Hidden Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hidden Hill Observatory clear sky chart from 2005-11-06 to 2024-04-10.

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	5% 4 2 4 4 2 4 4 4 6% 61%	83364
	Night	6% 4 2 4 4 3 4 4 5% 7% 57%	85518
Transparency	Day	24% 4 8% 19% 24% 21%	83082
	Night	25% 4 11% 18% 22% 21%	85321
Seeing	Day	8% 12% 22% 32% 21% 5%	14552
	Night	8% 6% 15% 31% 30% 8%	24078

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	9% 8% 3 7% 6% 3 5% 4 6% 6% 42%	2637
	11th to 20th	Day	11% 6% 3 7% 9% 5% 7% 6% 5% 6% 37%	2860
	21st to end	Day	14% 8% 4 8% 7% 4 5% 5% 4 8% 34%	3146
February	1st to 10th	Day	13% 6% 3 6% 5% 3 5% 4 5% 5% 46%	1710
	11th to 20th	Day	9% 6% 3 6% 6% 4 5% 5% 5% 7% 46%	1796
	21st to end	Day	12% 5% 3 5% 6% 3 4 4 5% 6% 46%	1570
March	1st to 10th	Day	8% 9% 4 9% 10% 6% 7% 7% 6% 6% 28%	3312
	11th to 20th	Day	6% 6% 2 5% 5% 3 4 4 4 7% 54%	3490
	21st to end	Day	9% 8% 3 7% 8% 4 6% 7% 7% 7% 35%	3938
April	1st to 10th	Day	9% 7% 3 6% 5% 3 5% 4 5% 6% 47%	2270
	11th to 20th	Day	8% 4 2 4 3 3 4 4 5% 7% 57%	2129
	21st to end	Day	5% 4 2 3 2 2 3 4 4 8% 64%	2160
May	1st to 10th	Day	4 3 2 3 3 2 3 4 6% 8% 63%	2162
	11th to 20th	Day	3 3 1 3 3 2 3 4 4 7% 68%	2395
	21st to end	Day	3 3 1 3 4 2 3 4 5% 8% 65%	2723
June	1st to 10th	Day	3 3 2 2 2 2 3 4 4 8% 67%	2520
	11th to 20th	Day	1 1 1 1 1 2 2 4 6% 81%	2520
	21st to end	Day	1 1 1 2 1 1 2 3 3 84%	2520
July	1st to 10th	Day	1 1 1 1 1 1 2 3 90%	2520
	11th to 20th	Day	1 1 1 1 1 2 2 2 4 85%	2408
	21st to end	Day	1 1 1 1 2 2 2 4 86%	2546
August	1st to 10th	Day	1 2 1 1 2 1 2 2 2 3 84%	2328
	11th to 20th	Day	1 1 1 1 1 1 2 4 88%	2140
	21st to end	Day	1 1 1 1 2 3 89%	2376
September	1st to 10th	Day	1 1 1 1 1 1 1 1 1 3 88%	2160
	11th to 20th	Day	1 1 1 1 1 2 3 4 7% 78%	2160
	21st to end	Day	3 1 1 1 2 1 2 3 3 4 79%	1936
October	1st to 10th	Day	2 2 2 3 3 2 3 3 4 6% 71%	1800
	11th to 20th	Day	3 2 1 3 3 2 3 3 4 6% 71%	1800
	21st to end	Day	4 3 2 3 3 2 4 4 4 6% 66%	1980
November	1st to 10th	Day	6% 4 2 5% 4 4 4 5% 7% 7% 53%	1780
	11th to 20th	Day	5% 4 2 5% 5% 3 4 4 6% 8% 54%	1710
	21st to end	Day	8% 4 2 4 5% 2 3 3 5% 8% 55%	1620
December	1st to 10th	Day	7% 6% 3 7% 5% 4 5% 4 5% 7% 46%	1520
	11th to 20th	Day	18% 11% 4 7% 6% 3 4 5% 5% 5% 32%	1928
	21st to end	Day	8% 10% 3 7% 7% 5% 5% 6% 6% 7% 36%	2794
January	1st to 10th	Night	8% 6% 3 7% 6% 4 5% 5% 5% 8% 45%	4309
	11th to 20th	Night	10% 8% 3 8% 8% 5% 6% 6% 6% 7% 32%	4110
	21st to end	Night	13% 7% 3 7% 7% 4 6% 6% 6% 7% 33%	4521
February	1st to 10th	Night	12% 6% 3 4 4 2 4 5% 6% 7% 48%	2470
	11th to 20th	Night	8% 5% 2 5% 5% 3 5% 5% 7% 9% 47%	2270
	21st to end	Night	8% 6% 2 4 5% 3 4 5% 5% 7% 51%	1884
March	1st to 10th	Night	8% 11% 3 7% 7% 4 6% 6% 6% 8% 34%	3560
	11th to 20th	Night	7% 5% 2 5% 4 2 3 3 4 7% 58%	3490
