1. January History Great Flood of 1937 70% of Louisville was submerged 3.3 billion in damages Crest was 85.4 feet and flood stage is only 55 feet. 15 inches of rain in 12 days

2. Chapter 1: Monitoring the Weather (Basics)

3. 3 Difference between Weather and Climate Weather is the state of the atmosphere at some place and time Weather is the state of the atmosphere at some place and time Described with quantitative variables Described with quantitative variables Temperature, humidity, cloudiness, precipitation, wind speed, wind direction Temperature, humidity, cloudiness, precipitation, wind speed, wind direction Meteorology is the study of the atmosphere and the processes that cause weather Meteorology is the study of the atmosphere and the processes that cause weather Climate is weather conditions at some locality averaged over a specified time period Climate is weather conditions at some locality averaged over a specified time period Climate is an average of the weather, figured over the last 30-years and updated every decade Climate is an average of the weather, figured over the last 30-years and updated every decade A locale’s climate also includes weather extremes A locale’s climate also includes weather extremes Seattle? Arizona?

4. 4 Sources of Weather Information Television Television The Weather Channel and local newscasts The Weather Channel and local newscasts Radio Radio NOAA Weather Radio NOAA Weather Radio Continuous broadcasts Continuous broadcasts repeated every 4 - 6 minutes repeated every 4 - 6 minutes Interrupted with warnings Interrupted with warnings and watches The Internet The Internet

5. 5 Weather Systems and Maps Weather info received via TV, Weather info received via TV, radio, or the Internet includes Weather maps Weather maps National National Regional Regional Satellite/radar images Satellite/radar images Data on current/past Data on current/pastconditions Weather forecasts Weather forecasts Short-term Short-term 24 – 48 hours 24 – 48 hours Long-term Long-term Up to 7 days or longer Up to 7 days or longer Automated Surface Observing System (ASOS)

6. 6 2 Types of Pressure Systems High Pressure Systems, or “Anticyclones” Low Pressure Systems, or “Cyclones”

7. 7 Pressure Systems, Cont. High and low refer to air pressure High and low refer to air pressure High pressure area is relatively high compared to surrounding air High pressure area is relatively high compared to surrounding air Low pressure area is relatively low compared to surrounding air Low pressure area is relatively low compared to surrounding air Highs Highs Fair weather Fair weather Clockwise rotation of sinking air (in Northern Hemisphere) Clockwise rotation of sinking air (in Northern Hemisphere) Generally track toward the east and southeast Generally track toward the east and southeast Lows Lows Stormy weather Stormy weather Counterclockwise rotation of rising air (in Northern Hemisphere) Counterclockwise rotation of rising air (in Northern Hemisphere) Generally track toward the east and northeast Generally track toward the east and northeast Lows tracking across the northern U.S. or southern Canada produce less moisture than lows tracking across the southern U.S. Lows tracking across the northern U.S. or southern Canada produce less moisture than lows tracking across the southern U.S. Weather to the west and north – usually cold Weather to the west and north – usually cold Weather to the south and east – usually warm Weather to the south and east – usually warm

8. 8 Pressure Systems, Continued High and Low Pressure Centers Arrows indicate surface horizontal winds

10. 10 Air Masses Huge volume of air covering thousands of square kilometers Huge volume of air covering thousands of square kilometers Horizontally relatively uniform in characteristics Horizontally relatively uniform in characteristics Temperature Temperature Humidity Humidity Gathers characteristics from its source region Gathers characteristics from its source region Cold, dry air masses form at higher latitudes over continents Cold, dry air masses form at higher latitudes over continents Cold, humid air masses form at higher latitudes over maritime surfaces Cold, humid air masses form at higher latitudes over maritime surfaces Warm, dry air masses form over continents in subtropical regions Warm, dry air masses form over continents in subtropical regions Warm, humid air masses form near the equator or in the subtropics over maritime surfaces Warm, humid air masses form near the equator or in the subtropics over maritime surfaces

11. AIR MASSES – large volume of air that has a relatively uniform temperature and humidity 1.Continental Polar – cP – cold and dry (Canada) 2.Maritime Polar – mP – cold and wet (Gulf of Alaska) 3.Continental Tropical – cT – hot and dry (Mexico) 4.Maritime Tropical – mT – hot and wet (Gulf of Mexico) 5.Arctic – A – very cold and dry (Northern Canada)

13. 13 Fronts Warm Front © American Meteorological Society Cold Front

14. Fronts – the boundary between air masses 1.Cold Front a.Generally, a narrow band of precipitation along or just ahead of the surface front, where precipitation is brief (couple of minutes to a few hours) b.Precipitation can be severe c.Boundary between advancing cold air and retreating warm air d.Plotted on a map as a blue line with triangles pointed in the direction of motion

15. 2. Warm Front a.Generally, a wide band of precipitation along or just ahead of the surface warm front, where precipitation can be persistent (12-24 hours) b.Precipitation is generally light to moderate c.Boundary between advancing warm air and retreating cold air d.Plotted on a map as a red line with semi-circles pointed in the direction of motion

16. A cyclone with the warm and cold fronts extending outward from the low pressure center. Showers generally form along the warm front, while more severe weather can occur along the cold front.

