Coronado State Monument
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Coronado State Monument clear sky chart from 2005-11-06 to 2025-06-10.

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 3 1 3 3 3 4 4 6% 8% 63%	123106
	Night	3 4 2 4 3 4 4 3 5% 7% 60%	124023
Transparency	Day	18% 5% 8% 22% 29% 18%	122870
	Night	22% 5% 7% 21% 28% 17%	123846
Seeing	Day	6% 13% 26% 32% 21% 3	15798
	Night	5% 8% 27% 41% 18% 1	26015

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 6% 3 5% 3 3 4 3 5% 6% 62%	4098
	11th to 20th	Day	2 3 1 3 3 3 3 3 5% 6% 68%	4100
	21st to end	Day	2 5% 2 6% 4 3 4 3 5% 6% 59%	4510
February	1st to 10th	Day	3 5% 2 6% 3 4 3 4 5% 7% 59%	1800
	11th to 20th	Day	2 5% 2 5% 4 3 4 3 6% 7% 58%	1944
	21st to end	Day	1 5% 1 5% 3 3 4 3 4 7% 64%	1650
March	1st to 10th	Day	1 2 1 4 3 3 3 4 5% 7% 66%	4837
	11th to 20th	Day	2 5% 2 5% 4 4 5% 4 6% 8% 55%	5000
	21st to end	Day	2 4 2 5% 3 4 3 4 6% 7% 61%	5610
April	1st to 10th	Day	2 3 1 4 3 3 3 3 4 7% 67%	2400
	11th to 20th	Day	3 4 1 4 4 3 4 3 5% 6% 65%	2371
	21st to end	Day	2 3 1 3 3 2 3 2 5% 7% 68%	2400
May	1st to 10th	Day	3 2 1 3 3 3 4 4 6% 8% 64%	5440
	11th to 20th	Day	2 2 1 3 3 3 4 4 6% 7% 65%	5636
	21st to end	Day	1 1 1 2 1 2 2 3 5% 7% 76%	6835
June	1st to 10th	Day	2 1 1 2 3 3 3 4 7% 9% 64%	2788
	11th to 20th	Day	1 2 1 2 2 2 3 3 5% 7% 73%	2660
	21st to end	Day	3 3 1 4 3 4 4 4 7% 8% 59%	2660
July	1st to 10th	Day	2 2 1 3 3 4 4 4 6% 9% 61%	4224
	11th to 20th	Day	1 2 1 3 3 3 5% 5% 11% 13% 53%	4110
	21st to end	Day	3 2 1 4 4 5% 7% 7% 11% 13% 42%	4454
August	1st to 10th	Day	2 2 1 3 4 4 5% 5% 10% 13% 50%	4031
	11th to 20th	Day	2 2 1 3 3 3 4 4 6% 11% 62%	3726
	21st to end	Day	2 2 1 4 4 5% 6% 6% 9% 13% 47%	4180
September	1st to 10th	Day	4 4 1 4 4 3 5% 5% 7% 8% 57%	2280
	11th to 20th	Day	4 2 1 4 3 3 5% 4 6% 7% 61%	2280
	21st to end	Day	2 2 3 2 3 3 3 5% 6% 70%	2046
October	1st to 10th	Day	3 1 1 2 2 2 3 2 4 5% 76%	3170
	11th to 20th	Day	2 1 1 2 2 3 3 3 6% 6% 70%	3150
	21st to end	Day	2 1 1 2 1 2 2 2 3 6% 78%	3438
November	1st to 10th	Day	2 2 1 3 2 2 2 3 5% 6% 72%	1954
	11th to 20th	Day	2 2 1 2 2 2 3 3 6% 6% 72%	1800
	21st to end	Day	3 4 2 4 3 3 4 2 3 6% 66%	1800
December	1st to 10th	Day	2 3 1 3 2 2 2 1 3 6% 77%	2630
	11th to 20th	Day	3 2 1 4 4 4 4 3 5% 8% 63%	3026
	21st to end	Day	2 3 1 3 3 3 3 3 4 7% 68%	4068
January	1st to 10th	Night	2 8% 3 5% 4 3 4 4 6% 7% 56%	5867
	11th to 20th	Night	3 3 1 3 3 3 4 2 4 6% 69%	5880
	21st to end	Night	4 5% 2 6% 3 3 3 3 5% 7% 57%	6468
February	1st to 10th	Night	2 5% 2 5% 3 3 3 3 5% 7% 63%	2600
	11th to 20th	Night	4 6% 2 5% 4 3 3 3 5% 7% 57%	2341
	21st to end	Night	4 5% 2 4 3 2 2 2 5% 5% 66%	1980
March	1st to 10th	Night	3 5% 2 5% 3 3 3 2 4 5% 64%	5036
	11th to 20th	Night	7% 7% 2 6% 4 4 3 3 4 5% 54%	5000
	21st to end	Night	3 4 1 4 3 3 3 3 4 7% 64%	5357
April	1st to 10th	Night	4 3 2 4 4 3 4 2 4 6% 64%	2000
	11th to 20th	Night	4 4 2 4 4 3 4 3 4 6% 62%	1977
	21st to end	Night	4 3 2 4 2 3 3 3 5% 6% 66%	2000
May	1st to 10th	Night	5% 4 2 5% 4 4 5% 4 6% 7% 54%	4540
	11th to 20th	Night	4 3 1 4 3 4 4 3 6% 6% 61%	4263
	21st to end	Night	3 2 1 3 2 4 4 3 5% 7% 66%	4044
June	1st to 10th	Night	2 2 1 4 4 4 4 5% 8% 9% 57%	1596
	11th to 20th	Night	2 2 1 3 3 3 3 3 4 7% 69%	1520
	21st to end	Night	4 4 1 6% 4 4 5% 6% 8% 8% 50%	1520
July	1st to 10th	Night	2 2 2 5% 5% 5% 6% 5% 8% 7% 55%	2725
	11th to 20th	Night	2 3 2 6% 5% 7% 6% 5% 10% 13% 39%	2860
	21st to end	Night	5% 5% 2 7% 6% 6% 6% 7% 10% 12% 34%	3109
August	1st to 10th	Night	2 4 3 8% 8% 7% 8% 8% 10% 12% 31%	2905
	11th to 20th	Night	3 3 1 6% 5% 6% 6% 6% 9% 12% 44%	3113
	21st to end	Night	3 3 2 7% 7% 7% 8% 7% 11% 13% 32%	3487
September	1st to 10th	Night	4 3 1 5% 5% 4 6% 5% 8% 9% 50%	1900
	11th to 20th	Night	4 4 1 4 4 4 4 4 5% 9% 58%	1900
	21st to end	Night	3 2 1 3 3 4 3 3 4 6% 67%	2127
October	1st to 10th	Night	3 2 1 3 2 2 2 2 3 5% 75%	3800
	11th to 20th	Night	3 2 1 4 4 5% 4 4 5% 7% 63%	3778
	21st to end	Night	2 2 1 2 1 2 2 2 3 5% 79%	4120
November	1st to 10th	Night	2 1 1 2 2 2 2 2 4 5% 76%	2340
	11th to 20th	Night	2 3 1 2 2 2 2 2 4 5% 75%	2583
	21st to end	Night	5% 6% 2 4 3 3 2 2 4 7% 63%	2600
December	1st to 10th	Night	2 2 1 2 2 1 2 2 4 7% 75%	4555
	11th to 20th	Night	2 3 1 3 3 2 3 3 6% 8% 66%	5181
	21st to end	Night	3 5% 2 4 3 3 3 3 4 6% 65%	6951

