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 2025-01-07.

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 6% 2 5% 4 4 4 4 7% 13% 47%	109232
	Night	5% 8% 2 5% 3 3 3 3 5% 9% 55%	108616
Transparency	Day	14% 45% 5% 9% 14% 13%	108997
	Night	14% 44% 4 10% 15% 13%	108441
Seeing	Day	7% 7% 17% 32% 28% 9%	16040
	Night	9% 6% 13% 27% 32% 12%	26037

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% 5% 2 3 3 3 3 3 5% 8% 61%	2662
	11th to 20th	Day	9% 6% 2 5% 5% 5% 5% 4 7% 8% 46%	2996
	21st to end	Day	11% 7% 2 5% 3 3 4 4 5% 8% 49%	3498
February	1st to 10th	Day	8% 5% 3 5% 5% 3 3 3 6% 9% 50%	1900
	11th to 20th	Day	7% 4 2 5% 5% 4 5% 4 6% 10% 49%	1850
	21st to end	Day	8% 5% 2 6% 4 4 4 3 6% 9% 49%	1570
March	1st to 10th	Day	5% 4 2 4 4 4 5% 6% 9% 12% 45%	3138
	11th to 20th	Day	3 6% 2 4 3 3 3 3 6% 10% 56%	3310
	21st to end	Day	5% 6% 2 5% 4 4 5% 4 7% 11% 48%	4165
April	1st to 10th	Day	7% 6% 1 4 3 3 4 4 6% 10% 52%	2280
	11th to 20th	Day	5% 6% 2 5% 3 3 3 4 5% 10% 55%	2249
	21st to end	Day	5% 6% 2 4 3 3 3 4 6% 12% 53%	2280
May	1st to 10th	Day	3 6% 2 4 3 2 3 2 5% 7% 63%	3800
	11th to 20th	Day	4 18% 4 10% 5% 5% 5% 4 7% 10% 29%	4031
	21st to end	Day	4 14% 3 7% 4 4 4 3 7% 12% 36%	4477
June	1st to 10th	Day	8% 14% 4 9% 6% 5% 4 4 7% 10% 31%	2470
	11th to 20th	Day	5% 9% 2 6% 4 3 4 4 8% 13% 40%	2612
	21st to end	Day	3 9% 3 6% 5% 4 4 4 9% 17% 36%	2660
July	1st to 10th	Day	3 7% 2 4 3 3 3 4 8% 16% 48%	4420
	11th to 20th	Day	2 5% 2 5% 5% 5% 6% 5% 11% 21% 33%	4133
	21st to end	Day	1 3 1 3 3 2 3 4 8% 22% 48%	4119
August	1st to 10th	Day	1 4 1 4 2 3 3 4 9% 24% 45%	3783
	11th to 20th	Day	2 3 1 2 2 2 3 3 6% 20% 56%	3724
	21st to end	Day	1 2 1 4 3 3 4 5% 10% 20% 47%	4180
September	1st to 10th	Day	3 6% 2 5% 3 4 4 4 8% 12% 50%	2280
	11th to 20th	Day	4 6% 2 5% 3 4 5% 4 8% 15% 45%	2157
	21st to end	Day	2 5% 2 5% 4 4 4 4 7% 14% 51%	2090
October	1st to 10th	Day	2 3 1 4 3 3 3 4 8% 18% 50%	3490
	11th to 20th	Day	5% 10% 2 6% 3 4 3 3 6% 11% 47%	3235
	21st to end	Day	3 3 2 4 3 3 4 3 6% 10% 59%	3448
November	1st to 10th	Day	2 4 2 4 4 4 5% 4 8% 11% 52%	1788
	11th to 20th	Day	4 6% 2 5% 4 4 4 4 6% 9% 53%	1800
	21st to end	Day	4 4 2 5% 5% 4 4 4 8% 10% 49%	1800
December	1st to 10th	Day	4 4 2 4 3 4 5% 5% 9% 11% 49%	2950
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 5% 6% 9% 45%	3409
	21st to end	Day	8% 11% 3 8% 5% 6% 5% 4 6% 10% 31%	4478
January	1st to 10th	Night	5% 4 1 4 3 3 3 3 4 6% 63%	4414
	11th to 20th	Night	7% 8% 2 6% 4 4 4 3 5% 8% 50%	3954
	21st to end	Night	10% 7% 2 4 3 3 4 3 5% 7% 52%	4180
February	1st to 10th	Night	7% 5% 2 6% 4 3 4 3 5% 7% 55%	2280
	11th to 20th	Night	7% 7% 2 4 4 3 4 3 5% 7% 54%	2218
	21st to end	Night	9% 6% 2 6% 4 4 4 4 5% 8% 49%	1884
March	1st to 10th	Night	4 5% 2 4 2 4 4 4 8% 11% 52%	3736
