Pinhead Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pinhead Observatory clear sky chart from 2005-11-06 to 2026-04-17.

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	2 2 1 3 2 2 2 2 4 5% 75%	140277
	Night	1 3 1 3 2 2 3 2 4 5% 72%	139434
Transparency	Day	14% 3 5% 14% 29% 35%	135364
	Night	15% 3 5% 14% 28% 35%	135320
Seeing	Day	7% 14% 32% 31% 13% 3	17481
	Night	4 6% 21% 36% 27% 5%	27370

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	3 3 2 5% 4 3 3 2 4 6% 65%	4722
	11th to 20th	Day	3 2 1 3 2 2 2 2 4 7% 73%	5160
	21st to end	Day	4 5% 2 6% 4 3 4 3 5% 8% 56%	6472
February	1st to 10th	Day	4 6% 2 5% 3 3 3 3 5% 5% 61%	2100
	11th to 20th	Day	4 4 2 5% 4 3 4 4 5% 8% 58%	2050
	21st to end	Day	3 6% 3 6% 4 3 3 2 4 6% 60%	1730
March	1st to 10th	Day	2 7% 3 7% 4 3 4 3 5% 8% 54%	4618
	11th to 20th	Day	2 5% 2 5% 4 4 4 3 6% 7% 58%	4802
	21st to end	Day	2 5% 2 3 4 4 4 4 6% 9% 58%	6101
April	1st to 10th	Day	3 5% 1 4 3 3 3 3 4 7% 63%	2520
	11th to 20th	Day	2 3 1 4 3 2 2 3 4 6% 71%	2442
	21st to end	Day	2 2 1 2 2 2 3 3 6% 7% 72%	2400
May	1st to 10th	Day	1 1 1 3 2 2 2 2 3 5% 78%	5607
	11th to 20th	Day	1 1 1 1 2 2 2 2 4 5% 80%	5841
	21st to end	Day	1 1 1 1 1 1 1 1 2 5% 84%	6423
June	1st to 10th	Day	1 2 1 2 2 2 2 2 4 5% 78%	2656
	11th to 20th	Day	1 1 1 1 1 2 4 88%	2800
	21st to end	Day	1 1 1 1 1 2 1 1 2 2 88%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 93%	6319
	11th to 20th	Day	1 1 1 1 1 1 1 1 2 3 87%	6320
	21st to end	Day	1 1 1 1 1 1 1 2 3 88%	6019
August	1st to 10th	Day	1 1 1 1 2 1 3 4 86%	5346
	11th to 20th	Day	1 1 1 1 2 94%	5364
	21st to end	Day	1 1 1 1 1 1 2 4 86%	5984
September	1st to 10th	Day	2 1 2 1 1 2 2 3 4 83%	2400
	11th to 20th	Day	1 1 1 1 2 1 2 3 88%	2257
	21st to end	Day	1 2 2 1 2 2 2 4 84%	2200
October	1st to 10th	Day	1 1 1 1 1 1 2 2 3 4 83%	3600
	11th to 20th	Day	1 1 1 1 1 2 2 3 5% 82%	3344
	21st to end	Day	1 1 1 3 2 3 3 3 4 5% 74%	3473
November	1st to 10th	Day	1 3 1 3 3 2 3 2 4 5% 73%	1854
	11th to 20th	Day	2 3 2 4 3 4 3 3 4 6% 67%	1890
	21st to end	Day	3 4 2 5% 4 4 3 3 5% 7% 60%	1890
December	1st to 10th	Day	2 2 1 4 3 4 4 3 6% 7% 65%	3040
	11th to 20th	Day	3 5% 2 5% 4 4 5% 5% 7% 7% 54%	3499
	21st to end	Day	5% 6% 3 7% 4 5% 4 3 5% 9% 49%	4234
January	1st to 10th	Night	3 4 2 4 3 3 3 3 4 6% 64%	8172
	11th to 20th	Night	1 3 1 3 2 2 2 2 4 6% 73%	7804
	21st to end	Night	3 6% 2 5% 4 4 4 4 6% 6% 57%	7768
February	1st to 10th	Night	3 6% 3 5% 4 3 3 3 5% 6% 59%	2520
	11th to 20th	Night	4 4 2 7% 3 3 4 3 4 6% 59%	2458
	21st to end	Night	3 5% 2 6% 4 3 4 4 5% 6% 58%	2076
March	1st to 10th	Night	3 8% 3 6% 3 3 4 4 5% 7% 54%	5496
	11th to 20th	Night	2 5% 2 6% 4 3 4 4 5% 7% 59%	5413
