Canonsburg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Canonsburg clear sky chart from 2005-11-06 to 2025-04-26.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	15% 11% 4 9% 5% 5% 5% 4 5% 7% 31%	113648
	Night	15% 11% 4 10% 5% 4 4 3 5% 6% 32%	114961
Transparency	Day	52% 3 10% 22% 11% 1	117298
	Night	52% 3 10% 22% 12% 2	119450
Seeing	Day	23% 14% 27% 20% 11% 4	15270
	Night	22% 11% 27% 27% 12% 1	25150

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	16% 18% 8% 20% 5% 3 4 2 4 4 17%	4056
	11th to 20th	Day	13% 22% 8% 16% 9% 6% 3 3 2 3 16%	4060
	21st to end	Day	19% 19% 6% 11% 8% 5% 4 3 4 4 17%	4466
February	1st to 10th	Day	20% 17% 5% 10% 6% 4 4 3 4 5% 23%	1800
	11th to 20th	Day	16% 16% 7% 11% 5% 4 4 3 6% 6% 22%	1753
	21st to end	Day	20% 14% 4 10% 6% 3 3 3 5% 5% 27%	1665
March	1st to 10th	Day	16% 14% 4 10% 5% 4 4 3 4 6% 30%	4935
	11th to 20th	Day	12% 9% 3 8% 5% 5% 5% 3 5% 6% 38%	4980
	21st to end	Day	16% 10% 4 9% 5% 5% 5% 4 5% 6% 31%	5465
April	1st to 10th	Day	16% 13% 3 9% 5% 4 5% 3 6% 7% 29%	2295
	11th to 20th	Day	14% 10% 4 8% 5% 4 4 4 4 6% 35%	2412
	21st to end	Day	20% 10% 3 7% 4 4 4 4 6% 6% 33%	2535
May	1st to 10th	Day	22% 10% 3 7% 5% 5% 5% 4 5% 6% 28%	4082
	11th to 20th	Day	19% 9% 3 8% 5% 4 5% 4 6% 7% 31%	4081
	21st to end	Day	11% 6% 3 7% 5% 6% 5% 5% 7% 10% 36%	4666
June	1st to 10th	Day	12% 8% 3 6% 5% 6% 5% 5% 7% 9% 35%	2660
	11th to 20th	Day	11% 7% 3 7% 5% 5% 5% 6% 6% 8% 36%	2660
	21st to end	Day	12% 7% 2 6% 5% 5% 6% 5% 6% 10% 36%	2660
July	1st to 10th	Day	9% 6% 3 7% 5% 6% 6% 4 7% 8% 40%	4226
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 11% 39%	4120
	21st to end	Day	12% 7% 3 8% 6% 5% 6% 5% 6% 8% 34%	4466
August	1st to 10th	Day	13% 7% 3 9% 6% 6% 6% 5% 7% 9% 30%	4104
	11th to 20th	Day	10% 7% 2 7% 5% 5% 6% 5% 8% 9% 36%	4044
	21st to end	Day	7% 4 2 6% 5% 6% 7% 6% 8% 9% 39%	4318
September	1st to 10th	Day	14% 6% 3 5% 4 4 4 4 6% 7% 44%	2271
	11th to 20th	Day	11% 6% 2 6% 4 4 3 4 5% 8% 46%	2090
	21st to end	Day	19% 9% 4 7% 5% 3 4 3 5% 5% 36%	2090
October	1st to 10th	Day	15% 7% 2 7% 5% 4 4 3 6% 6% 41%	1906
	11th to 20th	Day	18% 8% 2 7% 4 5% 4 4 5% 6% 36%	1900
	21st to end	Day	21% 10% 3 7% 4 4 3 3 4 5% 36%	2090
November	1st to 10th	Day	11% 9% 2 7% 4 4 4 4 5% 7% 43%	1877
	11th to 20th	Day	16% 13% 4 7% 6% 4 5% 3 5% 6% 31%	1695
	21st to end	Day	17% 14% 6% 9% 6% 4 4 3 5% 6% 27%	1600
December	1st to 10th	Day	17% 12% 6% 15% 6% 5% 4 4 4 4 22%	2600
	11th to 20th	Day	22% 17% 7% 11% 4 3 3 2 4 5% 22%	2990
	21st to end	Day	20% 19% 6% 12% 6% 4 4 3 4 5% 16%	4030
January	1st to 10th	Night	13% 16% 7% 22% 7% 5% 4 3 4 4 16%	5889
	11th to 20th	Night	15% 16% 8% 16% 9% 5% 5% 3 3 4 16%	5900
	21st to end	Night	21% 14% 6% 11% 7% 4 4 2 3 3 23%	6490
February	1st to 10th	Night	19% 14% 4 11% 6% 5% 4 4 4 5% 25%	2600
	11th to 20th	Night	20% 12% 4 11% 6% 4 4 5% 4 5% 25%	2533
