Hidden Valley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hidden Valley Observatory clear sky chart from 2005-11-06 to 2024-03-23.

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	6% 5% 2 4 4 3 4 5% 6% 8% 52%	78626
	Night	6% 5% 2 4 4 3 4 4 6% 8% 53%	81318
Transparency	Day	28% 9% 16% 26% 16% 4	78330
	Night	28% 9% 15% 27% 18% 4	81136
Seeing	Day	10% 12% 33% 30% 13% 2	14951
	Night	8% 12% 34% 35% 10% 1	25144

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	1 4 2 5% 5% 3 5% 4 6% 8% 56%	2538
	11th to 20th	Day	1 4 2 6% 6% 3 5% 5% 6% 8% 53%	2540
	21st to end	Day	1 4 2 5% 4 3 4 4 5% 7% 61%	2794
February	1st to 10th	Day	4 8% 4 7% 5% 3 6% 6% 6% 8% 42%	1693
	11th to 20th	Day	4 7% 3 7% 6% 3 5% 5% 6% 8% 45%	1815
	21st to end	Day	3 8% 4 6% 4 3 6% 5% 6% 9% 47%	1570
March	1st to 10th	Day	2 6% 3 5% 5% 4 6% 5% 6% 8% 49%	1900
	11th to 20th	Day	6% 5% 3 5% 5% 2 4 4 4 9% 54%	1943
	21st to end	Day	9% 10% 3 5% 6% 3 5% 4 6% 9% 39%	2401
April	1st to 10th	Day	10% 8% 3 4 4 3 4 4 6% 9% 44%	2160
	11th to 20th	Day	11% 7% 3 6% 6% 4 5% 6% 6% 8% 39%	2131
	21st to end	Day	13% 8% 2 6% 5% 3 4 5% 6% 7% 41%	2295
May	1st to 10th	Day	11% 6% 3 6% 4 3 5% 5% 7% 8% 40%	2388
	11th to 20th	Day	14% 7% 2 5% 4 3 5% 5% 6% 9% 40%	2478
	21st to end	Day	16% 7% 3 4 4 3 6% 5% 7% 9% 36%	2724
June	1st to 10th	Day	10% 4 2 4 4 3 4 7% 7% 10% 47%	2520
	11th to 20th	Day	9% 4 1 3 4 3 5% 6% 8% 10% 48%	2520
	21st to end	Day	5% 3 1 3 3 2 4 5% 7% 8% 60%	2520
July	1st to 10th	Day	5% 3 2 3 4 3 5% 6% 8% 10% 52%	2520
	11th to 20th	Day	5% 2 1 2 3 2 3 5% 7% 9% 61%	2520
	21st to end	Day	3 3 1 3 3 3 5% 5% 7% 10% 58%	2742
August	1st to 10th	Day	5% 3 2 5% 4 3 5% 5% 8% 11% 50%	2507
	11th to 20th	Day	4 2 1 3 3 2 4 5% 7% 9% 60%	2221
	21st to end	Day	5% 2 1 3 3 2 3 5% 5% 8% 63%	2376
September	1st to 10th	Day	6% 4 2 3 3 2 2 4 4 7% 63%	2160
	11th to 20th	Day	8% 3 1 3 3 2 3 4 5% 6% 62%	2080
	21st to end	Day	9% 3 1 3 4 3 2 3 4 7% 60%	1980
October	1st to 10th	Day	11% 6% 1 4 3 2 3 4 4 7% 54%	1895
	11th to 20th	Day	9% 6% 2 3 3 2 3 4 5% 6% 58%	1762
	21st to end	Day	5% 6% 2 5% 4 2 4 4 5% 7% 56%	1782
November	1st to 10th	Day	4 4 1 4 3 2 4 5% 6% 9% 57%	1673
	11th to 20th	Day	3 5% 2 5% 4 3 4 4 5% 8% 57%	1710
	21st to end	Day	3 5% 3 4 5% 2 4 4 6% 8% 55%	1528
December	1st to 10th	Day	2 6% 3 5% 5% 4 4 5% 6% 8% 53%	1520
	11th to 20th	Day	2 4 2 3 4 3 5% 5% 6% 8% 57%	1926
	21st to end	Day	6% 9% 3 5% 5% 3 4 4 5% 6% 52%	2794
January	1st to 10th	Night	2 6% 2 5% 5% 3 5% 5% 6% 8% 52%	4417
	11th to 20th	Night	1 4 3 6% 6% 4 7% 6% 5% 8% 49%	4430
	21st to end	Night	2 4 2 5% 5% 3 4 5% 6% 9% 56%	4873
February	1st to 10th	Night	3 8% 4 7% 5% 4 4 5% 6% 7% 46%	2504
	11th to 20th	Night	3 6% 3 6% 6% 3 5% 5% 6% 9% 47%	2251
	21st to end	Night	4 7% 2 6% 5% 3 4 5% 6% 7% 51%	1884
March	1st to 10th	Night	5% 6% 2 5% 5% 3 4 5% 5% 9% 51%	2280
