October 17, 2023

When is the first frost likely?  That depends on where you are located. With the start of the Fall season, this is the most common question I get. Early autumn is when the nights get longer than the days, with a loss of about two and a half minutes of sunlight each day.

You may be looking for the end of the growing season, allergy season, or even the end of many bugs. Whatever your reason, I’ve gathered as much information as I could for our region.  The focus here is on Maryland and Pennsylvania.

Frost Vs. Freeze

Frost and freeze both relate to ice crystals forming and damaging plant life. Official temperatures are measured between 5 and 6 Ft above the ground.

A frost can occur with temperatures above 32ºF at the thermometer, but closer to the ground the air can be colder where ice crystals can form on the surface of plants. This can also happen on cars and windshields which have thermal conductivity allowing that surface to both heat and cool faster. The conditions usually need light wind and an ample supply of atmospheric moisture to condense and then freeze.

A freeze can occur when the air temperature drops below and the water inside the cells of plants will freeze. This damages the internal structure resulting in the end of that plant’s life cycle.

The map and regional charts below are based on 26 locations around Maryland with the average date when temperatures will reach 32F. It is important to note that it is possible to get frost with temperatures in the upper 30s.

Also, consider that some areas with varied terrain can have a wide range of first frost dates since warmer air holds on hilltops and cold air sinks in valleys on long autumn nights.

Are we on schedule? Well, western Maryland might get their first frost over the next week. Colder air will come in a few impulses. The nights would need to be calm or have light winds to allow frost to form. The inland suburbs or Piedmont areas between the mountains and the cities tend to get their first frost in the middle of October. This includes places like Westminster, Mount Airy, Frederick, and Hagerstown.

The charts below have more details on early, average, and late dates. This is categorized into four regions of Maryland (western, central, southern, and eastern).

Average First Frost and Freeze Dates in Maryland

See the charts below for a breakdown of times per region.

Elevation and proximity to the water play a big role in temperatures. You may also want to compare this map of average snow in Maryland.

Save Your Plants

The University of Maryland points out that cold temperatures will improve the flavor and texture of kale, collards, cabbage, and turnip greens. But bringing tender annual flowers like geranium and begonia indoors before the first frost will help you keep them growing indoors through the winter. Larger pots and in-ground vegetation can be protected with a tarp or garbage bags to hold in the heat and give you a little extra growing time.

Microclimates

You may have noticed your own microclimate which might not be represented on the map. This is a general display, the best I could make with the information and research I’ve found.

If you live near the water, either by the Chesapeake, a reservoir, or river, that can be a source of heat delaying early frosts nearby.

Regional Breakdown

In my 20 years on TV, I spent 14 of them in Baltimore working with hundreds of local Weatherbug stations.  I have a noticed wide range of temperatures on autumn mornings across single towns. Even in metro Baltimore.

Ellicott City for example can have a range of 5 to 8 degrees on some mornings from the old historic valley area to the hilltop near Rt 40. I saw that between Dunloggin MS and Waverly ES often.

There are pockets of colder air near Bel Air/Fallston, Baltimore’s Hereford Zone, and even between Frederick and Mount Airy.

Western Maryland

Garrett, Allegheny, and Washington Counties

Central Maryland

Frederick, Montgomery, Carroll, Howard, Baltimore, and Harford Counties.

Also BWI for northern Anne Arundel County.

Southern Maryland

Anne Arundel (Annapolis), Prince Georges, Calvert, Charles, and St. Mary’s Counties.

Eastern Shore

Cecil and all Counties east of the Chesapeake Bay on the Delmarva Peninsula.

Pennsylvania

There is less detailed information for this larger state. But the map below may help give an overview of the Commonwealth.

What about winter?

I am working on my formal winter outlook. The timing of the first frost does not play a role, but there are many other factors. I have already presented a few, and I have a few more to share.  I aim to have my call for seasonal snowfall to show you later in October.

You may notice the influence of the mountains and water (Chesapeake Bay and Atlantic Ocean) playing a role in the frost.

This is similar to the impact on winter snowfall.

Winter Weather Page:  Stats, Maps, And Tracks

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RESTATING MY MESSAGE ABOUT DYSLEXIA

I am aware there are some spelling and grammar typos and occasional other glitches. I take responsibility for my mistakes and even the computer glitches I may miss. I have made a few public statements over the years, but if you are new here, you may have missed it: I have dyslexia and found out during my second year at Cornell University. It didn’t stop me from getting my meteorology degree and being the first to get the AMS CBM in the Baltimore/Washington region. One of my professors told me that I had made it that far without knowing and to not let it be a crutch going forward. That was Mark Wysocki, and he was absolutely correct! I do miss my mistakes in my own proofreading. The autocorrect spell check on my computer sometimes does an injustice to make it worse. I also can make mistakes in forecasting. No one is perfect at predicting the future. All of the maps and information are accurate. The ‘wordy’ stuff can get sticky.  There has been no editor who can check my work when I need it and have it ready to send out in a newsworthy timeline. Barbara Werner is a member of the web team that helps me maintain this site. She has taken it upon herself to edit typos when she is available. That could be AFTER you read this. I accept this and perhaps proves what you read is really from me… It’s part of my charm.

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