White Rock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Rock clear sky chart from 2005-11-06 to 2025-07-06.

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	2 2 1 3 3 4 4 4 6% 8% 62%	123556
	Night	3 3 1 4 3 3 4 4 6% 8% 61%	124166
Transparency	Day	18% 5% 9% 24% 28% 16%	123316
	Night	21% 4 9% 23% 28% 14%	123994
Seeing	Day	5% 11% 27% 31% 21% 5%	16044
	Night	4 5% 28% 42% 19% 2	26164

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 3 2 5% 4 4 4 3 6% 8% 61%	3988
	11th to 20th	Day	1 2 1 2 2 2 3 3 5% 8% 72%	4100
	21st to end	Day	1 3 1 4 4 4 5% 4 7% 7% 60%	4510
February	1st to 10th	Day	1 4 2 4 4 4 4 3 4 8% 63%	1807
	11th to 20th	Day	1 4 1 4 4 3 4 3 7% 8% 61%	1949
	21st to end	Day	4 1 5% 3 3 4 3 5% 8% 63%	1650
March	1st to 10th	Day	1 3 1 3 3 3 4 3 5% 7% 66%	4748
	11th to 20th	Day	3 5% 2 6% 3 4 3 4 7% 9% 54%	5000
	21st to end	Day	1 3 1 4 4 4 4 4 6% 8% 61%	5656
April	1st to 10th	Day	1 3 1 2 2 3 4 4 6% 7% 66%	2400
	11th to 20th	Day	2 3 1 4 4 3 4 3 5% 8% 64%	2371
	21st to end	Day	1 2 1 2 3 3 4 4 5% 9% 66%	2400
May	1st to 10th	Day	4 2 1 3 3 4 5% 4 5% 8% 62%	5440
	11th to 20th	Day	3 2 1 3 2 4 5% 4 6% 8% 64%	5723
	21st to end	Day	1 1 1 2 2 3 4 4 5% 8% 69%	6925
June	1st to 10th	Day	1 2 1 2 3 3 4 5% 7% 10% 63%	2800
	11th to 20th	Day	1 1 2 2 3 3 4 5% 8% 71%	2800
	21st to end	Day	4 3 1 5% 3 4 5% 5% 8% 9% 54%	2800
July	1st to 10th	Day	2 2 1 3 3 5% 5% 5% 8% 9% 55%	4469
	11th to 20th	Day	1 1 1 3 4 6% 8% 7% 10% 13% 46%	4110
	21st to end	Day	3 2 1 5% 5% 6% 8% 7% 11% 13% 38%	4454
August	1st to 10th	Day	2 3 1 4 5% 5% 7% 7% 10% 14% 42%	4010
	11th to 20th	Day	2 2 1 3 3 3 6% 5% 8% 11% 57%	3726
	21st to end	Day	3 2 1 4 4 5% 6% 6% 10% 13% 45%	4180
September	1st to 10th	Day	4 4 2 3 4 4 6% 5% 7% 9% 53%	2280
	11th to 20th	Day	4 3 1 4 3 3 4 4 6% 8% 60%	2280
	21st to end	Day	2 1 1 3 2 3 3 3 5% 6% 70%	2062
October	1st to 10th	Day	2 2 1 3 3 2 3 3 4 5% 73%	3170
	11th to 20th	Day	5% 2 1 3 3 3 4 3 6% 6% 64%	3150
	21st to end	Day	2 1 1 2 1 2 2 2 3 5% 79%	3438
November	1st to 10th	Day	2 2 1 3 2 1 3 3 4 6% 74%	1895
	11th to 20th	Day	2 1 2 2 2 3 3 4 6% 75%	1800
	21st to end	Day	3 4 2 3 3 2 2 3 5% 6% 69%	1800
December	1st to 10th	Day	1 1 1 2 1 2 2 2 3 7% 78%	2635
	11th to 20th	Day	1 2 1 3 2 3 4 3 4 8% 69%	3026
	21st to end	Day	1 4 1 3 2 3 3 3 5% 7% 69%	4004
January	1st to 10th	Night	1 4 2 5% 4 4 5% 4 7% 8% 57%	6005
	11th to 20th	Night	1 3 1 2 2 2 3 3 5% 7% 69%	5880
	21st to end	Night	2 4 2 5% 4 3 4 4 7% 8% 58%	6468
February	1st to 10th	Night	1 3 2 4 4 3 3 3 5% 7% 65%	2590
	11th to 20th	Night	2 4 1 4 3 3 3 3 6% 7% 63%	2338
	21st to end	Night	1 3 1 4 2 3 3 3 4 6% 69%	1980
March	1st to 10th	Night	2 5% 1 4 3 3 4 3 5% 5% 65%	5120
	11th to 20th	Night	7% 6% 1 4 3 3 4 3 6% 8% 56%	5000