	11th to 20th	Night	4 6% 2 5% 3 4 3 3 5% 8% 58%	3663
	21st to end	Night	3 4 1 4 3 3 4 3 6% 9% 58%	3488
April	1st to 10th	Night	7% 7% 2 4 3 3 3 3 5% 7% 56%	1900
	11th to 20th	Night	6% 9% 2 5% 2 2 2 2 4 6% 60%	1879
	21st to end	Night	6% 10% 2 5% 3 2 2 3 5% 6% 56%	1900
May	1st to 10th	Night	4 7% 1 4 2 2 2 2 3 5% 68%	3180
	11th to 20th	Night	6% 30% 3 5% 2 2 2 2 4 6% 38%	2871
	21st to end	Night	4 16% 3 5% 3 2 2 2 3 6% 53%	3110
June	1st to 10th	Night	9% 19% 3 8% 4 4 3 3 4 7% 35%	1710
	11th to 20th	Night	7% 12% 3 6% 3 4 3 3 4 12% 44%	1560
	21st to end	Night	4 14% 3 8% 4 3 4 4 6% 11% 40%	1520
July	1st to 10th	Night	4 8% 3 5% 3 2 2 2 4 9% 58%	2540
	11th to 20th	Night	3 7% 3 4 4 4 3 3 5% 13% 50%	2813
	21st to end	Night	2 5% 1 4 2 2 2 2 5% 13% 60%	3457
August	1st to 10th	Night	1 5% 2 4 2 3 3 3 7% 15% 56%	3166
	11th to 20th	Night	2 5% 1 3 2 2 2 2 6% 13% 63%	3126
	21st to end	Night	2 4 2 4 3 3 4 3 7% 11% 58%	3498
September	1st to 10th	Night	4 8% 2 5% 3 4 4 3 6% 9% 53%	1900
	11th to 20th	Night	5% 6% 1 5% 3 3 3 3 5% 11% 53%	2023
	21st to end	Night	2 5% 2 6% 4 4 4 3 5% 8% 58%	2090
October	1st to 10th	Night	2 3 3 4 2 2 2 2 4 9% 66%	3490
	11th to 20th	Night	6% 14% 2 4 2 2 3 2 4 7% 55%	3699
	21st to end	Night	3 3 1 3 2 3 3 3 4 7% 70%	4121
November	1st to 10th	Night	3 5% 2 3 3 3 3 3 5% 8% 63%	2510
	11th to 20th	Night	3 4 2 4 3 2 4 3 5% 7% 63%	2600
	21st to end	Night	4 7% 2 5% 4 4 4 4 6% 8% 53%	2600
December	1st to 10th	Night	4 6% 2 5% 3 3 3 3 5% 6% 61%	4240
	11th to 20th	Night	8% 5% 2 5% 3 4 5% 4 6% 8% 51%	4811
	21st to end	Night	7% 11% 2 5% 4 4 4 4 7% 9% 43%	6485

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	11% 35% 5% 23% 20% 7%	2662
	11th to 20th	Day	25% 40% 11% 13% 10% 2	2996
	21st to end	Day	21% 40% 5% 12% 18% 5%	3498
February	1st to 10th	Day	12% 65% 3 6% 7% 8%	1900
	11th to 20th	Day	12% 63% 2 5% 10% 9%	1860
	21st to end	Day	12% 65% 3 9% 7% 4	1570
March	1st to 10th	Day	15% 42% 9% 20% 10% 4	3138
	11th to 20th	Day	9% 41% 10% 20% 12% 8%	3310
	21st to end	Day	16% 42% 10% 21% 8% 3	4165
April	1st to 10th	Day	8% 66% 4 9% 9% 4	2280
	11th to 20th	Day	8% 65% 3 5% 12% 8%	2252
	21st to end	Day	8% 65% 4 9% 9% 4	2280
May	1st to 10th	Day	11% 40% 3 9% 30% 7%	3800
	11th to 20th	Day	30% 43% 8% 5% 11% 4	4034
	21st to end	Day	26% 41% 5% 9% 17% 2	4477
June	1st to 10th	Day	18% 65% 4 3 7% 3	2470
	11th to 20th	Day	12% 64% 2 4 10% 8%	2612
	21st to end	Day	13% 63% 2 5% 8% 10%	2660
July	1st to 10th	Day	11% 35% 3 3 8% 41%	4351
	11th to 20th	Day	13% 37% 4 5% 15% 26%	4059
	21st to end	Day	5% 35% 2 13% 17% 28%	3990
August	1st to 10th	Day	8% 36% 3 11% 28% 13%	3770
	11th to 20th	Day	4 36% 2 8% 16% 34%	3760
	21st to end	Day	7% 37% 2 5% 18% 32%	4179
September	1st to 10th	Day	9% 59% 3 4 13% 12%	2280
	11th to 20th	Day	9% 60% 3 4 16% 8%	2157
	21st to end	Day	8% 60% 2 6% 16% 8%	2090
