[aprssig] Weather Alert APRS Message

Dan Srebnick k2dls at k2dls.net
Sun Jul 30 11:22:05 CDT 2017

I seem to have figured part of Q2, at least as far as Xastir is

While comments in the Xastir alert.c code indicate that the underscores
in the "title" field (where the UGC zone codes are inserted) are
required by Xastir, what really happens is that Xastir wants to see the
UGC zone code without the underscore but then inserts it on display.

So if there is not a written APRS standard, it seems that the practice
(as witnessed by looking at data sent by WE7U-WX) is that the zones are
used in an APRS wx alert message and that they do not contain the

If someone much more knowledgeable can confirm, that would help.

Also with regard to county/zone data, http://www.aprs.org/APRS-docs/WX.
TXT mentions that a trailing comma is required.  I don't see this in
the WE7U-WX data feed and Xastir does not seem to care either.

For my Q1, Xastir doesn't seem to care if a multi word "alert_tag"
contains  underscores or not, despite comments to the contrary in
alert.c.  Underscores are the practice seen in the WE7U-WX data but it
also displays my feed fine without the underscores.

On Fri, 2017-07-28 at 17:43 -0400, Dan Srebnick wrote:
> Hi:
> I'm putting together a process to query the xml from my local NWS
> office, see if there are any active alerts, and gate them in weather
> alert format to RF.  After putting together information from various
> sources, I've come up with the following parsed APRS format:
> K2DLS-13>APRS::NWS-WATCH:291800z,Flash_Flood_Watch,NJ_Z020, {SJ8AA
> Is this format correct?
> Now for some more specific questions about data formats.
> Q1: Are the underscores required in what Xastir refer to as the
> "alert_tag" field?  I seem to get different display results with or
> without them in the Xastir Wx Alerts window, but none of them are
> what
> I expect.
> Q2: Is there a standard for county format?  One approach is described
> by http://www.aprs.org/APRS-docs/WX.TXT (NJ_MONMOU) and another is
> described in the Xastir comments (the derivative of the UGC value as
> displayed in my packet, NJ_Z020 rather than NJZ020).
> Q3: Is the compressed time value after the { required to be 5
> characters or can I leave off the last 2?  or see Q4...
> Q4: If I just use AA or 00 for the last two characters mentioned in
> Q4
> is that a problem or should I use a random algorithm?  Or is this
> value
> to support multiline messages?
> Any insight would be appreciated.
> 73,
> Dan Srebnick

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