Rating snow storms

It may be January, but with the relatively warm December¬†we had, I’m not ready to start thinking about snow (spoiler alert: I’m never ready to think about snow). But snow is bound to happen at some point, and the Weather Channel will be sure to name the storm. Humans like to assign numbers to things. We have ratings for tornadoes, we have ratings for hurricanes, but we don’t have ratings for snow storms. Or do we?

Paul Kocin and Louis Uccelini developed the Northeast Snowfall Impact Scale (NESIS) in 2014. NESIS considers the snow depth, the area, and the affected population. This last part makes it pretty unique among meteorological numbers. Meteorological phenomena are often considered without thought for population (for example, the National Weather Service will issue a tornado warning even if no one lives in the affected area). Tornadoes are rated based on damage (not wind speed!), which sort of proxies population, but not exactly.

NESIS doesn’t seem to be widely used, and it’s almost certainly unknown outside of the weather community. Maybe because we don’t tend to see snow storms as disasters in the same way that tornadoes and hurricanes are? It would be nice to see it catch on, though.

The amateur weather website hype machine

Word on the street is that a certain amateur meteorology site is starting to tease about a large snowfall event a week or so out. It must be winter again!

I don’t begrudge amateur meteorology sites in general. In the Internet age, there’s a lot that you can teach yourself and plenty of access to raw model data from which to build a forecast. As in most fields, the passionate amateur can be more skillful than the trained professional. Of course, this is generally limited to a specific skill, which is why the better amateur weather sites tend do focus on a particular thing.

Focusing on hyping winter weather events a week or more out is not an area that should be focused on. This is particularly true when the hype is completely unjustified meteorologocially and ends up requiring professional meteorologists in the National Weather Service and local media to spend time telling the public not to believe the “information” that should never have been shared in the first place.

Forecasting the weather is hard. Effectively communicating the uncertainty inherent to that forecast to the public is even harder (and not done nearly enough). Posting an outlier scenario to Facebook is easy. Any site that provides forecasts for public consumption and (somehow) finds a way to get partnerships with legitimate media outlets needs to eschew the easy. Otherwise, it’s simply self-service and not public service.

Why I hate winter

Whenever snow appears in the forecast, I’m filled with dread. There are two reasons: 1) I hate shoveling the driveway and 2) people ask me “how much snow are we going to get?” I consider myself a pretty decent severe weather forecaster. It’s my particular area of interest, and I’ve given myself some practice at it. Winter weather forecasting is a whole ‘nother beast.

It’s not just that I don’t like it, or that I haven’t practiced (both are true), but winter weather forecasting is really more challenging. There are a variety of reasons — some scientific, some psychological. The most obvious scientific reason is that temperature matters. A three degree difference doesn’t mean much when the temperature is 80 degrees; the rain will still be rain. When the temperature is in the lower 30s, a three degree difference can be the difference between rain, snow, or some awful mix. Surface temperatures aren’t the only ones that matter; small differences in the low-level air temperatures can have an impact on the precipitation type.

Even when you nail the precipitation type, how much snow do you get? A common rule of thumb is that one inch of rain is equal to 10 inches of snow, but that’s a really awful rule. The snow-to-liquid ratio can vary widely. I’ve measured from 2.7:1 to 30:1 at my house, with the average somewhere around 14:1. With half an inch of liquid, the difference between the rule of thumb and my observed average is 2″ of snow.

Then there’s the psychological aspect. For the most part, people don’t care how much rain falls in a given event. Sure, ridiculous torrents like southern Indiana saw last weekend are noticeable, but how many people can look outside and tell the difference between .25″ and .5″of rain? I bet they can tell the difference between 3″ and 7″ of snow, though. Snow also requires more preparation than rain does. You generally don’t see grocery store bread and milk shelves scoured clean before a rain storm. The highway department doesn’t put in overtime to salt the streets before it rains. Schools very rarely delay or cancel classes because of rain.

Snow draws attention to itself. It’s the biggest prima donna of the non-destructive weather phenomena. The natural result is that people become very sensitive to how well a forecast verifies. Unfortunately, it verifies “not good” all too often. I suppose this is my way of saying “is it spring yet?”

Winter storm forecast for Tippecanoe Co ARES

Prepared Monday, 31 January 2011 at 8:00 PM for Tippecanoe County Amateur Radio Emergency Services

Current conditions

An area of snow and sleet stretches from St. Louis to Champaign to Fort Wayne. Reports of 1″ of snow in Lafayette and 0.1″ of ice in Brownsburg have been received already this afternoon. Larger precipitation amounts are likely to have been received in places where convective development has occurred. Precipitation is likely to be ongoing for the next few hours as the system moves generally east-northeast.

Tippecanoe County is under a Winter Storm Warning from 7 PM this evening until 7 PM Wednesday. The surrounding counties of Warren, Fountain, Montgomery, Clinton, Carrol and White are included. Benton County is under a Blizzard warning from 4 PM EST Tuesday until 4 PM EST Wednesday.

Forecast: 0-12 hours

Models are in agreement that the precipitation will continue into the overnight hours. Although snow is expected to be the dominant type, periods of sleet and freezing rain will be included, especially before midnight. Heavy snow can be expected during portions of the evening hours as the stronger precipitation in Illinois moves east-northeast. Precipitation should slacken by 8 am, with 2-3″ of snow and potentially some ice on the ground. The exact amounts will depend on the mix of precip types.

Forecast: 12-24 hours

Tuesday morning will be relatively quiet. By mid-afternoon, winds will pick up to 15 knots, and snow will begin falling more heavily. Precipitation should remain light-to-moderate snow through the end of the period. Depending on the timing, an additional 4-6″ of snow may accumulate during this period.

Forecast: 24-36 hours

Tuesday night the snow returns in earnest, accompanied by winds of 20-25 knots. Heavy snow is likely through much of the period. The bulk of the weather impacts will occur from sunset on Tuesday into early Wednesday morning. Snowfall rates in excess of 2″ per hour are possible, leaving street crews unable to maintain passage on roads. By sunrise Wednesday, an additional 8-10″ of snow may have fallen, meaning total snowfall of 14-19″ is possible.

Forecast: 36 hours and beyond

Light snow will continue through the day on Wednesday, with perhaps another 1″ of accumulation. Winds will remain greater than 15 knots, creating the possibility of blowing snow. Temperatures will begin to drop Wednesday night and into Thursday as the winds shift to the north. Below-zero lows should be expected on Thursday and Friday mornings.

General impacts

The Lafayette area will be fortunate enough to miss the crippling ice storm that will impact the Interstate 70 corridor, including Indianapolis. Road crews should be able to keep streets passable through Tuesday afternoon. Travel will become difficult, if not impossible from Tuesday evening until at least Wednesday afternoon. Rural areas may remain blocked by snow until Thursday. Widespread power outages should be expected to our south and southeast, potentially lasting several days.