We at Blue Skies Meteorological Services were fortunate to escape (by a margin of about 50 miles) the late-January winter storm that crippled much of the southeastern US last week. That storm, which brought one to three inches of snow to areas that rarely receive even a trace of frozen precipitation, clearly demonstrated the danger and damage that can occur when weather does not agree with climate norms.

A common, if somewhat over-simplified, explanation of the difference between weather and climate is:
Climate is what you expect;
Weather is what you get.

The day-long traffic gridlock in Atlanta, GA, on Jan 28th epitomizes the hazards of getting climatologically unexpected weather (and of failing to incorporate updated forecast information into emergency management decisions, but that’s outside the scope of this article). The magnitude of the weather event itself is relatively unimportant (as several colleagues from the Upper Midwest have noted, “Two inches of snow is just a normal Monday commute back home”). What matters in terms of societal impacts is the deviation of the event from normal, expected values. And the reason for this is simple – we prepare for what we expect.

As a student at Purdue University, receiving a couple inches of snow was an almost weekly winter occurrence. Snow in northern Indiana is a climate norm, so everyone is generally well prepared for it. Life proceeds without interruption thanks to stockpiles of salt/sand, fleets of snowplows, and battalions of snow plow drivers.

It’s a different story in the South, though, where 50 degrees is deemed parka weather, and where ice is typically found in tidy cubes in your sweet tea, not in impenetrable sheets coating your car windshield.  Frozen precip is an anomaly, and as such, residents and municipalities don’t maintain the infrastructure nor have the experience to deal with it as “business as usual”.

However, what is lacking in infrastructure can be addressed through effective planning. By understanding the range of extreme weather events and their climatological recurrence intervals, businesses and municipalities can develop and implement emergency plans that mitigate the damage and disruption that inevitably accompanies extreme weather events.

Two inches of snowfall will always be a big deal in Atlanta (and normal January weather in the Midwest), just like temperatures above 100 degrees will always be a big deal in Maine (and a standard late July afternoon in Oklahoma). When planning for and understanding the impacts of extreme weather in any location, we must remember that it’s not the absolute magnitude of the event that matters – it’s the deviation from the norm. It’s the difference between what you expect and what you actually get.

Note: Blue Skies Meteorological Services provides climate analyses, including of extreme weather recurrence intervals, in support of business and municipal emergency planning and hazard mitigation.