Friday, April 27, 2012

A Little About Weather Radios

Hi it's Rebecca again, If you've followed my weather page or blog, you know not having a weather radio is a pet peeve of mine. Weather radios are the most  effective way of receiving  warnings  for life threaten weather events;  and come in a variety of prices. But most are highly affordable.  Tornadoes and other violent weather can strike with little warning, however a weather radio can be a great help by alerting you when dangerous weather is heading your way.  This post will talk about weather radio.  I will go into a bit on what a weather radio is, The features, and the types of weather radios on the market.

What is a weather radio?:

Weather Radio is a broadcast service provided by NOAA (National Oceanic and Atmospheric Administration). That airs weather reports, weather warnings, and civil and other types of national emergencies. The warnings are provided by the Emergency Alert Service (EAS). Weather radio broadcast over the frequencies between 162.40 and 162.55 MHz.


Here's what to look for in a weather radio.

SAME (Specific Area Message Encoding), with SAME you can program your radio so that the alert goes off only for the local areas you want to be notified about.

 Some radios let you block certain alerts, others don't. However, certain events like a Tornado warning can't be blocked, which kind you want is up to you. 

Audible Alarm, this is a must have. Many dangerous weather events happen at night while you're sleeping. Also, you will want an alarm that you can turn off.  For instance, if you live on high ground a flood watch or even an warning might be less important to you than a severe thunderstorm warning.

Some weather radios let you adjust the volume. If this is important to you, look for models that allow you to do so.

Battery Backup, Often during a weather emergency electric power is unavailable. Therefore, you will want to have a radio that has a battery backup.

There are radios that also will run on car adapters, and other alternate power sources.

External Antenna Jack, most weather radios are supplied with a built-in antenna; most of the time they do a very good job. But sometimes it can be difficult to receive an adequate signal. When that happens, you want a radio that allows you the ability to hookup an external antenna.

They sell external antennas. However, one thing many don't know, is the weather frequencies sit between the analog TV channels 6 and 7, so a standard VHF TV antenna can also do the job.

The weather alert channels:

All weather radios sold to the public are suppose to be able receive all seven NOAA channels...but it never hurts to make sure the one your buying can access them all.

162.400 MHz

162.425 MHz
162.450 MHz


162.500 MHz

162.525 MHz
162.550 MHz

Types of Weather Radios:

There are four types of weather radios, portables, desktops, hand crank, and combination.

Portable Radios:

These are the small hand held radios that are easy to take with you when you're on the go, and are exceptionally suited for remote work locations.

Desktop Radios:

These come in a wide range of sizes and styles. Also, prices vary, but the majority of them fall into the 50 to 80 dollar range. So you shouldn't have any trouble finding the perfect radio to match your decor and needs.

Hand Crank Radios:

Even if you buy a desktop weather radio, buying  an hand crank radio can be a good idea. They make a great addition to your emergency kit.  a few cranks of the handle can give you an hour  or more of reception.

Combination Radios:

This type of weather radio is a little different.  These are a blend of weather radio and a  home weather station, with temperature readout and other basic weather forecasting abilities.

You can find weather radios in many places. Such as, Wal-Mart, Target, Sears, Sam's, BJ's, Radio Shack. You can also find them online at such sites as Amazon and eBay.  The only thing I will add is buy a weather radio that is public alert certified and carry the Public Alert logo

Well that's about it, well, with the exception of you purchasing  a weather radio after reading this.


Monday, April 9, 2012

Dual Polarization radar and why you should care.

Hi it's Rebecca again, I thought I would take the time to talk about a major weather radar upgrade. This upgrade is being installed in all National Weather Service (NWS) radars across the nation. Starting next week it's being installed at the Albany radar site. The new radar is known as Dual-Polarization technology (Dual-Pol). This will significantly enhance the conventional WSR-88D doppler radars currently in use. This post will cover the basics of what Dual-Pol is, some of its advantages over current WSR-88D doppler radar, and some of its limitations.

Here's a link to a blog post I did, that talks about conventional doppler radar.

Normal Doppler radar sends out a horizontal pulse of energy which is then returned to the radar antenna. The data is sent to a computer which analyses it; precipitation is determined by measuring the strength of the echoes received by the radar antenna. The computer then displays this information. Unlike traditional doppler radar, Dual-Pol is polarized. This means it sends out two pulses at the same time, one horizontal and the other vertical. In essence conventional dopper sees in one dimension whereas Dual-Pol sees in two dimensions. Which gives a much better idea of the shape and how large something is, when the pulse is returned.  Before the upgrade, The radar could see areas of and the intensity of precipitation in a storm very well, but it had extremely hard time telling if it was seeing a rain drop, snow flake, hail stone, bird, exc. Adding the vertical pulse will greatly help fill in the missing pieces and provide other applications that I will go into later.

What advantages does it have?

Dual-Pol will have several advantages over conventional doppler radar.  Here are the major improvements. These will be covered in a little more detail later. However, I would be happy to answer any questions you have on these applications, either on this blog post or via e-mail. Just click on my name (highlighted web link) at the bottom of this page. This will take you to my profile / about me page.
1)  Improved accuracy of precipitation estimates, leading to better flash flood detection.
2)  Ability to distinguish between heavy rain, hail, snow, and sleet.
3)  Differentiation of weather vs. non-weather returns.
4)  Identification of the melting layer.
5)  New severe storm signatures (hail detection, updraft detection, tornadic debris detection )

One thing I would like to say about these applications. Dual-Pol radar products will be used alongside standard radar products.  Most of the time, you won’t be able to determine something on one  data product alone.  

