Phoenix Sky Sanctuary
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Phoenix Sky Sanctuary clear sky chart from 2005-11-06 to 2026-02-01.

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	8% 7% 2 3 2 2 3 2 4 5% 60%	136547
	Night	11% 9% 2 4 2 2 3 2 4 5% 56%	132874
Transparency	Day	29% 2 7% 21% 23% 18%	131410
	Night	34% 2 8% 22% 21% 13%	129001
Seeing	Day	17% 15% 30% 25% 11% 2	16478
	Night	17% 8% 21% 34% 18% 2	25729

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	15% 19% 4 5% 3 3 3 3 5% 6% 34%	3719
	11th to 20th	Day	15% 15% 2 4 2 2 2 1 2 3 52%	3932
	21st to end	Day	22% 9% 2 4 2 2 2 2 3 5% 47%	4609
February	1st to 10th	Day	17% 11% 3 5% 3 4 3 3 6% 7% 38%	1801
	11th to 20th	Day	14% 14% 2 4 3 3 3 3 5% 7% 43%	1780
	21st to end	Day	13% 15% 2 5% 3 3 3 3 5% 8% 40%	1650
March	1st to 10th	Day	14% 23% 6% 6% 3 2 2 2 3 5% 35%	4733
	11th to 20th	Day	12% 19% 4 4 3 3 3 2 4 5% 41%	5000
	21st to end	Day	14% 19% 3 6% 4 3 4 3 5% 7% 32%	5633
April	1st to 10th	Day	15% 13% 2 5% 4 4 4 2 4 7% 40%	2400
	11th to 20th	Day	13% 9% 2 4 3 3 3 3 5% 7% 48%	2369
	21st to end	Day	8% 7% 2 5% 4 3 3 3 6% 8% 52%	2407
May	1st to 10th	Day	7% 6% 2 3 3 2 3 2 5% 4 64%	6002
	11th to 20th	Day	5% 4 1 2 2 2 3 3 4 6% 67%	6277
	21st to end	Day	4 3 1 3 2 2 2 2 4 6% 71%	6902
June	1st to 10th	Day	9% 5% 1 4 3 4 4 4 5% 7% 55%	2800
	11th to 20th	Day	4 4 1 3 3 3 3 2 4 5% 69%	2800
	21st to end	Day	4 2 1 2 2 2 2 2 3 4 77%	2800
July	1st to 10th	Day	1 1 1 1 1 2 2 3 3 86%	6319
	11th to 20th	Day	1 1 1 1 1 2 1 2 4 85%	6320
	21st to end	Day	1 1 1 2 2 2 2 1 3 5% 80%	6582
August	1st to 10th	Day	2 1 1 2 2 2 2 3 5% 6% 76%	5777
	11th to 20th	Day	1 1 1 1 1 2 2 3 4 84%	5691
	21st to end	Day	2 2 1 2 2 2 2 2 3 5% 79%	5984
September	1st to 10th	Day	1 2 1 1 2 2 2 3 5% 81%	2400
	11th to 20th	Day	4 4 1 4 2 2 3 3 4 4 69%	2400
	21st to end	Day	4 2 1 3 2 2 2 1 4 5% 73%	2125
October	1st to 10th	Day	5% 2 1 2 2 2 2 2 2 4 76%	3280
	11th to 20th	Day	7% 4 2 3 3 2 3 3 4 7% 63%	3261
	21st to end	Day	10% 8% 2 5% 3 3 4 3 6% 6% 50%	3558
November	1st to 10th	Day	16% 9% 2 4 3 3 3 3 5% 7% 45%	1876
	11th to 20th	Day	16% 10% 2 5% 4 3 4 3 7% 8% 38%	1780
	21st to end	Day	12% 9% 2 5% 3 3 4 3 4 7% 50%	1680
December	1st to 10th	Day	11% 7% 2 4 3 2 3 3 5% 6% 54%	2700
	11th to 20th	Day	22% 18% 2 5% 3 4 5% 4 6% 7% 24%	3108
	21st to end	Day	25% 15% 3 6% 3 4 4 3 5% 6% 27%	4092
January	1st to 10th	Night	13% 16% 3 6% 3 4 5% 4 6% 7% 33%	6446
	11th to 20th	Night	12% 14% 3 5% 2 2 2 1 2 3 53%	6254
	21st to end	Night	18% 13% 2 5% 3 3 2 2 3 4 45%	6611
February	1st to 10th	Night	20% 9% 2 5% 3 3 3 2 4 8% 42%	2600
	11th to 20th	Night	14% 15% 3 4 3 4 4 3 4 6% 42%	2507
	21st to end	Night	13% 12% 3 4 3 2 3 3 5% 7% 45%	1980
March	1st to 10th	Night	13% 24% 5% 6% 2 3 3 2 3 6% 33%	5157
