Hidden Waters Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hidden Waters Observatory clear sky chart from 2005-11-06 to 2025-03-12.

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	12% 6% 2 6% 5% 5% 5% 4 6% 7% 40%	108812
	Night	12% 6% 2 6% 4 4 4 4 6% 7% 44%	110196
Transparency	Day	40% 5% 11% 23% 17% 4	112462
	Night	37% 4 12% 24% 18% 4	114685
Seeing	Day	21% 13% 25% 23% 13% 5%	15308
	Night	17% 12% 26% 31% 13% 1	25178

By Month

Percentage Cloud Cover SE (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	11% 6% 3 6% 5% 5% 5% 4 4 5% 46%	4056
	11th to 20th	Day	9% 9% 4 7% 5% 4 4 3 4 5% 45%	4060
	21st to end	Day	11% 8% 3 7% 5% 4 4 3 5% 6% 45%	4466
February	1st to 10th	Day	11% 9% 3 8% 6% 4 4 4 6% 7% 39%	1800
	11th to 20th	Day	14% 9% 3 6% 5% 4 5% 3 4 7% 39%	1753
	21st to end	Day	13% 8% 2 7% 4 4 5% 4 6% 6% 41%	1701
March	1st to 10th	Day	16% 10% 3 8% 5% 4 4 3 5% 6% 36%	3545
	11th to 20th	Day	8% 7% 2 5% 4 4 3 3 5% 7% 51%	3491
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 4 5% 7% 37%	3815
April	1st to 10th	Day	9% 7% 3 6% 6% 5% 5% 4 6% 7% 42%	2228
	11th to 20th	Day	12% 6% 2 6% 5% 5% 4 4 4 7% 45%	2254
	21st to end	Day	17% 7% 2 6% 4 4 5% 4 5% 7% 39%	2363
May	1st to 10th	Day	18% 7% 3 8% 6% 6% 6% 5% 6% 7% 29%	4082
	11th to 20th	Day	22% 8% 2 6% 4 4 4 4 5% 8% 33%	4081
	21st to end	Day	10% 5% 2 6% 6% 6% 6% 5% 7% 9% 39%	4715
June	1st to 10th	Day	12% 5% 2 5% 4 5% 6% 5% 7% 8% 40%	2660
	11th to 20th	Day	10% 6% 3 6% 5% 5% 7% 5% 7% 10% 36%	2660
	21st to end	Day	9% 4 2 5% 6% 5% 7% 6% 8% 11% 39%	2660
July	1st to 10th	Day	6% 4 2 7% 6% 5% 6% 5% 8% 10% 41%	4250
	11th to 20th	Day	8% 4 2 7% 6% 6% 7% 6% 8% 11% 35%	4120
	21st to end	Day	10% 7% 3 9% 6% 6% 7% 4 6% 8% 33%	4466
August	1st to 10th	Day	14% 5% 2 7% 6% 6% 7% 6% 8% 9% 31%	4104
	11th to 20th	Day	8% 5% 2 7% 5% 7% 5% 6% 8% 9% 38%	4022
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 7% 9% 45%	4180
September	1st to 10th	Day	14% 5% 2 6% 6% 4 4 3 5% 7% 44%	2280
	11th to 20th	Day	13% 5% 3 6% 5% 4 4 4 4 7% 45%	2171
	21st to end	Day	22% 6% 2 7% 5% 4 4 4 5% 6% 35%	2043
October	1st to 10th	Day	15% 6% 2 6% 4 3 4 4 5% 7% 44%	1900
	11th to 20th	Day	15% 6% 2 6% 5% 4 3 3 3 5% 48%	1900
	21st to end	Day	13% 6% 2 5% 3 4 3 4 5% 6% 50%	2090
November	1st to 10th	Day	9% 6% 2 5% 4 4 3 3 5% 6% 53%	1957
	11th to 20th	Day	13% 6% 2 4 4 3 4 3 7% 6% 47%	1725
