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 2024-11-03.

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 5% 4 4 4 4 6% 8% 51%	101466
	Night	6% 5% 2 5% 4 4 4 4 6% 8% 53%	97745
Transparency	Day	27% 9% 16% 26% 17% 4	101210
	Night	27% 9% 16% 27% 18% 4	97591
Seeing	Day	10% 13% 33% 30% 13% 2	15916
	Night	8% 12% 34% 35% 10% 1	25863

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% 4 4 5% 4 7% 8% 55%	2538
	11th to 20th	Day	1 5% 2 7% 5% 4 6% 4 6% 8% 53%	2540
	21st to end	Day	1 4 2 6% 4 4 3 3 5% 7% 61%	2794
February	1st to 10th	Day	4 9% 3 7% 5% 5% 6% 5% 6% 8% 42%	1693
	11th to 20th	Day	3 8% 4 7% 5% 5% 5% 4 6% 8% 45%	1815
	21st to end	Day	3 8% 4 6% 4 4 6% 3 6% 9% 46%	1570
March	1st to 10th	Day	2 6% 3 5% 4 4 5% 3 6% 7% 54%	3130
	11th to 20th	Day	6% 6% 2 5% 3 3 3 3 5% 9% 56%	3251
	21st to end	Day	12% 12% 4 7% 4 4 4 3 6% 7% 36%	4165
April	1st to 10th	Day	11% 9% 3 5% 4 4 4 4 6% 8% 44%	2280
	11th to 20th	Day	11% 7% 2 7% 5% 4 5% 5% 6% 7% 40%	2251
	21st to end	Day	13% 8% 2 6% 4 4 4 4 6% 7% 42%	2423
May	1st to 10th	Day	13% 9% 3 7% 4 5% 5% 4 6% 7% 36%	4207
	11th to 20th	Day	10% 6% 2 5% 4 4 5% 4 7% 9% 46%	4388
	21st to end	Day	14% 6% 2 5% 4 4 5% 4 7% 8% 41%	4825
June	1st to 10th	Day	9% 4 2 4 4 4 5% 5% 8% 10% 46%	2660
	11th to 20th	Day	9% 4 1 4 3 4 4 5% 8% 10% 47%	2660
	21st to end	Day	5% 3 1 3 3 3 3 4 6% 8% 59%	2660
July	1st to 10th	Day	4 3 2 5% 4 5% 5% 5% 8% 10% 51%	4430
	11th to 20th	Day	3 2 1 3 3 4 5% 5% 8% 10% 56%	4430
	21st to end	Day	2 2 1 3 3 4 5% 4 7% 9% 61%	4802
August	1st to 10th	Day	5% 3 2 6% 4 5% 5% 5% 7% 10% 49%	4411
	11th to 20th	Day	5% 3 1 4 4 4 5% 5% 8% 9% 50%	3889
	21st to end	Day	5% 2 1 3 2 3 3 3 5% 7% 65%	4180
September	1st to 10th	Day	6% 4 1 4 2 2 2 3 5% 7% 63%	2280
	11th to 20th	Day	7% 3 1 4 3 3 3 3 5% 6% 63%	2195
	21st to end	Day	9% 4 1 4 3 3 2 3 4 6% 62%	2090
October	1st to 10th	Day	10% 5% 1 4 3 3 3 4 4 7% 56%	2000
	11th to 20th	Day	9% 6% 2 3 3 3 3 3 5% 6% 59%	1859
	21st to end	Day	6% 6% 2 5% 4 3 4 3 6% 7% 55%	1881
November	1st to 10th	Day	4 4 1 4 3 3 5% 3 6% 9% 57%	1691
	11th to 20th	Day	3 5% 2 5% 4 3 4 4 5% 8% 56%	1710
	21st to end	Day	3 6% 2 5% 4 3 4 3 7% 8% 54%	1528
December	1st to 10th	Day	2 6% 3 5% 5% 5% 4 4 7% 8% 52%	1520
	11th to 20th	Day	2 4 1 4 4 4 5% 4 6% 8% 57%	1926
	21st to end	Day	6% 9% 3 6% 4 4 4 3 5% 6% 51%	2794
January	1st to 10th	Night	2 6% 2 6% 4 4 5% 4 6% 8% 52%	4417
	11th to 20th	Night	1 4 3 8% 5% 6% 6% 4 6% 8% 49%	4430
	21st to end	Night	1 4 2 5% 4 4 4 4 6% 9% 56%	4873
February	1st to 10th	Night	3 9% 4 8% 4 5% 4 4 6% 7% 46%	2504
	11th to 20th	Night	3 7% 2 7% 5% 4 5% 5% 6% 8% 47%	2251
	21st to end	Night	3 7% 2 7% 5% 4 5% 3 7% 7% 50%	1884
March	1st to 10th	Night	4 7% 2 7% 4 4 4 4 5% 8% 52%	3734
	11th to 20th	Night	5% 6% 2 5% 4 3 3 3 5% 9% 54%	3718
	21st to end	Night	9% 12% 3 8% 4 4 4 3 6% 8% 38%	3477
April	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 6% 7% 47%	1900
	11th to 20th	Night	12% 6% 3 4 3 4 5% 4 5% 7% 48%	1877
	21st to end	Night	11% 6% 2 5% 4 3 5% 3 6% 8% 48%	1755