	11th to 20th	Night	13% 17% 5% 5% 2 2 2 2 3 5% 44%	5000
	21st to end	Night	14% 21% 3 6% 4 4 3 3 4 7% 33%	5341
April	1st to 10th	Night	14% 13% 2 4 3 4 4 2 4 6% 43%	2000
	11th to 20th	Night	11% 9% 2 4 4 2 2 3 5% 7% 51%	1979
	21st to end	Night	12% 6% 2 4 2 2 4 3 5% 8% 54%	1990
May	1st to 10th	Night	6% 4 2 4 2 2 2 1 3 5% 70%	3969
	11th to 20th	Night	6% 5% 1 3 3 2 2 3 5% 5% 67%	3616
	21st to end	Night	5% 3 1 2 2 2 2 2 3 6% 72%	3972
June	1st to 10th	Night	8% 5% 2 4 3 2 4 4 6% 7% 55%	1600
	11th to 20th	Night	5% 2 1 2 1 2 3 2 4 5% 74%	1600
	21st to end	Night	4 2 1 2 2 2 2 3 3 3 78%	1600
July	1st to 10th	Night	1 1 1 1 1 1 2 3 3 86%	3640
	11th to 20th	Night	1 1 1 2 1 2 2 1 2 2 85%	3640
	21st to end	Night	2 2 1 2 2 2 2 2 3 6% 77%	4279
August	1st to 10th	Night	2 1 1 2 1 2 2 2 3 6% 77%	4035
	11th to 20th	Night	2 1 1 1 1 1 1 2 3 85%	4162
	21st to end	Night	4 2 1 2 2 2 2 2 2 4 79%	5015
September	1st to 10th	Night	2 1 1 2 1 1 1 1 2 5% 82%	2000
	11th to 20th	Night	4 4 1 2 2 2 2 2 3 5% 72%	2000
	21st to end	Night	4 2 1 3 2 2 3 2 4 5% 73%	2270
October	1st to 10th	Night	4 3 1 3 2 2 2 1 2 3 77%	3920
	11th to 20th	Night	7% 4 1 3 2 3 3 2 4 5% 66%	3897
	21st to end	Night	9% 5% 1 4 2 2 3 3 6% 8% 58%	4253
November	1st to 10th	Night	15% 9% 2 4 3 3 3 3 5% 7% 45%	2640
	11th to 20th	Night	16% 8% 2 5% 4 4 4 4 6% 8% 40%	2839
	21st to end	Night	13% 9% 2 4 3 3 3 3 5% 6% 49%	2940
December	1st to 10th	Night	12% 5% 1 3 2 2 2 2 4 6% 60%	4700
	11th to 20th	Night	21% 20% 3 6% 4 4 4 3 5% 6% 24%	5316
	21st to end	Night	29% 14% 3 4 3 3 3 2 3 5% 32%	7106

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	52% 4 11% 20% 13% 1	3719
	11th to 20th	Day	42% 2 7% 21% 20% 8%	3932
	21st to end	Day	44% 2 9% 11% 21% 14%	4609
February	1st to 10th	Day	46% 3 12% 19% 14% 5%	1801
	11th to 20th	Day	43% 4 9% 24% 16% 3	1789
	21st to end	Day	45% 4 11% 21% 14% 5%	1650
March	1st to 10th	Day	57% 1 5% 18% 14% 4	4733
	11th to 20th	Day	48% 2 13% 17% 20% 1	5000
	21st to end	Day	54% 3 11% 24% 7% 1	5633
April	1st to 10th	Day	47% 2 12% 21% 15% 3	2400
	11th to 20th	Day	37% 3 11% 25% 17% 7%	2372
	21st to end	Day	32% 4 14% 28% 20% 3	2407
May	1st to 10th	Day	25% 2 5% 25% 33% 10%	6002
	11th to 20th	Day	20% 2 6% 25% 34% 14%	6280
	21st to end	Day	17% 2 8% 36% 31% 5%	6904
June	1st to 10th	Day	29% 3 11% 24% 27% 6%	2800
	11th to 20th	Day	19% 2 7% 24% 34% 13%	2800
	21st to end	Day	14% 1 4 20% 34% 28%	2800
July	1st to 10th	Day	7% 1 2 13% 23% 54%	6251
	11th to 20th	Day	8% 1 2 8% 22% 59%	6245
	21st to end	Day	11% 1 4 21% 28% 35%	6392
August	1st to 10th	Day	14% 1 2 11% 23% 48%	4206
	11th to 20th	Day	7% 1 2 17% 42% 31%	4114
	21st to end	Day	11% 1 3 21% 37% 28%	4311
September	1st to 10th	Day	9% 2 2 14% 27% 46%	2400
	11th to 20th	Day	19% 2 6% 20% 33% 19%	2400
	21st to end	Day	16% 3 6% 22% 30% 23%	2125