	21st to end	Night	6% 8% 3 5% 7% 4 6% 7% 7% 9% 37%	3715
April	1st to 10th	Night	7% 6% 2 5% 5% 2 5% 5% 6% 7% 50%	1900
	11th to 20th	Night	6% 2 3 5% 5% 2 4 3 6% 7% 58%	1779
	21st to end	Night	4 3 1 3 2 2 4 4 5% 8% 64%	1800
May	1st to 10th	Night	3 3 1 3 3 2 3 3 4 9% 66%	1795
	11th to 20th	Night	3 2 1 1 2 1 2 3 6% 10% 69%	1498
	21st to end	Night	2 1 1 3 1 1 3 4 5% 8% 72%	1552
June	1st to 10th	Night	2 2 1 3 3 2 3 3 4 6% 72%	1440
	11th to 20th	Night	1 1 1 1 1 2 3 4 5% 82%	1440
	21st to end	Night	1 1 2 1 2 1 2 3 88%	1440
July	1st to 10th	Night	1 1 2 1 2 3 89%	1440
	11th to 20th	Night	1 1 1 1 1 1 2 2 3 4 86%	1548
	21st to end	Night	1 1 1 1 2 1 2 3 3 4 82%	1773
August	1st to 10th	Night	1 1 2 2 1 1 2 2 3 84%	1611
	11th to 20th	Night	1 1 1 1 1 1 2 2 4 86%	1759
	21st to end	Night	1 1 1 1 1 1 1 1 3 89%	1980
September	1st to 10th	Night	1 1 1 1 1 1 2 4 88%	1800
	11th to 20th	Night	1 1 1 2 2 1 2 2 2 5% 82%	1800
	21st to end	Night	2 2 1 2 1 1 1 3 5% 82%	2019
October	1st to 10th	Night	4 2 1 3 3 1 2 3 3 7% 73%	2160
	11th to 20th	Night	2 2 1 2 3 2 3 4 4 7% 70%	2160
	21st to end	Night	4 2 1 2 2 2 2 3 4 7% 71%	2376
November	1st to 10th	Night	4 2 1 3 4 2 4 4 7% 9% 59%	2296
	11th to 20th	Night	5% 4 2 5% 4 2 5% 5% 6% 9% 55%	2470
	21st to end	Night	5% 4 2 4 5% 3 5% 4 5% 7% 56%	2555
December	1st to 10th	Night	9% 6% 3 5% 5% 3 4 4 6% 6% 49%	2660
	11th to 20th	Night	17% 10% 5% 7% 6% 3 4 4 5% 7% 33%	3276
	21st to end	Night	10% 7% 4 8% 8% 5% 6% 6% 6% 7% 35%	4862

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	40% 4 13% 28% 11% 3	2637
	11th to 20th	Day	45% 6% 13% 17% 13% 7%	2860
	21st to end	Day	48% 4 12% 17% 14% 5%	3146
February	1st to 10th	Day	38% 4 7% 20% 20% 10%	1710
	11th to 20th	Day	34% 4 10% 20% 22% 9%	1806
	21st to end	Day	37% 4 10% 22% 20% 8%	1570
March	1st to 10th	Day	48% 6% 15% 13% 15% 3	3312
	11th to 20th	Day	27% 5% 10% 30% 16% 12%	3490
	21st to end	Day	41% 7% 18% 19% 12% 3	3938
April	1st to 10th	Day	36% 5% 11% 21% 20% 8%	2270
	11th to 20th	Day	26% 5% 12% 25% 25% 8%	2132
	21st to end	Day	20% 3 11% 31% 29% 7%	2160
May	1st to 10th	Day	18% 4 9% 27% 31% 12%	2162
	11th to 20th	Day	16% 4 6% 27% 33% 14%	2398
	21st to end	Day	17% 4 13% 29% 29% 8%	2724
June	1st to 10th	Day	16% 4 9% 23% 32% 16%	2520
	11th to 20th	Day	6% 2 7% 20% 37% 28%	2520
	21st to end	Day	7% 2 2 11% 29% 49%	2520
July	1st to 10th	Day	4 1 1 7% 24% 63%	2451
	11th to 20th	Day	7% 2 3 8% 24% 56%	2335
	21st to end	Day	5% 2 3 7% 27% 56%	2405
August	1st to 10th	Day	8% 2 1 11% 27% 51%	2312
	11th to 20th	Day	4 1 1 11% 31% 51%	2140
	21st to end	Day	4 1 1 11% 34% 49%	2376
September	1st to 10th	Day	6% 2 2 9% 28% 54%	2160
	11th to 20th	Day	7% 3 4 20% 39% 27%	2160
	21st to end	Day	10% 2 3 19% 39% 27%	1936
