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 2024-03-01.

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 6% 6% 3 5% 5% 6% 7% 38%	78542
	Night	14% 7% 3 6% 5% 3 5% 5% 5% 7% 39%	80863
Transparency	Day	45% 6% 12% 22% 13% 2	78259
	Night	44% 6% 12% 23% 13% 2	80665
Seeing	Day	22% 14% 25% 22% 13% 4	13885
	Night	19% 13% 24% 30% 12% 1	23691

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	15% 13% 4 7% 5% 3 4 4 4 5% 36%	2776
	11th to 20th	Day	10% 15% 7% 9% 10% 4 4 5% 4 4 28%	2840
	21st to end	Day	16% 11% 4 7% 7% 3 5% 5% 5% 6% 31%	3124
February	1st to 10th	Day	14% 12% 4 7% 6% 3 4 4 5% 6% 35%	1710
	11th to 20th	Day	14% 9% 4 8% 6% 5% 5% 4 5% 6% 34%	1663
	21st to end	Day	15% 10% 4 8% 6% 2 4 4 4 6% 36%	1594
March	1st to 10th	Day	13% 9% 4 6% 5% 2 4 4 5% 6% 43%	1980
	11th to 20th	Day	16% 9% 4 6% 5% 3 5% 4 5% 6% 36%	1980
	21st to end	Day	16% 9% 4 6% 7% 3 4 5% 5% 7% 34%	2178
April	1st to 10th	Day	11% 9% 4 7% 6% 3 4 6% 5% 8% 37%	2121
	11th to 20th	Day	13% 6% 3 6% 6% 3 4 4 4 7% 43%	2134
	21st to end	Day	19% 6% 2 6% 6% 3 5% 4 5% 7% 38%	2250
May	1st to 10th	Day	17% 6% 3 6% 7% 4 5% 5% 6% 7% 34%	2340
	11th to 20th	Day	19% 7% 3 6% 5% 3 5% 5% 6% 8% 35%	2301
	21st to end	Day	14% 5% 3 6% 6% 3 5% 5% 6% 8% 39%	2716
June	1st to 10th	Day	11% 5% 3 5% 5% 3 5% 6% 6% 10% 39%	2520
	11th to 20th	Day	11% 5% 2 5% 6% 4 6% 7% 7% 9% 36%	2520
	21st to end	Day	10% 4 2 5% 6% 3 6% 6% 6% 10% 41%	2520
July	1st to 10th	Day	8% 5% 3 7% 6% 4 6% 6% 7% 9% 40%	2485
	11th to 20th	Day	6% 4 3 6% 6% 5% 7% 6% 7% 10% 40%	2340
	21st to end	Day	11% 5% 3 6% 7% 4 6% 6% 7% 8% 36%	2547
August	1st to 10th	Day	9% 6% 3 5% 7% 5% 7% 6% 8% 10% 35%	2327
	11th to 20th	Day	11% 5% 3 6% 6% 4 6% 6% 7% 8% 38%	2301
	21st to end	Day	11% 5% 3 5% 5% 3 6% 6% 7% 8% 42%	2376
September	1st to 10th	Day	16% 4 2 6% 4 3 5% 5% 5% 7% 44%	2160
	11th to 20th	Day	12% 5% 3 5% 5% 3 5% 5% 6% 8% 46%	2070
	21st to end	Day	17% 7% 3 4 5% 4 4 5% 5% 6% 40%	1928
October	1st to 10th	Day	17% 6% 2 4 5% 3 3 4 5% 6% 45%	1800
	11th to 20th	Day	16% 5% 3 6% 6% 3 4 5% 5% 5% 43%	1800
	21st to end	Day	15% 7% 2 5% 4 3 4 4 5% 6% 44%	1980
November	1st to 10th	Day	10% 6% 3 5% 4 2 4 3 5% 6% 52%	1857
	11th to 20th	Day	13% 10% 3 5% 5% 3 4 4 5% 6% 41%	1582
	21st to end	Day	15% 8% 2 4 6% 3 5% 4 5% 7% 39%	1520
December	1st to 10th	Day	16% 10% 5% 7% 6% 4 5% 5% 6% 7% 30%	1520
	11th to 20th	Day	14% 12% 5% 6% 5% 3 4 4 5% 6% 36%	1910
	21st to end	Day	16% 9% 3 7% 8% 4 6% 5% 5% 6% 29%	2772
January	1st to 10th	Night	11% 14% 5% 8% 7% 4 5% 4 6% 6% 30%	4164
	11th to 20th	Night	15% 10% 4 9% 6% 3 4 4 4 5% 36%	4120
	21st to end	Night	18% 11% 4 7% 7% 3 4 5% 4 5% 32%	4532
February	1st to 10th	Night	13% 8% 4 7% 6% 3 4 5% 6% 7% 37%	2470
	11th to 20th	Night	15% 9% 4 7% 7% 4 6% 4 4 6% 34%	2403
	21st to end	Night	15% 10% 5% 7% 6% 3 4 4 6% 6% 33%	1856