	21st to end	Night	1 3 1 4 3 3 3 3 4 7% 66%	5310
April	1st to 10th	Night	2 3 1 4 2 3 4 3 5% 8% 65%	2000
	11th to 20th	Night	2 3 1 4 3 3 3 3 5% 7% 64%	1977
	21st to end	Night	3 2 1 3 3 3 4 3 5% 6% 68%	2000
May	1st to 10th	Night	6% 3 1 4 3 4 4 4 6% 7% 56%	4540
	11th to 20th	Night	3 3 2 5% 4 4 4 4 5% 7% 60%	4186
	21st to end	Night	2 1 1 3 3 3 3 3 5% 8% 68%	3972
June	1st to 10th	Night	1 2 1 4 3 4 5% 5% 6% 8% 62%	1600
	11th to 20th	Night	2 2 1 3 3 2 2 4 4 6% 71%	1600
	21st to end	Night	4 3 1 5% 3 4 5% 5% 7% 10% 53%	1600
July	1st to 10th	Night	2 3 1 6% 4 5% 5% 4 7% 8% 54%	2606
	11th to 20th	Night	2 2 1 5% 5% 5% 7% 8% 11% 14% 39%	2860
	21st to end	Night	6% 4 2 6% 6% 6% 5% 5% 8% 12% 39%	3109
August	1st to 10th	Night	2 3 2 8% 7% 7% 8% 6% 12% 13% 32%	2926
	11th to 20th	Night	3 3 1 5% 5% 6% 7% 7% 10% 13% 42%	3113
	21st to end	Night	3 3 2 7% 6% 8% 8% 8% 10% 12% 34%	3487
September	1st to 10th	Night	4 3 1 5% 3 4 5% 4 8% 10% 54%	1900
	11th to 20th	Night	4 3 1 3 3 4 4 5% 7% 7% 60%	1900
	21st to end	Night	4 2 1 3 3 3 3 3 4 7% 67%	2113
October	1st to 10th	Night	3 2 1 3 2 2 2 2 4 5% 75%	3800
	11th to 20th	Night	6% 2 1 2 2 3 3 3 5% 7% 65%	3778
	21st to end	Night	2 1 1 2 2 2 2 2 3 5% 77%	4120
November	1st to 10th	Night	2 2 1 2 1 1 2 2 4 5% 77%	2380
	11th to 20th	Night	1 2 2 2 2 2 2 4 5% 77%	2600
	21st to end	Night	3 4 1 3 2 3 3 2 5% 6% 68%	2600
December	1st to 10th	Night	1 2 1 2 2 2 3 2 6% 8% 72%	4553
	11th to 20th	Night	2 2 1 2 2 2 3 3 5% 9% 69%	5181
	21st to end	Night	2 3 1 4 3 3 4 3 5% 8% 64%	6974

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% 4 6% 33% 31% 3	3989
	11th to 20th	Day	14% 3 10% 30% 27% 16%	4100
	21st to end	Day	22% 4 9% 20% 31% 13%	4510
February	1st to 10th	Day	21% 4 10% 29% 26% 10%	1807
	11th to 20th	Day	22% 4 7% 28% 29% 9%	1959
	21st to end	Day	22% 3 4 20% 35% 17%	1650
March	1st to 10th	Day	17% 3 5% 16% 37% 22%	4748
	11th to 20th	Day	24% 5% 7% 24% 28% 12%	5000
	21st to end	Day	19% 5% 5% 32% 30% 9%	5656
April	1st to 10th	Day	17% 4 6% 21% 33% 19%	2400
	11th to 20th	Day	20% 4 4 19% 32% 20%	2374
	21st to end	Day	16% 4 5% 24% 33% 17%	2400
May	1st to 10th	Day	19% 6% 8% 20% 28% 18%	5440
	11th to 20th	Day	15% 6% 7% 19% 31% 23%	5726
	21st to end	Day	11% 3 9% 16% 25% 36%	6926
June	1st to 10th	Day	14% 5% 10% 22% 26% 24%	2800
	11th to 20th	Day	12% 3 5% 14% 25% 42%	2800
	21st to end	Day	24% 5% 6% 18% 24% 24%	2800
July	1st to 10th	Day	20% 7% 12% 17% 21% 23%	4401
	11th to 20th	Day	20% 7% 18% 33% 16% 5%	4041
	21st to end	Day	26% 10% 20% 31% 11% 2	4314
August	1st to 10th	Day	25% 10% 22% 26% 13% 5%	3996
	11th to 20th	Day	16% 6% 14% 29% 24% 12%	3762
	21st to end	Day	25% 9% 18% 26% 18% 4	4179
September	1st to 10th	Day	24% 6% 11% 24% 24% 12%	2280
	11th to 20th	Day	20% 5% 10% 21% 26% 18%	2280
