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 2026-08-30.

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	14% 10% 4 9% 5% 5% 5% 4 6% 7% 31%	143427
	Night	15% 11% 4 10% 5% 5% 4 3 5% 6% 32%	138754
Transparency	Day	51% 4 10% 22% 12% 1	147033
	Night	52% 4 10% 21% 12% 2	143218
Seeing	Day	23% 14% 27% 20% 11% 4	17077
	Night	22% 12% 27% 27% 12% 1	26782

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% 17% 7% 19% 5% 4 4 3 4 5% 16%	5258
	11th to 20th	Day	12% 20% 8% 18% 9% 6% 3 3 3 3 16%	5280
	21st to end	Day	17% 16% 6% 13% 9% 5% 4 3 5% 5% 18%	5780
February	1st to 10th	Day	19% 16% 5% 10% 6% 4 4 3 4 5% 24%	1890
	11th to 20th	Day	16% 16% 7% 11% 5% 4 4 3 5% 6% 23%	1843
	21st to end	Day	19% 14% 4 10% 5% 3 3 3 5% 5% 27%	1746
March	1st to 10th	Day	17% 14% 4 10% 5% 4 4 3 4 6% 30%	5045
	11th to 20th	Day	12% 9% 3 8% 5% 5% 5% 4 5% 6% 37%	5090
	21st to end	Day	16% 10% 4 9% 5% 5% 5% 4 5% 6% 31%	5586
April	1st to 10th	Day	15% 13% 3 9% 5% 5% 5% 3 6% 7% 30%	2410
	11th to 20th	Day	14% 10% 4 8% 5% 4 5% 4 5% 6% 35%	2534
	21st to end	Day	19% 9% 3 7% 4 4 4 4 5% 6% 34%	2730
May	1st to 10th	Day	18% 9% 3 8% 5% 6% 6% 4 6% 7% 27%	7616
	11th to 20th	Day	15% 8% 3 8% 5% 5% 5% 4 6% 8% 32%	7626
	21st to end	Day	20% 8% 3 7% 4 4 5% 4 6% 7% 32%	8749
June	1st to 10th	Day	12% 8% 3 6% 5% 6% 5% 4 7% 8% 36%	2940
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 5% 7% 8% 35%	2940
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 5% 6% 10% 36%	2940
July	1st to 10th	Day	9% 7% 3 7% 5% 6% 6% 4 6% 8% 40%	7870
	11th to 20th	Day	8% 7% 3 7% 5% 6% 6% 5% 8% 11% 35%	7680
	21st to end	Day	10% 7% 3 8% 5% 5% 6% 5% 7% 9% 36%	8340
August	1st to 10th	Day	13% 7% 3 8% 6% 6% 6% 4 7% 9% 30%	4364
	11th to 20th	Day	10% 8% 2 7% 5% 5% 6% 5% 7% 9% 36%	4304
	21st to end	Day	7% 4 2 6% 5% 6% 7% 6% 9% 10% 40%	4567
September	1st to 10th	Day	13% 6% 2 5% 4 4 4 4 6% 7% 44%	2390
	11th to 20th	Day	11% 6% 2 6% 4 4 3 4 5% 8% 46%	2200
	21st to end	Day	19% 8% 3 7% 5% 4 4 3 5% 5% 35%	2200
October	1st to 10th	Day	15% 7% 2 7% 5% 3 3 3 6% 6% 43%	2006
	11th to 20th	Day	17% 8% 2 7% 4 5% 5% 4 5% 6% 37%	2000
	21st to end	Day	20% 10% 3 7% 4 4 3 3 5% 5% 36%	2200
November	1st to 10th	Day	11% 9% 2 7% 5% 4 4 3 4 7% 43%	1973
	11th to 20th	Day	16% 13% 4 7% 6% 4 5% 3 5% 6% 31%	1780
	21st to end	Day	17% 14% 6% 9% 6% 4 4 3 5% 6% 27%	1680
December	1st to 10th	Day	17% 12% 6% 15% 6% 5% 4 4 4 4 22%	2680
	11th to 20th	Day	22% 16% 7% 11% 4 3 3 2 4 5% 22%	3070
	21st to end	Day	20% 19% 6% 13% 6% 4 4 3 4 5% 16%	4120
January	1st to 10th	Night	14% 16% 7% 19% 7% 5% 5% 3 4 4 15%	7635
	11th to 20th	Night	13% 16% 8% 16% 9% 5% 5% 3 4 4 17%	7680
	21st to end	Night	18% 14% 5% 11% 8% 6% 4 3 4 4 23%	8401
February	1st to 10th	Night	18% 13% 4 11% 6% 5% 4 4 4 5% 26%	2730
	11th to 20th	Night	19% 12% 5% 11% 6% 4 4 5% 4 5% 24%	2663
