Introduction

In order to be able to predict the conditions of the atmosphere, the "weather," a meteorologist must first understand what is producing the current weather conditions. The meteorologist does this by obtaining a "picture" of the atmosphere based on value of certain weather elements. The elements used to describe the condition of the atmosphere are: air temperature at various levels up through the atmosphere; wind speed and direction at various levels; moisture content; presence of clouds, their type and altitude; whether it is raining, snowing, foggy, hazy, etc., or none of the "present weather" phenomena, pressure, etc..

To get the best "picture" of the atmosphere at a particular time, the value of various weather elements needs to be collected from as much of the atmosphere surrounding the whole earth as possible. Thus, tremendous amounts of data must be considered by a meteorologist when looking at the "picture" of the atmosphere. One way to display this data in an easy to understand format is to depict the distribution of the elements on maps, charts and diagrams. The objective of the use of these in meteorology is to represent the state of the atmosphere as a function of space, either at fixed intervals of time or at varying intervals of time. A three-dimensional representation drawn to scale would be the most accurate and natural form, but it would present numerous difficulties in plotting the weather elements at their proper location, and in interpreting the information.

 That part of the atmosphere with which meteorologists are most directly concerned is a thin spherical shell with lateral dimensions thousands of times its vertical depth. The United States measures roughly 13,860,000 feet from the east coast to the west coast along latitude 39N. The troposphere, the lowest layer of the atmosphere in which the greatest amount of "weather" occurs is, on the average, 11 kilometers (7 miles or 36,960 feet) thick. To depict the atmosphere over the United States in a three dimensional representation drawn to scale in which the horizontal length was 2 feet would require a vertical distance of only 0.00534 feet (0.064 inches). Not very practical!
Either:

  • the vertical distance must be greatly exaggerated in relation to the horizontal distance, or
  • a series of maps must be used, each of which represents conditions at a particular height or element: such as a pressure surface. These are what weather maps are used for.
Maps refer to a representation, usually on a flat, horizontal surface of the whole or part of an area; or a representation of a sphere or part of it. The term chart is defined as an outline map representing something in its geographical aspects. Not much difference! The term "map" is more commonly used to refer to land areas (as a road map) and the term "chart" is used to refer to oceanic areas (as a navigational chart). Meteorologists normally use the term "map" to refer to horizontal depictions regardless of whether the surface is continental, oceanic, or some level above the surface. To better understand the representations of observed weather elements or forecasted weather elements on a map and how those elements may relate to processes occurring in the atmosphere requires the meteorologist to know something about geography of the surface over which the atmosphere is moving. In fact, it is a good idea for everyone to know something of geography, especially in the region where they live. With this in mind, answer question 1.

Problem 1.
On your answer sheet, match the state names with their corresponding number on the map of the United States.

Record your answer on the answer sheet.

A "diagram" is defined as a line drawing made for mathematical or scientific purposes; a graphic design that explains rather than represents. Graphs typically are used to relate one element to another, or several other elements, or an element to altitude.

Typically a chart or map displays information in the horizontal direction; north-south and east-west, like a road map which shows you where to go.

Maps

Maps in meteorology are used to display the element characteristics of the atmosphere, as measured by individual stations, such that the stations are in the proper horizontal relationship to each other. The map then provides a means to analyze the measured elements so the meteorologist can understand the "picture" of the atmosphere.

Open the image sfc_sp.gif in the Atmo 202 folder.

This image shows the condition of the atmosphere as measured at or viewed from near ground level by a weather observer.

  • The circles represent the location of stations at which weather observers are measuring the elements of the atmosphere; temperature, humidity, wind speed, wind direction, etc.
    • The air temperature value measured at these stations are plotted to the upper-left of the station circle. For most of the world, the standard is to plot temperatures to the nearest tenth of a degree Celsius. In the United States, the National Weather Service plots temperature for its surface maps to the nearest whole degree Fahrenheit. The dew point is plotted, in degrees Fahrenheit, to the lower-left of the station circle.
    •  
    • Below the station circle are usually three numbers or three letters which identify the station from which the data was obtained. There are no station identifiers on this plot, but they are plotted on those maps on the map display in the hallway.
    • At the upper-right of the map is the date and time that the weather elements were observed. The time is listed in Universal Coordinated Time (UTC), which is also sometimes called Greenwich Mean Time (GMT) and which is also identified by the letter Z. This time is given according to a 24-hour clock and is the "local time" at Greenwich, England. Thus, 18Z means 1800Z, which means 6:00 p.m. in Greenwich, England.

