Spring is just around the corner. It’s a time of brightening skies, lengthening days, new blooms – and potential meteorological chaos.
While astronomically, spring doesn’t begin until March 20 – when the sun’s most direct rays return to the Northern Hemisphere – meteorological spring begins on March 1. It’s the start of what is typically the most tempestuous time of the year. The Lower 48 becomes an atmospheric battleground, with swarms of tornadoes, blistering blizzards and drenching deluges all possible across the country.
And at least in the first half of the coming month, forecasts suggest a temperature roller coaster in the United States.
Here’s what happens, or can, during meteorological springtime.
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The days get longer
This is the time of year when the days are growing the fastest.
Throughout March, Washington, D.C., for example, gains roughly 2½ minutes of daylight every day – totaling 66 minutes over the course of the month.
Farther north, it’s even more dramatic. Boston tacks on up to 2 minutes 52 seconds of additional daylight per day, totaling 1 hour 26 minutes of day length by the end of the month.
In southern regions, the shift is more gradual. Orlando adds only 51 minutes of daylight in March.
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Temperatures warm up
The increasing sunlight means warmer temperatures.
Boston’s high temperatures climb by 8.7 degrees on average during the month. Temperatures in Washington increase by 10.7 degrees, and Orlando’s rise by 4.1 degrees.
Chicago’s average high increases 12 degrees, from 40.9 at the start of the month to 52.9 by the end of the month.
Glancing ahead, a temperature roller coaster is expected during the first half of March. In many places, unusually warm conditions will oscillate with brief cold spells – and high temperatures could swing 3o to 50 degrees or more over the course of a week.
This is a stark change from January and February, which were consistently colder than average, particularly across the northern half of the country.
As a whole, March is expected to feature near-average temperatures for much of the northern and northeastern United States, with above-average temperatures across the South and cooler weather in the Pacific Northwest, according to NOAA’s Climate Prediction Center.
It’s a pattern typical of La Niña conditions.
The jet stream slices from the northwestern United States eastward across the country, dividing the nation north to south. Warm air from the Gulf of Mexico wafts north across the Deep South and Mid-South. The land-falling jet stream, meanwhile, pumps clouds and storm systems into the northwestern United States, keeping temperatures chilly and leading to more precipitation.
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Snowfall wanes … usually
The warming temperatures typically lead to less snowfall in most places. The exception is in coastal New England, where late-winter nor’easters are quite common.
In 2018, an assembly line of four back-to-back coastal storms plastered Hartford, Connecticut; Providence, Rhode Island; and Boston with heavy snow. On average, Boston gets 9 inches of snow during the month – about 20 percent of its annual snowfall. Chicago averages 5.5 inches and Minneapolis 9.2 inches.
Looking ahead, warm air over the North Pacific will amplify a high-pressure system near Alaska, forcing the jet stream north into Canada. That jet stream will then dip over the eastern United States, allowing chilly weather and storminess to spill south over the Great Lakes and Northeast to kick off the month.
Weather models suggest there could be near-average to slightly above-average probabilities of snow over the Intermountain West, the northern Great Lakes and interior New England. There appear to be lower odds of snow in the northern Plains, the Midwest and coastal New England in the first week of March.
After that, the medium-range weather pattern could support continued cool and stormy weather in the Northeast between March 7 and 15, with increased snow odds.
The end of the month should be warmer than average, however.
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Severe weather chances climb
March is usually when tornado season begins to awaken – first over the Deep South and then by April in the southern Plains and perhaps the Midwest. That’s why places like Mississippi, Alabama, Tennessee, Georgia and Louisiana should be on alert during March.
As gulf moisture sneaks north, it provides ample instability, which is thunderstorm fuel. But leftover cold air masses from the Rockies can kick that moisture up, forming thunderstorms.
And since the jet stream is still in its wintertime position over the Lower 48, there’s plenty of wind in the upper atmosphere to sculpt storms into rotating supercells. Many of those storms produce tornadoes.
There are two time periods that may favor increased tornado chances – March 2 to 4, and more broadly during the second half of March.
For the March 2 to 4 period, meteorologists are eyeing a possible large-scale low-pressure system that could shift east out of the Rockies and help generate thunderstorms.
Thereafter, a large-scale jet stream dip filled with cold air will probably take shape over the western United States during the second half of the month. This could allow occasional low-pressure systems to push east as well, spawning more thunderstorms.