	21st to end	Night	18% 15% 4 12% 6% 4 4 3 5% 5% 25%	2056
March	1st to 10th	Night	21% 10% 4 9% 5% 4 3 3 4 5% 33%	5028
	11th to 20th	Night	10% 8% 4 8% 4 4 4 3 5% 7% 42%	5090
	21st to end	Night	15% 10% 4 9% 5% 4 4 3 5% 6% 35%	5588
April	1st to 10th	Night	18% 11% 3 8% 5% 4 4 3 5% 7% 33%	2209
	11th to 20th	Night	14% 10% 3 6% 5% 4 5% 4 5% 7% 37%	2053
	21st to end	Night	15% 9% 3 7% 4 4 4 4 4 7% 38%	1890
May	1st to 10th	Night	20% 11% 4 9% 5% 5% 4 4 5% 6% 27%	5237
	11th to 20th	Night	12% 8% 3 7% 5% 4 5% 4 6% 9% 37%	5234
	21st to end	Night	20% 8% 3 7% 4 5% 4 3 5% 8% 32%	5390
June	1st to 10th	Night	10% 6% 2 7% 5% 4 4 3 6% 7% 46%	1680
	11th to 20th	Night	10% 6% 2 6% 5% 5% 6% 4 6% 11% 38%	1680
	21st to end	Night	9% 5% 2 6% 5% 4 5% 4 6% 10% 43%	1680
July	1st to 10th	Night	9% 8% 3 8% 5% 5% 5% 4 5% 8% 40%	5055
	11th to 20th	Night	10% 8% 3 8% 5% 4 6% 4 7% 9% 37%	5277
	21st to end	Night	9% 7% 3 8% 5% 5% 5% 4 5% 8% 42%	5736
August	1st to 10th	Night	11% 9% 3 8% 5% 5% 5% 5% 7% 9% 33%	3005
	11th to 20th	Night	10% 8% 3 7% 5% 5% 5% 4 5% 7% 41%	2965
	21st to end	Night	7% 6% 2 5% 4 5% 6% 5% 7% 9% 44%	3496
September	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 5% 7% 50%	2005
	11th to 20th	Night	10% 4 2 4 4 3 4 4 5% 7% 53%	2200
	21st to end	Night	16% 8% 3 7% 4 4 4 2 5% 7% 40%	2200
October	1st to 10th	Night	13% 6% 3 6% 4 3 4 3 5% 6% 47%	2393
	11th to 20th	Night	15% 7% 2 7% 4 4 4 4 6% 6% 40%	2400
	21st to end	Night	20% 8% 3 6% 4 3 4 3 4 6% 38%	2640
November	1st to 10th	Night	12% 8% 2 6% 4 4 4 3 4 7% 47%	2543
	11th to 20th	Night	17% 11% 3 7% 5% 5% 5% 4 4 6% 32%	2836
	21st to end	Night	19% 12% 4 9% 5% 5% 4 4 4 5% 29%	2940
December	1st to 10th	Night	17% 14% 8% 15% 5% 4 4 4 5% 5% 19%	4720
	11th to 20th	Night	20% 16% 7% 11% 5% 4 3 3 4 5% 23%	5345
	21st to end	Night	19% 17% 6% 12% 6% 5% 4 3 5% 6% 18%	7074

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 10% 11% 4	5259
	11th to 20th	Day	74% 2 6% 9% 7% 2	5280
	21st to end	Day	70% 2 7% 15% 5%	5780
February	1st to 10th	Day	64% 2 9% 16% 8% 1	1890
	11th to 20th	Day	64% 2 8% 17% 8%	1852
	21st to end	Day	61% 2 10% 17% 8% 2	1746
March	1st to 10th	Day	57% 2 8% 24% 7% 1	5045
	11th to 20th	Day	48% 2 10% 28% 10% 2	5090
	21st to end	Day	55% 2 7% 21% 13% 1	5586
April	1st to 10th	Day	54% 3 10% 20% 11% 2	2410
	11th to 20th	Day	50% 4 11% 17% 16% 2	2534
	21st to end	Day	50% 4 9% 24% 12% 2	2730
May	1st to 10th	Day	54% 4 10% 21% 8% 2	7651
	11th to 20th	Day	49% 5% 10% 25% 10% 1	7630
	21st to end	Day	50% 4 9% 19% 15% 3	8764
June	1st to 10th	Day	44% 4 13% 24% 13% 1	2940
	11th to 20th	Day	45% 5% 13% 24% 13% 1	2940
	21st to end	Day	42% 6% 13% 25% 14% 1	2940
July	1st to 10th	Day	42% 5% 11% 26% 15% 1	7805
	11th to 20th	Day	40% 6% 11% 31% 11%	7611
	21st to end	Day	43% 5% 10% 23% 18% 1	8156
August	1st to 10th	Day	48% 6% 12% 23% 10%	4351