March	1st to 10th	Night	12% 8% 2 5% 5% 3 5% 5% 5% 6% 45%	1987
	11th to 20th	Night	16% 8% 3 6% 5% 3 5% 3 5% 7% 39%	1980
	21st to end	Night	17% 9% 3 5% 5% 3 4 4 5% 7% 39%	2178
April	1st to 10th	Night	15% 9% 3 7% 5% 2 5% 5% 5% 6% 38%	1837
	11th to 20th	Night	13% 6% 2 5% 5% 3 5% 4 7% 8% 41%	1775
	21st to end	Night	17% 6% 3 5% 4 3 4 5% 5% 7% 42%	1724
May	1st to 10th	Night	18% 6% 3 5% 4 3 5% 5% 6% 8% 38%	1620
	11th to 20th	Night	17% 6% 3 6% 5% 4 5% 4 5% 7% 39%	1592
	21st to end	Night	11% 5% 1 4 6% 3 6% 5% 7% 9% 42%	1559
June	1st to 10th	Night	10% 4 2 4 5% 3 4 5% 6% 9% 48%	1440
	11th to 20th	Night	10% 5% 2 5% 6% 4 5% 5% 6% 8% 42%	1440
	21st to end	Night	8% 3 2 4 6% 4 4 6% 7% 10% 45%	1440
July	1st to 10th	Night	10% 4 2 5% 5% 4 5% 5% 7% 8% 45%	1469
	11th to 20th	Night	6% 3 2 4 5% 3 6% 6% 6% 9% 50%	1620
	21st to end	Night	8% 3 3 5% 5% 3 6% 6% 7% 11% 42%	1771
August	1st to 10th	Night	7% 5% 2 5% 5% 4 6% 7% 8% 9% 44%	1611
	11th to 20th	Night	9% 4 2 6% 5% 4 5% 5% 6% 8% 45%	1598
	21st to end	Night	10% 5% 2 5% 4 4 4 5% 6% 9% 46%	1962
September	1st to 10th	Night	14% 5% 2 5% 4 3 4 5% 6% 6% 47%	1800
	11th to 20th	Night	12% 5% 2 4 4 3 4 3 5% 7% 51%	1885
	21st to end	Night	18% 4 2 4 5% 3 4 6% 5% 7% 43%	2031
October	1st to 10th	Night	17% 5% 2 5% 4 3 4 3 5% 6% 46%	2160
	11th to 20th	Night	15% 4 2 5% 4 2 4 4 6% 7% 48%	2160
	21st to end	Night	17% 6% 2 5% 5% 3 4 5% 4 5% 45%	2376
November	1st to 10th	Night	9% 8% 4 5% 4 3 5% 3 5% 6% 48%	2221
	11th to 20th	Night	13% 8% 3 6% 5% 3 4 4 5% 6% 42%	2593
	21st to end	Night	12% 7% 4 7% 6% 3 5% 5% 6% 6% 38%	2660
December	1st to 10th	Night	15% 9% 4 7% 7% 3 4 5% 5% 6% 33%	2660
	11th to 20th	Night	15% 9% 5% 6% 6% 4 5% 5% 5% 6% 36%	3285
	21st to end	Night	16% 9% 4 7% 7% 4 6% 6% 7% 7% 28%	4884

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% 9% 25% 10% 2	2777
	11th to 20th	Day	60% 4 8% 16% 10% 2	2840
	21st to end	Day	54% 4 10% 21% 9% 1	3124
February	1st to 10th	Day	51% 5% 12% 21% 10% 1	1710
	11th to 20th	Day	50% 5% 11% 20% 12% 2	1672
	21st to end	Day	49% 4 11% 20% 13% 2	1594
March	1st to 10th	Day	43% 4 12% 25% 15% 2	1980
	11th to 20th	Day	48% 5% 9% 20% 14% 3	1980
	21st to end	Day	50% 5% 10% 21% 12% 3	2178
April	1st to 10th	Day	45% 5% 12% 19% 15% 4	2121
	11th to 20th	Day	41% 5% 11% 21% 17% 5%	2134
	21st to end	Day	47% 5% 10% 23% 13% 3	2250
May	1st to 10th	Day	49% 7% 12% 19% 13% 1	2340
	11th to 20th	Day	48% 7% 10% 21% 11% 3	2305
	21st to end	Day	43% 7% 14% 24% 10% 2	2716
June	1st to 10th	Day	39% 9% 13% 24% 15% 1	2520
	11th to 20th	Day	42% 10% 13% 22% 13% 1	2520
	21st to end	Day	37% 8% 15% 26% 13% 2	2520
July	1st to 10th	Day	40% 8% 12% 23% 15% 3	2416
	11th to 20th	Day	37% 8% 13% 24% 16% 2	2271
	21st to end	Day	42% 8% 11% 21% 15% 2	2405
August	1st to 10th	Day	41% 10% 15% 23% 10% 1	2314
	11th to 20th	Day	40% 9% 14% 24% 13% 1	2301
