Hidden Bend Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hidden Bend Observatory clear sky chart from 2005-11-06 to 2025-05-11.

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	13% 8% 3 7% 5% 5% 5% 4 6% 7% 39%	113871
	Night	13% 8% 3 7% 5% 4 5% 4 6% 7% 40%	115062
Transparency	Day	42% 6% 11% 23% 14% 3	117517
	Night	42% 6% 12% 24% 14% 2	119555
Seeing	Day	22% 14% 25% 21% 13% 4	15475
	Night	19% 13% 25% 30% 12% 1	25253

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	13% 14% 3 11% 5% 4 4 4 4 5% 34%	3982
	11th to 20th	Day	10% 14% 6% 10% 7% 5% 4 4 4 5% 33%	4060
	21st to end	Day	14% 9% 3 7% 5% 4 4 5% 6% 6% 37%	4466
February	1st to 10th	Day	14% 13% 3 8% 5% 4 4 3 5% 6% 34%	1800
	11th to 20th	Day	14% 10% 3 9% 5% 6% 4 4 5% 6% 33%	1753
	21st to end	Day	14% 10% 3 9% 5% 4 4 3 4 6% 37%	1676
March	1st to 10th	Day	16% 11% 3 6% 5% 4 4 3 4 5% 40%	4935
	11th to 20th	Day	11% 7% 3 5% 4 3 4 3 5% 7% 47%	4980
	21st to end	Day	13% 9% 3 8% 6% 5% 4 3 5% 6% 36%	5465
April	1st to 10th	Day	13% 11% 3 8% 5% 4 4 5% 5% 7% 35%	2357
	11th to 20th	Day	13% 7% 2 7% 5% 4 4 4 5% 7% 42%	2374
	21st to end	Day	18% 6% 2 7% 5% 4 5% 3 6% 7% 38%	2500
May	1st to 10th	Day	23% 6% 3 8% 6% 5% 4 4 6% 7% 29%	4212
	11th to 20th	Day	22% 8% 2 6% 4 4 4 4 6% 7% 32%	4081
	21st to end	Day	11% 4 2 6% 5% 5% 5% 4 7% 10% 41%	4814
June	1st to 10th	Day	11% 5% 3 6% 5% 5% 4 5% 6% 10% 39%	2660
	11th to 20th	Day	10% 6% 2 6% 5% 6% 6% 6% 7% 9% 38%	2660
	21st to end	Day	9% 5% 2 6% 5% 4 6% 4 7% 10% 42%	2660
July	1st to 10th	Day	5% 4 2 7% 5% 6% 6% 5% 7% 10% 44%	4377
	11th to 20th	Day	6% 5% 2 7% 5% 5% 6% 5% 7% 10% 41%	4120
	21st to end	Day	11% 7% 3 8% 6% 5% 5% 5% 6% 8% 37%	4466
August	1st to 10th	Day	14% 6% 3 6% 5% 5% 6% 4 7% 9% 33%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 7% 5% 7% 8% 41%	4028
	21st to end	Day	8% 4 2 5% 4 5% 5% 4 6% 8% 48%	4180
September	1st to 10th	Day	15% 4 2 6% 3 4 5% 4 5% 7% 45%	2280
	11th to 20th	Day	12% 5% 2 5% 4 4 5% 3 6% 7% 46%	2185
	21st to end	Day	18% 8% 3 6% 4 5% 3 3 5% 6% 38%	2035
October	1st to 10th	Day	17% 6% 2 5% 4 3 3 3 5% 6% 46%	1900
	11th to 20th	Day	15% 5% 2 6% 6% 4 4 4 5% 5% 44%	1900
	21st to end	Day	14% 7% 2 6% 4 4 4 3 5% 7% 45%	2090
November	1st to 10th	Day	10% 6% 3 5% 3 4 4 3 5% 5% 52%	1957
	11th to 20th	Day	12% 10% 3 6% 5% 4 4 4 5% 6% 41%	1664
	21st to end	Day	15% 9% 2 6% 6% 4 4 4 5% 7% 38%	1600
December	1st to 10th	Day	12% 9% 3 8% 5% 4 4 3 5% 7% 41%	2600
	11th to 20th	Day	18% 12% 4 8% 4 4 4 3 5% 6% 34%	2990
	21st to end	Day	15% 10% 3 9% 6% 5% 5% 4 6% 7% 28%	3960
January	1st to 10th	Night	10% 13% 5% 13% 5% 5% 4 3 5% 6% 32%	5958
	11th to 20th	Night	11% 9% 5% 11% 5% 4 5% 3 5% 5% 36%	5900
	21st to end	Night	14% 9% 4 8% 4 4 4 4 5% 5% 40%	6490
February	1st to 10th	Night	13% 9% 3 8% 5% 5% 4 4 6% 6% 37%	2600
	11th to 20th	Night	15% 10% 4 8% 5% 5% 5% 4 5% 5% 33%	2533