	11th to 20th	Day	41% 5% 11% 30% 13%	4343
	21st to end	Day	35% 7% 13% 29% 14% 2	4567
September	1st to 10th	Day	39% 4 9% 23% 21% 4	2390
	11th to 20th	Day	37% 3 12% 30% 17% 2	2200
	21st to end	Day	51% 3 9% 22% 15% 1	2200
October	1st to 10th	Day	34% 4 8% 31% 22% 1	3266
	11th to 20th	Day	42% 4 11% 23% 14% 5%	3240
	21st to end	Day	37% 2 11% 29% 20% 1	3538
November	1st to 10th	Day	42% 3 11% 24% 17% 3	1973
	11th to 20th	Day	55% 4 8% 20% 11% 2	1780
	21st to end	Day	59% 3 12% 19% 7% 1	1680
December	1st to 10th	Day	66% 3 13% 14% 4	2680
	11th to 20th	Day	66% 2 11% 15% 5%	3066
	21st to end	Day	72% 2 9% 12% 5%	4120
January	1st to 10th	Night	72% 3 9% 12% 4	7636
	11th to 20th	Night	71% 3 7% 12% 7% 1	7680
	21st to end	Night	65% 3 8% 16% 6% 1	8401
February	1st to 10th	Night	61% 3 9% 19% 8%	2730
	11th to 20th	Night	62% 3 8% 18% 8%	2665
	21st to end	Night	62% 2 9% 17% 9% 1	2056
March	1st to 10th	Night	56% 2 7% 24% 10% 1	5028
	11th to 20th	Night	43% 2 11% 31% 10% 3	5090
	21st to end	Night	51% 2 9% 21% 15% 2	5588
April	1st to 10th	Night	53% 3 9% 20% 13% 2	2209
	11th to 20th	Night	47% 3 11% 20% 15% 3	2053
	21st to end	Night	47% 4 8% 25% 13% 3	1890
May	1st to 10th	Night	57% 4 10% 16% 10% 3	5264
	11th to 20th	Night	45% 5% 10% 28% 11% 1	5235
	21st to end	Night	52% 4 10% 21% 12% 2	5397
June	1st to 10th	Night	38% 5% 12% 25% 18% 2	1680
	11th to 20th	Night	40% 5% 14% 25% 15% 2	1680
	21st to end	Night	37% 6% 14% 25% 17% 2	1680
July	1st to 10th	Night	42% 6% 9% 23% 18% 2	5012
	11th to 20th	Night	42% 6% 14% 26% 12% 1	5226
	21st to end	Night	39% 6% 11% 20% 22% 2	5606
August	1st to 10th	Night	46% 6% 13% 24% 10% 1	2994
	11th to 20th	Night	41% 5% 10% 26% 18% 1	2992
	21st to end	Night	35% 6% 13% 32% 13% 2	3496
September	1st to 10th	Night	34% 4 9% 25% 21% 5%	2005
	11th to 20th	Night	32% 3 11% 30% 23% 1	2200
	21st to end	Night	45% 3 9% 23% 18% 1	2200
October	1st to 10th	Night	34% 3 8% 29% 24% 2	3913
	11th to 20th	Night	37% 3 10% 25% 17% 8%	3899
	21st to end	Night	35% 2 8% 29% 23% 2	4252
November	1st to 10th	Night	40% 3 10% 25% 19% 4	2543
	11th to 20th	Night	53% 3 8% 22% 12% 2	2836
	21st to end	Night	57% 3 10% 22% 7% 1	2940
December	1st to 10th	Night	67% 3 9% 16% 4	4720
	11th to 20th	Night	65% 2 13% 16% 4	5348
	21st to end	Night	69% 2 10% 15% 4	7074

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% 24% 10% 4 1	330
	11th to 20th	Day	39% 27% 26% 5% 2	330
	21st to end	Day	31% 34% 25% 7% 2	363
February	1st to 10th	Day	32% 23% 34% 10% 1 1	330
	11th to 20th	Day	40% 28% 25% 5% 1	330
	21st to end	Day	34% 26% 35% 5% 1	302
March	1st to 10th	Day	30% 24% 28% 15% 3	540
	11th to 20th	Day	33% 20% 31% 11% 4 1	540
	21st to end	Day	31% 20% 30% 14% 4 1	594
April	1st to 10th	Day	32% 16% 30% 16% 6% 1	540
	11th to 20th	Day	24% 23% 28% 14% 8% 3	532
	21st to end	Day	26% 17% 33% 15% 7% 2	540
