Lab7_Assignment (2)

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Dec 6, 2023

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LAB 7: WEATHER MAPPING 100 points Due at the beginning of lab next week in physical or digital forms. LEARNING OUTCOMES At the end of this lab, you will be able to: 1. Understand the components of a weather “station model.” 2. Decode station model features. 3. Analyze weather maps and interpret current and future conditions for a location. INTRODUCTION The station model is a graphic means of conveying measured meteorological information in compact form on a map. The station model includes information about temperature, wind direction and speed, atmospheric pressure, dew point, precipitation, and cloud cover. Information for decoding a simplified version is presented below (Figure 1). 1

Figure 1. Decoded station model. Image from Wikipedia. Some of the information in the station model is encoded. This is the case with pressure, wind direction and speed, precipitation, and cloud cover. Pressure is always given in millibars (mb), but the first digit (normally a 9 or 10) is left off. To decode the pressure value, look at the first number. If the first number is a 5 through 9 inclusive, then add a 9 to the front. If the first number is a 0 through 4 inclusive, then add a 10 to the front. The very last digit on the right is in the tenths place (on the right side of the decimal point). This method for decoding air pressure given on the station model works most of the time. However, there are times when this method will break down, as some of the strongest hurricanes, for example, have had air pressure readings below 900 mb. The station 2

model also contains information on pressure tendency and change over the last 3 hours. Pressure change is given in tenths of millibars over 3 hours (Figure 2: Barometric Tendency). 3

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Figure 2. Weather station symbols. Image from https://www.nj.gov/dep/seeds/wssym.htm . Another piece of information given on the station model that needs to be decoded is cloud cover (Figure 2: Cloud Coverage). Each station model locates the individual station (observation point) with a circle. The circle itself indicates the degree of cloud cover. In general, the more the circle is filled in, the more cloud cover there is. A meteorological image known as a wind barb is used to describe wind direction and speed on the station model (Figure 2: Wind Direction). This method uses the circle as a compass with north at the top. The wind barb is a line with flag(s) on one end like an arrow with feathers on one end). In meteorology, the wind is always identified by the direction in which it is coming from (a south wind comes from the south and blows toward the north). The wind speed is dependent on how many flags there are (Figure 2: Wind Speed and Figure 3). In general, the more flags, the faster the wind is blowing. Figure 3. Diagram showing how wind speed is plotted. It is plotted in increments of 5 knots, with the outer end of the symbol facing towards the direction the wind is blowing. Figure from https://www.wpc.ncep.noaa.gov/html/stationplot_printer.html . A final element encoded on the basic station model is present weather/precipitation. These are encoded in the form of weather symbols (Figure 2: Weather Conditions, Showers, and Misc. Sky Cover). Station models for each weather reporting site are placed on a weather map. You are provided with two surface weather maps for the U.S. from 18 December 2002 (Figures 6 and 7). Meteorologists will analyze these surface weather maps to find the different fronts, locate areas of atmospheric moisture, locate high pressure and low-pressure areas, and other meteorological factors. There are four different types of fronts, which are boundaries that separate contrasting air masses. Cold fronts replace warm air with cold air and are denoted as lines (blue color if colored) with triangles pointing in the direction the front is moving. Warm fronts replace cold air with warm air and are denoted as lines (red color if colored) with semicircles extending in the direction the front is moving. Another type of front is a stationary front. It has little movement associated with it (hence, the name stationary), and is denotes as a line (alternating blue and red color, if colored) with alternating triangles and semicircles on opposite sides of the 5

boundary (looks like a warm front-cold front mix). Finally, there is the occluded front, which comes in one of two types. A cold type is where the occluded front replaces cool air with cold air. A warm type is where the occluded front replaces cold air with cool air. In addition to fronts, meteorologists look for other boundaries, such as the dryline. Just as the name suggests, it is a boundary between moist air to the east and dry air to the west. 6

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Figure 4 . 6 am CST 18 December 2002 7