17. This shows how the warm and cold fronts act as boundaries between different air masses. Notice how the wind directions are different on either side of the fronts, and that the flow is counterclockwise and convergent.

18. Ways to locate a front on a surface weather map: 1.Precipitation/Clouds 2.Wind Shift 3.Temperature Difference 4.Dew Point Difference (change in relative humidity)

19. Other Fronts 1. Stationary – a non-moving front where winds on either side blow in opposite directions 2. Occluded – when the air behind the cold front overtakes the air ahead of the warm front

20. Wind directions are different on the two sides of a front Wind directions are different on the two sides of a front Some fronts have no clouds or precipitation. Some fronts have no clouds or precipitation. Passage indicated by wind shift, and temperature/humidity changes Passage indicated by wind shift, and temperature/humidity changes In summer, temperature can be nearly the same on both sides of a cold front In summer, temperature can be nearly the same on both sides of a cold front Difference will be humidity Difference will be humidity Fronts are anchored to lows on a weather map. Fronts are anchored to lows on a weather map. Counterclockwise flow brings contrasting air masses together to form fronts Counterclockwise flow brings contrasting air masses together to form fronts Thunderstorms/severe weather often occur in the warm, humid air mass located between the cold and warm front Thunderstorms/severe weather often occur in the warm, humid air mass located between the cold and warm front Characteristics of Air Masses & Fronts, Continued

21. 21 Describing the State of the Atmosphere What do Forecasters Tell Us? Maximum Temperature Maximum Temperature Usually occurs in early to mid-afternoon Usually occurs in early to mid-afternoon Minimum temperature Minimum temperature Usually occurs around sunrise Usually occurs around sunrise Dewpoint (frost point) Dewpoint (frost point) The temperature at which air must be cooled at constant pressure to become saturated with water vapor and for dew (or frost) to form The temperature at which air must be cooled at constant pressure to become saturated with water vapor and for dew (or frost) to form Relative humidity Relative humidity A percentage; the ratio of the actual concentration of the water vapor component of air compared to the concentration the air would have if saturated with water vapor A percentage; the ratio of the actual concentration of the water vapor component of air compared to the concentration the air would have if saturated with water vapor Relative humidity will change throughout the day as the temperature varies Relative humidity will change throughout the day as the temperature varies Generally highest around sunrise and lowest when warmest Generally highest around sunrise and lowest when warmest Precipitation amounts Precipitation amounts General rule – 10” of snow = 1” of precipitation General rule – 10” of snow = 1” of precipitation

22. Based on Temperature of 90 F Dew Point Temp FHuman PerceptionR. Humidity 75 + Extremely uncomfortable, oppressive62% 70-74 Very Humid, quite uncomfortable52-60% 65-69 Somewhat uncomfortable for most people44-52% 60-64OK for most37-46% 55-59Comfortable31-41% 50-54Very comfortable31-37% 49 or lowerFeels like the western US30%

23. 23 Describing the State of the Atmosphere What do Forecasters Tell Us? (Continued) Air Pressure Air Pressure And its tendency (rising or falling) And its tendency (rising or falling) Falling may indicate approaching Falling may indicate approaching cold front Wind direction and speed Wind direction and speed Wind direction is the direction wind Wind direction is the direction wind is blowing from Example; a west wind is blowing from the west, toward the east Example; a west wind is blowing from the west, toward the east Sky cover Sky cover Fraction of the sky covered in clouds Fraction of the sky covered in clouds NWS Weather watch – issued when hazardous weather is considered possible NWS Weather watch – issued when hazardous weather is considered possible NWS Weather warning – issued when hazardous weather is imminent or actually taking place NWS Weather warning – issued when hazardous weather is imminent or actually taking place