	21st to end	Day	13% 5% 2 5% 5% 4 4 4 6% 7% 46%	1600
December	1st to 10th	Day	10% 5% 2 6% 4 4 4 4 5% 6% 50%	2600
	11th to 20th	Day	16% 5% 2 6% 6% 5% 5% 3 4 6% 42%	2990
	21st to end	Day	16% 7% 2 7% 4 4 5% 5% 7% 8% 36%	4024
January	1st to 10th	Night	9% 7% 2 6% 4 4 4 4 5% 6% 48%	5889
	11th to 20th	Night	11% 8% 3 5% 3 4 4 3 5% 6% 49%	5900
	21st to end	Night	13% 7% 2 5% 4 3 3 3 5% 5% 49%	6490
February	1st to 10th	Night	12% 7% 3 6% 5% 4 5% 5% 7% 7% 41%	2600
	11th to 20th	Night	15% 9% 2 6% 5% 4 5% 4 6% 6% 38%	2533
	21st to end	Night	12% 9% 3 7% 4 4 5% 4 5% 8% 40%	1924
March	1st to 10th	Night	17% 7% 2 7% 5% 4 4 4 6% 6% 37%	3528
	11th to 20th	Night	9% 5% 2 5% 3 4 4 4 6% 8% 51%	3498
	21st to end	Night	12% 6% 2 5% 4 4 4 4 5% 6% 47%	3817
April	1st to 10th	Night	12% 7% 2 6% 5% 5% 5% 4 6% 6% 42%	1951
	11th to 20th	Night	12% 5% 2 5% 4 4 5% 3 6% 8% 46%	1875
	21st to end	Night	16% 5% 1 4 4 4 4 4 6% 8% 44%	1833
May	1st to 10th	Night	19% 8% 3 6% 5% 5% 4 5% 6% 8% 32%	2813
	11th to 20th	Night	23% 7% 2 7% 5% 4 4 3 4 5% 36%	2812
	21st to end	Night	10% 5% 2 5% 4 6% 5% 4 7% 10% 44%	2837
June	1st to 10th	Night	10% 5% 2 5% 5% 4 3 4 8% 8% 46%	1520
	11th to 20th	Night	10% 4 2 6% 5% 5% 5% 4 7% 10% 43%	1520
	21st to end	Night	9% 4 1 6% 4 4 5% 5% 8% 9% 45%	1520
July	1st to 10th	Night	5% 5% 2 6% 4 5% 5% 5% 9% 12% 41%	2704
	11th to 20th	Night	8% 5% 3 7% 5% 5% 5% 5% 8% 9% 39%	2840
	21st to end	Night	7% 7% 3 9% 6% 5% 7% 5% 7% 9% 37%	3087
August	1st to 10th	Night	14% 5% 2 6% 4 5% 4 5% 7% 10% 36%	2825
	11th to 20th	Night	8% 6% 2 7% 5% 6% 6% 5% 7% 9% 41%	2785
	21st to end	Night	9% 5% 2 5% 4 4 4 4 6% 8% 49%	3465
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 5% 8% 47%	1900
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 6% 7% 47%	2004
	21st to end	Night	22% 5% 2 6% 3 3 4 3 5% 6% 41%	2137
October	1st to 10th	Night	17% 5% 2 6% 4 3 4 3 4 6% 45%	2280
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 5% 7% 51%	2280
	21st to end	Night	13% 5% 2 4 3 4 3 3 5% 6% 51%	2508
November	1st to 10th	Night	9% 7% 2 5% 4 3 3 4 5% 6% 52%	2341
	11th to 20th	Night	12% 6% 2 5% 4 4 4 4 6% 6% 48%	2667
	21st to end	Night	12% 6% 2 5% 4 4 5% 4 6% 6% 46%	2800
December	1st to 10th	Night	8% 5% 3 6% 4 4 4 3 5% 7% 51%	4580
	11th to 20th	Night	14% 7% 3 7% 4 5% 4 3 5% 7% 41%	5205
	21st to end	Night	13% 5% 3 7% 5% 6% 5% 4 7% 10% 35%	6928

