Arctic Blast Plunges Millions into Deep Freeze as May Cold Front Shatters Spring Warmth

Key facts

• Temperatures are expected to plummet 20 to 30 degrees below average across millions of Americans.
• Frost advisories and freeze warnings are in effect for 18 states including Texas, Oklahoma, Colorado, Kansas, Nebraska, South Dakota, Iowa, Missouri, Minnesota, Wisconsin, Illinois, Michigan, Indiana, Kentucky, Ohio, West Virginia, Pennsylvania, and New York.
• The coldest weather is forecast for western and southern Wisconsin, where overnight lows could reach 23 degrees Fahrenheit.
• The polar vortex that hit in March and April created an 'atmospheric traffic jam,' allowing cold air to move south from Canada.
• AccuWeather lead long-range expert Paul Pastelok described the phenomenon as an 'atmospheric traffic jam.'
• AccuWeather senior meteorologist Brett Anderson noted that after this weekend, most nights should not bring frost or freeze conditions in the Midwest and Northeast.
• AccuWeather senior long-range meteorologist Chad Merrill stated that this May is not anticipated to be the coldest on record for the affected areas.

A Sudden Deep Freeze Descends on Spring

Millions of Americans from Texas to New York are under frost advisories and freeze warnings Friday afternoon as a massive cold front sweeps across the United States, bringing a sharp and unseasonable drop in temperatures at the start of May. The National Weather Service (NWS) issued a wide swath of cold-weather alerts across the Southern Plains, Midwest, Northeast and Mid-Atlantic as the front pushed east, with nighttime lows expected to plunge below freezing in some areas. Forecasters warned the sudden chill could damage early-season crops and sensitive vegetation, posing a particular risk as much of the country has already entered the growing season.

The Polar Vortex's Lingering Grip

The surge of cold temperatures is the result of a polar vortex that hit in March and April, AccuWeather lead long-range expert Paul Pastelok told Newsweek. It 'created an atmospheric traffic jam' that allowed waves of cold air to move south from Canada into the Midwest and Northeast, Pastelok said. 'Below-average departures during the first 10 days of May will be significant, especially in the Ohio Valley, Great Lakes and interior Northeast,' Pastelok added.

States Under the Chill

On Friday afternoon, frost advisories and or freeze warnings were in place for the following states: Texas, Oklahoma, Colorado, Kansas, Nebraska, South Dakota, Iowa, Missouri, Minnesota, Wisconsin, Illinois, Michigan, Indiana, Kentucky, Ohio, West Virginia, Pennsylvania and New York. The coldest weather will hit western and southern Wisconsin, where temperatures as low as 23 degrees were expected overnight Friday, the NWS office in La Crosse said in a freeze warning. Some areas were not expecting temperatures to fall below 32 degrees, but frost was still a risk.

The Science of Frost Formation

Frost forms based on the temperature of surfaces, not the official air temperature in a forecast. Air temperature is typically measured about 5 to 6 feet above the ground, but on clear, calm nights, surfaces like grass, car roofs, or rooftops can cool much faster than the surrounding air through radiational cooling. As these surfaces lose heat to the open sky, their temperature can fall below 32 degrees even while the air a few feet above them stays in the mid-30s or higher. When that surface temperature drops below freezing, and there’s enough moisture in the air, water vapor deposits directly as ice crystals, forming frost.

Extended Warnings and Weekend Outlook

In most cases, the warnings were in place for Friday night. However, a freeze watch was in place for Kentucky, Virginia, West Virginia, and Pennsylvania, warning of freezing temperatures on Saturday night as well. 'After this weekend, most nights should not bring frost or freeze conditions in the Midwest and Northeast, but a couple of nights could still see them, especially in the Midwest away from the Great Lakes,' AccuWeather senior meteorologist Brett Anderson told Newsweek. 'Clouds, breezes and showers will greatly limit the risk in the Northeast.'

Not a Record-Breaker, but a Significant Shock

Despite the frigid weather, AccuWeather is not anticipating that this May will be the coldest on record for the affected areas, AccuWeather senior long-range meteorologist Chad Merrill told Newsweek. The cold front is part of a larger pattern that has already brought severe storms, including tornadoes, to parts of the country in April. The sprawling system also has the potential to cause significant air travel delays in the eastern and Central US, as well as Denver, as the front drags across the nation through the week.

The bottom line

• A massive cold front is causing temperatures to drop 20 to 30 degrees below average across the U.S., with frost advisories in 18 states.
• The polar vortex from March and April created an 'atmospheric traffic jam' that allowed cold air to flow south from Canada.
• Nighttime lows could reach 23°F in western and southern Wisconsin, with frost risks even where air temperatures stay above freezing.
• Frost forms on surfaces that cool faster than the air, posing a threat to crops and vegetation during the growing season.
• Freeze watches extend into Saturday night for Kentucky, Virginia, West Virginia, and Pennsylvania.
• This May is not expected to be the coldest on record for the affected areas, but the sudden chill is significant.