Inflows and Outflows
Learning Goal 10b: Describe how inflow and outflow winds work in a
coastal inlet
While synoptic weather (meaning large
scale regional weather) determines the general wind patterns in British
Columbia (BC),
local land features can create localized wind patterns. The west coast
of BC has numerous fjords and inlets reaching from the
coast to the interior. These inlets act like highways carrying winds to
and from the coast. These winds are known as inflows
and outflows.
An outflow
is when air flow out from the mountains via fjords and valleys toward
the water. An inflow is when
air from the water is flowing into the inlets, fjords and
valleys.
In summer
in fair weather, the daytime solar heating of the land and the
mountains combines to create sea-breezes and anabatic winds that flow
from the cool water toward the warmer land as an inflow. At night
in summer when the earth's surface cools by radiating energy to space,
the opposite happens where katabatic winds combine with land-breezes to
channel colder air from the cold land to ward the water as an outflow.
In winter,
cold arctic air masses sometimes move into the BC interior, creating
strong high pressure east of the coast-range mountains. But lower
pressure is often on the other side of the mountains, over the Pacific
coast. The resulting pressure difference pushes air from the
interior of BC through the valleys and fjords to the coastline as a
very strong winter outflow wind. The leading edge of
a strong outflow can bring clouds, rain, or even snow with it,
followed by clear skies. Details of summer and winter inflows and
outflows are described next.
Summer Inflows and Outflows
Inflows typically occur in the spring and summer, when summer
weather creates higher temperatures in the interior than on the coast.
The pressure gradient reverses, causing the air to rush from the coast
inland to the area of lower pressure. Although inflow winds are
useful for sailors and wind surfers to know about, they are not usually
strong. Outflow winds, on the other hand, can be stronger and
hazardous.
The inflow and outflow winds are often named by local towns in the
valley or fjord FROM where the wind first passes over the water.
Aside
(not testable): Traditional Names for Local Winds.
Recall from our homepage: “We acknowledge that the
UBC Point Grey
campus is situated on the traditional, ancestral and unceded territory
of the Musqueam People.”
The following message is from an English teacher
at a Vancouver
high school, the UBC Continuing Studies program, and a First Nation’s
advocate for reconciliation:
"My uncle taught me a long time ago when we were
fishing near his
home in Alert Bay about the Nimpish wind and how the Namgis people wait
for it to sail their longboats back, and always have. This is one
of those winds of which the ATSC 113 course speaks about. We are
from a different nation, but we respect other nations as well."
"The naming was done by the local First Nations,
and European
settlers named towns after these people when they began settling. "
"Thus, when we sail up the Salish Sea, we see the
local winds,
including the most famous Squamish winds. They were named as
winds by these nations, not after towns which were also named after
them, but as living entities under their beliefs, many thousands of
years ago."
"As the towns are colonial enterprises, it
suggests that is when
the naming occurred, and perhaps even less sensitive in nature, by whom
the naming was done."
"Perhaps the best way here is to also put these
names into the
appropriate language next to the anglicized version, using agreed upon
and well accepted First Nation terms:
Qualicum wind (in Pentlatch language):
Xwkwa’luxwum
Squamish wind (in Squamish Nechim - language):
Sḵwx̱wú7mesh "
"The Westerlies coming across the Salish Sea are from the Great Tyee of
the West, Sagalie to Coast Salish peoples. When they reach the
"battle ground" off Pt. Grey, they face the cold wind from the North
billowing down Howe Sound, the Sḵwx̱wú7mesh. Holmosom Rock off
Wreck Beach is the point where the Creator deemed the battle to
stop. To the West Sagalie is in command, to the East is the land
airs, of the upriver and upland peoples, and to the North it is the
Squamish which reverses track during its day."
"UBC campus is on Point Grey. The First Nations name for Point Grey is
Elḵsn. English sea captain George Vancouver named the headland on his
chart in 1792 after his friend, Captain George Grey."
"Pauline Johnson, the famous Canadian poet of the
late 19th and
early 20th century, wrote of the First Nations legend of Point Grey:
https://www.legendsofvancouver.net/point-grey-vancouver
"
Source:
Stephen Culhane, PhD
English Department, Templeton Secondary
UBC Continuing Studies and Faculty of Education (retired)
.
Howe Sound is a fjord that is immensely popular with kite surfers (https://en.wikipedia.org/wiki/Kitesurfing)
for its
inflows and outflows (see image below). In the summer, Howe Sound
typically sees outflows (called Squamish Winds because they come from
over the town of Squamish, BC)
over night and early in the morning, switching to an afternoon inflow.
This is because overnight, the air over the Coast Mountains cools and
becomes denser, falling through the mountains as a katabatic wind that
gets channeled into a mountain wind that then passes out through Howe
Sound. By about noon, however, the air over the BC interior will have
warmed up and lost density, pulling the winds in from the coast.
Inflows and Outflows through
Howe Sound, just
northwest of the city of Vancouver, BC. Source: Google Maps
annotated by S. James.
In summer, both the outflow and inflow winds can be
strong. Here is a video showing very strong inflow winds in
August.
Here is an example of an Environment Canada weather warning
(image
below, for a different year, not for the video linked above) for the
Howe Sound area for a late summer situation under sunny skies.
Note the dramatic switch from morning outflows to afternoon inflows
with stronger winds at the head of the channel.