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	39% 5% 4 21% 22% 8%	4057
	11th to 20th	Day	41% 3 6% 18% 20% 13%	4060
	21st to end	Day	41% 3 8% 24% 20% 4	4466
February	1st to 10th	Day	44% 3 11% 24% 15% 3	1800
	11th to 20th	Day	46% 3 8% 21% 18% 4	1762
	21st to end	Day	42% 3 11% 20% 18% 5%	1701
March	1st to 10th	Day	49% 3 9% 20% 13% 6%	3545
	11th to 20th	Day	33% 3 8% 27% 24% 5%	3491
	21st to end	Day	47% 3 11% 21% 15% 3	3815
April	1st to 10th	Day	40% 3 11% 21% 18% 7%	2228
	11th to 20th	Day	39% 2 11% 22% 21% 6%	2254
	21st to end	Day	45% 4 10% 22% 15% 4	2363
May	1st to 10th	Day	51% 5% 11% 20% 10% 2	4120
	11th to 20th	Day	50% 5% 11% 23% 10% 1	4085
	21st to end	Day	38% 5% 17% 21% 16% 3	4729
June	1st to 10th	Day	39% 5% 14% 24% 17% 1	2660
	11th to 20th	Day	41% 6% 17% 22% 13% 2	2660
	21st to end	Day	35% 6% 16% 26% 15% 2	2660
July	1st to 10th	Day	36% 9% 18% 22% 10% 6%	4185
	11th to 20th	Day	39% 8% 15% 28% 9% 1	4051
	21st to end	Day	47% 6% 10% 23% 13% 1	4324
August	1st to 10th	Day	45% 7% 16% 24% 8%	4091
	11th to 20th	Day	38% 7% 13% 29% 13% 1	4061
	21st to end	Day	35% 5% 16% 30% 13% 1	4180
September	1st to 10th	Day	40% 4 14% 17% 21% 4	2280
	11th to 20th	Day	38% 3 8% 27% 20% 4	2171
	21st to end	Day	48% 5% 7% 21% 17% 3	2043
October	1st to 10th	Day	33% 4 8% 21% 27% 7%	3160
	11th to 20th	Day	27% 3 8% 29% 21% 12%	3140
	21st to end	Day	24% 2 9% 31% 25% 10%	3428
November	1st to 10th	Day	32% 3 9% 26% 25% 5%	1957
	11th to 20th	Day	36% 3 9% 22% 23% 7%	1725
	21st to end	Day	36% 4 10% 26% 22% 2	1600
December	1st to 10th	Day	35% 4 10% 26% 21% 5%	2600
	11th to 20th	Day	43% 4 10% 24% 16% 4	2986
	21st to end	Day	44% 5% 15% 19% 15% 1	4024
January	1st to 10th	Night	34% 5% 6% 23% 26% 5%	5889
	11th to 20th	Night	34% 3 7% 25% 21% 10%	5900
	21st to end	Night	36% 2 8% 28% 21% 4	6490
February	1st to 10th	Night	41% 3 12% 26% 15% 2	2600
	11th to 20th	Night	45% 3 9% 21% 17% 5%	2535
	21st to end	Night	42% 3 11% 23% 15% 6%	1924
March	1st to 10th	Night	47% 3 9% 24% 13% 4	3528
	11th to 20th	Night	30% 3 9% 27% 25% 5%	3498
	21st to end	Night	38% 2 12% 25% 19% 4	3817
April	1st to 10th	Night	41% 5% 10% 21% 19% 4	1951
	11th to 20th	Night	36% 3 13% 23% 20% 5%	1875
	21st to end	Night	38% 4 12% 27% 15% 3	1833
May	1st to 10th	Night	50% 5% 14% 19% 10% 2	2840
	11th to 20th	Night	50% 4 11% 25% 9% 1	2813
	21st to end	Night	35% 6% 20% 27% 9% 4	2844
June	1st to 10th	Night	34% 5% 16% 29% 14% 1	1520
	11th to 20th	Night	36% 7% 16% 26% 14% 1	1520
	21st to end	Night	33% 6% 18% 22% 18% 2	1520
July	1st to 10th	Night	34% 9% 23% 18% 13% 3	2659
	11th to 20th	Night	37% 8% 18% 25% 10% 1	2786
	21st to end	Night	42% 8% 16% 22% 11%	2988
August	1st to 10th	Night	42% 7% 18% 25% 7% 1	2814
	11th to 20th	Night	38% 8% 15% 25% 14%	2812
	21st to end	Night	33% 4 17% 32% 13% 1	3465
September	1st to 10th	Night	37% 5% 15% 20% 18% 5%	1900
	11th to 20th	Night	37% 3 10% 30% 19% 2	2004
	21st to end	Night	45% 4 9% 22% 18% 2	2137
October	1st to 10th	Night	39% 4 9% 22% 23% 3	3800
	11th to 20th	Night	25% 4 11% 22% 30% 9%	3779
	21st to end	Night	22% 3 10% 31% 28% 6%	4120
November	1st to 10th	Night	33% 3 11% 24% 24% 6%	2341
	11th to 20th	Night	36% 3 7% 26% 22% 6%	2667
	21st to end	Night	37% 3 11% 25% 20% 4	2800
December	1st to 10th	Night	33% 3 11% 29% 22% 2	4580
	11th to 20th	Night	43% 4 12% 19% 17% 5%	5208
	21st to end	Night	42% 6% 14% 21% 16% 1	6928