24. 24 Weather Satellite Imagery Two major types of satellite orbits Two major types of satellite orbits Geostationary Geostationary High orbits High orbits 36,000 km (22,300 miles) high 36,000 km (22,300 miles) high Orbits planet at same rate as Earth’s rotation and in same eastward direction Orbits planet at same rate as Earth’s rotation and in same eastward direction Currently 2 of these provide a complete view of much of N. America and adjacent oceans to latitudes of about 60 degrees Currently 2 of these provide a complete view of much of N. America and adjacent oceans to latitudes of about 60 degrees Positioned over equator at 75 0 W longitude, 135 0 W longitude Positioned over equator at 75 0 W longitude, 135 0 W longitude Polar orbiting Polar orbiting Low orbits Low orbits 800-1000 km (~500-600 miles) high 800-1000 km (~500-600 miles) high Provides overlapping north-south strips of images Provides overlapping north-south strips of images Passes over the same point twice every 24 hours Passes over the same point twice every 24 hours

25. 25 Orbit of a Geostationary Satellite

26. 26 Orbit of a Polar- Orbiting Satellite

27. 27 Visible Visible Black and white photograph of the planet Black and white photograph of the planet Only available during daylight hours Only available during daylight hours Highly reflective surfaces appear bright white and less reflective surfaces are darker Highly reflective surfaces appear bright white and less reflective surfaces are darker Weather Satellite Imagery

28. 28 Infrared Infrared Available anytime, not just during daylight Available anytime, not just during daylight Provides temperature comparison of features within image Provides temperature comparison of features within image Whiter = colder Whiter = colder Higher cloud tops appear whiter, because they are colder Higher cloud tops appear whiter, because they are colder Weather Satellite Imagery

29. 29 Water vapor imagery Water vapor imagery Enables tracking of plumes of moisture Enables tracking of plumes of moisture Shades of white = increasing moisture Shades of white = increasing moisture Upper-level clouds appear milky to bright white Upper-level clouds appear milky to bright white Weather Satellite Imagery GOES Imagery

30. 30 Weather Radar Complements satellite surveillance Complements satellite surveillance Doppler radar detects movement Doppler radar detects movement Excellent tool to forecast tornadoes Excellent tool to forecast tornadoes

31. 31 Sky Watching You can determine much about the weather by watching the sky You can determine much about the weather by watching the sky Clouds are aggregates of tiny water droplets, ice crystals, or some combination of both Clouds are aggregates of tiny water droplets, ice crystals, or some combination of both A cloud in contact with the ground is fog A cloud in contact with the ground is fog Cloud forms: Cloud forms: Stratiform clouds are sheet-like clouds formed in horizontal layers Stratiform clouds are sheet-like clouds formed in horizontal layers Form where air ascends gradually over a broad region Form where air ascends gradually over a broad region Cumuliform clouds are puffy, like cotton balls Cumuliform clouds are puffy, like cotton balls More vigorous ascent of air over a smaller area More vigorous ascent of air over a smaller area Under the right conditions can build vertically into a cumulonimbus (thunderstorm) cloud Under the right conditions can build vertically into a cumulonimbus (thunderstorm) cloud The appearance of high, wispy, feather-like clouds (composed of ice) in the western sky is often the first sign of an approaching warm front The appearance of high, wispy, feather-like clouds (composed of ice) in the western sky is often the first sign of an approaching warm front

32. 32 Cloud Forms These high thin cirrus clouds appear fibrous because they are composed of mostly tiny ice crystals These high thin cirrus clouds appear fibrous because they are composed of mostly tiny ice crystals

33. 33 Cloud Forms These relatively low clouds are composed of tiny water droplets and have more sharply defined edges than ice-crystal clouds These relatively low clouds are composed of tiny water droplets and have more sharply defined edges than ice-crystal clouds

34. Cloud Forms Fog, stratus clouds in contact with the ground, reduces visibility

35. 35 Cloud Forms Fair weather cumulus clouds are most common during the warmest time of day and then vaporize after sunset Fair weather cumulus clouds are most common during the warmest time of day and then vaporize after sunset

36. 36 Cloud Forms Clouds of vertical development Clouds of vertical development Merging and vertically-growing cumulus clouds Merging and vertically-growing cumulus clouds Can become Cumulonimbus clouds Can become Cumulonimbus clouds Nimbo, nimbus prefix or suffix = rain producing Nimbo, nimbus prefix or suffix = rain producing These clouds always produce lightning and sometimes heavy rain, hail, or strong and gusty surface winds These clouds always produce lightning and sometimes heavy rain, hail, or strong and gusty surface winds

37. 37 Cloud Forms Clouds may move in different directions at different altitudes Clouds may move in different directions at different altitudes Indicates horizontal wind shifts with altitude Indicates horizontal wind shifts with altitude