The synoptic winds (meaning
the
larger-scale winds in the region) can also influence the strength of
local inflows or outflows in summer. Often in summer there is high
pressure and weak synoptic-scale winds over BC and the northeast
Pacific Ocean. When these light synoptic winds blow from the
south,
they can build the strength of the afternoon inflows. However, if the
synoptic winds are blowing from the north or northwest, they can
diminish the inflow and strengthen the outflow. (Check out the yacht
race video at the bottom of
the page if you want to see some fierce inflow winds in Howe Sound!)
Another unique local wind system is the Qualicum wind on
Vancouver
Island. When a high pressure ridge forms on the west side of Vancouver
Island, a southwesterly inflow funnels through Port Alberni Inlet,
across the island through a gap in the mountains, finally emerging as
strong outflow winds into the
Strait of Georgia. Winds just off
Qualicum Beach tend to be much higher than the surrounding areas during
an inflow, and while the larger winds might be blowing down the Strait
of Georgia from the north, strong westerly outflow winds will be
blowing off
Qualicum Beach. These outflow winds have sometimes torn apart the
log booms pulled by tugboats down the Georgia Strait, when the tugs
travel through the Qualicum outflow winds.
Qualicum winds in the figures
above and
below. Sources: top image Google Maps annotated by S.
James; bottom image: R. Stull, from MM5 weather forecast.
Winds (black arrow in the image above) are channeled from
the
Pacific Ocean past the towns of Bamfield and Port Alberni, finally
exiting Vancouver Island near the town of Qualicum (not shown, but it
is near the tip of the black arrow). Notice the Qualicum outflow
winds are 16-20 knots (yellow-orange coloured arrows) over the Georgia
Strait (near the center of the black oval), while the winds elsewhere
in the Georgia Strait are generally 2 to 8 knots.
When sailing, it is important to look at both local and
regional
wind conditions (see some of the weather resources below). Start with
the regional forecast, and then look at local conditions for where you
will be sailing. In Howe Sound, for instance, there are numerous kite
surfing wind forecasts that will tell you what the inflow will look
like that day. Or, you can try to figure it out yourself by looking at
the temperature gradient between Vancouver and Lillooet to determine
whether or not there is a big enough pressure differential to generate
an inflow that day. When sailing up the Strait of Georgia, check the
winds off Qualicum Beach and be aware that they could be abnormally
high.
Another thing sailors should be wary of is crossing the
inlet
mouths. Outflow winds can come whistling down the inlet, creating
strong winds and rough seas at the mouth, while seas might be calm and
quiet further along the coast.
Winter Outflows
In winter, when a cold Arctic airmass is over central
British
Columbia, a strong high pressure often forms at the earth's surface
under the cold air. However, warmer air with lower pressure is
often just off the BC coast, over the Pacific Ocean. The figure below
shows a February example. The brown lines are the isobars,
connecting points of equal pressure.
A stationary front (red and blue line) is along the Pacific
Coast
(thin black line), marking the dividing line between colder air over
land and warmer air over water. Higher pressure (H) is under the
cold air east of the Coast Range Mountains, while Lower pressure (L) is
associated with the warmer air over the ocean. The resulting
pressure gradient is in the direction of the green arrows, which are
perpendicular to the brown isobar lines.
Source: NOAA Ocean Prediction
Center, annotated by Stull. 24 Feb 2019
https://ocean.weather.gov/Pac_tab.shtml
The but Coast Range Mountains (see figure below) right along
the
coastline act as a dam trapping the cold air in the interior of BC,
except where there are holes in the dam associated with valleys and
fjords. The figure below shows the higher mountains in the darker
colours, and the lower fjords and valleys as white or lighter
greys. The pressure gradient pushes the cold air through these
fjords and valleys toward the straits, sounds, and coast, to create
very strong outflow winds.
The net result in British Columbia is that cold air rushes
out of
the valleys and fjords towards the west, where it can create jets of
fast moving air over the water, disrupt shipping, sailing, and ferry
crossings. The figure below show the faster winds in red, orange
and yellow, and the slower winds in blue and green. You can see
the red colors (25 - 30 knots winds) spreading down Howe Sound and into
the Georgia Strait
(also known as the Salish Sea). There are also outflow winds down
the Lower Fraser Valley that sweep across the Georgia Strait towards
the Gulf Islands (northeast of Victoria) and towards parts of
Washington (WA) state including the San Juan Islands (which are popular
sailing destinations in summer).
High resolution wind forecast
produced by the Weather Forecast Research Team, directed by R. Stull,
UBC. To see the outflow winds in more detail, here is a pdf of
the same event, which you can zoom in your pdf viewer.
To get a different perspective, the sketch below is the view
from over central BC looking southwest
across the Coast Range Mountains toward the Pacific Ocean. The
cold air rushing through the mountain gap creates gap winds that are
the strong outflow
winds over the ocean.
The winter example below, from February, shows an outflow
wind
WARNING for the Pacific central coast of British Columbia, where the
outflow warnings are circled. Notice that the winds in this
winter case are GALE warnings (with speeds up to 45 knots for this
case), which are stronger than the summer case that was shown above.
Source: Courtesy of
Environment and Climate Change Canada. https://weather.gc.ca/marine/
Additional Resources:
(non-required material)
Seasonal Weather and Local Effects – BC:
http://www.navcanada.ca/EN/media/Publications/Local%20Area%20Weather%20Manuals/LAWM-BC-4-EN.pdf
Wind Patterns in the Georgia Basin – the Salish
Sea:
http://depts.washington.edu/uwconf/2005psgb/2005proceedings/papers/E7_LANGE.pdf
Weather Talk for BC: http://wtfbc.ca/viewforum.php?f=11