	21st to end	Night	1 4 1 7% 3 4 4 4 6% 7% 59%	5116
April	1st to 10th	Night	2 5% 2 5% 3 3 3 3 4 6% 65%	2100
	11th to 20th	Night	2 3 1 4 3 3 3 2 4 5% 71%	2039
	21st to end	Night	2 2 1 3 2 3 3 3 4 7% 71%	2000
May	1st to 10th	Night	1 2 1 2 2 2 3 2 4 5% 76%	4381
	11th to 20th	Night	1 1 1 2 2 2 4 4 83%	4074
	21st to end	Night	1 1 1 1 1 1 2 5% 87%	4474
June	1st to 10th	Night	1 1 2 2 2 3 2 4 6% 79%	1737
	11th to 20th	Night	1 1 1 2 1 2 4 88%	1600
	21st to end	Night	1 1 1 2 2 1 1 3 89%	1600
July	1st to 10th	Night	1 1 1 1 1 2 94%	3640
	11th to 20th	Night	1 1 1 1 1 1 2 3 89%	3640
	21st to end	Night	1 1 1 1 1 1 1 2 3 89%	4864
August	1st to 10th	Night	1 1 1 1 2 2 3 4 84%	4486
	11th to 20th	Night	1 1 1 94%	4506
	21st to end	Night	1 1 1 1 1 2 1 2 3 87%	5015
September	1st to 10th	Night	1 1 2 2 1 1 1 2 4 86%	2000
	11th to 20th	Night	1 1 2 2 1 2 3 88%	2141
	21st to end	Night	1 2 1 2 1 1 3 4 85%	2200
October	1st to 10th	Night	1 1 1 1 2 2 2 1 2 3 86%	3600
	11th to 20th	Night	1 1 2 1 1 2 2 3 5% 82%	3797
	21st to end	Night	1 2 1 3 2 2 2 2 2 4 78%	4332
November	1st to 10th	Night	1 2 1 3 3 3 2 3 4 6% 72%	2665
	11th to 20th	Night	2 3 1 4 3 3 4 3 5% 6% 68%	2730
	21st to end	Night	2 4 2 5% 3 4 4 4 5% 8% 60%	2730
December	1st to 10th	Night	2 2 1 4 3 3 3 3 5% 6% 67%	4370
	11th to 20th	Night	2 4 2 6% 3 4 5% 5% 7% 9% 52%	4941
	21st to end	Night	3 4 2 6% 5% 5% 6% 5% 7% 10% 48%	6949

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	21% 2 7% 18% 32% 19%	4723
	11th to 20th	Day	13% 3 8% 10% 24% 42%	5160
	21st to end	Day	25% 4 4 12% 30% 25%	6472
February	1st to 10th	Day	24% 4 5% 14% 26% 26%	2100
	11th to 20th	Day	25% 4 5% 17% 29% 20%	2060
	21st to end	Day	25% 5% 7% 18% 25% 20%	1730
March	1st to 10th	Day	25% 9% 7% 16% 22% 21%	4618
	11th to 20th	Day	24% 4 10% 27% 22% 13%	4802
	21st to end	Day	20% 7% 12% 29% 24% 8%	6101
April	1st to 10th	Day	22% 5% 9% 24% 27% 14%	2520
	11th to 20th	Day	17% 5% 7% 22% 31% 18%	2445
	21st to end	Day	13% 5% 9% 24% 38% 11%	2400
May	1st to 10th	Day	12% 3 8% 21% 36% 20%	5607
	11th to 20th	Day	9% 2 7% 19% 48% 15%	5844
	21st to end	Day	7% 4 4 20% 44% 21%	6424
June	1st to 10th	Day	12% 3 5% 20% 34% 26%	2656
	11th to 20th	Day	4 3 5% 10% 33% 44%	2800
	21st to end	Day	7% 1 3 5% 28% 56%	2800
July	1st to 10th	Day	3 1 3 13% 79%	6251
	11th to 20th	Day	7% 1 2 7% 16% 67%	6245
	21st to end	Day	5% 1 2 10% 26% 56%	5845
August	1st to 10th	Day	7% 1 2 6% 35% 49%	3890
	11th to 20th	Day	3 1 1 6% 28% 62%	3880
	21st to end	Day	5% 1 2 4 24% 65%	4311
September	1st to 10th	Day	8% 2 5% 6% 30% 49%	2400
	11th to 20th	Day	5% 1 3 10% 35% 47%	2257
	21st to end	Day	8% 2 4 11% 35% 41%	2200
October	1st to 10th	Day	9% 2 3 8% 19% 59%	3600
	11th to 20th	Day	7% 1 2 10% 37% 42%	3344
