Atm Ocn 100 1nd Edition Lecture 12 Outline of Last Lecture I Stability II Weather of the day a Convective weather b Clockwise motion air c Heat moving through a trough d Sever storms e Helicity III Stability and what it means IV Air Parcels V Basic Principle VI Adiabatic Process a Dry Adiabatic Process b Moist Adiabatic Process Outline of Current Lecture II Weather of the Day III More on Dry Adiabatic Process IV More on Moist Adiabatic Process V Lapse Rate VI Stability a Conditional Instability b Implications of Conditional Instability VII Stuve Diagram VIII LFC and LCL a Implications of LFC IX Mechanisms to lift a parcel to LFC Current Lecture Reminders Homework 2 is due tonight Test is one week from next Wednesday Monday before the test we will do a review so a week from this coming Monday We are a little behind in lectures so the test will not cover as much as was in the original syllabus We will hopefully get through thunderstorms and a little bit about tornados The test will mostly be about stability and thunderstorms which is what we are doing now Prof hasn t made the test yet not sure exactly what will be on there Weather of the Day Stephan is now going to cover this so we can get back to lecture Right now we are looking at a 250 mb map the wind We are seeing that there is an area of stronger winds There is a jetstreak over by Wisconsin We are looking at what areas the jetstreak leads to upper level divergence There is a development of low pressure at the surface There is pressure in the 900 s over Wisconsin The blue lines on this map are the surface pressure We should focus on the blue lines If we go ahead a few hours this would be later this morning the jetstreak has moved off to the north Now we see that the streak in the region now over lake superior moving into Canada and that there is still low pressure developing here Precipitation in the area we expected from the jet now is 994 pressure which is stronger then before A few more hours ahead the jet now is moved over Michigan so there might be low pressure here There looks to be low pressure a little north of us which is 986 by this afternoon We can see that there are low pressure systems in areas of upper divergence which are caused by a jet moving through Canada Associated with this pattern moving in here we can see there is a strong trough dipping into our area We have been watching this cold air push since last week Last Friday it looked very strong but it looked weaker on Monday The forecasts have been back and forth on this But now are in it that weather There is more confidence of what the forecast will be now that it is upon us and it looks as though there is a very strong trough moving into our area There is a forecast for snow tonight Air is very cold that is coming in which is making the atmosphere overturn colder temperatures which will not let snow melt before it hits the ground Even though the surface temperature will probably be above freezing there will not enough time for precipitation to melt before it hits the ground All the precipitation we get here begins at snow but in the fall most of the time it melts before it hits ground in wintertime though it doesn t melt Now we will look at an 850 mb map from the AOS site We can see that cold air is dropping in 850 mb isotherms As we discussed before where is the rain snow line on an 850 mb map Or in other words what isotherm at 850 mb determines rain verse snow at the surface near sea level Answer There is a 0 degree isotherm at 850 mb That is one way you determine whether there will be any precipitation and if it will be rain or snow On this map the 0 degree line is right around the light blue coloring Precisely the 0 degree line is between the light and dark blue The 0 degree line is moving into the U S right now toward our area right now We can see that cold air is coming down We can even see that some magenta is in there which is pretty cold That is about 14 or 10 at 850 mb This is pretty cold for this type of year The magenta coloring is in Canada so it may not make it to us but it is cold and it is something to look at for this time of year The yellow colorings are the polar vortex same of which we had last year As discussed a minute ago this is pretty cold air for early October If we watch the air come down we see that there is a low pressure at 850 mb that is coming down on the west side of the low The winds are going around counterclockwise into our area The counterclockwise is cyclonic vortex which is wrapped with cold air This is when you see on t v when they are talking about the polar vortex This is the polar vortex this low that is wrapping cold air around it is the polar vortex For us right now that cold air will pull out right away But we can see and visualize that last winter that cold air low sat near us and kept driving cold air in here This became a persistent condition for a long time At the end of this though it will pull out We shouldn t see this cold air for long after this weekend In news regarding tropical cyclones there is a little tropical cyclone in Baja right now that is suggesting it will move inland That isn t to be disregarded If this tropical cyclone is moving up it will bring moisture up towards us which could mean heavy rains next week in our area The trough will divert moisture to the southeast but if the cold air moves out of here fast enough some of that moisture from the tropical cyclone could come to our area If that moisture gets us we get the heavy rains of fall What would be causing the snow if we had snow tonight Assuming we get any snow tonight Well the cold air is coming down over us If we look at 24 hours which is midnight tonight we see that the cold air is right on top of us And if we go to 30 hours which is dawn tomorrow the cold air center has moved into Chicago but still looks cold over us We will have another push of cold air by tomorrow This looks like very cold air the air temperature is about 6 or 8 This is very cold it looks to be below 0 for sure If we say that Madison has an elevation of about 1100 meters …