Map Shows When Your State Gets Its First Frost as Cold Arrives Next Week

Cooler air moves into the northern tier early next week, and forecasters expect it to bring the season’s first frosts and freezes to parts of the region.

For drivers that means the first scraper morning is closer than the thermometer suggests. The Farmers’ Almanac sets out when it usually arrives where you live.

Frost Arrives Before the Thermometer Says It Should

The Farmers’ Almanac first frost dates, updated on September 10, track frost rather than freeze, and the gap between the two is where drivers get caught. A freeze is measured in the air at 32 degrees or below. Frost is the ice itself, and it turns up on glass and grass with the official reading still in the mid-30s, because the air at ground level runs colder than the thermometer a few feet above it.

That gap is why the first frost morning can catch drivers by surprise. A car parked outside under a clear, calm sky loses heat to the sky faster than the surrounding air, and glass facing up loses it fastest. The outside temperature can still be 36 degrees while the windshield is already glazed.

The Same Night Puts Ice on Bridges

Some of the same conditions that frost a windshield can also leave a bridge deck icy. The National Weather Service describes black ice as patchy, often clear ice that leaves the pavement visible underneath, most common in the early morning hours after overnight refreezing, and notes that bridges and overpasses freeze before the roads leading onto them.

An overpass loses heat from above and below at once, which is why it can carry ice while the approach a hundred yards back is merely wet. In late September, drivers are less likely to expect ice, which makes an isolated patch on an overpass easier to miss.

Where the First Frost Lands

More than four months separate the first frost in northern Alaska from the first frost in central Florida.

These are 50 percent probabilities rather than deadlines. Frost had already arrived by the listed date in about half of recorded years, which is another way of saying it turns up earlier in the other half.

What the First Cold Mornings Do to a Car

Tire pressure drops by roughly 1 psi for every 10-degree drop in temperature, so a set last checked in July is running low this week with nothing visibly wrong on the sidewall. Underinflated tires lengthen braking distances on exactly the surfaces that ice first.

As temperatures fall, all-season tire compounds become less flexible, which reduces grip well before conditions look anything like winter.

Scraping a windshield with anything other than a scraper is the other September mistake. Hot water on cold glass can crack it, and wiper blades dragged across frozen glass tear. Washer fluid rated for summer freezes in the reservoir and the lines, which is one of the items on the winterizing checklist worth clearing before the first cold morning rather than after it.

The Cold Arrives Next Week

The cold surges south early next week, and Fox Weather has temperatures across the Pacific Northwest and the Rockies dropping 10 to 15 degrees below average with it. The Climate Prediction Center follows that with a slight risk of much below normal temperatures across parts of the northern Plains, Upper Mississippi Valley and eastern Great Lakes from September 18 to 20, and across northern New England from September 19 to 22. Forecasters note that near-freezing nights are not unusual for late September there, while adding that a frost or freeze could still be “impactful to some vegetation and unsuspecting populations.”

Frost runs ahead of snow by weeks in most of the country, and the first snowfall map sets out what follows it.