Reminders about frost and freezing advisories from the National Weather ServiceSep 01, 2022 01:19PM ● By Editor
Typically, frost can occur when the temperature falls below 36°F, especially in rural areas. It is a localized phenomena and can be quite variable across a small area. While the National Weather Service does not keep track of "frost" in observations per se, we do keep track of when temperatures hit the freezing mark or fall below. Frost becomes more widespread when the temperature falls below 32°F with some freeze possible. A hard freeze is possible when temperatures fall below 28°F. In the 32F/28F Freeze Maps section, you'll find national and regional maps from the Midwest Regional Climate Center (MRCC) that depict the typical dates for freezes in the early fall, and the earliest/latest freeze dates observed in the past. In the Earliest/Latest Freeze Dates section, you'll find statistics on the earliest and latest fall freeze dates for selected sites across our forecast area. In the preparation section, we have information about NWS Frost Advisories and Freeze/Hard Freeze Watches/Warnings, along with some tips for protecting plants.
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When do we normally see our first 32°F freezes and 28ºF freezes? Check out these maps from the Midwest Regional Climate Center (MRCC) for freeze information on your location. Visit the link to the MRCC to view interactive maps where you can zoom in closer to your specific region.
Fig. 1. Climatological Date of Median First 32°F freeze for the United States.Earliest/Latest Dates for the First 32ºF Freezes
Below are images depicting the earliest and the latest dates for the first 32°F freezes across the U.S. and in our region.
Fig. 2. Climatological Date of Earliest First 32°F freeze for the United States.
Fig. 3. Climatological Date of the Median First 28°F freeze for the United States.
Do you know what products the National Weather Service issues about frost and freezes? Frost Advisories and Freeze Warnings can help you make decisions about what to do with temperature-sensitive plants at the beginning/near the end of the growing season. Once there is a hard freeze or killing freeze, these products are no longer issued.
Frost Advisories are only issued from May 1-October 20th (can be extended if necessary). A frost advisory is issued when temperatures, winds, and sky cover are favorable for frost development. This is most likely when temperatures are less than or equal to 36 degrees. Coverage of frost in these cases should be more than patchy. If a frost is sufficiently severe to end the growing season, it is commonly referred to as a 'killing frost.'
What to do: If a Frost Advisory is issued for your area, cover up plants before the sun sets so that it can help retain heat near the plants.
Freeze Warnings are only issued from May 1-October 20th (can be extended if necessary). A freeze warning is issued when low temperatures are expected to be 29-32 degrees. A Freeze Watch may be issued a few days ahead of time if the potential exists for temperatures to fall into these thresholds.
What to do: If a Freeze Warning/Watch is issued for your area, there is little you can do to protect plants. If you can move your sensitive plants inside, do so because the freeze will likely kill them, depending on the severity of conditions.
Hard Freeze Warnings are only issued from May 1-October 20th (can be extended if necessary). A hard freeze warning is issued when temperatures are expected to be 28 degrees or less. A Hard Freeze Watch may be issued a few days ahead of time if the potential exists for temperatures to fall into these thresholds.
What to do: If a Hard Freeze Warning/Watch is issued for your area, there is little you can do to protect plants. If you can move your sensitive plants inside, do so because the freeze will kill them.