Three Pines Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Three Pines Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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	12% 8% 3 8% 5% 4 4 4 6% 7% 40%	101891
	Night	11% 8% 3 8% 5% 4 4 4 5% 6% 42%	97922
Transparency	Day	42% 7% 13% 24% 13% 1	105500
	Night	41% 6% 13% 24% 15% 2	102443
Seeing	Day	15% 11% 32% 27% 12% 2	16086
	Night	14% 10% 36% 30% 9% 1	26011

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	9% 15% 4 16% 11% 8% 5% 2 3 4 24%	2247
	11th to 20th	Day	5% 13% 6% 11% 6% 6% 9% 6% 9% 7% 22%	2702
	21st to end	Day	5% 12% 12% 14% 6% 4 5% 4 6% 5% 26%	3135
February	1st to 10th	Day	9% 11% 4 11% 9% 6% 6% 6% 6% 6% 27%	1710
	11th to 20th	Day	8% 11% 6% 10% 5% 7% 6% 5% 6% 6% 30%	1664
	21st to end	Day	11% 12% 4 11% 7% 6% 4 4 4 5% 31%	1523
March	1st to 10th	Day	11% 11% 4 9% 5% 4 4 4 5% 6% 37%	3363
	11th to 20th	Day	10% 10% 3 8% 6% 4 4 3 4 7% 40%	3480
	21st to end	Day	25% 13% 4 13% 4 3 3 3 4 4 24%	3814
April	1st to 10th	Day	17% 9% 2 6% 4 4 4 4 6% 8% 37%	2188
	11th to 20th	Day	18% 11% 4 6% 4 4 3 3 4 6% 35%	2413
	21st to end	Day	22% 9% 3 7% 3 4 4 4 4 5% 35%	2470
May	1st to 10th	Day	15% 6% 2 6% 4 5% 5% 4 6% 8% 38%	4082
	11th to 20th	Day	14% 6% 3 6% 4 3 4 3 4 7% 46%	4257
	21st to end	Day	18% 6% 2 5% 4 4 4 4 6% 7% 39%	4824
June	1st to 10th	Day	12% 5% 2 5% 4 4 5% 4 6% 7% 46%	2745
	11th to 20th	Day	15% 6% 2 6% 4 4 5% 4 5% 7% 42%	2850
	21st to end	Day	8% 5% 2 6% 4 5% 5% 4 7% 9% 46%	2850
July	1st to 10th	Day	10% 4 2 6% 4 5% 6% 4 8% 11% 40%	4750
	11th to 20th	Day	4 3 1 5% 4 3 3 3 6% 8% 60%	4569
	21st to end	Day	5% 4 2 5% 4 4 5% 4 7% 9% 51%	4465
August	1st to 10th	Day	14% 7% 2 6% 4 3 5% 4 6% 7% 43%	4104
	11th to 20th	Day	12% 6% 3 6% 5% 5% 5% 4 7% 8% 39%	4041
	21st to end	Day	8% 5% 2 5% 3 4 5% 4 6% 7% 51%	4510
September	1st to 10th	Day	12% 4 2 5% 3 3 4 3 4 6% 53%	2266
	11th to 20th	Day	9% 5% 2 5% 4 4 3 3 7% 7% 51%	2090
	21st to end	Day	12% 6% 2 5% 3 3 3 3 4 6% 52%	2090
October	1st to 10th	Day	15% 8% 2 5% 5% 4 2 3 5% 6% 46%	1919
	11th to 20th	Day	13% 9% 2 5% 3 3 4 4 4 6% 47%	1900
	21st to end	Day	16% 9% 3 6% 4 3 3 3 4 5% 44%	2036
November	1st to 10th	Day	13% 9% 3 7% 4 3 4 4 4 7% 42%	1718
	11th to 20th	Day	9% 10% 3 13% 5% 5% 4 3 5% 6% 36%	1600
	21st to end	Day	11% 12% 3 9% 5% 4 4 4 6% 8% 35%	1600
December	1st to 10th	Day	9% 10% 4 10% 9% 6% 5% 3 6% 6% 32%	1560
	11th to 20th	Day	9% 11% 5% 10% 6% 5% 4 4 6% 8% 31%	1914
	21st to end	Day	18% 11% 5% 15% 6% 4 4 3 5% 6% 24%	2442
January	1st to 10th	Night	8% 12% 5% 13% 11% 9% 5% 3 4 4 26%	4705
	11th to 20th	Night	4 10% 5% 14% 9% 6% 8% 6% 9% 8% 22%	4263
	21st to end	Night	7% 13% 9% 14% 6% 4 4 4 5% 5% 31%	4532
February	1st to 10th	Night	8% 10% 5% 10% 7% 7% 6% 4 5% 6% 33%	2470
	11th to 20th	Night	8% 9% 4 8% 6% 5% 6% 4 6% 6% 38%	2403
	21st to end	Night	9% 10% 4 8% 7% 5% 4 5% 6% 6% 36%	1946
