The scale for measuring these geomagnetic storms is called "the G scale," ranging from a minor storm at G1 to an extreme storm at G5. "As this particular coronal hole rotated back into view – meaning we could see and analyze it – it was clear that it had diminished and we adjusted our forecast accordingly," Brasher told CBS News via email. EST.īryan Brasher, a project manager at NOAA's Space Weather Prediction Center told CBS News one coronal hole in particular had previously shown elevated activity, so forecasters expected it to do so again. NOAA has an interactive map that shows where above Earth the northern lights are positioned. Solar wind from coronal holes in the sun flow towards Earth and have a magnetic reaction that causes the northern lights, also called the aurora borealis, according to NASA. NOAA also initially predicted high activity for this week and then downgraded their forecast. This means that the high levels of activity previously expected are now considered much less likely." "However, now that the forecast activity is less than three days in the future, we can see that the solar features that produced the prior activity have actually diminished over the last month. "The features on the sun that produce activity like this typically last 1-3 months, so the active conditions were predicted to occur again this week," a representative for the institute told CBS News via email. University of Alaska's Geophysical Institute A map from University of Alaska's Geophysical Institute shows were above the Earth the northern lights will be on July 13. The institute told CBS News it originally predicted a moderate solar storm – which causes the dazzling phenomenon. 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.Last week, the institute projected the display would be visible in 17 states over those two days: Washington, Iowa, Illinois, Ohio and Massachusetts on July 12, and Alaska, Montana, Minnesota, Wisconsin, Michigan, Oregon, Idaho, Wyoming, Nebraska, Indiana, Vermont and Maryland on July 13. 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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