	11th to 20th	Night	5% 6% 3 5% 5% 2 4 4 6% 9% 50%	2235
	21st to end	Night	10% 8% 4 5% 4 2 4 4 5% 10% 44%	2000
April	1st to 10th	Night	12% 5% 3 4 4 3 5% 5% 6% 8% 47%	1800
	11th to 20th	Night	12% 6% 3 4 3 3 5% 5% 5% 7% 47%	1777
	21st to end	Night	12% 6% 2 4 4 3 4 4 6% 7% 48%	1663
May	1st to 10th	Night	10% 7% 2 5% 5% 3 4 4 5% 7% 49%	1569
	11th to 20th	Night	14% 6% 2 5% 3 2 4 3 6% 8% 47%	1417
	21st to end	Night	17% 6% 2 3 4 2 4 4 5% 9% 44%	1552
June	1st to 10th	Night	9% 5% 1 3 3 3 4 5% 4 9% 53%	1440
	11th to 20th	Night	10% 4 2 4 4 3 5% 4 7% 9% 48%	1440
	21st to end	Night	5% 3 1 3 4 3 4 5% 5% 9% 59%	1440
July	1st to 10th	Night	5% 2 1 3 4 2 5% 5% 8% 9% 55%	1440
	11th to 20th	Night	4 2 1 2 3 2 3 4 5% 10% 64%	1440
	21st to end	Night	2 2 1 3 3 3 5% 5% 7% 9% 61%	1576
August	1st to 10th	Night	4 3 2 4 4 3 5% 5% 7% 8% 54%	1432
	11th to 20th	Night	4 3 1 3 4 2 4 4 5% 8% 63%	1676
	21st to end	Night	3 2 1 4 4 2 3 4 5% 8% 64%	1980
September	1st to 10th	Night	6% 3 1 3 4 2 3 3 5% 7% 64%	1800
	11th to 20th	Night	7% 3 1 3 3 1 3 3 6% 8% 62%	1880
	21st to end	Night	11% 3 1 3 3 2 2 3 5% 5% 61%	1980
October	1st to 10th	Night	12% 6% 2 4 4 2 3 4 4 6% 53%	2061
	11th to 20th	Night	9% 4 2 3 4 2 3 4 5% 7% 57%	2178
	21st to end	Night	7% 6% 2 4 3 2 3 3 5% 8% 55%	2574
November	1st to 10th	Night	5% 5% 2 5% 4 2 4 5% 6% 9% 52%	2405
	11th to 20th	Night	4 5% 2 5% 4 2 3 5% 6% 6% 58%	2470
	21st to end	Night	4 4 2 4 4 3 4 5% 6% 7% 57%	2650
December	1st to 10th	Night	3 4 3 5% 4 3 5% 5% 5% 7% 56%	2660
	11th to 20th	Night	3 3 2 4 4 3 5% 5% 6% 9% 57%	3271
	21st to end	Night	6% 10% 3 5% 5% 3 4 4 5% 6% 51%	4873

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	23% 11% 22% 28% 15% 1	2539
	11th to 20th	Day	25% 12% 19% 26% 14% 4	2540
	21st to end	Day	22% 11% 20% 32% 15% 1	2794
February	1st to 10th	Day	38% 11% 15% 21% 13% 2	1693
	11th to 20th	Day	35% 10% 16% 21% 14% 4	1825
	21st to end	Day	33% 9% 17% 25% 14% 4	1570
March	1st to 10th	Day	30% 11% 16% 25% 15% 3	1900
	11th to 20th	Day	28% 8% 16% 31% 14% 3	1943
	21st to end	Day	40% 12% 15% 23% 8% 1	2401
April	1st to 10th	Day	35% 9% 20% 23% 10% 3	2160
	11th to 20th	Day	38% 11% 15% 22% 10% 2	2134
	21st to end	Day	39% 10% 18% 24% 9% 1	2295
May	1st to 10th	Day	37% 11% 17% 25% 10% 1	2388
	11th to 20th	Day	40% 9% 19% 22% 8%	2482
	21st to end	Day	41% 12% 18% 21% 6% 1	2724
June	1st to 10th	Day	29% 12% 20% 25% 12% 2	2520
	11th to 20th	Day	27% 11% 20% 24% 14% 4	2520
	21st to end	Day	20% 9% 17% 28% 21% 5%	2520
July	1st to 10th	Day	24% 10% 16% 29% 17% 4	2451
	11th to 20th	Day	18% 8% 13% 28% 24% 10%	2445
	21st to end	Day	19% 8% 14% 27% 22% 9%	2590
August	1st to 10th	Day	25% 10% 17% 25% 16% 6%	2491
	11th to 20th	Day	19% 8% 15% 31% 19% 7%	2221
	21st to end	Day	18% 7% 13% 24% 28% 9%	2376
September	1st to 10th	Day	22% 5% 11% 26% 27% 10%	2160
