WeatherWeather Science


The KOAA Storm Impact Scale (SIS), explained

Posted at 3:18 PM, Jan 09, 2019
and last updated 2019-01-22 10:35:04-05

Curious about how we determine expected conditions with the First Alert 5 Storm Impact Scale?

It is based on common sense human response to the effects of a weather event. Things like: making plans, school delays, closures, or heading to the basement for life-threatening events. It goes from 1 to 5, with 1 having the least impact on plans and activities to a 5, where life and property are definitely at risk.

The scale is shown only on the 7-Day Forecasts. It is a number, again 1 to 5, near the bottom of the day(s) in question. It is also color-coded.

Storm Impact Scale of “1” on Friday & Saturday, for ex

We have created on-air slides, to use from time to time, to explain each level, but they will serve you well here, where you can take your time to read them over and understand the way we perceive the way your average community would respond to each weather event. (Time is short on the air, so at best, we can realistically only gloss over the grade we have chosen.)

It is also worth noting, there is a “cold-season” version, and a “warm season” version. The cold season version deals with snow/ice/cold/wind impacts, the warm with heat/wind/hail/flooding rain/tornado impacts. Here are the slides, in increasing order of impact.

This is the lowest impact, for a winter storm
This is an impact #2, for a winter storm
This is an impact #3, for a winter storm
This is an impact #4, for a winter storm
This is an impact #5, top of the list, for a winter storm