October	1st to 10th	Day	12% 39% 4 6% 12% 27%	3490
	11th to 20th	Day	20% 39% 4 5% 20% 12%	3235
	21st to end	Day	11% 37% 2 7% 24% 19%	3448
November	1st to 10th	Day	7% 56% 3 6% 12% 16%	1788
	11th to 20th	Day	11% 58% 3 6% 10% 12%	1800
	21st to end	Day	12% 57% 5% 8% 8% 9%	1800
December	1st to 10th	Day	14% 38% 5% 13% 13% 16%	2950
	11th to 20th	Day	23% 33% 6% 12% 16% 9%	3408
	21st to end	Day	38% 29% 7% 14% 9% 3	4478
January	1st to 10th	Night	13% 37% 5% 15% 22% 9%	4414
	11th to 20th	Night	24% 39% 7% 19% 9% 3	3954
	21st to end	Night	23% 40% 4 12% 16% 6%	4180
February	1st to 10th	Night	11% 65% 4 4 9% 7%	2280
	11th to 20th	Night	11% 64% 2 4 8% 10%	2219
	21st to end	Night	12% 65% 2 7% 8% 5%	1884
March	1st to 10th	Night	12% 43% 7% 17% 16% 5%	3736
	11th to 20th	Night	12% 42% 6% 21% 11% 8%	3663
	21st to end	Night	11% 42% 9% 21% 14% 3	3488
April	1st to 10th	Night	11% 65% 2 7% 9% 6%	1900
	11th to 20th	Night	9% 65% 2 5% 12% 7%	1879
	21st to end	Night	9% 64% 3 9% 10% 5%	1900
May	1st to 10th	Night	11% 39% 3 9% 28% 10%	3180
	11th to 20th	Night	35% 40% 4 5% 14% 3	2872
	21st to end	Night	21% 39% 6% 13% 19% 2	3110
June	1st to 10th	Night	21% 64% 2 3 7% 3	1710
	11th to 20th	Night	13% 64% 2 3 10% 8%	1560
	21st to end	Night	16% 63% 2 4 6% 10%	1520
July	1st to 10th	Night	11% 35% 3 2 8% 40%	2500
	11th to 20th	Night	13% 36% 2 4 14% 31%	2765
	21st to end	Night	6% 34% 2 9% 19% 29%	3348
August	1st to 10th	Night	6% 36% 3 11% 31% 12%	3156
	11th to 20th	Night	6% 36% 2 8% 16% 33%	3156
	21st to end	Night	6% 36% 2 3 18% 36%	3498
September	1st to 10th	Night	12% 59% 3 3 10% 13%	1900
	11th to 20th	Night	10% 59% 3 4 13% 11%	2023
	21st to end	Night	8% 60% 2 4 15% 11%	2090
October	1st to 10th	Night	9% 37% 2 5% 12% 35%	3490
	11th to 20th	Night	20% 37% 1 6% 20% 15%	3699
	21st to end	Night	8% 36% 2 6% 23% 25%	4121
November	1st to 10th	Night	6% 55% 2 6% 11% 20%	2510
	11th to 20th	Night	10% 57% 3 6% 11% 13%	2600
	21st to end	Night	13% 57% 5% 9% 8% 9%	2600
December	1st to 10th	Night	14% 36% 3 12% 20% 14%	4240
	11th to 20th	Night	20% 33% 6% 10% 19% 13%	4811
	21st to end	Night	28% 29% 8% 23% 9% 4	6485

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	14% 8% 22% 31% 18% 7%	241
	11th to 20th	Day	12% 7% 20% 32% 24% 5%	410
	21st to end	Day	9% 13% 21% 29% 22% 5%	506
February	1st to 10th	Day	15% 11% 20% 22% 25% 8%	460
	11th to 20th	Day	12% 13% 23% 29% 20% 4	455
	21st to end	Day	12% 15% 24% 31% 16% 2	382
March	1st to 10th	Day	11% 12% 32% 27% 13% 4	460
	11th to 20th	Day	10% 9% 24% 34% 18% 4	460
	21st to end	Day	10% 18% 26% 29% 15% 2	506
April	1st to 10th	Day	10% 12% 23% 31% 19% 6%	460
	11th to 20th	Day	8% 13% 29% 30% 16% 4	452
	21st to end	Day	6% 10% 25% 32% 19% 8%	460
May	1st to 10th	Day	7% 10% 20% 31% 23% 8%	463
	11th to 20th	Day	11% 8% 24% 33% 19% 4	488
