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 2026-09-14.

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% 7% 3 7% 5% 5% 5% 4 6% 8% 38%	148799
	Night	13% 8% 3 8% 5% 5% 5% 4 6% 7% 38%	142238
Transparency	Day	43% 7% 12% 23% 14% 2	152401
	Night	43% 7% 12% 23% 13% 2	146706
Seeing	Day	22% 14% 25% 22% 13% 4	17285
	Night	19% 13% 24% 30% 12% 1	26898

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% 12% 4 11% 5% 5% 4 4 4 6% 33%	5158
	11th to 20th	Day	8% 13% 6% 10% 7% 5% 5% 4 5% 5% 33%	5280
	21st to end	Day	12% 7% 2 9% 5% 5% 6% 5% 6% 6% 36%	5780
February	1st to 10th	Day	13% 12% 3 8% 5% 4 4 3 5% 6% 36%	1890
	11th to 20th	Day	14% 10% 4 9% 5% 6% 4 4 5% 6% 33%	1843
	21st to end	Day	14% 11% 3 9% 5% 4 4 3 5% 6% 37%	1758
March	1st to 10th	Day	16% 11% 3 6% 5% 4 4 3 4 5% 39%	5045
	11th to 20th	Day	11% 7% 3 6% 4 3 4 3 5% 7% 46%	5090
	21st to end	Day	13% 9% 3 8% 6% 5% 4 3 5% 6% 36%	5586
April	1st to 10th	Day	12% 11% 3 7% 5% 4 4 5% 5% 7% 36%	2475
	11th to 20th	Day	13% 7% 2 7% 5% 4 4 3 5% 7% 42%	2494
	21st to end	Day	18% 7% 2 7% 5% 4 5% 3 6% 7% 38%	2625
May	1st to 10th	Day	17% 7% 3 8% 5% 6% 5% 5% 7% 8% 31%	7616
	11th to 20th	Day	17% 7% 2 7% 5% 5% 5% 5% 6% 8% 33%	7626
	21st to end	Day	22% 6% 2 6% 4 4 4 3 5% 7% 34%	9023
June	1st to 10th	Day	11% 5% 2 6% 5% 5% 4 5% 6% 10% 40%	2940
	11th to 20th	Day	11% 6% 2 7% 5% 5% 6% 6% 7% 9% 37%	2940
	21st to end	Day	10% 5% 2 6% 5% 4 6% 4 7% 10% 42%	2940
July	1st to 10th	Day	7% 5% 2 7% 5% 5% 5% 5% 6% 9% 42%	8161
	11th to 20th	Day	7% 6% 3 8% 5% 6% 6% 5% 8% 12% 35%	7680
	21st to end	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 9% 38%	8340
August	1st to 10th	Day	13% 7% 3 7% 6% 6% 6% 5% 7% 10% 29%	6014
	11th to 20th	Day	11% 6% 3 7% 5% 5% 6% 5% 7% 9% 36%	5935
	21st to end	Day	7% 4 2 5% 3 5% 5% 5% 7% 10% 47%	6080
September	1st to 10th	Day	14% 4 2 6% 3 4 5% 4 5% 7% 46%	2520
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 3 6% 7% 46%	2336
	21st to end	Day	18% 9% 3 6% 4 5% 3 4 5% 6% 37%	2142
October	1st to 10th	Day	16% 6% 2 5% 3 3 3 2 5% 7% 47%	2000
	11th to 20th	Day	15% 6% 2 6% 5% 4 4 4 5% 5% 45%	2000
	21st to end	Day	14% 8% 2 6% 4 4 4 4 5% 6% 44%	2200
November	1st to 10th	Day	9% 6% 3 5% 3 4 4 3 5% 6% 52%	2057
	11th to 20th	Day	12% 10% 3 6% 5% 4 4 4 5% 6% 41%	1747
	21st to end	Day	15% 9% 2 6% 6% 4 4 4 5% 7% 38%	1680
December	1st to 10th	Day	12% 9% 4 8% 4 4 4 3 5% 7% 41%	2680
	11th to 20th	Day	17% 11% 4 8% 4 4 4 3 5% 6% 34%	3070
	21st to end	Day	15% 10% 3 10% 6% 5% 5% 4 6% 7% 28%	4048
January	1st to 10th	Night	10% 13% 5% 13% 6% 5% 4 3 5% 6% 30%	7717
	11th to 20th	Night	10% 9% 5% 11% 5% 5% 5% 4 5% 5% 37%	7680
	21st to end	Night	12% 8% 3 8% 5% 5% 5% 4 5% 5% 40%	8401
February	1st to 10th	Night	13% 9% 3 8% 5% 5% 4 4 6% 6% 37%	2730
	11th to 20th	Night	15% 10% 4 8% 5% 5% 5% 4 5% 5% 33%	2663
	21st to end	Night	14% 11% 4 9% 5% 4 3 4 6% 6% 34%	2044
