Canyon Visitor Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Canyon Visitor Center clear sky chart from 2005-11-06 to 2025-03-27.

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	4 6% 2 6% 4 4 5% 4 6% 8% 51%	113132
	Night	4 7% 2 6% 4 4 4 4 6% 7% 51%	115064
Transparency	Day	27% 7% 10% 24% 21% 12%	112891
	Night	30% 5% 11% 25% 20% 9%	114895
Seeing	Day	7% 8% 23% 34% 23% 6%	15892
	Night	8% 4 18% 43% 24% 3	26197

By Month

Percentage Cloud Cover SW (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	2 6% 3 9% 7% 6% 6% 4 7% 11% 39%	3914
	11th to 20th	Day	3 5% 3 6% 5% 6% 8% 6% 9% 9% 41%	4100
	21st to end	Day	3 9% 4 9% 6% 6% 6% 5% 6% 9% 37%	4510
February	1st to 10th	Day	3 7% 4 8% 5% 6% 5% 6% 9% 11% 36%	1800
	11th to 20th	Day	5% 11% 3 8% 5% 4 6% 4 6% 8% 40%	1755
	21st to end	Day	4 9% 4 7% 5% 5% 5% 4 6% 9% 43%	1630
March	1st to 10th	Day	4 12% 4 8% 5% 5% 5% 3 5% 7% 42%	3554
	11th to 20th	Day	4 8% 3 7% 5% 5% 4 5% 5% 8% 46%	3600
	21st to end	Day	6% 14% 4 9% 5% 5% 5% 5% 7% 8% 32%	3892
April	1st to 10th	Day	4 9% 2 6% 5% 4 5% 4 6% 8% 45%	2241
	11th to 20th	Day	4 9% 2 7% 5% 4 5% 5% 7% 8% 45%	2251
	21st to end	Day	5% 7% 3 6% 5% 5% 6% 4 6% 7% 46%	2399
May	1st to 10th	Day	7% 9% 3 7% 5% 5% 6% 5% 7% 8% 38%	4110
	11th to 20th	Day	3 4 2 4 5% 5% 5% 4 7% 10% 49%	4129
	21st to end	Day	6% 5% 2 5% 3 4 4 4 6% 7% 53%	4825
June	1st to 10th	Day	3 4 2 3 4 4 3 4 6% 10% 57%	2660
	11th to 20th	Day	3 3 1 4 3 3 4 3 6% 8% 62%	2660
	21st to end	Day	2 2 1 3 2 3 4 3 5% 7% 67%	2660
July	1st to 10th	Day	2 1 1 2 2 2 3 3 5% 6% 73%	4430
	11th to 20th	Day	2 2 1 4 4 5% 5% 5% 9% 12% 50%	4128
	21st to end	Day	2 3 1 3 3 4 5% 5% 7% 9% 57%	4454
August	1st to 10th	Day	3 3 1 5% 4 4 6% 5% 7% 9% 55%	4092
	11th to 20th	Day	3 3 1 4 3 4 5% 4 7% 9% 59%	4028
	21st to end	Day	4 2 1 4 4 3 4 4 6% 7% 60%	4245
September	1st to 10th	Day	4 2 1 2 2 3 3 3 5% 8% 67%	2280
	11th to 20th	Day	3 3 1 4 4 3 3 3 5% 7% 64%	2176
	21st to end	Day	5% 3 1 4 2 2 2 2 3 5% 70%	2057
October	1st to 10th	Day	4 3 1 3 1 2 2 2 4 4 74%	3170
	11th to 20th	Day	6% 4 2 4 3 3 4 3 6% 8% 56%	3150
	21st to end	Day	6% 4 1 4 3 3 3 3 5% 6% 61%	3438
November	1st to 10th	Day	5% 6% 2 6% 4 3 3 3 6% 8% 53%	1944
	11th to 20th	Day	3 6% 2 6% 4 4 3 3 6% 6% 58%	1600
