Tag Archives: radar

Example of Radar Beam Ducting

Reflectivity image from the Kohala radar showing trade wind showers much farther away than it should. (341 pm HST 12/20/16)

Reflectivity image from the Kohala radar showing trade wind showers much farther away than it should. (Animated radar loop)

Yesterday afternoon something strange showed up on the Kohala radar–a bunch of trade wind showers north of the Big Island.  Showers were to be expected, as we were watching an area of open-cell cumulus clouds approach from the east.  The strange part is that they extended to the extreme edge of the radar range, about 285 miles away.  At that point, the radar beam could be sampling up to 50,000 feet, quite a bit higher than these showers.  What gives?  Since we weren’t looking at cumulonimbus clouds on satellite, we were looking at a nice example of radar beam ducting.

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Winds Aloft: Sources of Information

The Summer 2016 newsletter article on trade wind inversions referenced the weather balloons we launch twice a day from Lihue and Hilo, which measure winds aloft in addition to temperature and moisture.  In this article we’ll look at two additional sources of wind information:  radar wind observations and the automated winds aloft forecasts.

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When Weather Radar Measures More Than Weather

Note:  I originally wrote this article for the General Aviation Council of Hawaii Spring 2015 newsletter.  Hopefully you will find it interesting and educational as well. –JB

(For more background on weather radar basics and an overview of the different radars in Hawaii, see the GACH newsletter from Fall 2012.)

Not everything you see on a weather radar image is necessarily a weather feature. Weather radars use a series of complex algorithms to filter out energy from non-meteorological returns. In general terms, if an object is stationary, then it’s most likely not weather-related. For example, a mountain will reflect a lot of energy back to the radar. Luckily, mountains don’t move (much), and the radar will identify and filter out these types of returns. However, no algorithm is perfect, and some returns make it into the final reflectivity product even though they’re not actually precipitation. Here are a few of the more common non-meteorological returns we see in Hawaii:

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Weather Radar in Hawaii

Note:  I originally wrote this article for the General Aviation Council of Hawaii Fall 2012 newsletter. Had to make a couple tweaks to the dual-polarization section, since upgrades at all Hawaii radars were completed in 2013. –JB

Radar image of a supercell thunderstorm from March 9th, 2012. This storm brought large hail to Kailua and Kaneohe, including a record-setting hailstone that measured 4.25 inches long, and generated a tornado that damaged homes in Lanikai.

Radar image of a supercell thunderstorm from March 9th, 2012. This storm brought large hail to Kailua and Kaneohe, including a record-setting hailstone that measured 4.25 inches long, and generated a tornado that damaged homes in Lanikai.

Weather radars are one of the most effective tools for detecting rainfall. This article includes information about weather radar in general, and about the specific radar sites we have in Hawaii.

Weather Radar Basics

The radar transmits an electromagnetic pulse, which reflects off objects in the atmosphere. (The objects could be anything, not just precipitation; one common problem around Hawaii is with sea spray being detected during windy days.) A small fraction of the energy is returned to the radar. The radar measures how much energy is reflected back, and how long it took to return. The energy is converted into reflectivity, and the time is converted into distance from the radar. Larger or more numerous objects return more energy, and result in a higher reflectivity.

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