March	1st to 10th	Night	7% 8% 3 7% 5% 4 4 4 5% 6% 47%	3493
	11th to 20th	Night	9% 7% 3 7% 6% 5% 4 3 5% 7% 44%	3480
	21st to end	Night	26% 13% 4 9% 5% 3 3 2 4 5% 27%	3817
April	1st to 10th	Night	15% 10% 2 6% 4 4 4 4 4 6% 40%	1991
	11th to 20th	Night	16% 10% 3 6% 4 4 4 4 4 6% 39%	1716
	21st to end	Night	18% 8% 2 6% 5% 3 4 3 4 6% 40%	1710
May	1st to 10th	Night	18% 8% 1 5% 3 3 3 3 5% 6% 46%	2823
	11th to 20th	Night	10% 5% 2 5% 4 4 4 5% 5% 8% 48%	2644
	21st to end	Night	16% 5% 2 6% 3 4 4 3 4 6% 45%	2743
June	1st to 10th	Night	8% 4 1 5% 3 4 3 4 6% 8% 53%	1430
	11th to 20th	Night	9% 4 2 4 5% 4 4 3 5% 8% 50%	1330
	21st to end	Night	8% 3 1 4 3 3 4 3 6% 7% 58%	1330
July	1st to 10th	Night	10% 5% 2 4 3 4 5% 5% 7% 9% 46%	2220
	11th to 20th	Night	2 3 1 4 2 3 3 3 5% 8% 66%	2395
	21st to end	Night	4 3 1 4 3 3 4 4 7% 11% 55%	3098
August	1st to 10th	Night	12% 5% 2 5% 3 3 4 3 5% 8% 50%	2836
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 5% 7% 52%	2798
	21st to end	Night	8% 4 2 4 3 4 4 3 5% 7% 57%	3156
September	1st to 10th	Night	8% 4 2 4 3 2 3 3 6% 6% 59%	1911
	11th to 20th	Night	8% 4 2 4 4 3 4 3 5% 7% 57%	2090
	21st to end	Night	11% 4 2 3 3 3 4 3 4 7% 57%	2090
October	1st to 10th	Night	16% 6% 2 4 2 3 3 2 5% 6% 51%	2242
	11th to 20th	Night	13% 8% 2 5% 3 3 3 3 5% 6% 48%	2280
	21st to end	Night	15% 9% 3 6% 4 3 3 3 4 6% 44%	2560
November	1st to 10th	Night	10% 8% 2 6% 5% 4 4 3 5% 6% 47%	2579
	11th to 20th	Night	10% 10% 3 10% 5% 4 4 3 5% 5% 42%	2800
	21st to end	Night	10% 9% 3 9% 5% 4 4 3 5% 7% 40%	2800
December	1st to 10th	Night	8% 10% 4 11% 8% 5% 4 4 5% 6% 35%	2737
	11th to 20th	Night	11% 10% 4 10% 6% 4 5% 4 5% 8% 32%	3279
	21st to end	Night	18% 12% 5% 14% 6% 5% 4 4 5% 5% 24%	5225

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	65% 5% 10% 14% 5%	2248
	11th to 20th	Day	55% 6% 8% 23% 7%	2702
	21st to end	Day	58% 7% 12% 17% 6%	3135
February	1st to 10th	Day	56% 6% 14% 16% 8%	1710
	11th to 20th	Day	53% 6% 12% 19% 9% 2	1673
	21st to end	Day	53% 6% 11% 17% 11% 2	1523
March	1st to 10th	Day	45% 8% 11% 25% 10% 1	3363
	11th to 20th	Day	44% 5% 11% 26% 13% 2	3480
	21st to end	Day	65% 5% 9% 14% 7%	3814
April	1st to 10th	Day	45% 7% 13% 22% 11% 1	2188
	11th to 20th	Day	51% 4 12% 20% 12% 1	2413
	21st to end	Day	50% 6% 12% 23% 8%	2470
May	1st to 10th	Day	43% 7% 12% 24% 14%	4120
	11th to 20th	Day	38% 6% 11% 27% 15% 3	4261
	21st to end	Day	42% 7% 13% 25% 12% 1	4837
June	1st to 10th	Day	35% 7% 15% 28% 13% 1	2745
	11th to 20th	Day	41% 7% 13% 22% 14% 2	2850
	21st to end	Day	33% 8% 17% 26% 14% 2	2850
July	1st to 10th	Day	34% 10% 21% 23% 11% 1	4676
	11th to 20th	Day	22% 7% 15% 35% 19% 3	4488
	21st to end	Day	27% 9% 16% 27% 19% 2	4325
August	1st to 10th	Day	38% 8% 11% 29% 13% 2	4090
	11th to 20th	Day	41% 9% 15% 29% 6% 1	4080
	21st to end	Day	30% 7% 18% 27% 15% 2	4509