	11th to 20th	Day	23% 7% 13% 25% 25% 8%	2080
	21st to end	Day	25% 5% 11% 33% 24% 3	1980
October	1st to 10th	Day	30% 7% 15% 23% 22% 3	1895
	11th to 20th	Day	27% 6% 12% 28% 20% 6%	1762
	21st to end	Day	26% 8% 18% 27% 16% 5%	1782
November	1st to 10th	Day	23% 8% 17% 24% 21% 7%	1673
	11th to 20th	Day	24% 8% 14% 28% 20% 6%	1710
	21st to end	Day	26% 7% 15% 30% 17% 4	1528
December	1st to 10th	Day	27% 9% 18% 26% 18% 2	1520
	11th to 20th	Day	22% 9% 20% 33% 14% 2	1924
	21st to end	Day	33% 8% 10% 27% 20% 2	2794
January	1st to 10th	Night	29% 11% 14% 30% 15% 2	4417
	11th to 20th	Night	30% 12% 16% 24% 15% 3	4430
	21st to end	Night	21% 13% 19% 30% 15% 2	4873
February	1st to 10th	Night	36% 9% 16% 23% 14% 2	2504
	11th to 20th	Night	32% 9% 16% 25% 14% 4	2251
	21st to end	Night	31% 8% 15% 25% 15% 6%	1884
March	1st to 10th	Night	29% 9% 16% 26% 17% 3	2280
	11th to 20th	Night	29% 8% 16% 25% 19% 3	2235
	21st to end	Night	36% 9% 20% 22% 11% 2	2000
April	1st to 10th	Night	35% 11% 14% 23% 15% 3	1800
	11th to 20th	Night	36% 8% 16% 24% 13% 3	1777
	21st to end	Night	33% 11% 17% 25% 14% 1	1663
May	1st to 10th	Night	33% 9% 16% 28% 13% 1	1569
	11th to 20th	Night	35% 9% 18% 28% 9%	1418
	21st to end	Night	37% 10% 17% 25% 10% 1	1552
June	1st to 10th	Night	29% 10% 20% 25% 13% 2	1440
	11th to 20th	Night	31% 10% 22% 20% 14% 3	1440
	21st to end	Night	21% 10% 17% 27% 20% 5%	1440
July	1st to 10th	Night	23% 8% 18% 30% 17% 4	1400
	11th to 20th	Night	17% 6% 16% 25% 24% 11%	1392
	21st to end	Night	16% 10% 15% 27% 24% 7%	1488
August	1st to 10th	Night	24% 11% 13% 27% 18% 6%	1424
	11th to 20th	Night	20% 6% 12% 30% 25% 7%	1676
	21st to end	Night	18% 7% 12% 24% 29% 8%	1980
September	1st to 10th	Night	21% 6% 10% 27% 26% 10%	1800
	11th to 20th	Night	21% 7% 14% 25% 26% 8%	1880
	21st to end	Night	26% 5% 9% 29% 25% 6%	1980
October	1st to 10th	Night	33% 7% 12% 23% 21% 4	2061
	11th to 20th	Night	28% 6% 11% 27% 21% 7%	2178
	21st to end	Night	28% 7% 17% 23% 19% 6%	2574
November	1st to 10th	Night	28% 7% 17% 22% 20% 6%	2405
	11th to 20th	Night	26% 7% 14% 26% 22% 6%	2470
	21st to end	Night	25% 8% 15% 26% 20% 5%	2650
December	1st to 10th	Night	27% 8% 16% 27% 18% 4	2660
	11th to 20th	Night	23% 8% 15% 38% 14% 1	3272
	21st to end	Night	33% 8% 13% 30% 14% 3	4873

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	3 12% 32% 30% 17% 5%	270
	11th to 20th	Day	9% 14% 35% 30% 9% 3	270
	21st to end	Day	5% 23% 43% 21% 6% 1	297
February	1st to 10th	Day	9% 19% 46% 20% 6%	270
	11th to 20th	Day	10% 17% 45% 22% 6%	270
	21st to end	Day	8% 23% 40% 23% 4 1	225
March	1st to 10th	Day	3 22% 42% 21% 10% 1	270
	11th to 20th	Day	8% 16% 37% 28% 8% 2	297
	21st to end	Day	17% 18% 34% 21% 8% 1	471
April	1st to 10th	Day	15% 22% 38% 19% 5%	420
	11th to 20th	Day	19% 23% 40% 15% 3	412
	21st to end	Day	18% 15% 31% 25% 9% 1	555