Open the image timezone.gif in the Atmo 202 folder. As you can see from the table below, and this image, the local time in Texas (Central Standard Time) is 6 hours behind the local time in Greenwich, England, (UTC), unless Texas is on Daylight Saving Time, during which period the local time in Texas is only 5 hours behind Greenwich, England.

Table 1. Time Conversions
UTC to Local time Local time to UTC
UTC - 5 = Eastern Eastern + 5 = UTC
UTC - 6 = Central Central + 6 = UTC
UTC - 7 = Mountain Mountain + 7 = UTC
UTC - 8 = Pacific
(California & western Canada)
Pacific + 8 = UTC
(California & western Canada)
UTC - 9 = Alaska
(Some offset from timezone
longitude lines)
Alaska + 9 = UTC
(Some offset from timezone
longitude lines)
UTC - 10 = Hawaii-Aleutians
(Some offset from timezone
longitude lines)
Hawaii-Aleutians + 10 = UTC
(Some offset from timezone
longitude lines)
NOTE: During Daylight Saving Time,
add or subtract 1 less hour than indicated.

For more information on time and timezones, check out this site.

Problem 2.
What is the current date and local time in the Hawaii-Aleutian Standard Time zone according to the US Naval Observatory Master Clock?

Record your answer on the answer sheet.

Problem 3.
Assume that you are busy working on your Atmospheric Sciences Lab exercise at 8:00 p.m. this evening and you get an e-mail from a friend studying abroad in Tokyo, Japan. If we assume that the e-mail was delivered as soon as it was sent from Tokyo, what was the date and local time in Japan that your friend sent the message?

Record your answer on the answer sheet.


Problem 4.
On the first map you opened, sfc_sp.gif, find the southeast corner of Texas, next to Louisiana. The station just to its left is a data plot representing conditions at Beaumont. To the left of the plot for Beaumont is a plot representing George Bush (Houston) International Airport.

What is the temperature recorded at Houston?

Record your answer on your answer sheet.

Be certain to use the proper units.

What is the date and time, UTC, of this map?

Record the date and time on your answer sheet.

With just the air temperature values plotted, it is hard to see any pattern to the temperature of the near-ground air across Texas. However, if this temperature field is analyzed, then a pattern emerges.

Open the image, sfc_con_temp.gif in the Atmo 202 folder.

This map shows an analysis of temperatures across the United States, not just for Texas. The area between the analysis lines has been colored to aid in interpretation. This map has been analyzed at an interval of 5F degrees. NOTE: The analysis lines are the dividing lines between the colors and represent specific temperature values. The scale at the bottom shows the temperature value occurring at the dividing line between the colors. These temperature values are also plotted at some locations on the map.  

Problem 5.
According to the temperature analysis, sfc_con_temp.gif, where did the coldest temperatures occur in Texas at the time of this analysis?

What is the date and local time in Texas, (Central Standard Time or Daylight Saving Time, whichever is appropriate for today), for this analysis?

Record your answer on your answer sheet.

The lines drawn on the map are called isolines, or isopleths, which is a line along which the value of some element is everywhere the same. NOTE: In the temperature analysis, the isolines are the dividing lines between the different colors. The map which has these isopleth lines drawn is said to be isoplethed, or more commonly, to be analyzed or sometimes contoured.

It is very important for a meteorologist, especially those involved in synoptic meteorology and weather forecasting, to see "at a glance" how the various elements vary in two- and sometimes three-dimensional space. This plotted map represents a field of the variable (or element), and can be applied to any element which has a continuous distribution in at least two dimensions. Temperature and pressure are the two most common elements in meteorology to which this is done. Having an analyzed field to interpret is much preferable to having to interpret only the numbers, as in a table, from which these fields are drawn. However, since there are many elements which may be plotted on weather maps, and analyzed by such isopleth lines, specific names are given to the various kinds of isopleths. The following gives some of the more common isopleths used on weather maps.

Know these isopleth names.



Problem 6.
According to the temperature analysis, sfc_con_temp.gif, what is the value of the coldest isotherm drawn on the temperature analysis of the United States, Canada and Mexico? Record your answer on your answer sheet.


Problem 7.
What is the value of the warmest isotherm drawn on the temperature analysis of the United States, Canada and Mexico?

Record your answer on your answer sheet.

