[aprssig] Snow and Visibility on APRS

Max Harper kg4pid at yahoo.com
Wed Aug 18 23:48:57 CDT 2010

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.
The original APRS defines SNOW Sxxx and LUMINOSITY Lxxx fields
for the weather format, and I thought it included visibility
Vxxx, though I cannot find it right now.  Does anyone recall if
anyone uses these.  If not, I propose a Vxxx field if someone
can recommend the right units.

Lets look at this original APRSdos file:

www.aprs.org/APRS-docs/WX.TXT  see extract below

And it appears to cover Snow, but not Visibility.  Though I was
sure I had proposed Visibility at some time or other....  SO
check the original spec, or the addendum
www.aprs.org/aprs11.html and there find this link:

> FORMATS:  APRS re-formats data from attached WX units 
> and transmits the data as shown below.  For remote 
> Ultimeters, where there is no PC, the TNC just transmits 
> the raw data, but APRSdos converts them to these formats
> for display on the P-LIST.

_DIR/SPDgXXXtXXXrXXXpXXXdU-II              Original U-II auto
_DIR/SPDgXXXtXXX#XXXdU2r                   Original U-II remote
_DIR/SPDgXXXtXXXrXXXpXXXbXXXXhXXdDvs       Davis WX station
_DIR/SPDgXXXtXXXrXXXpXXXbXXXXhXXdU2k       U-500/2000 with APRS
_DIR/SPDgXXXtXXXPXXXbXXXXhXXdU2kr          Remote
_DIR/SPDgXXXtXXX#XXXbXXXXhXXdUpkm          Remote Ultimeter


CSE/SPD is wind direction and sustained 1 minute speed
txxx   is in degrees F
Rxxx   is Rain per last 60 minutes
pxxx   is precipitation per last 24 hours (sliding 24 hour
Pxxx   is precip per last 24 hours since midnight
sxx    is snow in inches
bxxxxx is Baro in tenths of a mb
hxx    is humidity in percent.  00=100
gxxx   is Gust (peak winds in last 5 minutes)
#xxx   is raw rain counts for remote stations. See notes on
%xxx.. 1st letter shows software d=Dos, m=Mac, w=Win, U=Uiview,
       and remainder shows type of WX instrument

Note, in the complete WX format, the _DIR/SPDgxxxtxxx fields
must exist.  All the others are optional.  Though there is no
confidence that all clients implemented it that way...


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