Meteorology 302.01, Spring 2004
Class Notes for February 13, 2004

Anya Givental & Mara La Verne

Assignments:

Sheets and Williams: Preface; Chapter 1

Williams, Up through Page 36; 63-71; Chapter 9, 139-147; Chapter 12

Homework Assignment #1 Distributed Friday 2/13/04, Due Friday 2/20/04

Review for Homework #1:

1. Surface Weather Map

• Upper left corner measurement represents current temperature in Fahrenheit.
• Lower left corner measurement represents current due point temperature in Fahrenheit.
• Relative humidity is 100% at the surface if temperature and due point temperature are the same. Closer the two measurements are, higher the relative humidity. Warmer the due point temperature, higher the water vapor concentration.
• Upper right corner number represents current atmospheric pressure. This number is encoded. To convert to actual measurement we need to add a decimal point between second and third digits, and write down 10 or 9 in front of the number, depending on the number, so the final pressure measurement is between 960.0 and 1050.0 mb. For example, 893 would become 989.3 mb, 186 would become 1018.6 mb.
• Time is shown in Standard Greenwich Time. Standard Pacific Time equals to Standard Greenwich Time minus 8 hours. For example, 14Z 18 FEB 04 is 6 am Standard Pacific on February 18, 2004.

2. Convective Outlook

· Convective outlook map shows regions of the United Stated where thunderstorms are predicted.

· Inside the brown lines is the region, where thunderstorms are predicted.

· Inside the green lines is the region, where slight severe thunderstorms are predicted.

· Inside the yellow lines is the region, where moderate severe thunderstorms are predicted.

3. Visible vs. Infrared images

• Visible image can be taken only during the day. It shows reflected light from the clouds. On the visible image the kind of clouds can not be seen.
• Infrared image is not a picture but a colored image representing temperature of the surface. Cumulonimbus clouds, that produce rain and thunderstorms, are very high, and therefore their surface temperature is very cold (about -50 Celsius). These clouds are shown in color on the infrared image. By using both, infrared and visible images, it can be inferred where the cumulonimbus clouds are present.
• With the infrared image, the clouds that have cold tops, are the one’s who are going to have storms (green are expected to get thunderstorms)

Pressure:

• Air flows from high pressure to low pressure, unless there are some other factors present.
• Low pressure is usually labeled “Low” or “L” in red color.
• High pressure is usually labeled “High” or “H” in blue color.
• Atmospheric pressure ranges from 960mb-1050mb. The pressure would be to low if it fell below 960mb and too high if it was above 1050mb
• Iso Bars – They’re in 4mb intervals and non go below 1000mb
• Air moves locally from higher pressure to lower pressure to equal out the pressure

Wind:

• Wind is created by air flow from high pressure to low pressure. Higher the difference between pressure in two places, higher the wind.
• Sometimes other factors create violation to the general rule, and it appears that air flows towards high pressure. Western part of the United States (Rocky Mountains) is often the playground for the violation of the rule, because of the mountain ranges. It appears that air flows towards high pressure area, but it really just taking a detour around mountain ranges to go from high pressure to low pressure. Appalachians are another area, where winds might appear to blow towards high pressure areas.

Latitude and Longitude:

• There’s different degrees that we use in this 0 degrees is the tropics, 22 ½ Degrees N is the Tropic of Cancer, 22 ½ Degrees S is the tropic of Capricorn
• On the Tropic of cancer or the tropic of Capricorn, the sun us directly above at a 90 degree angle on two different day, in the north on the tropic of cancer, it’s June 21 the summer solstice ( the first day of summer for us) and then on Dec. 21 the winter solstice (the first day of winter for us)
• Our location (San Francisco) on the globe is 37 ½ degrees N, 123 ½ degrees W