Temperature Extremes: Heat Advisories in the South and Frost Alerts in the North

As millions face heat advisories warning of dangerous temperatures across the South, frost advisories have been issued in five states. This contrasts with predictions for prolonged warmth in some areas. On Monday, heat advisories extended to parts of Texas, Oklahoma, Kansas, Louisiana, Arkansas, Missouri, Illinois, Indiana, Kentucky, Tennessee, Alabama, and Mississippi, reflecting a summer-long trend with record-breaking temperatures in various cities.

According to the National Weather Service’s (NWS) Climate Prediction Center, the temperature outlook through late September suggests that nearly all of the U.S. might experience above-average temperatures till month’s end. Nevertheless, frost advisories for Tuesday highlight the impending shift to colder weather.

Frost advisories were issued by NWS offices in Pocatello, Idaho; Gray, Maine; Burlington, Vermont, affecting New Hampshire and New York. These alerts are set to commence early Tuesday morning with temperatures potentially dropping to the low 30s. It is the first advisory of the season for these offices. In Maine, meteorologist Cameron Barker indicated the likelihood of further frost notices in the upcoming weeks.

Analyzing historical data from the National Centers for Environmental Information (NCEI), the timing of cold temperatures aligns with climate normals. A Newsweek map illustrates average first freeze dates, some as early as August 31 in certain regions. Northern states tend to witness earlier freeze dates, while high elevation zones in southern states also see early freezes. However, elevation causes variability in freeze dates across states.

Importantly, frost can occur without temperatures dropping below freezing. Frost, harmful to plants and pets, can form when ground temperatures are cooler due to radiational cooling, as stated by the NWS.

A frost advisory is issued when temperatures are expected to be between 33 and 36 degrees on cool, clear nights, possibly leading to frost. A more severe freeze warning is issued when extensive freezing temperatures are anticipated. Both alerts are relevant during seasons when such temperatures may damage crops or plants. Other notifications include winter weather advisories, winter storm warnings, and extreme cold warnings.

Details of current frost advisories:

• Maine: Effective from 2 a.m. to 8 a.m. Tuesday in Oxford County, temperatures might drop to 33 degrees causing frost.
• New Hampshire: Similar advisory applies to Coos County.
• Vermont: Frost advisory from 2 a.m. to 8 a.m. Tuesday in Essex County with potential 32 degrees temperatures.
• New York: Franklin, Clinton, and Essex counties included within the advisory area.
• Idaho: Effective from 3 a.m. to 9 a.m. Tuesday with temperatures potentially dropping to 34 degrees in several cities.