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 2024-03-18.

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 4 3 4 5% 6% 9% 61%	78857
	Night	3 3 1 3 4 2 4 4 6% 8% 62%	80972
Transparency	Day	20% 5% 9% 24% 28% 14%	78579
	Night	22% 4 10% 24% 27% 13%	80772
Seeing	Day	4 11% 28% 31% 21% 5%	14208
	Night	4 5% 28% 42% 19% 2	24496

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 4 4 3 5% 5% 6% 10% 59%	2776
	11th to 20th	Day	1 2 1 2 2 2 3 4 6% 8% 69%	2860
	21st to end	Day	2 4 2 4 5% 3 5% 5% 8% 8% 54%	3146
February	1st to 10th	Day	1 4 2 3 4 3 4 4 4 8% 62%	1716
	11th to 20th	Day	1 3 2 4 5% 2 4 4 6% 8% 61%	1849
	21st to end	Day	4 1 4 4 2 4 5% 4 8% 63%	1570
March	1st to 10th	Day	1 2 1 3 4 3 5% 5% 7% 8% 61%	2000
	11th to 20th	Day	2 4 3 5% 5% 2 3 4 5% 7% 59%	2058
	21st to end	Day	1 2 2 3 4 2 4 5% 6% 8% 62%	2245
April	1st to 10th	Day	2 2 1 2 2 2 4 4 6% 8% 68%	2160
	11th to 20th	Day	2 3 1 4 4 2 4 4 5% 8% 63%	2131
	21st to end	Day	2 2 1 2 3 2 5% 5% 5% 9% 65%	2160
May	1st to 10th	Day	2 1 1 3 3 2 4 4 4 8% 67%	2160
	11th to 20th	Day	3 2 1 3 4 3 6% 5% 6% 8% 59%	2243
	21st to end	Day	2 2 1 3 3 3 4 4 5% 8% 66%	2724
June	1st to 10th	Day	1 1 1 2 3 2 4 5% 7% 10% 64%	2520
	11th to 20th	Day	1 1 1 2 2 3 4 5% 8% 72%	2520
	21st to end	Day	4 2 1 4 4 3 5% 5% 7% 10% 56%	2520
July	1st to 10th	Day	3 3 2 4 4 3 6% 8% 9% 11% 48%	2502
	11th to 20th	Day	2 2 1 4 4 4 8% 9% 9% 14% 43%	2340
	21st to end	Day	3 2 2 5% 6% 4 9% 9% 11% 13% 35%	2545
August	1st to 10th	Day	3 2 1 4 6% 4 7% 8% 10% 11% 43%	2285
	11th to 20th	Day	3 3 2 4 4 3 6% 7% 9% 11% 48%	2123
	21st to end	Day	3 2 1 3 4 3 6% 7% 9% 13% 49%	2376
September	1st to 10th	Day	4 3 2 3 4 3 5% 6% 7% 9% 52%	2160
	11th to 20th	Day	4 3 1 4 3 2 4 4 7% 8% 60%	2160
	21st to end	Day	2 1 1 2 2 2 3 4 5% 6% 70%	1954
October	1st to 10th	Day	4 3 1 3 5% 3 4 5% 5% 8% 60%	1800
	11th to 20th	Day	3 2 1 2 2 1 3 2 3 4 77%	1800
	21st to end	Day	3 2 1 2 2 2 2 3 3 4 74%	1980
November	1st to 10th	Day	1 1 1 2 3 1 2 3 4 6% 76%	1799
	11th to 20th	Day	2 1 2 2 2 2 4 4 6% 74%	1710
	21st to end	Day	3 4 2 3 3 2 2 3 4 6% 69%	1710
December	1st to 10th	Day	1 2 1 3 3 2 3 4 5% 7% 68%	1535
	11th to 20th	Day	2 3 1 3 3 3 5% 5% 5% 10% 59%	1926
	21st to end	Day	1 4 1 4 3 2 3 4 6% 8% 64%	2794
January	1st to 10th	Night	1 4 2 5% 5% 3 5% 4 6% 9% 55%	4193
	11th to 20th	Night	2 2 1 1 2 1 4 4 5% 7% 72%	4110
	21st to end	Night	2 5% 2 4 4 3 4 5% 7% 9% 55%	4521
February	1st to 10th	Night	1 3 2 4 4 2 3 3 5% 7% 65%	2461
	11th to 20th	Night	2 4 1 3 4 2 3 4 6% 7% 64%	2218
	21st to end	Night	1 3 1 3 3 2 3 4 4 6% 69%	1884
March	1st to 10th	Night	2 5% 1 3 3 2 4 3 5% 7% 66%	2176
	11th to 20th	Night	4 5% 2 4 3 3 4 4 5% 7% 60%	2068
	21st to end	Night	2 3 1 4 4 3 4 5% 4 6% 65%	2110
