San Clemente Island (North)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Clemente Island (North) clear sky chart from 2005-11-06 to 2026-05-02.

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	4 7% 2 5% 4 4 4 4 7% 13% 47%	140776
	Night	5% 8% 2 5% 3 3 3 3 5% 8% 56%	139336
Transparency	Day	16% 37% 5% 10% 16% 15%	135868
	Night	16% 36% 4 11% 17% 16%	135218
Seeing	Day	7% 7% 16% 32% 28% 9%	17868
	Night	9% 6% 13% 27% 32% 12%	27858

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	5% 4 2 4 3 3 3 2 4 6% 63%	4881
	11th to 20th	Day	5% 3 1 3 3 3 4 3 5% 8% 63%	5616
	21st to end	Day	8% 6% 2 6% 4 4 5% 4 6% 9% 47%	6500
February	1st to 10th	Day	8% 5% 3 5% 5% 3 3 3 6% 9% 49%	2100
	11th to 20th	Day	8% 4 2 5% 5% 3 5% 4 6% 10% 49%	2050
	21st to end	Day	7% 5% 2 5% 4 4 4 3 6% 9% 52%	1730
March	1st to 10th	Day	6% 5% 2 4 3 3 4 5% 8% 11% 50%	4618
	11th to 20th	Day	6% 6% 2 5% 3 3 3 3 6% 9% 54%	4846
	21st to end	Day	7% 7% 2 5% 4 4 4 4 6% 10% 49%	6101
April	1st to 10th	Day	6% 6% 1 4 3 3 4 3 6% 10% 53%	2520
	11th to 20th	Day	5% 5% 2 5% 3 3 3 4 6% 10% 55%	2489
	21st to end	Day	5% 7% 2 4 3 3 3 4 6% 12% 51%	2520
May	1st to 10th	Day	5% 10% 2 5% 3 3 3 2 5% 8% 55%	5453
	11th to 20th	Day	4 15% 3 8% 5% 5% 5% 4 6% 10% 36%	5788
	21st to end	Day	4 15% 3 8% 4 4 4 3 6% 11% 38%	6423
June	1st to 10th	Day	7% 15% 4 9% 6% 5% 4 4 7% 10% 29%	2600
	11th to 20th	Day	5% 8% 2 6% 4 3 4 4 8% 13% 40%	2750
	21st to end	Day	3 9% 3 6% 5% 4 4 4 9% 17% 37%	2800
July	1st to 10th	Day	2 6% 2 4 3 3 4 4 8% 19% 47%	6319
	11th to 20th	Day	2 7% 2 6% 5% 6% 6% 6% 12% 20% 28%	5916
	21st to end	Day	3 5% 2 4 4 4 5% 5% 9% 21% 39%	5923
August	1st to 10th	Day	1 3 1 3 2 2 3 3 8% 24% 50%	5346
	11th to 20th	Day	2 5% 1 3 2 2 3 3 6% 18% 55%	5364
	21st to end	Day	1 2 1 3 2 3 4 4 9% 19% 52%	5984
September	1st to 10th	Day	3 6% 2 5% 3 4 4 5% 8% 12% 50%	2400
	11th to 20th	Day	4 7% 2 5% 3 4 5% 4 8% 15% 45%	2270
	21st to end	Day	2 5% 2 5% 4 4 5% 4 7% 14% 49%	2200
October	1st to 10th	Day	2 3 1 4 3 3 4 4 8% 18% 51%	3600
	11th to 20th	Day	5% 10% 2 6% 3 4 3 3 6% 11% 48%	3337
	21st to end	Day	3 3 2 4 3 3 4 3 6% 10% 59%	3558
November	1st to 10th	Day	2 4 2 4 4 4 5% 4 8% 11% 51%	1879
	11th to 20th	Day	5% 6% 2 6% 4 4 4 4 6% 9% 52%	1890
	21st to end	Day	4 3 2 6% 5% 5% 5% 4 8% 10% 49%	1890
December	1st to 10th	Day	4 4 2 4 3 4 5% 5% 8% 11% 50%	3040
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 5% 6% 9% 45%	3499
	21st to end	Day	8% 11% 3 9% 5% 6% 5% 4 6% 10% 31%	4576
January	1st to 10th	Night	6% 4 2 4 4 4 3 3 4 6% 60%	8018
	11th to 20th	Night	4 5% 1 3 2 2 3 2 4 6% 68%	7351
	21st to end	Night	7% 7% 2 6% 4 4 4 3 5% 7% 53%	7747
February	1st to 10th	Night	7% 5% 2 6% 4 3 4 3 5% 7% 54%	2520
	11th to 20th	Night	8% 7% 2 4 4 3 4 4 5% 7% 52%	2458
	21st to end	Night	8% 6% 2 5% 4 3 3 3 5% 8% 52%	2076
