Robinson Preserve
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robinson Preserve clear sky chart from 2005-11-06 to 2025-02-21.

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	7% 5% 2 6% 5% 5% 5% 5% 8% 10% 44%	109035
	Night	8% 5% 2 6% 5% 5% 5% 5% 7% 10% 43%	109554
Transparency	Day	33% 11% 19% 20% 14% 4	112852
	Night	34% 10% 17% 20% 14% 4	113876
Seeing	Day	8% 4 18% 29% 26% 15%	15795
	Night	9% 4 17% 32% 28% 10%	25915

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	8% 6% 3 6% 4 4 4 4 5% 7% 48%	4056
	11th to 20th	Day	20% 9% 3 7% 4 4 4 4 5% 8% 32%	4060
	21st to end	Day	13% 6% 2 6% 3 3 4 3 6% 8% 45%	4947
February	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 7% 7% 46%	2000
	11th to 20th	Day	7% 4 2 5% 4 3 4 3 6% 6% 56%	1948
	21st to end	Day	7% 4 2 5% 4 3 2 3 6% 7% 57%	1609
March	1st to 10th	Day	6% 5% 3 7% 5% 5% 6% 5% 7% 8% 42%	3435
	11th to 20th	Day	6% 4 2 5% 4 4 4 3 7% 11% 51%	3480
	21st to end	Day	9% 5% 1 4 4 2 4 3 6% 8% 54%	3815
April	1st to 10th	Day	6% 3 1 4 4 3 4 5% 7% 10% 53%	2090
	11th to 20th	Day	8% 4 2 6% 5% 4 4 4 7% 8% 50%	2066
	21st to end	Day	4 2 1 4 3 4 4 4 6% 8% 59%	2252
May	1st to 10th	Day	2 2 1 2 2 2 3 3 6% 10% 67%	4082
	11th to 20th	Day	8% 4 1 5% 4 4 5% 5% 8% 11% 44%	4081
	21st to end	Day	4 3 1 3 3 3 4 3 5% 9% 62%	4476
June	1st to 10th	Day	10% 6% 3 7% 5% 4 6% 5% 8% 11% 36%	2470
	11th to 20th	Day	6% 5% 2 5% 5% 6% 7% 6% 10% 13% 35%	2470
	21st to end	Day	6% 5% 2 7% 6% 5% 7% 7% 11% 12% 32%	2470
July	1st to 10th	Day	6% 3 2 6% 6% 6% 7% 8% 11% 15% 31%	4120
	11th to 20th	Day	3 4 2 7% 6% 8% 9% 8% 12% 14% 27%	4120
	21st to end	Day	4 3 2 7% 6% 7% 9% 7% 11% 15% 28%	4466
August	1st to 10th	Day	6% 4 2 8% 6% 7% 8% 7% 10% 13% 29%	3983
	11th to 20th	Day	3 3 2 6% 4 5% 7% 6% 10% 13% 41%	3729
	21st to end	Day	6% 5% 2 7% 6% 6% 8% 7% 12% 14% 28%	3833
September	1st to 10th	Day	7% 5% 2 7% 7% 8% 7% 7% 10% 12% 28%	2090
	11th to 20th	Day	8% 6% 3 7% 6% 7% 7% 5% 10% 10% 32%	2090
	21st to end	Day	7% 5% 2 7% 5% 6% 6% 5% 9% 11% 36%	2090
October	1st to 10th	Day	8% 5% 2 7% 5% 6% 6% 5% 7% 10% 38%	2090
	11th to 20th	Day	6% 4 2 5% 5% 4 4 4 6% 8% 53%	1966
	21st to end	Day	7% 5% 2 5% 4 3 4 3 6% 9% 52%	2090
November	1st to 10th	Day	7% 4 1 5% 5% 3 5% 4 6% 8% 52%	1957
	11th to 20th	Day	8% 5% 2 5% 5% 4 5% 4 5% 8% 50%	2000
	21st to end	Day	8% 5% 2 4 4 4 5% 3 7% 8% 51%	1835
December	1st to 10th	Day	4 3 1 4 3 4 3 3 6% 8% 61%	2930
	11th to 20th	Day	7% 6% 2 6% 5% 4 4 3 6% 7% 49%	3373
	21st to end	Day	10% 7% 3 8% 6% 5% 5% 4 5% 9% 39%	4466
January	1st to 10th	Night	8% 5% 2 6% 4 4 4 4 6% 10% 46%	5889
	11th to 20th	Night	17% 11% 4 9% 6% 5% 4 4 6% 7% 28%	5900
	21st to end	Night	13% 6% 2 7% 4 4 5% 4 6% 8% 41%	6005
February	1st to 10th	Night	10% 8% 3 6% 4 4 3 4 6% 8% 45%	2400
	11th to 20th	Night	9% 6% 2 5% 3 4 4 4 5% 7% 51%	2338
	21st to end	Night	6% 5% 1 5% 4 3 3 6% 6% 8% 53%	1843
