Sperry-Piltz Ice Accumulation Index 

NWS logoNOAA logo

 National Weather Service

 Memphis TN



The Sperry-Piltz Ice Accumulation Index categorizes damage potential through the use of: (1) researched weather parameters and utility impacts and (2) the combination of forecast parameters including radial ice accumulation, wind and temperatures. The Sperry-Piltz Ice Accumulation (SPIA) Index is an Experimental Product with coordination with National Weather Service Offices in Missouri, Oklahoma, Arkansas, Texas and Tennessee. Additional information on the SPIA Index can be found in the Presentations and Paper sections of this webpage.  If you have questions, comments or feedback on this test product, please contact the National Weather Service at the contact infomation listed at the bottom of the page.



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.



Ice Accumulation

Maximum Sustained
Wind Speed (mph)

SPIA Index 

Day 1

Day 2




Day 3







Forecast Info

 Forecast Discussion       

 Hazardous Weather Outlook      


 Utility Ice Index Informational Presentation  Sidney K. Sperry 


 Utility Ice Index Paper Gary D. McManus, S.F. Piltz, S. Sperry, R.A. McPherson, A.D. Gartside, D. McClain, T.Meyer, C.Fetsch and M.A. Shafer



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.