Cypress Point Club
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cypress Point Club clear sky chart from 2005-11-06 to 2026-02-01.

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	6% 10% 3 7% 4 4 4 3 6% 10% 45%	135779
	Night	8% 12% 3 8% 4 3 3 3 4 6% 46%	133720
Transparency	Day	33% 5% 10% 18% 22% 13%	130736
	Night	37% 6% 8% 16% 20% 13%	129747
Seeing	Day	10% 6% 18% 32% 28% 7%	17107
	Night	12% 4 13% 28% 32% 11%	26624

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	10% 6% 2 5% 4 4 3 3 5% 8% 52%	4095
	11th to 20th	Day	9% 5% 2 6% 4 3 4 3 4 5% 54%	4190
	21st to end	Day	13% 9% 3 7% 4 4 4 3 5% 7% 41%	4609
February	1st to 10th	Day	13% 7% 2 5% 4 4 4 4 5% 6% 46%	1801
	11th to 20th	Day	11% 7% 2 7% 3 4 4 4 6% 8% 43%	1881
	21st to end	Day	10% 7% 3 6% 5% 4 4 3 5% 7% 47%	1650
March	1st to 10th	Day	11% 9% 3 7% 6% 5% 6% 5% 7% 9% 33%	4868
	11th to 20th	Day	9% 6% 3 7% 4 4 4 3 5% 8% 49%	5000
	21st to end	Day	9% 8% 2 6% 5% 5% 5% 5% 7% 10% 37%	5571
April	1st to 10th	Day	9% 7% 3 5% 4 4 4 4 6% 8% 46%	2400
	11th to 20th	Day	7% 9% 3 6% 4 3 4 4 5% 8% 48%	2369
	21st to end	Day	6% 9% 2 6% 3 3 3 4 7% 10% 47%	2400
May	1st to 10th	Day	5% 5% 1 4 2 2 3 2 4 8% 63%	5474
	11th to 20th	Day	4 7% 2 5% 3 3 3 3 6% 11% 53%	5857
	21st to end	Day	5% 15% 4 9% 3 3 4 3 5% 8% 41%	6902
June	1st to 10th	Day	5% 12% 3 6% 4 4 5% 3 6% 10% 42%	2800
	11th to 20th	Day	4 7% 2 5% 3 3 4 3 6% 13% 50%	2800
	21st to end	Day	3 10% 4 7% 3 3 5% 3 5% 10% 46%	2800
July	1st to 10th	Day	1 9% 3 6% 3 3 4 4 7% 14% 47%	6189
	11th to 20th	Day	1 12% 5% 10% 4 4 5% 4 8% 15% 32%	5880
	21st to end	Day	1 30% 6% 10% 4 4 3 4 6% 10% 23%	6402
August	1st to 10th	Day	2 16% 6% 13% 5% 4 4 3 7% 11% 29%	5777
	11th to 20th	Day	3 12% 4 7% 4 3 4 3 7% 12% 41%	5415
	21st to end	Day	1 10% 4 8% 3 4 4 4 7% 14% 42%	5984
September	1st to 10th	Day	3 6% 2 5% 4 3 4 3 6% 11% 53%	2400
	11th to 20th	Day	4 9% 4 6% 3 4 4 4 7% 11% 44%	2400
	21st to end	Day	3 6% 2 4 3 3 4 4 6% 8% 59%	2130
October	1st to 10th	Day	2 4 1 4 3 3 3 2 5% 9% 64%	3280
	11th to 20th	Day	3 12% 3 6% 3 3 3 3 4 7% 53%	3261
	21st to end	Day	4 5% 2 4 3 3 4 3 5% 8% 58%	3558
November	1st to 10th	Day	6% 4 2 4 4 4 4 3 6% 7% 55%	2054
	11th to 20th	Day	7% 7% 2 6% 3 4 4 3 5% 6% 51%	1890
	21st to end	Day	9% 5% 1 4 4 3 4 3 5% 6% 55%	1792
December	1st to 10th	Day	5% 5% 2 5% 4 4 4 3 6% 9% 54%	2700
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 6% 8% 40%	3108
	21st to end	Day	18% 9% 3 7% 5% 5% 4 3 5% 7% 34%	4092
January	1st to 10th	Night	9% 6% 2 5% 3 3 3 3 5% 8% 52%	6070
	11th to 20th	Night	9% 7% 3 7% 4 3 3 3 5% 7% 49%	6010
	21st to end	Night	13% 10% 3 8% 4 3 3 3 5% 6% 42%	6611
February	1st to 10th	Night	14% 8% 2 5% 4 3 4 3 4 6% 47%	2600
	11th to 20th	Night	12% 9% 3 7% 4 4 4 3 5% 7% 42%	2406
	21st to end	Night	12% 8% 2 6% 4 3 4 3 6% 7% 46%	1980
March	1st to 10th	Night	16% 14% 4 8% 5% 5% 4 3 4 5% 32%	5011
