Module 11 | Scenario 2: Interpreting Radar
- Due Mar 30 at 11:59pm
- Points 7
- Questions 7
- Available after Mar 17 at 12am
- Time Limit None
- Allowed Attempts 2
Instructions
Overview
Weather radars provide CAT scans of winter storms, but interpreting radar images, typically based on radar reflectivity (i.e., the energy returned to the radar from precipitation or other targets) can be tricky. After completing this learning activity, you should be able to recognize some common wintertime precipitation features observed by radar, but also some of the issues that can make radar interpretation difficult in mountainous regions.
Instructions
Utilize the information located in the Scenario and Key Concepts to answer the questions located in this activity. You may refer to your textbook and notes to help you work through the assigned questions if desired. You will have two attempts to complete this activity. The highest grade will automatically be recorded. Once you have submitted your activity for a second time, you will be able to see the correct answers. Discuss with your instructor if you have questions about your answers or feedback.
- Activity is due Sunday, by 11:59 p.m. MT
Submission and Assessment Guidelines
- You will complete the quiz associated with this scenario within Canvas. For help on how to take a quiz in Canvas, review How do I take a quiz.
- This learning activity is worth 7 points toward your final grade.
Scenario
You are an avid skier living in Salt Lake City and are always on the hunt for fresh powder. You have an Epic pass and an Ikon pass and want to be skiing at whatever resort is getting the most snow. You often examine radar imagery to decide where to go to find freshies in the morning or if you should skip afternoon classes for some late-day storm skiing.
Key Concepts
a. National Weather Service NEXRAD WSR-88D Radar on Promontory Point
The National Weather Service operates a NEXRAD WSR-88D weather radar, known as KMTX, on a 6,457-foot peak on Promontory Point, a peninsula that extends southward into the Great Salt Lake (Figure 1).
Figure 1. Coverage and scanning characteristics of the KMTX radar. Top: Areas where the 0.5˚ radar scan is partially or fully blocked by topography. Bottom: Height and width of the 0.5˚ radar scan over Salt Lake City (SLC), Little Cottonwood Canyon (LCC), and Soldier Hollow (SH), including partial blockage by the high terrain around the Cottonwood Canyons. White line depicts the center of the beam. From Steenburgh (2014).
KMTX enables decent radar coverage across much of northwest radar, but there are still a number of important interpretation challenges. These challenges include:
- Beam blockage
- Ground clutter
- Overshooting
- Bright banding
b. Beam blockage
As illustrated by Figure 1, the radar beam can intersect the topography, where it is blocked. If the radar beam is partially blocked, as in the bottom of Figure 1, a portion of the radar energy is lost, and as a result, less radar energy can return to the radar. This leads to artificially lower radar reflectivities in partially blocked areas compared to unblocked areas.
c. Ground clutter
When the radar beam intersects the terrain, some of the radar energy reflects off the ground and is returned to the radar, resulting in radar echoes that are not produced by precipitation, but by the Earth's surface. These echoes are known as ground clutter (Figure 2).
Figure 2. Radar image on a clear day showing ground clutter radar echoes where the KMTX radar beam intersects the terrain. From Steenburgh (2014).
d. Overshooting
Because KMTX is located on a peak and the radar beam becomes more elevated away from the radar, the radar often samples the atmosphere at altitudes above the Earth's surface. This can lead to overshooting. For example, the radar could overshoot a shallow storm (Figure 3, top), so that snowfall rates are higher than you might infer from radar reflectivity, or overshoot the sublimation of snow at low levels within a valley so that snowfall rates are lower than you might infer from radar reflectivity (Figure 3, bottom).
Figure 3. Schematic depiction of radar overshooting a shallow mountain storm (top) and radar overshooting sublimation with dry air over a valley (bottom). From Steenburgh (2014).
e. Bright Banding
Wet snow reflects more radar energy back to the radar than dry snow or rain. This often leads to a donut-like ring of high radar reflectivity around the radar site where the radar beam slices up through the transition zone, where falling snow is melting and changing to rain (Figure 4). Although the radar reflectivities are higher in this ring, this reflects the tendency for wet snow to reflect more energy back to the radar rather than higher snowfall rates.
Figure 4. Example of a radar bright band encircling the KMTX radar. From Steenburgh (2014).
f. Geography for radar images used in this activity
This map illustrates the background geography used for the questions in this learning activity, which may be useful for orientation. The area covered includes the Great Salt Lake and the Wasatch Mountains, with ski resort boundaries identified by red lines and Utah county borders identified by black lines. The topography is shaded.
Citations
Images:
Key Concepts
- Figure 1. Coverage and scanning characteristics of the KMTX radar. Top: Areas where the 0.5˚ radar scan is partially or fully blocked by topography. Bottom: Height and width of the 0.5˚ radar scan over Salt Lake City (SLC), Little Cottonwood Canyon (LCC), and Soldier Hollow (SH), including partial blockage by the high terrain around the Cottonwood Canyons. White line depicts the center of the beam.
- Citation: Steenburgh, J. (2014). Secrets of the greatest snow on earth: Weather, climate change, and finding deep powder in Utah’s Wasatch mountains and around the world. Utah State University Press.
- Figure 2. Radar image on a clear day showing ground clutter radar echoes where the KMTX radar beam intersects the terrain
- Citation: Steenburgh, J. (2014). Secrets of the greatest snow on earth: Weather, climate change, and finding deep powder in Utah’s Wasatch mountains and around the world. Utah State University Press.
- Figure 3. Schematic depiction of radar overshooting a shallow mountain storm (top) and radar overshooting sublimation with dry air over a valley (bottom)
- Citation: Steenburgh, J. (2014). Secrets of the greatest snow on earth: Weather, climate change, and finding deep powder in Utah’s Wasatch mountains and around the world. Utah State University Press.
- Figure 4. Example of a radar bright band encircling the KMTX radar
- Citation: Steenburgh, J. (2014). Secrets of the greatest snow on earth: Weather, climate change, and finding deep powder in Utah’s Wasatch mountains and around the world. Utah State University Press.
- Figure 5. Map illustrating the location of the KMTX radar, radar range rings, and geographic locations used for questions in this Scenario
- Citation: Steenburgh, J. Map illustrating the location of the KMTX radar, radar range rings, and geographic locations used for questions in this Scenario.
Quiz
- Question 1: NASA Satellite Image and KMTX radar image for 2000 UTC 27 Feb 2020
- Citation: NASA (n.d.). NASA satellite image. NASA.
- Citation: Steenburgh, J. KMTX radar image for 2000 UTC 27 Feb 2020.
- Question 3: KMTX radar image for 0756 UTC 7 Feb 2020
- Citation: Steenburgh, J. KMTX radar image for 0756 UTC 7 Feb 2020.
- Question 5: KMTX radar image for 1327 UTC 21 April 2017
- Citation: Steenburgh, J. KMTX radar image for 1327 UTC 21 April 2017.
- Question 6: KMTX radar image for 0804 UTC 9 March 2013
- Citation: Steenburgh, J. KMTX radar image for 0804 UTC 9 March 2013.
- Question 7: KMTX radar image for 00:57 UTC 13 December 2018
- Citation: Steenburgh, J. KMTX radar image for 00:57 UTC 13 December 2018.