San Antonio weather by month — averages, rainfall & climate trends
Texas's old Spanish heartland grew up on the Balcones Escarpment, the seam where the humid Gulf plain runs up against the dry Hill Country, and its weather leans one way or the other depending on which has the upper hand. Average temperatures and rainfall by month, a climate graph, today's conditions versus the long-term average, and how the climate has shifted since 1940 — all on one page for San Antonio, United States.
Today vs average
+2.5°Cwarmer than usual
How it’s changed
Right now
What it's doing today vs the historical average for this date.
Right now
25.5°
37°25°38°23°40°25°
38°28°38°26°38°24°38°23°On this date — July 20
Warmer than usual · 2.5°C above the average high
- Record high: 39.0° · 2017
- Record low: 21.2° · 1974
- One year ago: 33.2°
Every July 20 in history — coldest to hottest
Dots show daily highs (top) and lows (bottom) for each July 20 on record (n = 86). Outlined dots are today's forecast.
Area we sample
Each city's history comes from one ERA5 grid cell — about 28 km across, shown by the dashed box. Near mountains or coasts, conditions can vary across the cell.
Location & data
Historical weather for San Antonio is sampled from the ECMWF ERA5 reanalysis at 29.42°N, 98.49°W, with daily records since 1940.
- Coordinates
- 29.42°N, 98.49°W
- Time zone
- America/Chicago
- Period
- 1940–2026
- Data source
- ERA5 (ECMWF)
Last 30 days
20 of the last 30 days were warmer than the historical average for that date. Average difference: +0.1°C.
Each bar is one day, from morning low to afternoon high. Warm-colored bars are days whose mean ran above average; cool bars ran below. The dot inside the bar is the daily mean. The shaded band is the typical 10–90% range expected for that date. Average = the day's mean temperature averaged across every year of record (1940–2026) for that calendar date.
This date over the years
One dot per year — the mean temperature on this calendar date. Dots are warmer or cooler than the long-term average (dashed line); the shaded band is the typical 10–90% range, and the highlighted dot is today's forecast. Based on ERA5 reanalysis — modelled estimates, not station readings.
Weather by month
Average temperatures and rainfall for each month — what a typical year looks like, from the full record.Climate overview
San Antonio sits on the Balcones Escarpment in south-central Texas, a geological fault line that doubles as a climate boundary: humid subtropical (Köppen Cfa) across most of the city, shading toward semi-arid (BSh) on its drier western side. Summers are long, hot and sticky, fed by moisture drawn off the Gulf of Mexico. Winters stay mild, interrupted now and then by cold fronts dropping out of the north that can bring a raw overnight chill.
The bigger story here is water, or the lack of it. The city lies in a stretch of central Texas nicknamed Flash Flood Alley, where slow storms stall against the hills and drop rain faster than the limestone can absorb it; the floods of 1998 and 2002 each killed dozens and ran into hundreds of millions of dollars in damage. Drought is the other face of the same climate, and the region swings between the two. Snow is a genuine novelty, the last real accumulation dating back to 1985.
August brings the year's peak warmth: daily means of 29.1°C, with afternoons typically reaching 35.2°C. Around 160 nights a year stay above 20°C. In January, daily means drop to roughly 10.7°C, with nights dipping to 6.3°C.
In total, San Antonio averages about 825 mm of precipitation a year; May is usually the wettest month (115 mm) and August the driest (47 mm).
Comparing the record's first decade with its most recent one, San Antonio now averages 1.8°C warmer than it did in the 1940s. The count of days past 30°C has risen from roughly 120 a year to 170 between the record's first and last decades.
Climate graph (climograph)
August is the warmest month, January the coolest — a yearly swing of 18°C. Wettest month: May (~115 mm). Whole year averages ~825 mm of rain.
Bars = average monthly rainfall (right axis). Lines = average daily high and low (left axis). Average = each month's value averaged across every year of record (1940–2026).
Monthly wind
Average daily peak wind at 10 m, by month.