	21st to end	Day	15% 2 2 8% 33% 39%	3473
November	1st to 10th	Day	15% 3 4 14% 35% 29%	1854
	11th to 20th	Day	20% 3 5% 14% 24% 34%	1890
	21st to end	Day	24% 2 7% 12% 25% 29%	1890
December	1st to 10th	Day	20% 3 5% 11% 29% 33%	3040
	11th to 20th	Day	27% 5% 5% 17% 31% 15%	3498
	21st to end	Day	32% 4 7% 20% 24% 13%	4234
January	1st to 10th	Night	22% 3 6% 16% 31% 22%	8172
	11th to 20th	Night	13% 3 5% 12% 21% 45%	7804
	21st to end	Night	25% 5% 5% 9% 29% 28%	7768
February	1st to 10th	Night	25% 4 5% 13% 24% 28%	2520
	11th to 20th	Night	25% 4 6% 15% 27% 23%	2459
	21st to end	Night	23% 7% 7% 17% 22% 23%	2076
March	1st to 10th	Night	23% 10% 6% 17% 24% 20%	5496
	11th to 20th	Night	23% 3 11% 27% 23% 14%	5413
	21st to end	Night	19% 8% 8% 28% 28% 9%	5116
April	1st to 10th	Night	21% 3 8% 25% 25% 18%	2100
	11th to 20th	Night	17% 4 7% 23% 27% 22%	2039
	21st to end	Night	13% 4 9% 21% 38% 14%	2000
May	1st to 10th	Night	12% 4 6% 21% 34% 22%	4378
	11th to 20th	Night	6% 2 5% 22% 47% 19%	4075
	21st to end	Night	5% 3 5% 19% 45% 24%	4474
June	1st to 10th	Night	9% 2 7% 20% 32% 29%	1737
	11th to 20th	Night	4 2 6% 13% 28% 48%	1600
	21st to end	Night	4 2 3 4 24% 62%	1600
July	1st to 10th	Night	3 1 2 14% 80%	3600
	11th to 20th	Night	5% 1 2 7% 16% 69%	3592
	21st to end	Night	5% 1 2 9% 24% 60%	4726
August	1st to 10th	Night	7% 2 2 5% 34% 51%	3256
	11th to 20th	Night	3 1 1 6% 27% 63%	3256
	21st to end	Night	5% 2 4 22% 67%	3608
September	1st to 10th	Night	7% 2 3 6% 26% 56%	2000
	11th to 20th	Night	5% 1 3 6% 35% 49%	2141
	21st to end	Night	7% 1 3 11% 32% 46%	2200
October	1st to 10th	Night	8% 1 3 7% 17% 64%	3600
	11th to 20th	Night	8% 2 3 9% 35% 45%	3797
	21st to end	Night	14% 2 2 6% 29% 48%	4332
November	1st to 10th	Night	15% 3 4 14% 30% 35%	2665
	11th to 20th	Night	17% 2 6% 12% 28% 35%	2730
	21st to end	Night	22% 3 7% 16% 22% 30%	2730
December	1st to 10th	Night	18% 3 3 9% 29% 38%	4370
	11th to 20th	Night	24% 8% 7% 17% 25% 20%	4941
	21st to end	Night	28% 5% 9% 23% 26% 10%	6949

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	19% 15% 37% 23% 6%	220
	11th to 20th	Day	15% 21% 34% 23% 7%	367
	21st to end	Day	13% 22% 34% 24% 6% 1	587
February	1st to 10th	Day	13% 23% 35% 21% 7% 1	540
	11th to 20th	Day	16% 24% 33% 21% 5% 1	535
	21st to end	Day	12% 24% 35% 24% 5%	446
March	1st to 10th	Day	19% 25% 31% 18% 6%	540
	11th to 20th	Day	15% 19% 37% 21% 8% 1	540
	21st to end	Day	13% 24% 36% 22% 5%	594
April	1st to 10th	Day	11% 17% 37% 23% 11% 1	540
	11th to 20th	Day	9% 24% 36% 22% 8% 2	517
	21st to end	Day	7% 20% 32% 24% 12% 4	500
May	1st to 10th	Day	6% 17% 38% 27% 10% 2	503
	11th to 20th	Day	5% 16% 35% 28% 11% 4	528
	21st to end	Day	5% 12% 38% 29% 12% 4	573