March	1st to 10th	Night	4 5% 2 4 2 3 4 4 7% 9% 55%	5496
	11th to 20th	Night	5% 7% 2 5% 4 4 3 3 5% 6% 57%	5367
	21st to end	Night	5% 8% 2 4 3 3 3 3 5% 8% 57%	5116
April	1st to 10th	Night	6% 7% 2 4 3 3 3 3 5% 7% 57%	2100
	11th to 20th	Night	5% 8% 2 5% 3 2 2 2 4 7% 60%	2079
	21st to end	Night	6% 11% 2 5% 3 3 2 3 5% 6% 55%	2100
May	1st to 10th	Night	4 10% 1 5% 2 2 2 2 3 5% 63%	4570
	11th to 20th	Night	6% 24% 3 4 2 2 2 2 4 6% 45%	4125
	21st to end	Night	4 16% 3 4 2 2 2 2 3 6% 55%	4474
June	1st to 10th	Night	8% 20% 3 9% 4 4 3 3 4 7% 34%	1800
	11th to 20th	Night	7% 11% 3 6% 3 3 3 2 4 12% 45%	1642
	21st to end	Night	4 13% 3 8% 4 3 4 4 6% 12% 40%	1600
July	1st to 10th	Night	3 9% 3 5% 3 2 2 2 4 7% 60%	3640
	11th to 20th	Night	2 13% 4 5% 4 4 3 3 6% 13% 43%	4039
	21st to end	Night	4 9% 2 5% 3 3 3 3 5% 12% 52%	4974
August	1st to 10th	Night	1 4 1 3 2 2 2 2 5% 12% 66%	4486
	11th to 20th	Night	2 8% 1 3 2 2 1 2 5% 11% 63%	4506
	21st to end	Night	2 3 1 4 3 3 4 3 6% 10% 61%	5015
September	1st to 10th	Night	4 7% 2 5% 3 4 3 3 6% 9% 54%	2000
	11th to 20th	Night	5% 6% 1 5% 3 4 3 3 5% 11% 53%	2130
	21st to end	Night	3 6% 2 6% 4 4 4 3 5% 8% 58%	2200
October	1st to 10th	Night	2 3 2 4 2 2 2 2 4 9% 67%	3600
	11th to 20th	Night	6% 14% 2 4 2 2 2 2 4 7% 56%	3816
	21st to end	Night	3 3 1 3 2 3 3 3 4 7% 70%	4253
November	1st to 10th	Night	3 5% 2 3 3 3 3 3 5% 8% 63%	2639
	11th to 20th	Night	4 4 2 4 3 2 4 3 5% 7% 61%	2730
	21st to end	Night	4 7% 2 5% 4 4 4 3 6% 8% 54%	2730
December	1st to 10th	Night	4 6% 2 5% 3 3 3 3 4 6% 62%	4370
	11th to 20th	Night	8% 5% 2 5% 3 4 5% 4 6% 7% 52%	4941
	21st to end	Night	7% 11% 2 5% 4 4 4 4 7% 9% 43%	6628

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	17% 21% 6% 16% 22% 17%	4882
	11th to 20th	Day	15% 22% 7% 9% 17% 30%	5616
	21st to end	Day	24% 24% 5% 12% 18% 17%	6500
February	1st to 10th	Day	14% 59% 3 8% 8% 9%	2100
	11th to 20th	Day	14% 58% 2 9% 9% 8%	2060
	21st to end	Day	11% 59% 3 10% 10% 7%	1730
March	1st to 10th	Day	18% 30% 9% 17% 18% 8%	4618
	11th to 20th	Day	16% 30% 8% 19% 19% 7%	4846
	21st to end	Day	21% 30% 9% 24% 12% 3	6101
April	1st to 10th	Day	9% 59% 4 10% 13% 5%	2520
	11th to 20th	Day	9% 59% 3 7% 14% 7%	2492
	21st to end	Day	10% 60% 5% 12% 10% 4	2520
May	1st to 10th	Day	18% 31% 6% 10% 26% 9%	5453
	11th to 20th	Day	29% 30% 7% 10% 17% 6%	5791
	21st to end	Day	27% 30% 6% 12% 18% 7%	6424
June	1st to 10th	Day	20% 62% 4 3 7% 3	2600
	11th to 20th	Day	12% 61% 2 4 10% 10%	2750
	21st to end	Day	13% 60% 2 4 9% 12%	2800
July	1st to 10th	Day	12% 26% 3 7% 11% 41%	6251
	11th to 20th	Day	20% 28% 4 7% 21% 18%	5842
	21st to end	Day	11% 27% 3 13% 23% 24%	5753
August	1st to 10th	Day	8% 35% 3 11% 29% 13%	3890
	11th to 20th	Day	5% 35% 2 8% 17% 33%	3880
	21st to end	Day	7% 36% 2 5% 18% 32%	4311
September	1st to 10th	Day	9% 56% 3 4 15% 13%	2400
	11th to 20th	Day	11% 57% 3 4 17% 9%	2270
