Lab #4 Geo

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University of Wyoming *

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2080

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Geography

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Apr 3, 2024

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Name: _____________________________________ Section: _______ Laboratory 5: Midlatitude Weather Description: This lab uses our previous knowledge of atmospheric temperature, pressure and moisture to understand the most common forms of weather in the midlatitudes. Low pressure systems, or midlatitude cyclones, are responsible for most precipitation in the midlatitudes. The presentation of meteorological data on maps permits the analysis, interpretation and forecasting of weather. Key Terms: Midlatitude cyclone Cold front Warm front Occluded front Stationary front Station model Atmospheric pressure Wind speed Wind direction Weather Precipitation Forecast Learning Outcomes: At the conclusion of this exercise, you will be able to: 1. Identify and label fronts on a weather map. 2. Identify relationships between air temperature, humidity and wind direction around a mid-latitude cyclone. 3. Use meteorological station models to identify mid-latitude cyclones. 4. Examine 500-millibar pressure charts to explain wind direction, the presence or absence of mid-latitude cyclones, and make weather forecasts. 5-1

Exercise 5-A: Midlatitude Cyclones. Midlatitude Weather The leading edge of an advancing air mass is known as a front. This boundary marks the boundary between air masses of different temperatures. Warm fronts occur as warm air moves toward cold air and are always shown as a red line with “half-circle” markings. Cold fronts occur as cold air moves toward warm air. This situation will always be shown as a blue line with triangular markings. Occasionally, these systems won’t move much and are thus considered Stationary fronts and are always represented by an alternating red and blue line. When we work with maps here, we are working with a top view map and a sideview/cross section map . A top view map is what we usually assume a map looks like – an area we are looking down on from above. A side view or cross section map is one as if we are looking at an area (in this case a weather front) from the ground to the side of it. ( http://www.weatherquestions.com/What_are_fronts.htm ) The conflict between contrasting air masses can develop a midlatitude cyclone. They are characterized by a large area of low pressure, from several hundred up to 1000 miles wide and may last from 3-10 days. Also, the wind flow around midlatitude cyclones is counterclockwise in the Northern Hemisphere and Clockwise in the Southern Hemisphere. The life cycle of this weather system includes: 1) Cyclogenesis – an atmospheric process in which low pressure wave cyclones develop and strengthen. This usually occurs where cold and warm air masses converge and are drawn into conflict. 2) Open stage – To the east of the low-pressure center, warm air begins to move northward along an advancing front, while cold air advances southward to the west of the center of low pressure. 3) Occluded stage – cooler, denser air quickly bulldozes through the warm front, causing the warmer air to rise. Cold fronts can travel at an average of 40 kmph, or 25 mph. This creates an occluded front . 4) Dissolving stage – This stage occurs when its lifting mechanism is completely cut off from the warm air mass, which was its source of energy and moisture. The cyclonic system will eventually dissipate in the atmosphere. 1) Label each of the following features on the map on the following page: a) Cold front b) Warm front 5-2

c) Cool air masses d) Warm air mass e) Direction of cold front movement f) Direction of warm front movement 2) Use arrows to show the wind direction in four locations on the map . 3) On the cross-section diagram, label: a) Cold front b) Warm front c) Cold air masses d) Warm air mass e) Direction of cold front movement f) Direction of warm front movement 4) What is the wind direction at point B? Remember, winds are named for the direction from which they come. At point B wind is Northwest 5) Where is precipitation more likely to be occurring on the cross-section , at point B or D (at the moment, not after the system moves)? Explain your answer. 5-3

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Prceipitation would be more lilkey to occur at point B due to there being a warm air mass at point B 6) How will the temperature change at point D when the cold front passes? When the cold front passes D the temp will decrease Exercise 5-B: Weather Map Symbols A standard system exists for reporting atmospheric conditions at weather stations: the station model . The following is an example of a station model and an explanation of its symbols: Use this website for additional explanation, especially for air/barometric pressure: https://www.shsu.edu/~dl_www/bkonline/GenRef111/Applets/Decode/L_decodestation.htm . 5-4

If you need more speed indicators for your legend, use this photo: ALWAYS remember that your wind speed flag should point in the direction of what kind of wind it is. Above, it is a Northwest wind, so the flag points to what would be the Northwest on a map where North is at the “top” and West is to the “left”. 1) Construct a station model for the following conditions: overcast skies, air temperature 67°F, dew point 35°F, air pressure 1005.2 mb, winds from S at 15 knots. 2) Completely describe the weather conditions at the following station: The sky is overcast, and there is a major difference between depoint temp and real temp. This means it will rain a lot. 5-5 31 31

Use the station models below to answer the following questions related to the following two hypothetical weather maps. NOTE the positions of warm and cold air masses, direction of winds, humidity, and type of precipitation to help you draw in the position of the fronts. Assume that weather is moving from West to East (left to right) for both maps as it does in North America. Also, be sure to use the website mentioned in Part A to help with reading your symbols (cloud cover especially in this part). 5-6

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1) Draw the front that is occurring on each map above (hint: one contains a cold front, the other a warm front). 2) In what direction (ie North, Northeast, Northwest, etc) is the front on Map A advancing? To the northwest 3) In what direction is the front on Map B advancing? To the east 5-7 North

Exercise 5-C: Weather Maps The following questions are based on the accompanying surface weather map from October 18, 1990. Assume storm movement to be approximately 500 miles per day. 1) What is the current weather like in Amarillo, TX? Do you think the weather is clear or stormy? Why? Air temperature _33 F______ Dew Point __21 F_____ Wind Speed ___5 knots____ Wind Direction __SW_____ The numbers shows that’s it’s stable, along with high pressure, meaning that its clear. 2) Which city is more likely to receive precipitation in the next 12 hours, Wichita, KS, or Buffalo, NY? Why? Buffalo is the most likely to receive precipitation due to the fact that’s its close to a front formation. 3) Considering the information given on the surface map, what kind of weather has Minneapolis, MN experienced over the past 24 hours? Why? Minnealoplis has seen fair weather over the last 24 hours. It’s had a temp of around 33, a dew point around 26 F and a high pressure. This most likely means fair weather. 5-8

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Lab #4 Geo

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