- AprilBest month
- 247 daysWorkable days/yr
- 10 moSeason length
- 1–22%Rain-day odds
- Fontana by month
The next 10 days in Fontana
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 Fontana'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 Fontana'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 Fontana'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 Fontana garage is the contract.
Best months for concrete pouring in Fontana
| Month | Avg high | Avg low | Rain odds/day | Workable days | |
|---|---|---|---|---|---|
| January | 68°F | 45°F | 17% | 26 | |
| February | 68°F | 46°F | 22% | 23 | |
| March | 72°F | 49°F | 18% | 25 | |
| April | 76°F | 51°F | 12% | 27 | |
| May | 80°F | 56°F | 6% | 29 | |
| June | 86°F | 60°F | 1% | 26 | |
| July | 94°F | 65°F | 2% | 0 | |
| August | 95°F | 65°F | 1% | 0 | |
| September | 91°F | 64°F | 2% | 10 | |
| October | 83°F | 57°F | 7% | 29 | |
| November | 75°F | 49°F | 12% | 26 | |
| December | 67°F | 44°F | 18% | 26 |
The working season runs September through June — about 246 workable days a year. The edges are night-limited: label rules want overnight lows of 40°F+, and Fontana's nights only average that from January to December. For the statewide picture, the California page compares peak months city by city.
Midsummer is the trap month in Fontana — 94°F average highs against a 90°F limit. The best-months table is honest about it: May beats July with 29 workable days to 0.
Fontana has a real wet/dry rhythm: February brings rain on 22% of days versus 1% in June. When the calendar gives you a June-side window, the dry-before and dry-after rules nearly take care of themselves.
Flip side of the driveway calendar: sealing in Fontana opens later and closes earlier than pouring, on the same forecast.
Numbers above come from NOAA's 1991–2020 normals for Ontario Intl Ap, Ca Us, 11.8 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.
Comparing calendars along the loop? See how the season shifts for concrete pouring in Folsom, CA, or jump ahead to concrete pouring in Fremont, CA.
Fontana by the numbers
- August is Fontana's heat peak: 95°F typical high, 31 days over 90°F.
- Coldest month: December — 67°F highs over 44°F nights.
- Wet-to-dry spread: 22% rain days in February versus 1% in June.
- Add it up and Fontana banks 246 workable days a year for concrete pouring.
Prep checklist
- Check two nights, not one afternoon: both must hold 40°F+. In Fontana that math works September through June — outside it, 44°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 — Fontana sees rain on 6% of May 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 Fontana 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 Fontana 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.
-
Curing blanket
Holds heat through cold nights in the critical 48 hours.
-
Plastic sheeting
Emergency rain cover and moisture-holding cure layer.
-
Edger + float set
Rounded edges and a flat surface before it sets.
-
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 Fontana, nights average 40°F+ only January–December, 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. Fontana's February sees rain 22% 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. Fontana's freeze risk lives at the season edges: December averages 0 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. Fontana's July highs average 94°F, so hot-weather tactics (dawn pour, shade, fast finishing) are standard kit in midsummer.
How long before you can drive on new concrete?
About 7 days for a passenger car in Fontana's May conditions (80°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 Fontana?
September through june — the months with 40°F+ nights, sub-90°F days, and manageable rain. May leads at 29 workable days; December bottoms out near 26.
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 Fontana, April 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 ONTARIO INTL AP, CA US (11.8 km from Fontana center, elevation 949 ft); live outlook by Open-Meteo.