	21st to end	Day	9% 58% 3 6% 16% 9%	2200
October	1st to 10th	Day	12% 38% 4 6% 13% 27%	3600
	11th to 20th	Day	19% 38% 4 5% 21% 13%	3337
	21st to end	Day	11% 36% 2 7% 24% 19%	3558
November	1st to 10th	Day	8% 53% 3 6% 13% 16%	1879
	11th to 20th	Day	13% 55% 4 6% 10% 11%	1890
	21st to end	Day	13% 55% 5% 9% 8% 10%	1890
December	1st to 10th	Day	14% 37% 5% 14% 14% 16%	3040
	11th to 20th	Day	23% 33% 6% 12% 17% 9%	3498
	21st to end	Day	38% 29% 6% 14% 9% 4	4576
January	1st to 10th	Night	20% 23% 5% 14% 23% 15%	8018
	11th to 20th	Night	15% 21% 4 12% 14% 33%	7351
	21st to end	Night	25% 24% 3 12% 19% 17%	7747
February	1st to 10th	Night	13% 59% 4 5% 10% 8%	2520
	11th to 20th	Night	14% 58% 3 7% 9% 10%	2459
	21st to end	Night	12% 59% 2 8% 11% 8%	2076
March	1st to 10th	Night	14% 31% 7% 16% 21% 11%	5496
	11th to 20th	Night	18% 30% 6% 22% 15% 9%	5367
	21st to end	Night	19% 29% 10% 20% 19% 3	5116
April	1st to 10th	Night	12% 59% 2 9% 12% 6%	2100
	11th to 20th	Night	11% 59% 2 7% 15% 7%	2079
	21st to end	Night	11% 59% 4 11% 10% 4	2100
May	1st to 10th	Night	18% 30% 4 13% 25% 10%	4567
	11th to 20th	Night	31% 29% 3 9% 23% 6%	4126
	21st to end	Night	21% 28% 5% 17% 19% 9%	4474
June	1st to 10th	Night	23% 61% 2 4 8% 3	1800
	11th to 20th	Night	13% 61% 2 3 11% 10%	1642
	21st to end	Night	15% 60% 2 4 6% 13%	1600
July	1st to 10th	Night	13% 26% 2 7% 10% 42%	3600
	11th to 20th	Night	20% 27% 3 6% 21% 23%	3991
	21st to end	Night	15% 25% 2 10% 22% 26%	4832
August	1st to 10th	Night	6% 35% 3 11% 32% 13%	3256
	11th to 20th	Night	7% 34% 2 8% 17% 32%	3256
	21st to end	Night	6% 35% 2 3 19% 36%	3608
September	1st to 10th	Night	11% 56% 3 3 12% 15%	2000
	11th to 20th	Night	12% 57% 3 4 14% 11%	2130
	21st to end	Night	9% 57% 2 5% 15% 11%	2200
October	1st to 10th	Night	9% 36% 2 5% 13% 35%	3600
	11th to 20th	Night	20% 36% 2 6% 21% 15%	3816
	21st to end	Night	8% 36% 2 6% 23% 25%	4253
November	1st to 10th	Night	7% 52% 2 7% 12% 20%	2639
	11th to 20th	Night	11% 55% 3 7% 11% 12%	2730
	21st to end	Night	13% 55% 4 10% 8% 10%	2730
December	1st to 10th	Night	14% 35% 3 12% 21% 14%	4370
	11th to 20th	Night	20% 32% 6% 10% 19% 13%	4941
	21st to end	Night	29% 28% 8% 23% 9% 4	6628

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	13% 9% 23% 33% 17% 6%	275
	11th to 20th	Day	11% 6% 18% 33% 27% 6%	480
	21st to end	Day	9% 11% 21% 30% 23% 7%	594
February	1st to 10th	Day	13% 10% 19% 25% 25% 8%	540
	11th to 20th	Day	13% 13% 23% 29% 19% 3	535
	21st to end	Day	10% 13% 21% 33% 20% 3	446
March	1st to 10th	Day	11% 14% 31% 28% 13% 4	540
	11th to 20th	Day	10% 9% 22% 31% 19% 8%	540
	21st to end	Day	10% 16% 24% 29% 18% 4	594
April	1st to 10th	Day	9% 11% 21% 32% 20% 6%	540
	11th to 20th	Day	8% 12% 25% 32% 19% 5%	532
	21st to end	Day	5% 10% 26% 34% 18% 7%	540
May	1st to 10th	Day	8% 9% 19% 32% 24% 8%	508
