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Driveway Sealing Weather in Alton, IL: 10-Day Windows & Best Months

The driveway sealing season in Alton runs May through September — 6 months averaging at least 8 workable days by NOAA 1991–2020 normals. The single best month is August, averaging 24 days that clear every check — highs of 86°F, lows near 67°F, and a 22% daily rain chance. Below: today through day 10 against the label rules, then the year at a glance.

GOOD — every label check passes MARGINAL — one soft fail NO — hard fail or several soft

The rules this check uses

The Alton verdicts run on these rows — consensus pail numbers with one editorial call: 36 cure hours, the honest middle of the 24–48 range labels print.

Typical label thresholds for driveway sealing — the ruleset behind every Alton verdict above.
CheckThresholdWhy it matters
Air temperature 55–90°F, and rising The film (or mix) chemistry runs on temperature — both while you work and for the first hours after.
Overnight low ≥50°F during the first 24 h Curing continues after dark; the first night can undo a perfect afternoon.
Dry before ≤0.05" rain in the prior 24 h Checked backward from your start hour using the two look-back days in the forecast data.
Dry after <0.05" rain for 36 h after (48 h cool or shaded driveways want 48 h) The engine sums forecast rain hour by hour through the cure window for Alton.
Evening dew-point spread ≥5°F from 6–11 pm When air temperature meets the dew point, water condenses on your fresh work first.
Daytime humidity ≤85% Read as the daytime maximum, 10 a.m.–5 p.m.; within 3 points of the limit counts as marginal.
Wind ≤20 mph (dust and debris in wet sealer up to 28 mph) Strong wind drops leaves and grit into the wet coat.

Always follow your product label — formulas vary. The table above is the typical range across major manufacturers, not a promise about your can.

Best months for driveway sealing in Alton

Alton's calendar, scored: each month's days passing the temperature rules, discounted by that day's historical rain odds (NOAA 1991–2020). Not a forecast.
MonthAvg highAvg lowRain odds/dayWorkable days 
January 39°F 22°F 24% 0
February 44°F 25°F 26% 0
March 54°F 35°F 31% 0
April 66°F 45°F 35% 1
May 75°F 56°F 36% 20
June 84°F 66°F 28% 21
July 87°F 69°F 24% 24
August 86°F 67°F 22% 24
September 80°F 60°F 22% 23
October 68°F 48°F 25% 8
November 54°F 36°F 28% 0
December 44°F 27°F 26% 0

Figure 122 workable days a year in Alton, spread across May through September. Shoulder months turn on the overnight rule: an afternoon at 75°F passes, but the 50°F night floor is what actually opens the season in May. The Illinois table ranks every listed city by the same math.

Pouring before you seal? Concrete in Alton trades the pavement-warmth rule for a 48-hour freeze watch.

Source honesty: every monthly figure on this page is the 1991–2020 normal at Alton - Melvin Price L&D, Il Us, 4.1 km from Alton's center — your block's shade lines and wind exposure sit on top of that baseline. Scoring details are on the methodology page.

Alton by the numbers

Prep checklist

  1. Wait for a rising pair: 55°F+ and climbing, first night over 50°F, 36 dry hours — in Alton that pattern lives May through September.
  2. Day-before job: crack filler in every crack, so it cures before the sealcoat lands.
  3. Hit oil spots with degreaser and sweep hard; sealer over dust peels in playing-card flakes.
  4. Check yesterday, not just today: 24 h under 0.05" of rain. Alton's September makes that nearly automatic at 22% rain-day odds.
  5. Tape the garage slab and sidewalk lines with edging tape — drips on concrete are forever.
  6. Pull thin passes with a squeegee/brush combo, back-brushing the texture as you go.
  7. Start early at the top of the slope: a August morning coat gets the whole 86°F afternoon to break before dew.
  8. Keep tires off through the full cure — with August nights at 67°F, shaded strips need the long end of 24–48 h.

Gear that saves a window

Transparency note: gear links here become affiliate links only when the program is enabled — today they are plain references. See the affiliate disclosure.

FAQ

What temperature do you need to seal a driveway?

55–90°F and rising, with the first night at 50°F or better. The 'rising' part is why Alton's May start matters: sealing on the front of a warm spell, not the back. Pavement lags air — a shaded slab can fail a passing afternoon.

How long after rain can I sealcoat?

24 hours after the last 0.05"+ rain, and only once cracks and shade strips are visibly dry — asphalt pores hold water after the surface grays out. In Alton's May (36% rain days) that lookback eats most of the calendar; September barely notices it.

How long does driveway sealer take to dry before rain or cars?

Plan 36 rain-free, car-free hours (labels range 24–48; shade and cool nights need the long end). A 0.05"+ shower inside the window streaks the coat gray. September is Alton's easiest month to find that window; May the hardest.

Can you seal a driveway in the fall?

Yes, until the nights quit. The 50°F overnight rule closes Alton's season after September; the classic October mistake is a 62°F Saturday over a 41°F night. Spring restarts around May when pavement warms.

How often should a driveway be sealed?

When the surface tells you: graying, no beading, spreading hairlines — typically every 2–4 years. In Alton, seal before the freeze-thaw season; January averages 22°F nights that pry open every unfilled crack. Fresh asphalt waits 6–12 months.

Best month to seal a driveway in IL?

August tops Alton's table at 24 days clearing the 55–90°F-rising, 50°F-night, 36-dry-hour stack; August and July together carry the season. Check the IL state page for how the ranking shifts across the state.

Other projects in Alton

Driveway Sealing nearby

Guides

Climatology: NOAA 1991–2020 normals via ALTON - MELVIN PRICE L&D, IL US (4.1 km from Alton center, elevation 405 ft); live outlook by Open-Meteo.