	21st to end	Night	14% 11% 4 9% 6% 4 4 4 6% 6% 34%	1950
March	1st to 10th	Night	16% 8% 2 6% 4 4 4 3 5% 6% 43%	4918
	11th to 20th	Night	10% 10% 3 6% 3 3 3 3 5% 7% 47%	4980
	21st to end	Night	12% 8% 3 7% 5% 4 4 3 5% 6% 44%	5467
April	1st to 10th	Night	15% 10% 3 8% 4 4 5% 3 5% 5% 37%	2041
	11th to 20th	Night	14% 7% 2 6% 4 4 5% 3 7% 8% 40%	1975
	21st to end	Night	15% 6% 2 6% 4 5% 3 4 5% 7% 42%	1915
May	1st to 10th	Night	24% 8% 3 7% 4 4 4 4 6% 7% 29%	2903
	11th to 20th	Night	22% 8% 2 7% 4 4 3 3 5% 6% 35%	2818
	21st to end	Night	11% 5% 2 5% 5% 5% 5% 5% 7% 9% 42%	2741
June	1st to 10th	Night	10% 5% 1 5% 4 4 5% 4 6% 8% 47%	1520
	11th to 20th	Night	10% 5% 2 6% 6% 5% 5% 4 6% 9% 43%	1520
	21st to end	Night	8% 4 2 5% 6% 4 4 5% 7% 10% 45%	1520
July	1st to 10th	Night	6% 4 2 6% 5% 5% 6% 4 7% 10% 44%	2577
	11th to 20th	Night	5% 5% 2 7% 6% 5% 7% 5% 6% 10% 42%	2840
	21st to end	Night	9% 7% 3 8% 5% 5% 6% 5% 7% 9% 37%	3087
August	1st to 10th	Night	14% 5% 3 6% 4 5% 5% 5% 7% 9% 37%	2825
	11th to 20th	Night	10% 5% 2 6% 4 5% 5% 4 6% 8% 44%	2785
	21st to end	Night	9% 5% 2 6% 4 5% 4 4 6% 8% 48%	3444
September	1st to 10th	Night	13% 5% 2 6% 4 4 5% 3 6% 6% 47%	1900
	11th to 20th	Night	12% 6% 2 4 3 4 3 3 6% 7% 51%	1990
	21st to end	Night	19% 6% 2 6% 3 4 5% 4 5% 7% 41%	2144
October	1st to 10th	Night	17% 5% 2 6% 3 4 4 3 5% 6% 46%	2280
	11th to 20th	Night	14% 5% 2 6% 3 3 4 3 6% 7% 49%	2280
	21st to end	Night	16% 6% 2 6% 4 4 4 3 4 5% 47%	2508
November	1st to 10th	Night	9% 9% 3 6% 3 4 4 3 5% 6% 49%	2341
	11th to 20th	Night	13% 9% 3 7% 4 5% 4 3 5% 6% 41%	2731
	21st to end	Night	12% 8% 3 8% 6% 5% 5% 4 6% 6% 37%	2800
December	1st to 10th	Night	10% 8% 3 9% 5% 4 4 4 6% 7% 41%	4580
	11th to 20th	Night	15% 10% 4 8% 6% 5% 4 4 5% 6% 32%	5205
	21st to end	Night	14% 10% 4 9% 6% 6% 6% 5% 7% 7% 26%	6996

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	51% 5% 8% 22% 11% 3	3983
	11th to 20th	Day	53% 5% 9% 15% 15% 4	4060
	21st to end	Day	46% 5% 12% 24% 12% 2	4466
February	1st to 10th	Day	50% 5% 12% 22% 10% 1	1800
	11th to 20th	Day	51% 5% 11% 19% 12% 1	1762
	21st to end	Day	48% 4 11% 21% 13% 3	1676
March	1st to 10th	Day	47% 4 8% 23% 13% 6%	4935
	11th to 20th	Day	36% 5% 10% 29% 16% 4	4980
	21st to end	Day	48% 6% 9% 20% 15% 3	5465
April	1st to 10th	Day	48% 5% 11% 18% 14% 3	2357
	11th to 20th	Day	42% 5% 11% 21% 17% 5%	2374
	21st to end	Day	46% 5% 10% 24% 13% 2	2500
May	1st to 10th	Day	54% 6% 9% 21% 9% 1	4250
	11th to 20th	Day	51% 6% 8% 25% 8% 1	4085
	21st to end	Day	37% 8% 13% 25% 14% 2	4828
June	1st to 10th	Day	39% 8% 12% 24% 15% 1	2660
	11th to 20th	Day	40% 10% 13% 23% 13% 1	2660
	21st to end	Day	36% 8% 15% 26% 13% 2	2660
July	1st to 10th	Day	34% 10% 15% 27% 11% 4	4308
	11th to 20th	Day	34% 9% 16% 28% 12% 1	4051
	21st to end	Day	44% 7% 10% 22% 16% 1	4324
August	1st to 10th	Day	44% 10% 15% 24% 8%	4091
	11th to 20th	Day	36% 8% 12% 29% 14%	4067