	21st to end	Day	37% 9% 14% 24% 13% 2	2376
September	1st to 10th	Day	39% 7% 13% 19% 18% 4	2160
	11th to 20th	Day	36% 6% 10% 28% 18% 3	2070
	21st to end	Day	44% 6% 10% 21% 17% 1	1928
October	1st to 10th	Day	40% 5% 12% 26% 14% 3	1800
	11th to 20th	Day	43% 5% 10% 24% 17% 1	1800
	21st to end	Day	41% 5% 9% 26% 17% 2	1980
November	1st to 10th	Day	34% 4 11% 26% 21% 4	1857
	11th to 20th	Day	43% 5% 11% 18% 19% 3	1582
	21st to end	Day	45% 4 12% 25% 13% 1	1520
December	1st to 10th	Day	53% 5% 12% 21% 8% 1	1520
	11th to 20th	Day	51% 3 11% 25% 8% 2	1906
	21st to end	Day	54% 5% 13% 17% 10% 1	2772
January	1st to 10th	Night	54% 5% 9% 20% 11% 1	4164
	11th to 20th	Night	51% 5% 10% 22% 10% 2	4120
	21st to end	Night	55% 5% 9% 23% 7% 1	4532
February	1st to 10th	Night	46% 5% 13% 24% 11% 1	2470
	11th to 20th	Night	51% 6% 10% 19% 13% 1	2405
	21st to end	Night	52% 5% 10% 19% 10% 4	1856
March	1st to 10th	Night	40% 5% 10% 29% 14% 2	1987
	11th to 20th	Night	46% 5% 11% 23% 13% 2	1980
	21st to end	Night	46% 6% 10% 21% 13% 4	2178
April	1st to 10th	Night	47% 5% 10% 20% 15% 3	1837
	11th to 20th	Night	40% 7% 11% 22% 15% 5%	1775
	21st to end	Night	42% 7% 10% 24% 14% 3	1724
May	1st to 10th	Night	43% 7% 12% 23% 11% 3	1620
	11th to 20th	Night	46% 7% 11% 20% 15% 2	1593
	21st to end	Night	35% 9% 18% 25% 11% 1	1560
June	1st to 10th	Night	34% 8% 12% 28% 16% 2	1440
	11th to 20th	Night	39% 8% 14% 26% 12% 2	1440
	21st to end	Night	32% 8% 16% 26% 16% 2	1440
July	1st to 10th	Night	36% 10% 15% 23% 13% 4	1428
	11th to 20th	Night	30% 9% 15% 27% 17% 2	1566
	21st to end	Night	32% 10% 17% 25% 16% 1	1672
August	1st to 10th	Night	34% 10% 18% 25% 14% 1	1600
	11th to 20th	Night	36% 7% 16% 26% 15% 1	1598
	21st to end	Night	36% 7% 14% 27% 15% 2	1962
September	1st to 10th	Night	37% 7% 14% 20% 18% 4	1800
	11th to 20th	Night	33% 5% 10% 30% 20% 2	1885
	21st to end	Night	41% 7% 11% 23% 18% 1	2031
October	1st to 10th	Night	39% 6% 11% 26% 17% 2	2160
	11th to 20th	Night	35% 6% 11% 29% 19% 1	2160
	21st to end	Night	41% 4 9% 26% 18% 2	2376
November	1st to 10th	Night	37% 5% 12% 23% 19% 4	2221
	11th to 20th	Night	43% 4 8% 25% 16% 4	2593
	21st to end	Night	46% 4 12% 22% 14% 2	2660
December	1st to 10th	Night	52% 6% 11% 22% 9% 1	2660
	11th to 20th	Night	49% 6% 10% 22% 13% 1	3288
	21st to end	Night	54% 7% 14% 16% 9%	4884

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	36% 26% 20% 13% 4 1	254
	11th to 20th	Day	38% 22% 28% 10% 3	270
	21st to end	Day	34% 21% 30% 11% 4	297
February	1st to 10th	Day	33% 23% 28% 13% 3	270
	11th to 20th	Day	46% 19% 28% 7%	270
	21st to end	Day	35% 24% 23% 16% 1	336
March	1st to 10th	Day	30% 23% 24% 21% 2	420
	11th to 20th	Day	34% 21% 24% 15% 6%	420
	21st to end	Day	28% 19% 30% 16% 6% 1	462
April	1st to 10th	Day	26% 25% 21% 21% 6% 1	420
	11th to 20th	Day	22% 19% 28% 18% 9% 4	412