	21st to end	Day	12% 11% 17% 33% 23% 3	529
June	1st to 10th	Day	10% 7% 16% 29% 30% 10%	490
	11th to 20th	Day	6% 2 16% 33% 32% 12%	490
	21st to end	Day	6% 3 10% 37% 34% 11%	490
July	1st to 10th	Day	6% 1 6% 34% 37% 15%	486
	11th to 20th	Day	4 1 2 28% 46% 18%	484
	21st to end	Day	3 1 5% 28% 46% 17%	531
August	1st to 10th	Day	3 1 8% 34% 39% 15%	487
	11th to 20th	Day	3 1 5% 36% 39% 16%	477
	21st to end	Day	3 1 6% 39% 42% 10%	539
September	1st to 10th	Day	4 1 10% 36% 40% 9%	490
	11th to 20th	Day	6% 2 17% 41% 26% 8%	490
	21st to end	Day	2 6% 14% 32% 36% 10%	490
October	1st to 10th	Day	3 4 15% 37% 30% 10%	490
	11th to 20th	Day	8% 4 17% 35% 27% 9%	490
	21st to end	Day	5% 5% 17% 31% 29% 12%	539
November	1st to 10th	Day	4 9% 15% 24% 33% 15%	324
	11th to 20th	Day	5% 6% 15% 32% 29% 12%	300
	21st to end	Day	4 13% 16% 28% 28% 10%	300
December	1st to 10th	Day	10% 3 19% 30% 34% 5%	300
	11th to 20th	Day	6% 9% 17% 30% 26% 11%	300
	21st to end	Day	12% 17% 20% 26% 19% 6%	321
January	1st to 10th	Night	12% 6% 12% 30% 32% 9%	784
	11th to 20th	Night	8% 5% 11% 32% 35% 9%	760
	21st to end	Night	12% 7% 15% 32% 28% 6%	836
February	1st to 10th	Night	11% 7% 16% 27% 29% 10%	760
	11th to 20th	Night	11% 8% 16% 31% 26% 7%	744
	21st to end	Night	13% 9% 20% 30% 23% 4	628
March	1st to 10th	Night	10% 9% 22% 30% 24% 5%	760
	11th to 20th	Night	10% 7% 18% 33% 24% 8%	760
	21st to end	Night	8% 11% 22% 29% 25% 5%	836
April	1st to 10th	Night	10% 8% 23% 30% 22% 6%	760
	11th to 20th	Night	11% 11% 21% 25% 25% 6%	751
	21st to end	Night	11% 10% 19% 27% 26% 8%	760
May	1st to 10th	Night	12% 8% 16% 28% 27% 9%	760
	11th to 20th	Night	17% 8% 17% 27% 23% 8%	585
	21st to end	Night	14% 9% 19% 25% 27% 6%	617
June	1st to 10th	Night	19% 5% 11% 30% 25% 10%	570
	11th to 20th	Night	15% 3 7% 25% 34% 15%	420
	21st to end	Night	10% 3 7% 24% 43% 12%	380
July	1st to 10th	Night	12% 1 6% 14% 40% 26%	370
	11th to 20th	Night	10% 2 1 15% 42% 30%	524
	21st to end	Night	7% 2 3 18% 42% 27%	832
August	1st to 10th	Night	5% 1 6% 24% 39% 25%	756
	11th to 20th	Night	8% 1 3 17% 42% 30%	752
	21st to end	Night	6% 1 3 23% 43% 23%	836
September	1st to 10th	Night	7% 2 4 22% 44% 22%	760
	11th to 20th	Night	8% 2 11% 33% 33% 14%	760
	21st to end	Night	4 5% 9% 24% 41% 16%	760
October	1st to 10th	Night	4 4 14% 29% 38% 12%	760
	11th to 20th	Night	9% 4 11% 27% 34% 14%	760
	21st to end	Night	7% 5% 10% 26% 34% 17%	836
November	1st to 10th	Night	5% 6% 11% 28% 34% 15%	780
	11th to 20th	Night	5% 5% 11% 27% 40% 14%	800
	21st to end	Night	6% 6% 14% 30% 36% 8%	800
December	1st to 10th	Night	10% 5% 12% 31% 35% 7%	800
	11th to 20th	Night	12% 8% 13% 34% 29% 5%	800
	21st to end	Night	9% 12% 14% 28% 29% 8%	880

Page generated at 2025-01-04 00:24:01. Version ac07

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