March	1st to 10th	Night	16% 8% 2 6% 4 4 4 3 5% 6% 43%	5028
	11th to 20th	Night	10% 10% 3 6% 3 3 4 3 5% 7% 47%	5090
	21st to end	Night	12% 8% 2 7% 5% 4 4 3 5% 6% 44%	5588
April	1st to 10th	Night	14% 10% 3 8% 4 4 5% 3 5% 6% 37%	2143
	11th to 20th	Night	13% 7% 2 6% 4 4 5% 3 7% 8% 40%	2075
	21st to end	Night	15% 6% 2 6% 4 5% 4 4 6% 7% 42%	2011
May	1st to 10th	Night	18% 8% 3 7% 5% 5% 5% 4 6% 7% 32%	5237
	11th to 20th	Night	18% 8% 3 6% 4 4 5% 4 6% 8% 34%	5234
	21st to end	Night	23% 8% 3 6% 5% 5% 4 3 5% 6% 32%	5117
June	1st to 10th	Night	10% 5% 2 5% 5% 4 5% 4 6% 8% 47%	1680
	11th to 20th	Night	10% 5% 2 7% 5% 5% 5% 4 6% 9% 42%	1680
	21st to end	Night	8% 4 2 5% 6% 4 5% 5% 6% 10% 44%	1680
July	1st to 10th	Night	9% 6% 2 7% 5% 5% 5% 4 6% 8% 43%	4791
	11th to 20th	Night	8% 6% 3 9% 6% 6% 6% 5% 7% 9% 34%	5277
	21st to end	Night	9% 7% 3 7% 5% 5% 6% 5% 7% 9% 37%	5736
August	1st to 10th	Night	12% 6% 3 8% 5% 6% 7% 6% 8% 10% 31%	4135
	11th to 20th	Night	12% 6% 3 8% 5% 5% 6% 4 6% 8% 37%	4095
	21st to end	Night	9% 5% 2 6% 5% 5% 5% 4 7% 9% 44%	4999
September	1st to 10th	Night	12% 5% 2 6% 3 4 5% 3 6% 6% 49%	2100
	11th to 20th	Night	12% 6% 2 5% 4 4 3 3 6% 6% 50%	2126
	21st to end	Night	18% 6% 2 6% 3 4 5% 4 5% 7% 39%	2257
October	1st to 10th	Night	16% 5% 2 6% 3 3 4 2 5% 6% 48%	2400
	11th to 20th	Night	14% 5% 2 6% 3 3 4 3 6% 7% 49%	2400
	21st to end	Night	16% 6% 2 6% 4 4 4 3 5% 5% 46%	2640
November	1st to 10th	Night	8% 8% 3 6% 3 4 5% 3 5% 6% 49%	2461
	11th to 20th	Night	14% 10% 3 7% 4 5% 4 3 5% 6% 41%	2868
	21st to end	Night	12% 8% 4 8% 6% 5% 5% 4 6% 6% 36%	2940
December	1st to 10th	Night	10% 8% 3 9% 5% 4 4 4 6% 8% 40%	4720
	11th to 20th	Night	15% 10% 4 8% 6% 5% 4 4 5% 6% 32%	5345
	21st to end	Night	14% 10% 4 9% 6% 6% 6% 5% 7% 7% 27%	7150

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% 6% 10% 21% 10% 2	5159
	11th to 20th	Day	50% 5% 9% 16% 15% 4	5280
	21st to end	Day	45% 5% 13% 26% 10% 2	5780
February	1st to 10th	Day	49% 5% 11% 22% 11% 1	1890
	11th to 20th	Day	51% 5% 10% 19% 12% 1	1852
	21st to end	Day	48% 4 11% 21% 13% 2	1758
March	1st to 10th	Day	47% 4 9% 23% 13% 5%	5045
	11th to 20th	Day	36% 5% 10% 29% 15% 4	5090
	21st to end	Day	47% 6% 9% 20% 15% 3	5586
April	1st to 10th	Day	47% 6% 11% 19% 15% 3	2475
	11th to 20th	Day	41% 5% 11% 21% 17% 4	2494
	21st to end	Day	46% 5% 10% 25% 13% 2	2625
May	1st to 10th	Day	48% 7% 11% 22% 11% 2	7651
	11th to 20th	Day	47% 7% 10% 27% 8% 1	7630
	21st to end	Day	48% 7% 9% 18% 15% 3	9038
June	1st to 10th	Day	38% 8% 12% 24% 17% 1	2940
	11th to 20th	Day	41% 10% 13% 23% 13% 1	2940
	21st to end	Day	36% 8% 15% 25% 13% 2	2940
July	1st to 10th	Day	37% 10% 12% 25% 14% 2	8092
	11th to 20th	Day	38% 11% 14% 27% 9% 1	7611
	21st to end	Day	39% 8% 11% 23% 18% 1	8156
August	1st to 10th	Day	47% 11% 15% 20% 7%	6001
	11th to 20th	Day	41% 9% 14% 25% 11%	5974
