Weather Maps
-The labels on a chart indicate the patterns of the isobars. If no label is present, the chart's information can be determined by the windspeed and how smooth the images are.
-Wind moves parallel to the contours, unless there are mountains in the way, which alters the wind patterns.
High Pressure Areas:
The air around the high in the Great Basin (1116, 1020, 1024) should be blowing clockwise and outward. In this case it doesn't work well because of the surrounding mountains. Physical obstacles are not exceptions to the rules of thumb. Instead, the air must blow around the mountains.-An anticyclone is encircled by one isobar.
-If air pressure is low, it must be moving inward and in a counterclockwise motion.
-Air moves from the direction that the arrows point.
-A warm front is shown on a weather map as a line with red semi-circles. A cold front is shown as a line with blue triangles. A dashed line shows a front that is still forming. The center of a low is where the warm and cold fronts meet.
-Two small dots are symbols for "light continuous rain".
-Weather radars are useful because they show weather everywhere, not just at the station where the reading is being taken from. Radar sends energy that is bounced back, sensing anything that is larger then a raindrop, but can't see clouds. Yellow on a radar map denotes torrential rain. Blue numbers refer to how high above the ground the rain is found.
-When temperture and dewpoint are the same, the relative humidity is one hundred percent.
-A wave cyclone, is a cyclone with fronts in it resembling a wave.
-The symbols "xx" on a weather map indicate "light snow".
-Air at the top of 4,000 feet is cooler then it is on the ground. Air moves to equalize the pressure difference. Air drifts from high to low pressure.
-Some Cumulonimbus clouds cause thunderstorms, some do not.
-Cirrus clouds are light and fluffy, cool clouds.
Discussion on winds:
Know differences between cyclones, anticyclone, ridges, and troughs
The question was raised, "What characteristics would you expect to find from air that is moving towards a Low pressure system." To answer this we used an example of a Low pressure system located in the Northern United States; therefore, the different air masses moving into the Low are warm/moist air from the Gulf and cold/dry air from the North.
Fronts
When you look at a weather map you would notice that the air really spirals out of surface highs and into lows. The reason for that has to do with the fact that earth is rotating. As the air moves from high to low pressure in a straight line (which you would notice from space), the earth turns out of its way. This creates the illusion that the air is spiraling (and that illusion is real to people on the earth's surface moving with the surface).
Often times, because air is in motion, we find contrasting masses of air clashing with each other on the weatehr map. Such clashes are marked by lines on the surface weather map called fronts.
A front is a boundary between a warm air mass and a cold air mass. A line is drawn to indicate the boundary. The polar front is the boundary between a polar air mass and a tropical air mass.
Symbols are used on the front line to indicate whether the line is moving or stationary. A stationary front line is indicated by blue triangles on one side of the line alternating with red semi-circles on the opposite side of the line. The triangles point away from the colder air while the semi-circles point away from the warmest air.
A cold front is a front that is moving in the direction of the warmer air. A cold front is indicated on the line by blue triangles pointing away from the colder air. A warm front is a front that is moving in the direction of the colder air. A warm front is indicated on the line by red semi-circles pointing away from the warmer air.
A wave cyclone in a region of low pressure completely encircled by an isobar. As the air moves counter clockwise and inward, a wave like form is created in the front.
Dry Adiabatic Lapse Rate:
when air moves up it expands, and compresses as it goes down.
When air moves up or down it experiences a change in temperature, 5 1/2 degrees F per thousand feet if moving from the mountains to sea level. Air sinking compresses and warms at this rate. That is why when the temperature in Reno is 44 degrees, the temperature in San Francisco is 72 degrees.
Advection Fog
-The water off the coast of California is so cold, because of upwelling adjacent to the coast due to the California current.
-As air drifts along the coast, the air is cooled to dewpoint by conduction, but only in the surface layer. This works up to an elevation of 4,000 feet.
-Fog along the coast extends inland, but does not make it into the Central Valley because it evaporates. Similiar as when air moves over warm mountains. Despite cooling, there are no clouds or rainfall in the Central Valley.
-Geography is more limiting to air flow then the temperture.
Fog is a cloud that has formed on the ground. This happens when air at the surface is cooled to its dew point. In the case of California's coastal fog, air over the ocean cools to its dew point and the resulting fog is blown typically toward the coast by persistent north or northwest winds.
This raises two questions: why does the air farther to the west over the ocean have lower relative humidity, and why does the wind blow so consistently from the west?
If we look at a map of typical summer sea surface temperatures off the California coast, we see that water temps just off shore run in the 50s, while farther to the west they climb into the 70s. Air to the west moving over the immediate coastal waters is thus cooled significantly, resulting in fog. The colder water is brought south by the California Current, a kind of "river" in the ocean that moves down from cold northern waters all year. The western coasts of all continents have similar cold currents just offshore, although in the southern hemisphere they flow rom the south rather than north.
The California Current is part of a large-scale clockwise circulation in the northern Pacific Ocean called the Pacific Gyre. This larger current relates to a large-scale clockwise wind circulation at the ocean surface. Similar patterns are found in other oceans, with clockwise circulations in the northern hemisphere and counterclockwise circulations in the southern hemisphere. Thus, when warm air moves over the cold California Current, it is cooled to its dew point and fog forms. The west winds blow it into the coast, but the fog usually is not deep enough to flow over the coastal mountains and therefore cannot penetrate farther inland. The exceptions are gaps like the Golden Gate. Here the fog can flow inland and can reach the Central Valley via the Carquinez Straits. The farther inland the fog moves, however, the more it heats up because the land is much warmer than the California Current. Thus it evaporates as it moves inland and the air temperature rises above the dew point.
As for the reason for the west winds along the coast, the explanation involves the distribution of atmospheric pressurein the eastern Pacific and western North America.
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