Lost Park
Tonight: low 37 °F, frost likely, breezy.
Nights by month
Night lows from 2016 to 2025: a typical night, and the cold one that comes 1 night in 10.
The mildest nights are in July, typically 47°F. The coldest are in January, when 1 night in 10 drops to -5°F. Frost is common in January, February, March, April, May, October, November and December.
- Jan8°F -5°FBag comfortable to -5°F · frost 100% · rain or snow 19% of days
- Feb9°F -4°FBag comfortable to -5°F · frost 100% · rain or snow 27% of days
- Mar13°F 2°FBag comfortable to 5°F · frost 99% · rain or snow 30% of days
- Apr20°F 8°FBag comfortable to 10°F · frost 98% · rain or snow 31% of days
- May28°F 18°FBag comfortable to 20°F · frost 70% · rain or snow 52% of days
- Jun41°F 35°FBag comfortable to 35°F · frost 4% · rain or snow 50% of days
- Jul47°F 42°FBag comfortable to 45°F · frost 0% · rain or snow 57% of days
- Aug46°F 41°FBag comfortable to 40°F · frost 0% · rain or snow 52% of days
- Sep (this month)40°F 32°FBag comfortable to 35°F · frost 10% · rain or snow 29% of days
- Oct30°F 16°FBag comfortable to 15°F · frost 66% · rain or snow 21% of days
- Nov20°F 5°FBag comfortable to 5°F · frost 94% · rain or snow 14% of days
- Dec12°F -3°FBag comfortable to 0°F · frost 100% · rain or snow 21% of days
| = 32°F
History: ERA5 and ERA5-Land reanalysis via Open-Meteo, corrected to the site's elevation. Bag rating: the comfort rating that keeps you warm in a tent on 9 of 10 nights that month.
Tonight
Worth a lookFriday, September 25, 10 p.m. to 7 a.m.
Your setup looks too cold for this night
Expected from around 1 a.m.
The cold comes from underneath: your pad does not insulate enough from the ground.
Best change
Add insulation underneath until you have about R2.5 in total (estimate).
- A closed-cell foam mat under your pad adds about R2.
- Folded blankets or spare clothes help if you have nothing else.
This is based on typical values for the gear types you picked, so treat it as an estimate.
Your night
- 10 p.m. to 1 a.m.ComfortableAir around you 45 to 43°F, some dew, gusty from 11 p.m. (up to 26 mph).
- 1 a.m. to 6 a.m.Chilly. Add a layerAir around you 39 to 36°F, frost.
- 6 a.m. to 7 a.m.Cold. Your setup is not warm enoughAir around you 34°F, frost.
- 7 a.m. until morningChilly. Add a layerAir around you 35°F, frost.
Every hour
- 10 p.m.43°Fcomfortable, some dew
- 11 p.m.45°Fcomfortable, gusty
- midnight44°Fcomfortable
- 1 a.m.39°Fchilly, frost
- 2 a.m.37°Fchilly, frost
- 3 a.m.36°Fchilly, frost
- 4 a.m.36°Fchilly, frost
- 5 a.m.36°Fchilly, frost
- 6 a.m.34°Fcold, frost
- 7 a.m.35°Fchilly, frost
This spot sits about 33 m below the land around it. On clear, calm nights cold air pools here, so expect it colder and wetter than the forecast.
Times are local time at your spot (GMT-6).
What works tonight
The gear this night calls for, for someone who sleeps like you.
- Missing
Sleeping bag
Comfort 30°F or colder
Usually sold as a 21° bag. The number in a bag's name is the limit, not the comfort.
- Missing
Underneath you
R2.5 or more
The R-value says how well a pad keeps the cold ground out.
- Worth adding
Also useful
A bag liner
Adds a few degrees to the bag you already own.
Before you sleep
- Put on a warm layer and a hat before about 1 a.m., or go to bed already wearing them.
- Eat a proper meal with some fat before bed. Your body keeps burning it through the night.
- Pee right before you get in your bag. Getting out at 3 a.m. in the cold is worse.
- Sleep in dry clothes, not the ones you wore all day. Damp fabric pulls heat out of you.
- Fill a sturdy water bottle with hot (not boiling) water, check the lid does not leak, and put it in your bag by your core or feet.
- Your spot sits lower than the ground around it. On a clear, calm night cold air drains into spots like this, so expect it colder and wetter than the forecast. If you can, move a little higher up, away from the creek or valley floor.
- Stake out every guyline and point the low, narrow end of the tent into the wind.
- Bring shoes, clothes and electronics inside. Anything left out will be wet by morning.
- Open the tent vents and keep the door zip open a bit at the top. Some condensation inside is normal on a night like this, so bring a small towel to wipe it off.
How we estimated this
At the coldest hour (6 a.m.):
- Outside at your spot
- 37°F
- Warmth your shelter holds
- +2 °F
- Clear-sky cooling
- −1 °F
- Low spot
- −4 °F
- Air around you
- 34°F
- Your bag's comfort rating
- 39°F
- Cold ground through what you lie on
- +4 °F
- Your comfort limit
- 43°F
9 °F short, so you will likely be cold.
Assumptions
- Bag categories use typical ratings as sold: summer about 50 °F (10 °C), 3-season about 30 °F (-1 °C), winter about 15 °F (-9 °C). The number in a bag's name is usually its lower limit, so its comfort rating is about 9 °F (5 °C) warmer.
- What you lie on: foam mat about R2, thin air pad about R1.5, insulated pad about R3.5, winter pad R5 and up, van bed about R4, air mattress about R0.5. Colder ground needs a higher R-value.
- Shelters hold a few degrees early in the night and less towards morning. Wind and clear, calm skies take warmth away.
- Weather: Open-Meteo forecast for your spot, on a grid of a few kilometers, corrected to its height.
- These are rules of thumb, not measurements. People and gear vary.
A forecast, not a promise. Mountains, valleys and water make their own weather, so trust what you see and feel on site. Terms and liability
Checked for a double-wall tent, a 3-season bag and a thin air pad. Check your own gear here.
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