You can close the temperature analysis now.

Rules for Drawing Isopleths

For meteorologists throughout the world to be able to understand the analyzed maps developed in other counries, there must be guideline to analyzing data so one does not get lost in the forest of information plotted on weather maps. The procedure and guidelines for analyzing meteorological data on maps has been standardized and agreed upon by all nations which are members of the World Meteorological Organization. Following are some of these rules.
  1. An isopleth must pass through a station if the value for the element being analyzed for that station is exactly the same as the isopleth value. On weather maps, the value of the weather elements measured at the station is plotted around a small circle which represents the station. The isopleth, thus, should pass directly through the station circle if the station value and the isopleth are exactly the same. See the map below.
  2. Isopleths can only begin or end at the edge of the map, or in a region of the map where data does not exist, otherwise they must form a closed loop. If the map covered the whole globe, and data existed for all regions across the map, all isopleths would form closed loops on the map. See the map below.
  3. Isopleths separate values which are greater than the isopleth value from values which are lower than the isopleth value. Thus, when moving along an isopleth, all values greater than the isopleth should always be on one side of the isopleth and values lower than the isopleth should be on the other side of the isopleth.
  4. Isopleths never intersect each other or branch.
  5. Isopleths are drawn at equal incremental values determined by the element represented and must be drawn for all values between the highest value of data plotted and the lowest value of data plotted.
  6. When an isopleth passes between two stations, the isopleth should be drawn proportionally closer to the station whose plotted element value is closest to the value of the isopleth. See map below.

The following figure illustrates these rules. The numbers represent a value of some measured weather element; e.g. temperature. For the isopleth whose value 5, the isopleth is drawn at the location between stations where a value of 5 is most likely to occur, and through the station where the plotted value at the station is exactly the same as the isopleth value.

Helpful Hints for Drawing Isopleths

  1. Scan the map and note the location of the parameter being analyzed which has lowest values and also those which have the highest values. Begin by drawing the isopleths around these centers of low or high values and gradually work outward from these centers, drawing the next higher, or lower, isopleth until the map is completed.
  2. Sketch lightly with a soft lead pencil the orientation and spacing of the isopleths as a preliminary analysis. These Isopleths can be adjusted and darkened later. It is much easier to make corrections if an easily erasable pencil is first used.
  3. After lightly sketching the isopleths, look for any errors and correct them. Then smooth the isopleths. Isopleths generally do not have sharp bends. However, along weather fronts, isobars often show a kink toward higher pressure as it crosses the frontal zone.
Problem 8.
On your answer sheet is a field of values which represent temperatures. The temperature values are plotted to the upper-left of the station circle. Draw isotherms for every 5 degrees. Isotherms values should end in either a "0" or a "5."

Plotted Data on Weather Maps

As shown on the first figure you opened, the one with weather observation data plotted for Texas, weather plotting charts are printed with a small circle at the geographic location of the major reporting stations. The image below is the model for plotting surface data.

The station circle is shown as the circle with capital N in the center.

Stations are identified on the printed weather map by their assigned three-digit station number, or a three-letter identifier, next to (usually beneath) the station circle.

Meteorological data from the weather observation is plotted about the station circle in specified locations which must not be violated. If any mandatory plotted element is garbled, or partly missing, an "M" should be plotted in its place. Some data is not mandatory for reporting or plotting so if it is missing, the space for it is simply left blank and no "M" is plotted.

The surface data plotting model figure, shown again below, shows the location of data plotted about a station. The figure includes the location of data reported by ship stations as well as by land stations. The following defines the symbols of the data (as plotted on National Weather Service surface analyses) and indicates whether the data is mandatory or not.
"N" represents the Total Amount of Cloud Cover. Only a digit from 0 to 9 is reported for total amount of clouds. The symbol that these numbers represent is plotted in the middle of the station circle. The symbols are found below, and on table 2 in your manual under the column headed N. Total amount of cloud cover is a mandatory element.

"dd" represents the wind direction plotted as a shaft extending outward from the station circle in the direction from which the wind is blowing. When plotting the wind direction shaft, imagine the top of the circle is north and moving clockwise around the circle represents moving from 0o (at the top of the circle) through 90o to the right of the circle, which represents wind blowing from the east, then to 180o at the bottom of the circle, which represents wind blowing from the south, to 270o to the left of the circle, which represents wind blowing from the west and finally back to 360o, which represents wind blowing from the north. So, in the image to the right, the wind is shown (beginning at 0o) as blowing from the north, then northeast (45o), then east (90o), then southeast (135o), then south (180o), then southwest (225o), then west (270o), then northeast (315o), then north (360o).

