Lecture 11Outline of Last Lecture I. Weather of the daya. Knowing that there are different forecast predictions we should look atII. Geostrophic AdjustmentIII. ModelIV. Physic’s ApproachV. Air ParcelsVI. Gradient Wind Balance…VII. Wave PatternsOutline of Current Lecture II. StabilityIII. Weather of the daya. Convective weatherb. Clockwise motion airc. Heat moving through a troughd. Severe stormse. HelicityIV. Stability and what it meansV. Air Parcels VI. Basic PrincipleVII. Adiabatic Processa. Dry Adiabatic Processb. Moist Adiabatic ProcessCurrent LectureStability:Reminders:Homework #2 is due this Friday! Today we are going to talk about Stability. Atm Ocn 100 1nd EditionStability: 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 Centerhttp://www.spc.noaa.govThis 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 anotherThe 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 withheight.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 movingtoward 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 thatcold air will come south which is what will give us a cold weekend. In advance of that we have other stuff goingon. 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