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Weather & Climate in Unionville CDP (Chester County), PA
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Unionville CDP (Chester County) experiences four distinct seasons with an average annual temperature of 52°F (11°C). Winters average 31°F in January while summers reach 74°F in July. The area gets 293 sunny days per year, well above the U.S. average of 205 / making it one of the sunnier locations in the country. Annual precipitation totals 47.1 inches (wetter than the 38-inch national average). Air quality is rated Good with a median AQI of 40. The city sits at an elevation of 488 feet.
Temperature
31°F Jan (-1°C)
74°F Jul (23°C)
| Annual Average | 52.3°F |
| 3% below US avg | |
| January Average | 31°F (-1°C) |
| July Average | 74°F (23°C) |
| Sunny Days | 293 days/yr |
Geography
| Elevation | 488 ft (149 m) |
| Area | 0.9 sq mi (2.2 km²) |
| Population Density | 888/sq mi |
| Coordinates | 39.9005°N, 75.7304°W |
| Timezone | America/New_York |
| County | Chester County County |
| Nearest Airport | Philadelphia International (PHL) 26 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 40.0 |
| Rating | Good |
Natural Hazard Risk
| Overall Risk | Relatively Moderate |
| Risk Score | 91.9 / 100 |
| Social Vulnerability | 10.6 / 100 |
| Community Resilience | 85.2 / 100 |
Hazard Breakdown
| Tornado | Relatively Moderate |
| Hurricane | Relatively Moderate |
| Earthquake | Relatively Moderate |
| Wildfire | Very Low |
| Flood | Relatively High |
| Hail | Relatively Low |
| Strong Wind | Relatively High |
| Heat Wave | Relatively Moderate |
| Winter Weather | Very High |
| Lightning | Relatively High |
| Ice Storm | Relatively High |
| Drought | Relatively High |
| Cold Wave | Relatively Moderate |
| Landslide | Relatively Low |
| Coastal Flood | No Rating |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Earthquake History
35 earthquakes (M2.5+) recorded within 150 km since 1990. Strongest on record: M4.8.
| Apr 5, 2024 | 2024 Tewksbury, New Jersey Earthquake | M4.8 | 121 km | 3 km |
| Jan 16, 1994 | 2 km W of Sinking Spring, Pennsylvania | M4.6 | 54 km | 5 km |
| Jan 16, 1994 | 0 km E of Sinking Spring, Pennsylvania | M4.2 | 53 km | 5 km |
| Apr 5, 2024 | 7 km WSW of Gladstone, New Jersey | M3.7 | 121 km | 4 km |
| Oct 23, 1990 | 3 km W of Hancocks Bridge, New Jersey | M3.2 | 47 km | 10 km |
| Jan 9, 1992 | 4 km WNW of Robertsville, New Jersey | M3.1 | 129 km | 8 km |
| Aug 26, 2003 | 4 km NNW of Milford, New Jersey | M3.1 | 95 km | 3 km |
| Jun 3, 2010 | 4 km ENE of Franklintown, Pennsylvania | M3.1 | 108 km | 2 km |
| Nov 14, 1997 | 0 km S of Rothsville, Pennsylvania | M3.0 | 52 km | 5 km |
| Feb 3, 2009 | 1 km ESE of Victory Gardens, New Jersey | M3.0 | 148 km | 0 km |
| Apr 24, 2009 | 1 km S of Franklintown, Pennsylvania | M2.9 | 112 km | 1 km |
| Apr 27, 2024 | 7 km WSW of Gladstone, New Jersey | M2.9 | 121 km | 5 km |
| May 24, 2024 | 6 km E of Califon, New Jersey | M2.9 | 122 km | 7 km |
| Jan 16, 1994 | 0 km SSE of Sinking Spring, Pennsylvania | M2.9 | 52 km | 5 km |
| Sep 15, 2019 | 5 km ESE of East Berlin, Pennsylvania | M2.8 | 101 km | 5 km |
| May 10, 1993 | 1 km NW of Whitfield, Pennsylvania | M2.8 | 55 km | 5 km |
| Jul 1, 2009 | 3 km ESE of Pennsville, New Jersey | M2.8 | 36 km | 5 km |
| Oct 25, 2009 | 4 km ENE of Franklintown, Pennsylvania | M2.8 | 108 km | 1 km |
| Mar 11, 1995 | 0 km ENE of Landisville, Pennsylvania | M2.7 | 61 km | 5 km |
| Oct 28, 1994 | 1 km E of Mount Vernon, Maryland | M2.7 | 100 km | — |
Source: USGS Earthquake Catalog (M2.5+, 1990–2025). Sorted by magnitude.
Hurricane History
5 hurricanes (Category 1+) recorded within 500 km since 1980. Strongest on record: Category 2.
| Year | Name | Category | Max Wind | Closest |
| 2012 | Sandy | Category 1 | 92 mph | 282 km |
| 2011 | Irene | Category 1 | 75 mph | 210 km |
| 1991 | Bob | Category 3 | 109 mph | 260 km |
| 1986 | Charley | Category 1 | 75 mph | 282 km |
| 1985 | Gloria | Category 2 | 98 mph | 182 km |
Source: NOAA IBTrACS (Category 1+, 1980–2026).
