![]() (Right): Composite Reflectivity shows two intense cores within the main cluster of storms to the west. These storms have a small “hook” shape to their appearance. Notice the two smaller storms (arrows) ahead of the main cluster. (Left): A cluster of severe thunderstorms approaches Fort Worth, TX, on April 3, 2012, as seen in the Base Reflectivity (0.5° elevation). Storm scale features such as hook echoes and outflow boundaries are often masked.Įxcellent situational awareness tool to use during scattered summertime thunderstorms. Only produced after the radar has completed a volume scan (4-7 minutes)ĭeveloping storms near the radar are shown in the composite reflectivity. Storm intensity can be quickly assessed as the highest reflectivity is shown. Strongest part of the storm may not be sampled by lowest elevation.Ĭan update as frequently as every 90 seconds depending on VCP configuration.ĭeveloping storms near the radar may go undetected.Ĭan show important storm scale features such as hook echoes and outflow boundaries. As mentioned above, both base and composite reflectivity have strengths and weaknesses, and we’ll discuss those below:Įxcellent for long range precipitation detection. Ideally, both of these images are used together to help obtain a clearer picture of what is occurring. So when do I use Base Reflectivity and when do I use Composite Reflectivity? The scale runs from around -35 dBZ to +85 dBZ. Instead of working with difficult units, after the logarithmic scale is applied, we have units of decibels (dB) of reflectivity (Z) or dBZ. So, the radar applies a logarithmic scale to significantly compress these values. This would be rather difficult for anyone to work with. For example, tiny water droplets may have a raw reflectivity value of 0.001 mm 6 / m 3 while hail within a severe thunderstorm may have a raw reflectivity value of 36,000,000 mm 6 / m 3. These units are difficult to work with, and the raw values of reflectivity vary greatly depending on the target. The units of reflectivity (denoted by the letter z), as derived from the radar equation, are in mm 6 / m 3. In fact, the power return is so weak that it must be passed through amplifiers before the signal can be processed. The WSR-88D transmits a pulse with 750,000 watts of power, but only receives a fraction of that power back to the receiver. Reflectivity is a measurement of returned power back to the radar, however this power return can vary significantly depending on the target that is hit. National Centers for Environmental Prediction.Preparedness and Mitigation: Individuals (You!).Preparedness and Mitigation: Communities.The Positive and Negative Side of Lightning.
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