Bixby Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bixby Creek Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	11% 6% 2 5% 4 4 4 3 5% 7% 48%	101250
	Night	11% 6% 2 5% 3 3 3 3 5% 6% 53%	97888
Transparency	Day	34% 5% 10% 25% 21% 5%	104927
	Night	31% 5% 10% 24% 23% 7%	102338
Seeing	Day	12% 7% 22% 28% 23% 7%	15392
	Night	13% 7% 25% 36% 17% 2	25208

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	12% 11% 4 6% 3 3 3 2 4 6% 45%	2847
	11th to 20th	Day	9% 6% 2 6% 3 2 3 2 3 5% 58%	2850
	21st to end	Day	22% 10% 2 4 3 2 2 2 3 5% 44%	3135
February	1st to 10th	Day	18% 10% 2 7% 4 3 3 3 4 4 42%	1710
	11th to 20th	Day	16% 7% 3 6% 4 3 3 2 5% 7% 44%	1776
	21st to end	Day	18% 8% 2 5% 4 4 4 3 4 6% 42%	1653
March	1st to 10th	Day	16% 7% 2 5% 4 3 3 2 3 5% 50%	3436
	11th to 20th	Day	11% 6% 3 6% 4 4 4 3 5% 6% 49%	3480
	21st to end	Day	16% 9% 3 7% 5% 3 4 3 5% 7% 37%	3814
April	1st to 10th	Day	12% 5% 2 6% 4 4 4 3 5% 6% 47%	2120
	11th to 20th	Day	15% 7% 2 7% 4 4 3 3 5% 6% 45%	2254
	21st to end	Day	18% 8% 3 7% 4 4 4 3 5% 5% 41%	2356
May	1st to 10th	Day	17% 8% 3 7% 4 4 4 4 4 5% 40%	4082
	11th to 20th	Day	12% 6% 3 7% 4 4 4 4 5% 7% 44%	4082
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	4477
June	1st to 10th	Day	8% 5% 2 6% 5% 4 4 4 7% 9% 46%	2470
	11th to 20th	Day	6% 4 1 5% 5% 5% 5% 4 6% 9% 50%	2470
	21st to end	Day	3 4 1 4 5% 4 4 3 6% 8% 58%	2470
July	1st to 10th	Day	7% 5% 2 5% 5% 5% 5% 5% 7% 9% 47%	4120
	11th to 20th	Day	4 3 1 5% 4 4 4 4 6% 9% 56%	4120
	21st to end	Day	5% 4 2 5% 5% 5% 5% 5% 8% 10% 47%	4465
August	1st to 10th	Day	3 3 2 4 4 3 4 4 6% 8% 59%	4104
	11th to 20th	Day	8% 4 2 4 4 3 4 4 6% 9% 51%	4041
	21st to end	Day	4 2 2 4 4 4 5% 5% 7% 8% 56%	4219
September	1st to 10th	Day	10% 5% 2 4 3 3 4 3 6% 7% 53%	2180
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 3 5% 7% 49%	2090
	21st to end	Day	8% 3 2 4 4 4 5% 4 6% 5% 56%	2090
October	1st to 10th	Day	8% 4 2 5% 3 3 4 3 4 5% 59%	1938
	11th to 20th	Day	11% 4 2 4 3 3 2 2 3 5% 62%	1900
	21st to end	Day	17% 5% 2 5% 3 3 3 2 4 5% 52%	2090
November	1st to 10th	Day	11% 5% 1 4 3 4 2 3 5% 7% 56%	1898
	11th to 20th	Day	11% 5% 2 4 2 2 3 2 3 6% 60%	1797
	21st to end	Day	15% 6% 2 5% 3 3 2 3 5% 6% 51%	1710
December	1st to 10th	Day	13% 7% 3 4 4 3 4 3 3 7% 49%	1710
	11th to 20th	Day	15% 9% 3 5% 4 4 4 2 5% 5% 44%	2161
	21st to end	Day	18% 11% 4 8% 4 4 4 3 4 6% 35%	3135
January	1st to 10th	Night	12% 9% 3 7% 5% 3 4 3 4 5% 45%	4108
	11th to 20th	Night	10% 6% 2 5% 3 3 3 3 3 6% 57%	4120
	21st to end	Night	23% 8% 2 4 3 2 2 2 3 5% 45%	4532
February	1st to 10th	Night	15% 10% 3 5% 3 3 3 2 4 6% 46%	2470
	11th to 20th	Night	15% 8% 2 7% 3 3 2 2 4 6% 49%	2306
	21st to end	Night	14% 7% 2 6% 4 3 3 3 5% 5% 48%	1799
March	1st to 10th	Night	18% 7% 3 5% 4 3 3 3 4 5% 46%	3419
