Probability of Precipitation

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SWBAT interpret graphs and predict the relative probability of precipitation featuring data on air temperature, dew point, and relative humidity.

Big Idea

Students examine how probability of precipitation increases when air temperature and dew point get closer together, and when relative humidity increases

Lesson Introduction

In this lesson, students grasp the complex relationships inherent in this unit - specifically, in this lesson, students learn about the relationships that exist between temperature, dew point, relative humidity, and how that ultimately affects the probability of precipitation. This lesson starts with students examining the local weather for any type of relationship between humidity and dew point, and then involves the deeper analysis of some other weather variable graphical relationships. As a note, students need to be reasonably comfortable creating and plotting points on line graphs (or you need to be prepared to very deliberately guide them through this process - here's a link from a previous lesson on how I might structure it). Other than that, there are no special materials or equipment needed for this lesson (save for rulers, assuming you want to have your students plot some pretty graphs!). 

[Note: For embedded comments, checks for understanding (CFUs), and key additional information on transitions and key parts of the lesson not necessarily included in the below narrative, please go to the comments in the following document: 5.4 - Precipitation & Humidity (Whole Lesson w/comments). Additionally, if you would like all of the resources together in a PDF document, that can be accessed as a complete resource here: 5.4 - Precipitation & Humidity (Whole Lesson)[PDF]. Finally, students may need their Earth Science Reference Tables [ESRT] for parts of the lesson (a document used widely in the New York State Earth Science Regents course) as well.]

Do Now & Objective(s)

10 minutes

Students come in silently and complete the (attached) Do Now. In this case, the Do Now is a review of material from the previous few days, particularly the calculations of relative and humidity and dew point. After time expires (anywhere from 2-4 minutes depending on the type of Do Now and number of questions), we collectively go over the responses (usually involving a series of cold calls and/or volunteers), before I call on a student and ask them to read the objective out loud to start the lesson.

As a general note, the Do Now serves a few purposes:

  1. It serves as a general review of the previous day's material; (again, this is a bit different, as they are reviewing for the quarterly Interim Assessment)
  2. It is a re-activation of student knowledge to get them back into "student mode" and get them thinking about science after transitioning from another content area or alternate class;
  3. as a strategy for reviewing material students have struggled with (for example, using this as a focused review for material that they have struggled with on unit assessments or recent quizzes); and,
  4. It is an efficient and established routine for entering the classroom that is repeated each day with fidelity (I never let students enter the classroom talking. While it may seem potentially severe to have students enter silently each day, this is both a school wide expectation and a key component of my classroom. In many respects, I find that students readily enjoy the focus that starting with a quiet classrooms brings each day).

Atmospheric Variables

20 minutes

Immediately after the Do Now, students explore Atmospheric Variables by examining their local weather report (the one in the resource is one pulled from Google Weather) and being asked to examine the humidity and % of precipitation rows. In this particular example on the top of the Atmospheric Variables resource, both are relatively low percentages, but students are asked to extrapolate when I ask: "Look at the humidity and precipitation chance for a second. Are they related at all? Would precipitation be likely here or not? How do you know?"

After taking a few reposes from students, we jump into the text on the first page of the Atmospheric Variables resource. The text itself is a brief, two-paragraph piece explaining the relationships between air temperature, relative humidity, and dew point, and the notion of how humidity changes as a function of temperature because the air can hold more or less water dependent on its overall temperature. 

After reading this collectively, I then ask students to examine the graph on the bottom of the first page in the Atmospheric Variables resource. This graph shows a very explicit inverse relationship between air temperature and relative humidity. I ask to see if anyone can identify this (which they can generally do without any difficulty), and then ask them to hone their attention on 6:00 am. There, the air temperature is at its minimum point in the day, which likewise means that the relative humidity has increased to its highest value in the graph. I then ask them what they think is likely to happen at that time, given what the graph shows. Eventually, students are able to get that since the relative humidity is so high and the air temperature has reached the dew point, that indicates that the air is close to, if not fully saturated, and precipitation is very likely. 

On the next page of the Atmospheric Variables resource, we look at a few more graphs detailing the relationship between temperature, dew point, and relative humidity. At the top of the second page, I ask students to study the graph and determine when precipitation is most likely (the answer is right around 5-6 PM, when the dew point and air temperature are closest together. Indeed, that is one of the key components of the lesson - the less the distance between air temperature and dew point, the greater the probability of precipitation! We then look at the same graph at the bottom of the page, but with relative humidity added in. In this sense, I ask students to observe how at 5-6 PM, when the dewpoint and air temperature have the smallest difference, that the relative humidity is also highest.  


25 minutes

The Practice section in this lesson is, like the vast majority of questions found in all of my classwork and homework, is 100% Regents-based (including the "Quick Check" problem at the top of the first page of the resource). All of the questions come from prior Regents examinations. Likewise, as I try to generally do with all of my lessons, the questions are mostly organized to get increasingly more difficult and increase in complexity, which is why the harder questions tend to come toward the end. For whatever reason, I've found that many students struggle with this content - they mix up the shadow lengths, the inverse relationships, all that stuff. The best way I've found to combat this is to give them the chance to identify and correct their mistakes in questions of this type, which is why this section is a little extended as per my usual lessons. Additionally, one of the ways the Regents course likes to add or modify the rigor to questions is to take a scientific definition and replace that for the vocabulary word. For example, question #7 in the Practice asks students about "which has the greatest capacity to hold water vapor," which is just a long-winded way of saying "which has the highest humidity." Make sure your students (and you as the teacher) are vigilant in watching out for those terms, as they have the tendency to trip some kids up here and there if their in-use vocabulary isn't as firm as it needs to be.

In terms of student work habits, I tend to sometimes make this decision in the moment, and as a response of what I know about the students and how they're processing the material on, but I'll either ask them to work independently, in partners, or (sometimes) give them the option. Usually, before starting practice, we tend to go over some steps for self-help ("What should you do if you're stuck?"), and I might reference a previously used multiple-choice or free response strategy in order to build their skills while simultaneously learning content (as an example - one popular one we always use - "If you aren't sure what the right answer is, see if you can eliminate some wrong answer choices"). I tend to circulate for compliance and then hone in on specific students while they're doing this. 

After about 10 minutes, we go over their responses. Students who finish early are encouraged to work on the exit ticket (resource below) and double-check their responses. We use a combination of strategies (active voting, cold calling, popsicle sticks, volunteers) to go over the responses, where students correct their work and ask any clarifying questions. 

Exit Ticket & Closing

5 minutes

In the last few minutes of class, I have students complete the daily Exit Ticket. For the sake of time, I have students grade them communally, with a key emphasis on particular questions and items that hit on the key ideas of the lesson (Note: This usually manifests as students self-grading, or having students do a "trade and grade" with their table partners). After students grade their exit tickets, they usually pass them in (so that I can analyze them) and track their exit ticket scores on a unit Exit Ticket Tracker. 

After students take a few seconds to track their scores, we usually wrap up in a similar way. I give students time to pack up their belongings, and I end the class at the objective, which is posted on the whiteboard, and ask students two questions:

  1. Do you feel that you mastered the objective for the day?
  2. Can you reiterate one thing you learned about (in this case, how to calculate the probability of precipitation, etc.)?

Once I take 2-3 individual responses (sometimes I'll ask for a binary "thumbs up/thumbs down" or something similar), I have students leave once the bell rings.