Collected%20Rules%20of%20Thumb

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Collected Rules of Thumb

• Edward J. Hopkins

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Rule of Thumb!Weather Systems move

• From West to East in midlatitudes
• From East to West in tropics

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Rules of Thumb

• Unsettled weather (clouds and precipitation) is
  typically associated with Low pressure systems !
• Relatively tranquil weather is usually found in
  the vicinity of high pressure systems.

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Rule of Thumb

• The tighter the packing of the isobars, the
  stronger the winds!

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Rules of Thumb

• Other things being equal
• Cloudy nights have higher temperatures than clear
  nights.
• Cloudy days have lower temperatures than clear
  days.

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Rule of thumb

• When
• Air temperature falls to within 2 to 3 Fahrenheit
  degrees of dewpoint and
• Winds are light
• Then
• Fog often forms.

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Rule of thumb

• If you can expect
• Clear skies
• Near Calm conditions
• Then
• The afternoon dewpoint provides a good predictor
  of the following mornings low temperature.

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Rules of ThumbFrom Table 16.5 (p. 391) Moran
Morgan (1997)

• At night, air temperatures will be lower if the
  sky were clear thin if the sky were
  cloud-covered.
• Clear skies, light winds and a fresh snow cover
  favor extreme radiative cooling and very low air
  temperature by dawn.
• Falling air pressure may indicate the approach of
  stormy weather, whereas rising air pressure
  suggests that fair weather is approaching.

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Rule of Thumb!Concerning large-scale high
pressure systems

• Highs are typically fair-weather systems
• Winds circulate in a clockwise outflow direction
  from a surface high

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Rule of Thumb!Concerning large-scale low
pressure systems

• Lows are typically stormy-weather systems
• Winds circulate in a counterclockwise inflow
  direction into a surface low

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Rule of Thumb!Concerning large-scale storm
systems in midlatitudes

• Systems typically move from west to east in
  midlatitudes.
• Southern storms produce more precipitation than
  northern storms.
• Weather on cold side of storm differs from
  weather on warm side of storm.

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Rule of Thumb!Concerning regional weather

• Cooling effects of sea (lake) breeze during