The direction, North, is identified as a wind from 360 degree. A direction of zero degrees is used to represent calm winds. The wind direction shown in the Surface Plotting Model image is for a wind from 330 degrees. Wind direction is not a mandatory element.

"ff" represents the wind speed. Wind speed is plotted as barbs and/or flags extending from the wind direction shaft.
Each half barb equals 05 knot,;
a full barb equals 10 knots;
each flag equals 50 knots.
Barbs and flags should extend to the left of the shaft when looking along the shaft toward the station circle. Wind speed is a mandatory element if wind direction is reported. If wind direction is given but wind speed is missing, place an X at the end of the wind direction shaft rather than an M.
Winds which are calm (reported as 000 for wind direction and 02 or less for wind speed) are identified as calm by plotting a circle about the station circle. The figure to the right shows a circle (to represent calm winds) drawn around a station circle which is also indicating that 3/8ths of the sky is covered by clouds. 
 
"TTT" represents Air Temperature. Although the standard for most of the world is to plot air temperature to the nearest tenth of a degree Celsius, the National Weather Service plots air temperature to the nearest whole degree Fahrenheit. Air temperature is a mandatory element.
"VV" represents the Prevailing Visibility. In the United States, prevailing visibility is plotted in whole statute miles and/or fractions, just as it is reported. Visibility is an mandatory element.
"ww" represents Present Weather. A symbol is plotted which represents the type of present weather occurring. Each symbol is associated with a two-digit number which is reported in the weather observation message. Table 1 of Exercise 1 of your Laboratory Manual shows the symbols associated with each present weather number. Present weather is not a mandatory element.
"TdTdTd" represents Dew Point. The reported dew point is plotted in the same manner as air temperature, rounded to the nearest whole degree Fahrenheit for stations in the United States. Dew point is a mandatory element.
"Cl" represents the type of Low level Cloud. In the weather observation report, the type of cloud is reported as just a number. The symbol associated with the reported number is plotted. See table 2 in your Laboratory Manual for the symbols associated with each type of cloud reported. Low cloud type is not a mandatory element.
"Cm" represents the type of Middle level Cloud. The symbol for the middle level cloud type is plotted just above the station circle and the various symbols are found on table 2. Middle level cloud type is not a mandatory element.
"Ch" represents the type of High level Cloud. The symbol for the type of high level cloud is plotted just above the middle level cloud symbol. The various symbols are found on table 2. High level cloud type is not a mandatory element.
"PPP" represents the Sea-Level Pressure plotted in tens, units, and tenths of hectopascals (or millibars which is the same as a hectopascal). Sea-level pressure is a mandatory element. Sea-level pressure values generally fall between 950 and 1050 hectopascals. A pressure of 1012.5 hPa would be plotted as 125, without the decimal point. A pressure of 996.4 hPa would be plotted as 964. Since only the tens, units and tenths digits are plotted, then to decode the plotted values and obtain the actual sea-level pressure, either a 9 or a 10 must be prefixed to the plotted values and the decimal point placed between the middle and last digit of the plotted values. If prefixing a 9 to the plotted digits makes the result lower than 950.0 hectopascals, then you should prefix a 10 rather than a 9. If prefixing a 10 makes the result greater than 1050 hectopascals, then you should prefix a 9 rather than a 10. This works for most sea level pressure values.
"ppp" represents the Amount of Pressure Change that occurred during the last three hours at the station. The tens, units and tenths of hectopascals is plotted without the decimal point. Thus, a pressure change of 02.4 hPa would be plotted as 024. The amount of pressure change is plotted in conjunction with the pressure tendency symbol and both are mandatory elements.
"a" represents the Pressure Tendency, sometimes called the barometric trace characteristic. It shows how the pressure behaved during the past 3 hours. Look under the column labeled "a" on table 2 in exercise 1 of your Laboratory Manual. This shows the symbols to be used to indicate the pressure tendency. Notice that the symbols for numbers 0 to 3 all end at a higher point than they begin. This means that the sea-level pressure is now higher than it was 3 hour ago. Notice that the symbol for number 4 is a straight line. This means the pressure is now the same as it was 3 hours ago. Note, it may have increased, then decreased, or decreased, then increased, but it is now the same as 3 hours ago. For numbers 5 to 8, the symbol ends at a point lower than it began. This means the sea-level pressure is lower than 3 hours ago. When plotting the pressure tendency and amount of pressure change, the first symbol to the right of the station circle will be either a + (when using symbol 0, or 1, or 2, or 3), a blank (when using symbol 4), or a - (when using symbol 5, or 6, or 7, or 8). Next is plotted the amount of pressure change, ppp, with no decimal point. Next is plotted the pressure tendency symbol.
"W" represents the Past Weather, the weather that occurred during either the past 3 hours or the past 6 hours depending on the time of the observation. Look under the column labeled "W" on table 2 in exercise 1 of your Laboratory Manual. This shows the symbols to be used to indicate the past weather. Notice that the symbols follow a similar pattern as the symbols on the rows of table 1 for present weather. The plotting model provides for plotting the two most significant past weather events; however, past weather is not a mandatory element and there may be no past weather or only one type of past weather. if past weather is not reported, no symbol is plotted. If past weather is reported, the proper symbol is plotted to the lower right of the station circle.
The image to the right shows an example of surface data plotted about a station circle. The station shows winds from about 45o at 10 knots. The sky is overcast, (8/8 covered) with type 5 (stratocumulus) low clouds; type 2 (altostratus) mid clouds and type 8 (cirrostratus) high clouds. The temperature is 09oF (or C, depending on the station's location). The dew point is 07oF (or C). The present weather is type 58 (slight drizzle and rain). The visibility is 5 statute miles. The sea-level pressure is 1003.8 hPa and the pressure steadily decreased by 01.7 hPa from what it was 3 hours ago. The past weather was rain.

