I've Been Thunderstruck

The other evening I was checking out the NWS page for Tucson, and I clicked on the local Radar image. This is what I saw:

Tucson Base Reflectivity

At first glance, it would appear that it was raining outside in the areas indicated in blue. But, having spent the evening outside coaching a softball game, and having checked the skies before heading in for the evening, I knew that, if anything, the only thing in the sky was some high clouds. So, why would the radar indicate that it was raining? I decided that it was time to get a better understanding of what Base Reflectivity was all about.

Turning to Google, I found a link to the National Weather Service page on Base Reflectivity. I started reading the FAQs on weather radar, and it became very apparent that there is more than meets the eye when reading weather radar output.

To begin, we need to understand how weather radar works. Basically, the Next Generation Radar (NEXRAD) obtains weather information (precipitation and wind) by measuring returned energy. The radar sends out a burst of energy (green), and if the energy strikes an object like rain drops, bugs, birds, etc., the energy is scattered in all directions (blue). A small fraction of that energy gets directed back to the radar. The radar has a listening period, in which it collects and analyzes the signals that it receives. The whole process to analyze the signal is super fast, and occurs around 1300 times per second! In an average hour, the radar spends about 7 minutes sending signals, and 53 minutes listening for them. Based on some geeky physics stuff, the analysis can tell the “phase shift” of the signals it receives, which lets it know in what direction, and how fast the object it got bounced off of is going. Information on the movement of objects either toward or away from the radar can be used to estimate the speed of the wind. This ability to “see” the wind is what enables the National Weather Service to detect the formation of tornados which, in turn, allows us to issue tornado warnings with more advanced notice.

Base Reflectivity, which is what’s on the map above, is a display of echo intensity (reflectivity) measured in dBZ (decibels of Z, where Z represents the energy reflected back to the radar). “Reflectivity” is the amount of transmitted power returned to the radar receiver. Base Reflectivity images are available at several different elevation angles (tilts) of the antenna and are used to detect precipitation, evaluate storm structure, locate atmospheric boundaries and determine hail potential.

When you look at the Base Reflectivity map, you’ll see various colors on it, and one of the scales that you see to the left of this text. If the radar is operating in “clear aid” mode, then the values range from -28 to +28 dBZ. If the radar is operating in “precipitation mode,” then the values range from 5 to 75 dBZ. Turns out, the map I was viewing was operating in clear air mode, which was something I had never heard of. Typically, light rain is falling when the values reach approximately 20 dBZ. As you can see from my map, I was nowhere near that. I suppose that the high clouds or other particulates in the air could have accounted for the return that I saw on the map, but it certainly wasn’t raid. Had I known about the two scales, and the 20 dBZ threshold, I wouldn’t have been confused!

There’s quite a bit to learn about weather radars and how they are used to predict the weather. I would highly encourage you to visit the NWS Radar Image WSR-88D Radar FAQs to learn more. By understanding the concepts, scales and technologies used to predict the weather, you can get a better understanding of the weather potential for your area. And, it never hurts to learn some geeky science!

At this particular moment, I have a total of 10 weather related apps on my iPhone. All but a couple of them are very good, and I figured other people might be interested in benefiting from my purchases! Having an iPhone that can run weather apps is a huge bonus for me. I love weather data, and being able to whip out my phone and check the local radar is very exciting…especially during the summer monsoon months, when I want to know where the next thunderstorm will hit. As more weather apps are developed for the iPhone, I’m sure I’ll purchase those as well. That being said, let’s start with a review of WeatherBug Elite.

Clicking on the WeatherBug Elite icon on your iPhone will launch the following splash screen:

WeatherBug Elite Splash Screen

As soon as the data is loaded, you are presented with the main screen. From here, you’ll be given information about conditions in the default area you choose. For me, these are the conditions in Tucson, AZ. Current temperature, wind speed and direction, humidity and dew point are some of the data available. You also get a nice little graphic that indicates wind speed and direction. Below that is an indication of any active alerts, a synopsis of the current forecast, and buttons for other features at the bottom of the screen.

WeatherBug Elite Main Screen

Clicking on the forecast button gives you a synopsis of the coming days. You can get more detailed information for each part of the day – morning and evening – by clicking on the high and low temperature sections. Not only can you get the next seven days worth of forecasts, but you can also check out things on an hourly basis.

WeatherBug Elite Forecast Page

WeatherBug Elite Forecast Details

Now comes my absolute favorite part – data on maps! I spend a lot of time on this page when storms are in the area, and when I want to know how long until we get rain! WeatherBug Elite does an excellent job displaying data on maps provided by Microsoft Virtual Earth. In addition to the radar/satellite data, you can also get local conditions of a particular area by clicking on a pushpin already in the map, or by pushing and holding on an area you are interested in, placing a pushpin there, and then getting the local data. Unfortunately, WeatherBug Elite does not work in landscape mode, so you have to pinch/pull in order to get the area you want to look at. But, the data is awesome, and this is my favorite page!