May	1st to 10th	Day	27% 20% 27% 16% 8% 2	543
	11th to 20th	Day	21% 13% 33% 18% 11% 4	567
	21st to end	Day	19% 10% 27% 24% 15% 6%	617
June	1st to 10th	Day	15% 8% 32% 29% 12% 4	570
	11th to 20th	Day	17% 13% 26% 25% 16% 3	570
	21st to end	Day	15% 10% 28% 27% 16% 3	570
July	1st to 10th	Day	13% 7% 18% 32% 18% 13%	565
	11th to 20th	Day	12% 5% 26% 30% 19% 8%	564
	21st to end	Day	14% 5% 27% 30% 16% 8%	620
August	1st to 10th	Day	12% 6% 25% 27% 21% 9%	566
	11th to 20th	Day	17% 6% 19% 30% 16% 11%	559
	21st to end	Day	9% 5% 23% 30% 22% 11%	619
September	1st to 10th	Day	15% 9% 22% 25% 21% 8%	530
	11th to 20th	Day	13% 3 17% 33% 23% 11%	530
	21st to end	Day	26% 9% 25% 21% 15% 4	530
October	1st to 10th	Day	18% 8% 26% 26% 18% 5%	530
	11th to 20th	Day	22% 14% 32% 22% 8% 2	530
	21st to end	Day	28% 15% 31% 20% 5% 1	583
November	1st to 10th	Day	21% 17% 33% 18% 8% 3	451
	11th to 20th	Day	34% 15% 30% 14% 5% 1	272
	21st to end	Day	31% 17% 40% 10% 1	220
December	1st to 10th	Day	32% 25% 30% 8% 4 1	220
	11th to 20th	Day	34% 23% 31% 11% 1	220
	21st to end	Day	38% 22% 27% 11% 3	260
January	1st to 10th	Night	30% 20% 33% 15% 3	840
	11th to 20th	Night	34% 17% 30% 16% 3	840
	21st to end	Night	29% 19% 31% 17% 3	924
February	1st to 10th	Night	28% 18% 29% 23% 2	840
	11th to 20th	Night	31% 18% 35% 14% 1	823
	21st to end	Night	29% 18% 33% 17% 3	692
March	1st to 10th	Night	27% 17% 30% 23% 3	840
	11th to 20th	Night	27% 18% 27% 21% 6% 1	840
	21st to end	Night	25% 16% 32% 22% 4 1	924
April	1st to 10th	Night	26% 16% 31% 22% 5%	840
	11th to 20th	Night	21% 15% 32% 21% 9% 1	809
	21st to end	Night	21% 10% 33% 30% 7%	630
May	1st to 10th	Night	22% 9% 27% 30% 12% 1	630
	11th to 20th	Night	19% 9% 29% 31% 12% 1	621
	21st to end	Night	14% 4 24% 34% 21% 2	556
June	1st to 10th	Night	11% 5% 25% 40% 19% 1	420
	11th to 20th	Night	11% 7% 25% 38% 17% 1	420
	21st to end	Night	10% 3 28% 35% 22% 1	420
July	1st to 10th	Night	9% 5% 15% 39% 27% 5%	535
	11th to 20th	Night	9% 4 20% 34% 28% 4	612
	21st to end	Night	11% 3 17% 40% 28% 2	690
August	1st to 10th	Night	11% 2 17% 42% 27% 2	627
	11th to 20th	Night	11% 4 15% 39% 28% 4	624
	21st to end	Night	13% 3 17% 34% 28% 4	801
September	1st to 10th	Night	14% 3 18% 37% 25% 4	800
	11th to 20th	Night	11% 5% 15% 37% 28% 4	800
	21st to end	Night	19% 8% 24% 27% 20% 3	800
October	1st to 10th	Night	16% 8% 21% 32% 22% 2	800
	11th to 20th	Night	21% 9% 32% 26% 11% 1	800
	21st to end	Night	25% 11% 29% 27% 7% 1	880
November	1st to 10th	Night	17% 12% 30% 27% 13%	820
	11th to 20th	Night	27% 14% 28% 23% 6% 1	840
	21st to end	Night	29% 15% 30% 20% 5%	840
December	1st to 10th	Night	33% 15% 29% 20% 4	840
	11th to 20th	Night	28% 18% 30% 20% 3	840
	21st to end	Night	29% 16% 32% 22% 2	924

Page generated at 2026-08-27 04:07:14. Version ac07

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