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 2024-10-24.

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%	101180
	Night	5% 7% 2 6% 4 4 4 4 6% 7% 50%	97827
Transparency	Day	28% 7% 10% 23% 20% 12%	100939
	Night	31% 6% 11% 23% 19% 10%	97658
Seeing	Day	7% 8% 23% 34% 23% 6%	15400
	Night	8% 4 17% 43% 24% 3	25524

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 10% 8% 7% 8% 5% 7% 11% 34%	2730
	11th to 20th	Day	4 7% 3 8% 5% 6% 6% 6% 8% 9% 37%	2860
	21st to end	Day	5% 10% 4 11% 7% 6% 5% 3 5% 8% 36%	3146
February	1st to 10th	Day	3 7% 4 8% 5% 6% 5% 6% 9% 10% 35%	1710
	11th to 20th	Day	5% 10% 3 8% 5% 3 6% 4 5% 9% 41%	1665
	21st to end	Day	4 9% 4 8% 5% 5% 5% 4 6% 8% 42%	1550
March	1st to 10th	Day	4 12% 4 8% 5% 5% 5% 3 5% 7% 42%	3444
	11th to 20th	Day	4 8% 3 7% 5% 5% 4 4 5% 8% 47%	3490
	21st to end	Day	6% 15% 4 9% 5% 5% 5% 5% 7% 8% 31%	3825
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	7% 5% 2 5% 2 2 3 2 5% 5% 61%	1900
	11th to 20th	Day	5% 3 2 4 3 3 4 3 5% 7% 61%	1900
	21st to end	Day	5% 4 1 5% 3 3 3 4 5% 8% 58%	2010
November	1st to 10th	Day	5% 6% 2 5% 4 3 3 3 6% 8% 54%	1845
	11th to 20th	Day	3 6% 2 6% 4 4 3 3 6% 6% 57%	1520
	21st to end	Day	4 7% 2 8% 5% 3 4 3 5% 8% 50%	1520
December	1st to 10th	Day	5% 8% 3 9% 7% 5% 5% 3 6% 8% 42%	1520
	11th to 20th	Day	5% 9% 3 8% 6% 6% 6% 5% 8% 12% 32%	1926
	21st to end	Day	5% 10% 4 9% 6% 6% 6% 5% 7% 9% 34%	2794
January	1st to 10th	Night	2 7% 4 11% 6% 6% 5% 5% 6% 8% 40%	4253
	11th to 20th	Night	3 9% 2 9% 6% 5% 5% 4 6% 9% 42%	4110
	21st to end	Night	4 12% 4 8% 5% 5% 5% 3 5% 8% 41%	4521
February	1st to 10th	Night	3 8% 3 6% 5% 5% 4 5% 6% 9% 45%	2470
	11th to 20th	Night	3 10% 3 8% 5% 5% 5% 4 6% 7% 44%	2402
	21st to end	Night	3 11% 3 7% 5% 5% 4 4 5% 7% 46%	1899
March	1st to 10th	Night	4 13% 3 7% 4 4 4 4 6% 7% 45%	3430
	11th to 20th	Night	5% 10% 2 6% 5% 4 4 4 6% 7% 48%	3490
	21st to end	Night	9% 15% 4 9% 5% 5% 4 4 5% 6% 33%	3828
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	8% 5% 1 3 3 3 3 3 5% 6% 61%	2280
	11th to 20th	Night	5% 4 1 4 3 2 3 3 5% 6% 64%	2280
	21st to end	Night	5% 6% 2 5% 3 3 4 3 5% 7% 59%	2412
November	1st to 10th	Night	6% 6% 2 5% 4 3 3 3 5% 6% 57%	2220
	11th to 20th	Night	3 5% 2 5% 4 3 4 4 6% 7% 58%	2647
	21st to end	Night	4 8% 2 6% 4 4 4 4 4 6% 53%	2660
December	1st to 10th	Night	5% 7% 3 8% 5% 4 4 3 6% 8% 48%	2660
	11th to 20th	Night	6% 8% 3 8% 5% 6% 6% 5% 7% 10% 38%	3271
	21st to end	Night	5% 10% 4 9% 5% 5% 5% 4 6% 8% 40%	4873