Figure 5 . 3 pm CST 18 December 2002 8

LAB 10: WEATHER MAPPING Name: _____________________________ Section: _____________________________ Take measurements, perform the following calculations, and answer the questions [100 pts] . 1. Decode the requested information from each of the following station models [25 points) : Barometric Pressure: 024 Temperature: 37 Dew-Point Temperature: 21 Barometric Pressure:998 Temperature:63 Dew-Point Temperature: 60 Sky Coverage: Thunder with no precipitation 9

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Current Weather: Partly cloudy Barometric Pressure:117 Temperature: 43 Dew-Point Temperature: 20 Sky Coverage: Clear Wind Speed: 15 knots Wind Direction: Southwest Pressure Change during last 3 hours: Pressure Tendency: 17/ 10

Barometric Pressure: 997 Temperature: 27 Dew-Point Temperature: 25 Sky Coverage: Overcast rain Wind Speed: 25knots Wind Direction: Northwest Pressure Change during last 3 hours: .31 Pressure Tendency:11/w 2. Figures 4 and 5 already have pressure analyzed with low- and high-pressure centers plotted with isobars (lines of equal pressure). Draw isotherms for 30°F and 40°F on both maps and compare them. (5 pts.) For figure 4 and 5 both maps for there isotherms are around the same as each other. They are around the same areas for which figure. 11

3. Explain the changes you see in the position of the isotherm between the two maps. What would cause this/these change(s)? (Pay attention to the time change) (5 pts.) Figure 4 most of the 30’s and 40’s was around the Northeast of the world, while foe figure 5 the temperatures were more around the northwest. The difference between both is that there is a 9-hour gap between both and would slightly change on where and how the temperatures can change within each figure. 4. Plot the 55°F and 60°F isodrosotherms (lines of equal dew point) on Figures 4 and 5 and shade in areas which have a dew point of 60°F or greater. Use a different color for these (5 pts.) 5. Focus on NW Arkansas and describe the changes to the 55°F isodrosotherm in this area. Then look at the entire 55 and 60°F+ isodrosotherms. Did the area of 60°F+ dew points increase or decrease between 6 am CST (Figure 4) and 3 pm CST (Figure 5)? Does the overall movement of the 55°F line agree with what happened in NW Arkansas? Finally does dew point appear to relate strongly to changes in temperature throughout the day? (10 pts.) 6. Locate and plot the warm front on Figures 4 and 5. (Look for a sharp increase in temperature and draw the front along this approximate boundary using the correct symbology. Use red for this if you can, but the symbology is more important). (5 pts.) 7. Locate and plot the cold front on Figure 4 and 5. Use blue and be sure to use the correct symbology. (5 pts.) 12

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8. Locate and plot the dryline with a dotted line on Figures 4 and 5. (Hint: look for a sharp change in dew points i.e., a gradient) (5 pts.) 9. What direction has the dryline moved between 6 am CST (Figure 4) and 3 pm CST (Figure 5)? (5 pts.) 10. Given what you have analyzed so far, what would you expect in Little Rock, AR during the rest of the afternoon and nighttime? Why? (5 pts.) For the remainder of the lab, use the NOAA Jet Stream website to answer the following questions. Read the introductory slides to understand the meaning of the different layers and how to interact with the maps. 11. Using the 200 mb map, observe the pattern of the jet stream and the wind contours for North America. Where would the windiest parts of the country be on average throughout the year according to the 200 mb map? Why? (5 pts.) 12. Using the 500 mb map, what is the geopotential height and estimate its range for this pressure above northwest Arkansas? (5 pts.) 13. Using the 500 mb map, turn on the “Surface Weather” layer. Note the cold front to the northwest of Texas as well as the nearby low-pressure system. If current trends continue, what kind of weather would you expect in southwestern Texas in the next few days? Why? (5 pts.) 13

14. What is the wind speed over NW Arkansas at 500 mb? (5 pts.) 15. Finally, navigate to the 850 mb map and turn on the “Precipitable Water” (PW) layer. Which part of the country should be most concerned about heavy rains and flooding according to this weather pattern? Why? (5 pts.) 14

Lab7_Assignment (2)

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