1. ATM OCN 100 (2) Fall 2001 1 Collected Rules of Thumb Edward J. Hopkins

2. ATM OCN 100 (2) Fall 2001 2 Rule of Thumb! Weather Systems move: u From West to East in midlatitudes u From East to West in tropics

3. ATM OCN 100 (2) Fall 2001 3 Rules of Thumb u Unsettled weather (clouds and precipitation) is typically associated with Low pressure systems ! u Relatively tranquil weather is usually found in the vicinity of high pressure systems.

4. ATM OCN 100 (2) Fall 2001 4 Rule of Thumb u The tighter the packing of the isobars, the stronger the winds!

5. ATM OCN 100 (2) Fall 2001 5 Rules of Thumb u Other things being equal: –Cloudy nights have higher temperatures than clear nights. –Cloudy days have lower temperatures than clear days.

6. ATM OCN 100 (2) Fall 2001 6 Rule of thumb u When: –Air temperature falls to within 2 to 3 Fahrenheit degrees of dewpoint and –Winds are light u Then: –Fog often forms.

7. ATM OCN 100 (2) Fall 2001 7 Rule of thumb u If you can expect –Clear skies –Near Calm conditions u Then: –The afternoon dewpoint provides a good predictor of the following morning’s low temperature.

8. ATM OCN 100 (2) Fall 2001 8 Rules of Thumb From Table 16.5 (p. 391) Moran & Morgan (1997) u At night, air temperatures will be lower if the sky were clear thin if the sky were cloud-covered. u Clear skies, light winds and a fresh snow cover favor extreme radiative cooling and very low air temperature by dawn. u Falling air pressure may indicate the approach of stormy weather, whereas rising air pressure suggests that fair weather is approaching.

9. ATM OCN 100 (2) Fall 2001 9 Rule of Thumb! Concerning large-scale high pressure systems: u Highs are typically fair-weather systems u Winds circulate in a clockwise outflow direction from a surface high

10. ATM OCN 100 (2) Fall 2001 10 Rule of Thumb! Concerning large-scale low pressure systems: u Lows are typically stormy- weather systems u Winds circulate in a counterclockwise inflow direction into a surface low

11. ATM OCN 100 (2) Fall 2001 11 Rule of Thumb! Concerning large-scale storm systems in midlatitudes: u Systems typically move from west to east in midlatitudes. u Southern storms produce more precipitation than northern storms. u Weather on cold side of storm differs from weather on warm side of storm.

12. ATM OCN 100 (2) Fall 2001 12 Rule of Thumb! Concerning regional weather: u Cooling effects of sea (lake) breeze during