White Bluff
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Bluff clear sky chart from 2005-11-06 to 2025-11-18.

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	12% 7% 3 7% 4 4 5% 4 6% 8% 40%	126745
	Night	13% 8% 3 7% 4 4 4 3 5% 7% 42%	123728
Transparency	Day	42% 3 10% 24% 17% 3	130422
	Night	41% 3 9% 23% 19% 4	128110
Seeing	Day	17% 12% 24% 23% 16% 7%	16622
	Night	18% 11% 24% 28% 17% 3	26323

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	14% 12% 7% 12% 4 4 4 3 4 5% 32%	3617
	11th to 20th	Day	15% 8% 3 12% 3 3 3 2 3 5% 44%	3635
	21st to end	Day	19% 8% 4 5% 3 3 3 3 5% 6% 40%	4953
February	1st to 10th	Day	17% 12% 4 8% 4 4 4 2 4 6% 36%	2000
	11th to 20th	Day	20% 11% 4 8% 5% 4 3 2 4 5% 34%	1948
	21st to end	Day	18% 10% 4 6% 4 4 4 3 5% 5% 37%	1650
March	1st to 10th	Day	17% 13% 3 8% 4 4 3 3 3 4 36%	4480
	11th to 20th	Day	13% 8% 3 6% 4 4 3 3 4 5% 47%	4699
	21st to end	Day	11% 8% 3 7% 5% 4 4 3 5% 7% 43%	5870
April	1st to 10th	Day	13% 6% 2 6% 4 5% 4 3 6% 7% 45%	2400
	11th to 20th	Day	14% 8% 2 6% 5% 4 4 3 5% 6% 43%	2374
	21st to end	Day	13% 7% 3 7% 5% 5% 4 3 6% 7% 40%	2406
May	1st to 10th	Day	19% 8% 3 7% 5% 5% 6% 5% 7% 8% 27%	5862
	11th to 20th	Day	14% 9% 4 9% 5% 5% 5% 4 5% 7% 31%	5861
	21st to end	Day	15% 8% 3 7% 4 4 5% 3 5% 7% 38%	6433
June	1st to 10th	Day	8% 6% 2 6% 5% 5% 6% 5% 6% 9% 41%	2674
	11th to 20th	Day	5% 4 2 6% 6% 5% 6% 5% 8% 10% 44%	2800
	21st to end	Day	4 4 2 5% 5% 6% 6% 5% 8% 12% 42%	2800
July	1st to 10th	Day	6% 5% 2 7% 5% 6% 6% 6% 8% 10% 39%	6360
	11th to 20th	Day	6% 5% 2 7% 6% 6% 7% 7% 9% 12% 33%	6360
	21st to end	Day	11% 7% 3 8% 5% 6% 6% 5% 8% 11% 30%	6429
August	1st to 10th	Day	4 3 1 4 3 4 5% 5% 7% 10% 53%	3948
	11th to 20th	Day	7% 5% 3 6% 5% 5% 6% 5% 8% 10% 40%	3849
	21st to end	Day	5% 4 2 4 4 4 5% 4 6% 8% 53%	4312
September	1st to 10th	Day	11% 6% 2 5% 4 5% 6% 4 6% 8% 42%	2395
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 3 4 8% 45%	2200
	21st to end	Day	11% 6% 2 6% 4 4 4 4 5% 6% 48%	2200
October	1st to 10th	Day	10% 4 1 4 4 4 3 3 4 7% 56%	2200
	11th to 20th	Day	11% 5% 2 5% 3 3 3 3 5% 6% 54%	2117
	21st to end	Day	18% 7% 2 5% 3 3 4 3 4 5% 48%	2025
November	1st to 10th	Day	13% 6% 2 4 3 3 3 2 5% 6% 54%	1852
	11th to 20th	Day	13% 7% 2 5% 4 2 3 3 5% 7% 49%	1863
	21st to end	Day	15% 8% 3 5% 3 4 4 4 4 6% 46%	1800
December	1st to 10th	Day	15% 9% 2 5% 4 3 4 3 4 5% 45%	2930
	11th to 20th	Day	19% 11% 4 9% 5% 4 4 3 4 5% 34%	3373
	21st to end	Day	16% 11% 4 8% 5% 5% 5% 4 5% 7% 30%	4070
January	1st to 10th	Night	15% 13% 4 9% 4 3 4 3 4 5% 36%	6348
	11th to 20th	Night	17% 10% 3 9% 4 3 3 2 3 3 42%	6342
	21st to end	Night	19% 11% 4 6% 4 3 3 2 4 4 39%	5986
February	1st to 10th	Night	19% 11% 4 8% 4 4 4 3 5% 5% 33%	2400
	11th to 20th	Night	22% 9% 4 8% 4 4 3 2 4 5% 35%	2338
	21st to end	Night	21% 10% 3 7% 4 3 4 4 4 5% 35%	1980
