Atm Ocn 100 Edition 1nd Lecture 11 Outline of Last Lecture I Weather of the day a Knowing that there are different forecast predictions we should look at II Geostrophic Adjustment III Model IV Physic s Approach V Air Parcels VI Gradient Wind Balance VII Wave Patterns Outline of Current Lecture II Stability III Weather of the day a Convective weather b Clockwise motion air c Heat moving through a trough d Severe storms e Helicity IV Stability and what it means V Air Parcels VI Basic Principle VII Adiabatic Process a Dry Adiabatic Process b Moist Adiabatic Process Current Lecture Stability Reminders Homework 2 is due this Friday Today we are going to talk about Stability Stability This is when atmospheric forces match each other so there is no net movement This has a lot of implications of why clouds form and storms form Weather of the day National Centers for Environmental Prediction Today is a chase day Chasers are out in the field today looking for tornados One of the centers predicts that and we are going to look at that today This center is divided into a lot of sub centers The main office is located in Washington DC There s a tropical prediction center in Miami Storm prediction center is what we are going to look at today Storm Prediction Center http www spc noaa gov This site has information for assessing the potential for severe weather It has real time diagnostics of severe weather and weather systems that are causing severe weather Extensive tools for personal forecasting of severe weather We did not have this 20 years ago now we have so much more technology Now you can log on to this and see where you are relative to the storm Let s look at forecast for this afternoon An hour after this class ends What is being predicted is that there will be some cloudiness Today in the Kansas Missouri area that is where a lot of action is going to be By 0 z a lot of stuff is happening in Kansas area Looks like some rain The precipitation map shows that there is a yellow line around it Yellow contours say that the precipitation will be convective Convective The transfer of heat from one place to another The rain will be about half an inch Model is saying there will be this change because it is becoming unstable this means that the air rises not because it is being lifted but it rises and is buoyant Buoyant Force that equals its own weight it neither rises nor falls For buoyancy to push something up in the air the thing has to be light than an equal volume of air around it Air pressure causes an upward buoyant force in the air Air pressure is greater below us so air pushes up more than it pushes down On the supercell index of the model It says whether it sees any of these or not The model is predicting that in the Kansas Missouri region it is up in the yellow We don t see the yellow often mostly if the area is red is most unstable but we see it as yellow now This is saying that there is a commination of conditions that will lead to severe weather It is not just instability that produces thunderstorms You can have thunderstorms but not have severe storms like tornados The way the wind is structured with height matters for this The direction of speed with height is called wind sheer This happens when a weather system is moving in a trough up in upper levels a southerly flow below and then west wind comes in The wind turns clockwise with height When wind turns in the clockwise matter This occurs because there is warm air being drawn pull ward just before a cold front comes through As we have seen there is a trough of cold air and rossby wave trough associated with that That cold front is moving toward us and is supposed to get here by Friday It is coming close This weather is unraveling in preparation for that In the upper airfields we can see the air mass coming in We can see the trough to the north which has cooler temperatures The cooler temperatures are to the northwest At 48 hours which would be midnight Thursday night we can see that cold air is really driving in Today is the advance of the cold air Air has started to produce northerly flows along the Rockies By Friday that cold air will come south which is what will give us a cold weekend In advance of that we have other stuff going on At 500 mb which is the middle of atmosphere we can see major rossby wave trough which is associated with the push of cold air If we look at previous maps we can see that the trough is a reaction to the ridging out in pacific which was from tropical storms in west Colors on these models show a range of motion which is basically if air is going up or air is going down We can see there are a couple places where it is going up One of those places is by us There is changes in the trough or in other words a big trough here of low pressure inside of that there are little troughs Little troughs are called short wave troughs There are the big long wave trough and the little shortwaves within the long waves Fronts are associated with individual short waves Little ones are associated with anomalies in the trough When you have air moving through a trough There is air movement that goes through the trough or big features the troughs are going slower than the air Air parcels are moving through the trough Relative to the air the trough is moving toward the west But nevertheless parcels are moving through the trough they move through sharp coverture of the trough have a cyclonic turning which then creates a centrifugal force toward the south a coriolis effect toward the south and a pressure gradient toward the north After this the curvature is changed depending on the wave which means the air parcels will curve the other way This causes flow to speed up Usually flow goes through trough slow and speeds up at the end because of this change of curvature The force is divergent on the other side of the trough which then causes air to rise The air is sucked up at divergence in lower levels Air is raising movement inside the trough will lead to the severe weather this afternoon So what is happening now is that the little wave is moving fast through the trough The shorter the rossby wave the faster then moves through the westerly s The big one moves the slowest toward the east Flow is going faster then these big waves Relative to the wind the waves are actually moving toward the west Relative to the ground though they are moving to the east The longer waves though in actually are faster …