Monthly solar energy
Average daily incoming solar energy in megajoules per square metre — a measured proxy for how sunny the month is.
San Antonio month by month — what to expect
Typical conditions for each month, averaged across the full record (since 1940). Daylight is the time from sunrise to sunset. Record high/low are the most extreme values in the ERA5 dataset (modelled since 1940), so they can differ from official weather-station readings.
| Month | Avg high | Avg low | Rain | Daylight | Record high | Record low |
|---|---|---|---|---|---|---|
| January | 17.1° | 6.3° | 55 mm | 10.3 h | 31.5° (1971) | -14.4° (1949) |
| February | 19.5° | 8.2° | 61 mm | 11.0 h | 37.3° (1996) | -11.8° (2021) |
| March | 23.5° | 11.7° | 70 mm | 11.8 h | 36.0° (1991) | -5.6° (1980) |
| April | 27.2° | 15.8° | 90 mm | 12.7 h | 37.2° (1963) | 0.7° (1987) |
| May | 30.1° | 19.7° | 115 mm | 13.5 h | 38.9° (1989) | 7.2° (2013) |
| June | 33.1° | 22.6° | 72 mm | 13.9 h | 42.0° (2013) | 13.2° (1955) |
| July | 34.7° | 23.5° | 48 mm | 13.7 h | 41.6° (1954) | 17.1° (1985) |
| August | 35.2° | 23.6° | 47 mm | 13.1 h | 43.6° (2011) | 17.5° (1940) |
| September | 32.2° | 21.4° | 76 mm | 12.2 h | 42.7° (2000) | 9.0° (1981) |
| October | 27.9° | 16.7° | 74 mm | 11.3 h | 36.9° (2020) | -1.6° (1993) |
| November | 22.2° | 11.4° | 64 mm | 10.5 h | 34.1° (1949) | -4.0° (1976) |
| December | 18.3° | 7.7° | 53 mm | 10.1 h | 30.3° (1954) | -13.1° (1989) |
How it has changed
Year-by-year signals from 1940 to today.Climate stripes
Annual mean shifted from 1940–1949 to 2016–2025 by +1.8°C.
Each vertical stripe is one year. Color encodes how much that year's annual mean differed from the long-term average. Average = each year's annual mean compared to the average of all years (1940–2026). cooler ← → warmer
Annual mean temperature
Long-term trend: +0.18°C per decade.
One point per year — the temperature averaged across the whole year. The dashed line is the least-squares long-term trend. Based on ERA5 reanalysis — modelled estimates, not station readings.
Seasonal warming
Mar–May is warming fastest: +0.25°C per decade.
Each faint line is one three-month period's average per year; the bold dashed line is its long-term trend. Different parts of the year often warm at different rates. Based on ERA5 reanalysis — modelled estimates, not station readings.
Hot days vs frost days
Days ≥ 30°C per year: 117.9 early in the record → 168.8 recently. Frost days: 6 → 7.
Thin lines are raw yearly counts; thick lines are the smoothed trend that removes year-to-year noise. The hot-day threshold is auto-picked per city so the line actually moves. Average = a centered 5-year rolling average to smooth weather noise.
Yearly hot & cold extremes
All-time high in 2011, all-time low in 1949: 43.6°C / -14.4°C.
One point per year — the single hottest and coldest day recorded that year.
Annual rainfall
~825 mm/year on average. Last decade ran −2% vs that average. Long-term trend: +10 mm per decade.
One bar per year of total rainfall. Dashed line is the long-term average. Average = the average annual rainfall across every year of record (1940–2026).
Day-by-day grid
Each tiny square is one calendar day across the full record — ~30,000 days per city. Use the mode switch above the chart: Anomaly colors each day by how far it ran from the historical average for that date (red = warmer, blue = cooler), Daily mean temp shows the absolute mean temperature for the day (useful to see seasons and heatwaves), and Precipitation shows daily rainfall (useful to spot wet/dry seasons and droughts). Average = the long-term average for that calendar date (1940–2026).