October	1st to 10th	Day	16% 1 5% 18% 23% 37%	3280
	11th to 20th	Day	24% 2 6% 32% 27% 10%	3261
	21st to end	Day	35% 2 9% 25% 20% 9%	3558
November	1st to 10th	Day	40% 4 9% 23% 18% 6%	1876
	11th to 20th	Day	44% 5% 13% 19% 14% 5%	1780
	21st to end	Day	36% 4 11% 22% 18% 9%	1680
December	1st to 10th	Day	32% 3 6% 20% 30% 9%	2700
	11th to 20th	Day	61% 2 13% 15% 8% 2	3108
	21st to end	Day	59% 3 9% 18% 9% 1	4092
January	1st to 10th	Night	52% 4 11% 20% 11% 1	6446
	11th to 20th	Night	40% 2 5% 19% 24% 9%	6254
	21st to end	Night	47% 1 6% 11% 20% 15%	6611
February	1st to 10th	Night	44% 4 10% 22% 14% 5%	2600
	11th to 20th	Night	45% 4 10% 21% 17% 4	2509
	21st to end	Night	41% 4 13% 20% 17% 5%	1980
March	1st to 10th	Night	56% 1 9% 18% 12% 4	5157
	11th to 20th	Night	46% 2 10% 24% 18% 1	5000
	21st to end	Night	55% 3 14% 20% 7% 1	5341
April	1st to 10th	Night	43% 3 15% 24% 13% 2	2000
	11th to 20th	Night	34% 5% 15% 24% 17% 6%	1979
	21st to end	Night	30% 5% 17% 30% 16% 2	1990
May	1st to 10th	Night	22% 1 6% 33% 30% 8%	3966
	11th to 20th	Night	22% 2 9% 29% 28% 10%	3616
	21st to end	Night	18% 2 13% 41% 25% 2	3972
June	1st to 10th	Night	29% 5% 12% 30% 21% 3	1600
	11th to 20th	Night	15% 3 10% 28% 33% 11%	1600
	21st to end	Night	13% 2 6% 22% 38% 19%	1600
July	1st to 10th	Night	7% 1 2 16% 25% 48%	3600
	11th to 20th	Night	9% 1 1 10% 28% 52%	3592
	21st to end	Night	13% 1 9% 24% 23% 30%	4157
August	1st to 10th	Night	13% 1 3 13% 26% 43%	2929
	11th to 20th	Night	8% 1 3 22% 43% 25%	3013
	21st to end	Night	12% 1 3 26% 38% 21%	3608
September	1st to 10th	Night	10% 1 2 13% 30% 44%	2000
	11th to 20th	Night	16% 3 6% 23% 31% 20%	2000
	21st to end	Night	16% 3 6% 23% 26% 26%	2270
October	1st to 10th	Night	17% 1 4 13% 31% 34%	3920
	11th to 20th	Night	23% 1 8% 35% 25% 8%	3897
	21st to end	Night	27% 2 9% 31% 23% 9%	4253
November	1st to 10th	Night	40% 5% 12% 20% 16% 7%	2640
	11th to 20th	Night	43% 6% 12% 21% 15% 4	2839
	21st to end	Night	37% 4 12% 20% 19% 8%	2940
December	1st to 10th	Night	28% 2 7% 22% 31% 11%	4700
	11th to 20th	Night	63% 2 8% 16% 9% 2	5316
	21st to end	Night	59% 2 11% 16% 12% 1	7106

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	44% 17% 22% 13% 4	220
	11th to 20th	Day	31% 13% 28% 20% 7% 1	315
	21st to end	Day	28% 15% 25% 22% 10% 1	473
February	1st to 10th	Day	29% 18% 27% 22% 4	401
	11th to 20th	Day	29% 21% 29% 17% 3	408
	21st to end	Day	24% 19% 26% 25% 6%	414
March	1st to 10th	Day	39% 20% 23% 14% 4	500
	11th to 20th	Day	33% 18% 26% 16% 7% 1	500
	21st to end	Day	33% 22% 22% 17% 5%	550
April	1st to 10th	Day	30% 18% 29% 19% 4 1	500
	11th to 20th	Day	25% 22% 27% 18% 7% 1	492
	21st to end	Day	17% 19% 31% 21% 10% 1	500
May	1st to 10th	Day	16% 24% 33% 17% 7% 2	503
	11th to 20th	Day	21% 16% 31% 21% 10% 2	528
