UW-Madison ATMOCN 100 - Mountain Snowstorms (7 pages)

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Mountain Snowstorms

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Mountain Snowstorms


A lecture about mountain snowstorms and how they effect life.

Lecture number:
Lecture Note
University of Wisconsin, Madison
Atmocn 100 - Weather and Climate
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Atm Ocn 100 Edition 1nd Lecture 37 Outline of Last Lecture I Reminders II Weather of the day III Lake Effect Storms IV Snow climatology highly influenced by lake effects V Why Lake Effect VI Lake Effect Storm Types VII Different Animations of Lake Effect Storm Types Outline of Current Lecture II Reminders III Weather of the day IV Mountain Snowstorms V Orographic Clouds in the Rockies VI Water Rights in the West VII Major Issues VIII Rocky Mountain Eastern Slope Upslope Storms IX Cold Air Damming Current Lecture Reminders Homework due Friday Cloud Project due Sunday Final Review either this Friday at 4 pm or Sunday at 4 pm Final is next Wednesday the 17th at 12 25pm in Agr Hall 125 Final is cumulative but focus also on current section Weather of the day Sea level pressure is the pressure that you would have at sea level elevation But we have topography 1025 pressure would be at sea level in Denver instead of mile high at the city Why don t we plot surface pressure instead of sea level pressure The reason is that pressure varies very dramatically with height If Denver is at 850 mb and you plotted that on there on the coast would be 1000 mb It would be 150 mb difference in pressure just because of elevation All that we would see on a surface map would be topography It would be difficult to see weather systems So we normalize the weather we plot to sea level which is all the same elevation In order to do that extrapolate the pressure of Denver down to sea level This then allows us to see weather patterns Then we can look for the rain snow line and see what that looks like It looks like New York and all of Pennsylvania will have some snow but light snow The east has a lot of ski areas Particularly in New Hampshire and Vermont They can get up to 15 feet of snow really from the upslope Because there is warm air from the east the rain snow line plays tricks with this There isn t the nice Christmas snow in Maine or New Hampshire yet The coast and the ocean as a source of moisture are good and bad news for ski areas There is a lot of moisture but it tends to be warm so it is a problem for the good powder snow There is a system going into California with heavy participation This is on Friday The El Nino years are good for this This is fairly active for this time of year In 5 days there is another big amount of rain coming into the Southern California coast again California would like to see a lot more than this Mountain Snowstorms Lake effect storms account for moisture and precipitation They are important in certain areas There is something in common between lake effect storms and orographic storms This picture shows us that the clouds are shallow they aren t very high The clouds in this orographic storm are barely higher then the Rockies themselves And yet in this situation this would be looking at the east from the Rockies On the other side the clouds coming over could be getting snow at a couple inches per hour and it could last for days Lake effect storms work similar they have shallow clouds The problem with forecasting how much snow or precipitation you would get was what Because shallow clouds the critical issue with forming precipitation is that they don t get cold enough at the top to always form ice In order for a cloud to form a viable ice process the top of the cloud has to be 20 This may or may not be there The other issue that comes into play with mountain snowstorms is that the snow that falls and melts and fills reservoirs is what keeps the west alive The west lives off of the snow from these systems It is important to the west that the clouds get to 20 degrees When this happens the economy does well because of the snow What kinds of rates of rising motion happen here Air being lifted over a front we are talking about 5 centimeters to 10 centimeters If you have precipitation band from convection of course the precipitation is more intense buoyant unstable and rises And then you get a different rising When there are convective bands there is heavy precipitation from thunderstorms and so on Clouds away from the front it is slower rising motion When there is a steep slope you get 1 to 5 meters per second that is strong it is equivalent to precipitation band because just having a mountain Orographic Clouds in the Rockies They produce the snow that fills the reservoirs and rivers and facilitates many recreational activities skiing xcountry skiing snowmobiling etc Can lead to flash flooding that threatens commerce and lives Have the potential to be improved in their yield through weather modification or does that just rob some other region of their water This can happen through cloud seeding which is putting artificial ice in the cloud to make them produce ice The snow pack of the western mountains of North America melts to provide precious water for the West Domestic use has first priority for water Industry has second priority Irrigation has third priority but uses 95 of all of the water They prioritize what is going to be put where Only about 5 used by first two categories until big drought then it changes Water Rights in the West There simply is not enough water in the West Water rights are a property in the West more valuable than the land itself in many cases The Colorado River the life blood of the West fed by the snowmelt of the Rockies never reaches the Gulf of California Major fight between Northern California and Southern California is over water Southern California diverts water from Northern California drainage by aqueducts taking away potential commerce from the North Someone owns the water The Front Range Cities and agriculture receive a large portion of their water from the West slopes via a large siphon Big Thompson Project built during the depression They fill reservoirs in the spring runoff and empty them during the growing season They divided up the waterfronts that they sell to people Big fight on the Front Range of Colorado Thornton a suburb of Denver secretly bought up the water rights from some farmers in Northern Front Range near Ft Collins and then announced a plan to build an irrigation ditch to bring their water south but Ft Collins is taking it to court because that will limit the ability of Ft Collins to grow The Colorado River water rights were based on the flow of the river during a 10 year period I think in the 1880 s and that period was above normal Colorado is responsible for delivering a certain number of acre feet of water to Utah and Utah

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