March	1st to 10th	Night	9% 7% 3 9% 6% 5% 5% 4 6% 6% 40%	3418
	11th to 20th	Night	4 3 2 4 4 5% 5% 5% 9% 12% 47%	3480
	21st to end	Night	9% 5% 2 5% 4 4 4 3 4 8% 52%	3817
April	1st to 10th	Night	5% 4 2 3 4 3 4 5% 7% 9% 54%	2090
	11th to 20th	Night	6% 3 2 5% 3 4 5% 5% 6% 10% 50%	2063
	21st to end	Night	4 3 2 5% 3 4 4 3 5% 8% 58%	1939
May	1st to 10th	Night	2 3 1 4 3 4 3 4 6% 9% 61%	2813
	11th to 20th	Night	7% 4 2 5% 4 4 5% 4 6% 10% 48%	2812
	21st to end	Night	3 3 1 3 4 3 3 3 5% 7% 64%	3079
June	1st to 10th	Night	10% 6% 2 7% 4 5% 5% 5% 6% 11% 40%	1710
	11th to 20th	Night	6% 4 2 5% 5% 5% 6% 5% 9% 12% 41%	1710
	21st to end	Night	6% 5% 2 7% 5% 6% 6% 5% 8% 14% 36%	1710
July	1st to 10th	Night	5% 6% 2 9% 6% 6% 7% 8% 10% 14% 27%	2840
	11th to 20th	Night	3 4 2 7% 6% 6% 9% 8% 11% 14% 30%	2840
	21st to end	Night	4 6% 4 12% 9% 9% 9% 7% 10% 12% 19%	3087
August	1st to 10th	Night	5% 4 2 7% 5% 6% 6% 6% 10% 14% 35%	2940
	11th to 20th	Night	3 3 2 6% 5% 6% 6% 6% 11% 17% 35%	3100
	21st to end	Night	6% 4 2 8% 6% 8% 9% 7% 10% 14% 26%	3787
September	1st to 10th	Night	5% 6% 2 7% 6% 8% 8% 6% 9% 13% 30%	2090
	11th to 20th	Night	8% 6% 3 8% 7% 7% 7% 5% 8% 10% 30%	2090
	21st to end	Night	8% 6% 3 9% 6% 6% 7% 5% 7% 11% 33%	2090
October	1st to 10th	Night	9% 5% 3 7% 5% 5% 6% 5% 7% 9% 40%	2090
	11th to 20th	Night	6% 6% 2 5% 4 4 4 4 6% 8% 51%	2213
	21st to end	Night	8% 5% 1 6% 4 5% 4 4 6% 9% 48%	2508
November	1st to 10th	Night	7% 3 2 6% 5% 4 5% 4 6% 7% 51%	2341
	11th to 20th	Night	9% 5% 2 6% 5% 4 4 4 5% 8% 48%	2400
	21st to end	Night	7% 5% 2 7% 4 3 4 4 6% 9% 48%	2560
December	1st to 10th	Night	4 3 1 3 3 3 3 4 5% 9% 62%	4250
	11th to 20th	Night	10% 7% 2 5% 3 4 4 3 5% 7% 50%	4822
	21st to end	Night	12% 8% 3 8% 5% 5% 5% 4 7% 9% 35%	6490

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	31% 7% 10% 18% 24% 9%	4057
	11th to 20th	Day	50% 5% 7% 18% 15% 4	4060
	21st to end	Day	35% 6% 9% 29% 17% 4	4947
February	1st to 10th	Day	33% 7% 12% 20% 18% 10%	2000
	11th to 20th	Day	26% 6% 12% 21% 25% 9%	1958
	21st to end	Day	27% 5% 13% 19% 27% 8%	1609
March	1st to 10th	Day	35% 12% 15% 19% 15% 5%	3435
	11th to 20th	Day	23% 9% 18% 27% 18% 5%	3480
	21st to end	Day	26% 6% 12% 32% 18% 7%	3815
April	1st to 10th	Day	24% 9% 20% 24% 18% 6%	2090
	11th to 20th	Day	30% 7% 16% 18% 22% 5%	2066
	21st to end	Day	21% 8% 15% 26% 26% 4	2252
May	1st to 10th	Day	12% 7% 23% 32% 21% 5%	4120
	11th to 20th	Day	28% 12% 23% 22% 14% 1	4085
	21st to end	Day	19% 8% 18% 36% 18% 1	4489
June	1st to 10th	Day	39% 13% 24% 19% 4	2470
	11th to 20th	Day	37% 14% 27% 19% 3	2470
	21st to end	Day	40% 17% 27% 14% 3	2470
July	1st to 10th	Day	38% 18% 34% 9% 1	4055
	11th to 20th	Day	42% 19% 34% 5%	4051
	21st to end	Day	40% 22% 29% 9%	4324
August	1st to 10th	Day	41% 17% 29% 9% 3	3970
	11th to 20th	Day	31% 17% 29% 18% 5%	3765