May	1st to 10th	Day	14% 16% 31% 25% 12% 2	603
	11th to 20th	Day	20% 12% 27% 27% 13% 2	625
	21st to end	Day	17% 11% 35% 23% 12% 2	679
June	1st to 10th	Day	8% 7% 28% 34% 18% 4	630
	11th to 20th	Day	12% 10% 38% 29% 10% 1	630
	21st to end	Day	7% 9% 29% 37% 17% 2	630
July	1st to 10th	Day	5% 3 27% 42% 20% 3	621
	11th to 20th	Day	4 4 30% 44% 17% 1	618
	21st to end	Day	4 6% 23% 43% 23% 2	684
August	1st to 10th	Day	5% 3 28% 43% 19% 2	626
	11th to 20th	Day	5% 4 27% 43% 17% 5%	509
	21st to end	Day	3 9% 25% 40% 18% 4	495
September	1st to 10th	Day	6% 7% 35% 33% 15% 4	450
	11th to 20th	Day	9% 7% 25% 37% 17% 5%	370
	21st to end	Day	13% 13% 35% 23% 13% 4	270
October	1st to 10th	Day	17% 9% 29% 26% 12% 6%	270
	11th to 20th	Day	17% 18% 31% 19% 10% 5%	270
	21st to end	Day	10% 20% 34% 23% 11% 2	297
November	1st to 10th	Day	7% 20% 36% 25% 9% 3	270
	11th to 20th	Day	11% 16% 34% 25% 13% 1	270
	21st to end	Day	9% 17% 31% 30% 12% 1	270
December	1st to 10th	Day	7% 19% 39% 26% 8% 2	270
	11th to 20th	Day	9% 17% 45% 25% 5%	270
	21st to end	Day	8% 20% 36% 26% 8% 2	297
January	1st to 10th	Night	5% 14% 39% 30% 11% 1	950
	11th to 20th	Night	4 23% 38% 27% 7% 2	950
	21st to end	Night	5% 19% 42% 28% 5%	1045
February	1st to 10th	Night	6% 16% 45% 25% 6% 1	794
	11th to 20th	Night	6% 16% 37% 33% 7%	744
	21st to end	Night	8% 11% 40% 32% 7% 1	628
March	1st to 10th	Night	8% 12% 40% 33% 6% 1	760
	11th to 20th	Night	8% 10% 35% 38% 7% 1	743
	21st to end	Night	14% 13% 30% 35% 8% 1	600
April	1st to 10th	Night	14% 10% 36% 33% 7%	540
	11th to 20th	Night	16% 14% 37% 28% 5%	533
	21st to end	Night	16% 12% 28% 34% 10% 1	540
May	1st to 10th	Night	12% 8% 31% 33% 14% 1	540
	11th to 20th	Night	17% 8% 26% 35% 13% 1	531
	21st to end	Night	18% 6% 36% 28% 11%	584
June	1st to 10th	Night	10% 7% 29% 37% 15% 1	540
	11th to 20th	Night	12% 7% 35% 37% 8%	540
	21st to end	Night	6% 6% 29% 47% 12%	540
July	1st to 10th	Night	5% 4 25% 43% 22% 1	525
	11th to 20th	Night	4 3 25% 53% 15% 1	522
	21st to end	Night	2 2 24% 55% 16%	591
August	1st to 10th	Night	4 3 23% 53% 15% 1	537
	11th to 20th	Night	4 3 23% 48% 21% 1	534
	21st to end	Night	3 4 23% 48% 21% 1	594
September	1st to 10th	Night	7% 4 27% 42% 18% 1	540
	11th to 20th	Night	7% 6% 24% 45% 17% 2	540
	21st to end	Night	14% 8% 27% 37% 14% 1	540
October	1st to 10th	Night	15% 10% 26% 36% 12% 1	621
	11th to 20th	Night	11% 13% 31% 33% 12% 1	738
	21st to end	Night	11% 14% 34% 31% 10% 1	990
November	1st to 10th	Night	7% 13% 38% 33% 7% 2	925
	11th to 20th	Night	8% 16% 36% 31% 8% 1	950
	21st to end	Night	6% 17% 39% 31% 6%	950
December	1st to 10th	Night	6% 17% 42% 28% 7%	950
	11th to 20th	Night	6% 11% 40% 33% 8% 1	950
	21st to end	Night	10% 18% 37% 28% 7%	1045

Page generated at 2024-03-19 21:31:03. Version ac07

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