April	1st to 10th	Night	2 2 1 3 3 2 3 4 5% 8% 67%	1800
	11th to 20th	Night	3 3 2 4 4 3 3 4 4 7% 64%	1777
	21st to end	Night	3 2 1 3 3 2 4 4 5% 7% 69%	1800
May	1st to 10th	Night	3 2 1 3 4 3 4 3 4 6% 68%	1800
	11th to 20th	Night	4 4 2 5% 4 2 4 4 5% 7% 57%	1646
	21st to end	Night	2 1 1 3 3 2 3 3 4 7% 70%	1552
June	1st to 10th	Night	1 1 1 3 4 3 5% 5% 6% 8% 64%	1440
	11th to 20th	Night	2 1 1 2 3 1 3 4 4 7% 72%	1440
	21st to end	Night	3 3 1 4 3 2 5% 6% 7% 10% 55%	1440
July	1st to 10th	Night	4 2 2 5% 6% 5% 7% 7% 9% 10% 44%	1452
	11th to 20th	Night	2 2 2 4 6% 4 6% 8% 10% 13% 44%	1620
	21st to end	Night	4 3 3 5% 7% 5% 8% 7% 9% 14% 35%	1773
August	1st to 10th	Night	2 2 1 4 5% 4 6% 7% 10% 14% 46%	1651
	11th to 20th	Night	4 3 3 5% 5% 4 6% 9% 10% 12% 38%	1778
	21st to end	Night	3 2 1 3 4 3 5% 8% 9% 13% 49%	1980
September	1st to 10th	Night	4 2 1 4 4 2 6% 5% 8% 10% 53%	1800
	11th to 20th	Night	4 3 1 2 4 2 4 6% 7% 8% 60%	1800
	21st to end	Night	4 2 1 3 3 2 3 3 4 7% 67%	2001
October	1st to 10th	Night	5% 3 1 3 4 2 4 5% 5% 7% 61%	2160
	11th to 20th	Night	3 2 1 1 2 2 2 3 3 5% 78%	2160
	21st to end	Night	4 2 1 2 3 2 2 2 4 6% 73%	2376
November	1st to 10th	Night	2 2 1 1 1 1 3 4 5% 80%	2258
	11th to 20th	Night	1 2 2 2 2 2 3 3 5% 78%	2470
	21st to end	Night	4 4 2 3 2 2 3 3 5% 5% 68%	2470
December	1st to 10th	Night	2 3 1 2 3 2 3 3 5% 7% 68%	2643
	11th to 20th	Night	3 2 2 3 4 2 4 5% 6% 10% 59%	3271
	21st to end	Night	2 4 2 4 4 3 4 4 6% 9% 59%	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	22% 5% 8% 35% 28% 2	2777
	11th to 20th	Day	15% 5% 12% 42% 23% 3	2860
	21st to end	Day	25% 6% 11% 28% 26% 4	3146
February	1st to 10th	Day	22% 4 10% 30% 25% 9%	1716
	11th to 20th	Day	22% 4 7% 29% 29% 9%	1859
	21st to end	Day	22% 3 4 20% 35% 15%	1570
March	1st to 10th	Day	20% 4 5% 24% 33% 13%	2000
	11th to 20th	Day	25% 4 6% 22% 31% 11%	2058
	21st to end	Day	20% 5% 6% 25% 30% 13%	2245
April	1st to 10th	Day	16% 4 6% 22% 32% 20%	2160
	11th to 20th	Day	21% 4 4 20% 32% 19%	2134
	21st to end	Day	18% 4 6% 25% 32% 16%	2160
May	1st to 10th	Day	16% 4 5% 20% 36% 20%	2160
	11th to 20th	Day	23% 5% 9% 22% 26% 15%	2246
	21st to end	Day	16% 4 7% 20% 26% 26%	2724
June	1st to 10th	Day	13% 5% 10% 21% 27% 24%	2520
	11th to 20th	Day	12% 3 4 14% 25% 42%	2520
	21st to end	Day	22% 5% 6% 18% 25% 24%	2520
July	1st to 10th	Day	26% 8% 13% 18% 19% 16%	2434
	11th to 20th	Day	23% 8% 19% 26% 16% 8%	2271
	21st to end	Day	29% 12% 23% 26% 9% 2	2404
August	1st to 10th	Day	27% 10% 18% 22% 14% 9%	2270
	11th to 20th	Day	24% 8% 14% 25% 21% 8%	2123
	21st to end	Day	22% 8% 14% 28% 22% 6%	2376
September	1st to 10th	Day	25% 6% 11% 23% 23% 11%	2160
	11th to 20th	Day	20% 5% 10% 21% 25% 18%	2160