Problem 9.
On your answer sheet is a map of plotted observations taken on September 12, 1998, during passage of Tropical Storm Frances which had decreased in intensity as it came ashore in Texas.

Decode the stations marked with letters A through E. Only decode the wind speed and direction, the temperature, dew point, cloud cover amount, sea level pressure, and the present weather.

Problem 10.
Analyze the pressure on the map for problem 9 for pressures of 992, 996, 1004, 1008, 1012 mb.

Problem 11.
On your answer sheet, plot the following surface weather observations. Elements represented by a / (solidus, not the number 1), indicate the observer does not know the value of the element or cannot observe the element for some reason. The / is not plotted but an M may be required if the element is a mandatory element. Some of the stations are identified with three or four letters. Some of the stations are identified with five digits. The three and four letters are assigned by aviation organizations; the Federal Aviation Administration for the United States or other national aviation organizations in other countries. The five-digit identifiers are assigned by the World Meteorological Organization.

 Use the surface plotting model, the example surface plot, the definitions for the symbols, table 1 and table 2, included in your exercise manual to plot the surface observation data given below.

 
Station VV N dd ff TTT TdTdTd PPPPP a ppp ww W Cl Cm Ch
Cordoba,
Argentina
1 1/2 8 25 08 17 16 1021.2 3 017 58 6 7 2 8
Sault Ste.
Marie, Canada
2 9 33 12 -10 -14 1010.6 8 023 71 7 / / /
Zurich,
Switzerland
3 3 02 05 05 01 1018.3 6 003 51 5 6 0 0
Mosjoen,
Norway
4 6 16 18 02 -01 998.5 5 011 85 8 9 8 /

Open sat_sfc_map.gif in the Atmo 202 folder.

This is a composite map composed of a satellite image, plotted surface observations for selected stations, an analysis of sea level pressure with fronts and information from weather radars which show the location and intensity of precipitation.

At the bottom of the map are intensity levels (from 1 to 6) which show the relative intensity of precipitation, six being the heaviest precipitation. The clouds are shown as white areas across the map. The dark, blue, thin lines are isobars (lines of equal pressure). The heavy blue lines are cold fronts and the heavy red lines are warm fronts. Alternating blue and read mean a stationary front and a heavy purple line is an occluded front. Centers of high pressure are indicated with a H and centers of low pressure are indicated with a L .

Study the composite map and answer the following questions.

Problem 12.
Is (are) there any fronts located in Texas?

If so, what type of front is indicated, cold, warm, stationary, occluded?

 Record your answer on the answer sheet.

Problem 13.
Is there any precipitation indicated from the radar data located in Texas?

