9/19/2023 0 Comments Shreveport weather radar in motion![]() ![]() Dual polarization technology adds new information about the size and shape of an object, which will improve estimates of how much rain is falling, improving flash flood detection and warnings. National Weather Service radars provide forecasters information on precipitation intensity and movement (direction and speed). More information: NWS JetStream - Online School for Weather (Doppler Radar) Dual-Polarization (Dual-Pol) Technology View a sample Storm Relative Motion image (scroll down). In effect, what is seen is the wind's motion as if the storms were stationary. This motion is removed to make the view of the wind relative to the storm. As storms move, their own motion can mask circulations within themselves. What separates storm relative motion from base velocity is the motion of storms are "subtracted" from the overall flow of the wind. Often, these small scale circulations are areas where tornadoes form. Storm Relative Motion images are very useful images to look for small scale circulations (called mesocyclones) in thunderstorms. As distance increases from the radar, the reported value will be for increasing heights above the earth's surface. However, since the radar only measures radial velocity, the strength of the wind will always be less than what is actually occurring unless the wind is moving directly toward or away from the radar.Īlso, the surface winds are only for areas near the radar. It is useful for determining areas of strong wind from downbursts or detecting the speed of cold fronts. It is very important to know where the radar is located as that is your reference point for proper interpolation of the wind's motion.īase Velocity images provides a picture of the basic wind field from the ½° elevation scan. In all velocity images, red colors indicate wind moving away from the radar with green colors representing wind moving toward the radar. This is called radial velocity as it is the component of the target's motion that is along the direction of the radar beam. However, the only motion it can "see" is either directly toward or away from the radar. One of the best features on the 88d Doppler radar is its ability to detect motion. View a sample composite reflectivity image (scroll down). ![]() It is used to reveal the highest reflectivity in all echoes. It is composed of the greatest echo intensity (reflectivity) from any elevation angle seen from the radar. View a sample base reflectivity image.Ĭomposite Reflectivity images utilize all elevation scans during each volume scan to create the image. This image is available upon completion of the ½° elevation scan during each volume scan. There are two versions of Base Reflectivity image the short range version which extends out to 124 nm (about 143 miles) and the long range version which extends out to 248 nm (about 286 miles). Taken from the lowest (½° elevation) slice, it is the primary image used to "see what's out there". There are two types available on the web Base (or ½° elevation) reflectivity and Composite reflectivity.īase Reflectivity is the default image. Since hail can cause the rainfall estimates to be higher than what is actually occurring, steps are taken to prevent these high dBZ values from being converted to rainfall.These images are just as they sound as they paint a picture of the weather from the energy reflected back to the radar. Hail is a good reflector of energy and will return very high dBZ values. These values are estimates of the rainfall per hour, updated each volume scan, with rainfall accumulated over time. Depending on the type of weather occurring and the area of the U.S., forecasters use a set of rainrates which are associated to the dBZ values. The higher the dBZ, the stronger the rainrate. Typically, light rain is occurring when the dBZ value reaches 20. The scale of dBZ values is also related to the intensity of rainfall. The value of the dBZ depends upon the mode the radar is in at the time the image was created. Notice the color on each scale remains the same in both operational modes, only the values change. The other scale (near left) represents dBZ values when the radar is in precipitation mode (dBZ values from 5 to 75). One scale (far left) represents dBZ values when the radar is in clear air mode (dBZ values from -28 to +28). ![]() Each reflectivity image you see includes one of two color scales. The dBZ values increase as the strength of the signal returned to the radar increases. So, a more convenient number for calculations and comparison, a decibel (or logarithmic) scale (dBZ), is used. Reflectivity (designated by the letter Z) covers a wide range of signals (from very weak to very strong). "Reflectivity" is the amount of transmitted power returned to the radar receiver. The colors are the different echo intensities (reflectivity) measured in dBZ (decibels of Z) during each elevation scan. ![]()
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