Invest the time to tap forecast data from a range of sources — its accuracy may be better than you expect.

Not many people sleep with a radar image on the computer screen beside their beds. But if you are winter contractor Alan White and you’ve been warned that a storm is approaching, you want to know what’s coming and precisely where and when it will arrive in order to provide the service that your clients expect.

White owns Turf Systems, a lawn care firm that also provides snow and ice management for schools and other public institutions in Burlington, Oakville and Milton, Ont. “With our clients the expectation is bare asphalt within a short period of time,” he says. Serving schools means night work only. “We can’t plow during the day, because no equipment is allowed on site when the kids are there,” White says. Thanks to radar, he eliminates the costly risk of deploying crews and equipment to a job site at 11 p.m., only to have them wait around for three hours for the storm to begin.

Radar lets him track the progression of a storm several hours before it’s expected to hit. “In the radar images, I can see the type of precipitation (snow, freezing rain, etc.), the amount that is going to fall, as well as how fast the storm is moving and its direction,” says White. “Since the image is usually updated every five minutes, it’s like flipping through pages in an animation book. You see the still image move. So we can tell if the storm will be here in an hour, a half hour, 15 minutes or if the bulk of it is not going to happen.”

Predicting the unpredictable

Improvements in the technology and methods used in forecasting are taking much of the guesswork out of winter weather prediction. But just how confident have forecasters become?

Meteorologists agree that 12-hour forecasts are often highly accurate, thanks to radar and satellite technology. “Radar informa-tion will show you what’s happening now, and also provide very short term forecasts,” says Kent Johnson, manager, National Services Office, Meteorological Service of Canada. “If you’re concerned about whether the snow is going to arrive in five minutes or two hours, I would rather look at the radar and see where it is as opposed to just looking at the forecast which can be vague and say things like snow beginning this afternoon.”

Forecasts ranging from 12 hours to a few days have also improved. According to a December 2007 report from the American Meteorological Society (AMS) on the current state of weather forecasting science, 48-hour precipitation forecasts are now as reliable as 24-hour forecasts were a decade ago — and winter storm watch lead time for the season ending in 2006 was 17 hours, an increase of 70 per cent since 1999.

As forecast length increases, accuracy erodes. Still, major winter storms are often forecast a week or more in advance. Three-day forecasts of one inch or more of precipitation are as accurate as two-day forecasts were in 1998 and the accuracy of five-day forecasts has more than doubled since the late 1970s, reports the AMS. These improvements are largely due to numerical weather prediction and ensemble forecasting.

Narrowing the odds

Numerical weather prediction and ensemble forecasts are revolutionizing the entire forecasting process. Numerical weather prediction uses current weather conditions as input into mathematical models of the atmosphere to predict the weather. Complex computer programs, also known as forecast models, run on supercomputers and provide predictions on many atmospheric variables such as temperature, pressure, wind and precipitation.

However, numerical weather prediction is flawed because the equations used by the models to simulate the atmosphere are not precise. This leads to some error in the predictions. In addition, there may be gaps in the initial data, since scientists don’t receive weather observations from certain areas. If the current state is not completely known, the computer’s prediction of how that state will evolve will not be entirely accurate.

To help compensate for this, forecasters use ensemble methods. Ensemble forecasts are multiple predictions from a set of numerical weather prediction systems with slightly different initial conditions and/or slightly different versions of atmospheric models. Differences between the individual predictions give forecasters a better sense of the probability of various weather events.

Says Kent Johnson, “We have something called the North American Ensemble Forecast System (NAEFS), which is a joint project involving the Meteorological Service of Canada, the United States National Weather Service and the National Meteorological Service of Mexico. With the NAEFS, we currently do about 30 different simulations of the atmosphere. This provides a better range of probabilities as to what will happen in one to 14 days, rather than basing the forecast on only one simulation. The more the simulations converge, the greater the confidence in the forecast. Conversely if there is more spread in the simulations, then forecast confidence is reduced.”

Johnson’s office is currently engaged with various users of weather information to learn how best to communicate forecasts in a meaningful way. Last year, they hosted a workshop with provincial road main-tenance people whose weather information needs are similar to other snow and ice management professionals.

