1. Meteorologists sometimes assess the stability of the lower troposphere (and thus the potential for thunderstorm development)...

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1. Meteorologists sometimes assess the stability of the lower troposphere (and thus the potential for thunderstorm development) by calculating simple indices that are based on the temperature and the amount of moisture at various levels in the atmosphere. One such stability index is the Total Totals Index(or TTI), which is computed as follows:

Total Totals Index = T850 + Td850 ? (2 ? T500)

Where:

T850 is the 850-mb air temperature,

Td850 is the 850-mb dew point, and

T500 is the 500-mb air temperature.

(all temperatures are in ?C).

Note how warm, moist air at low levels increases the value of the index (low levels are represented by the 850-mb level). Also note that the colder the air at middle levels of the troposphere (midlevels are represented by the 500-mb level in the equation), the larger the value of the index. The effect of cold air at middle levels on the Total Totals Index can be seen by realizing that 500-mb temperatures are typically below zero on the Celsius scale; thus, T500 is usually negative, and subtracting a negative number creates a positive number, increasing the index. Thus, the Total Totals Index is large when warm, moist, low-level air underlies cold air at midlevels. East of the Rocky Mountains, the value of the Total Totals Index can be interpreted in Table 10.1 below:

Table 10.1

Total Totals Index Thunderstorm Outlook

44?45 Isolated or few thunderstorms

46?47 Scattered thunderstorms

48?49 Scattered thunderstorms, isolated severe thunderstorms

50?51 Scattered thunderstorms, few severe thunderstorms, isolated tornadoes

52?55 Scattered to numerous thunderstorms, few to scattered severe thunderstorms, few tornadoes

> 56 Numerous thunderstorms, scattered severe thunderstorms, scattered tornadoes

Consider the following temperature data (in ?C) observed on different days during the summer of 1995.

	850-mb Temperature (?C)	850-mb Dew Point (?C)	500-mb Temperature (?C)
Greensboro, North Carolina	12	11	-5
Little Rock, Arkansas	21	16	-5
West Palm Beach, Florida	19	18	-4
Peoria, Illinois	20	15	-9

Calculate the Total Totals Indexes for each city, and verify that the thunderstorm outlooks for each are:

Greensboro: Thunderstorms unlikely

Little Rock: Scattered thunderstorms

West Palm Beach: Isolated or few thunderstorms

Peoria: Scattered to numerous thunderstorms, few to scattered severe thunderstorms, few tornadoes

Show your work. Remember to follow the rules of algebra in your calculations -- always multiply & divide before adding and subtracting unless parentheses indicate otherwise.

TTI Data from:

A World of Weather: Fundamentals of Meteorology . Lee M. Grenci & Jon M. Nese. Kendall/Hunt Publishing.

2. Now that the Total Totals Index was introduced to you in Activity #1, and you?ve been able to do a check on its use and calculation from given data, choose a city near a low-pressure center, near a weather front, or one that is experiencing significant precipitation or under heavy cloudiness.

Calculate the Total Totals Index for that city.

Determine the thunderstorm outlook for your chosen city.

Include a copy of all weather products you used in your work. That includes any

surface weather maps, upper air weather maps, Stuve Diagrams, or radar precipitation maps.

Be sure to show your calculations.

(For the purposes of this exercise, whether you choose a city east or west of the Rockies, you may use the same table in Activity #1 to determine the thunderstorm outlook).

3. On the surface weather map, Figure 10.1, below, clearly indicate the location of Larko?s Triangle by shading in the appropriate region.

Figure 10.1

Lesson 10 Lab &