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	35% 26% 25% 11% 2	300
	11th to 20th	Day	34% 22% 28% 14% 2	300
	21st to end	Day	33% 25% 30% 9% 2	330
February	1st to 10th	Day	32% 27% 30% 9% 2	300
	11th to 20th	Day	44% 25% 25% 5% 1	300
	21st to end	Day	34% 22% 28% 15% 2	370
March	1st to 10th	Day	25% 24% 27% 20% 4	500
	11th to 20th	Day	27% 22% 27% 18% 5% 1	464
	21st to end	Day	27% 19% 30% 18% 6% 1	506
April	1st to 10th	Day	23% 25% 25% 18% 8%	460
	11th to 20th	Day	23% 17% 26% 21% 9% 3	452
	21st to end	Day	28% 15% 28% 17% 10% 1	460
May	1st to 10th	Day	25% 16% 27% 18% 10% 4	463
	11th to 20th	Day	23% 13% 28% 23% 10% 4	487
	21st to end	Day	17% 7% 26% 25% 18% 7%	529
June	1st to 10th	Day	14% 11% 25% 29% 15% 6%	490
	11th to 20th	Day	17% 7% 26% 26% 17% 7%	490
	21st to end	Day	10% 9% 30% 33% 14% 4	490
July	1st to 10th	Day	10% 5% 21% 29% 25% 10%	485
	11th to 20th	Day	6% 4 20% 35% 25% 11%	484
	21st to end	Day	13% 5% 19% 30% 24% 9%	532
August	1st to 10th	Day	14% 7% 19% 29% 19% 12%	486
	11th to 20th	Day	14% 5% 20% 27% 24% 10%	479
	21st to end	Day	11% 4 19% 29% 22% 15%	539
September	1st to 10th	Day	17% 8% 19% 23% 21% 12%	490
	11th to 20th	Day	17% 4 17% 27% 26% 10%	490
	21st to end	Day	28% 9% 21% 23% 15% 3	490
October	1st to 10th	Day	21% 6% 22% 28% 18% 5%	490
	11th to 20th	Day	18% 16% 22% 27% 14% 2	490
	21st to end	Day	18% 15% 32% 24% 9% 2	539
November	1st to 10th	Day	17% 13% 30% 26% 12% 2	495
	11th to 20th	Day	26% 15% 31% 20% 6% 1	295
	21st to end	Day	26% 18% 38% 16% 3 1	200
December	1st to 10th	Day	26% 22% 36% 13% 4 1	200
	11th to 20th	Day	27% 20% 33% 15% 6% 1	200
	21st to end	Day	27% 19% 34% 15% 5%	233
January	1st to 10th	Night	21% 20% 34% 22% 3	800
	11th to 20th	Night	21% 17% 33% 26% 3	800
	21st to end	Night	17% 17% 42% 23% 2	880
February	1st to 10th	Night	18% 18% 36% 25% 3	800
	11th to 20th	Night	27% 20% 34% 18% 1	783
	21st to end	Night	23% 17% 38% 20% 2	660
March	1st to 10th	Night	18% 19% 36% 24% 3	800
	11th to 20th	Night	23% 18% 30% 25% 4 1	767
	21st to end	Night	21% 17% 32% 24% 6% 1	836
April	1st to 10th	Night	18% 21% 31% 25% 6%	760
	11th to 20th	Night	16% 16% 31% 26% 10% 1	751
	21st to end	Night	20% 11% 30% 31% 8%	693
May	1st to 10th	Night	19% 9% 25% 32% 13% 1	570
	11th to 20th	Night	17% 7% 24% 35% 16% 1	561
	21st to end	Night	13% 2 21% 40% 21% 2	478
June	1st to 10th	Night	12% 4 20% 42% 21% 1	380
	11th to 20th	Night	11% 5% 14% 48% 20% 2	380
	21st to end	Night	9% 4 16% 51% 19% 1	380
July	1st to 10th	Night	11% 3 10% 38% 32% 5%	471
	11th to 20th	Night	7% 3 10% 40% 35% 5%	552
	21st to end	Night	7% 3 11% 43% 31% 4	624
August	1st to 10th	Night	11% 2 11% 41% 32% 3	567
	11th to 20th	Night	12% 3 10% 39% 33% 3	564
	21st to end	Night	12% 4 12% 39% 30% 4	825
September	1st to 10th	Night	16% 3 14% 34% 27% 6%	760
	11th to 20th	Night	14% 4 14% 36% 28% 4	760
	21st to end	Night	24% 5% 20% 29% 21% 2	760
October	1st to 10th	Night	19% 8% 18% 31% 20% 3	760
	11th to 20th	Night	16% 10% 29% 30% 14% 1	760
	21st to end	Night	17% 12% 25% 34% 11% 1	836
November	1st to 10th	Night	15% 10% 27% 35% 11% 1	780
	11th to 20th	Night	18% 14% 27% 31% 9% 1	800
	21st to end	Night	18% 15% 30% 30% 7% 1	800
December	1st to 10th	Night	19% 16% 33% 29% 4	800
	11th to 20th	Night	18% 12% 35% 31% 4	800
	21st to end	Night	17% 14% 32% 33% 3	880

Page generated at 2025-03-09 08:08:47. Version ac07

Copyright © 2025 Attilla Danko.