October	1st to 10th	Day	14% 3 6% 19% 27% 31%	1800
	11th to 20th	Day	15% 3 7% 21% 24% 30%	1800
	21st to end	Day	19% 2 8% 20% 26% 25%	1980
November	1st to 10th	Day	26% 4 9% 21% 25% 15%	1780
	11th to 20th	Day	26% 4 11% 23% 26% 10%	1710
	21st to end	Day	27% 3 9% 20% 30% 11%	1620
December	1st to 10th	Day	34% 4 12% 18% 19% 12%	1520
	11th to 20th	Day	53% 3 8% 16% 15% 6%	1928
	21st to end	Day	44% 4 13% 21% 14% 4	2794
January	1st to 10th	Night	32% 5% 20% 25% 14% 4	4309
	11th to 20th	Night	44% 5% 15% 16% 10% 8%	4110
	21st to end	Night	44% 5% 14% 17% 13% 7%	4521
February	1st to 10th	Night	32% 4 9% 21% 21% 13%	2470
	11th to 20th	Night	29% 3 12% 21% 24% 11%	2271
	21st to end	Night	29% 3 11% 28% 20% 8%	1884
March	1st to 10th	Night	40% 7% 19% 15% 15% 4	3560
	11th to 20th	Night	26% 4 9% 25% 21% 16%	3490
	21st to end	Night	35% 7% 20% 20% 13% 5%	3715
April	1st to 10th	Night	30% 5% 13% 22% 21% 9%	1900
	11th to 20th	Night	24% 3 13% 26% 22% 12%	1779
	21st to end	Night	17% 3 11% 30% 30% 10%	1800
May	1st to 10th	Night	15% 4 10% 21% 33% 17%	1795
	11th to 20th	Night	12% 2 10% 23% 35% 17%	1498
	21st to end	Night	10% 2 15% 28% 33% 11%	1552
June	1st to 10th	Night	14% 4 9% 18% 31% 24%	1440
	11th to 20th	Night	7% 1 7% 15% 29% 40%	1440
	21st to end	Night	5% 1 2 10% 29% 52%	1440
July	1st to 10th	Night	4 1 2 5% 20% 68%	1400
	11th to 20th	Night	5% 1 4 7% 23% 60%	1498
	21st to end	Night	8% 2 2 7% 21% 60%	1674
August	1st to 10th	Night	8% 2 2 12% 24% 52%	1602
	11th to 20th	Night	6% 2 1 9% 29% 53%	1759
	21st to end	Night	4 1 2 9% 32% 52%	1980
September	1st to 10th	Night	5% 1 2 7% 21% 64%	1800
	11th to 20th	Night	7% 2 5% 17% 33% 36%	1800
	21st to end	Night	8% 1 3 17% 37% 34%	2019
October	1st to 10th	Night	13% 3 7% 18% 23% 35%	2160
	11th to 20th	Night	15% 3 7% 18% 25% 33%	2160
	21st to end	Night	14% 2 7% 18% 31% 28%	2376
November	1st to 10th	Night	18% 4 11% 22% 25% 20%	2296
	11th to 20th	Night	23% 4 11% 21% 29% 11%	2470
	21st to end	Night	24% 3 10% 20% 26% 16%	2555
December	1st to 10th	Night	32% 5% 10% 19% 20% 15%	2660
	11th to 20th	Night	48% 4 9% 15% 17% 6%	3276
	21st to end	Night	43% 5% 16% 17% 13% 5%	4862

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	28% 18% 22% 21% 10% 1	239
	11th to 20th	Day	13% 17% 25% 29% 13% 3	370
	21st to end	Day	16% 11% 28% 24% 18% 2	407
February	1st to 10th	Day	18% 20% 23% 21% 14% 4	370
	11th to 20th	Day	17% 20% 26% 27% 11%	430
	21st to end	Day	18% 17% 28% 26% 10% 1	382
March	1st to 10th	Day	19% 18% 31% 24% 7% 1	460
	11th to 20th	Day	18% 20% 22% 23% 14% 3	460
	21st to end	Day	18% 19% 32% 22% 9%	506
April	1st to 10th	Day	17% 19% 28% 22% 13% 1	457
	11th to 20th	Day	12% 23% 29% 24% 12% 1	412
	21st to end	Day	6% 19% 28% 29% 14% 5%	420
May	1st to 10th	Day	9% 16% 28% 31% 12% 4	423
	11th to 20th	Day	6% 16% 31% 25% 17% 4	448