	21st to end	Day	29% 9% 19% 29% 14% 1	6080
September	1st to 10th	Day	36% 7% 13% 21% 20% 3	2520
	11th to 20th	Day	36% 6% 9% 29% 18% 2	2336
	21st to end	Day	47% 6% 10% 20% 16% 1	2142
October	1st to 10th	Day	31% 4 9% 27% 24% 4	3260
	11th to 20th	Day	34% 5% 10% 24% 19% 8%	3240
	21st to end	Day	28% 4 11% 31% 24% 2	3538
November	1st to 10th	Day	34% 5% 11% 25% 22% 4	2057
	11th to 20th	Day	43% 5% 11% 18% 19% 3	1747
	21st to end	Day	46% 4 12% 24% 12% 1	1680
December	1st to 10th	Day	43% 5% 14% 27% 8% 3	2680
	11th to 20th	Day	51% 4 14% 20% 9% 1	3066
	21st to end	Day	53% 7% 15% 14% 11%	4048
January	1st to 10th	Night	52% 6% 9% 21% 11% 1	7718
	11th to 20th	Night	46% 6% 9% 19% 15% 5%	7680
	21st to end	Night	44% 5% 11% 27% 12% 1	8401
February	1st to 10th	Night	46% 5% 13% 23% 12% 1	2730
	11th to 20th	Night	52% 6% 10% 19% 12% 1	2665
	21st to end	Night	50% 5% 10% 20% 11% 4	2044
March	1st to 10th	Night	41% 4 9% 28% 12% 5%	5028
	11th to 20th	Night	37% 5% 10% 32% 12% 4	5090
	21st to end	Night	41% 5% 11% 23% 17% 3	5588
April	1st to 10th	Night	47% 6% 10% 20% 14% 3	2143
	11th to 20th	Night	41% 7% 11% 22% 14% 4	2075
	21st to end	Night	40% 7% 11% 25% 14% 2	2011
May	1st to 10th	Night	49% 8% 13% 18% 10% 2	5264
	11th to 20th	Night	46% 7% 12% 26% 9% 1	5235
	21st to end	Night	51% 7% 11% 19% 10% 2	5124
June	1st to 10th	Night	36% 8% 11% 27% 17% 2	1680
	11th to 20th	Night	39% 8% 13% 26% 13% 1	1680
	21st to end	Night	33% 8% 15% 25% 17% 1	1680
July	1st to 10th	Night	37% 9% 16% 21% 13% 3	4752
	11th to 20th	Night	42% 11% 14% 22% 10% 1	5226
	21st to end	Night	37% 11% 14% 21% 16% 1	5606
August	1st to 10th	Night	46% 11% 15% 21% 8%	4124
	11th to 20th	Night	43% 9% 14% 20% 13% 1	4122
	21st to end	Night	34% 8% 17% 28% 11% 1	4999
September	1st to 10th	Night	35% 7% 14% 21% 19% 3	2100
	11th to 20th	Night	34% 5% 10% 30% 20% 2	2126
	21st to end	Night	44% 7% 11% 21% 16% 1	2257
October	1st to 10th	Night	35% 6% 10% 26% 23% 2	3920
	11th to 20th	Night	28% 5% 10% 25% 26% 6%	3899
	21st to end	Night	28% 4 10% 30% 24% 3	4252
November	1st to 10th	Night	36% 5% 12% 23% 20% 4	2461
	11th to 20th	Night	44% 4 8% 24% 16% 4	2868
	21st to end	Night	48% 5% 11% 21% 13% 2	2940
December	1st to 10th	Night	41% 6% 16% 29% 8% 1	4720
	11th to 20th	Night	51% 6% 12% 20% 10% 1	5348
	21st to end	Night	53% 7% 13% 16% 9%	7150

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	39% 23% 19% 13% 4 1	311
	11th to 20th	Day	40% 22% 27% 9% 2	330
	21st to end	Day	35% 21% 30% 11% 3	363
February	1st to 10th	Day	34% 23% 28% 12% 3	330
	11th to 20th	Day	48% 18% 26% 7%	330
	21st to end	Day	34% 23% 26% 15% 2	396
March	1st to 10th	Day	30% 22% 23% 21% 3	540
	11th to 20th	Day	35% 20% 25% 14% 6% 1	540
	21st to end	Day	27% 21% 30% 16% 5% 1	594
April	1st to 10th	Day	28% 24% 22% 19% 6% 1	540
	11th to 20th	Day	24% 19% 29% 17% 8% 3	532
	21st to end	Day	26% 19% 28% 18% 8% 1	540