Tornado History
415 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF3. Total: 13 fatalities, 311 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Sep 1, 2021 | EF3 | 48 km | 12.4 mi | 0 |
| Jul 29, 2021 | EF3 | 67 km | 3.4 mi | 0 |
| Jul 14, 2004 | EF3 | 84 km | 7.5 mi | 0 |
| May 31, 1998 | EF3 | 66 km | 8.3 mi | 0 |
| Jul 27, 1994 | EF3 | 41 km | 2.0 mi | 3 |
| Jul 27, 1994 | EF3 | 19 km | 4.0 mi | 0 |
| Jul 26, 1981 | EF3 | 98 km | 3.3 mi | 0 |
| Jun 18, 1970 | EF3 | 74 km | 1.9 mi | 1 |
| Apr 28, 1961 | EF3 | 29 km | 0.3 mi | 0 |
| Jun 24, 1960 | EF3 | 92 km | 12.9 mi | 0 |
| Mar 22, 1955 | EF3 | 12 km | 9.6 mi | 1 |
| Nov 4, 1950 | EF3 | 47 km | 15.9 mi | 0 |
| Feb 21, 2023 | EF2 | 97 km | 5.8 mi | 0 |
| Sep 1, 2021 | EF2 | 25 km | 5.9 mi | 0 |
| Sep 1, 2021 | EF2 | 48 km | 8.3 mi | 1 |
| Jul 29, 2021 | EF2 | 83 km | 6.3 mi | 0 |
| Aug 4, 2020 | EF2 | 91 km | 35.8 mi | 0 |
| Aug 4, 2020 | EF2 | 69 km | 20.8 mi | 0 |
| Oct 31, 2019 | EF2 | 18 km | 0.5 mi | 0 |
| May 28, 2019 | EF2 | 33 km | 3.1 mi | 0 |
Source: NOAA Storm Prediction Center (EF0+, 1950–2024, US only).
Tsunami History
2 tsunamis recorded within 500 km.
| Year | Location | Cause | Max Wave | Deaths | Distance |
| 1895 | HIGH BRIDGE, NJ | Earthquake | — | — | 112 km |
| 1840 | PHILADELPHIA, PENNSYLVANIA | Earthquake | — | — | 47 km |
Source: NOAA/NCEI Historical Tsunami Database.
Wildfire History
20 wildfires (100+ acres) recorded within 100 km. Largest: MULLICA RIVER FIRE (13,082 acres, 2022).
| Year | Name | Acres Burned | Distance |
| 2022 | MULLICA RIVER FIRE | 13,082 | 93 km |
| 2024 | TEA TIME HILL | 4,444 | 97 km |
| 2006 | UNNAMED | 3,780 | 97 km |
| 2017 | PENN SWAMP FIRE | 3,587 | 97 km |
| 2007 | ATSION | 2,705 | 89 km |
| 1990 | UNNAMED | 2,367 | 83 km |
| 1996 | UNNAMED | 2,122 | 82 km |
| 1997 | UNNAMED | 2,121 | 92 km |
| 1993 | UNNAMED | 1,860 | 82 km |
| 2008 | SAUNDERS DITCH | 1,814 | 86 km |
| 1985 | UNNAMED | 1,685 | 82 km |
| 2020 | SPLIT DITCH | 1,518 | 84 km |
| 2020 | BIG TIMBER | 1,434 | 76 km |
| 2014 | RAILROAD | 1,431 | 84 km |
| 1991 | UNNAMED | 1,411 | 95 km |
| 1998 | UNNAMED | 1,386 | 92 km |
| 1989 | UNNAMED | 1,355 | 95 km |
| 1991 | KENTIS WEST | 1,273 | 79 km |
| 2006 | UNNAMED | 1,224 | 95 km |
| 1992 | UNNAMED | 1,094 | 98 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 31°F (-1°C) | 3.7 in | Coldest |
| February | 32°F (-0°C) | 2.9 in | Driest |
| March | 41°F (5°C) | 3.8 in | |
| April | 50°F (10°C) | 3.8 in | |
| May | 60°F (16°C) | 4.4 in | |
| June | 69°F (21°C) | 4.2 in | |
| July | 74°F (23°C) | 4.6 in | Warmest, Wettest |
| August | 73°F (23°C) | 3.9 in | |
| September | 66°F (19°C) | 4.3 in | |
| October | 54°F (12°C) | 3.4 in | |
| November | 45°F (7°C) | 3.9 in | |
| December | 35°F (2°C) | 3.7 in |
Unionville CDP (Chester County) has a seasonal temperature swing of 43°F / from 31°F in January to 74°F in July. Total annual precipitation is 46.5 inches, with July being the wettest month (4.6") and February the driest (2.9").