	11th to 20th	Night	10% 9% 3 7% 4 3 4 3 4 6% 47%	5000
	21st to end	Night	13% 11% 3 8% 5% 4 4 3 4 7% 38%	5402
April	1st to 10th	Night	9% 10% 4 6% 4 3 3 4 5% 7% 46%	2000
	11th to 20th	Night	10% 9% 3 6% 3 3 3 3 5% 6% 49%	1979
	21st to end	Night	6% 9% 2 5% 3 3 3 3 6% 9% 49%	2000
May	1st to 10th	Night	5% 8% 3 6% 2 2 2 2 3 5% 62%	4521
	11th to 20th	Night	4 16% 6% 9% 3 3 2 2 3 7% 45%	4039
	21st to end	Night	4 15% 3 9% 2 2 2 2 3 4 53%	3972
June	1st to 10th	Night	6% 13% 3 7% 3 4 4 3 4 8% 46%	1600
	11th to 20th	Night	3 10% 2 7% 4 2 2 3 4 8% 56%	1600
	21st to end	Night	3 12% 3 8% 4 3 2 2 4 7% 53%	1600
July	1st to 10th	Night	11% 4 10% 5% 3 3 2 3 5% 54%	3770
	11th to 20th	Night	1 25% 6% 12% 5% 3 2 2 3 6% 36%	4100
	21st to end	Night	3 40% 4 14% 3 2 2 1 3 5% 23%	4472
August	1st to 10th	Night	2 23% 8% 18% 6% 2 2 2 2 4 31%	4035
	11th to 20th	Night	2 18% 5% 11% 3 2 2 1 2 4 49%	4451
	21st to end	Night	2 17% 5% 10% 4 2 2 2 3 6% 47%	5015
September	1st to 10th	Night	3 9% 3 6% 4 3 3 2 5% 9% 54%	2000
	11th to 20th	Night	4 13% 4 8% 3 2 2 2 4 7% 49%	2000
	21st to end	Night	3 8% 2 4 3 3 3 3 3 8% 60%	2266
October	1st to 10th	Night	3 5% 2 4 2 3 3 2 4 5% 68%	3920
	11th to 20th	Night	5% 13% 3 9% 3 3 3 2 3 5% 51%	3897
	21st to end	Night	5% 8% 2 5% 3 3 3 3 4 6% 58%	4253
November	1st to 10th	Night	7% 7% 2 6% 4 3 3 4 4 8% 53%	2463
	11th to 20th	Night	8% 7% 3 5% 4 4 4 3 5% 8% 50%	2730
	21st to end	Night	7% 6% 2 5% 3 3 4 3 5% 6% 57%	2825
December	1st to 10th	Night	6% 4 2 4 3 3 4 3 5% 7% 59%	4700
	11th to 20th	Night	14% 9% 3 7% 4 4 5% 4 7% 8% 35%	5316
	21st to end	Night	17% 9% 3 8% 5% 5% 5% 4 5% 6% 32%	7106

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	32% 7% 16% 24% 16% 5%	4095
	11th to 20th	Day	33% 5% 9% 13% 20% 20%	4190
	21st to end	Day	43% 6% 7% 11% 20% 14%	4609
February	1st to 10th	Day	38% 7% 9% 17% 18% 11%	1801
	11th to 20th	Day	39% 7% 12% 17% 18% 7%	1890
	21st to end	Day	38% 8% 9% 22% 17% 6%	1650
March	1st to 10th	Day	46% 10% 10% 14% 17% 2	4868
	11th to 20th	Day	35% 5% 13% 27% 12% 8%	5000
	21st to end	Day	39% 11% 16% 23% 10% 1	5571
April	1st to 10th	Day	36% 8% 14% 23% 16% 4	2400
	11th to 20th	Day	35% 7% 12% 23% 17% 6%	2372
	21st to end	Day	30% 8% 16% 25% 17% 4	2400
May	1st to 10th	Day	21% 4 8% 26% 31% 10%	5474
	11th to 20th	Day	21% 2 16% 28% 25% 7%	5860
	21st to end	Day	34% 5% 11% 21% 25% 4	6904
June	1st to 10th	Day	33% 7% 13% 20% 21% 6%	2800
	11th to 20th	Day	22% 4 14% 23% 25% 12%	2800
	21st to end	Day	24% 3 10% 18% 26% 20%	2800
July	1st to 10th	Day	23% 2 4 10% 22% 40%	6123
	11th to 20th	Day	33% 3 5% 8% 23% 28%	5811
	21st to end	Day	53% 1 5% 14% 14% 11%	6217
August	1st to 10th	Day	47% 2 5% 12% 23% 12%	4206
	11th to 20th	Day	29% 2 7% 13% 34% 17%	3919
	21st to end	Day	26% 1 7% 17% 31% 18%	4311
September	1st to 10th	Day	19% 2 7% 16% 26% 30%	2400