May	1st to 10th	Night	12% 8% 3 6% 4 4 4 4 6% 7% 44%	2760
	11th to 20th	Night	8% 5% 1 5% 3 3 3 3 7% 9% 54%	2517
	21st to end	Night	14% 7% 2 5% 4 4 4 4 6% 8% 44%	2762
June	1st to 10th	Night	8% 5% 1 4 3 4 4 4 5% 9% 53%	1520
	11th to 20th	Night	10% 4 2 4 4 5% 4 4 8% 9% 48%	1520
	21st to end	Night	6% 3 1 3 3 4 4 4 5% 9% 59%	1520
July	1st to 10th	Night	5% 3 1 4 3 3 4 4 7% 7% 59%	2540
	11th to 20th	Night	2 2 1 3 3 4 5% 3 8% 10% 60%	2540
	21st to end	Night	3 2 1 3 3 3 4 4 6% 9% 61%	2761
August	1st to 10th	Night	6% 4 2 5% 4 4 5% 4 8% 8% 50%	2528
	11th to 20th	Night	5% 4 1 4 3 4 4 4 6% 10% 55%	2946
	21st to end	Night	3 3 1 5% 4 3 4 4 4 6% 63%	3487
September	1st to 10th	Night	6% 3 1 3 3 2 3 2 5% 6% 66%	1900
	11th to 20th	Night	6% 3 1 4 3 2 3 3 6% 8% 62%	1985
	21st to end	Night	11% 4 1 3 2 2 2 2 4 5% 62%	2090
October	1st to 10th	Night	11% 6% 2 4 3 3 3 3 4 6% 55%	2176
	11th to 20th	Night	8% 4 2 4 3 3 3 3 5% 7% 57%	2300
	21st to end	Night	7% 6% 3 5% 3 3 3 3 6% 7% 55%	2717
November	1st to 10th	Night	5% 6% 2 5% 4 3 4 4 7% 9% 52%	2432
	11th to 20th	Night	4 6% 2 5% 4 3 3 4 6% 6% 57%	2470
	21st to end	Night	3 5% 2 5% 4 4 3 5% 6% 7% 56%	2650
December	1st to 10th	Night	3 5% 3 6% 3 3 5% 4 6% 7% 55%	2660
	11th to 20th	Night	3 4 1 5% 4 4 4 4 6% 9% 57%	3271
	21st to end	Night	6% 10% 3 6% 4 4 4 3 5% 6% 50%	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	24% 9% 15% 24% 23% 6%	3130
	11th to 20th	Day	23% 9% 20% 32% 14% 2	3251
	21st to end	Day	43% 14% 17% 21% 5% 1	4165
April	1st to 10th	Day	35% 9% 19% 23% 10% 3	2280
	11th to 20th	Day	38% 11% 15% 22% 11% 2	2254
	21st to end	Day	38% 10% 18% 24% 9%	2423
May	1st to 10th	Day	40% 13% 15% 21% 9% 2	4207
	11th to 20th	Day	29% 11% 19% 26% 12% 3	4392
	21st to end	Day	34% 13% 17% 24% 10% 1	4825
June	1st to 10th	Day	28% 12% 21% 25% 12% 2	2660
	11th to 20th	Day	28% 11% 20% 24% 14% 4	2660
	21st to end	Day	20% 9% 16% 29% 21% 5%	2660
July	1st to 10th	Day	24% 8% 14% 32% 21% 2	4361
	11th to 20th	Day	20% 7% 13% 29% 24% 7%	4355
	21st to end	Day	16% 7% 13% 27% 27% 10%	4651
August	1st to 10th	Day	27% 9% 18% 20% 18% 8%	4396
	11th to 20th	Day	26% 9% 17% 28% 16% 4	3928
	21st to end	Day	18% 5% 11% 26% 28% 12%	4179
September	1st to 10th	Day	21% 5% 11% 26% 27% 10%	2280
	11th to 20th	Day	22% 7% 12% 26% 25% 8%	2195
	21st to end	Day	24% 5% 10% 32% 25% 4	2090
October	1st to 10th	Day	28% 7% 14% 22% 23% 5%	2000
	11th to 20th	Day	27% 6% 12% 29% 21% 6%	1859
	21st to end	Day	26% 8% 18% 27% 16% 5%	1881
November	1st to 10th	Day	22% 8% 17% 25% 21% 7%	1691
	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	27% 10% 13% 25% 23% 3	3734
	11th to 20th	Night	25% 9% 20% 26% 19% 2	3718
	21st to end	Night	39% 13% 21% 20% 6% 1	3477
April	1st to 10th	Night	34% 10% 15% 24% 14% 3	1900
	11th to 20th	Night	34% 8% 16% 24% 15% 3	1877
	21st to end	Night	33% 11% 17% 25% 13% 1	1755
May	1st to 10th	Night	35% 13% 13% 23% 14% 2	2760
	11th to 20th	Night	23% 10% 19% 37% 10% 1	2518
	21st to end	Night	34% 11% 16% 27% 11% 1	2762
June	1st to 10th	Night	28% 10% 21% 25% 14% 2	1520
