Characteristics of the extra tropical cyclone Winds and clouds circulate in a CCW direction comma 1000s of miles sno w Dry Slot f re et in e l s g ra in ez rain t storms Key features of the extra tropical cyclone A review slide Cold Dry Cool Moist Warm Moist Origin and tracks of extra tropical cyclones affecting North America Alberta Clipper Move quickly along the US Canada Boarder Typical track Time to cross the US Colorado Low Track across the central US from CO Chicago NE Ark La Tex Low Name tells us where they start Gulf Low Very powerful because they extract heat and moisture directly from Gulf of Mexico Hatteras Low Very powerful and rack up the east coast 100 million people Why do the winds in a ETC circulate CCW 2 Primary Forces that control the wind Pressure gradient force Change in pressure PGF Change in distance Always directed from H L Acts perpendicularly to isobars Spacing of the isobars wind speed Coriolis Force Air crosses isobars into the low pressure center spirals inward H H H L H H H Development of High and Low pressure systems Main Idea To increase the surface pressure put more air molecules in the column To decrease the surface pressure remove some of the air molecules in the column This is accomplished by Convergence and Divergence For a high pressure system to strengthen aloft must be than at the surface Sinking air above a high clear skies nice weather For a low pressure system to strengthen aloft must be than at the surface Rising air above a low clouds and precipitation The Jet Stream Definition Band of strong winds that encircle the earth in a wave like pattern that moves from the west to the east Size 200 300 miles wide 1 mile thick 1000s of miles long Location 30 N 80 N 9 km above the sfc 300 mb Jet streaks regions of the jet stream with exceptionally fast winds warm cold warm warm Constant Pressure Maps Sloping Pressure Surfaces Real World T R O U G H R I D G E W A R M R I D G E T C R O O L U D G H 300mb map look for jet stream Winds color coded with arrows Heights contoured white Key Idea The thickness of a layer in atmosphere is governed by the mean air temperature between the top and bottom of the layer How Do Meteorologists View the Jet Stream another example Main trough axis cold air under the trough of the j e t s str axi ea n i a m M Jet Streaks Main ridge axis warm air under the ridge Air flow parallel to isoheights same as isobars faster when the isoheights are close together Air Flow Aloft Key Feature 300 mb the air flow in the jet stream slows down and piles up here the air flow in the jet stream speeds up and spreads apart here surface FAST FAST Div Conv SLOW 300 mb Map height contours only How does the jet stream create low pressure Curvature Effects Je t St r ea m top down view side view C D C D D C 300 mb Surface Surface high pressure forms here Surface low pressure forms here Putting it all together