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By Anna Skinner
Associate News Editor
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As millions of people face heat advisories warning of dangerous temperatures across the South on Monday, frost advisories were issued in five states, serving as a reminder that the first hard freeze of the season could hit as soon as this month for some, even as oppressive temperatures remain a reality for the foreseeable future for others.
More advisories were issued by two additional states on Tuesday night.
On Monday, heat advisories were in place for parts of Texas, Oklahoma, Kansas, Louisiana, Arkansas, Missouri, Illinois, Indiana, Kentucky, Tennessee, Alabama, and Mississippi as part of a summer-long trend that produced some of the warmest temperatures ever recorded in some cities across the country. While a temperature outlook through late September from the National Weather Service's (NWS) Climate Prediction Center anticipates that nearly all of the U.S. could experience above-average temperatures through the end of the month, a few NWS offices issued frost advisories for Tuesday, a stark reminder that chilly weather is not far off.
Read More on Weather
The NWS offices in Pocatello, Idaho; Gray, Maine, which was also forecasting for New Hampshire; and Burlington, Vermont, which was also forecasting for New York, issued the cold weather alerts, which are all set to go into effect early Tuesday morning as temperatures could dip into the low 30s. It was the first advisory of the season for each of the three offices, NWS meteorologists at each location told Newsweek, and in Maine, NWS meteorologist Cameron Barker told Newsweek that more frost advisories were expected to be issued in the coming weeks.
Then, on Tuesday, the NWS offices in Grand Forks, North Dakota, and Duluth, Minnesota also issued frost advisories, warning of temperatures as low as 36 degrees that could harm outdoor vegetation.
When compared to historical data from the National Centers for Environmental Information (NCEI), the timing of the frigid temperatures is right on track when it comes to climate normals.
How El Niño Could Impact Freeze Dates This Year
Some states could see freeze dates occurring later than normal this year because of the formation of El Niño, the warm phase of the El Niño-Southern Oscillation cycle, which causes above-average sea temperatures and weakened trade winds in the tropical Pacific. Forecasts anticipate El Niño will continue strengthening through the end of the year, with a greater than 90 percent chance it will become "very strong" in the fall and winter months.
El Niño's impacts in the U.S. are most strongly felt during the colder months. According to a map from NOAA, El Niño impacts in the U.S. often lead to warmer temperatures in the northern states, which could potentially delay frost dates in the Northern U.S., Pacific Northwest, and Great Lakes region. Meanwhile, wetter conditions are expected in the South, with drier winter conditions more common in the Midwest and East Coast.
Next spring, El Niño could also influence frost dates, with the last spring frost potentially occurring earlier than normal.
Map Shows First Freeze Dates for Every State
Average first freeze dates each year can occur as soon as August 31 or earlier in certain parts of the country. A map created by Newsweek shows which month every state typically sees its first hard freeze.
Northern states are more likely to see earlier first-freeze dates, although high-elevation regions of southern states also have earlier averages. In nearly every state, first-freeze dates can vary widely because of elevation.
However, frost can form even before temperatures dip below freezing. Frost, which can damage sensitive vegetation and harm outdoor pets, can occur even when air temperatures remain above freezing. This is because the temperature near the ground can be as much as 5 degrees cooler than the official air temperature because of radiational cooling, according to the NWS.
Frost Advisory vs. Freeze Warning
There are several different alerts the NWS issues when it comes to cold temperatures.
A frost advisory, which was in place for Idaho, New York, New Hampshire, Vermont, and Maine, is issued when air temperatures are expected to be between 33 and 36 degrees on cool, clear nights, which could result in frost forming.
The more severe freeze warning is issued "when significant, widespread freezing temperatures are expected," the NWS said on its webpage about alerts, watches and warnings. Both frost advisories and freeze warnings are issued during seasons where such cold temperatures could cause harm to crops or plants.
There are also winter weather advisories, winter storm warnings, and extreme cold warnings, among other alerts.
Frost Advisories: What We Know
The most recent frost advisories issued by the NWS are in place for Wednesday morning. Although the Grand Forks, North Dakota, NWS office issued one of the advisories, both advisories were in place for Minnesota counties, including Lake of the Woods, Roseau, and Koochiching counties. The advisory will be in effect from 4 a.m. to 8 a.m. Wednesday morning.
In Maine, the frost advisory will be in effect between 2 a.m. and 8 a.m. Tuesday morning, when temperatures as low as 33 degrees could result in frost formation for Oxford County. The same advisory applies to New Hampshire, where Coos County will be impacted.
In Vermont, the frost advisory will be in effect from 2 a.m. to 8 a.m. local time Tuesday morning, when temperatures as low as 32 degrees Fahrenheit could cause frost to form. Essex County was included within the advisory area.
The same advisory, issued by NWS Burlington, applied to Franklin, Clinton and Essex counties in New York.
In Idaho, the advisory will go into effect at 3 a.m. local time Tuesday morning and remain in place until 9 a.m., when temperatures as low as 34 degrees could result in frost formation in cities of St. Anthony, Shelley, Idaho Falls, Mud Lake, Pocatello, Blackfoot, Carey, Fort Hall, Craters of the Moon NM, Richfield, Shoshone, Rexburg, and American Falls.
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Contact Newsweek editors for this story: Jason Lemon, Anthony Murray, Gray R. Thomas.
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