The New Scaled Predictive Ice Storm Aftermath (SPIA) Index


Ice Impact Index 

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 National Weather Service

Nashville, TN



The NWS is accepting comments from through April 15, 2014, on an experimental product called the         Scaled Predictive Ice Storm Aftermath (SPIA) Index.

SPIA Survey - comments welcome

Select NWS Weather Forecast Offices (WFOs) will produce Web graphics depicting the potential impact of freezing rain and wind on exposed electrical systems to enhance their decision support services.

Current NWS Ice Storm Warnings are issued based on forecast ice accumulation only, typically one quarter of an inch or greater. The combined effect of ice and wind, which more realistically describes damage potential, is not formally set as warning criteria.

By using the SPIA scaled index, NWS should be able to provide a better understanding of ice storm impact potential to local, state, and federal response entities. The potential impacts are scaled from 0 to 5 and suggest potential electrical outage coverage and duration.

Until now, the NWS has not attempted to routinely quantify the impact of ice storms. The use of this scaled index will allow the NWS to evaluate the potential of providing these specifics. For example, a level 5 ice storm would be defined as one causing catastrophic damage to entire exposed utility systems, including both distribution and transmission networks. Outages could last several weeks in some locations.

Further details on this product can be found here



Day 1

Day 2

Day 3 

Ice Impact Index



Utility Damage and Impact Description


Some local utility interruptions possible...typically lasting a few hours.


Scattered utility interruptions possible...typically lasting less than 12 hours.


Numerous utility interruptions possible...lasting up to 5 days.  Damage to some main feeder lines possible.


Prolonged and widespread utility interruptions. Damage to many main feeder lines possible. Utility outages lasting up to 10 days possible.


Catastrophic damage to exposed utility systems possible. Outages lasting several weeks possible in some areas.



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