	21st to end	Day	41% 18% 31% 10% 1	3833
September	1st to 10th	Day	44% 18% 26% 11% 1	2090
	11th to 20th	Day	44% 14% 25% 14% 3	2090
	21st to end	Day	38% 13% 19% 19% 8% 2	2090
October	1st to 10th	Day	51% 13% 14% 10% 8% 4	3480
	11th to 20th	Day	26% 7% 9% 22% 33% 4	3245
	21st to end	Day	27% 6% 8% 26% 27% 7%	3428
November	1st to 10th	Day	29% 7% 13% 23% 19% 10%	1957
	11th to 20th	Day	33% 6% 11% 22% 20% 8%	2000
	21st to end	Day	30% 7% 14% 20% 20% 9%	1835
December	1st to 10th	Day	21% 5% 16% 30% 21% 8%	2930
	11th to 20th	Day	33% 6% 10% 19% 21% 10%	3370
	21st to end	Day	41% 7% 13% 21% 14% 3	4466
January	1st to 10th	Night	32% 6% 9% 20% 25% 7%	5889
	11th to 20th	Night	54% 6% 10% 15% 13% 3	5900
	21st to end	Night	38% 8% 9% 23% 17% 5%	6005
February	1st to 10th	Night	36% 6% 11% 20% 20% 8%	2400
	11th to 20th	Night	31% 6% 11% 20% 22% 9%	2339
	21st to end	Night	28% 7% 13% 20% 26% 7%	1843
March	1st to 10th	Night	40% 11% 13% 19% 13% 4	3418
	11th to 20th	Night	23% 10% 23% 23% 16% 4	3480
	21st to end	Night	29% 6% 11% 27% 21% 6%	3817
April	1st to 10th	Night	23% 7% 20% 27% 16% 6%	2090
	11th to 20th	Night	25% 10% 17% 22% 22% 4	2063
	21st to end	Night	22% 7% 14% 26% 26% 4	1939
May	1st to 10th	Night	15% 12% 21% 29% 18% 5%	2840
	11th to 20th	Night	27% 11% 22% 28% 10% 1	2813
	21st to end	Night	17% 8% 16% 38% 20% 1	3087
June	1st to 10th	Night	37% 10% 25% 22% 6%	1710
	11th to 20th	Night	31% 13% 29% 22% 4	1710
	21st to end	Night	36% 17% 27% 15% 6%	1710
July	1st to 10th	Night	43% 17% 31% 9% 1	2795
	11th to 20th	Night	39% 20% 35% 6%	2786
	21st to end	Night	53% 17% 23% 6%	2988
August	1st to 10th	Night	35% 16% 30% 12% 6%	2929
	11th to 20th	Night	29% 16% 36% 17% 1	3130
	21st to end	Night	42% 20% 28% 9% 1	3787
September	1st to 10th	Night	39% 20% 26% 13% 2	2090
	11th to 20th	Night	46% 14% 24% 14% 2	2090
	21st to end	Night	42% 12% 19% 18% 8% 1	2090
October	1st to 10th	Night	54% 11% 13% 10% 8% 4	3480
	11th to 20th	Night	26% 6% 9% 28% 25% 5%	3673
	21st to end	Night	29% 6% 9% 26% 25% 5%	4120
November	1st to 10th	Night	29% 8% 13% 21% 19% 10%	2341
	11th to 20th	Night	33% 7% 12% 22% 19% 8%	2400
	21st to end	Night	32% 7% 12% 22% 19% 8%	2560
December	1st to 10th	Night	20% 5% 18% 30% 17% 11%	4250
	11th to 20th	Night	33% 6% 11% 21% 21% 8%	4824
	21st to end	Night	42% 9% 14% 18% 14% 3	6490

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	11% 10% 41% 30% 7%	300
	11th to 20th	Day	10% 14% 33% 29% 11% 2	300
	21st to end	Day	15% 11% 43% 25% 5%	330
February	1st to 10th	Day	7% 11% 31% 34% 16% 2	300
	11th to 20th	Day	7% 6% 39% 31% 15% 2	300
	21st to end	Day	6% 9% 30% 40% 13% 2	264
March	1st to 10th	Day	5% 8% 42% 32% 12% 1	460
	11th to 20th	Day	7% 9% 33% 31% 18% 1	460
	21st to end	Day	8% 8% 34% 33% 16% 3	506
April	1st to 10th	Day	8% 7% 35% 34% 14% 2	460
	11th to 20th	Day	8% 8% 31% 36% 13% 3	452