	21st to end	Day	15% 3 5% 23% 37% 18%	1954
October	1st to 10th	Day	24% 5% 7% 21% 27% 17%	1800
	11th to 20th	Day	14% 1 3 15% 41% 26%	1800
	21st to end	Day	17% 2 6% 23% 38% 15%	1980
November	1st to 10th	Day	12% 2 5% 26% 39% 16%	1799
	11th to 20th	Day	13% 3 7% 27% 41% 9%	1710
	21st to end	Day	20% 2 5% 25% 36% 12%	1710
December	1st to 10th	Day	18% 2 12% 34% 27% 6%	1535
	11th to 20th	Day	23% 4 11% 28% 28% 5%	1924
	21st to end	Day	20% 4 8% 27% 32% 9%	2794
January	1st to 10th	Night	27% 5% 9% 32% 25% 3	4193
	11th to 20th	Night	17% 4 11% 39% 24% 5%	4110
	21st to end	Night	27% 5% 11% 27% 25% 4	4521
February	1st to 10th	Night	21% 3 10% 27% 29% 9%	2461
	11th to 20th	Night	22% 4 7% 29% 27% 11%	2218
	21st to end	Night	21% 3 4 18% 37% 17%	1884
March	1st to 10th	Night	22% 3 4 25% 33% 13%	2176
	11th to 20th	Night	27% 3 4 23% 31% 12%	2068
	21st to end	Night	23% 4 5% 20% 36% 12%	2110
April	1st to 10th	Night	17% 4 6% 22% 32% 19%	1800
	11th to 20th	Night	23% 3 6% 19% 28% 22%	1777
	21st to end	Night	17% 4 8% 19% 36% 15%	1800
May	1st to 10th	Night	21% 4 5% 16% 33% 21%	1800
	11th to 20th	Night	27% 6% 10% 20% 20% 17%	1647
	21st to end	Night	16% 4 9% 18% 24% 27%	1552
June	1st to 10th	Night	19% 5% 13% 20% 23% 20%	1440
	11th to 20th	Night	14% 3 6% 13% 24% 40%	1440
	21st to end	Night	24% 5% 12% 16% 19% 24%	1440
July	1st to 10th	Night	30% 8% 16% 16% 14% 16%	1412
	11th to 20th	Night	26% 9% 23% 20% 13% 9%	1566
	21st to end	Night	34% 11% 28% 19% 8% 1	1674
August	1st to 10th	Night	27% 10% 23% 18% 13% 10%	1642
	11th to 20th	Night	31% 10% 19% 19% 12% 8%	1778
	21st to end	Night	24% 8% 18% 26% 16% 8%	1980
September	1st to 10th	Night	25% 7% 16% 25% 17% 11%	1800
	11th to 20th	Night	22% 5% 14% 15% 24% 20%	1800
	21st to end	Night	18% 4 9% 19% 31% 20%	2001
October	1st to 10th	Night	25% 4 9% 19% 23% 21%	2160
	11th to 20th	Night	13% 2 4 16% 38% 28%	2160
	21st to end	Night	16% 3 5% 23% 37% 18%	2376
November	1st to 10th	Night	10% 2 5% 25% 43% 16%	2258
	11th to 20th	Night	12% 2 5% 28% 41% 12%	2470
	21st to end	Night	22% 2 4 24% 34% 14%	2470
December	1st to 10th	Night	20% 3 9% 36% 28% 6%	2643
	11th to 20th	Night	23% 5% 10% 29% 29% 5%	3272
	21st to end	Night	25% 4 7% 27% 32% 5%	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	1 14% 43% 31% 10%	270
	11th to 20th	Day	9% 13% 41% 32% 4 1	270
	21st to end	Day	2 8% 43% 29% 15% 1	297
February	1st to 10th	Day	1 19% 36% 36% 8%	270
	11th to 20th	Day	4 16% 44% 29% 6%	270
	21st to end	Day	7% 28% 36% 22% 7%	225
March	1st to 10th	Day	3 24% 33% 31% 8% 1	370
	11th to 20th	Day	8% 23% 31% 25% 10% 2	449
	21st to end	Day	7% 32% 35% 20% 6%	462
April	1st to 10th	Day	6% 21% 40% 24% 8% 1	420
	11th to 20th	Day	7% 27% 39% 21% 6% 1	412
