[aprssig] Snow and Visibility on APRS

Gerry Creager gerry.creager at tamu.edu
Thu Aug 19 19:39:35 CDT 2010

In my world, we do NOT have an "It's raining now" sensor. Nice idea, but 
a lot of the "real" meteorological instrumentation is based on 
techniques and procedures from long ago. The concept of hourly 
measurements, and occasional higher frequency measurements, via SPECI 
observations is how we get finer temporal granularity.

Newer instruments, however, can provide higher frequency measurements. 
The problem is, at what rate do you sample these things? And, some 
instruments, like Vaisala's "Weather Transmitter" (WXT-510/520) do 
provide rate information.

Generally, in METARs, the instrumentation can provide when the first 
bucket tip occurred, but it's back-stopped by the certified weather 
observer (or tower controller) looking out the window.

Officially, a light, misting rain, with less than 0.01 inch accumulation 
would be recorded as "trace" precipitation and wouldn't qualify as rain.

gerry n5jxs
CWOP servers

Max Harper wrote:
> Then maybe I need to come up with a "Raining Now" sensor. We can have a 
> light misting rain
> that can go on for some time before the rain guage registers .01 or 
> 1/100 of an inch. If you were
> outside during this you would be soaking wet LONG before the rain guage 
> registered anything.
> Max
> On Wed, 18 Aug 2010, Max Harper wrote:
>  >/ Something that has been on my wishlist for some time now is a "It's
> />/ Raining Now" flag. All the  rainfall fields are after the fact, or how
> />/ much it HAS rained. I'd also like to see a "Rate of  Rainfall" 
> field. In
> />/ a heavy rain the console of my Davis Vantage Pro2 wil say "It's 
> rainging
> />/ Cats  and Dogs" so I know the data is in there. Just need a field to 
> put
> />/ it in and a software update  from Davis to output it to APRS. Thinking
> />/ about it more, if there was just a "Rate of Rainfall"  field then
> />/ anything above 0 (zero) would mean it's raining now.   Max KG4PID  
> /
> I suppose that would be duplicate data from the other counters, and would
> unnecessary grow the packets. The "raining now" status can be derived from
> two sequential packets - if the "amount of rain since X" counters are
> getting incremented, it is raining now. It's straightforward to improve
> the receiving software to do this calculation, and it'll work for all the
> existing weather stations which don't send such a preprocessed value.
> I guess i'll simply have to add "raining now" or "rate of rain" display in
> aprs.fi weather indications, it's simple to do and quite useful.
> Thanks for the inspiration!
>    - Hessu
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Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843

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