Here's what to expect from a weekend blizzard forecasters said could bring one of Baltimore's top 10 biggest snowfalls and life-threatening travel conditions.
How much are we going to get?
Weather forecasting models suggested we would be getting 2 to 3 inches of rain if it were warmer, but with temperatures expected to be around freezing or colder for the duration of the storm, it is largely expected to fall as snow. The general rule of thumb is 10 inches of snow for every inch of liquid precipitation, which translates to 20 to 30 inches of snow.
National Weather Service meteorologists' best guess for the Baltimore area is in the realm of 24 to 30 inches, with more than 30 inches possible if the storm overperforms. If it underperforms, we're still looking at a foot of snow.
It is expected to snow the heaviest overnight Friday and into Saturday morning, not tapering off until some time before dawn Sunday morning. You can expect as much as a foot by the time the sun rises Saturday, and as much as another foot by Sunday morning.
Factors that could put us on the lower end of predictions include the storm's track and whether relatively mild air moves in overhead, creating sleet or other mixed precipitation. But we could also end up on the higher end if, say, temperatures stay in the 20s. Highs are forecast in the lower 30s. Colder air means finer, fluffier snow that packs down less (and isn't good for snowballs or snowmen).
How long is it going to last?
Heavy snow is forecast from late Friday night through Saturday. It is expected to start tapering off by about midnight Sunday, with some light snow possibly continuing into the early morning hours.
A blizzard warning is in effect from 3 p.m. Friday through 6 a.m. Sunday.
Is it safe to go out?
Travel conditions are expected to be treacherous, with 30 mph winds and gusts of more than 50 mph blowing snow and limiting visibilities to a quarter of a mile or less. A statewide snow emergency plan went into effect at noon Friday, restricting travel and parking on all state roads designated as snow emergency routes. A state of emergency declared by Maryland Gov. Larry Hogan also went into effect at 7 a.m. Friday.
Residents were urged by nightfall Friday to get wherever they plan to stay for the duration of the storm.
"Now is the time for Marylanders to stay at home and off the roads," said Governor Larry Hogan. "This is the safe choice. It will also allow emergency services vehicles to maneuver and road crews to begin the long process of clearing highways and streets."
Why is this storm so intense?
The storm is considered a classic "nor'easter," the name for the large coastal storms responsible for the East Coast's biggest snowfalls. Nor'easters thrive on a clash between cold air to their north and west and relatively warmer, moister air over the Atlantic. They also typically carry heavy amounts of tropical moisture from the Gulf of Mexico. Strong winds from the northeast give these storms the nor'easter name.
This storm is already intense as it moves across the Gulf Coast states Thursday, prompting tornado watches in Texas and Louisiana and causing a flurry of lightning strikes. It is forecast to move toward Alabama and Tennessee before transferring its energy to a low-pressure system expected to form over the Carolinas on Friday. It will then sweep up the coast, intensifying thanks to the aforementioned clash of air masses.
What is a blizzard?
A blizzard is not just a name for a big snowstorm -- for a storm to qualify as a blizzard, it must bring winds of 35 mph or greater and considerable falling or blowing snow that reduces visibility to less than a quarter of a mile.
This storm is expected to bring, along with the aforementioned massive snowfall, sustained winds of 25 to 35 mph and gusts up to 55 mph. The combination of the snow and winds could lead to massive drifts, dangerous travel conditions and power outages.
How does this forecast compare to past storms?
Snowfall of at least 18 inches would put this storm among Baltimore's top 10 biggest snowfalls. More than 2 feet would put it in the top five. You can go through the list here.
When a blizzard watch was issued across the region Wednesday, it was for the first time in this region since 1993 (it has since been upgraded to a blizzard warning). There have been a handful of blizzard warnings since then when such conditions have developed, but the bottom line is that blizzard conditions are rare, and having any foresight of them is rarer still.
Why are people calling this storm "Jonas"?
The Weather Channel launched an effort in 2012 to name winter storms in the same way we name hurricanes, to simplify messaging about storms and to communicate their severity. They have announced a new set of names each year, this winter already going through names like Bella, Echo and Goliath. Jonas is the tenth name on the list.