	21st to end	Day	15% 15% 30% 26% 14% 1	573
June	1st to 10th	Day	13% 16% 31% 25% 12% 3	530
	11th to 20th	Day	13% 21% 31% 25% 9% 1	530
	21st to end	Day	5% 13% 32% 32% 16% 2	530
July	1st to 10th	Day	4 10% 38% 31% 13% 3	526
	11th to 20th	Day	1 8% 35% 36% 17% 3	524
	21st to end	Day	2 5% 34% 36% 18% 6%	575
August	1st to 10th	Day	2 6% 36% 31% 20% 5%	527
	11th to 20th	Day	3 9% 29% 33% 18% 7%	517
	21st to end	Day	4 7% 38% 27% 20% 4	583
September	1st to 10th	Day	3 11% 32% 35% 17% 2	530
	11th to 20th	Day	8% 12% 31% 30% 17% 2	530
	21st to end	Day	8% 15% 31% 31% 15% 1	530
October	1st to 10th	Day	12% 14% 30% 26% 15% 2	530
	11th to 20th	Day	14% 13% 27% 32% 13% 1	530
	21st to end	Day	17% 18% 25% 26% 12% 1	583
November	1st to 10th	Day	28% 12% 23% 24% 12% 1	352
	11th to 20th	Day	23% 12% 27% 26% 11% 1	272
	21st to end	Day	19% 10% 30% 32% 9%	220
December	1st to 10th	Day	25% 11% 28% 23% 12% 1	220
	11th to 20th	Day	29% 11% 27% 22% 10%	220
	21st to end	Day	33% 15% 29% 17% 7%	242
January	1st to 10th	Night	27% 9% 24% 27% 11% 2	840
	11th to 20th	Night	24% 11% 25% 28% 12% 1	840
	21st to end	Night	23% 10% 25% 27% 13% 2	924
February	1st to 10th	Night	26% 8% 25% 31% 10% 1	800
	11th to 20th	Night	25% 11% 22% 30% 11% 1	784
	21st to end	Night	21% 14% 24% 33% 7% 1	660
March	1st to 10th	Night	32% 14% 20% 23% 9% 3	800
	11th to 20th	Night	25% 11% 20% 26% 17% 1	800
	21st to end	Night	30% 13% 21% 24% 10% 1	880
April	1st to 10th	Night	22% 13% 26% 29% 9% 1	800
	11th to 20th	Night	20% 12% 27% 27% 12% 3	791
	21st to end	Night	15% 12% 25% 32% 15% 2	790
May	1st to 10th	Night	12% 15% 29% 28% 15% 1	547
	11th to 20th	Night	14% 9% 23% 36% 16% 2	394
	21st to end	Night	14% 12% 19% 34% 20% 1	433
June	1st to 10th	Night	10% 8% 21% 39% 21% 2	400
	11th to 20th	Night	6% 10% 21% 48% 15% 1	400
	21st to end	Night	5% 3 17% 50% 25% 1	400
July	1st to 10th	Night	1 2 15% 47% 33% 1	390
	11th to 20th	Night	1 1 12% 53% 32%	388
	21st to end	Night	3 1 6% 46% 42% 3	568
August	1st to 10th	Night	3 1 8% 47% 38% 4	597
	11th to 20th	Night	3 2 12% 41% 38% 4	639
	21st to end	Night	3 2 16% 45% 31% 3	880
September	1st to 10th	Night	3 3 18% 45% 28% 3	800
	11th to 20th	Night	6% 5% 14% 36% 34% 6%	800
	21st to end	Night	7% 6% 20% 37% 26% 6%	800
October	1st to 10th	Night	10% 9% 18% 37% 24% 3	800
	11th to 20th	Night	11% 6% 19% 40% 21% 3	800
	21st to end	Night	16% 7% 20% 34% 19% 4	880
November	1st to 10th	Night	21% 9% 15% 35% 17% 3	820
	11th to 20th	Night	20% 9% 26% 32% 12% 2	840
	21st to end	Night	18% 10% 28% 29% 14% 1	840
December	1st to 10th	Night	23% 10% 23% 33% 10% 1	840
	11th to 20th	Night	32% 8% 21% 28% 9% 1	840
	21st to end	Night	31% 11% 25% 27% 7%	924

Page generated at 2026-01-28 22:21:41. Version ac07

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