Exercise One: Understanding a Weather Map and Station Models
Temperature Conversion
For this portion of the exercise, the group used three conversion formulas to convert Fahrenheit, Celsius, and Kelvin temperatures. The three formulas are as follows:
F
= C*1.8 + 32
C
= (F-32)/1.8
K
= C + 273.15
1.
32 F to C
C
= (F-32)/1.8
C
= (32-32)/1.8 = 0 C
2.
68 F to C
20 C
3.
90 F to K
K
= (F-32)*(5/9) + 273.15
K
= (90-32)*5/9 + 273.15 = 305.372 K
4.
30 C to F
F
= C*1.8 + 32
F
= 30*1.8 + 32 = 22 F
5.
-40 C to F
-40 F
6.
-23 F to C
-30.56 C
7.
-122 C to K
K
= C + 273.15
K
= -122 + 273.15 = 151.15 K
Weather Map Symbols
Symbols on weather maps are often referencing the conditions derived from different fronts. A front is the boundary separating two different air masses in terms of temperature and humidity. There are four types:- Cold front: a cold front is the leading edge of a cold and dry mass of air.
- Warm front: a warm front is the leading edge of a warm and moist mass of air.
- Occluded front: this front is formed when a cold front overtakes a warm front and usually results with a drying of the air mass.
- Stationary front: a non-moving or stalled boundary between two air mass. This occurs when neither is strong enough to replace the other.
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| Figure 1. The four types of fronts. |
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| Figure 2. Annotated surface map of the United States. High and low pressure systems are labeled in green boxes. Cold, warm, and stationary fronts are labeled in light blue boxes. Warm air is labeled in pink boxes. Cold air is labeled in dark blue boxes. High winds are labeled in yellow boxes. The fronts were all labeled based on the symbols mentioned in figure 1. High and low pressure systems were labeled based on the H or L. Cold and warm air masses were identified by the direction of the red half circles or the blue triangles. Both shapes point 'away' from the air mass its referencing. For example, if the blue triangles are pointing south, then the cold air mass is in the north. The high wind areas were located based on isobar distances. If the the isobars were closer together, then that means there is a larger pressure gradient. At a larger pressure gradient air is moving from high to low quicker which results in higher winds. |
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| Figure 3. Annotated Map of North America of major air masses. Each air mass is labeled with a blue circle. The characteristics of each air mass are listed in light brown boxes. The direction of the air masses are labeled with various colored arrows. The continental arctic and polar air masses originate in the arctic and spill down across Canada and into the northern United States in the winter. The maritime polar (Pacific) affects the west coast including Washington and Oregon. The maritime tropical Pacific, Gulf, and Atlantic all originate in the south and head up towards the southern United States. The continental tropical also originates in the south and heads upwards but like the continental arctic and polar its air mas sis dry. The maritime polar (Atlantic) is similar to the maritime polar (Pacific) but affects the northeastern coast of the U.S. |
Surface Data Plot Maps
The interpretation of surface maps relies on the standard notation system on U.S. weather maps. These notations correlate to data collected from weather station models. The group took a current surface map and annotated two regions shown in figures 6 and 7. Figure 4 is a chart with all the data symbols and their meaning and figure 5 is the full scale weather map from which the sections for annotation were taken. |
| Figure 4. Weather map symbol legend. |
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| Figure 5. Surface data map of the United States. |
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| Figure 6. Nevada/Utah region, a subsection of the surface data map in figure 5. In the northeast corner is a stationary front with the cold air in the northeast and the warmer air in the southwest. The temperatures are taken from the top left number. in the far southwest there are clearer skies denoted by the hollow circle on the wind barb. Closer to the stationary front cloud cover increases. The winds are between 1-10 mph which is denoted by the wind barbs. The lack of strong winds is due to the stationary front which stalls air masses. There are relatively few isobars in this region which indicates a gradual pressure gradient. Finally, there are haze and snow events in this region which is illustrated by the yellow symbol next to the wind barb. |
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| Figure 7. Great Lakes region, a subsection of the surface data map in figure 5. Along the southeast corner is a mixed high and low front with a low pressure system situated over Lake Michigan and the lower peninsula. The center of the low is directly over the lower peninsula of Michigan because the wind barbs around that area are rotating in a counterclockwise manner (this is the direction of low pressure systems in the northern hemisphere). The circle portion of the wind barb points towards the direction the wind is blowing. Based on the filled in circles of the wind barbs there is near 100% cloud cover in the area. The light green mass indicates a rain event along the mixed front. The closely packed isobars indicate a steep pressure gradient with pressure decreasing closer to the center of the low pressure system. Overall there is light snow in the north and light to heavy rain in the south/southeast. |
Barometric Pressure Conversions
In surface data maps like the one in figure 5 barometric pressures are given in shorthand. This means that either a 9 or 10 is omitted from the beginning of the pressure reading. Conversion to long or short hand requires knowing what to add and subtract. To go from short to longhand, a 9 is added if the first number is an 8 or 9. For all other numbers a 10 is added. Both instances require the number to be written as a decimal going to the tenths position. When converting from longhand to shorthand, the beginning 9 or 10 is removed.
