Conowingo Dam, Maryland climate: Climate normals at a NOAA weather station
Conowingo Dam's normal year runs from 25°F January nights to 88°F July afternoons, with 48.3 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 13.0°C, January lows of −4°C, July highs of 31°C, 1,226 mm of precipitation a year.
- NOAA stationConowingo Dam
- Station IDUSC00182060
- Location39.66°N 76.17°W
- Elevation40 ft (12 m)
On October 23, the normal high in Conowingo Dam is 64°F and the normal low 45°F, and the chance of measurable rain or snow is 27%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Conowingo Dam.
- Jan 40° 25°
- Feb 43° 26°
- Mar 51° 34°
- Apr 64° 44°
- May 74° 54°
- Jun 83° 64°
- Jul 88° 69°
- Aug 85° 67°
- Sep 79° 60°
- Oct 67° 48°
- Nov 55° 37°
- Dec 45° 31°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like at Conowingo Dam each month?
July is the warmest month, with normal highs of 88°F; January the coldest, with normal lows of 25°F. The most precipitation falls in September (5.05 in), the least in February (2.64 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 40°F | 25°F | 32.5°F | 3.63 | 11 | <1 | 26 | 9 h 40 min |
| February | 43°F | 26°F | 34.6°F | 2.64 | 9 | <1 | 23 | 10 h 40 min |
| March | 51°F | 34°F | 42.3°F | 4.18 | 11 | <1 | 17 | 11 h 50 min |
| April | 64°F | 44°F | 53.9°F | 3.44 | 10 | <1 | 3 | 13 h 10 min |
| May | 74°F | 54°F | 63.7°F | 3.86 | 11 | 2 | <1 | 14 h 20 min |
| June | 83°F | 64°F | 73.3°F | 4.46 | 10 | 8 | <1 | 15 h |
| July | 88°F | 69°F | 78.0°F | 4.69 | 9 | 14 | <1 | 14 h 40 min |
| August | 85°F | 67°F | 76.2°F | 4.54 | 9 | 11 | <1 | 13 h 50 min |
| September | 79°F | 60°F | 69.4°F | 5.05 | 9 | 3 | <1 | 12 h 30 min |
| October | 67°F | 48°F | 57.4°F | 4.50 | 8 | <1 | 1 | 11 h 10 min |
| November | 55°F | 37°F | 45.8°F | 3.23 | 8 | <1 | 13 | 10 h |
| December | 45°F | 31°F | 37.8°F | 4.04 | 10 | <1 | 23 | 9 h 20 min |
| Year (annual) | 64°F | 46°F | 55.4°F | 48.26 | 115 | 37 | 106 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 5°C | −4°C | 0.3°C | 92 mm |
| February | 6°C | −3°C | 1.4°C | 67 mm |
| March | 11°C | 1°C | 5.7°C | 106 mm |
| April | 18°C | 7°C | 12.2°C | 87 mm |
| May | 23°C | 12°C | 17.6°C | 98 mm |
| June | 28°C | 18°C | 22.9°C | 113 mm |
| July | 31°C | 20°C | 25.6°C | 119 mm |
| August | 30°C | 19°C | 24.6°C | 115 mm |
| September | 26°C | 16°C | 20.8°C | 128 mm |
| October | 19°C | 9°C | 14.1°C | 114 mm |
| November | 13°C | 3°C | 7.7°C | 82 mm |
| December | 7°C | −1°C | 3.2°C | 103 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Octoraro Lake (12 miles away), gets 18 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00182060; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
Which months are mildest at Conowingo Dam?
Normal highs sit between 65°F and 85°F in May, June, September and October. Of those, October has the fewest days with rain (8).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00182060.
When is the last frost at Conowingo Dam?
In Conowingo Dam, the last spring frost (32°F) comes after April 3 in half of years and after April 18 in one year in ten; the first autumn frost comes before November 6 in half of years and before October 26 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 31 year in 10 after April 18; 9 in 10 after March 22
- First autumn frost, half of years before
- November 61 year in 10 before October 26; 9 in 10 before November 19
NOAA puts the median frost-free season at 217 days, and the season without a hard freeze (28°F) at 238 days.
A hard freeze (28°F) comes after March 24 in half of springs and before November 17 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Conowingo Dam in zone 7a in ZIP code 21918, the nearest ZIP area.
Frost dates for every NOAA station in Maryland · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00182060; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get at Conowingo Dam?
In a normal year in Conowingo Dam, 37 days a year reach 90°F (3 of them 100°F or more), 106 nights fall to 32°F or colder and 115 days bring measurable precipitation.
