Home Emergency Boise freeze alert: should I drip my faucets tonight?
Pick your town. We check tonight's National Weather Service forecast and tell you whether your pipes need protecting, using the 20°F alert threshold the Insurance Institute for Business & Home Safety cites from University of Illinois tests.
Tonight's freeze check
Checking tonight's forecast…
Next 7 nights
| Night | Low | What to do |
|---|
What each freeze level means
| Forecast low | Level | What to do |
|---|---|---|
| 20°F or colder | Drip tonight | Drip cold water at faucets on outside walls, open the cabinets under those sinks, keep the thermostat the same day and night, keep the garage door closed. |
| 21–27°F | Protect exposed pipes | Drip faucets whose pipes run through a crawl space, garage, attic or drafty exterior wall, especially on windy nights. |
| 28–32°F | Light freeze | Disconnect hoses; shut off and drain outdoor faucets and irrigation lines. Close the garage door and any open foundation vents. |
| Above 32°F | Above freezing | No action needed if the forecast holds. |
| If daytime highs nearby stay at or below 32°F, the alert raises the level by one step, because pipes never get a chance to warm up. | ||
Why the alert uses 20°F
Water freezes at 32°F, but the pipes inside your house sit in spaces that stay a few degrees warmer than the air outside. Field tests by the University of Illinois Building Research Council found that uninsulated pipes in an unheated attic began to freeze when the outdoor temperature dropped to about 20°F, and a survey of plumbers found burst-pipe calls started when temperatures fell into the teens. The Insurance Institute for Business & Home Safety uses 20°F as its "temperature alert threshold".
When pipes freeze above 20°F
Wind and drafts change the math. A pipe next to a gap where a cable enters the wall, in a crawl space with open foundation vents, or in a garage with the door open can freeze well above 20°F. That is why the alert flags 21–27°F nights for exposed pipes.
How often Boise gets cold enough
Average overnight lows at the Boise airport weather station are November 32.3°F, December 24.5°F, January 24.9°F, February 29.3°F (1991–2020 NOAA Climate Normals). Those are averages: on the colder nights of a normal December or January the low drops past 20°F, and arctic air pushes it far lower. The danger nights are rarely a surprise; they are in the forecast a few days ahead, which is what this alert is for.
Dripping a faucet: how to do it right
Which faucets
The ones fed by pipes on exterior walls or running through the crawl space, garage or attic. Kitchen sinks under a window are the classic case. You do not need to drip every faucet in the house.
How much
A slow, steady drip of cold water is enough. Moving water is much harder to freeze, and an open faucet also relieves pressure if ice does form. On a single-handle faucet, set the handle to the middle so both lines move a little.
What else on a drip night (American Red Cross advice)
- Open cabinet doors under sinks on outside walls so house heat reaches the pipes.
- Keep the thermostat at the same temperature day and night.
- Away from home? Leave the heat at 55°F or higher.
- Know where your main water shutoff is before you need it.
If a pipe already froze or burst
No water at a faucet means a frozen section. Leave the faucet open and warm the pipe with a hair dryer or heating pad, starting nearest the faucet, never with an open flame. If water is spraying, close the main valve first. Step by step: burst or frozen pipe: the first 60 minutes.
Quick answers
How does the freeze alert work?
It loads the current National Weather Service forecast for your Treasure Valley town and compares each overnight low with the 20°F threshold from University of Illinois pipe-freezing research. At or below 20°F it says to drip faucets; between 21°F and 27°F it flags exposed pipes; between 28°F and 32°F it reminds you about hoses and outdoor faucets.
Why 20°F and not 32°F?
Pipes inside a house are a few degrees warmer than the outdoor air. University of Illinois field tests found pipes in an unheated attic began freezing when the outdoor temperature fell to about 20°F. Wind and drafts can freeze exposed pipes at warmer temperatures.
Which towns does it cover?
Boise, Meridian, Nampa, Caldwell, Kuna, Eagle, Star and Garden City in Idaho's Treasure Valley. Each uses the National Weather Service forecast grid for that town.
Is the freeze alert free?
Yes. It is free, needs no sign-up and uses public National Weather Service data.
Related
- Printable one-page winter checklist
- Winterize your home before the first hard freeze
- At what temperature do pipes freeze?