	21st to end	Day	30% 17% 26% 18% 8% 2	420
May	1st to 10th	Day	25% 18% 27% 18% 8% 3	423
	11th to 20th	Day	26% 16% 28% 18% 10% 2	447
	21st to end	Day	17% 9% 27% 21% 20% 6%	485
June	1st to 10th	Day	17% 10% 29% 23% 17% 4	450
	11th to 20th	Day	15% 13% 30% 22% 14% 6%	450
	21st to end	Day	11% 12% 27% 29% 16% 4	450
July	1st to 10th	Day	11% 6% 23% 26% 23% 10%	445
	11th to 20th	Day	7% 6% 24% 30% 25% 9%	444
	21st to end	Day	14% 5% 23% 30% 22% 6%	488
August	1st to 10th	Day	11% 8% 20% 28% 22% 10%	446
	11th to 20th	Day	13% 5% 22% 26% 23% 12%	439
	21st to end	Day	11% 7% 21% 29% 21% 11%	495
September	1st to 10th	Day	18% 7% 20% 24% 22% 9%	450
	11th to 20th	Day	13% 6% 21% 27% 23% 10%	450
	21st to end	Day	26% 8% 22% 24% 16% 4	450
October	1st to 10th	Day	21% 8% 20% 27% 19% 4	450
	11th to 20th	Day	20% 17% 23% 24% 14% 2	450
	21st to end	Day	22% 17% 28% 22% 8% 3	495
November	1st to 10th	Day	17% 13% 25% 27% 15% 2	455
	11th to 20th	Day	24% 15% 34% 18% 8% 1	234
	21st to end	Day	27% 17% 30% 21% 4 1	180
December	1st to 10th	Day	31% 19% 29% 13% 6% 1	180
	11th to 20th	Day	36% 18% 23% 21% 3	180
	21st to end	Day	26% 19% 26% 23% 5% 1	198
January	1st to 10th	Night	24% 22% 32% 19% 3	760
	11th to 20th	Night	25% 20% 30% 24% 2	760
	21st to end	Night	24% 21% 33% 20% 2	836
February	1st to 10th	Night	23% 19% 28% 28% 2	760
	11th to 20th	Night	27% 26% 29% 16% 1	743
	21st to end	Night	29% 20% 32% 17% 2	628
March	1st to 10th	Night	24% 17% 34% 22% 3	723
	11th to 20th	Night	28% 19% 26% 21% 5% 1	720
	21st to end	Night	23% 17% 33% 21% 5% 1	792
April	1st to 10th	Night	25% 18% 29% 22% 5%	720
	11th to 20th	Night	19% 16% 28% 27% 9%	711
	21st to end	Night	23% 13% 26% 30% 8%	644
May	1st to 10th	Night	20% 11% 22% 31% 14% 1	540
	11th to 20th	Night	19% 7% 23% 36% 12% 1	531
	21st to end	Night	12% 4 22% 39% 22% 2	399
June	1st to 10th	Night	10% 3 25% 41% 20% 1	360
	11th to 20th	Night	14% 6% 18% 39% 21% 2	360
	21st to end	Night	7% 4 24% 47% 17% 1	360
July	1st to 10th	Night	9% 2 14% 45% 25% 5%	378
	11th to 20th	Night	7% 2 12% 39% 37% 3	522
	21st to end	Night	9% 3 18% 36% 32% 2	591
August	1st to 10th	Night	10% 2 12% 45% 28% 3	537
	11th to 20th	Night	10% 2 10% 45% 30% 3	534
	21st to end	Night	12% 3 14% 38% 30% 3	774
September	1st to 10th	Night	15% 3 15% 36% 25% 5%	720
	11th to 20th	Night	14% 5% 13% 33% 31% 3	720
	21st to end	Night	19% 7% 19% 33% 21% 2	720
October	1st to 10th	Night	19% 8% 19% 31% 20% 2	720
	11th to 20th	Night	17% 13% 24% 32% 12% 1	720
	21st to end	Night	21% 12% 27% 29% 10% 1	792
November	1st to 10th	Night	15% 12% 24% 36% 12% 1	740
	11th to 20th	Night	22% 17% 25% 28% 9% 1	760
	21st to end	Night	20% 18% 26% 31% 5%	760
December	1st to 10th	Night	26% 16% 28% 25% 4	760
	11th to 20th	Night	19% 20% 30% 28% 3	760
	21st to end	Night	23% 16% 29% 30% 2	836

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