This week is North Carolina’s Winter Weather Preparedness Week – time to transition our thought processes from autumn and hurricane season to winter safety.
National Weather Service Definitions
Blizzard Warning – Severe winter weather is expected within the next 12 to 36 hours or is occurring – including whiteout conditions. Do not travel.
Winter Storm Warning – Dangerous winter weather is expected within the next 12 to 36 hours or is occurring. Considerable travel problems are expected.
Winter Weather Advisory – Potentially dangerous winter weather is expected within the next 12 to 36 hours or is occurring. Travel difficulties are expected.
Snow Squall – An intense, but limited duration period of moderate to heavy snowfall, accompanied by strong, gusty surface winds and possibly lightning. Snowfall rates may be significant.
The absolute worst-case scenario – one that we rarely see in the Triangle – is a blizzard. High winds whip heavy snow around and lower visibility to nearly zero. Nobody should be on the road in a blizzard. Your inability to see what’s in front of you means that other people can’t see what’s in front of them either. A bunch of snow-blind drivers on the road will only lead to misery.
Typically, around here, we experience winter storm warnings and winter weather advisories. The warning is issued when road conditions are expected to deteriorate to the point where travel is hazardous and should be avoided. The advisory is usually issued when some icy and slushy spots are expected, but it may not be widespread or long lived. Travel is still discouraged, but if you must travel, you should slow down, leave extra stopping space between you and the car ahead of you, and avoid any distractions while driving. (These are good driving rules in general, but especially in hazardous conditions.)
A snow squall is a dangerous situation because of the white-out conditions it creates. We don’t see this situation often in the Triangle, but under the right circumstances, it’s possible. If snow squall warning is issued for your area, stay put. It will only last up to three hours. Once it is over, you can check road conditions to determine if it’s safe to travel.
You’ve probably heard the advice to keep your tank over half-full during the winter. This practice helps avoid problems caused when condensation freezes and collects into icy blockages in your fuel lines. It also helps ensure you’ll have plenty of fuel to run your car for heat if you are stranded somewhere.
Cold weather can affect your car battery by slowing down the chemical reactions that take place inside it. According to AAA’s Automotive Research Center, at 32 degrees Fahrenheit, your car battery can lose about 35% of its strength, and it gets worse as the temperature drops.
AAA suggests using a quarter to check your tires’ tread. “When the top of Washington’s head is exposed, the tread depth is 4/32 inches or less and it’s time to start shopping for new tires.” Keep your tires properly inflated as well. Always use a reliable tire gauge and the manufacturer’s recommended pressure when you check them regularly.
Another useful tip that I’ve needed firsthand is to keep cat litter, or something similar, in your car to use on the road for traction if your car gets stuck. It’s also a good idea to keep a blanket, water, and some snacks in the car for the same reason. If you get stranded and are low on fuel, you’ll need a way to stay warm. Keep your cell phone charged. Charging it in the car while the engine isn’t running adds to battery drain.
Winter weather preparedness at home is similar to hurricane preparedness in some ways. You’ll want to have your emergency kit ready. If the power goes out, having a way to stay warm in your home – a generator, a fire place and dry wood, etc. Battery or kinetically-powered lanterns and a NOAA weather radio will be helpful, too. If you don’t have a fireplace or a generator, have a backup place to stay in case the power goes out for an extended period of time.
Checking the forecast often
In our part of North Carolina, winter weather forecasts are dynamic to say the least. They usually change with every model run. The mountains to our west and the coast to our east create the possibility for cold air damming (CAD) scenarios and coastal lows/Nor’easters. Both can bring anything from rain to ice to snow to the Triangle.
Whether we experience rain or frozen precipitation with a CAD scenario depends on how far east the cold air that’s damming up against the mountains extends and how deep the cold layer is. The farther east and deeper the layer, the more likely we see snow. A shallow cold layer may bring sleet or freezing rain. If the cold air stays to our west, we’ll likely just see rain if anything.
The opposite is true with a coastal storm. The proximity of the storm to the coastline and how quickly the cold air moves into our area determine what kind of precipitation we see.
In both cases, the details of the forecast are difficult to nail down until the storm actually takes shape. The forecast models tend to suffer from low resolution more than a few days in advance. The ingredients needed to create the winter weather may not really fall into place as the models predict. Sometimes they do, but sometimes the cold air doesn’t arrive until after the precipitation ends. Other times, the air at the surface is drier than expected and the precipitation takes longer to reach the surface, limiting precipitation amounts. Don’t assume the winter weather forecast you see today will be the situation that plays out two days from now.
Graphic courtesy of the National Weather Service