	11th to 20th	Night	12% 6% 2 4 3 2 3 2 4 6% 55%	3480
	21st to end	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	3817
April	1st to 10th	Night	12% 5% 2 5% 4 3 4 3 5% 6% 51%	2058
	11th to 20th	Night	12% 5% 2 4 4 3 3 3 5% 7% 52%	1875
	21st to end	Night	13% 6% 2 5% 5% 4 3 3 5% 6% 48%	1820
May	1st to 10th	Night	13% 7% 2 5% 4 4 4 3 5% 8% 45%	2823
	11th to 20th	Night	12% 6% 2 5% 4 4 4 4 6% 7% 46%	2823
	21st to end	Night	12% 6% 2 6% 4 4 4 3 6% 9% 44%	3090
June	1st to 10th	Night	5% 3 2 4 3 4 4 4 6% 9% 56%	1710
	11th to 20th	Night	4 4 1 3 3 3 3 4 7% 8% 59%	1710
	21st to end	Night	3 2 1 3 3 3 3 3 5% 8% 65%	1710
July	1st to 10th	Night	8% 5% 1 4 4 3 4 4 6% 9% 52%	2850
	11th to 20th	Night	2 2 1 4 2 3 3 3 5% 9% 66%	2850
	21st to end	Night	4 4 1 4 4 3 4 3 7% 9% 56%	3098
August	1st to 10th	Night	2 2 1 4 3 3 5% 3 5% 8% 64%	2836
	11th to 20th	Night	5% 3 1 3 3 3 4 4 7% 9% 58%	2798
	21st to end	Night	2 3 1 4 3 3 4 3 6% 9% 62%	3435
September	1st to 10th	Night	8% 5% 2 4 2 3 4 3 5% 6% 59%	1995
	11th to 20th	Night	9% 4 2 5% 3 3 5% 4 5% 6% 52%	2090
	21st to end	Night	7% 4 1 5% 3 3 3 3 5% 6% 60%	2090
October	1st to 10th	Night	7% 4 1 3 2 3 3 3 4 5% 64%	2221
	11th to 20th	Night	12% 4 2 3 2 3 3 2 3 4 63%	2280
	21st to end	Night	16% 5% 1 4 3 3 2 2 3 5% 55%	2508
November	1st to 10th	Night	11% 5% 2 3 3 3 2 2 4 4 61%	2280
	11th to 20th	Night	8% 5% 2 4 3 3 3 3 4 5% 59%	2379
	21st to end	Night	15% 6% 2 4 4 3 2 2 4 5% 54%	2470
December	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 6% 51%	2470
	11th to 20th	Night	14% 7% 3 5% 4 3 3 3 4 4 49%	3036
	21st to end	Night	16% 8% 4 7% 3 3 4 3 4 5% 43%	4532

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	42% 3 7% 23% 23% 2	2848
	11th to 20th	Day	31% 4 13% 27% 22% 3	2850
	21st to end	Day	45% 4 6% 19% 23% 3	3135
February	1st to 10th	Day	46% 3 10% 20% 16% 4	1710
	11th to 20th	Day	43% 3 8% 22% 19% 5%	1785
	21st to end	Day	45% 3 7% 18% 21% 7%	1653
March	1st to 10th	Day	37% 4 7% 19% 21% 12%	3436
	11th to 20th	Day	37% 5% 12% 24% 18% 5%	3480
	21st to end	Day	46% 5% 9% 27% 11% 1	3814
April	1st to 10th	Day	36% 6% 11% 21% 19% 6%	2120
	11th to 20th	Day	40% 6% 10% 22% 17% 5%	2254
	21st to end	Day	45% 6% 8% 22% 17% 2	2356
May	1st to 10th	Day	45% 6% 8% 22% 18% 2	4120
	11th to 20th	Day	38% 8% 11% 24% 19% 1	4086
	21st to end	Day	44% 9% 11% 20% 14% 3	4489
June	1st to 10th	Day	33% 8% 15% 27% 15% 2	2470
	11th to 20th	Day	30% 7% 14% 27% 19% 3	2470
	21st to end	Day	24% 7% 13% 30% 22% 4	2470
July	1st to 10th	Day	30% 8% 15% 30% 15% 2	4056
	11th to 20th	Day	24% 6% 11% 33% 24% 2	4051
	21st to end	Day	28% 7% 16% 33% 15% 1	4325
August	1st to 10th	Day	22% 7% 12% 27% 27% 5%	4090
	11th to 20th	Day	29% 5% 16% 30% 16% 2	4080
	21st to end	Day	24% 8% 14% 39% 13% 2	4218
September	1st to 10th	Day	30% 6% 9% 22% 23% 10%	2180
