* **10 to 20 dBZ (Light Blue to Light Green):** This range indicates very light precipitation, such as drizzle or light snow. In some cases, it may represent ground clutter, which includes non-weather targets like insects, birds, or terrain reflections. * **20 to 40 dBZ (Dark Green to Yellow):** This represents moderate rain. When tracking storms in Bristol, a steady band of green and yellow usually indicates a prolonged period of steady, non-severe rainfall. * **40 to 55 dBZ (Orange to Red):** This range signifies heavy rain and active thunderstorms. If you see cells of orange and red moving toward the Tri-Cities area, expect gusty winds, lightning, and heavy downpours. * **55 dBZ and Above (Pink, Purple, or White):** This indicates extremely intense precipitation, often accompanied by hail or severe convective activity. A small, concentrated core of purple or white within a storm cell suggests a high likelihood of hail. ## Distinguishing Base Reflectivity from Composite Reflectivity When viewing weather radar, you will often have the option to choose between different radar products. The two most common reflectivity views are: * **Base Reflectivity:** This displays the radar reflectivity from a single, low-angle sweep of the radar antenna (usually the 0.5-degree tilt). It shows precipitation closest to the ground. This is the most useful view for determining what is currently falling at the surface in Bristol. * **Composite Reflectivity:** This view combines the maximum reflectivity values from all elevation scans. It shows the strongest precipitation at any altitude. Composite reflectivity is helpful for identifying developing storms or hail cores high in the atmosphere before they descend to the ground.

## Identifying Storm Signatures and Movement To track storms effectively, you must observe how the radar images change over time. Using the loop or animation feature on your radar map is essential for this. * **Storm Direction:** Most storm systems approaching East Tennessee travel from the west, southwest, or northwest. By looping the radar for 15 to 30 minutes, you can project the storm's path toward Bristol. * **Bow Echoes:** A bow echo occurs when a line of thunderstorms bends outward, resembling an archer's bow. This signature indicates strong, localized winds pushing the storm forward. A bow echo moving toward Bristol suggests a high risk of damaging straight-line winds. * **Hook Echoes:** A hook-shaped extension on the rear-flank of a supercell thunderstorm indicates rotation. This signature often precedes or accompanies tornado formation. If a hook echo is visible near the Tennessee-Virginia border, immediate shelter is typically required. ## Terrain and Radar Limitations in Bristol, TN

The local geography of Bristol and the surrounding Appalachian region introduces specific challenges when reading radar maps. * **Radar Beam Height:** The primary National Weather Service (NWS) radar site serving Bristol is located in Morristown, Tennessee. Because Bristol is approximately 60 miles northeast of Morristown, the radar beam travels upward at an angle and is relatively high off the ground by the time it reaches Bristol. Consequently, the radar may overshoot low-level weather activity, such as shallow winter precipitation or low-level wind rotation. * **Terrain Blockage:** The mountains surrounding the Holston Valley can block or deflect the lowest radar beams. This can create "shadows" on the radar map where precipitation is occurring but cannot be detected by the Morristown radar. * **Cross-Referencing Radars:** To get a more accurate view of storms entering Bristol from the north or east, meteorologists often compare the Morristown radar data with neighboring radar sites, such as the Wytheville, Virginia radar or the Blacksburg/Roanoke radar. ## Utilizing Velocity Radar for Wind Tracking In addition to reflectivity, velocity radar (radial velocity) is a critical tool for tracking severe weather. Velocity radar measures the speed of particles moving toward or away from the radar antenna.

* **Green Colors:** Indicate wind or precipitation moving toward the radar station. * **Red and Orange Colors:** Indicate wind or precipitation moving away from the radar station. * **Velocity Couplets:** When bright green and bright red colors are positioned directly next to each other, it indicates rapid rotation (winds moving in opposite directions in close proximity). This signature is used by meteorologists to detect tornadoes and issue warnings. ## Verifying Radar Accuracy When tracking active storms, always check the timestamp on your radar map to ensure the data is current. During fast-moving severe weather events, a delay of even five minutes can mean the storm is much closer than it appears on the screen. For official, real-time alerts and uncompromised radar data, refer directly to the National Weather Service Morristown office.