	21st to end	Night	19% 15% 4 11% 6% 4 4 3 5% 4 25%	1961
March	1st to 10th	Night	21% 10% 4 9% 5% 4 3 3 4 5% 33%	4918
	11th to 20th	Night	10% 8% 4 8% 4 4 4 3 4 7% 43%	4980
	21st to end	Night	15% 10% 4 9% 5% 5% 4 3 5% 6% 35%	5467
April	1st to 10th	Night	18% 11% 3 8% 4 4 4 3 5% 7% 33%	2104
	11th to 20th	Night	15% 10% 3 6% 5% 4 5% 4 5% 7% 37%	1954
	21st to end	Night	15% 9% 3 7% 4 4 4 4 4 7% 38%	1761
May	1st to 10th	Night	23% 11% 4 8% 5% 5% 4 3 5% 6% 26%	2813
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 3 5% 6% 37%	2812
	21st to end	Night	10% 7% 3 7% 4 5% 5% 4 7% 11% 38%	2874
June	1st to 10th	Night	9% 6% 2 7% 6% 4 4 3 7% 7% 45%	1520
	11th to 20th	Night	10% 6% 2 6% 5% 5% 6% 5% 6% 11% 39%	1520
	21st to end	Night	9% 5% 2 6% 5% 4 5% 4 6% 10% 43%	1520
July	1st to 10th	Night	9% 8% 3 7% 5% 4 4 4 5% 8% 42%	2729
	11th to 20th	Night	9% 6% 2 7% 4 4 5% 4 7% 9% 43%	2840
	21st to end	Night	7% 8% 3 8% 5% 6% 5% 4 6% 7% 40%	3087
August	1st to 10th	Night	11% 9% 3 8% 5% 5% 5% 5% 7% 10% 33%	2825
	11th to 20th	Night	9% 8% 3 7% 5% 5% 5% 4 5% 8% 41%	2785
	21st to end	Night	7% 5% 2 6% 4 5% 6% 5% 7% 9% 44%	3306
September	1st to 10th	Night	11% 5% 2 6% 4 4 4 3 5% 7% 50%	1905
	11th to 20th	Night	10% 4 2 4 4 3 4 4 5% 8% 52%	2090
	21st to end	Night	15% 7% 3 7% 4 4 4 2 5% 7% 42%	2090
October	1st to 10th	Night	13% 6% 3 6% 4 4 4 3 5% 6% 46%	2273
	11th to 20th	Night	16% 7% 2 7% 4 4 4 4 6% 6% 39%	2280
	21st to end	Night	20% 8% 3 6% 4 3 4 3 4 6% 38%	2508
November	1st to 10th	Night	12% 8% 2 6% 4 4 4 3 4 6% 47%	2419
	11th to 20th	Night	17% 11% 3 7% 5% 5% 5% 4 4 6% 32%	2701
	21st to end	Night	19% 12% 4 8% 5% 5% 4 4 4 6% 30%	2800
December	1st to 10th	Night	18% 14% 8% 15% 5% 4 4 4 5% 5% 20%	4580
	11th to 20th	Night	20% 16% 7% 11% 5% 4 3 3 4 5% 23%	5205
	21st to end	Night	20% 17% 6% 11% 6% 5% 4 3 5% 6% 18%	6922

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	73% 2 9% 11% 5%	4057
	11th to 20th	Day	76% 2 5% 10% 5% 2	4060
	21st to end	Day	72% 2 7% 13% 6%	4466
February	1st to 10th	Day	65% 3 9% 15% 8% 1	1800
	11th to 20th	Day	64% 2 8% 17% 8%	1762
	21st to end	Day	61% 2 10% 17% 8% 2	1665
March	1st to 10th	Day	57% 2 8% 25% 7% 1	4935
	11th to 20th	Day	48% 2 10% 28% 10% 2	4980
	21st to end	Day	55% 2 7% 21% 14% 1	5465
April	1st to 10th	Day	55% 3 9% 20% 11% 2	2295
	11th to 20th	Day	51% 3 11% 17% 16% 2	2412
	21st to end	Day	51% 4 9% 23% 12% 2	2535
May	1st to 10th	Day	58% 2 9% 22% 9% 1	4120
	11th to 20th	Day	53% 3 9% 25% 9% 1	4085
	21st to end	Day	43% 4 13% 25% 13% 3	4680
June	1st to 10th	Day	45% 4 14% 24% 12% 1	2660
	11th to 20th	Day	44% 5% 13% 24% 13% 1	2660
	21st to end	Day	42% 5% 13% 25% 14% 1	2660
July	1st to 10th	Day	41% 5% 12% 25% 15% 3	4161
	11th to 20th	Day	38% 5% 11% 29% 16% 1	4051
	21st to end	Day	46% 5% 10% 21% 16% 2	4324
August	1st to 10th	Day	49% 6% 12% 23% 9%	4091