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	41% 8% 19% 22% 9% 1	2731
	11th to 20th	Day	37% 11% 20% 25% 7%	2860
	21st to end	Day	43% 11% 22% 18% 5% 1	3146
February	1st to 10th	Day	38% 8% 20% 23% 10% 1	1710
	11th to 20th	Day	38% 7% 14% 27% 12% 2	1674
	21st to end	Day	37% 7% 13% 27% 14% 2	1550
March	1st to 10th	Day	35% 10% 11% 28% 15% 1	3444
	11th to 20th	Day	33% 6% 14% 33% 12% 1	3490
	21st to end	Day	42% 11% 10% 25% 10% 2	3825
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	24% 6% 8% 25% 28% 9%	1900
	11th to 20th	Day	22% 6% 6% 32% 28% 7%	1900
	21st to end	Day	23% 6% 13% 35% 20% 3	2010
November	1st to 10th	Day	27% 6% 10% 33% 21% 3	1845
	11th to 20th	Day	26% 5% 16% 35% 16% 1	1520
	21st to end	Day	31% 5% 16% 30% 17% 1	1520
December	1st to 10th	Day	38% 7% 22% 20% 12% 1	1520
	11th to 20th	Day	40% 8% 18% 26% 8%	1924
	21st to end	Day	42% 9% 18% 19% 11% 1	2794
January	1st to 10th	Night	40% 6% 17% 24% 11% 1	4253
	11th to 20th	Night	37% 10% 19% 26% 8% 1	4110
	21st to end	Night	41% 8% 21% 22% 7% 2	4521
February	1st to 10th	Night	34% 7% 20% 26% 12% 1	2470
	11th to 20th	Night	37% 6% 13% 24% 17% 2	2403
	21st to end	Night	36% 7% 14% 27% 15% 3	1899
March	1st to 10th	Night	35% 6% 9% 31% 18% 1	3430
	11th to 20th	Night	32% 7% 12% 33% 13% 3	3490
	21st to end	Night	46% 9% 11% 22% 10% 1	3828
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	23% 6% 6% 23% 29% 13%	2280
	11th to 20th	Night	21% 4 5% 27% 32% 10%	2280
	21st to end	Night	25% 5% 10% 32% 24% 4	2412
November	1st to 10th	Night	26% 5% 9% 30% 26% 3	2220
	11th to 20th	Night	24% 6% 13% 34% 21% 1	2647
	21st to end	Night	32% 4 11% 31% 19% 3	2660
December	1st to 10th	Night	34% 5% 21% 26% 13% 1	2660
	11th to 20th	Night	39% 9% 15% 26% 11%	3272
	21st to end	Night	40% 6% 16% 20% 16% 1	4873

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% 35% 26% 4	270
	11th to 20th	Day	8% 4 21% 45% 20% 2	270
	21st to end	Day	6% 4 18% 45% 24% 3	297
February	1st to 10th	Day	10% 3 29% 47% 10% 1	270
	11th to 20th	Day	10% 6% 30% 37% 17% 1	270
	21st to end	Day	9% 8% 30% 39% 11% 3	272
March	1st to 10th	Day	10% 8% 26% 33% 18% 4	460
	11th to 20th	Day	10% 12% 24% 34% 17% 3	460
	21st to end	Day	11% 13% 30% 34% 10% 2	506
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% 22% 40% 21% 4	306
November	1st to 10th	Day	9% 12% 23% 30% 21% 5%	270
	11th to 20th	Day	4 6% 29% 40% 16% 5%	270
	21st to end	Day	9% 4 20% 41% 23% 3	270
December	1st to 10th	Day	9% 4 26% 41% 16% 4	270
	11th to 20th	Day	5% 3 21% 53% 16% 1	270
	21st to end	Day	12% 9% 22% 38% 16% 3	297
January	1st to 10th	Night	8% 3 14% 47% 25% 3	851
	11th to 20th	Night	8% 3 18% 49% 19% 4	760
	21st to end	Night	11% 3 14% 52% 17% 3	836
February	1st to 10th	Night	7% 2 23% 52% 14% 2	760
	11th to 20th	Night	7% 4 23% 49% 16% 1	744
	21st to end	Night	7% 7% 26% 46% 13% 1	628
March	1st to 10th	Night	10% 5% 21% 46% 18% 1	760
	11th to 20th	Night	9% 5% 19% 45% 22%	760
	21st to end	Night	12% 7% 24% 41% 16% 1	836
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% 16% 42% 26% 3	804
November	1st to 10th	Night	9% 3 14% 45% 27% 2	740
	11th to 20th	Night	5% 4 21% 49% 19% 3	942
	21st to end	Night	8% 4 18% 43% 24% 3	950
December	1st to 10th	Night	7% 3 19% 53% 16% 1	950
	11th to 20th	Night	12% 3 16% 49% 20% 1	950
	21st to end	Night	10% 6% 18% 51% 13% 2	1045

Page generated at 2024-10-21 00:20:05. Version ac07

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