	11th to 20th	Day	33% 6% 9% 24% 22% 6%	2090
	21st to end	Day	28% 6% 9% 21% 28% 8%	2090
October	1st to 10th	Day	17% 4 6% 13% 40% 21%	3224
	11th to 20th	Day	17% 2 4 18% 42% 17%	3140
	21st to end	Day	28% 3 7% 29% 26% 7%	3428
November	1st to 10th	Day	28% 4 9% 26% 27% 6%	1898
	11th to 20th	Day	28% 3 8% 28% 25% 9%	1797
	21st to end	Day	34% 4 9% 20% 27% 6%	1710
December	1st to 10th	Day	37% 4 9% 27% 20% 3	1710
	11th to 20th	Day	43% 3 5% 21% 23% 5%	2159
	21st to end	Day	49% 6% 7% 20% 14% 3	3135
January	1st to 10th	Night	41% 4 7% 22% 23% 3	4108
	11th to 20th	Night	31% 6% 14% 19% 26% 4	4120
	21st to end	Night	43% 3 7% 19% 23% 4	4532
February	1st to 10th	Night	41% 3 10% 23% 17% 6%	2470
	11th to 20th	Night	39% 3 7% 24% 20% 6%	2307
	21st to end	Night	38% 3 8% 19% 23% 9%	1799
March	1st to 10th	Night	41% 4 7% 18% 18% 11%	3419
	11th to 20th	Night	31% 6% 9% 31% 17% 7%	3480
	21st to end	Night	38% 6% 10% 26% 17% 2	3817
April	1st to 10th	Night	34% 6% 9% 20% 21% 10%	2058
	11th to 20th	Night	32% 6% 8% 24% 19% 10%	1875
	21st to end	Night	35% 6% 9% 25% 22% 3	1820
May	1st to 10th	Night	37% 7% 11% 23% 18% 5%	2850
	11th to 20th	Night	36% 8% 12% 26% 17% 2	2824
	21st to end	Night	35% 8% 15% 23% 16% 3	3099
June	1st to 10th	Night	23% 7% 14% 31% 21% 4	1710
	11th to 20th	Night	21% 6% 13% 32% 24% 4	1710
	21st to end	Night	16% 5% 13% 31% 28% 6%	1710
July	1st to 10th	Night	27% 7% 16% 27% 18% 4	2805
	11th to 20th	Night	16% 4 10% 39% 27% 4	2796
	21st to end	Night	23% 5% 20% 31% 20% 1	2999
August	1st to 10th	Night	17% 5% 13% 27% 29% 8%	2826
	11th to 20th	Night	21% 6% 18% 31% 21% 3	2825
	21st to end	Night	19% 6% 12% 38% 22% 3	3435
September	1st to 10th	Night	25% 7% 8% 25% 22% 13%	1995
	11th to 20th	Night	31% 5% 10% 21% 25% 8%	2090
	21st to end	Night	24% 5% 8% 24% 30% 9%	2090
October	1st to 10th	Night	14% 3 6% 13% 36% 28%	3702
	11th to 20th	Night	19% 2 4 14% 41% 21%	3779
	21st to end	Night	28% 3 5% 29% 26% 9%	4120
November	1st to 10th	Night	27% 4 8% 23% 28% 10%	2280
	11th to 20th	Night	28% 3 8% 24% 27% 10%	2379
	21st to end	Night	35% 3 7% 21% 28% 7%	2470
December	1st to 10th	Night	35% 5% 10% 22% 22% 7%	2470
	11th to 20th	Night	39% 3 7% 21% 24% 6%	3037
	21st to end	Night	42% 5% 8% 22% 17% 6%	4532

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	18% 14% 33% 27% 7% 1	270
	11th to 20th	Day	18% 17% 38% 23% 4	270
	21st to end	Day	18% 14% 38% 22% 8%	297
February	1st to 10th	Day	26% 15% 32% 22% 5%	270
	11th to 20th	Day	23% 17% 39% 17% 4	270
	21st to end	Day	29% 17% 36% 15% 3	225
March	1st to 10th	Day	19% 15% 34% 24% 7%	270
	11th to 20th	Day	20% 20% 33% 20% 6%	270
	21st to end	Day	26% 14% 39% 16% 5% 1	297
April	1st to 10th	Day	14% 15% 41% 21% 7% 2	300
	11th to 20th	Day	20% 14% 33% 26% 6% 1	452
	21st to end	Day	20% 14% 32% 23% 9% 2	536