June	1st to 10th	Day	2 11% 29% 34% 18% 6%	530
	11th to 20th	Day	1 10% 33% 33% 16% 7%	530
	21st to end	Day	3 7% 35% 32% 15% 7%	530
July	1st to 10th	Day	1 4 29% 42% 17% 7%	526
	11th to 20th	Day	1 1 23% 42% 23% 9%	524
	21st to end	Day	2 1 24% 41% 22% 10%	575
August	1st to 10th	Day	2 3 31% 40% 19% 6%	527
	11th to 20th	Day	1 4 21% 45% 20% 9%	517
	21st to end	Day	3 27% 42% 19% 8%	583
September	1st to 10th	Day	2 6% 26% 40% 20% 5%	530
	11th to 20th	Day	2 8% 35% 37% 17% 2	530
	21st to end	Day	1 12% 30% 35% 19% 3	530
October	1st to 10th	Day	3 12% 33% 35% 15% 2	530
	11th to 20th	Day	5% 11% 30% 39% 13% 2	530
	21st to end	Day	4 12% 33% 32% 16% 2	534
November	1st to 10th	Day	6% 14% 28% 31% 19% 2	330
	11th to 20th	Day	10% 15% 32% 30% 12% 2	330
	21st to end	Day	11% 17% 33% 28% 10% 1	330
December	1st to 10th	Day	9% 12% 38% 29% 10% 2	330
	11th to 20th	Day	7% 16% 29% 33% 13% 2	330
	21st to end	Day	21% 23% 27% 22% 7% 1	275
January	1st to 10th	Night	12% 10% 27% 34% 14% 3	840
	11th to 20th	Night	8% 10% 30% 36% 15% 1	840
	21st to end	Night	13% 12% 27% 34% 13% 2	924
February	1st to 10th	Night	9% 11% 28% 33% 16% 3	840
	11th to 20th	Night	8% 11% 29% 32% 16% 4	824
	21st to end	Night	6% 11% 31% 35% 14% 3	692
March	1st to 10th	Night	8% 12% 31% 33% 15% 2	840
	11th to 20th	Night	5% 9% 25% 33% 21% 6%	840
	21st to end	Night	6% 9% 27% 38% 18% 3	924
April	1st to 10th	Night	5% 6% 26% 38% 22% 3	840
	11th to 20th	Night	3 9% 28% 35% 22% 2	815
	21st to end	Night	3 9% 22% 36% 25% 5%	800
May	1st to 10th	Night	3 6% 25% 42% 21% 4	725
	11th to 20th	Night	2 7% 23% 35% 30% 4	591
	21st to end	Night	1 5% 25% 41% 25% 3	650
June	1st to 10th	Night	3 16% 42% 36% 2	537
	11th to 20th	Night	1 10% 46% 38% 6%	400
	21st to end	Night	1 8% 40% 46% 6%	400
July	1st to 10th	Night	1 4 33% 55% 8%	390
	11th to 20th	Night	1 2 31% 55% 10%	388
	21st to end	Night	2 6% 35% 46% 11%	818
August	1st to 10th	Night	2 1 7% 37% 44% 10%	796
	11th to 20th	Night	1 4 32% 49% 14%	792
	21st to end	Night	1 6% 33% 45% 14%	880
September	1st to 10th	Night	2 1 8% 31% 46% 14%	800
	11th to 20th	Night	1 1 12% 37% 39% 11%	800
	21st to end	Night	1 1 15% 39% 36% 9%	800
October	1st to 10th	Night	2 3 15% 48% 28% 4	800
	11th to 20th	Night	3 5% 17% 39% 30% 6%	800
	21st to end	Night	2 6% 24% 34% 26% 9%	880
November	1st to 10th	Night	3 5% 22% 39% 25% 5%	820
	11th to 20th	Night	5% 6% 25% 39% 20% 5%	840
	21st to end	Night	5% 9% 28% 35% 19% 4	840
December	1st to 10th	Night	8% 9% 28% 35% 19% 2	840
	11th to 20th	Night	7% 8% 28% 41% 15% 2	840
	21st to end	Night	8% 11% 30% 35% 13% 2	924

Page generated at 2026-04-13 23:44:27. Version ac07

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