March	1st to 10th	Night	18% 11% 3 7% 4 4 4 3 5% 7% 35%	5373
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 5% 6% 49%	5259
	21st to end	Night	13% 8% 3 7% 5% 4 4 3 5% 8% 40%	5100
April	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 5% 7% 46%	2000
	11th to 20th	Night	15% 7% 2 4 3 4 4 3 5% 7% 48%	1975
	21st to end	Night	12% 8% 3 5% 4 4 4 4 6% 8% 42%	1991
May	1st to 10th	Night	13% 10% 4 8% 6% 5% 5% 4 6% 7% 33%	4033
	11th to 20th	Night	14% 10% 3 8% 6% 5% 4 4 6% 7% 34%	4032
	21st to end	Night	13% 6% 2 8% 6% 4 5% 4 6% 9% 37%	4421
June	1st to 10th	Night	8% 6% 3 5% 5% 4 4 4 6% 10% 45%	1720
	11th to 20th	Night	3 4 1 4 4 4 4 5% 7% 10% 54%	1600
	21st to end	Night	3 3 2 4 4 4 5% 6% 9% 13% 49%	1600
July	1st to 10th	Night	6% 4 2 6% 4 5% 5% 5% 8% 12% 42%	3618
	11th to 20th	Night	4 4 2 5% 5% 4 5% 5% 8% 15% 43%	3617
	21st to end	Night	7% 6% 3 9% 5% 6% 6% 5% 8% 14% 31%	4417
August	1st to 10th	Night	4 3 1 4 3 3 4 3 6% 9% 61%	3197
	11th to 20th	Night	4 3 1 5% 4 4 6% 5% 8% 12% 49%	3200
	21st to end	Night	5% 3 1 3 3 4 5% 3 7% 9% 57%	3586
September	1st to 10th	Night	11% 5% 1 6% 4 4 5% 4 5% 6% 50%	2000
	11th to 20th	Night	11% 5% 2 4 4 4 4 3 5% 8% 50%	2185
	21st to end	Night	11% 4 2 6% 3 3 4 3 5% 5% 53%	2200
October	1st to 10th	Night	9% 5% 1 3 3 3 3 2 3 5% 63%	2200
	11th to 20th	Night	15% 5% 2 4 3 4 3 2 4 5% 54%	2280
	21st to end	Night	16% 7% 2 5% 3 3 3 3 5% 5% 49%	2814
November	1st to 10th	Night	13% 6% 2 6% 4 3 3 3 4 5% 53%	2666
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 5% 7% 50%	2692
	21st to end	Night	15% 8% 2 5% 4 3 4 2 4 6% 46%	2600
December	1st to 10th	Night	17% 11% 3 8% 4 3 3 3 4 4 41%	4250
	11th to 20th	Night	21% 10% 3 6% 3 3 2 3 3 5% 41%	4822
	21st to end	Night	18% 12% 5% 10% 5% 5% 5% 3 4 5% 28%	6886

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	56% 1 8% 20% 13% 2	3618
	11th to 20th	Day	46% 2 4 22% 25% 1	3635
	21st to end	Day	46% 2 6% 23% 18% 6%	4953
February	1st to 10th	Day	51% 3 8% 21% 15% 3	2000
	11th to 20th	Day	54% 3 7% 20% 14% 4	1958
	21st to end	Day	49% 2 7% 18% 16% 6%	1650
March	1st to 10th	Day	53% 2 4 15% 17% 9%	4480
	11th to 20th	Day	41% 2 7% 22% 20% 8%	4699
	21st to end	Day	43% 2 9% 27% 18% 1	5872
April	1st to 10th	Day	39% 3 10% 23% 21% 3	2400
	11th to 20th	Day	43% 2 7% 22% 20% 5%	2374
	21st to end	Day	44% 3 10% 25% 16% 2	2406
May	1st to 10th	Day	53% 3 14% 20% 9% 1	5897
	11th to 20th	Day	53% 3 14% 20% 10%	5865
	21st to end	Day	46% 4 8% 23% 17% 2	6447
June	1st to 10th	Day	38% 6% 12% 24% 18% 2	2674
	11th to 20th	Day	33% 6% 15% 26% 18% 3	2800
	21st to end	Day	32% 8% 15% 25% 16% 4	2800
July	1st to 10th	Day	38% 4 17% 28% 12% 1	6291
	11th to 20th	Day	40% 4 20% 27% 6% 1	6285
	21st to end	Day	47% 3 21% 22% 6% 1	6245
August	1st to 10th	Day	25% 5% 13% 34% 21% 2	3935
	11th to 20th	Day	37% 4 13% 28% 16% 2	3885