	21st to end	Day	31% 9% 15% 28% 15% 1	4180
September	1st to 10th	Day	38% 6% 13% 20% 20% 4	2280
	11th to 20th	Day	36% 6% 9% 28% 18% 3	2185
	21st to end	Day	46% 6% 10% 21% 16% 1	2035
October	1st to 10th	Day	32% 4 9% 26% 24% 4	3160
	11th to 20th	Day	34% 5% 10% 24% 19% 8%	3140
	21st to end	Day	27% 4 11% 31% 25% 2	3428
November	1st to 10th	Day	34% 4 10% 26% 22% 4	1957
	11th to 20th	Day	43% 5% 11% 18% 19% 3	1664
	21st to end	Day	46% 4 12% 24% 13% 1	1600
December	1st to 10th	Day	43% 5% 13% 27% 8% 3	2600
	11th to 20th	Day	51% 4 14% 20% 9% 1	2986
	21st to end	Day	53% 7% 15% 14% 11%	3960
January	1st to 10th	Night	52% 5% 8% 21% 13% 1	5958
	11th to 20th	Night	48% 6% 9% 19% 12% 6%	5900
	21st to end	Night	45% 5% 10% 26% 11% 2	6490
February	1st to 10th	Night	46% 5% 13% 23% 11% 1	2600
	11th to 20th	Night	51% 6% 10% 19% 12% 1	2535
	21st to end	Night	51% 5% 10% 20% 11% 4	1950
March	1st to 10th	Night	41% 4 9% 28% 12% 5%	4918
	11th to 20th	Night	37% 5% 10% 32% 12% 4	4980
	21st to end	Night	41% 5% 11% 23% 17% 3	5467
April	1st to 10th	Night	48% 6% 10% 19% 14% 3	2041
	11th to 20th	Night	41% 7% 11% 22% 14% 5%	1975
	21st to end	Night	41% 7% 10% 25% 15% 3	1915
May	1st to 10th	Night	53% 7% 10% 19% 9% 2	2930
	11th to 20th	Night	52% 5% 9% 25% 9% 1	2819
	21st to end	Night	36% 9% 16% 26% 9% 4	2748
June	1st to 10th	Night	35% 8% 12% 28% 16% 2	1520
	11th to 20th	Night	38% 8% 13% 27% 13% 1	1520
	21st to end	Night	33% 8% 16% 26% 16% 2	1520
July	1st to 10th	Night	33% 9% 21% 21% 12% 5%	2536
	11th to 20th	Night	34% 11% 16% 25% 13% 1	2786
	21st to end	Night	39% 10% 14% 21% 14% 1	2988
August	1st to 10th	Night	40% 10% 17% 24% 8%	2814
	11th to 20th	Night	36% 7% 13% 25% 18% 1	2812
	21st to end	Night	34% 7% 14% 32% 13% 1	3444
September	1st to 10th	Night	37% 7% 13% 20% 19% 4	1900
	11th to 20th	Night	33% 5% 10% 30% 20% 2	1990
	21st to end	Night	43% 7% 11% 22% 17% 1	2144
October	1st to 10th	Night	35% 6% 10% 26% 22% 2	3800
	11th to 20th	Night	27% 6% 10% 25% 26% 6%	3779
	21st to end	Night	28% 4 10% 30% 24% 3	4120
November	1st to 10th	Night	36% 4 12% 23% 20% 4	2341
	11th to 20th	Night	44% 4 8% 24% 16% 4	2731
	21st to end	Night	47% 4 12% 21% 13% 2	2800
December	1st to 10th	Night	40% 6% 15% 29% 8% 1	4580
	11th to 20th	Night	51% 6% 12% 19% 10% 1	5208
	21st to end	Night	53% 7% 13% 16% 9%	6996

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	40% 25% 19% 12% 4 1	283
	11th to 20th	Day	39% 21% 28% 9% 2	300
	21st to end	Day	33% 22% 30% 12% 3	330
February	1st to 10th	Day	35% 23% 27% 12% 2	300
	11th to 20th	Day	49% 18% 26% 6%	300
	21st to end	Day	35% 23% 25% 15% 1	366
March	1st to 10th	Day	30% 23% 23% 21% 3	500
	11th to 20th	Day	33% 21% 25% 14% 6% 1	500
	21st to end	Day	27% 21% 31% 15% 5% 1	550
April	1st to 10th	Day	29% 25% 21% 19% 5% 1	500
	11th to 20th	Day	24% 19% 28% 17% 9% 3	492
	21st to end	Day	28% 18% 27% 18% 8% 2	500