	21st to end	Day	7% 11% 26% 31% 21% 5%	485
June	1st to 10th	Day	6% 12% 25% 30% 19% 8%	450
	11th to 20th	Day	3 11% 26% 38% 17% 5%	450
	21st to end	Day	2 5% 22% 37% 26% 8%	450
July	1st to 10th	Day	2 14% 43% 33% 7%	446
	11th to 20th	Day	1 11% 42% 34% 12%	444
	21st to end	Day	1 10% 43% 30% 16%	487
August	1st to 10th	Day	2 3 17% 39% 29% 10%	447
	11th to 20th	Day	1 17% 39% 29% 13%	437
	21st to end	Day	1 1 9% 41% 36% 12%	495
September	1st to 10th	Day	1 4 13% 40% 34% 8%	450
	11th to 20th	Day	2 6% 20% 40% 25% 7%	450
	21st to end	Day	3 7% 18% 41% 27% 4	450
October	1st to 10th	Day	3 12% 24% 32% 25% 4	450
	11th to 20th	Day	6% 10% 20% 34% 26% 5%	450
	21st to end	Day	7% 8% 24% 35% 22% 5%	495
November	1st to 10th	Day	7% 13% 19% 31% 26% 3	376
	11th to 20th	Day	6% 11% 19% 33% 22% 9%	270
	21st to end	Day	10% 8% 24% 32% 21% 5%	228
December	1st to 10th	Day	13% 16% 18% 29% 14% 8%	180
	11th to 20th	Day	18% 15% 17% 29% 16% 6%	180
	21st to end	Day	16% 22% 23% 20% 13% 6%	198
January	1st to 10th	Night	17% 5% 21% 27% 21% 9%	760
	11th to 20th	Night	13% 7% 15% 34% 22% 9%	760
	21st to end	Night	15% 8% 15% 31% 23% 7%	836
February	1st to 10th	Night	18% 9% 15% 30% 22% 6%	760
	11th to 20th	Night	13% 11% 19% 30% 20% 8%	744
	21st to end	Night	12% 11% 21% 34% 18% 4	628
March	1st to 10th	Night	16% 12% 19% 31% 19% 4	760
	11th to 20th	Night	13% 12% 20% 27% 23% 5%	760
	21st to end	Night	13% 11% 23% 31% 19% 3	836
April	1st to 10th	Night	11% 9% 24% 30% 22% 4	760
	11th to 20th	Night	8% 14% 22% 30% 21% 5%	711
	21st to end	Night	5% 10% 25% 29% 23% 8%	720
May	1st to 10th	Night	4 6% 26% 31% 26% 7%	715
	11th to 20th	Night	3 4 17% 34% 36% 6%	436
	21st to end	Night	3 7% 16% 35% 34% 5%	389
June	1st to 10th	Night	4 4 18% 34% 34% 6%	360
	11th to 20th	Night	1 4 14% 42% 35% 4	360
	21st to end	Night	1 1 8% 39% 44% 8%	360
July	1st to 10th	Night	1 8% 35% 47% 9%	350
	11th to 20th	Night	1 2 29% 54% 13%	454
	21st to end	Night	2 3 27% 55% 14%	591
August	1st to 10th	Night	2 1 6% 32% 48% 12%	537
	11th to 20th	Night	6% 37% 45% 12%	691
	21st to end	Night	1 3 28% 56% 12%	792
September	1st to 10th	Night	1 2 8% 31% 48% 11%	720
	11th to 20th	Night	2 2 9% 35% 41% 10%	720
	21st to end	Night	2 3 11% 29% 40% 14%	720
October	1st to 10th	Night	4 4 12% 35% 33% 12%	720
	11th to 20th	Night	5% 5% 11% 32% 35% 11%	720
	21st to end	Night	6% 4 14% 30% 28% 17%	792
November	1st to 10th	Night	5% 7% 15% 31% 30% 11%	740
	11th to 20th	Night	7% 5% 18% 34% 27% 9%	760
	21st to end	Night	7% 7% 18% 34% 26% 8%	760
December	1st to 10th	Night	14% 8% 17% 31% 23% 7%	760
	11th to 20th	Night	17% 9% 18% 30% 21% 5%	760
	21st to end	Night	14% 14% 22% 28% 19% 4	836

Page generated at 2024-04-07 06:28:13. Version ac07

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