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WEATHER BEAT: Forecasting the Impossible

| March 1, 2016 | 0 Comments | Weather

weatherbeatlogoAs we make our way into March and the beginning of Meteorological Spring, we begin to shift our thoughts to warmer weather, but before we do that, with the help of two friends, both aspiring meteorologists, I’d like to go back and discuss what goes into forecasting winter weather.

First off, when it comes to predicting a long-term winter forecast, your credibility comes from your ability to create an accurate forecast, something that The Bristow Weather Association (BWA) has been known to do in it’s five-year history covering local weather. With that said, I’m proud to say that the BWA was one of a few weather organizations to predict in excess of 30 inches of snow for this season.

This was definitely not our finest season for forecasting. While I did accurately predict this season’s snowfall, most of that snow fell primarily in one storm. Is it normal to see a one-storm season with that large of a snow total? Yes it is. In fact, most seasons in Virginia receive the majority of its snows from one or two snowstorms. That’s just how it is south of the Mason-Dixon Line.

Earlier this week, I asked Ben Michaux to share his thoughts on long-range winter forecasts. Michaux says its good to compare this year’s weather with past years to get a good feel of what it might do.

“I compared this year’s strong El Nino to an El Nino we had back in 1982-1983, where the ocean temperature of that El Nino was stronger and in a similar place off the South American coast,” he said.

By comparing these two El Nino’s, he said he was able to come up with a pretty accurate forecast. He was also able to accurately predict the blizzard back in January as a result.

I also had the privilege of speaking with Paula Hermsdorf, a local student studying meteorology at The Pennsylvania State University.

Hermsdorf has always reminded me that models are guidance and not gospel, and I totally agree with this. In fact, we’ve seen so many crazy shifts in models this winter that truer words have never been spoken.

“When you are learning about how to forecast winter weather in lecture, you are told to take into account many factors. You are not supposed to just look at one model and say it’s going to snow,” she said.

She explained that you must look into various models, maps and even forecast discussions.

“It’s also important to look at similarities and differences in these models. She also stated that analyzing the jet stream, sea level pressure, current station models, and fronts that show current precipitation and cloud cover is also important,” she said . “It’s good to get a feel for how the storm is moving and what the storm has done along its track.”

Another important consideration in forecasting winter weather is predicting the all-important snow totals. How do meteorologists know how much snow we are going to get? Its easy to say its going to snow, but how much snow is the question. When forecasting snow, you want to look at the snow ratio. Typically, the warmer the temperature is, the higher the snow ratio. Obviously, you don’t want it to be too warm, or you will just get rain or a wintry mix.

“A typical snow ratio is 10:1 meaning if you melt 10 inches of snow, you will get an inch of water.” That is why we generally say that an inch of rain is about a foot of snow roughly speaking,” she said. “Occasionally, we see snow ratios as high as 20:1 or 30:1, but not very often. Sometimes you will get a snow squall with those types of snow ratios.”

Another important element that comes into play with forecasting snow is the type of precipitation. The key to a big snowstorm is getting the entire atmosphere below freezing, which can be hard to do in Virginia. This is one of the reasons why forecasting winter storms are one of the hardest types of storms to forecast. I like to call it, “Forecasting the Impossible.”

Forecasting the impossible is not necessarily impossible. There are many things that help us do this. As previously mentioned, snow ratios can help with this, but looking at soundings to see the temperature in the atmosphere helps as well. Therefore, we are able to determine the type of precipitation. Also, following the 540mb line helps significantly. Despite all of that, it is still hard to predict precipitation type. Meteorologists of all skill levels struggle with this every winter; however, following the storm closely helps you to narrow down the options. The most convenient scenario is when the 540mb line is way down in South Carolina, but that almost never happens. It can never be that easy.

The take away from this Weather Beat is that forecasting winter storms are not necessarily impossible, but they are not exactly easy to forecast, which is why its my favorite season to forecast. Thanks for reading.

Ben Michaux and Paula Hermsdorf were contributors to this column.

My favorite thing to do is study the weather. It is truly fascinating. Nothing beats a good thunderstorm. I became very interested in weather when I lived in Okinawa, Japan for four years and was actually inside a super typhoon.

Please check out my Facebook page for daily, local weather exclusive to Western Prince William County.

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