Re: [ldm-users] NEXRAD3 Again ... part III

On Tue, 2 Aug 2011, Chad Johnson wrote:

All,

We found that the high rate of retransmitted products ended on Monday 08/01 - around 
14:44 UTC. Up until that point, we were seeing retransmissions at a rate of thousands per 
hour and the difference between the time of original transmission and the time of 
retransmission was around 6000 seconds or between 1.5 to 2.0 hours. Then, there was a 
half hour gap between 14:44 and 15:13 where no retransmissions were sent, followed by the 
typical random low rate of restrans we're used to seeing. The time difference between the 
original and the retrans product also settled down to a typical 30 and 60 seconds. After 
8/01 14:44, I'd guesstimate that we had already seen 95% of the retransmissions. Before 
that, I'd say it was the inverse (possibly because products were no longer in the 
"seen it" list). Anyway...something happened at 14:44 on the 1st. Is anybody 
aware of any changes made by the NCF/TOC around that time?

I talked to the TOC late yesterday afternoon and they said everything was fine. 
Which I guess, technically, at the time was true but they didn't provide any 
additional information.

What seems really odd to me, is the length of time between the original 
transmission and the restransmission. It's almost as if there is a rogue NWS 
office out there requesting retransmissions long after the product has been 
transmitted. Here, a slug of radar products were retransmitted nearly two hours 
after the original was broadcast. We were also seeing the same for some GRIB 
data.

2011/08/01 00:03:07 Retranmission already exists: skipping "SDUS54 KOUN 
312215"; Secs=6370
2011/08/01 00:03:07 Retranmission already exists: skipping "SDUS54 KOUN 
312215"; Secs=6370
2011/08/01 00:03:07 Retranmission already exists: skipping "SDUS23 KIND 
312211"; Secs=6370
2011/08/01 00:03:07 Retranmission already exists: skipping "SDUS23 KARX 
312214"; Secs=6370
2011/08/01 00:03:07 Retranmission already exists: skipping "SDUS23 KIND 
312211"; Secs=6370

They may have even retransmitted the same product multiple times, unless 
multiple unique products are transmitted under the SDUS54 KOUN header (not up 
on my WMO headers like I used to be).

2011/07/31 22:16:21 Retranmission doesn't exist: saving "SDUS54 KOUN 312215"
2011/08/01 00:01:34 Retranmission already exists: skipping "SDUS54 KOUN 
312215"; Secs=6335
2011/08/01 00:01:34 Retranmission already exists: skipping "SDUS54 KOUN 
312215"; Secs=6335
2011/08/01 00:03:07 Retranmission already exists: skipping "SDUS54 KOUN 
312215"; Secs=6370
2011/08/01 00:03:07 Retranmission already exists: skipping "SDUS54 KOUN 
312215"; Secs=6370

At that time, we lost all METARs. The NWS sent out a memo saying that a SAN had gone crazy; they had switched to a "backup system" and that SAN was having issues. Once fixed, the METARs came back and the duplicate products stopped. So it wasn't the satellite broadcast or NWS offices having trouble getting the broadcast.

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Gilbert Sebenste                                                     ********
(My opinions only!)                                                  ******
Staff Meteorologist, Northern Illinois University                      ****
E-mail: sebenste@xxxxxxxxxxxxxxxxxxxxx                                  ***
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