WeatherBug Elite Maps

WeatherBug Elite provides you many different layers for your maps, including temperature, pressure, humidity, wind speed, IR satellite, visible satellite, radar, tomorrow’s high temp and tomorrow’s low temp. You can adjust the opacity of the layers, and you can even remove all dropped pins with a single tap!

For those of you who like video weather reports, WeatherBug Elite has that as well. Click on the video button at the bottom, and you are presented with the latest WeatherCast from Rachel.

WeatherBug Elite WeatherCast

I’ll admit, I’ve never actually watched a WeatherCast, so I can’t yet comment on it.

Finally, on the last page, you can check out cameras for the areas you have set. I have seen up to three cameras for a particular area, and they are generally of pretty good quality. That depends largely, I suspect, on the area you live in. I think these are typically cameras that local weather forecasters use as well.

WeatherBug Elite Camera View

All in all, I believe WeatherBug Elite is fully worth the $0.99 I had to pay for it. I started with the free version of WeatherBug, which gives you essentially the same features, but includes ads. Spending nintey-nine cents to remove the adds, and get a few more features, seemed like a good investment to me.

If you have an iPhone, and like to stay up with the current weather, but require more information than just current temperature and high/low, then you can’t really go wrong with WeatherBug Elite. I’ve fond it to be stable, useful application, and became very quickly addicted to the maps feature. I don’t think you can go wrong by giving it a try!

In my last post, I talked a bit about the National Weather Service, and how it contributes to predicting the chances of precipitation. We learned that they send up a radiosonde twice a day, from locations all over the country, to collect data about the atmosphere. Quite a bit of that data they post online for anybody to look at, and combined with other bits of data from things like satellites and ground observations, you can get an amazing picture of how things are shaping up in your area (or almost anywhere in the world!). Let’s take a look at a few of the things you can find online at the National Weather Service web site.

Current observations are an important part of determining what will happen with the weather. If you know how conditions are now, and how they have changed from the past, you can get a clue as to how they might be in the future. One tool that the NWS provides is a Surface Plot graph.

Surface Plot Chart

The official term for this is Mesonet Observations. According to wikipedia, “a mesonet is a network of automated weather stations designed to observe mesoscale meteorological phenomena. Dry lines, squall lines, and sea breezes are examples of phenomena that can be observed by mesonets. Due to the space and time scales associated with mesoscale phenomena, weather stations comprising a mesonet will be spaced closer together and report more frequently than synoptic scale observing networks, such as ASOS. The term mesonet refers to the collective group of these weather stations, and are typically owned and operated by a common entity.” So, basically, this is a series of stations that report current observations on wind speed and direction, temperature, relative humidity, and other items. If you know how to read these reports, and can spot trends, you can tell when a frontal system moves through, or when you might expect a thunderstorm. It’s good on the ground information.

One area at the NWS site that I spend a lot of time checking during stormy periods is the local weather radar image. This image gives me a great idea of where precipitation is occurring at the moment, and in what amounts and intensity. This is particularly valuable if you are going storm chasing, as you can see where the local thunderstorm cells are dumping their rain. It also provides a time-lapse ability, so you can see what direction the storm is moving. I enjoy watching the radar, especially when storms are headed my way.

Radar Image

Now, let’s say you’re interested in what the current forecast is for your region. The NWS is particularly good at providing that information, and does so in a wonderful graphical format. You can find out great things like temperature, wind speed and direction, dew point (handy in the summer for monsoon prediction), sky cover, precipitation, and more for up to the next week or so. This is very handy for planning activities, and the graphical format of the data is exceptional.

Graphical Forecast

Finally, though by no means even close to the end of the great things you can get from the NWS, is the Weather Story that they produce from time to time. In Tucson, I tend to see these when a weather event is on the way, and right after an event. Any significant change in the expected weather pattern also seems to generate a Weather Story. Essentially, these are a couple slides that show the basics of what’s going on in the area, and what to expect in the near future. I find them interesting because it’s a good synopsis of what’s going on. I don’t know if all major locations produce weather stories, but I suspect they do.

Weather Story

So, there you have it…some of the free products that you can get from the NWS. These items only touch on the rich repository of information that is the National Weather Service. If you are interested in weather, I encourage you to take some time and look around. You’ll find data on things that you didn’t even know they collected data on!

If you plan on following the weather seriously, you should bookmark the National Weather Service. Operated by the National Oceanic and Atmospheric Association (NOAA), the NWS web site provides you with detailed weather information for all of the United States. Of particular interest to those who love to track the weather are:

• Detailed warning information
• Forecast discussions
• Graphical forecasts
• Forecast discussions with a glossary to help you understand terms
• Radar
• Satellite
• Severe weather

There is tons more there, and it’s all worth a look. You can get local forecasts, with great discussions about them, for your local area. You can also monitor severe weather in the event that you’re looking to do some storm chasing. And, you can watch the satellite to see when that next rain or snowstorm will hit your area. The NWS site is a treasure trove of information for people like me who love the weather. Check it out, and I’m sure you’ll find it interesting as well!