sequim recorded 7 mostly
sunny days, compared to 5 in Port Angeles, and only 3 in Seattle.
The Sequim site recorded 7
mostly sunny days, to Seattle's 3 mostly sunny days. Seattle had 6 dreary days,
compared to only 2 in Sequim, and 4 in Port Angeles.
Partly Sunny Days
Mostly Sunny Days
On average for the month, the
Sequim site had 1.02 hours of clear sunny skies per day, where as Seattle had
.52 hours. The Port Angeles site recorded .68 hours of clear sunny skies per day
on average. In terms of pure solar radiation, the Sequim site for the month
recorded 1.27 times as much overall solar radiation as
Seattle, and 1.17 times as much as the Port Angeles site.
Hours per Day Clear Sunny
Total Solar Radiation (Relative Multiplier)
Finally, let’s look at two stormy periods, a "Pineapple Express" event on November
1st, and an "Arctic Express" which blew in on the 21st and lasted till roughly the
During the Pineapple Express, Sequim recorded 2.13 times the solar
radiation of Seattle, showing that the rain shadow provided significant relief
from this soggy storm. However, the following Pineapple Express, which hit in
December soaked Sequim pretty well. See additional
blog post on this event.
During the "Arctic Express" period of Thanksgiving
week, which was a near blizzard along the NE Olympic Peninsula, Sequim
recorded 1.37 times the solar radiation of Seattle, while Port Angeles recorded
Seattle. The radiation charts are below.
Looking at just Sequim vs. Seattle, the brighter
days are clear, especially after the "main event" on Monday and Tuesday.
Comparing just Sequim to Port Angeles, it is clear
that the sunshine in the two locations is very similar.
In a dark and stormy "winter" month, rain
shadow areas recorded significantly more light than the urban Seattle area.
Port Angeles received some benefit from the
rain shadow, but not to the degree of Sequim.
are feeling you are living in a dreary neighborhood in the eastern Puget
Sound or Cascade foothills, take a road trip to the Olympic Rain Shadow, and
you will likely see *a lot* more light during the darker months and stormy
Full month radiation chart
This study was conducted by examining incident solar radiation. Solar radiation is measured in watts per square meter. This
measurement is directly related to illuminance, a measure of how much light
falls on a given area.
We used data
from three different weather stations.
The first station, the Sequim station,
is located on the roof of a single story home on Jamestown Beach Rd,
in Sequim, directly on the shores of the Strait of Juan de Fuca. This location
may be very close to the epicenter of the Olympic Rain Shadow. As with many
locations on the Dungeness plain in Sequim, this one is not shaded by tall
trees, nor does it have any hills affecting its exposure. When the sun rises in
the morning, it clears the horizon almost immediately as the areas to the south
and east are open water. When the sun sets in the evening, it sets to the west,
over the Dungeness plain, so stays above the horizon for quite some time. The
Sequim location uses a Davis Instruments Vantage Pro 2 with optional solar
sensor. This station measures solar radiation every 2 minutes and records the
average over 10 minutes.
The second station is in downtown Port Angeles, at
Lincoln High School. The school's Davis Instruments Vantage Pro2 Plus sensors
are mounted on the rooftop of the high school, about a mile southwest of
ferry dock to Victoria B.C. at an elevation of about 200 feet. There is excellent
exposure clockwise from northeast to southwest and good exposure for the other
directions. The sensors record solar radiation every five minutes. Special
thanks to Peter Alexander, his math classes, and
for the data and support..
The third station is atop the Atmospheric Sciences Department building of the University
of Washington, in the University District of Seattle. This seven story building
is not in the classical Olympic Rain Shadow area, but is still slightly shadowed
by the Olympics. Given that the sensor is located atop a tall building, this
location has ideal exposure and receives maximum solar radiation. This station records solar radiation
every minute. Data was retrieved by downloading public information from the
University of Washington’s Department of Atmospheric Sciences website.
For purposes of this study, skies were defined as follows:
“Clear Sunny” sensors record at least 60% of the maximum radiation possible
for that day of that year
“Bright” sensors record between 20% and 60% of the maximum radiation for
that day of that year
“Gray” sensors record between 50 w/m^2 and 20% of the maximum radiation
for that day of that year
“Dark Gray” sensors record between 1 and 49 w/m^2
Days were categorized as follows:
"Mostly Sunny Day" over ½ the day had at least “bright” skies, with at
least 22% of daylight hours “clear sunny”.
"Partly Sunny Day" over ½ the day had at least “bright” skies, but less
than 22% of daylight hours “clear sunny”.
"Overcast Day" over ½ the day had gray or dark gray skies, but at least
22% of daylight hours “gray”.
"Dreary Day" daylight hours predominately dark gray, with less then
22% of daylight hours “gray”.
aggregated, analyzed, and graphed using Microsoft Excel.