	11th to 20th	Day	26% 3 12% 23% 24% 12%	2400
	21st to end	Day	18% 3 11% 21% 31% 16%	2130
October	1st to 10th	Day	18% 3 6% 12% 27% 35%	3280
	11th to 20th	Day	31% 2 8% 18% 26% 15%	3261
	21st to end	Day	24% 3 7% 21% 27% 17%	3558
November	1st to 10th	Day	26% 7% 12% 22% 22% 11%	2054
	11th to 20th	Day	32% 6% 13% 17% 22% 10%	1890
	21st to end	Day	30% 5% 10% 17% 26% 13%	1792
December	1st to 10th	Day	28% 4 6% 20% 32% 10%	2700
	11th to 20th	Day	45% 5% 11% 17% 15% 8%	3108
	21st to end	Day	50% 7% 12% 18% 10% 4	4092
January	1st to 10th	Night	32% 8% 16% 23% 18% 4	6070
	11th to 20th	Night	35% 7% 10% 13% 21% 14%	6010
	21st to end	Night	44% 5% 6% 10% 20% 15%	6611
February	1st to 10th	Night	39% 6% 9% 15% 18% 13%	2600
	11th to 20th	Night	42% 7% 10% 15% 19% 7%	2408
	21st to end	Night	37% 9% 10% 24% 14% 7%	1980
March	1st to 10th	Night	54% 8% 7% 14% 14% 2	5011
	11th to 20th	Night	37% 6% 13% 20% 17% 8%	5000
	21st to end	Night	45% 10% 13% 19% 10% 3	5402
April	1st to 10th	Night	37% 10% 13% 21% 15% 5%	2000
	11th to 20th	Night	36% 7% 12% 23% 15% 7%	1979
	21st to end	Night	32% 9% 13% 24% 17% 6%	2000
May	1st to 10th	Night	25% 11% 6% 22% 26% 10%	4518
	11th to 20th	Night	28% 3 19% 21% 21% 9%	4040
	21st to end	Night	34% 8% 7% 18% 27% 6%	3972
June	1st to 10th	Night	36% 7% 10% 19% 20% 9%	1600
	11th to 20th	Night	27% 4 11% 14% 26% 19%	1600
	21st to end	Night	25% 3 5% 17% 25% 25%	1600
July	1st to 10th	Night	27% 7% 2 8% 17% 38%	3728
	11th to 20th	Night	47% 2 3 7% 12% 29%	4046
	21st to end	Night	63% 2 3 9% 11% 12%	4345
August	1st to 10th	Night	61% 3 3 7% 12% 15%	2929
	11th to 20th	Night	31% 1 3 8% 34% 23%	3214
	21st to end	Night	32% 1 5% 10% 30% 22%	3608
September	1st to 10th	Night	23% 1 6% 13% 23% 33%	2000
	11th to 20th	Night	31% 3 7% 19% 25% 15%	2000
	21st to end	Night	20% 3 8% 19% 31% 19%	2266
October	1st to 10th	Night	19% 2 6% 13% 24% 37%	3920
	11th to 20th	Night	36% 3 5% 19% 22% 16%	3897
	21st to end	Night	27% 3 6% 21% 26% 17%	4253
November	1st to 10th	Night	31% 5% 9% 20% 22% 14%	2463
	11th to 20th	Night	34% 5% 12% 19% 21% 10%	2730
	21st to end	Night	29% 6% 8% 20% 21% 16%	2825
December	1st to 10th	Night	27% 4 6% 23% 29% 12%	4700
	11th to 20th	Night	48% 5% 10% 14% 16% 7%	5316
	21st to end	Night	52% 9% 12% 15% 8% 4	7106

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	22% 11% 20% 26% 17% 4	388
	11th to 20th	Day	12% 7% 19% 33% 26% 3	430
	21st to end	Day	13% 7% 21% 30% 24% 5%	473
February	1st to 10th	Day	15% 12% 18% 26% 21% 7%	401
	11th to 20th	Day	14% 12% 23% 31% 19% 1	460
	21st to end	Day	9% 11% 25% 36% 18% 2	414
March	1st to 10th	Day	17% 12% 23% 33% 13% 2	500
	11th to 20th	Day	16% 10% 22% 30% 18% 4	500
	21st to end	Day	12% 12% 27% 31% 15% 2	550
April	1st to 10th	Day	15% 8% 24% 31% 19% 3	500
	11th to 20th	Day	10% 9% 27% 30% 20% 3	492
	21st to end	Day	8% 8% 28% 28% 21% 6%	500
May	1st to 10th	Day	9% 8% 24% 30% 24% 5%	503