	21st to end	Day	4 7% 2 7% 5% 4 4 3 5% 8% 51%	1600
December	1st to 10th	Day	3 5% 2 6% 4 3 3 2 4 7% 61%	2620
	11th to 20th	Day	3 6% 2 6% 4 5% 5% 5% 7% 12% 44%	3026
	21st to end	Day	6% 10% 4 9% 5% 6% 6% 5% 7% 8% 34%	4004
January	1st to 10th	Night	2 6% 3 9% 6% 6% 5% 5% 7% 9% 42%	6079
	11th to 20th	Night	2 8% 2 8% 6% 5% 6% 5% 8% 9% 42%	5880
	21st to end	Night	3 10% 4 8% 4 4 4 4 6% 7% 46%	6468
February	1st to 10th	Night	4 8% 3 6% 5% 5% 4 5% 6% 10% 45%	2600
	11th to 20th	Night	4 10% 3 8% 5% 5% 5% 4 6% 8% 43%	2532
	21st to end	Night	3 11% 3 7% 5% 5% 4 3 5% 7% 47%	1995
March	1st to 10th	Night	4 13% 3 7% 4 4 4 4 6% 6% 45%	3540
	11th to 20th	Night	5% 9% 2 6% 5% 4 4 4 6% 7% 48%	3600
	21st to end	Night	9% 15% 4 9% 5% 5% 4 4 5% 6% 34%	3899
April	1st to 10th	Night	6% 10% 3 6% 4 4 4 3 6% 6% 47%	1938
	11th to 20th	Night	8% 9% 3 8% 5% 5% 5% 3 7% 7% 41%	1877
	21st to end	Night	8% 8% 3 7% 4 5% 4 4 7% 6% 44%	1778
May	1st to 10th	Night	8% 12% 2 7% 4 5% 5% 4 5% 6% 43%	2860
	11th to 20th	Night	6% 5% 2 6% 4 4 4 4 6% 7% 52%	2774
	21st to end	Night	8% 5% 2 5% 3 4 4 4 6% 6% 51%	2762
June	1st to 10th	Night	4 4 2 5% 4 5% 5% 5% 6% 8% 52%	1520
	11th to 20th	Night	7% 5% 2 6% 3 3 4 3 5% 6% 57%	1520
	21st to end	Night	3 3 1 4 4 4 4 3 6% 8% 59%	1520
July	1st to 10th	Night	3 2 1 3 3 3 3 4 5% 6% 65%	2540
	11th to 20th	Night	3 3 1 6% 4 5% 5% 5% 8% 12% 46%	2823
	21st to end	Night	1 2 1 5% 4 4 5% 4 8% 9% 57%	3109
August	1st to 10th	Night	3 3 1 4 3 4 6% 4 8% 9% 53%	2847
	11th to 20th	Night	3 3 3 5% 5% 5% 6% 5% 6% 8% 51%	2811
	21st to end	Night	4 3 1 4 3 4 4 4 7% 7% 59%	3420
September	1st to 10th	Night	4 4 1 4 2 3 3 3 5% 6% 65%	1900
	11th to 20th	Night	5% 3 2 5% 3 3 3 3 6% 6% 60%	2000
	21st to end	Night	5% 3 1 4 2 2 2 2 4 5% 70%	2122
October	1st to 10th	Night	5% 3 1 2 2 2 2 2 3 4 73%	3800
	11th to 20th	Night	6% 3 1 4 3 3 4 3 5% 7% 59%	3778
	21st to end	Night	6% 6% 2 5% 3 3 3 2 4 7% 59%	4120
November	1st to 10th	Night	6% 6% 2 5% 4 4 3 3 5% 6% 56%	2340
	11th to 20th	Night	3 5% 2 5% 4 3 4 3 6% 7% 58%	2787
	21st to end	Night	4 8% 2 6% 4 4 4 4 4 6% 53%	2800
December	1st to 10th	Night	3 5% 2 5% 3 3 3 2 4 6% 65%	4570
	11th to 20th	Night	4 6% 3 7% 4 5% 6% 5% 6% 8% 46%	5181
	21st to end	Night	5% 9% 3 9% 5% 5% 6% 4 6% 8% 39%	6974

