ATMO 336 1st Edition Lecture 2Outline of Last Lecture II. Definition of 500mbA. Air pressure vs. water pressureIII.Contour maps and their significanceIV. Relationship between 500mb height patter and air temperaturea. Defining closed lowsb. Defining closed highsc. Warm air in relationship with ridgesd. Cold air in relationship with troughsOutline of Current Lecture V. Wind direction and speed at 500mba. Closed lows= air turns counter clockwiseb. Closed highs= air turns clockwise VI. Estimating likely areas for precipitation from 500mb height patternsa. Precipitation and clouds= air risingb. Fair weather=air sinkingc. Precipitation around “wrap around” closed lowsVII. Tucson January 2013 exampleVIII. Forecast mapsCurrent Lecture- Wind direction and speed AT 500mbo Wind @ 500mb can be determined from height pattern o Wind blows PARALLEL to height contours Lower heights to the left of the wind direction and higher heights to the right of the wind direction EX: in winter, air blows west towards east but follow wavy pattern of height contours. This 500mb height level weakens during summer months (temp differences between tropics and arctic become weaker)o Wind trajectory: traces motion of air Troughs and ridges do not have to be oriented along a north-south axis. With troughs (and closed lows) the air makes counter clockwise turn With ridges (closed highs) air makes clockwise turn in northern hemisphereo Wind faster where height lines are CLOSER together and slower where spaced FURTHER apartThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o 500mb winds=large influence on motion of smaller scale weather features (low pressure areas, movement of hurricanes, thunderstorms, ect.)-Estimating likely areas for precipitation from 500mb height patternso Clouds and precipitation most likely occur downwind (or downstream) from location of 500mb troughsRegion just after wind has passed trough and heading into the ridgeClouds and precipitation happen were air RISESClouds do not develop where air is SINKING= fair weather 500mb air flow= counter clockwise around closed lows, thus, it is common for there to be precipitation “wrap around” a closed low.-Precipitation uncommon in closed highs= air forced to sink vertically on these ridgeso Example in Tucson on Jan 2013Not enough moisture in the air to produce precipitation at a closed low over Tucson.-Forecast mapso Numerical weather forecast models in winter are quite accurate for 1-5 days into future. Less accurate as time moves on.-Two different forecasts maps, both use ONLY the 500mb map (other maps include other details)o University of Wyoming’s model forecast page (forecasts from US weather models)Uses GFS (global forecast system) or medium range Forecast (MRF) Both run in the US by NOAAo Weather online UK (forecasts form the European model)This model performs better than the US model (more accurate)-Made more accurate predictions of hurricane sandy than the US
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