	21st to end	Day	28% 5% 8% 32% 25% 2	4311
September	1st to 10th	Day	39% 6% 10% 23% 19% 4	2395
	11th to 20th	Day	39% 5% 8% 23% 23% 2	2200
	21st to end	Day	37% 4 9% 24% 22% 5%	2200
October	1st to 10th	Day	21% 3 5% 17% 44% 9%	3590
	11th to 20th	Day	24% 2 6% 25% 29% 15%	3422
	21st to end	Day	32% 2 5% 24% 31% 7%	3250
November	1st to 10th	Day	33% 3 8% 24% 27% 5%	1852
	11th to 20th	Day	37% 2 8% 23% 25% 6%	1863
	21st to end	Day	41% 3 7% 25% 19% 5%	1800
December	1st to 10th	Day	43% 2 5% 28% 21% 2	2930
	11th to 20th	Day	55% 2 6% 21% 14% 3	3370
	21st to end	Day	55% 2 9% 25% 9% 1	4070
January	1st to 10th	Night	53% 1 7% 22% 15% 1	6348
	11th to 20th	Night	49% 2 4 20% 21% 4	6342
	21st to end	Night	50% 2 4 22% 17% 5%	5986
February	1st to 10th	Night	55% 2 8% 18% 16% 1	2400
	11th to 20th	Night	54% 2 6% 19% 16% 4	2339
	21st to end	Night	52% 3 7% 17% 17% 5%	1980
March	1st to 10th	Night	50% 3 5% 16% 19% 7%	5373
	11th to 20th	Night	38% 2 7% 21% 19% 14%	5259
	21st to end	Night	45% 2 8% 25% 17% 2	5100
April	1st to 10th	Night	38% 3 10% 25% 21% 3	2000
	11th to 20th	Night	38% 3 7% 22% 22% 7%	1975
	21st to end	Night	40% 3 11% 26% 17% 2	1991
May	1st to 10th	Night	52% 2 14% 20% 10% 1	4060
	11th to 20th	Night	51% 4 15% 18% 12% 1	4033
	21st to end	Night	44% 4 13% 24% 14% 1	4429
June	1st to 10th	Night	35% 5% 14% 24% 18% 3	1720
	11th to 20th	Night	23% 6% 16% 31% 20% 4	1600
	21st to end	Night	23% 9% 18% 30% 16% 4	1600
July	1st to 10th	Night	34% 5% 17% 30% 12% 2	3580
	11th to 20th	Night	31% 6% 25% 31% 7% 2	3572
	21st to end	Night	45% 4 22% 22% 7% 1	4288
August	1st to 10th	Night	22% 3 11% 40% 23% 1	3186
	11th to 20th	Night	27% 4 21% 31% 16% 1	3230
	21st to end	Night	24% 4 11% 33% 25% 3	3586
September	1st to 10th	Night	34% 5% 11% 25% 20% 5%	2000
	11th to 20th	Night	33% 5% 9% 23% 27% 3	2185
	21st to end	Night	32% 4 8% 24% 25% 6%	2200
October	1st to 10th	Night	20% 2 5% 19% 43% 12%	3590
	11th to 20th	Night	22% 1 4 23% 33% 17%	3701
	21st to end	Night	28% 2 6% 25% 29% 10%	4539
November	1st to 10th	Night	36% 3 6% 23% 25% 7%	2666
	11th to 20th	Night	34% 3 6% 23% 26% 7%	2692
	21st to end	Night	41% 2 7% 24% 21% 5%	2600
December	1st to 10th	Night	48% 1 6% 18% 24% 2	4250
	11th to 20th	Night	49% 1 5% 24% 19% 2	4824
	21st to end	Night	60% 2 6% 21% 9% 2	6886

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	25% 23% 35% 11% 5%	300
	11th to 20th	Day	32% 28% 26% 11% 1 1	300
	21st to end	Day	24% 28% 36% 9% 2	330
February	1st to 10th	Day	30% 24% 31% 13% 1 1	300
	11th to 20th	Day	37% 27% 28% 6% 2	300
	21st to end	Day	35% 27% 28% 9% 2	249
March	1st to 10th	Day	30% 21% 34% 12% 3	300
	11th to 20th	Day	27% 25% 32% 12% 3 1	375
	21st to end	Day	27% 19% 34% 15% 4	550
April	1st to 10th	Day	25% 18% 30% 20% 6% 1	500
	11th to 20th	Day	24% 17% 28% 23% 7% 1	492
	21st to end	Day	19% 20% 30% 20% 10% 2	500