	21st to end	Day	5% 27% 38% 26% 4	420
May	1st to 10th	Day	4 17% 42% 28% 8% 1	423
	11th to 20th	Day	4 15% 34% 31% 14% 2	485
	21st to end	Day	4 12% 32% 34% 17% 1	679
June	1st to 10th	Day	2 7% 22% 39% 29% 2	630
	11th to 20th	Day	3 7% 23% 37% 27% 3	630
	21st to end	Day	5% 4 21% 34% 30% 5%	630
July	1st to 10th	Day	4 1 12% 35% 38% 10%	604
	11th to 20th	Day	3 8% 28% 43% 18%	444
	21st to end	Day	4 1 7% 26% 42% 20%	487
August	1st to 10th	Day	4 2 9% 29% 40% 17%	447
	11th to 20th	Day	4 1 14% 34% 38% 9%	437
	21st to end	Day	2 1 12% 34% 37% 13%	495
September	1st to 10th	Day	4 3 14% 35% 34% 10%	450
	11th to 20th	Day	3 2 22% 37% 30% 6%	450
	21st to end	Day	2 8% 20% 33% 29% 9%	298
October	1st to 10th	Day	4 9% 27% 30% 26% 4	270
	11th to 20th	Day	4 9% 29% 28% 26% 5%	270
	21st to end	Day	8% 9% 24% 33% 22% 3	297
November	1st to 10th	Day	3 14% 33% 35% 15%	270
	11th to 20th	Day	3 8% 31% 39% 17% 3	270
	21st to end	Day	5% 12% 40% 27% 15% 1	270
December	1st to 10th	Day	3 9% 42% 31% 14% 1	270
	11th to 20th	Day	4 13% 42% 32% 9% 1	270
	21st to end	Day	10% 15% 42% 29% 4	297
January	1st to 10th	Night	3 5% 35% 43% 13% 1	817
	11th to 20th	Night	4 5% 36% 40% 12% 2	760
	21st to end	Night	4 4 34% 44% 12% 2	836
February	1st to 10th	Night	3 6% 38% 43% 9%	760
	11th to 20th	Night	5% 6% 44% 38% 7%	744
	21st to end	Night	3 8% 48% 38% 4	628
March	1st to 10th	Night	4 7% 41% 39% 8% 1	760
	11th to 20th	Night	6% 8% 34% 39% 13%	752
	21st to end	Night	3 10% 39% 40% 8%	724
April	1st to 10th	Night	3 8% 50% 34% 6%	540
	11th to 20th	Night	5% 11% 40% 35% 9%	533
	21st to end	Night	4 7% 44% 38% 7%	540
May	1st to 10th	Night	4 6% 36% 44% 10%	540
	11th to 20th	Night	5% 5% 29% 41% 19% 1	531
	21st to end	Night	4 6% 33% 42% 14% 1	584
June	1st to 10th	Night	1 5% 21% 50% 22% 1	540
	11th to 20th	Night	3 2 24% 52% 20%	540
	21st to end	Night	3 2 17% 47% 31% 1	540
July	1st to 10th	Night	4 1 11% 41% 41% 3	525
	11th to 20th	Night	2 2 5% 37% 50% 5%	522
	21st to end	Night	4 1 6% 25% 56% 8%	591
August	1st to 10th	Night	4 6% 29% 52% 9%	537
	11th to 20th	Night	5% 1 8% 40% 42% 3	534
	21st to end	Night	4 2 6% 37% 48% 4	594
September	1st to 10th	Night	5% 1 9% 45% 38% 3	540
	11th to 20th	Night	5% 2 10% 48% 33% 2	540
	21st to end	Night	5% 2 17% 47% 27% 2	589
October	1st to 10th	Night	5% 4 23% 45% 22% 1	720
	11th to 20th	Night	3 3 23% 49% 19% 2	720
	21st to end	Night	6% 4 25% 42% 20% 3	792
November	1st to 10th	Night	3 3 24% 48% 20% 1	778
	11th to 20th	Night	2 4 27% 48% 17% 2	950
	21st to end	Night	5% 7% 30% 36% 19% 2	950
December	1st to 10th	Night	4 6% 34% 44% 11% 1	950
	11th to 20th	Night	5% 7% 35% 42% 10%	950
	21st to end	Night	6% 8% 38% 41% 7% 1	1045

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