September	1st to 10th	Day	32% 6% 11% 33% 17% 1	2266
	11th to 20th	Day	32% 7% 17% 30% 14% 1	2090
	21st to end	Day	34% 5% 10% 30% 19% 2	2090
October	1st to 10th	Day	29% 4 8% 28% 30% 1	3192
	11th to 20th	Day	37% 5% 11% 23% 21% 2	3140
	21st to end	Day	41% 4 15% 26% 14% 1	3341
November	1st to 10th	Day	42% 5% 12% 23% 14% 3	1718
	11th to 20th	Day	49% 6% 13% 21% 11% 1	1600
	21st to end	Day	47% 6% 15% 20% 11% 2	1600
December	1st to 10th	Day	52% 7% 14% 17% 9% 1	1560
	11th to 20th	Day	50% 7% 19% 18% 6%	1911
	21st to end	Day	60% 5% 11% 17% 6% 1	2442
January	1st to 10th	Night	61% 6% 7% 18% 8%	4705
	11th to 20th	Night	56% 6% 14% 17% 8% 1	4263
	21st to end	Night	56% 5% 12% 19% 9% 1	4532
February	1st to 10th	Night	50% 6% 12% 20% 10% 2	2470
	11th to 20th	Night	45% 6% 12% 22% 12% 3	2404
	21st to end	Night	46% 7% 12% 19% 12% 4	1946
March	1st to 10th	Night	36% 6% 12% 28% 16% 2	3493
	11th to 20th	Night	39% 5% 11% 30% 14% 1	3480
	21st to end	Night	61% 5% 13% 14% 6% 1	3817
April	1st to 10th	Night	45% 6% 13% 24% 12% 1	1991
	11th to 20th	Night	46% 4 11% 22% 15% 2	1716
	21st to end	Night	45% 6% 11% 24% 12% 2	1710
May	1st to 10th	Night	40% 5% 13% 21% 17% 3	2850
	11th to 20th	Night	32% 7% 11% 27% 20% 3	2645
	21st to end	Night	40% 6% 11% 26% 15% 1	2751
June	1st to 10th	Night	27% 8% 16% 29% 17% 4	1430
	11th to 20th	Night	32% 7% 15% 22% 20% 3	1330
	21st to end	Night	24% 6% 17% 31% 20% 2	1330
July	1st to 10th	Night	32% 9% 20% 23% 15% 2	2185
	11th to 20th	Night	17% 5% 14% 39% 21% 3	2353
	21st to end	Night	21% 8% 19% 30% 19% 2	2999
August	1st to 10th	Night	34% 6% 15% 26% 16% 3	2826
	11th to 20th	Night	31% 7% 16% 33% 12% 1	2825
	21st to end	Night	27% 6% 18% 28% 18% 3	3156
September	1st to 10th	Night	25% 5% 14% 33% 21% 2	1911
	11th to 20th	Night	28% 7% 14% 32% 18% 2	2090
	21st to end	Night	29% 6% 10% 31% 23% 2	2090
October	1st to 10th	Night	22% 3 6% 28% 37% 4	3736
	11th to 20th	Night	28% 4 14% 29% 23% 3	3779
	21st to end	Night	39% 4 12% 29% 14% 1	4208
November	1st to 10th	Night	39% 5% 13% 22% 18% 3	2579
	11th to 20th	Night	44% 5% 11% 23% 14% 2	2800
	21st to end	Night	43% 6% 16% 23% 12% 1	2800
December	1st to 10th	Night	50% 5% 16% 20% 9% 1	2737
	11th to 20th	Night	49% 7% 19% 19% 6%	3281
	21st to end	Night	61% 6% 10% 17% 6% 1	5225

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	17% 10% 36% 27% 8% 2	270
	11th to 20th	Day	14% 14% 43% 22% 6% 1	270
	21st to end	Day	14% 12% 40% 25% 9% 1	297
February	1st to 10th	Day	16% 16% 47% 19% 2	270
	11th to 20th	Day	13% 19% 42% 20% 6%	270
	21st to end	Day	18% 17% 41% 21% 2	225
March	1st to 10th	Day	19% 14% 41% 23% 3	270
	11th to 20th	Day	21% 9% 39% 24% 6% 1	270
	21st to end	Day	26% 14% 29% 21% 9% 2	297
April	1st to 10th	Day	29% 15% 31% 22% 4	368
	11th to 20th	Day	27% 16% 28% 22% 6% 1	611
	21st to end	Day	23% 18% 28% 20% 10% 2	650
