- JulyBest month
- 173 daysWorkable days/yr
- 9 moSeason length
- 11–64%Rain-day odds
- Portland by month
The next 10 days in Portland
GOOD — clears every rule MARGINAL — exactly one soft miss NO — a hard fail, or two soft
The rules this check uses
Every verdict above applies this table to Portland's hours. DIY scope only: the freeze row outranks everything, and structural work belongs to engineer/ACI specifications.
| Check | Threshold | Why it matters |
|---|---|---|
| Air temperature | 40–90°F — ideal 50–85°F | Checked across the working day, 8 a.m.–6 p.m., against Portland's hourly forecast — not just the daily high. |
| Overnight low | ≥40°F during the first 48 h | The engine reads every overnight hour in the cure window, not just Portland's forecast low. |
| Dry before | no soaking (≥1.0") in the prior 24 h | Rain before the pour only matters if the ground is soaked or standing in water. |
| Dry after | <0.1" rain for 6 h after (12 h light rain after finishing still risks surface marks) | A downpour in the first 6 hours can wash the surface; after final set, rain actually helps curing. |
| Wind | ≤20 mph (rapid surface drying up to 28 mph) | Wind wrecks application first (drift, lap marks) and carries debris into wet work second. |
Always follow your product label — formulas vary. These rows are the industry-typical range; the can in your Portland garage is the contract.
Best months for concrete pouring in Portland
| Month | Avg high | Avg low | Rain odds/day | Workable days | |
|---|---|---|---|---|---|
| January | 47°F | 37°F | 62% | 0 | |
| February | 51°F | 39°F | 57% | 0 | |
| March | 56°F | 41°F | 57% | 12 | |
| April | 61°F | 44°F | 53% | 14 | |
| May | 68°F | 49°F | 40% | 19 | |
| June | 73°F | 53°F | 28% | 22 | |
| July | 80°F | 58°F | 12% | 27 | |
| August | 81°F | 59°F | 11% | 28 | |
| September | 75°F | 55°F | 23% | 23 | |
| October | 63°F | 48°F | 41% | 18 | |
| November | 52°F | 42°F | 59% | 10 | |
| December | 46°F | 37°F | 64% | 0 |
The working season runs March through November — about 172 workable days a year. The edges are night-limited: label rules want overnight lows of 40°F+, and Portland's nights only average that from March to November. For the statewide picture, the Oregon page compares peak months city by city.
Portland has a real wet/dry rhythm: December brings rain on 64% of days versus 11% in August. When the calendar gives you a August-side window, the dry-before and dry-after rules nearly take care of themselves.
Flip side of the driveway calendar: sealing in Portland opens later and closes earlier than pouring, on the same forecast.
Numbers above come from NOAA's 1991–2020 normals for Portland Kgw-Tv, Or Us, 3.7 km from the city center — close enough that neighborhood microclimates (shade lines, river valleys, urban heat) matter more than station distance. See how these day counts are scored.
Route check: the previous stop covers concrete pouring in Medford, OR; the next one maps concrete pouring windows in Salem, OR.
Portland by the numbers
- August is Portland's heat peak: 81°F typical high, 0 days over 90°F.
- Coldest month: December — 46°F highs over 37°F nights.
- Wet-to-dry spread: 64% rain days in December versus 11% in August.
- Overnight lows clear 40°F from March to November in a normal year.
- Add it up and Portland banks 172 workable days a year for concrete pouring.
Prep checklist
- Check two nights, not one afternoon: both must hold 40°F+. In Portland that math works March through November — outside it, 37°F lows own the calendar.
- Set the stage first: forms braced, subgrade compacted and lightly damp, every tool within reach, help confirmed.
- Cut plastic sheeting and weight it at the pour's edge — Portland sees rain on 11% of August days, and the 6-hour rule doesn't negotiate.
- Keep the mix stiff (oatmeal, not soup) — every extra quart of water is permanent surface strength lost.
- Screed while it sheens, float when the sheen dulls, and never trowel bleed water back in.
- Edge and joint with an edger + float set — control joints every 2–3 slab-thicknesses in feet.
- Cure damp: sheeting or misting for days; against a Portland cold snap, a curing blanket guards the first 48 hours.
- Feet after 24–48 h, cars after about a week — and structural work follows engineer/ACI specs, not this list.
Pro moves for Portland conditions
- Order air-entrained ready-mix for any outdoor slab in a freeze-thaw climate — no finishing technique or sealer can add that protection after the pour.
- Dampen the subgrade and forms before placing concrete on a warm, dry day so they don't suck water out of the bottom of the slab.
- Wait until the bleed-water sheen disappears before floating and troweling; working water back into the surface causes dusting and scaling later.
- Mixing bagged concrete solo invites cold joints — line up help so batches stay continuous, because a slab that stiffens between loads bonds poorly.