1.
A barometric pressure of
1013.4= 134
2.
A barometric pressure of
1002.4= 024
3.
A barometric pressure of
982.3= 823
4.
A barometric pressure of
995.3= 953
5.
A barometric pressure of
1021.2= 212
6.
Shorthand of 243= 1024.3
7.
Shorthand of 179= 1017.9
8.
Shorthand of 207= 1020.7
9.
Shorthand of 824= 982.4
10.
Shorthand of 623=
1062.3
11.
Shorthand of 839 (Hint:
record high)= 1083.9
12.
Shorthand of 699 (Hint:
record low)= 869.9
13.
How do high and low
pressure barometric pressure values correspond to weather conditions. That is,
under what conditions might one expect to see very high barometer readings? How
about record low?
Under
high barometric pressures there are cooler and calmer weather with clear
skies. Under low barometric pressures
there are warmer weather with precipitation.
Under record low barometric pressures there are hurricanes.
Weather Website Navigation
There are a multitude of weather websites each with its own strengths and weaknesses. For this portion of the exercise the group navigated a few of these websites. For more information, visit my weather links page on this blog.One website is accuweather.com. This website has a nice weather events blog with interesting stories. Some examples include "Icy conditions from Missouri to Michigan will make travel difficult and cause power outages" and "Thunderstorms are sever in south central U.S." The site also has nice graphics to accompany the stories such as figure 8.
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| Figure 8. Graphic accompanying a story on accuweather about unseasonable cold air in the western U.S. The shaded blue area is showing the area of the western United States that is experiencing uncharacteristically cold temperatures right now and will continue to for the duration of the month of February. The map also states how many degrees below the average the current temperatures are. |
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| Figure 9. Map of the jet stream from intellicast.com. In this map the jet stream is coming from the northwest and dipping down through the Pacific Ocean to southern California and northern Mexico and then heading northeast across the United States. This is pulling warm moist air from the Pacific to the Midwest resulting in warmer temperatures across the United States. |
The final website the group visited was NOAA's satellite information section. On this website satellite data can be viewed as infrared, visible, and water vapor. Figure 10 shows the water vapor map on February 19th, 2018.
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| Figure 10. Water vapor map of the United States on February 19th, 2018. The strong white line from Mexico to Wisconsin is a line of water vapor that is feeding a series of low pressure systems and causing heavy precipitation events. This line also follows the jet stream path. |
Conclusions
This exercise allowed the group to become familiar with several weather terms and concepts such as fronts and air masses. It also introduced several new weather websites for obtaining quality weather data. The skills and knowledge learned in this exercise will provide a foundation for the rest of the class.Lab 1
Cincinnati Fire Kite
This lab focused on the principle of positive buoyancy. Groups of student made a Cincinnati Fire Kite and launched a Chinese lantern to demonstrate the positive buoyancy principle. Both are systems that create a pocket of warm air through the burning of an object and then trap that air. The pocket of warm air expands and rises relative to the cooler air around it and sends the object upwards. In the fire kit demonstration the four corners of a piece of newspaper were taped together in the center. Then the four corners of the kite were lit at the same time (figure 1). |
| Figure 1. Cincinnati Fire Kite launched from the footbridge at the University of Wisconsin-Eau Claire. The ignited newspaper warms the air within the newspaper pocket and traps it creating a buoyant force that sends the kite upwards. |
Chinese Lantern
The Chinese lantern was a bit more successful than the Cincinnati Fire Kite. After the lantern was expanded, it had to be held so the warm air could accumulate inside before sending it off. The fuel source was a block of paraffin wax attached to a wire loop at the bottom of the lantern (figure 2). |
| Figure 2. Chinese Lantern expanded and accumulating hot air. |
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| Figure 3. Chinese lantern rising in the sky. The warm air created by the paraffin wax accumulated within the lantern and eventually caused the lantern to become more buoyant than the air around it and rose into the sky. |
Exercise 2
This exercise aimed to introduce stuve diagrams and what information can be derived from them.Figure 1 is an example of an stuve diagram, or chart used to document conditions obtained from a weather balloon, that was used in each of the following sections. |
| Figure 1. Stuve diagram. |
Relative Humidity
Put simply, relative humidity is the amount of moisture in the air compared to what the air can hold at maximum capacity. The relative humidity can be determined on a stuve diagram by plotting a line from the temperature at a certain pressure and following the blue lines, or saturation mixing ratio lines to the line of blue numbers in figure 1 and then doing the same with the dewpoint temperature. The resulting numbers are then divided in the following formula:
Relative Humidity = actual mixing ratio / saturation mixing ratio * 100
What is the 700 mb RH when the 700 mb temperature is 10 °C and the 700 mb dewpoint is -15 °C?