- Days at 90°F or more
- 37a normal year
- Days at 100°F or more
- 3a normal year
- Nights at 32°F or colder
- 106a normal year
- Days that stay below freezing
- 11high of 32°F or less
- Days with 0.01 inch of precipitation
- 115a normal year
The highest temperature in this station's record (since 1936) is 109°F, on June 21, 1988; the lowest is −10°F, on February 14, 1979.
The wettest calendar year on that record is 2018, with 70.25 in; the snowiest season is 2009–10, with 82.4 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00182060; records: ACIS (NOAA Regional Climate Centers), station USC00182060. Records use complete months only; a month missing more than three days is left out.
How sunny is it at Conowingo Dam?
Over a year 74% of the sunlight that would reach the ground under clear skies gets through the clouds at Conowingo Dam, 4.0 kWh per square metre a day. July is the sunniest month (82%) and December the cloudiest (67%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 67% | 2.0 |
| February | 69% | 2.9 |
| March | 68% | 3.8 |
| April | 72% | 5.0 |
| May | 72% | 5.5 |
| June | 78% | 6.2 |
| July | 82% | 6.2 |
| August | 80% | 5.4 |
| September | 76% | 4.3 |
| October | 72% | 3.2 |
| November | 73% | 2.3 |
| December | 67% | 1.8 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How many heating and cooling degree days does Conowingo Dam record?
A normal year at Conowingo Dam brings 4,736 heating degree days, 12% fewer than the median U.S. place (5,373), and 1,278 cooling degree days, 41% more than the median (908). Six months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 3,882 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,007 | 0 |
| February | 850 | 0 |
| March | 704 | 1 |
| April | 346 | 12 |
| May | 112 | 74 |
| June | 9 | 259 |
| July | 0 | 403 |
| August | 1 | 346 |
| September | 31 | 163 |
| October | 256 | 21 |
| November | 576 | 0 |
| December | 843 | 0 |
| Year (annual) | 4,736 | 1,278 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00182060. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Have recent years at Conowingo Dam been warmer than normal?
2025 averaged 55.1°F, 0.3°F below the 1991-2020 normal of 55.4°F. 3 of the 4 complete years since 2022 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2022 | 55.7°F | +0.3°F | 53.23 |
| 2023 | 57.1°F | +1.7°F | 40.71 |
| 2024 | 57.4°F | +2.0°F | 41.87 |
| 2025 | 55.1°F | −0.3°F | – |
Over 40 complete years from 1936 to 2025, the station's annual mean temperature rose at a fitted 4.0°F per century (+0.22°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00182060; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Conowingo Dam's climate compare?
Conowingo Dam is warmer than 10 of the 26 places with their own NOAA record in Maryland, and wetter than 21. Across the 7,247 U.S. stations with normals, its annual mean of 55.4°F is warmer than 62%.
In the Köppen classification computed from these normals, Conowingo Dam is Cfa: temperate, no dry season, hot summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Conowingo Dam share this climate record?
8 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Quarryville, PA2,867 people · 17 mi N
- Susquehanna Trails, PA2,219 people · 12 mi NW
- Nottingham, PA1,405 people · 10 mi NE
- Delta, PA717 people · 9 mi NW
- Wakefield, PA577 people · 8 mi N
- Fawn Grove, PA478 people · 16 mi W
- Darlington, MD349 people · 2 mi SW
- Little Britain, PA336 people · 9 mi N
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Conowingo Dam's climate
What is the coldest month at Conowingo Dam?
January, with a normal high of 40°F and a normal low of 25°F. The warmest is July (88°F by day, 69°F at night).
Does it snow at Conowingo Dam?
Yes. NOAA publishes no 1991-2020 snowfall normal for the station; the nearest record that keeps one, Octoraro Lake (12 miles away), records 18 inches of snow in a normal year.
What is the rainiest month at Conowingo Dam?
September, with 5.05 in of precipitation in a normal year; the driest is February with 2.64 in.
What plant hardiness zone is Conowingo Dam in?
The USDA's 2023 map puts Conowingo Dam in zone 7a in ZIP code 21918, the nearest ZIP area.
How late can frost come at Conowingo Dam?
In half of years the last 32°F night comes after April 3; in one year in ten it comes after April 18. Waiting until April 18 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Maryland climateThe statewide normals and every place in the state
- Octoraro Lake, PA12 miles from this station, 52.7°F a year
- Aberdeen, MD12 miles from this station, 55.2°F a year
- Safe Harbor Dam, PA22 miles from this station, 54.6°F a year
- Newark, DE23 miles from this station, 55.7°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made