Know when the first freeze is expected to happen in your area
Halloween is coming up and the fall season is fully underway. Fall brings cool, temperate weather that is anticipated after a hot summer. However, fall also means that winter is right around the corner. The first day of astronomical winter is December 21, and in some places, you’ll definitely need to break out the ice scraper for your car before then.
Using data from the 1991–2020 U.S. Climate Normals, we have a good idea of when to expect the first freeze of fall. The first freeze can be described as when the surface air temperature is expected to be 32°F or below over a widespread area for a climatologically significant period of time. According to data, the first freeze in some high mountain and northern latitude locations can happen even earlier than August 31. A few of the coldest places can even experience freezing temperatures in any month!
The “Historical Date of First Freeze: Median Date” map depicts the average date of each area's first fall freeze and is often used for things like agriculture. A simple way to think of it, is a freeze is expected to have happened on or before the listed date in five out of the 10 years recorded.
The “Historical Date of First Freeze: Earliest 10%” map depicts when a freeze is earlier than usual, more specifically when it is before nine out of the 10 years recorded. Normally, it would only be that early in one year out of 10.
The “Historical Date of First Freeze: Latest 10%” map shows when to normally expect a freeze based on nine out of 10 years. If a freeze happens past this date, it is unusually late for a freeze to occur.
It is important to take into consideration that these maps are a generalization and not absolute, as many factors can go into the first freeze of the year based on area. NOAA’s National Weather Service will issue frost and freeze watches and warnings for your area.
Generally speaking, it is expected that areas in higher latitudes will experience the very first freeze each year followed by cold temperatures making their way southward. Exceptions are mountainous regions, which, despite their location geographically, experience colder temperatures due to having a higher elevation. Also, locations near large bodies of water, say a Great Lake, river, or ocean, generally have a later first fall freeze than locations further inland as the water is slower to cool down and moderates the nearby locales. In the maps above, one can see the general later first freeze occurrence in lower latitudes with areas such as the Rocky and Appalachian Mountains and shoreline locations bucking that trend.
It is also expected that urban and shoreline areas will have a later first freeze than more rural, inland areas due to a warmer temperature. Elevation, latitude, topography, and development (for example, urban versus rural) can all play a role in affecting the date of the first freeze.
We can see this play out in that despite being on the same latitude, the west and east coast experience their first freeze at different times due to the marine layer across southern California.
Read About What To Expect From Each Region
This region in particular shows some variation on when to expect the first freeze. Using the median map, we can suggest that the first freeze should/should have occurred between the beginning of September and November.
In most of California and southern Arizona, outside of high elevations, the first freeze should not occur until at least December. However, in northern Arizona, Nevada, Utah, Colorado, and New Mexico, the first freeze is projected to be in the September–November bracket, same as the Northwest.
In the Midwest, we see some of the coldest temperatures in the contiguous United States. This being the case, the first freeze is projected to be between mid-September and early October.
The Northeast fairs similar to the Midwest, and should expect their first freeze in mid-September to early October, or even early September farther north.
We can see the date of the first freeze start in Virginia in early October, and the dates trickle down to December further south. Warmer areas like parts of Florida might not see a freeze every year. Areas like the Florida Keys have not recorded freezing temperatures.
HAWAII AND ALASKA
Only the highest elevations in Hawaii experience freezing temperatures. The complex topography and northerly location of Alaska exhibits a wide variety in the date of the first freeze.
Fall Is For Planting!
As we creep closer to the coldest time of the year, use this time to begin planning your spring bulbs. Hardier green vegetables, such as cabbage, brussels sprouts, and kale can be safely planted in some areas as they are cold tolerant. Be sure to use our maps above to coordinate with your garden, and keep the first freeze dates in mind when covering up your plants.