Davis Instruments Weather Club
April 1999.
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Here's a quick preview of this month's contents:
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Tips on positioning your rain collector for more representative readings... Suggestions on how to contact folks here at Davis... A snippet from the life of an avid weather-watcher... And a Today-at-the-North-Pole weather challenge....Enjoy!
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How-to: Position your rain collector for the most representative readings
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Locating your sensors to get the best picture of what's happening outside is a tricky business. For example, if you put the temperature sensor smack in the middle of a field with no shadows and no shield, you'll soon be measuring the cooking temperature of the sensor casing rather than the field's ambient air temperature. Similarly, Larry Huff of Ohio wrote in with the following concern about rain collector positioning:
>I notice that many users of the Davis rain gauge (see the January 1999 Weather Club E-newsletter photo taken by Jay Neale) will mount it well above the ground. In fact, many times the rain gauge is mounted on the roof just below the wind sensors.
>This is a concern of mine since the National Weather Service (NWS) recommends the following: "The exposure of a rain gauge is very important for obtaining accurate measurements. Gauges should not be located close to isolated obstructions such as trees and buildings, which may deflect precipitation due to erratic turbulence. Gauges should not be located in wide-open spaces or on elevated sites such as tops of buildings, because of wind and the resulting turbulence problems" (from the National Weather Service Observing Handbook, Number 2, July 1989).
>I thought that this might make for a helpful article for a future Davis Weather Club E-newsletter. By the way, I have my Davis rain gauge mounted on top of a three-foot post in my backyard.
Good point, Larry, thanks for writing in. We asked Jason, our resident meteorologist, to reply:
>I would have to agree with Larry's concern. It's a good idea to use the NWS Observing Handbook for advice on sensor siting to obtain "representative" measurements. The NWS guidelines have been written based on general international guidelines set forth by the World Meteorological Organization (WMO), which specify that obstructions should not be closer to the collector than a distance twice the objects' heights above the rim of the collector.
>As a rule of thumb, if you're placing the collector on the ground, try to position it at least 15 to 25 feet away from a single-story house (or, if possible, twice as far away from a two-story house) and at least 12 feet away from any standard privacy fences. And, of course, avoid nearby trees or power poles. That's tough for many people who live in urban and suburban areas. So, I would recommend going ahead and installing the rain collector on a fence post or the roof if you can't meet the above requirements (in order to lessen the required distance between the rain collector and other objects). Just try to mount the collector near the top of the roof (for sloped roofs) to avoid excessive splash-in and away from the chimney (to avoid blocking the collector).
>What are the experts doing? Well, the rim of NWS's own tipping bucket rain collector sits about 2.5 feet above the ground. Some National Oceanic and Atmospheric Administration (NOAA) installations have instruments installed on rooftops in urban areas - it seems even the standard bearers have trouble not violating the NWS requirements when it comes to precipitation.
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Davis: Contact Info
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Each month after the E-newsletter goes out, we receive messages back. Sometimes the messages are in response to a story we shared; other times they are a request for help of some kind. We read all the e-mails, answer those we can, and pass the rest on to the appropriate departments.
We think you should know, though, that if you're interested in the fastest possible reply, news@davisnet.com may not be the best place to send your message. Questions about how things work should be addressed to tech support directly at support@davisnet.com. For general information about the products, such as how much cable comes with a station, or to request a catalog, contact sales@davisnet.com.
Please continue to send your comments, weather URLs, and story suggestions to news@davisnet.com. We look forward to getting your comments and any responses you have to the E-newsletter. Member participation is what keeps the E-newsletter alive and kicking.
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Member Spotlight: A snippet from the life of a roof-sitting weather-watcher
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Our request for photos and stories in recent E-newsletters elicited this gem from Bob Marton - a self-described "closet weather nut" - in California. Bob writes to us about his long-time weather watching and his trials and tribulations finding just the right positioning for his external sensors:
>I have been a closet weather nut since junior high school when I built a station from an old "minimum/maximum" mercury thermometer, a dial barometer, a plastic rain gauge, and a homemade wind vane. I kept handwritten logs of the daily readings faithfully for several years (OK, I missed several days). It is interesting to compare the data recorded from my Monitor II station to my many handwritten logs (yes, I still have them). So much was missing then.
>I had first installed my Monitor II sensors in three different places on the roof of my house. The rain collector was mounted on the heater exhaust roof vent, the temperature/humidity probe was mounted under the northeast second floor roof eave, and the anemometer was mounted on the TV antenna mast mounted to the chimney.
>After a year of data analysis I found that none of these chosen locations were adequate. My temperatures were colder than expected at night and hotter than expected during the day. The wind readings would change whenever I lit a fire in the fireplace. The rain collector vibrated whenever the wind was up giving me false readings. I then spent many hours on your web site sifting out related information - and many hours sitting on the roof looking for the best locations -and finally determined the best course of action.
>I bought a sensor arm and radiation shield to mount the temperature/humidity probe and rain collector out away from the second story roof and constructed a new mounting arm for the anemometer. It is amazing how many other people experience the same problems and your FAQs are a great way for us to share and learn.
>Now that my station is primed and ready, I get goosebumps when the TV weather guys foretell a big front coming through. It's a challenge to try to nail down the actual time when the front passes my house (usually I can pinpoint it down within a single capture interval).
Thanks so much for writing in, Bob! If you'd like to know where to find the FAQs (Frequently Asked Questions) Bob mentioned, you can check out our support home page at http://davisnet.com/support/weather/.
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Talk Back: North Pole Challenge
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Remember our intrepid doctor-by-day/explorer-by-night Santaland reporter? In December's e-news we brought you the story of Dr. Curtis Lieber and the 4 hot air balloons, 1 Russian ex-Cosmonaut, 40 parachutists, and 1 Weather Wizard III that accompanied him to the North Pole. As you read this, Curtis should be just now landing on the Pole for an improbable third time. Before he left, Curtis sent us all this tempting challenge:
>We're off again to the North Pole on expedition with a brand new Weather Monitor II! I'd like to invite e-news club members to join (virtually) in the adventure, so I've come up with a little contest. Here goes:
>In 1997, the North Pole weather was -32 degrees F with a wind chill of -63 degrees F.
In 1998, the North Pole averaged -1 degree F with a wind chill of -12 degrees F.
Care to wager on what I'll find this year? Do you think we're recording global warming or were last year's temperatures simply the effects of El Nino?
>Guess the average temperature and wind chill at the North Pole in April during our stay (between the 19th and the 23rd) and win an Expedition Patch and Insignia Pin! You can e-mail your best guess - along with your name and e-mail address - to northpole47@hotmail.com.
>In May, once I've thawed out, I'll announce the winner and invite e-news to publish their name in an upcoming E-newsletter. In the meantime, you can visit the expedition at http://pages.prodigy.net/curtislieber/. Wish us luck!
Thanks, Curtis! Our warm thoughts are with you!
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That's it for April's E-news! (Happy birthday, David!)
The Davis Weather Club E-newsletter
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