I've Been Thunderstruck

Next year I plan on being much better at updating this blog! For starters, every week there will be “Weather Word Wednesday,” which will feature a word that deals with meteorology, with a short discussion of what it means. So, you can count on learning one new thing (hopefully!) each week! In addition, I plan on posting an interesting weather image each week, and will have more long posts about particular topics. If there is something about the weather that has always interested you, please post a comment about it, and I’ll look into writing about it for you!

Here’s to a great 2010, and an even better 2011. May the weather be interesting wherever you live!

I stumbled (by using StumbleUpon!) an interesting website today called Contrail Science. The tagline for the site is “The Science and Pseudoscience of Contrails and Chemtrails,” and the current article on the home page is a very detailed explanation, using pictures, flight info and good science, about the alleged “missile launch” in Los Angeles a few weeks ago. The author of the site has numerous posts detailing the basics about contrails, some good stuff about contrail chemistry, and pictures galore! Contrails come in many shapes and sizes, and there are additional phenomena seen in the weather that act similarly to contrails. If you are at all interested in those trails you see in the sky, or want a lively debate on the “LA missile launch,” you should absolutely check out this site!

"LA Missile Launch"

It’s not often we get a tornado in Arizona, but today we got TWO of them, within minutes of each other! Thanks to a low pressure system in California creating some serious storms in Arizona, the conditions were just perfect for this type of activity. Unfortunately, 7 people were injured, and lots of property destroyed. Check out the video capture of this event.

When I drove to work this morning, around 9AM, the sky was almost perfectly clear.  A few high cirrus clouds, but nothing aside from that…just blue sky. Below is a snapshot from my phone on what the sky looked like around 1:30PM today:

Quick Storm Development

Since this picture was taken, our area has seen multiple Severe Thunderstorm alerts, along with several Flash Flood warnings! It absolutely amazes me how quickly the weather can turn in our area of the wood, and why it’s always important to keep an eye on weather when outside doing fun things. Dry washes and rivers can turn into raging torrents without a single drop falling in your particular area. Always know the weather!

I was flying to Seattle earlier this week, and snapped this picture from the plane. I love how clouds look from the top! Notice the vertical development punching it’s way through the deck!

View From The Top

I have created a new website aimed at showing people the best locations to take lightning and storm pictures. It’s called Lightning Shot Spots and I just launched it today! So far it’s a bare bones site while I work to collect location data (provided by users like you!), but I have plans to develop it into a world class storm photography resources. So, head over, take a look, and please contribute a location if you have one. Thanks!

When you start seeing vertical development in storm clouds, there’s a good chance rain is on the way. Here’s a picture of some clouds outside right now, and the associated radar image from my iPhone.

Afternoon thunderstorms are starting to pop up. Not long before they become daily events!

I stumbled across this today, and thought it was worth sharing. There are lots of ways to forecast the weather without relying on gadgets. Knowing how to do it old school is a great skill to have, and helps you understand the fundamental properties of weather. Check out this graphic, and have fun learning!

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!