 If precipitation is occurring, where in Texas is it located? (Indicate using the terms North, Northeast, East, Southeast, South, Southwest, West, Northwest, Central or a combination.

 If precipitation is occurring, what is the maximum intensity level indicated? Levels are 1 through 6.

Record your answers on the answer sheet.

 

Problem 14.
What is the surface wind speed and direction being reported by Amarillo, Texas? Give wind speed in knots and wind direction in degrees.

Record your answer on the answer sheet.

 
Problem 15.
Does the composite map you opened show any present weather being reported for any station in Texas? If so, record the present weather number from Table 2 and record the station(s) reporting the present weather. The following figure can be used to determine the station name.

Record your answer on the answer sheet

Plotting Upper-Air Observation Elements.

Open ModelUAplot.gif in the Atmo 202 folder.

This image is the model for plotting data about a station circle on a constant-pressure map. The maps of upper-air observations are called constant-pressure maps because the air temperature, dew point temperature, the wind speed and direction plotted on a particular map; e.g., a 500-hPa (or 500-mb) map, are all measured at the level above each station where the pressure is 500 hectopascals (or millibars). The height at which a particular pressure value is found is different for each station. Therefore, instead of doing an analysis of pressure on an upper-air map, (constant-pressure map), an analysis of height is done, much as a topographic map.

Common upper-air (constant-pressure) maps which you will see on the hallway map display are: 850-mb, 700-mb, 500-mb, 300-mb, 250-mb, 200-mb. The following describes the procedure for plotting the observed data.

TT represents Air Temperature. Air Temperature is plotted to the nearest whole degree Celsius.
hhh represents the Height of the Constant-Pressure Surface above sea level. The height of the constant-pressure surface is plotted to the nearest whole meters on the 850- and 700-hPa map and to the nearest tens of meters on the 500-hPa map and those maps aove 500 hPa. Only three digits are plotted. On the 850- and 700-hPa map, the thousands digit is dropped. on the 500-hPa map and above the units digit is dropped.
DD represents the Dew Point Depression. The dew point depression is the difference between the air temperature and the dew point. The dew point is always less than, or the same as the air temperature. The dew point depression is plotted to the nearest whole degree Celsius. If the dew point depression is equal to 5 or less, the station circle is shaded.
hchc represents the12-hour Height Change. The 12-hour height change is the difference between the height of the particular pressure surface 12-hours ago and the current height.

An example plot of upper air data for the 500 mb level is shown to the right. The plot shows the winds are from about 070o at 50 knots, the temperature is -5oC, the dew point depression is 12 degrees, making the dew point -17oC. The height of the 500 mb surface above sea level is 5650 meters.

Open the image, up850.gif, in the Atmo 202 folder.

This image shows the latest analysis for upper-air conditions at a level of 850 hPa, approximately 1500 meters (5000 feet) above sea level. The black lines are contours, or isoheights. The, dashed lines are isotherms.

Data is plotted about the station circles in blue. Note: Contrary to the standard format given above, on this image map and the next map for 500 millibars the height value is plotted using four digits rather than three. Normally, for plots of the height at which 850 hPa is found, a height of 1468 meters would be plotted as 468, however on this image, all four digits are plotted as 1468.

Problem 16.
What is the wind speed and wind direction (in degrees) at the pressure level of 850 hPa at Fort Worth? Be certain you use the proper units for the wind speed.

Record your answer on the answer sheet.

Close the 850 hPa map when finished with problem 16.


Open the image, up500.gif in the Atmo 202 folder.

This next image is an example of an analyzed 500 hPa map. The standard method is for the units digit of the height of 500 hPa to be rounded up or down to the nearest tens of meters when plotted on the map. Thus, a height of 5854 meters is normally plotted as 585 to the upper right of the station. However, on this image, the complete height, including the units digit, is plotted. Like the 850 hPa map, the black lines represent isoheights (contours), lines of equal height; the dashed, lines represent isotherms, lines of equal temperature. Wind speed, wind direction, air temperature, dew point and height are all plotted in blue about the station circle. The center of low height centers and high height centers are indicated by an L or H, respectively.

Problem 17.
What is the temperature recorded at a pressure of 500hPa above Brownsville? What is the dew point?

Be certain to include the proper units with your answers.

Record your answers on your answer sheet.

Close the 500-hPa map when finished with problem 17.


