Observing Weather

 

Note: Remember you are responsible for graphs, charts and other items that form part of the overall summary of this topic.

 

I) Observing Weather

A) Properties of the Atmosphere

1) Mixture of gases

(a) Nitrogen

(b) Oxygen

(c) Carbon dioxide

(d) Ozone

(e) Other trace gases

2) Reaches from Earth’s surface to edge of space

3) Resource

(a) Life

4) Protection

(a) Radiation

(b) Temperature extremes

5) Layers of atmosphere

(a) Troposphere

(1) Closest to ground

(b) Stratosphere

(1) Contains ozone

(i) Blocks harmful radiation

(c) Mesosphere

(1) Temperature decreases

(i) Coldest spot in atmosphere

(d) Thermosphere

(1) Warmed by ultraviolet light

(2) Ionosphere

(i) Region where molecules have absorbed so much ultraviolet energy they become ionized

B) Observing the Weather

1) Instruments

(a) Temperature

(1) Thermometer

(b) Wind

(1) Wind vane

(i) Direction

(2) Anemometer

(i) Speed

(c) Pressure

(1) Barometer

(d) Humidity

(1) Hygrometers

(i) Relative humidity

1. amount of water vapor in the air compared to the greatest amount the air can hold

(e) Cloud cover

(1) Measure as a percentage of the amount of sky covered by clouds

(f) Precipitation

(1) Precipitation gauge

(i) Rain, snow, hail, sleet

2) Other instruments

(a) Computers

(b) Radiosonde

(1) Measures weather conditions high above the ground

(c) Radar

(d) Satellites

C) Reading Weather Data and Weather Patterns

1) Isobars

(a) Lines connecting places of equal pressure

2) Isotherms

(a) Lines connecting places of equal temperature

3) Air Masses

(a) A large region of air with similar properties throughout

(1) Maritime Polar

(i) Cool and moist

(2) Continental Polar

(i) Cool and dry

(3) Maritime Tropical

(i) Warm and moist

(4) Continental Tropical

(i) Warm and dry

4) Fronts

(a) Boundary between two different air masses

(1) Cold front

(i) Cold air moves in, pushing warm air above it

(2) Warm front

(i) Warm air moves in, pushing out cold air

(3) Occluded front

(i) One cold front overtakes a warm front and joins with another cold front

(4) Stationary front

(i) Front that does not move

 

Characteristics of Cold Fronts

  • usually bring in cooler weather, clearing skies and a sharp change in wind direction
  • slope of a typical cold front is 1:100 (vertical to the horizontal)
  • tend to move faster than all other types of fronts
  • tend to be associated with the most violent weather
  • tend to move the farthest while maintaining their intensity
  • tend to be associated with cirrus well ahead of the front and a broad area of clouds immediately behind the front
  • fast moving fronts may be mostly clear behind the front
  • associated with squall lines (lines of strong thunderstorms parallel to and ahead of the front)
  • during winter, cold fronts move into Oklahoma mainly from the Canadian prairies but sometimes from the Artic Circle or the eastern Pacific

Characteristics of Warm Fronts

  • slope of a typical warm front is 1:200 (more gentle than a cold front)

  • tend to move slowly

  • typically less violent than cold fronts

  • although they can trigger thunderstorms, warm fronts more likely to be associated with large regions of gentle ascent, stratiform clouds and light to moderate continuous rain

  • usually preceded by cirrus first (1000 km ahead). then altostratus or alto cumulus (500 km ahead), then stratus and possibly fog

  • behind warm front, skies are relatively clear (but change gradually)

  • associated with a frontal inversion (warm air overrunning cooler air)

  • on weather map, warm front will be northeast of cold front and to the east of a surface low pressure area

  • clouds and precipitation prevalent to the north of the warm front (result from low-level southerly winds in the "warm sector" of the cyclone rise up and over the cooler, more dense air at the surface located north of the warm front.  This lifting leads to saturation, cloud formation and to some form of precipitation)

  • in Oklahoma, warm fronts are rare in the winter and non-existent in the summer

Characteristics of Occluded Fronts

  • indicative of mature storm systems (storm about to dissipate)

  • most common type of occlusion in North America is a cold-front occlusion (occurs when the cold front forces itself under the warm front; the weather ahead of the cold occlusion is similar to that of a warm front while that along and behind the cold occlusion is similar to that of a cold front

Characteristics of a Stationary Front

  • behaves like warm fronts, but are more quiet
  • winds on both sides of a stationary front are parallel to the front
  • typically form when polar air masses are modified significantly so as to lose their character
  • cold fronts which stall

 

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