Lab: Using Correlation Coefficient During Winter Events Objective: In this lab exercise we will investigate a couple winter weather events from late 2013 to see how the correlation coefficient radar product could be used to help us identify changes in precipitation type. We will also take a look at Skew-T s and Mesonet data to diagnose precipitation type. Instructions: You will need to use the latest version of RadarFirst to complete this lab. Please read each question carefully and answer them as best you can in the space provided. You are welcome to work on your own or in a group. Region of Focus for this Exercise: For the purposes of this lab we will keep our attention on central Oklahoma and will only use the KTLX (Oklahoma City) radar. Terminology: The following are definitions of several meteorological terms you may see during this lab: Base Reflectivity (BREF) Radar product that measures how much of the radar s energy is reflected back to the radar. More particles and/or bigger particles reflect more energy. This is the most common radar product shown on TV. Correlation Coefficient (CC) Dual-pol radar product that measures how uniform or diverse radar targets are. The following are values and what they mean: o Values greater than 0.97 uniform precipitation o Values between 0.8 and 0.97 mixed precipitation (such as snow and sleet, sleet and freezing rain, etc.) o Values less than 0.8 non-precipitation targets Skew-T Diagram A way to plot information from a weather balloon that shows how temperatures, dew point temperatures, and winds change going upward in the atmosphere. Temperature lines are skewed diagonally giving this chart its funny name. Conditions nearest the ground are at the bottom of the chart, while conditions higher in the atmosphere are found by moving up the chart. 1
Cheat Sheets: 2
Lab Exercise: Open RadarFirst. Put the software in 2-pane mode (View à Two Panes) and make cities visible (Edit à Options à Show Cities). At the top of RadarFirst Go to Edit à Date... and set your date to 11/22/2013 and your time to 12:00PM. For your radar, choose KTLX Oklahoma City. In the left radar window pick radar product BREF2 and in the right radar window pick CC2. Your software should be set as follows: Radar Date Time Left Pane Right Pane KTLX Oklahoma City 11/22/2013 12:00PM BREF2 (Base Reflectivity 2) CC2 (Correlation Coefficient 2) Question 1. Base Reflectivity shows what looks to be precipitation going through central Oklahoma. Looking at Correlation Coefficient in the right window, what do the dark red colors mean? What do the yellow colors in the right window mean? Question 2. What do we call the yellow area in Correlation Coefficient in the right window? Scroll your mouse over this yellow area in Correlation Coefficient. About how high up is it? Question 3. At the top of RadarFirst go to Edit à Date and change your time to 2:00PM. How has the shape of the yellow area in Correlation Coefficient changed since 12:00PM? Briefly describe. Question 4. Relying only on radar (not something we should do in reality!) make a prediction of the type of precipitation you think might be occurring in the OKC metro area that afternoon. 3
Question 5. 2PM Mesonet surface temperatures, freezing line (yellow), and winds plus radar Correlation Coefficient 2 are shown below in the top image. The 6PM Skew-T (with freezing line in blue) from Norman is shown below in the bottom image. Given this added information, what type of precipitation do you think occurred in the OKC metro that afternoon? 4
Let s check out another event. At the top of RadarFirst go to Edit à Date and change your date to December 5, 2013 and the time to 3:00PM. Make sure your software is set as follows: Radar Date Time Left Pane Right Pane KTLX Oklahoma City 12/5/2013 3:00PM BREF2 (Base Reflectivity 2) CC2 (Correlation Coefficient 2) Question 6. Describe what you are seeing in the Correlation Coefficient product in the right window. Again, what do the dark red colors mean? The yellow colors? Question 7. Scroll your mouse over the yellow area in Correlation Coefficient in the right window. About how high up is it? Question 8. Look at the reflectivity data in the left window. Describe what you are seeing. Question 9. Relying only on radar (again, not something we should do in reality!), make a prediction of the type of precipitation you think might be occurring in the OKC metro area that afternoon. 5
Question 10. 3PM Mesonet surface temperatures, freezing line (yellow), and winds plus radar Correlation Coefficient 2 are shown below in the top image. The 6PM Skew-T (with freezing line in blue) from Norman is shown below in the bottom image. Given this added information, what type of precipitation do you think occurred in the OKC metro that afternoon? 6
Let s move forward in time to the next morning. At the top of RadarFirst go to Edit à Date and change your date to December 6, 2013 and the time to 6:00AM. Make sure your software is set as follows: Radar Date Time Left Pane Right Pane KTLX Oklahoma City 12/6/2013 6:00AM BREF2 (Base Reflectivity 2) CC2 (Correlation Coefficient 2) Question 11. We have moved forward in time 15 hours. Describe how the Correlation Coefficient product in the right window has changed from earlier. What is different? Question 12. Base Reflectivity data has a different appearance than it did 15 hours ago. Describe it. What is the highest reflectivity value you can find? Question 13. Again only using radar, what is your prediction of precipitation type in the OKC metro area that morning? 7
Question 14. 6AM Mesonet surface temperatures, freezing line (yellow), and winds plus radar Correlation Coefficient 2 are shown below in the top image. The 6AM Skew-T (with freezing line in blue) from Norman is shown below in the bottom image. Given this added information, what type of precipitation do you think occurred in the OKC metro that morning? 8