DES MOINES, Iowa -- A damaged communications cable led to minutes-long delays for some to receive Tornado Warnings and other emergency weather alerts during the severe weather outbreak that spawned several tornadoes in Iowa, the National Weather Service said Monday.
Eight tornadoes touched down across the state, including an EF-4 that killed six people and an EF-3 tornado that killed another.
A National Weather Service spokesperson said their forecast office in Des Moines issued warnings in advance of each tornado with an average lead time of 20 minutes -- well above the national average of 10 minutes. The delay issue did not affect NOAA Weather Radio or the Emergency Alert System and all tornado warnings were immediately broadcast upon issuance.
However, the damaged fiber optic cable meant there were some delays as long as 2-7 minutes in getting the warnings out to other platforms, such as the NWS's weather.gov website and cell phone alerts. The delays lasted for over 2.5 hours, according to data submitted by Daryl Herzmann with Iowa State University.
"The Des Moines forecast office was aware of the delay and took the precaution to issue warnings earlier than they normally would have under similar circumstances to compensate and ensure that warnings reached the public in a timely manner," said Susan Buchanan, the director of public affairs for the National Weather Service.
The NWS office also live-tweeted urgent warnings via Twitter and kept emergency partners updated directly via an internal chat, Buchanan said.
Technicians traced the problem to a damaged cable that served the NWS office in Dallas. A backup system engaged, sending all forecasts products issued from the Dallas office to a satellite-based network that serves all NWS offices.
"The uptick in messages flowing to the central message handler from NWS Central Region offices due to the severe weather, combined with the performance characteristics of the satellite network in use at a co-located site, slowed down the queue of message transmissions and created a brief backlog across multiple offices," Buchanan said.
Once the Dallas office was removed from the network, the transmission delays disappeared.
NWS officials are now implementing procedures to avoid a repeat.