If you’ve lived in Virginia – especially the western part of the state – for any amount of time, you’ve probably seen a scenario like this play out before: the forecast calls for a significant snowstorm and when time comes for the event to happen – you either see very little compared to your neighbor in the next county or nothing at all.
If that’s frustrating for you, just know it’s also frustrating for meteorologists as well.
“This is undoubtedly – I think – one of the most challenging parts of being a meteorologist,” says Phil Hysell with the National Weather Service office in Blacksburg.
He says winter weather forecasting requires meteorologists to take into account so many variables.
“A, is it going to precipitate? Yes or no? But B, how much? And C, what is the temperature profile going to be? Not only at the surface, but above the ground as well. And all those things, all those variables, go into the type, the amount and location of precipitation.”
When it comes to temperature, most people think about what the thermometer says for them as they go to work or school. That reading is only for the surface, though. Winter weather forecast requires us to take account of the temperature profile throughout the atmosphere. For example, at the surface, temperatures may be below freezing, but just above our heads, it’s warmer than freezing, which would mean we’d likely see sleet or freezing rain at the surface.
Big snowstorms require below freezing temperatures and a lot of moisture at the surface, but also up into the atmosphere.
Another variable for western Virginia is the geography. That part of the state is more mountainous, which can have a huge impact on what kind of wintry precipitation ends up falling to the surface. Hysell uses the elevation difference between Roanoke City and the surrounding Roanoke County – from Bent Mountain down to the city – as an example.
“When you have a temperature profile where the temperature cools with height – Roanoke City will typically get a cold rain. But then, as you drive up in southeast Roanoke County, you’ll see those temperatures drop and the precipitation change to either freezing rain or snow. And just the opposite can occur as well. During a freezing rain event, you may have what we call a warm nose above the surface where it’s snow at lower elevations, but as you go up in elevation into the warmer air where it goes above freezing – that precipitation can then change to freezing rain and even rain.”
In other words, just a couple of degrees one way or another throughout the atmosphere can really make or break a winter weather forecast. There are also instances where air above our heads is too dry to maintain snow, and we don’t see as much at the surface.
All of these variables are very hard to nail down, and especially several days out from the actual event. Meteorologists with the National Weather Service rely on weather balloons to get a snapshot of the atmosphere above our heads. These balloons send back data like moisture content and temperature throughout the various layers of the atmosphere. It’s with that information – known as a sounding or Skew-T plot – that weather models and eventually forecasters piece together how a winter storm will behave.
This data can’t really be utilized effectively until a system is over land; you can’t launch a weather balloon from the ocean, where many of these systems often start out. And oftentimes, that doesn’t occur until two to three days before wintry precipitation is expected to fall.
Weather models are helpful to forecasters and the public alike, but when it comes to winter weather, it’s important to take everything you see on social media with a grain of salt. Some models will show a massive snowstorm several days in advance of the system even getting over land – which are then posted on social media causing all kinds of hype that doesn’t pan out.
Long story short, weather models can give us an idea of how things might be from a week from now but shouldn’t be taken as rock solid. If a model shows a big snowstorm a week or more ahead, it’s just something for us to be aware of. Within three to five days of the system moving through is when more concrete details will start to better come into focus.
Nevertheless, as with anything in this era, winter storms are ripe for misinformation or overhyping too soon. Because of that, it’s always important to turn to reliable sources for weather information. That definitely includes the National Weather Service, but your local TV or radio meteorologist is also a good place to turn.
Thanks for checking out this edition of CommonWx — the weather and climate newsletter from Radio IQ. Use this link to get the newsletter sent to your inbox.