May	1st to 10th	Day	14% 8% 33% 32% 12%	653
	11th to 20th	Day	15% 5% 27% 34% 16% 4	675
	21st to end	Day	14% 5% 25% 31% 20% 6%	734
June	1st to 10th	Day	9% 3 13% 31% 34% 10%	680
	11th to 20th	Day	7% 2 13% 37% 34% 8%	680
	21st to end	Day	3 2 16% 38% 32% 10%	680
July	1st to 10th	Day	8% 1 11% 28% 36% 17%	671
	11th to 20th	Day	3 1 7% 32% 43% 14%	668
	21st to end	Day	6% 1 6% 27% 42% 18%	739
August	1st to 10th	Day	5% 1 7% 33% 44% 9%	676
	11th to 20th	Day	10% 3 7% 31% 40% 10%	665
	21st to end	Day	5% 1 5% 23% 46% 20%	565
September	1st to 10th	Day	8% 2 7% 23% 39% 22%	390
	11th to 20th	Day	4 1 9% 36% 32% 18%	300
	21st to end	Day	10% 3 16% 27% 28% 15%	300
October	1st to 10th	Day	5% 5% 23% 33% 23% 12%	300
	11th to 20th	Day	9% 8% 28% 35% 18% 1	300
	21st to end	Day	22% 11% 25% 28% 11% 2	330
November	1st to 10th	Day	16% 6% 32% 31% 13% 2	282
	11th to 20th	Day	15% 9% 34% 27% 14% 1	270
	21st to end	Day	21% 13% 30% 27% 8% 1	270
December	1st to 10th	Day	16% 11% 35% 25% 11% 2	270
	11th to 20th	Day	23% 11% 35% 25% 6%	270
	21st to end	Day	18% 17% 38% 23% 5%	297
January	1st to 10th	Night	17% 10% 35% 31% 7% 1	950
	11th to 20th	Night	18% 13% 36% 28% 5%	950
	21st to end	Night	16% 9% 36% 35% 4	1045
February	1st to 10th	Night	21% 12% 33% 30% 4	950
	11th to 20th	Night	20% 10% 38% 29% 3	832
	21st to end	Night	19% 13% 39% 27% 2	543
March	1st to 10th	Night	18% 9% 34% 35% 4	570
	11th to 20th	Night	20% 9% 31% 35% 5%	570
	21st to end	Night	16% 9% 38% 29% 7%	627
April	1st to 10th	Night	15% 10% 37% 32% 6%	570
	11th to 20th	Night	14% 11% 34% 32% 9%	563
	21st to end	Night	16% 9% 32% 33% 9% 1	570
May	1st to 10th	Night	12% 6% 29% 43% 9%	570
	11th to 20th	Night	13% 6% 22% 42% 16% 2	561
	21st to end	Night	10% 3 24% 39% 23% 2	617
June	1st to 10th	Night	5% 2 12% 42% 35% 3	570
	11th to 20th	Night	6% 2 14% 52% 25% 2	570
	21st to end	Night	2 2 13% 44% 36% 4	570
July	1st to 10th	Night	5% 1 6% 41% 42% 6%	555
	11th to 20th	Night	2 1 6% 38% 48% 5%	552
	21st to end	Night	5% 1 4 39% 46% 6%	624
August	1st to 10th	Night	2 1 6% 41% 45% 4	567
	11th to 20th	Night	6% 1 7% 39% 44% 4	564
	21st to end	Night	4 2 6% 35% 47% 7%	627
September	1st to 10th	Night	10% 1 8% 36% 42% 3	570
	11th to 20th	Night	11% 2 9% 39% 34% 4	570
	21st to end	Night	9% 2 16% 36% 32% 4	570
October	1st to 10th	Night	8% 2 16% 41% 30% 3	701
	11th to 20th	Night	15% 4 26% 40% 14% 1	760
	21st to end	Night	17% 7% 26% 33% 15% 1	836
November	1st to 10th	Night	14% 4 29% 39% 13% 1	760
	11th to 20th	Night	10% 10% 32% 35% 11%	859
	21st to end	Night	19% 9% 30% 34% 9%	950
December	1st to 10th	Night	17% 9% 33% 34% 7%	950
	11th to 20th	Night	22% 7% 32% 33% 5%	950
	21st to end	Night	18% 11% 35% 31% 6%	1045

Page generated at 2024-11-03 01:11:30. Version ac07

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