Improved the accuracy of precipitation estimates.
Conventional radar has to rely on how reflective the return is when it assigns rainfall rates.(reflectivity is the amount of transmitted power returned to the radar receiver)  This can be a big problem if there is hail present in the storm cell. Hail is a good reflector of energy and will return very high dBZ values. Because of this hail can cause the accumulated rainfall estimates to be higher than what is actually occurring.  Dual-Pol radar can see the hail; so it does a much better job of accounting for areas of rain that have hail mixed in. Therefore, it can give a much better assessment on how much rain has fallen over a given area. This is crucial since flooding is the #1 weather killer. Better rainfall estimation leads to more reliable flood warnings and helps people get out of harm’s way.

Ability to distinguish between heavy rain, hail, snow, and sleet.
With conventional doppler radar  you can see the presence and movement of precipitation. However, it's almost impossible to tell the difference between various types of winter precipitation. Like I said above, Dual-Pol radar transmits and receives pulses in both a horizontal and vertical orientation.  Consequently it can measure the width and height of objects in its path. the ability to detect the presence and movement of winter precipitation, but it is very difficult to infer whether it is rain, snow, or a mixture of both. Because Dual-Pol radar can see individual shapes it solves this problem.  As a result, precipitation types at all levels of the lower atmosphere can be seen (with-in the radar beam). This will allow forecasters to see which atmospheric zones have rain, snow, or mixed precipitation and how fast these zones are changing.  Therefore, based on environmental conditions from the radar beam to the surface, forecasters have a great deal of  certainty as to where rain, snow, or mixed precipitation is falling. Standard doppler radar has detected the melting layer in some situations, through bright banding (a circular or arcing band of higher reflectivity around the radar site). This area of bright banding is where the snow is melting. Dual-Pol radar is very good at identifying where this melting layer is and thus indicate where  snow is actually falling through a warmer layer.

                                                                 An example of bright banding

The ability to see shapes doesn't only help during wintertime. Hail can be a big issue in severe thunderstorms. Because Dual-Pol radar can see horizontally and vertically; it won't only be able to tell where hail is falling, but it will give a better idea where there might be large hail. A  pulse thunderstorm can form within a few minutes, develop It's core of hail and wind, and dissipate shortly thereafter. Weather forecasters need to be able to quickly see into these cells, in order to see which cells contain hail (sometimes large hail) and damaging winds.  So they can issue warning before any of that hail or damaging wind reaches the ground.

The radar upgrade will also be better at discriminating between precipitation types (snow, sleet, hail, and rain), and  non-meteorological types (Ground clutter, chaff, birds, smoke plumes from wildfires)
Tornadic Debris Detection
This is where the Dual-Pol upgrade will shine. Tornadoes often have debris whirling around. In fact, lighter debris such as insulation, leaves, and so forth  can be pulled to heights  of over 10,000 feet. Dual-Pol greatly increases our ability to see this debris. So when there's a strong velocity couplet showing a tornado vortex signature along with debris detection, there will be little doubt that a damaging tornado is on the ground. This will be particularly valuable at night or when the tornado is rain wrapped; when it's extreamly difficult for spotters and chasers to visibly see tornadoes. 

Dual-Pol WILL NOT improve initial tornado warnings or increase warning lead times. Also while it will significantly improve our ability to see and track large destructive tornado; it won't do nearly as good a job on smaller weaker tornadoes. While it has detected tornadoes in the EF1 won't catch as many of them as it does EF3's thru EF5's. Also the farther away the tornado is from the radar site the harder it will be to identify.  

There are 11 classification types possible on the radar return

 Biological (Light Gray)
 Clutter (Dark Gray)
 Ice Crystals (Pink)
 Wet Snow (Dark Blue)
 Dry Snow (Light Blue)
 Rain (Light Green)
 Heavy Rain (Dark Green)
 Big Drops (Gold/yellow)
 Graupel (Dark Pink)
 Hail/Hail Mixed with Rain (Red)
 Unknown (Light Purple)

Limitations of the Dual-Pol upgrade:

As I said, while Dual- Pol radar provides specific information about the location of a tornado. At least for now, it doesn't provide added information about where a tornado will form ahead of time.
During the wintertime Dual-Pol's  ability to see precipitation type will be limited to the beam height.  Also while it's a good tool at finding the melting layer. There can often be more than one melting layer; in which case melting layer data can blend in with other radar data. Therefore forecasters will still have to rely on surface readings, reports, and sample environmental conditions.

It also has the same limitations as standard radar, as the beam moves farther away from the radar site, it also broadens.  This means at long range, the radar is sampling all the things in a much larger area. However, it will only show up as a pixel or two. which can lead to a noisy image.

You will remember, I said Dual-Pol radar is good at detecting non weather related echoes, this can lead to blank areas. Sometimes the radar algorithm won't calculate the legitimate precipitation because of it.  while it doesn't happen all the time it does happen.

Dual-Pol radar has a very steep learning curve.  

A few links for more info

A lesson by the NWS

Video that briefly goes into Dual-Pol

I guess that's about it. You now have a working knowledge of Dual-Pol radar. While it won't replace conventional WSR-88D doppler radar, it does give the forecaster a vast array of additional tools that will greatly increase forecast accuracy in many areas, particularly in the area of storm tracking.  As always, I hope you enjoyed this post and learned a thing or two.