	21st to end	Day	14% 3 5% 23% 36% 18%	2062
October	1st to 10th	Day	15% 3 5% 16% 35% 27%	3170
	11th to 20th	Day	21% 3 7% 15% 36% 18%	3150
	21st to end	Day	12% 2 5% 21% 41% 19%	3438
November	1st to 10th	Day	13% 2 5% 25% 39% 15%	1895
	11th to 20th	Day	13% 3 7% 27% 41% 10%	1800
	21st to end	Day	19% 2 5% 25% 36% 13%	1800
December	1st to 10th	Day	11% 1 7% 34% 39% 8%	2635
	11th to 20th	Day	17% 3 7% 35% 33% 4	3024
	21st to end	Day	16% 3 10% 31% 33% 7%	4004
January	1st to 10th	Night	26% 3 8% 31% 26% 6%	6005
	11th to 20th	Night	17% 3 10% 30% 27% 14%	5880
	21st to end	Night	24% 4 11% 21% 33% 7%	6468
February	1st to 10th	Night	21% 3 10% 26% 29% 11%	2590
	11th to 20th	Night	22% 4 7% 29% 27% 11%	2338
	21st to end	Night	20% 2 4 18% 37% 18%	1980
March	1st to 10th	Night	21% 3 5% 14% 41% 16%	5120
	11th to 20th	Night	28% 4 5% 19% 30% 13%	5000
	21st to end	Night	19% 5% 5% 28% 34% 9%	5310
April	1st to 10th	Night	19% 4 5% 21% 31% 20%	2000
	11th to 20th	Night	22% 3 5% 18% 27% 24%	1977
	21st to end	Night	17% 5% 7% 19% 37% 15%	2000
May	1st to 10th	Night	27% 7% 8% 18% 21% 20%	4537
	11th to 20th	Night	21% 7% 8% 17% 23% 24%	4187
	21st to end	Night	16% 5% 9% 13% 17% 40%	3972
June	1st to 10th	Night	20% 5% 13% 19% 22% 21%	1600
	11th to 20th	Night	14% 4 6% 12% 24% 39%	1600
	21st to end	Night	26% 4 12% 16% 19% 23%	1600
July	1st to 10th	Night	26% 8% 12% 15% 13% 26%	2566
	11th to 20th	Night	29% 9% 23% 27% 8% 5%	2806
	21st to end	Night	35% 8% 20% 26% 10% 1	3011
August	1st to 10th	Night	38% 10% 20% 16% 10% 6%	2917
	11th to 20th	Night	29% 9% 19% 15% 16% 12%	3143
	21st to end	Night	38% 10% 17% 20% 11% 4	3487
September	1st to 10th	Night	24% 6% 15% 25% 18% 12%	1900
	11th to 20th	Night	22% 5% 13% 14% 25% 20%	1900
	21st to end	Night	18% 4 9% 18% 32% 20%	2113
October	1st to 10th	Night	15% 2 6% 14% 38% 26%	3800
	11th to 20th	Night	20% 4 7% 16% 30% 23%	3778
	21st to end	Night	12% 2 6% 23% 38% 20%	4120
November	1st to 10th	Night	12% 2 5% 24% 42% 15%	2380
	11th to 20th	Night	12% 2 6% 27% 41% 13%	2600
	21st to end	Night	22% 2 5% 23% 34% 15%	2600
December	1st to 10th	Night	12% 2 6% 38% 31% 11%	4553
	11th to 20th	Night	15% 3 7% 33% 36% 6%	5182
	21st to end	Night	20% 3 8% 30% 35% 3	6974

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	2 13% 41% 33% 10%	300
	11th to 20th	Day	8% 13% 39% 33% 6% 1	300
	21st to end	Day	2 9% 42% 31% 15% 2	330
February	1st to 10th	Day	2 19% 35% 36% 7%	300
	11th to 20th	Day	6% 16% 41% 30% 6%	300
	21st to end	Day	6% 27% 35% 25% 7%	249
March	1st to 10th	Day	4 23% 32% 32% 8% 1	405
	11th to 20th	Day	8% 23% 32% 25% 10% 1	500
	21st to end	Day	8% 30% 33% 23% 6%	550
April	1st to 10th	Day	7% 21% 39% 24% 8% 1	500
	11th to 20th	Day	8% 28% 39% 20% 6% 1	492
	21st to end	Day	6% 26% 36% 26% 5% 1	500