The table of problem 18 provides data obtained from rawinsonde observations.
A rawinsonde or radiosonde is an instrument package carried upward by a balloon to sense and transmit the value of air temperature, amount of water vapor in the air, air pressure and -for a rawinsonde- wind speed and direction can be obtained. The basic difference between a radiosonde and a rawinsonde observation is that a rawinsonde observation also has wind data which is may be obtained by ground equipment tracking the "sonde" and obtaining elevation and azimuth angles from which the wind speed and direction can be determined, or by navigation aids, the latest being Global Positioning Satellites, from which the location of the "sonde" can be determined.

Vaisala RS80 Sonde


Vaisala Radiotheodolite
This is an example of the "ground equipment" used to track "sondes" and also to collect the temperature, humidity, and pressure information transmitted from the "sonde." The system is called a rawinsonde system.

If tracking is not possible, only information which is transmitted by radio back to the ground equipment is available. This is typically temperature, humidity and reference signals from which pressure values can be obtained. Only a simple antenna is required to receive the informaiton. This system is a radiosonde system. Global positioning sondes have an additional antenna to receive signals from global positioning satellites, making positioning of the sonde more accurate and wind information more accurate.

The table below gives the station name, the five-digit identifier for the station, (called the block and station number), the temperature, the dew point, the height at which the measurement was made and the wind direction and wind speed at this height. We are using data only for the level at which a pressure of 500 hPa is found. As you can see, a pressure of 500 hPa is found at different heights in the atmosphere. A pressure of 500 hPa is approximately 7.25 pounds per square inch.


Problem 18.
On your answer sheet, plot the following upper air data in the proper location and manner about the station circles on the answer sheet using the upper-air plot model and definitions of symbols provided.
 
Station
Id.
Air
Temp.
(C)
Dew Point
Temp.
(C)
Height
(meters)
Wind
Direction
(degrees)
Wind
Speed
(knots)
McGrath
Alaska

70231
-30 -34 5450 100 27
Rapid City,
South Dakota
72662
-12 -36 5870 320 85
The Pass,
Canada
71867
-38 -47 5420 015 34
Egedesminde,
Greenland
04339
-40 -62 5130 185 18

Obtain the latest weather observations for College Station.

Problem 19.
What does the official observation from Easterwood say about the "weather" outside?
Return Home to the Meteorology Dept. homepage.
Go to the Weather and Climate link.
Next, go next to the Weather Data Interface link.
Starting in the top box, type CLL.
In the Select a time period box, choose 0: Last.
Select the circle next to Decoded Data.
In the menu next to Decoded Data, select 2:Fully decoded METAR Obs.
Click the Get Data button.

Record the last observation information on your answer sheet.

 

Obtain a forecast for College Station.

Forecasts for College Station are issued by the National Weather Service Forecast Office in Houston, Texas. You can obtain the forecast for College Station by returning to the Weather Interface page.
  • Type CLL in the Select a station box.
  • Again, in the Select a time period box, choose 0: Last
  • Select the circle next to Forecast Data
  • In the menu next to Forecast Data, select 11: NWS Zone Forecasts
Click the Get Data button.  
Problem 20.
What is the forecast for College Station for TOMORROW?

Record your answers on your answer sheet.

Problem 21.
What is the extended forecast for Brazos County?

Record your answers on your answer sheet.

Return BACK to exercise 1 after obtaining the forecast.

You have looked at the latest 850 mb and the latest 500 mb upper-air analyses and seen how the height of these pressure surfaces is represented by contour lines, much as the contour lines on a topographic map. You should have noticed that the contour lines nearly parallel the direction of the plotted wind barbs. This is an aid when analyzing upper-air maps.

Problem 22.
On your answer sheet is a map of the United States with plotted data valid for a pressure surface of 500 mb.

Analyze this map using contour heights of 5880, 5820, 5760, 5700, 5640, 5580, 5520, 5460, 5400 and 5340 meters.

Remember, the contours will parallel the wind directions that are plotted. Remember also that the plotted height values have the units digit dropped.

You will see some plots that have a square and some that have a star in place of the station circle. The square means the data was taken from an aircraft observation. The star means the data was taken from satellite measurements. For both of these, the height is given in hundreds of feet. Thus, a plot of 160 means 16,000 feet. Do not try to determine what this height means in meters. Just recognize that the contour in that area should be paralleling the plotted wind at that location.

This concludes exercise 1. Please exit the program and sign off.


Copyright © 1996-2007 Texas A&M University, Texas A&M Meteorology Department and Marion Alcorn.