Agenda
1. Convergence seems to happen on the west side of troughs.
2. Instability is when the air spontaneously rises and it is warmer than the air around it at a given height. If you need more information about this concept look on page 317 of the Reader.
One factor that helps to contribute to instability is the uneven heating of the ground. A southerly wind can also contribute to instability. This wind can increase the dew point, and when you increase the dew point you create a higher latent heat. Unstable air is what helps to create thunderstorms. If there is a greater dew point there is more water vapor. Water vapor plays a great role in instability. If there is more water vapor there are more thunderstorms. Why?
Evaporation occurs when water changes, for every gram there is a tremendous amount of cooling. Evaporation chills/cools whatever it is on. It is associated with latent heat. Condensation does the opposite. Moisture condenses, heat lets out in the atmosphere. Thus, if moisture is condensing in a rising air parcel that is the same temperature as the surrounding air, latent heat makes the air parcel warmer and it becomes unstable by being made warmer than the surrounding air. Thus, meteorologists often look for regions of high surface dewpoint and assume that the air there is pretty unstable.
3. Current Weather The wind is coming from the North and then curving into the coast. What does this do? It creates instability and "darn cold weather." These types of cyclones are called higher latitude cyclones. What would you expect this storm to do? You expect it to be colder with the snow level reaching down to 2,500 feet tonight. You also expect less precipitation because the colder air can’t hold as much water which in turn creates a lower dew point. These fronts are not continuous cloud bands because there is a lower dew point. A web site that we really used in class was WWW.rap.ucar.edu we used this to check out all the current weather maps.
4. Writing Assignment #2 The title of this assignment has to be Diablo Winds: A Foehn-Type wind in San Francisco Bay Regions. The first paragraph must be the Intro paragraph. This is only one paragraph whose purpose is to define and explain the why’s and the how’s. In this paragraph you will establish the purpose for the paper. The last paragraph should be the conclusion. Do not include Platitudes in this paragraph!!! You should summarize what you said. Remember to label figures clearly and have them in sequential order in the text.
From now on when we need a reference section to refer to when we quote something in the paper. We can no longer have any footnotes or direct quotes. The way that you show that you understand something is by paraphrasing it. The only time that you may use quotes is if you come along something in your reading that is so profound that no one else ever said it. We must have at least four references in our paper.
If you are quoting Prof. Monteverdi’s paper you would do it like this (Monteverdi, 1970). If we quote a textbook we do it like this (Jones, 1986, p16).
5. Summer Patterns Concluded There are three dominate pressure fields over the United States. If you are having trouble with this go back to our hand out on thermal highs and lows. The low that is over America is what brings in the high dew point air. Reminder: The higher the dew point the more unstable that the air is and the more thunderstorms there are. Why don’t we (being in San Francisco) get coastal rainfall in the summer? The dew point is relatively low, but not enough to create clouds and precipitation (we have stable weather). Unlike us, South East California gets its peak rainfall during the summer. While looking at this map we notice that even slight changes in position can create dramatic changes (like LA to Death Valley). To make rain in the summer, you want the winds to come from the south.
Handout This pattern occurs most often during El Nino seasons. Hurricanes are on the maps because the warm weather/water is farther north than normal.
Next we discussed thunderstorms and what happened on September 22, 1999. We also looked at a water vapor image for the first time.
6. Mediterranean Climate The average temperature gets cooler as you go northward and as you go east it gets hotter. The coldest temperatures are restricted to the coast during the summer. The warmest areas are the protected areas like the Central Valley. Summer wind is faster around 4 in the afternoon and onshore. At night it is slower because the low is weakened.