May	1st to 10th	Day	5% 18% 41% 28% 8% 2	503
	11th to 20th	Day	4 15% 33% 31% 14% 2	570
	21st to end	Day	4 12% 31% 34% 17% 2	789
June	1st to 10th	Day	2 6% 22% 39% 29% 2	730
	11th to 20th	Day	2 7% 25% 35% 27% 3	730
	21st to end	Day	5% 5% 20% 34% 30% 5%	730
July	1st to 10th	Day	3 1 13% 37% 37% 9%	679
	11th to 20th	Day	3 7% 26% 44% 19%	484
	21st to end	Day	4 1 7% 27% 43% 18%	531
August	1st to 10th	Day	3 1 9% 27% 41% 18%	487
	11th to 20th	Day	4 1 13% 33% 39% 10%	477
	21st to end	Day	3 1 12% 35% 37% 12%	539
September	1st to 10th	Day	4 2 14% 34% 36% 10%	490
	11th to 20th	Day	3 2 24% 36% 30% 6%	490
	21st to end	Day	2 8% 19% 33% 29% 9%	329
October	1st to 10th	Day	4 8% 25% 30% 27% 5%	300
	11th to 20th	Day	5% 10% 27% 27% 25% 6%	300
	21st to end	Day	8% 10% 24% 34% 22% 3	330
November	1st to 10th	Day	5% 14% 32% 34% 15%	300
	11th to 20th	Day	2 8% 31% 39% 17% 2	300
	21st to end	Day	5% 12% 40% 27% 15% 1	300
December	1st to 10th	Day	3 8% 39% 33% 15% 2	300
	11th to 20th	Day	3 12% 39% 35% 10% 1	300
	21st to end	Day	9% 14% 40% 31% 5%	330
January	1st to 10th	Night	3 5% 35% 44% 12% 1	860
	11th to 20th	Night	4 5% 36% 42% 12% 2	800
	21st to end	Night	4 5% 35% 43% 12% 2	880
February	1st to 10th	Night	3 6% 39% 43% 8%	800
	11th to 20th	Night	5% 7% 44% 38% 7%	784
	21st to end	Night	3 8% 47% 38% 4	660
March	1st to 10th	Night	5% 7% 41% 38% 9% 1	800
	11th to 20th	Night	6% 8% 33% 41% 12%	800
	21st to end	Night	3 9% 40% 40% 8%	804
April	1st to 10th	Night	4 8% 49% 33% 6%	600
	11th to 20th	Night	4 11% 41% 35% 8%	593
	21st to end	Night	4 7% 44% 39% 7%	600
May	1st to 10th	Night	5% 7% 35% 43% 10%	600
	11th to 20th	Night	5% 5% 31% 41% 18% 1	591
	21st to end	Night	4 6% 33% 43% 13%	650
June	1st to 10th	Night	1 5% 20% 52% 21% 1	600
	11th to 20th	Night	3 2 24% 52% 19% 1	600
	21st to end	Night	5% 2 17% 46% 30% 1	600
July	1st to 10th	Night	4 1 11% 43% 38% 2	570
	11th to 20th	Night	2 1 5% 37% 49% 5%	552
	21st to end	Night	4 1 6% 26% 55% 8%	624
August	1st to 10th	Night	4 6% 30% 52% 8%	567
	11th to 20th	Night	5% 1 8% 40% 42% 3	564
	21st to end	Night	4 1 6% 38% 47% 4	627
September	1st to 10th	Night	5% 1 10% 45% 38% 3	570
	11th to 20th	Night	5% 2 10% 50% 31% 2	570
	21st to end	Night	5% 2 17% 47% 27% 2	622
October	1st to 10th	Night	5% 4 22% 46% 22% 1	760
	11th to 20th	Night	4 3 24% 48% 20% 2	760
	21st to end	Night	6% 3 25% 43% 20% 3	836
November	1st to 10th	Night	4 3 24% 49% 19% 1	820
	11th to 20th	Night	2 4 28% 49% 16% 2	1000
	21st to end	Night	5% 7% 30% 37% 19% 2	1000
December	1st to 10th	Night	4 6% 33% 45% 12% 1	1000
	11th to 20th	Night	5% 7% 35% 43% 10%	1000
	21st to end	Night	6% 8% 38% 41% 7% 1	1100

Page generated at 2025-07-02 23:30:17. Version ac07

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