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	37% 6% 21% 22% 13% 1	3915
	11th to 20th	Day	33% 10% 14% 26% 13% 4	4100
	21st to end	Day	39% 11% 16% 21% 12% 1	4510
February	1st to 10th	Day	38% 7% 19% 22% 11% 2	1800
	11th to 20th	Day	40% 7% 13% 27% 12% 2	1764
	21st to end	Day	36% 7% 13% 27% 14% 3	1630
March	1st to 10th	Day	35% 10% 10% 28% 15% 2	3554
	11th to 20th	Day	34% 6% 14% 32% 13% 1	3600
	21st to end	Day	42% 11% 10% 25% 10% 2	3892
April	1st to 10th	Day	32% 9% 11% 22% 19% 7%	2241
	11th to 20th	Day	34% 7% 10% 24% 21% 4	2254
	21st to end	Day	33% 9% 7% 30% 20% 2	2399
May	1st to 10th	Day	35% 11% 7% 18% 22% 6%	4110
	11th to 20th	Day	21% 11% 8% 33% 21% 5%	4132
	21st to end	Day	25% 7% 6% 24% 32% 5%	4825
June	1st to 10th	Day	20% 7% 7% 23% 28% 14%	2660
	11th to 20th	Day	18% 6% 4 15% 30% 27%	2660
	21st to end	Day	15% 5% 3 13% 31% 34%	2660
July	1st to 10th	Day	12% 5% 4 9% 17% 53%	4361
	11th to 20th	Day	22% 7% 5% 14% 28% 25%	4058
	21st to end	Day	20% 6% 6% 15% 20% 33%	4314
August	1st to 10th	Day	24% 5% 8% 26% 18% 19%	4078
	11th to 20th	Day	22% 4 7% 23% 26% 17%	4067
	21st to end	Day	22% 4 7% 19% 26% 23%	4244
September	1st to 10th	Day	17% 4 5% 18% 29% 28%	2280
	11th to 20th	Day	19% 5% 6% 22% 29% 18%	2176
	21st to end	Day	18% 3 3 23% 40% 13%	2057
October	1st to 10th	Day	15% 4 5% 17% 33% 25%	3170
	11th to 20th	Day	26% 4 6% 31% 30% 4	3150
	21st to end	Day	25% 4 10% 36% 22% 3	3438
November	1st to 10th	Day	28% 5% 10% 33% 21% 2	1944
	11th to 20th	Day	26% 5% 16% 36% 17% 1	1600
	21st to end	Day	31% 5% 16% 31% 17% 1	1600
December	1st to 10th	Day	24% 4 13% 46% 12%	2620
	11th to 20th	Day	31% 5% 25% 28% 10%	3024
	21st to end	Day	45% 6% 17% 20% 11% 1	4004
January	1st to 10th	Night	38% 5% 18% 25% 12% 3	6079
	11th to 20th	Night	35% 8% 14% 29% 14% 1	5880
	21st to end	Night	35% 6% 16% 22% 19% 2	6468
February	1st to 10th	Night	34% 7% 19% 26% 12% 2	2600
	11th to 20th	Night	38% 6% 13% 24% 17% 2	2533
	21st to end	Night	35% 6% 13% 26% 16% 4	1995
March	1st to 10th	Night	35% 6% 9% 31% 18% 2	3540
	11th to 20th	Night	32% 7% 12% 33% 13% 3	3600
	21st to end	Night	45% 9% 12% 22% 10% 1	3899
April	1st to 10th	Night	36% 6% 9% 23% 19% 7%	1938
	11th to 20th	Night	39% 7% 8% 22% 20% 4	1877
	21st to end	Night	35% 7% 9% 26% 20% 3	1778
May	1st to 10th	Night	38% 7% 8% 17% 24% 6%	2860
	11th to 20th	Night	27% 7% 9% 29% 21% 7%	2775
	21st to end	Night	29% 7% 6% 24% 30% 4	2762
June	1st to 10th	Night	25% 7% 8% 20% 25% 16%	1520
	11th to 20th	Night	26% 6% 5% 12% 23% 29%	1520
	21st to end	Night	20% 6% 3 11% 26% 34%	1520
July	1st to 10th	Night	18% 4 4 9% 17% 48%	2500
	11th to 20th	Night	27% 6% 5% 15% 26% 22%	2771
	21st to end	Night	20% 5% 7% 15% 22% 31%	3011
August	1st to 10th	Night	24% 5% 8% 25% 17% 22%	2838
	11th to 20th	Night	31% 4 10% 16% 24% 16%	2838
	21st to end	Night	23% 5% 8% 16% 22% 25%	3420
September	1st to 10th	Night	20% 4 4 17% 26% 28%	1900
	11th to 20th	Night	23% 6% 7% 19% 24% 22%	2000
	21st to end	Night	18% 3 4 18% 38% 19%	2122
October	1st to 10th	Night	16% 4 4 15% 36% 26%	3800
	11th to 20th	Night	25% 4 5% 27% 32% 8%	3778
	21st to end	Night	26% 4 7% 35% 26% 3	4120
November	1st to 10th	Night	27% 5% 8% 30% 26% 3	2340
	11th to 20th	Night	24% 6% 12% 35% 22% 2	2787
	21st to end	Night	32% 4 11% 32% 19% 2	2800
December	1st to 10th	Night	23% 3 13% 44% 17% 1	4570
	11th to 20th	Night	34% 6% 17% 35% 8%	5182
	21st to end	Night	41% 6% 15% 22% 15% 1	6974

