Weather of the San Francisco Bay Region
Weather: How to Observe and Predict
Weather of the San Francisco Bay Region by Harold Gilliam
- The weather funnel:
the San Francisco Bay region is the place of meeting and battling between the continental air masses and the oceanic air masses.
- The subdivided range: the complexity of the Coast Range, a double chain of mountains running NNW and SSE:
- The west range is the Santa Cruz Mountains (south of the Golden Gate) and the Marin Hills (north of the Golden Gate).
- The east range is the Berkeley Hills, paralleled to the east by the higher Diablo Range; to the north these extend
into the Sonoma, Mayacmas, and Vaca mountains.
- Microclimates: drier toward the east (away from Pacific Ocean); modified by bodies of waters (Bays, Deltas, rivers).
- The year:
- Spring: offshore Pacific High intensifies and moves closer to shore, strengthening onshore winds;
Ocean River of a strong southward moving surface current with upwelling of colder water;
Great Fog Bank where damp ocean-traveled air meets the cold upwelled water causing
- Summer: increase in features of Spring;
strong inland heating with rising convected air provokes strong west winds to replace the risen air;
multicycles in fog ebb and flow over periods from a few days (weekly cycle), during the day (daily cycle),
high fog (with an elevated fog floor).
- Autumn: decrease of features of Summer;
weather clears and warms by the coast,
- Winter: storms begin September or October;
normal frontal systems,
and occluded fronts develop;
wind directions experienced depend on whether the storm (wind flowing counter clockwise)
passes to the north or to the south or the area, or directly over;
the cold Polar Continental River of Air from the north competes with
the warm Tropical Pacific River of Air from the south
and the warm Tropical Gulf River of Air from the Gulf of Mexico.
- Concludes with:
- Is the Climate Changing? A rather dated look
- Reading list
Weather: How to Observe and Predict the Weather by Storm Dunlop
What a delightful book, showing you where the magic of predicting the weather comes from:
Simply learn that the forms of the clouds are telling you about current
and future weather.
The book's sections:
- Watching the sky.
"Clouds provide clues to weather patterns
and observing them can help you gain an overall understanding of the weather." [p.10]
"Watch the movement [of clouds] downwind.
This will give a much clearer idea [than watching upwind] of the actual wind direction." [p.10]
"When facing downwind in the northern hemisphere,
the surface wind is always further to the left than the wind at low cloud level." [p.11]
"An easy way to estimate angles is
to use your hand held at arm's length ...
1° = width of 1 finger
7° = width over top of first 4 knuckles
22° = width over spread fingers (thumb to little finger)." [p.14]
"Some approximate common angular sizes:
... 5° or more = width of
5° to 1° = width of
1° or less = width of
- Identifying clouds.
"If you spend a little time, ...
the different speeds at which the clouds move across the sky,
and their changing appearance,
enable you to sort out the different layers and types of clouds that are present."
- Clouds: three families:
- cumulus, 'fair-weather', or cumiliform clouds:
- stratus, 'dull-weather', or layer clouds can occur in patches or sky-wide:
- cirrus, feathery or hair-like clouds:
- Cloud species.
This is one of the most helpful sections, with its photographs that show each species.
Varieties of shape and form are grouped in 14 species that include Fractus (ragged shreds)
and Nebulosus (thin layer or veil without distinct features).
- Cloud varieties.
- Accessory clouds.
Clouds found in association with the
10 main cloud types.
- How clouds form.
- Sky colors.
- Cloud colors.
- Shadows and crepuscular rays.
- Optical phenomena.
- The global circulation.
- Satellite images.
- Weather situations.
- Severe weather.
- Observing weather.
- advection fog
formed by the horizontal movement of warm moist air over a colder surface
(such as upwelled deep cold ocean water).
- altocumulus (Ac).
- altostratus (As).
- High-pressure area from which air spreads out
and air in the center falls.
- Changing wind direction backward from the clockwise motion of the sun
from east to north to west to south to east.
- Beaufort wind scale
||Wind speed in Knots
||Wind speed in mph
||World Meteorological Organization Description
||Indicators on land
||Indicators on sea
||Smoke rises vertically.
||Small ripples on water surface.
||Small sailboat has just enough wind to steer by.
||Leaves rustle. You notice wind on your face. Wind vanes begin to move.
