I wanted to switch gears today and talk forecasting. Now we all know that forecasting is done with weather models, but you can’t just press “Start” on a model everyday. You need to enter a great deal of current observation. Across the nation surface observations are taken hourly at airports and NWS forecast offices, but vertical observations need to be taken as well. Today’s high-tech models need pressure, temperature, wind, and moisture values at a number of different heights to work properly.
So how does the NWS get these vertical measurements? The answer is a radiosonde, an instrument package attached to a weather balloon. The radiosonde measures pressure, temperature, and relative humidity while antennae tracking the balloons calculate the wind speed and direction. Balloons are launched from dozens of installations each day, with NWS offices launching twice a day.
The balloon is launched from the ground, rising hundreds of feet per minutes high into the atmosphere. As it rises the drop in pressure causes the balloon to expand from several feet to over twenty. After a while, when it gets to over 100,000 feet in altitude the balloon pops. The radiosonde then falls, with parachute, back to Earth where it can be retrieved and re-used. Only a small percentage of these instrument packages are ever recovered so if you find one please call your local office.
Want to send a digital camera up with a weather balloon? Look at this page! Project Icarus, from an MIT group, lays out an easy(ish) and affordable method for taking and retrieving digital images from a weather balloon. I tried this a few years ago and was able to track the balloon… until it landed in the Atlantic Ocean off of Cape Cod. NOTE: Learn from my mistake! Buy a weather balloon on the smaller side and pay attention to upper level winds. If you launch on a day when the jet stream is right above you that balloon is going a loooooooooong way east.
Here’s some pictures from my launch. The rig and GPS worked great, the balloon just traveled way too far,
BONUS photo: We’re having some severe weather today in my neck of the woods. Look at the amount of spin on this storm! Maybe I’ll have tornado pics for this storm tomorrow.
Til next time,