To complete this problem a point at 10 °C is plotted at the 700 mb height and then a line is plotted up along the blue line. The same is done with the dewpoint. The values for the saturation mixing ratio and the actual mixing ratio are obtained and then placed into the formula as follows:
RH = (0.18/1.1) * 100 = 16.36%
Lifting Condensation Level
Lifting condensation level (LCL) is the pressure level in the atmosphere where a RH of 100% first occurs and leads to air at that particular pressure level being forcefully lifted. To find the LCL, the temperature line is drawn parallel to the black lines, or dry adiabatic lines starting at the surface (1,000 mb) and a dewpoint line is drawn parallel along the nearest blue lines. The point where they cross is the LCL mb value.The 1,000 mb surface temperature is 28 °C while the dewpoint is 14 °C. What is the LCL?
Following the directions above, the LCL is 815 mb.
Convective Condensation Level
Convective condensation level (CCL) is the pressure in the atmosphere where a RH of 100% first occurs when air at the surface is heated to a sufficient temperature that allows the air to rise buoyantly on its own. In other words, its the pressure level that we see a RH of 100% from the surface temperature that allowed the air to rise on its own. To calculate the CCL, a line is drawn between the surface temperature and the new temperature reading given. Then, a line is drawn from the dewpoint parallel to the blue line. The intersection of the lines is the CCL.The 1,000 mb surface temperature is 24 °C while the dewpoint is 14 °C. The temperature decreases by 20 °C between 1,000 mb and 700 mb. What is the CCL?
Using the previous directions, the CCL = 790 mb
Convective Temperature
The convective temperature (CT) is the surface temperature air must warm to in order for it to buoyantly rise to the CCL. It is the same temperature referenced in the convective condensation level section previously. To find the CT, start at the CCL point and follow the black line back to the surface (1,000 mb). Then read the temperature on the x axis.This will be demonstrated using the previous problem:
The 1,000 mb surface temperature is 24 °C while the dewpoint is 14 °C. The temperature decreases by 20 °C between 1,000 mb and 700 mb. What is the CCL?
The CCL is 790 mb. Following this line, we get a CT of 31 °C.
Reporting the Lifted Index and the K Index
Two indices that are useful in reporting the potential for severe weather are the lifted index (LI) and the K Index (KI). The lifted index assesses the stability of the lowest part of the atmosphere. A value above 3 is very stable and the lower the number from 3 the higher the potential for severe weather with a value of -6 or lower indicating severe thunderstorms and possible tornadoes. The K index assesses convective potential and thus is related to the probability of a thunderstorm occurrence. For the K index, less than 20 is no convective potential and anything above 35 indicates numerous thunderstorms. In this section of the lab 10 stuve charts from weather stations around the country were analyzed and the LI and KI values were reported. One example is given below.KGRB - Green Bay, WI.
LI: 11.6
KI: 17
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| Figure 2. Stuve diagram of Green Bay, WI on March 15, 2018. |
The LI indicates conditions are very stable with no significant activity and the KI value states there is no probability of thunderstorms. On the sounding the parcel path is below the environmental temperature and dew point, thus the sounding mirrors the consensus of the KI and LI values and no significant lifting is occurring.