	11th to 20th	Day	11% 8% 23% 33% 19% 5%	528
	21st to end	Day	12% 11% 16% 34% 23% 4	573
June	1st to 10th	Day	11% 7% 15% 30% 28% 9%	530
	11th to 20th	Day	6% 2 15% 33% 32% 12%	530
	21st to end	Day	6% 3 9% 36% 35% 11%	530
July	1st to 10th	Day	6% 2 6% 34% 38% 15%	526
	11th to 20th	Day	4 2 3 26% 47% 19%	524
	21st to end	Day	4 1 6% 29% 44% 16%	575
August	1st to 10th	Day	3 1 8% 32% 41% 16%	527
	11th to 20th	Day	3 1 5% 35% 39% 17%	517
	21st to end	Day	3 1 6% 39% 42% 10%	583
September	1st to 10th	Day	4 1 10% 36% 40% 9%	530
	11th to 20th	Day	6% 3 17% 40% 28% 7%	530
	21st to end	Day	3 6% 15% 33% 35% 9%	530
October	1st to 10th	Day	3 4 15% 38% 30% 10%	530
	11th to 20th	Day	8% 4 17% 35% 28% 9%	530
	21st to end	Day	4 5% 17% 31% 30% 12%	583
November	1st to 10th	Day	4 8% 14% 24% 34% 16%	355
	11th to 20th	Day	6% 6% 15% 33% 28% 11%	330
	21st to end	Day	4 12% 15% 28% 30% 12%	330
December	1st to 10th	Day	9% 3 17% 31% 35% 6%	330
	11th to 20th	Day	6% 9% 15% 31% 28% 11%	330
	21st to end	Day	13% 16% 22% 25% 18% 5%	353
January	1st to 10th	Night	12% 6% 13% 31% 30% 8%	840
	11th to 20th	Night	8% 5% 11% 32% 37% 8%	840
	21st to end	Night	11% 8% 14% 33% 28% 6%	924
February	1st to 10th	Night	10% 7% 16% 29% 29% 9%	840
	11th to 20th	Night	11% 9% 17% 31% 25% 7%	824
	21st to end	Night	12% 9% 19% 31% 25% 4	692
March	1st to 10th	Night	10% 10% 22% 31% 23% 5%	840
	11th to 20th	Night	9% 7% 17% 32% 25% 9%	840
	21st to end	Night	9% 10% 21% 27% 27% 5%	924
April	1st to 10th	Night	10% 8% 23% 30% 23% 6%	840
	11th to 20th	Night	11% 10% 20% 26% 26% 7%	831
	21st to end	Night	10% 9% 19% 29% 25% 7%	840
May	1st to 10th	Night	13% 8% 16% 28% 27% 8%	804
	11th to 20th	Night	17% 8% 17% 27% 22% 8%	616
	21st to end	Night	15% 9% 18% 25% 26% 7%	650
June	1st to 10th	Night	19% 6% 11% 30% 25% 10%	600
	11th to 20th	Night	15% 4 7% 26% 34% 15%	442
	21st to end	Night	10% 3 7% 26% 42% 13%	400
July	1st to 10th	Night	12% 2 6% 14% 42% 25%	390
	11th to 20th	Night	10% 2 1 15% 41% 31%	553
	21st to end	Night	8% 2 3 19% 41% 26%	876
August	1st to 10th	Night	5% 1 6% 23% 41% 24%	796
	11th to 20th	Night	9% 1 3 16% 41% 30%	792
	21st to end	Night	6% 1 3 22% 44% 24%	880
September	1st to 10th	Night	7% 2 4 22% 44% 21%	800
	11th to 20th	Night	8% 3 11% 33% 32% 14%	800
	21st to end	Night	4 5% 9% 25% 41% 16%	800
October	1st to 10th	Night	4 4 14% 29% 38% 12%	800
	11th to 20th	Night	9% 4 11% 28% 34% 14%	800
	21st to end	Night	6% 5% 10% 26% 35% 18%	880
November	1st to 10th	Night	5% 6% 11% 27% 35% 15%	820
	11th to 20th	Night	5% 4 11% 27% 39% 13%	840
	21st to end	Night	6% 6% 14% 30% 37% 8%	840
December	1st to 10th	Night	10% 5% 11% 32% 35% 8%	840
	11th to 20th	Night	11% 8% 12% 33% 30% 6%	840
	21st to end	Night	10% 12% 15% 28% 27% 7%	924

Page generated at 2026-04-28 23:21:45. Version ac07

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