- Keep DIY pours to pads, walkways, and fence posts; structural footings, retaining walls, and suspended slabs need engineered specs per ACI, not a weather window.
Gear that saves a window
FTC note: the gear below is unlinked until the affiliate program is switched on. See the affiliate disclosure.
-
Plastic sheeting
Emergency rain cover and moisture-holding cure layer.
-
Curing blanket
Holds heat through cold nights in the critical 48 hours.
-
IR surface thermometer
Track slab temperature, not just the forecast.
-
Concrete mix
An 80-lb bag yields about 0.6 cu ft — do the math twice.
Frequently asked questions
What temperature is too cold to pour concrete?
For DIY: any low under 40°F within 48 hours of the pour — that's cold-weather concreting (blankets, accelerators, monitoring), not a weekend job. In Portland, nights average 40°F+ only March–November, which is what actually frames the season above.
Can you pour concrete before rain?
Only with 6+ hours of margin: a 0.1"+ downpour before final set washes cement paste off the finish. After set, rain helps the cure. Portland's December sees rain 64% of days — keep plastic sheeting cut and weighted at the pour's edge regardless of the forecast.
How long does concrete need to be protected from freezing?
48 hours minimum — that's when early strength forms, and ice inside that window scales the surface and weakens the slab for good. Portland's freeze risk lives at the season edges: December averages 31 nights under 40°F. Insulated curing blankets are the DIY answer to a surprise cold snap.
Is it OK to pour concrete in hot weather?
The ideal band is 50–85°F; 85–90°F earns a flag and 90°F+ is out. Portland's July highs average 80°F, so heat rarely closes the window here — cold nights are the local constraint.
How long before you can drive on new concrete?
About 7 days for a passenger car in Portland's August conditions (81°F average highs — textbook cure speed); foot traffic after 24–48 hours. Cool weather stretches everything, because cure runs on temperature. Heavy vehicles wait longest, and the bag's schedule outranks any general rule, including this one.
Best season for concrete work in Portland?
March through november — the months with 40°F+ nights, sub-90°F days, and manageable rain. August leads at 28 workable days; December bottoms out near 0.
How windy is too windy to pour concrete?
Wind matters as much as temperature. Breezes above about 10 to 15 mph, especially with low humidity or warm sun, can evaporate surface moisture faster than bleed water rises — ACI guidance flags evaporation rates above 0.2 pounds per square foot per hour as plastic-shrinkage-cracking territory. For a small DIY slab, wait for a calm morning or rig windbreaks and fog-mist the air above the surface.
How long should I keep new concrete wet?
Keep it continuously wet for at least 7 days — the moist-curing period ACI guidance specifies for conventional concrete (3 days for high-early mixes). Use soaker hoses, wet burlap, curing blankets, or sheet plastic, or spray on a curing compound after finishing. Concrete allowed to dry out early can lose a large share of its potential strength and is far more likely to dust, scale, and crack.
When can I remove the forms from a small concrete pour?
For slabs, walkways, and post footings, side forms can usually come off 24 to 48 hours after the pour — leave them at least 72 hours when temperatures run below 50°F, since strength gain slows dramatically. Pry against the ground, never the green concrete, and keep curing the exposed edges afterward. Forms supporting structural or suspended concrete follow engineering rules, not DIY timelines.
How soon can I seal new concrete?
Wait until it reaches full cure — about 28 days — before applying most penetrating or acrylic sealers; sealing earlier traps moisture and can cause clouding or poor bond. The exception is a cure-and-seal product designed to go on the day of the pour. Pick a dry stretch with temperatures roughly 50 to 90°F — in Portland, July typically offers the most reliable window — so the sealer itself cures properly.
Concrete Pouring glossary
- Evaporation rate
- How fast surface moisture leaves fresh concrete, driven by temperature, wind, and humidity; rates above about 0.2 lb per square foot per hour invite plastic shrinkage cracking.
- Plastic shrinkage cracking
- Shallow, random cracks forming within hours of placement when the surface dries faster than bleed water can replace it; wind and sun are the usual culprits.
- Bleed water
- Mix water that rises to the surface after placement; finishing before it evaporates traps it under the trowel, creating a weak, dusty top layer.
- Hydration
- The chemical reaction between cement and water that hardens concrete; it needs moisture and temperatures above roughly 40°F, and continues gaining strength for weeks.
- Curing compound
- A sprayed or rolled membrane that seals moisture inside fresh concrete when wet curing isn't practical; some types must be stripped before paint or sealer.
- Air entrainment
- Microscopic air bubbles added to the mix that give exterior concrete freeze-thaw and deicer resistance; it must be ordered in the mix, not added later.
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Guides
Climatology: NOAA 1991–2020 normals via PORTLAND KGW-TV, OR US (3.7 km from Portland center, elevation 159 ft); live outlook by Open-Meteo.