May	1st to 10th	Day	21% 19% 27% 21% 9% 3	503
	11th to 20th	Day	18% 11% 28% 23% 16% 5%	527
	21st to end	Day	15% 8% 23% 27% 18% 10%	573
June	1st to 10th	Day	12% 6% 24% 26% 19% 13%	604
	11th to 20th	Day	6% 4 20% 32% 26% 12%	730
	21st to end	Day	6% 5% 21% 32% 23% 12%	730
July	1st to 10th	Day	8% 3 15% 32% 28% 15%	721
	11th to 20th	Day	8% 3 14% 30% 31% 14%	718
	21st to end	Day	10% 3 14% 29% 27% 17%	581
August	1st to 10th	Day	9% 3 14% 30% 30% 13%	526
	11th to 20th	Day	11% 4 14% 34% 30% 7%	519
	21st to end	Day	11% 2 11% 25% 32% 17%	583
September	1st to 10th	Day	11% 3 15% 30% 29% 12%	530
	11th to 20th	Day	14% 3 13% 25% 32% 13%	530
	21st to end	Day	16% 6% 19% 29% 22% 7%	530
October	1st to 10th	Day	12% 4 25% 29% 23% 6%	530
	11th to 20th	Day	13% 15% 33% 23% 13% 2	447
	21st to end	Day	26% 15% 29% 23% 6% 1	363
November	1st to 10th	Day	22% 14% 31% 25% 7% 2	330
	11th to 20th	Day	17% 20% 38% 21% 4	321
	21st to end	Day	22% 18% 31% 18% 8% 2	300
December	1st to 10th	Day	31% 19% 29% 18% 4	300
	11th to 20th	Day	26% 22% 30% 15% 6% 1	300
	21st to end	Day	28% 21% 34% 16% 1	330
January	1st to 10th	Night	23% 20% 30% 23% 4	1000
	11th to 20th	Night	28% 21% 29% 19% 4	1000
	21st to end	Night	22% 18% 36% 22% 2	882
February	1st to 10th	Night	27% 16% 32% 22% 3	800
	11th to 20th	Night	30% 20% 29% 20% 2	783
	21st to end	Night	30% 20% 31% 18% 2	660
March	1st to 10th	Night	24% 18% 29% 25% 5%	800
	11th to 20th	Night	21% 17% 35% 21% 6% 1	800
	21st to end	Night	21% 14% 32% 25% 7%	720
April	1st to 10th	Night	17% 14% 34% 27% 8% 1	600
	11th to 20th	Night	20% 12% 33% 26% 9% 1	593
	21st to end	Night	16% 12% 32% 28% 12% 1	600
May	1st to 10th	Night	14% 9% 33% 27% 15% 2	600
	11th to 20th	Night	12% 7% 28% 31% 19% 3	591
	21st to end	Night	10% 3 20% 37% 24% 5%	650
June	1st to 10th	Night	11% 3 18% 36% 28% 4	600
	11th to 20th	Night	5% 3 13% 38% 36% 6%	600
	21st to end	Night	4 2 16% 37% 35% 7%	600
July	1st to 10th	Night	8% 2 9% 31% 37% 12%	585
	11th to 20th	Night	6% 2 11% 31% 40% 10%	582
	21st to end	Night	7% 2 9% 33% 40% 9%	657
August	1st to 10th	Night	7% 2 8% 32% 44% 7%	597
	11th to 20th	Night	7% 2 10% 39% 35% 6%	594
	21st to end	Night	9% 1 10% 32% 39% 9%	660
September	1st to 10th	Night	11% 2 11% 34% 36% 5%	600
	11th to 20th	Night	14% 3 12% 27% 37% 7%	785
	21st to end	Night	13% 4 17% 30% 32% 4	800
October	1st to 10th	Night	11% 6% 18% 33% 27% 5%	800
	11th to 20th	Night	18% 8% 24% 31% 18% 1	800
	21st to end	Night	20% 10% 27% 28% 14% 1	880
November	1st to 10th	Night	17% 10% 22% 34% 15% 2	820
	11th to 20th	Night	15% 13% 33% 27% 11%	829
	21st to end	Night	21% 13% 27% 28% 11%	800
December	1st to 10th	Night	26% 15% 28% 25% 6%	800
	11th to 20th	Night	23% 12% 32% 25% 7% 1	800
	21st to end	Night	28% 17% 27% 24% 4	1055

Page generated at 2025-11-14 23:55:58. Version ac07

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