	21st to end	Day	4 4 26% 40% 22% 4	460
May	1st to 10th	Day	4 4 23% 39% 22% 8%	463
	11th to 20th	Day	10% 2 17% 38% 24% 9%	487
	21st to end	Day	5% 2 10% 34% 34% 15%	529
June	1st to 10th	Day	13% 3 8% 30% 29% 17%	490
	11th to 20th	Day	7% 2 6% 30% 33% 22%	490
	21st to end	Day	5% 1 4 18% 38% 34%	490
July	1st to 10th	Day	6% 2 1 13% 39% 39%	485
	11th to 20th	Day	5% 1 1 14% 37% 42%	484
	21st to end	Day	8% 2 3 15% 36% 35%	532
August	1st to 10th	Day	8% 1 3 16% 39% 34%	486
	11th to 20th	Day	8% 2 1 13% 38% 39%	479
	21st to end	Day	7% 2 4 17% 37% 32%	539
September	1st to 10th	Day	8% 2 3 17% 35% 35%	490
	11th to 20th	Day	8% 2 2 27% 34% 25%	490
	21st to end	Day	7% 1 4 25% 38% 26%	490
October	1st to 10th	Day	12% 3 12% 36% 29% 8%	490
	11th to 20th	Day	7% 2 19% 35% 29% 9%	490
	21st to end	Day	9% 3 17% 41% 26% 4	539
November	1st to 10th	Day	8% 4 19% 36% 28% 5%	495
	11th to 20th	Day	12% 5% 23% 35% 21% 5%	500
	21st to end	Day	9% 5% 28% 36% 19% 3	335
December	1st to 10th	Day	5% 9% 32% 35% 16% 4	300
	11th to 20th	Day	9% 5% 35% 32% 17% 1	300
	21st to end	Day	7% 7% 32% 38% 14% 2	330
January	1st to 10th	Night	11% 8% 26% 37% 16% 1	800
	11th to 20th	Night	13% 6% 25% 37% 17% 1	800
	21st to end	Night	15% 10% 29% 33% 14%	880
February	1st to 10th	Night	13% 6% 29% 32% 19% 1	800
	11th to 20th	Night	11% 6% 25% 37% 19% 2	783
	21st to end	Night	8% 4 24% 44% 19% 1	629
March	1st to 10th	Night	6% 6% 34% 40% 12% 2	760
	11th to 20th	Night	7% 6% 22% 41% 22% 1	760
	21st to end	Night	8% 5% 27% 38% 20% 2	836
April	1st to 10th	Night	6% 7% 25% 41% 20% 1	760
	11th to 20th	Night	8% 5% 27% 41% 17% 2	751
	21st to end	Night	6% 3 25% 45% 20% 1	732
May	1st to 10th	Night	4 2 14% 43% 34% 4	570
	11th to 20th	Night	8% 1 14% 39% 31% 6%	561
	21st to end	Night	5% 1 10% 37% 38% 9%	617
June	1st to 10th	Night	11% 1 4 26% 43% 15%	570
	11th to 20th	Night	8% 1 5% 18% 40% 29%	570
	21st to end	Night	8% 1 2 12% 43% 34%	570
July	1st to 10th	Night	7% 1 2 8% 42% 39%	555
	11th to 20th	Night	4 2 1 8% 40% 45%	552
	21st to end	Night	5% 2 1 11% 44% 38%	624
August	1st to 10th	Night	5% 1 1 10% 44% 38%	567
	11th to 20th	Night	6% 1 1 9% 38% 45%	564
	21st to end	Night	10% 2 3 21% 38% 26%	808
September	1st to 10th	Night	7% 2 3 20% 44% 24%	760
	11th to 20th	Night	11% 2 3 25% 40% 19%	760
	21st to end	Night	11% 2 6% 29% 39% 14%	760
October	1st to 10th	Night	12% 2 14% 34% 31% 7%	760
	11th to 20th	Night	9% 3 13% 37% 33% 5%	760
	21st to end	Night	10% 4 20% 39% 24% 3	836
November	1st to 10th	Night	7% 3 26% 40% 20% 3	780
	11th to 20th	Night	11% 3 22% 40% 22% 2	800
	21st to end	Night	9% 4 25% 41% 20% 1	800
December	1st to 10th	Night	8% 5% 24% 36% 25% 2	800
	11th to 20th	Night	10% 6% 22% 38% 21% 3	800
	21st to end	Night	12% 4 26% 36% 21% 1	880

Page generated at 2025-02-18 03:26:27. Version ac07

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