Recalls Johnson, “One of the things we heard from them almost unanimously is their need to know what’s going to happen in the next two hours and in the next two to three days. They said the time in between is less important because in two hours they can deploy crew and trucks. In two to three days they need to make sure they have chemicals, sand, etc., and ensure that everything is in the right places for the coming storm. They also often mentioned rate of precipitation. They told us it’s not as important to know there’s going to be 10 to 15 cm of snow; what’s important is knowing if it’s all going to fall in a two or three hour period or whether it’s going to fall slowly over a 24 hour period.”

“What we would like to do,” Johnson adds, “is get probable information into their hands that says, for example, in three days you’ve got a 90 per cent chance of getting 2 cm of snow, a 30 per cent chance of 10 cm and a small but significant 15 per cent chance of getting 30 cm. That’s the kind of information they can use to make better decisions.”

Challenges going forward

However, predicting the rate of precipitation beyond 48 hours remains difficult, says John H. Dlugoenski Jr., meteorologist and product manager for AccuWeather. “Two days before a storm we might say the snow will come down between one to two inches per hour and may not be able to predict the time frame. But as the storm gets closer, we can determine a time frame of when the heaviest snow will fall. Usually we can get pretty much within the hour. We can say the snow is going to begin at 9 a.m. and end at 6 p.m. The heaviest will be between noon and 4 p.m., and the snowfall rate is going to be between a half inch to one inch per hour,” he explains.

For snow professionals serving the Great Lakes areas, lake effect storms can still be hard to pin down. These squalls or streamers occur when cold air travels for long distances over the relatively warm waters of a large lake. The air picks up moisture and heat from the lake and then drops the moisture in the form of snow upon reaching the downwind shore. Since the Great Lakes are so large and retain their summer heat into the winter, considerable heat and moisture is picked up to fuel the squalls.

“In general terms, you can forecast lake effect snow a long way in advance because all of the things that bring it about are pretty much established,” says researcher Jaymie Gadal, national manager, Science Transfer and Professional Training, Meteorological Service of Canada. “Our models of 25 years ago would give you a reasonable idea what the wind direction could be, even three, four or five days ahead. What we can’t do even now is predict exact location, intensity and onset time.”

Gadal’s research ran high resolution models that accurately predicted some lake events within 10 kilometres. “In other cases the results were puzzling,” he admits.

Says Chris Scott, forecast operations manager at Pelmorex Media, parent company of The Weather Network, “In terms of lake effect snow squalls, we try to give our clients a sense of the possibilities. We’re getting better with these forecasts, but for the exact amount of snow there will always be a spread. And there will always be occasions where one part of a city gets a lot of snow and the other part doesn’t get as much.”

Wired for weather

In the 18 years Alan White has been fighting snow and ice, he’s spoken with many meteorologists. In fact, he is often the source that other contractors turn to when they want to know what Mother Nature has in store. His office is lined with computer and TV screens that spew out everything from long-term forecasts to current road conditions. “When I first started in the snow business, I did nightly runs to physically check the weather in different cities, but now I don’t have to,” White says. “Traffic cameras show me current weather conditions in multiple locations simultaneously.”

For a look at road conditions in the areas he services, White logs on to the Ontario Ministry of Transportation’s COMPASS Freeway Traffic Management system. For strictly weather information, he uses a combination of four different services and formulates his own forecast probabilities. “Their predictions can sometimes differ quite a bit,” White says. Three of the services offer free access; one is fee-based. “The fee-based web site gives us a lot more detail and a lot more updates. I think an important consideration is how often they give you the information.”

For radar imagery, he consults Environment Canada’s website and sub-scribes to a live radar feed to radar stations in the northern U.S. Armed with this information, he can track storms from every movement.

If White’s fascination and proficiency with weather information gives him a professional edge, he admits to feeling “at a disadvantage whenever I leave the office because I don’t have as good a linkup to weather that’s not here yet.” He has limited weather alerts via his cell phone, “but they don’t show me details. I can’t see what’s about to happen and what’s about to end. So I always find myself going back to my office or logging on to the Internet through my cell phone or through a local WIFI port on my laptop. I’ll pull up to a place where I know I can get back online.”