Flags stir and wave slightly.
||Small wavelets with unbroken glassy crests.
||Wind fills small boat's sails; sailboat travels 1-2 knots.
||Leaves and twigs move.
Light-weight flags extend.
||Crests start to break, putting some whitecaps on the wavelets.
||Sailboats heel; travel about 3-4 knots.
||Small branches move, raises dust, leaves and paper.
||Small waves develop, becoming longer, whitecaps.
||Sailboats carry all sail; good heel.
||Small trees sway.
||Whitecaps (white-crested wavelets) and spray form.
||Sailboats shorten sail.
||Large tree branches move. Telephone wires whistle. Umbrellas difficult to control.
Flags snap and beat.
||Larger waves, most with whitecaps; spray.
||Sailboats double-reef their mainsails.
||Large trees sway. Difficult to walk.
||Larger waves developing. White foam begins to be blown from breaking waves.
||Boats do not leave harbor; boats at sea heave too.
||Twigs and small branches break off. Difficulty walking.
||Moderately large waves; blown foam.
||Boats make for harbor.
||Large branches break from trees.
Slight damage to buildings; tiles and shingles blown off roofs.
||High waves, rolling seas, dense foam.
Visibility reduced by blowing spray.
||Trees blown over, broken, or uprooted; considerable building damage.
||Large waves with overhanging crests;
sea heavy and rolling and white with foam. Visibility reduced.
||Extensive and widespread damage to trees and buildings.
||Large waves , white foam, visibility greatly reduced.
|| Sea white with foam and driving spray; negligible visibility.
||The rest is silence.
- Cirrus clouds (Ci), in particular.
- Feathery or hair-like clouds in general,
including cirrostratus (Cs)
and cirrocumulus (Cc)
as well as cirrus (Ci).
- cirrocumulus (Cc).
- cirrostratus (Cs).
- Natural convection: bubbles of air move freely and vertically,
due to the buoyancy of warmer air above cooler air.
- Forced convection: eddies in the air cause mixing.
- Coriolis effect.
- Deflection caused by the rotation of the earth; an object moving
in a straight line is deflected clockwise (to the right) in the northern hemisphere;
in the southern hemisphere, it is deflected counter-clockwise (to the left).
- cumulonimbus (Cb).
- Tropical cyclone: a hurricane (self-sustaining tropical storm)
with both ascending and descending air currents.
- Extra-tropical cyclone; a depreesion; a low-pressure area where air in
the center rises.
- dew point
- The temperature where condensation into
occurs in cooling air.
- The process in which water turns into water vapor.
- High cloud.
- Bases above about 6 km. or 20,000 feet.
- The amount of invisible water vapor in the air.
When the air can hold no more water, it is saturated.
Then it condenses as
- Air is cold at the surface and warms at higher elevations.
This is the reverse of the normal decrease of temperature with elevation.
- Low cloud.
- Bases below about 2 km. or 6,500 feet.
- Medium-level cloud.
- Bases between about 2-to-6 km. or 6,500-to-20,000 feet.
- Region above the
- nimbostratus (Ns).
- stratocumulus (Sc).
- Region above the
troposphere (where temperature falls with height)
and below the
- Temperature rises with height,
mainly due to absortion of the sun's UV in the ozone of the stratosphere.
- Stratus clouds (St) in particular.
Layered clouds in general;
'dull-weather' or layer clouds that can occur in patches or sky-wide;
as well as
- Air rising because its temperature is higher
and density lower
than that of the surrounding air.
- Boundary between the
troposphere (below, where temperature falls with height)
stratosphere (above, where temperature rises with height).
- Higher at the equator (16-18 km.),
than the mid-latitudes (11-12 km.)
and the poles (8-9 km.).
- Sometimes seen in the limit of
where they are forced to spread out sideways as
- Lowest region of the atmosphere;
most clouds and weather occur here.
Temperature tends to descend about 6°C per km.
- Bounded at the top by the
- Changing wind direction in the clockwise motion of the sun
from east to south to west to north to east.
Trails of falling water droplets or ice crystals
falling from clouds and evaporating in the sky.
Their trails are often curved, as the droplets slow down as they descend and evaporate.
Forest and Tree Home,
© 2007-2011 by J. Zimmerman.
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