May	1st to 10th	Day	24% 20% 29% 17% 8% 3	543
	11th to 20th	Day	25% 16% 27% 20% 11% 2	567
	21st to end	Day	20% 12% 26% 20% 17% 5%	617
June	1st to 10th	Day	16% 12% 28% 24% 16% 4	570
	11th to 20th	Day	16% 13% 28% 23% 14% 6%	570
	21st to end	Day	11% 11% 27% 29% 17% 5%	570
July	1st to 10th	Day	10% 6% 23% 27% 25% 9%	565
	11th to 20th	Day	7% 6% 24% 30% 23% 9%	564
	21st to end	Day	14% 5% 23% 30% 21% 6%	620
August	1st to 10th	Day	12% 8% 22% 28% 20% 9%	566
	11th to 20th	Day	11% 6% 25% 27% 21% 10%	559
	21st to end	Day	9% 6% 22% 29% 24% 9%	627
September	1st to 10th	Day	15% 7% 21% 25% 23% 9%	570
	11th to 20th	Day	13% 6% 20% 26% 23% 11%	542
	21st to end	Day	27% 10% 21% 23% 15% 3	530
October	1st to 10th	Day	19% 8% 20% 26% 19% 7%	530
	11th to 20th	Day	19% 17% 24% 23% 14% 3	530
	21st to end	Day	21% 17% 27% 23% 9% 3	583
November	1st to 10th	Day	18% 14% 27% 27% 13% 2	535
	11th to 20th	Day	26% 15% 34% 18% 7% 1	279
	21st to end	Day	30% 17% 29% 19% 5%	220
December	1st to 10th	Day	31% 18% 33% 12% 5% 1	220
	11th to 20th	Day	34% 19% 22% 20% 4	220
	21st to end	Day	29% 18% 26% 21% 5%	242
January	1st to 10th	Night	25% 22% 31% 19% 3	840
	11th to 20th	Night	25% 21% 30% 23% 2	840
	21st to end	Night	25% 21% 34% 19% 1	924
February	1st to 10th	Night	23% 18% 29% 28% 2	840
	11th to 20th	Night	29% 25% 30% 16% 1	823
	21st to end	Night	28% 20% 33% 17% 2	692
March	1st to 10th	Night	25% 17% 33% 22% 3	840
	11th to 20th	Night	27% 20% 26% 21% 5% 1	840
	21st to end	Night	23% 17% 34% 20% 5% 1	924
April	1st to 10th	Night	24% 19% 29% 23% 5%	840
	11th to 20th	Night	20% 17% 28% 27% 8%	831
	21st to end	Night	21% 12% 26% 32% 9%	751
May	1st to 10th	Night	21% 10% 23% 31% 13% 1	630
	11th to 20th	Night	19% 8% 23% 37% 12% 1	621
	21st to end	Night	14% 4 24% 36% 20% 2	465
June	1st to 10th	Night	10% 4 26% 40% 20% 1	420
	11th to 20th	Night	13% 7% 17% 41% 20% 2	420
	21st to end	Night	8% 4 24% 44% 18% 2	420
July	1st to 10th	Night	8% 3 13% 45% 27% 4	444
	11th to 20th	Night	7% 3 12% 40% 36% 3	612
	21st to end	Night	8% 4 18% 37% 31% 2	690
August	1st to 10th	Night	10% 2 12% 44% 28% 3	627
	11th to 20th	Night	9% 3 10% 46% 29% 3	624
	21st to end	Night	11% 3 16% 39% 30% 2	903
September	1st to 10th	Night	14% 4 15% 39% 24% 4	840
	11th to 20th	Night	14% 5% 12% 34% 31% 3	813
	21st to end	Night	19% 7% 19% 34% 19% 2	800
October	1st to 10th	Night	18% 8% 19% 31% 21% 3	800
	11th to 20th	Night	17% 13% 24% 33% 12% 1	800
	21st to end	Night	20% 12% 26% 31% 10% 1	880
November	1st to 10th	Night	15% 12% 24% 36% 11% 1	820
	11th to 20th	Night	24% 16% 25% 27% 8%	840
	21st to end	Night	22% 17% 26% 30% 5%	840
December	1st to 10th	Night	25% 16% 30% 25% 4	840
	11th to 20th	Night	21% 20% 30% 27% 3	840
	21st to end	Night	23% 16% 30% 29% 2	924

Page generated at 2026-09-11 04:11:53. Version ac07

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