	11th to 20th	Day	41% 5% 11% 30% 13%	4083
	21st to end	Day	37% 7% 12% 28% 14% 2	4318
September	1st to 10th	Day	39% 4 10% 22% 21% 4	2271
	11th to 20th	Day	37% 3 12% 30% 16% 2	2090
	21st to end	Day	50% 3 9% 23% 15% 1	2090
October	1st to 10th	Day	34% 4 8% 31% 21% 1	3166
	11th to 20th	Day	43% 4 11% 23% 14% 5%	3140
	21st to end	Day	37% 2 11% 29% 20% 1	3428
November	1st to 10th	Day	42% 3 10% 25% 17% 3	1877
	11th to 20th	Day	54% 4 8% 20% 12% 2	1695
	21st to end	Day	59% 2 12% 19% 8% 1	1600
December	1st to 10th	Day	65% 3 13% 14% 4	2600
	11th to 20th	Day	67% 2 11% 15% 5%	2986
	21st to end	Day	72% 2 9% 12% 5%	4030
January	1st to 10th	Night	72% 2 7% 14% 5%	5889
	11th to 20th	Night	73% 3 8% 12% 5% 1	5900
	21st to end	Night	67% 3 8% 14% 6% 1	6490
February	1st to 10th	Night	62% 3 9% 19% 8%	2600
	11th to 20th	Night	61% 3 8% 19% 8% 1	2535
	21st to end	Night	62% 2 8% 17% 10% 1	1961
March	1st to 10th	Night	56% 2 7% 24% 10% 1	4918
	11th to 20th	Night	43% 2 11% 31% 10% 3	4980
	21st to end	Night	51% 2 8% 21% 15% 2	5467
April	1st to 10th	Night	53% 3 9% 20% 14% 2	2104
	11th to 20th	Night	47% 3 10% 20% 16% 3	1954
	21st to end	Night	47% 3 8% 26% 13% 3	1761
May	1st to 10th	Night	60% 3 7% 18% 10% 2	2840
	11th to 20th	Night	48% 3 10% 27% 10% 2	2813
	21st to end	Night	41% 4 14% 26% 12% 4	2881
June	1st to 10th	Night	38% 5% 13% 25% 17% 2	1520
	11th to 20th	Night	39% 5% 15% 26% 14% 2	1520
	21st to end	Night	36% 6% 15% 25% 17% 2	1520
July	1st to 10th	Night	41% 5% 10% 24% 17% 4	2684
	11th to 20th	Night	36% 6% 13% 28% 16% 1	2786
	21st to end	Night	42% 5% 11% 19% 19% 4	2988
August	1st to 10th	Night	46% 6% 13% 24% 11%	2814
	11th to 20th	Night	41% 5% 10% 26% 18% 1	2812
	21st to end	Night	35% 5% 12% 32% 13% 2	3306
September	1st to 10th	Night	35% 4 9% 25% 21% 6%	1905
	11th to 20th	Night	32% 3 12% 29% 24% 1	2090
	21st to end	Night	44% 3 10% 23% 19% 1	2090
October	1st to 10th	Night	35% 3 8% 29% 22% 2	3793
	11th to 20th	Night	38% 3 9% 25% 16% 8%	3779
	21st to end	Night	35% 2 8% 29% 23% 2	4120
November	1st to 10th	Night	40% 3 10% 25% 19% 4	2419
	11th to 20th	Night	53% 3 7% 21% 13% 3	2701
	21st to end	Night	57% 2 10% 22% 8% 1	2800
December	1st to 10th	Night	67% 3 10% 17% 3	4580
	11th to 20th	Night	65% 2 14% 15% 3	5208
	21st to end	Night	69% 2 10% 15% 4	6922

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	33% 29% 23% 10% 4 1	300
	11th to 20th	Day	36% 28% 28% 6% 2	300
	21st to end	Day	29% 36% 25% 7% 3	330
February	1st to 10th	Day	34% 24% 33% 9% 1	300
	11th to 20th	Day	40% 29% 25% 5% 1	300
	21st to end	Day	36% 25% 34% 5% 1	277
March	1st to 10th	Day	29% 24% 28% 16% 3	500
	11th to 20th	Day	32% 19% 32% 12% 4 1	500
	21st to end	Day	31% 20% 30% 14% 4 1	550
April	1st to 10th	Day	32% 16% 29% 15% 6% 1	500
	11th to 20th	Day	24% 23% 27% 14% 9% 3	492
	21st to end	Day	27% 17% 33% 15% 7% 2	480