	11th to 20th	Day	13% 5% 23% 31% 22% 6%	528
	21st to end	Day	15% 5% 19% 31% 23% 6%	573
June	1st to 10th	Day	6% 5% 17% 40% 24% 8%	530
	11th to 20th	Day	4 4 25% 35% 29% 3	530
	21st to end	Day	5% 2 13% 38% 35% 6%	530
July	1st to 10th	Day	6% 2 14% 35% 38% 6%	526
	11th to 20th	Day	5% 6% 30% 48% 10%	524
	21st to end	Day	9% 1 6% 35% 40% 10%	575
August	1st to 10th	Day	8% 2 11% 37% 35% 6%	527
	11th to 20th	Day	6% 1 9% 36% 38% 9%	517
	21st to end	Day	3 2 11% 33% 43% 9%	583
September	1st to 10th	Day	7% 1 12% 30% 39% 11%	530
	11th to 20th	Day	9% 3 14% 33% 33% 8%	530
	21st to end	Day	5% 4 14% 28% 40% 9%	530
October	1st to 10th	Day	4 3 15% 31% 37% 8%	530
	11th to 20th	Day	7% 6% 13% 28% 32% 14%	530
	21st to end	Day	8% 3 16% 31% 32% 10%	583
November	1st to 10th	Day	6% 5% 18% 29% 33% 11%	530
	11th to 20th	Day	12% 7% 16% 29% 27% 10%	330
	21st to end	Day	9% 5% 22% 29% 29% 6%	278
December	1st to 10th	Day	12% 4 25% 25% 26% 8%	220
	11th to 20th	Day	12% 7% 22% 25% 25% 9%	220
	21st to end	Day	19% 12% 23% 26% 15% 5%	242
January	1st to 10th	Night	18% 7% 14% 33% 23% 6%	840
	11th to 20th	Night	11% 5% 14% 32% 30% 8%	840
	21st to end	Night	17% 5% 11% 33% 30% 5%	924
February	1st to 10th	Night	17% 6% 18% 27% 25% 8%	800
	11th to 20th	Night	16% 8% 16% 31% 24% 6%	784
	21st to end	Night	14% 8% 18% 32% 25% 3	660
March	1st to 10th	Night	19% 8% 17% 29% 23% 5%	800
	11th to 20th	Night	16% 7% 15% 30% 26% 6%	800
	21st to end	Night	14% 8% 19% 29% 25% 4	880
April	1st to 10th	Night	13% 6% 18% 29% 29% 6%	800
	11th to 20th	Night	13% 9% 16% 28% 27% 7%	791
	21st to end	Night	10% 6% 16% 31% 28% 10%	800
May	1st to 10th	Night	10% 5% 15% 32% 30% 9%	787
	11th to 20th	Night	14% 4 13% 23% 34% 12%	583
	21st to end	Night	15% 3 15% 29% 26% 12%	433
June	1st to 10th	Night	11% 2 12% 30% 35% 11%	400
	11th to 20th	Night	6% 2 17% 29% 39% 7%	400
	21st to end	Night	6% 2 8% 23% 44% 17%	400
July	1st to 10th	Night	5% 2 10% 24% 43% 17%	440
	11th to 20th	Night	7% 1 7% 14% 42% 29%	582
	21st to end	Night	15% 8% 19% 38% 19%	657
August	1st to 10th	Night	13% 1 11% 21% 39% 15%	597
	11th to 20th	Night	8% 1 8% 24% 41% 18%	762
	21st to end	Night	8% 1 8% 19% 44% 20%	880
September	1st to 10th	Night	7% 1 5% 19% 49% 21%	800
	11th to 20th	Night	11% 1 8% 24% 42% 14%	800
	21st to end	Night	6% 1 7% 22% 42% 22%	800
October	1st to 10th	Night	9% 2 6% 30% 38% 16%	800
	11th to 20th	Night	7% 3 11% 25% 37% 17%	800
	21st to end	Night	8% 3 9% 28% 34% 19%	880
November	1st to 10th	Night	10% 3 10% 29% 36% 12%	820
	11th to 20th	Night	12% 3 12% 30% 36% 8%	840
	21st to end	Night	9% 3 13% 38% 30% 7%	840
December	1st to 10th	Night	13% 5% 14% 38% 25% 6%	840
	11th to 20th	Night	18% 5% 16% 32% 24% 5%	840
	21st to end	Night	19% 8% 19% 31% 19% 3	924

Page generated at 2026-01-28 22:21:41. Version ac07

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