	11th to 20th	Night	30% 10% 22% 20% 15% 3	1520
	21st to end	Night	21% 9% 17% 27% 20% 5%	1520
July	1st to 10th	Night	22% 6% 16% 29% 24% 3	2500
	11th to 20th	Night	18% 6% 16% 32% 22% 6%	2492
	21st to end	Night	18% 7% 14% 31% 24% 6%	2674
August	1st to 10th	Night	29% 9% 16% 20% 18% 8%	2520
	11th to 20th	Night	25% 8% 19% 25% 19% 4	2973
	21st to end	Night	21% 6% 12% 24% 29% 8%	3487
September	1st to 10th	Night	20% 5% 9% 28% 28% 9%	1900
	11th to 20th	Night	21% 7% 13% 26% 27% 7%	1985
	21st to end	Night	25% 5% 8% 29% 26% 8%	2090
October	1st to 10th	Night	31% 7% 12% 23% 22% 6%	2176
	11th to 20th	Night	27% 6% 11% 28% 22% 7%	2300
	21st to end	Night	28% 6% 16% 24% 19% 7%	2717
November	1st to 10th	Night	28% 7% 17% 22% 20% 6%	2432
	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% 17% 37% 28% 8% 2	297
	21st to end	Day	17% 18% 35% 20% 8% 1	506
April	1st to 10th	Day	15% 23% 37% 20% 5%	460
	11th to 20th	Day	19% 24% 38% 17% 3	452
	21st to end	Day	17% 16% 32% 26% 9% 1	603
May	1st to 10th	Day	15% 17% 31% 24% 11% 2	653
	11th to 20th	Day	19% 12% 27% 26% 15% 2	675
	21st to end	Day	16% 12% 36% 23% 11% 2	734
June	1st to 10th	Day	8% 8% 29% 34% 18% 4	680
	11th to 20th	Day	12% 11% 38% 28% 10% 1	680
	21st to end	Day	7% 9% 30% 36% 16% 1	680
July	1st to 10th	Day	5% 4 27% 41% 20% 3	671
	11th to 20th	Day	4 4 30% 44% 17% 1	668
	21st to end	Day	3 5% 24% 42% 23% 2	739
August	1st to 10th	Day	5% 4 29% 42% 18% 2	676
	11th to 20th	Day	5% 5% 28% 41% 16% 4	553
	21st to end	Day	3 9% 27% 39% 17% 4	539
September	1st to 10th	Day	6% 6% 34% 34% 16% 4	490
	11th to 20th	Day	9% 8% 26% 36% 16% 5%	405
	21st to end	Day	13% 13% 34% 23% 14% 4	300
October	1st to 10th	Day	16% 10% 31% 25% 13% 6%	300
	11th to 20th	Day	16% 17% 31% 21% 10% 5%	300
	21st to end	Day	12% 19% 33% 22% 12% 2	330
November	1st to 10th	Day	7% 20% 36% 25% 9% 3	276
	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% 34% 8% 1	627
April	1st to 10th	Night	14% 11% 36% 32% 7%	570
	11th to 20th	Night	15% 15% 37% 27% 5%	563
	21st to end	Night	15% 12% 28% 35% 10% 1	570
May	1st to 10th	Night	12% 9% 32% 32% 14% 1	570
	11th to 20th	Night	16% 9% 26% 36% 13% 1	561
	21st to end	Night	18% 7% 35% 29% 11%	617
June	1st to 10th	Night	10% 7% 30% 37% 14% 1	570
	11th to 20th	Night	11% 8% 35% 38% 8%	570
	21st to end	Night	6% 6% 29% 46% 12%	570
July	1st to 10th	Night	5% 5% 25% 43% 21% 1	555
	11th to 20th	Night	4 3 24% 54% 15% 1	552
	21st to end	Night	2 2 25% 55% 16%	624
August	1st to 10th	Night	5% 4 23% 53% 15% 1	567
	11th to 20th	Night	4 2 24% 48% 20% 1	564
	21st to end	Night	3 4 23% 49% 20% 1	627
September	1st to 10th	Night	7% 4 25% 44% 19% 1	570
	11th to 20th	Night	7% 6% 25% 44% 16% 2	570
	21st to end	Night	13% 8% 27% 38% 13% 1	570
October	1st to 10th	Night	14% 10% 26% 37% 12% 1	656
	11th to 20th	Night	11% 12% 31% 34% 12% 1	780
	21st to end	Night	11% 14% 33% 31% 9% 1	1045
November	1st to 10th	Night	7% 13% 38% 33% 7% 2	936
	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 2024-10-31 01:39:28. Version ac07

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