May	1st to 10th	Day	28% 18% 25% 18% 9% 3	463
	11th to 20th	Day	21% 13% 32% 18% 11% 4	487
	21st to end	Day	15% 9% 27% 26% 16% 7%	529
June	1st to 10th	Day	15% 8% 31% 29% 13% 4	490
	11th to 20th	Day	16% 11% 25% 26% 18% 4	490
	21st to end	Day	16% 10% 29% 28% 15% 3	490
July	1st to 10th	Day	13% 7% 20% 30% 17% 13%	485
	11th to 20th	Day	12% 6% 24% 31% 18% 8%	484
	21st to end	Day	14% 5% 28% 29% 17% 8%	532
August	1st to 10th	Day	13% 5% 23% 27% 23% 9%	486
	11th to 20th	Day	16% 6% 20% 30% 16% 12%	479
	21st to end	Day	10% 5% 22% 29% 23% 12%	539
September	1st to 10th	Day	15% 8% 23% 26% 21% 7%	490
	11th to 20th	Day	14% 3 17% 33% 22% 11%	490
	21st to end	Day	26% 9% 25% 20% 16% 4	490
October	1st to 10th	Day	18% 8% 28% 24% 17% 4	490
	11th to 20th	Day	23% 14% 30% 23% 8% 3	490
	21st to end	Day	29% 14% 30% 21% 5% 1	539
November	1st to 10th	Day	20% 16% 33% 19% 8% 3	415
	11th to 20th	Day	31% 16% 31% 15% 5% 2	247
	21st to end	Day	29% 18% 44% 9% 2	200
December	1st to 10th	Day	33% 24% 30% 8% 5% 1	200
	11th to 20th	Day	35% 21% 31% 12% 2	200
	21st to end	Day	35% 22% 27% 11% 4	236
January	1st to 10th	Night	30% 20% 32% 15% 3	800
	11th to 20th	Night	34% 16% 31% 16% 3	800
	21st to end	Night	29% 19% 31% 18% 4	880
February	1st to 10th	Night	30% 18% 29% 22% 2	800
	11th to 20th	Night	32% 19% 34% 15% 1	783
	21st to end	Night	29% 17% 33% 17% 3	660
March	1st to 10th	Night	26% 17% 31% 24% 3	800
	11th to 20th	Night	26% 18% 27% 21% 6% 1	800
	21st to end	Night	25% 15% 33% 23% 4 1	880
April	1st to 10th	Night	27% 15% 31% 22% 5%	800
	11th to 20th	Night	22% 14% 32% 22% 10% 1	770
	21st to end	Night	21% 10% 34% 29% 6%	587
May	1st to 10th	Night	22% 9% 25% 30% 13% 1	570
	11th to 20th	Night	20% 9% 27% 31% 13% 1	561
	21st to end	Night	11% 4 23% 36% 23% 3	502
June	1st to 10th	Night	11% 4 25% 39% 20% 1	380
	11th to 20th	Night	12% 6% 23% 39% 18% 1	380
	21st to end	Night	10% 3 28% 36% 22% 1	380
July	1st to 10th	Night	10% 5% 15% 40% 25% 6%	483
	11th to 20th	Night	9% 3 21% 35% 27% 5%	552
	21st to end	Night	11% 3 17% 39% 29% 2	624
August	1st to 10th	Night	10% 1 17% 41% 28% 2	567
	11th to 20th	Night	10% 4 14% 39% 28% 4	564
	21st to end	Night	13% 3 17% 34% 29% 5%	731
September	1st to 10th	Night	14% 3 18% 36% 25% 4	760
	11th to 20th	Night	11% 5% 15% 37% 28% 4	760
	21st to end	Night	19% 8% 24% 27% 20% 3	760
October	1st to 10th	Night	16% 8% 22% 31% 21% 2	760
	11th to 20th	Night	21% 9% 31% 26% 11% 1	760
	21st to end	Night	25% 11% 29% 27% 7% 1	836
November	1st to 10th	Night	17% 11% 31% 27% 13% 1	780
	11th to 20th	Night	26% 15% 28% 23% 7% 1	800
	21st to end	Night	29% 15% 31% 21% 5% 1	800
December	1st to 10th	Night	33% 15% 28% 20% 4	800
	11th to 20th	Night	28% 18% 30% 21% 4	800
	21st to end	Night	29% 14% 32% 22% 2	880

Page generated at 2025-04-23 09:25:04. Version ac07

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