May	1st to 10th	Day	24% 18% 28% 18% 8% 3	503
	11th to 20th	Day	25% 16% 27% 19% 11% 2	487
	21st to end	Day	16% 9% 28% 22% 19% 6%	529
June	1st to 10th	Day	17% 11% 29% 23% 16% 4	490
	11th to 20th	Day	14% 12% 29% 23% 15% 7%	490
	21st to end	Day	11% 13% 28% 28% 16% 4	490
July	1st to 10th	Day	10% 6% 24% 27% 24% 9%	485
	11th to 20th	Day	7% 6% 25% 30% 23% 8%	484
	21st to end	Day	15% 5% 23% 30% 22% 6%	532
August	1st to 10th	Day	12% 9% 21% 28% 21% 9%	486
	11th to 20th	Day	12% 5% 24% 26% 22% 11%	479
	21st to end	Day	10% 7% 21% 29% 24% 10%	539
September	1st to 10th	Day	17% 7% 21% 24% 22% 9%	490
	11th to 20th	Day	13% 6% 21% 26% 23% 11%	490
	21st to end	Day	27% 10% 21% 23% 15% 3	490
October	1st to 10th	Day	20% 9% 21% 27% 19% 4	490
	11th to 20th	Day	19% 16% 24% 24% 14% 3	490
	21st to end	Day	20% 16% 28% 24% 9% 3	539
November	1st to 10th	Day	17% 14% 26% 27% 14% 2	495
	11th to 20th	Day	23% 15% 36% 18% 7% 1	256
	21st to end	Day	30% 17% 29% 20% 5% 1	200
December	1st to 10th	Day	31% 18% 32% 13% 6% 1	200
	11th to 20th	Day	35% 18% 23% 21% 4	200
	21st to end	Day	27% 18% 26% 23% 5%	220
January	1st to 10th	Night	25% 23% 31% 19% 3	800
	11th to 20th	Night	25% 21% 29% 23% 2	800
	21st to end	Night	24% 21% 34% 19% 1	880
February	1st to 10th	Night	24% 19% 29% 27% 2	800
	11th to 20th	Night	29% 25% 29% 16% 1	783
	21st to end	Night	28% 20% 33% 17% 2	660
March	1st to 10th	Night	25% 17% 33% 22% 3	800
	11th to 20th	Night	27% 20% 26% 21% 5% 1	800
	21st to end	Night	23% 17% 34% 21% 5% 1	880
April	1st to 10th	Night	25% 19% 29% 22% 5%	800
	11th to 20th	Night	20% 17% 28% 27% 8%	791
	21st to end	Night	21% 13% 26% 31% 9%	715
May	1st to 10th	Night	21% 10% 22% 32% 14% 1	600
	11th to 20th	Night	19% 8% 23% 36% 13% 1	563
	21st to end	Night	11% 4 23% 38% 21% 2	421
June	1st to 10th	Night	9% 4 27% 39% 19% 1	380
	11th to 20th	Night	13% 6% 17% 40% 22% 2	380
	21st to end	Night	7% 4 24% 47% 17% 1	380
July	1st to 10th	Night	9% 3 13% 46% 25% 5%	400
	11th to 20th	Night	7% 3 12% 40% 36% 3	552
	21st to end	Night	9% 3 18% 37% 31% 2	624
August	1st to 10th	Night	10% 2 12% 46% 28% 3	567
	11th to 20th	Night	10% 3 10% 46% 29% 3	564
	21st to end	Night	11% 3 14% 39% 30% 3	817
September	1st to 10th	Night	15% 4 15% 38% 24% 5%	760
	11th to 20th	Night	15% 5% 12% 33% 31% 3	760
	21st to end	Night	20% 7% 18% 33% 20% 2	760
October	1st to 10th	Night	18% 8% 20% 31% 20% 3	760
	11th to 20th	Night	17% 13% 25% 32% 13% 1	760
	21st to end	Night	20% 12% 26% 31% 11% 1	836
November	1st to 10th	Night	14% 12% 25% 36% 12% 1	780
	11th to 20th	Night	22% 16% 25% 28% 8% 1	800
	21st to end	Night	22% 17% 26% 30% 5%	800
December	1st to 10th	Night	26% 16% 29% 25% 5%	800
	11th to 20th	Night	20% 20% 30% 28% 3	800
	21st to end	Night	23% 16% 29% 30% 2	880

Page generated at 2025-05-08 09:34:00. Version ac07

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