May	1st to 10th	Day	19% 13% 34% 23% 9% 1	653
	11th to 20th	Day	20% 11% 31% 23% 12% 3	675
	21st to end	Day	19% 8% 31% 29% 12% 2	734
June	1st to 10th	Day	10% 9% 26% 32% 19% 4	680
	11th to 20th	Day	16% 10% 34% 27% 9% 3	680
	21st to end	Day	9% 9% 33% 32% 15% 2	680
July	1st to 10th	Day	9% 4 23% 36% 22% 6%	671
	11th to 20th	Day	5% 6% 32% 33% 17% 5%	668
	21st to end	Day	6% 3 25% 39% 22% 4	739
August	1st to 10th	Day	12% 4 21% 37% 21% 4	676
	11th to 20th	Day	14% 4 23% 32% 21% 5%	665
	21st to end	Day	7% 6% 31% 33% 19% 3	739
September	1st to 10th	Day	13% 6% 33% 29% 15% 4	476
	11th to 20th	Day	10% 6% 33% 32% 14% 4	300
	21st to end	Day	16% 16% 31% 22% 11% 4	300
October	1st to 10th	Day	17% 13% 29% 24% 13% 3	300
	11th to 20th	Day	15% 21% 35% 21% 8% 1	300
	21st to end	Day	21% 19% 34% 20% 6%	330
November	1st to 10th	Day	23% 17% 33% 19% 7% 1	300
	11th to 20th	Day	17% 19% 44% 16% 4	300
	21st to end	Day	19% 18% 36% 21% 6% 1	300
December	1st to 10th	Day	12% 16% 40% 25% 7%	285
	11th to 20th	Day	16% 17% 44% 18% 6%	270
	21st to end	Day	25% 19% 35% 19% 2 1	297
January	1st to 10th	Night	12% 13% 44% 23% 6% 1	950
	11th to 20th	Night	12% 14% 42% 25% 5% 1	950
	21st to end	Night	17% 14% 38% 25% 5%	1045
February	1st to 10th	Night	13% 12% 44% 25% 5% 1	950
	11th to 20th	Night	13% 16% 41% 24% 7%	929
	21st to end	Night	13% 13% 40% 26% 7% 1	690
March	1st to 10th	Night	13% 12% 40% 28% 6% 1	622
	11th to 20th	Night	18% 13% 38% 25% 5%	570
	21st to end	Night	23% 11% 29% 28% 9% 1	627
April	1st to 10th	Night	21% 12% 39% 24% 5%	570
	11th to 20th	Night	23% 13% 29% 26% 8% 1	563
	21st to end	Night	21% 10% 34% 25% 9% 1	570
May	1st to 10th	Night	19% 10% 35% 27% 8%	570
	11th to 20th	Night	17% 6% 37% 30% 10% 1	561
	21st to end	Night	15% 6% 35% 31% 11% 1	617
June	1st to 10th	Night	10% 6% 27% 40% 16%	570
	11th to 20th	Night	12% 5% 37% 36% 9%	570
	21st to end	Night	8% 5% 26% 47% 13%	570
July	1st to 10th	Night	6% 5% 24% 43% 21% 2	555
	11th to 20th	Night	4 3 28% 46% 19% 1	552
	21st to end	Night	5% 2 26% 46% 19% 2	624
August	1st to 10th	Night	9% 2 24% 45% 19% 1	567
	11th to 20th	Night	10% 4 23% 41% 19% 2	564
	21st to end	Night	7% 3 28% 41% 19% 2	627
September	1st to 10th	Night	9% 4 29% 39% 16% 2	570
	11th to 20th	Night	9% 6% 34% 35% 14% 2	570
	21st to end	Night	12% 10% 34% 33% 11% 1	570
October	1st to 10th	Night	18% 10% 32% 30% 9% 1	722
	11th to 20th	Night	16% 14% 38% 24% 7% 1	760
	21st to end	Night	20% 13% 34% 26% 6%	888
November	1st to 10th	Night	15% 12% 38% 28% 7%	975
	11th to 20th	Night	15% 15% 41% 22% 7% 1	1000
	21st to end	Night	14% 14% 42% 25% 5%	1000
December	1st to 10th	Night	13% 13% 43% 25% 5%	978
	11th to 20th	Night	19% 10% 39% 25% 6%	950
	21st to end	Night	22% 14% 38% 21% 4	1045

Page generated at 2024-12-03 05:45:10. Version ac07

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