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	10% 3 22% 36% 25% 4	300
	11th to 20th	Day	7% 4 20% 45% 20% 3	300
	21st to end	Day	6% 3 17% 47% 23% 3	330
February	1st to 10th	Day	11% 3 30% 45% 10% 1	300
	11th to 20th	Day	11% 5% 27% 39% 16% 1	300
	21st to end	Day	8% 7% 28% 38% 14% 4	299
March	1st to 10th	Day	9% 8% 26% 34% 19% 4	500
	11th to 20th	Day	10% 12% 26% 33% 16% 3	500
	21st to end	Day	11% 13% 30% 34% 10% 2	531
April	1st to 10th	Day	9% 18% 28% 24% 17% 4	460
	11th to 20th	Day	13% 19% 31% 25% 11% 1	452
	21st to end	Day	8% 18% 30% 21% 19% 3	460
May	1st to 10th	Day	10% 15% 33% 27% 14% 1	463
	11th to 20th	Day	9% 11% 25% 27% 23% 5%	520
	21st to end	Day	10% 10% 21% 29% 25% 5%	734
June	1st to 10th	Day	4 8% 22% 33% 27% 6%	680
	11th to 20th	Day	6% 10% 25% 34% 21% 3	680
	21st to end	Day	3 7% 22% 35% 27% 5%	680
July	1st to 10th	Day	3 3 18% 35% 34% 8%	671
	11th to 20th	Day	3 3 18% 38% 30% 8%	501
	21st to end	Day	5% 2 12% 37% 34% 10%	531
August	1st to 10th	Day	6% 2 19% 37% 29% 7%	487
	11th to 20th	Day	5% 3 14% 41% 29% 8%	477
	21st to end	Day	4 2 18% 32% 35% 9%	539
September	1st to 10th	Day	6% 5% 16% 28% 32% 14%	490
	11th to 20th	Day	4 7% 25% 32% 23% 9%	490
	21st to end	Day	7% 8% 18% 27% 28% 12%	457
October	1st to 10th	Day	8% 8% 19% 22% 24% 18%	300
	11th to 20th	Day	7% 8% 22% 29% 27% 6%	300
	21st to end	Day	8% 7% 21% 39% 21% 4	330
November	1st to 10th	Day	9% 12% 23% 29% 22% 4	300
	11th to 20th	Day	4 5% 28% 41% 16% 5%	300
	21st to end	Day	10% 3 19% 40% 25% 3	300
December	1st to 10th	Day	8% 4 24% 40% 19% 5%	300
	11th to 20th	Day	5% 3 21% 52% 17% 2	300
	21st to end	Day	12% 8% 22% 39% 16% 3	330
January	1st to 10th	Night	8% 3 16% 46% 24% 3	895
	11th to 20th	Night	8% 2 18% 49% 19% 4	800
	21st to end	Night	11% 3 15% 52% 17% 3	880
February	1st to 10th	Night	8% 2 25% 50% 13% 2	800
	11th to 20th	Night	7% 4 24% 48% 16% 1	784
	21st to end	Night	7% 6% 27% 47% 13% 1	660
March	1st to 10th	Night	10% 5% 20% 46% 18% 1	800
	11th to 20th	Night	9% 5% 20% 45% 21%	800
	21st to end	Night	11% 7% 24% 40% 16% 1	862
April	1st to 10th	Night	14% 7% 23% 41% 14% 1	608
	11th to 20th	Night	12% 10% 28% 33% 15% 2	563
	21st to end	Night	11% 9% 24% 33% 20% 4	570
May	1st to 10th	Night	12% 9% 26% 34% 16% 3	570
	11th to 20th	Night	8% 5% 19% 38% 25% 4	561
	21st to end	Night	9% 8% 19% 38% 23% 3	617
June	1st to 10th	Night	6% 6% 15% 44% 28% 2	570
	11th to 20th	Night	9% 5% 22% 44% 18% 2	570
	21st to end	Night	4 3 14% 46% 31% 3	570
July	1st to 10th	Night	5% 1 13% 35% 42% 4	555
	11th to 20th	Night	4 1 9% 37% 45% 5%	552
	21st to end	Night	2 1 7% 33% 53% 5%	624
August	1st to 10th	Night	5% 2 8% 42% 39% 4	567
	11th to 20th	Night	3 2 10% 44% 37% 4	564
	21st to end	Night	6% 2 8% 38% 41% 6%	627
September	1st to 10th	Night	6% 2 11% 37% 39% 6%	570
	11th to 20th	Night	6% 3 15% 39% 33% 6%	670
	21st to end	Night	6% 3 14% 34% 34% 9%	760
October	1st to 10th	Night	10% 3 12% 44% 27% 4	760
	11th to 20th	Night	7% 3 17% 43% 26% 4	760
	21st to end	Night	8% 5% 17% 42% 26% 3	836
November	1st to 10th	Night	9% 4 14% 45% 26% 2	780
	11th to 20th	Night	5% 4 22% 49% 18% 3	992
	21st to end	Night	8% 4 18% 44% 24% 3	1000
December	1st to 10th	Night	7% 3 18% 53% 17% 1	1000
	11th to 20th	Night	11% 3 17% 49% 19% 1	1000
	21st to end	Night	11% 5% 18% 51% 13% 2	1100

Page generated at 2025-03-24 07:04:33. Version ac07

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