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Weather 2013

Weather 2013. 24. 986. *. 1.5. 15 /. 21. .5. Part 1. Station Model. Barometric Pressure – millibars (mb) If # > 500, move decimal 1 place to left and put a “9” in front. Ex. 998.6 mb If # < 500, move decimal 1 place to left and put “10” in front. Ex. 232 = 1023.2 mb. Air Temp ( °F).

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Weather 2013

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  1. Weather 2013

  2. 24 986 * 1.5 15 / 21 .5 Part 1. Station Model • Barometric Pressure – millibars (mb) • If # > 500, move decimal 1 place to left and put a “9” in front. Ex. 998.6 mb • If # < 500, move decimal 1 place to left and put “10” in front. Ex. 232 = 1023.2 mb Air Temp (°F) Visibility (miles) Barometric Trend (change) during last 3 hours (move one decimal to left) = 1.5 mb Dew Point (°F) Amount of precipitation in last 6 hours (in)

  3. 24 986 * 1.5 15 / 21 .5 Part 1. Station Model Wind Direction – like an arrow coming in from where the wind originated (ex. East) Wind Speed -------- = 10 knots ---- = 5 knots Present Weather = 50 knots

  4. Part 1. Station Model

  5. Part 2. Air Masses • Characteristics of air masses • Determined by where they originate • Air over land = dry, water = humid • Air near poles = cold, equator = warm • Naming Air Masses • Continental – form over land; dry air • Maritime – form over water; wet air • Polar – form near poles; colder air • Tropical – form near equator; warmer air • Arctic – form over poles; Very cold air

  6. Part 3. Air Pressure Systems • LOW Pressure • Low density air (lighter), rising air • Usually warm, moist air • Has precipitation • Counter clockwise, into the center

  7. Part 3. Air Pressure Systems • HIGH Pressure • High density air (heavier), sinking air • Usually cooler, drier air • Fair, clear weather • Wind clockwise AWAY from center

  8. Part 3. Air Pressure Systems • Measurement of Air Pressure • Barometer – measures air pressure • Units • Inches of mercury • Millibars (mb) • Barometric Trends • Rising – clearing weather likely • Falling – increasing chance of precipitation • Steady - unchanging

  9. Part 4. Fronts • Cold Front

  10. Part 4. Fronts • Cold fronts move QUICKLY (less friction) • Weather conditions • Cooler temps • Short period of precipitation • As front passes, air becomes cooler and drier (clearing skies) • Wind shifts to north (cold air from north) • Air pressure rises since cooler, drier air is heavier than warm, moist air

  11. Part 4. Fronts • Warm Front

  12. Part 4. Fronts • Warm fronts move SLOWLY (more friction) • Weather conditions • Gradually warmer temps • Increased clouds • Steady precipitation for a longer time • Winds shift to a south direction • Air pressure decreases (warm, moist air weighs less)

  13. Part 4. Fronts • Stationary Front

  14. Part 4. Fronts • Occluded Front • Clouds and precipitation

  15. Part 4. Fronts • Finding Fronts on Weather Maps • Look for sudden changes in • Temperature • Air Pressure • Wind direction

  16. mT cP Part 4. Fronts • Development of Low Pressure Centers (Cyclones) • Form at interface between warm and cold air masses

  17. Part 5. Forecasting Weather • Weather patterns in US move from West to East (or SW to NE) • Low pressure = cloudy and precipitation • Rising, unstable air • Falling air pressure usually means the approach of stormy weather • High pressure = fair weather (cool, dry air) • Rising air pressure usually means fair weather is approaching

  18. Part 5. Forecasting Weather • Fronts cause unsettled weather, rising air causes precipitation • Warm fronts have longer periods of precipitation since they move slower than cold fronts (cold fronts have short and heavy periods of precip)

  19. Part 5. Forecasting Weather • Large pressure differences cause strong winds • Isobars are close together = greater wind speed

  20. Part 6. Violent Weather • When very cool, dry air collides with warm, humid air violent weather can occur (thunderstorms or tornadoes)

  21. Over land from collision of very different air masses (temp and moisture); spring - summer Over tropical water (energy from warm water); summer – early fall; lose strength when go over land Most common in mid-west states Coastal areas of SE and Eastern US 100 meters (up to a mile wide) 650 km (up to 400 miles) Days Minutes 200+ miles/hr 75 – 150+ miles/hr Funnel Huge spiraling low pressure area

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