Will Pipes Freeze in St. Mary's County, MD? 10 nights a Year
Freeze nights in St. Mary's County
In a normal year St. Mary's County, MD gets 10 nights at or below 20°F, the point where bare pipes in a garage, attic or outside wall start to freeze. That is more than 26% of US counties.
Risk level: Regular. The risk season runs December to March, worst in January.
It depends where the pipe is
| Pipe | Freezes near | Nights a year |
|---|---|---|
| Outdoor spigot, open crawlspace | 32°F | 65 nights |
| Bare pipe in garage, attic or outside wall | 20°F | 10 nights |
| Insulated pipe in unheated space | 10°F | 1 night |
| Inside the heated house | 0°F | under 1 night |
Foam-sleeving a bare pipe in unheated space takes it from 10 nights of risk to 1 night. A 12 ft heat-tape kit runs $17 to $37; an average burst-pipe repair is about $500.
Month by month
Nights at or below 20°F in a normal year.
First 32°F night is usually around 11/15, last around 03/29. For 20°F: 12/29 to 02/21.
How cold St. Mary's County nights get
Average winter (Dec-Feb) low: 32°F; the coldest month, January, averages 30°F overnight. 6 months normally bring at least one night below 32°F (Jan, Feb, Mar, Apr, Nov, Dec). Nights below 10°F, cold enough to freeze insulated pipe in an unheated space, come in January: 1 night a year, and under 1 night below zero.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 30°F | 31°F | 37°F | 47°F | 57°F | 67°F | 72°F | 69°F | 63°F | 52°F | 42°F | 34°F |
St. Mary's County next to its neighbours
Westmoreland County, VA, 27 km southwest, gets 12 nights below 20°F to St. Mary's County's 10 nights.
| County | Distance | Below 32°F | Below 20°F | Jan low |
|---|---|---|---|---|
| St. Mary's County, MD | - | 65 nights | 10 nights | 30°F |
| Westmoreland County, VA | 27 km southwest | 74 nights | 12 nights | 29°F |
| Calvert County, MD | 33 km north | 82 nights | 16 nights | 27°F |
| Richmond County, VA | 36 km southwest | 77 nights | 13 nights | 29°F |
| Northumberland County, VA | 43 km south | 73 nights | 11 nights | 30°F |
| Essex County, VA | 47 km southwest | 78 nights | 14 nights | 29°F |
| Dorchester County, MD | 48 km northeast | 77 nights | 14 nights | 28°F |
St. Mary's County within MD
St. Mary's County ranks 23 of 24 MD counties for nights below 20°F. The most is Garrett County, MD at 57 nights, with a 20°F average winter low. The fewest is Baltimore city, MD: 10 nights, winter lows near 32°F. At 114 ft, St. Mary's County sits close to the state's median county elevation of 138 ft.
What to do here
- Insulate every pipe in unheated space before the season starts.
- Heat tape on the runs you cannot insulate well.
- Shut off and drain outdoor spigots for the season.
When to have the house ready: when freeze season starts.
Where this comes from
NOAA 1991-2020 climate normals, blended from 3 nearby stations and adjusted for elevation; closest is Patuxent River Naval Air Station, MD, 13 km away (close match). A normal year, not tonight's forecast: check the forecast low for the night itself. Why elevation is part of the blend: how county numbers are made.