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% 5% 35% 29% 3	4099
	11th to 20th	Day	17% 4 11% 26% 26% 16%	4100
	21st to end	Day	26% 3 6% 19% 34% 12%	4510
February	1st to 10th	Day	23% 5% 8% 26% 27% 11%	1800
	11th to 20th	Day	25% 4 7% 25% 29% 11%	1954
	21st to end	Day	23% 3 4 18% 30% 22%	1650
March	1st to 10th	Day	17% 4 4 14% 39% 23%	4837
	11th to 20th	Day	23% 5% 8% 22% 28% 14%	5000
	21st to end	Day	21% 5% 5% 24% 35% 11%	5610
April	1st to 10th	Day	18% 4 4 17% 36% 20%	2400
	11th to 20th	Day	21% 4 4 17% 31% 24%	2374
	21st to end	Day	16% 5% 5% 20% 35% 20%	2400
May	1st to 10th	Day	16% 5% 9% 22% 29% 20%	5440
	11th to 20th	Day	16% 4 6% 15% 31% 28%	5639
	21st to end	Day	9% 3 7% 14% 22% 45%	6836
June	1st to 10th	Day	15% 4 8% 19% 27% 26%	2788
	11th to 20th	Day	13% 3 4 11% 24% 45%	2660
	21st to end	Day	22% 4 7% 20% 22% 25%	2660
July	1st to 10th	Day	18% 7% 9% 13% 22% 30%	4160
	11th to 20th	Day	17% 7% 16% 31% 22% 8%	4041
	21st to end	Day	24% 9% 17% 32% 15% 2	4314
August	1st to 10th	Day	20% 8% 20% 26% 18% 8%	4017
	11th to 20th	Day	16% 6% 11% 24% 27% 16%	3762
	21st to end	Day	25% 9% 18% 25% 19% 5%	4179
September	1st to 10th	Day	23% 6% 9% 21% 26% 15%	2280
	11th to 20th	Day	20% 6% 10% 17% 26% 21%	2280
	21st to end	Day	16% 3 5% 22% 33% 21%	2046
October	1st to 10th	Day	14% 3 4 13% 32% 35%	3170
	11th to 20th	Day	13% 5% 5% 17% 35% 24%	3150
	21st to end	Day	10% 3 4 21% 39% 23%	3438
November	1st to 10th	Day	14% 2 5% 22% 40% 16%	1954
	11th to 20th	Day	14% 4 6% 25% 40% 12%	1800
	21st to end	Day	23% 3 4 22% 34% 14%	1800
December	1st to 10th	Day	13% 2 6% 32% 35% 12%	2630
	11th to 20th	Day	21% 3 7% 35% 29% 5%	3024
	21st to end	Day	18% 3 9% 29% 32% 9%	4068
January	1st to 10th	Night	26% 5% 6% 28% 27% 7%	5867
	11th to 20th	Night	19% 3 6% 28% 29% 14%	5880
	21st to end	Night	26% 3 7% 18% 34% 12%	6468
February	1st to 10th	Night	22% 3 9% 23% 31% 13%	2600
	11th to 20th	Night	26% 5% 5% 24% 27% 13%	2341
	21st to end	Night	21% 3 3 17% 36% 20%	1980
March	1st to 10th	Night	22% 4 3 12% 37% 22%	5036
	11th to 20th	Night	30% 3 7% 16% 29% 14%	5000
	21st to end	Night	18% 6% 4 23% 36% 12%	5357
April	1st to 10th	Night	23% 3 3 17% 33% 21%	2000
	11th to 20th	Night	24% 4 4 15% 27% 27%	1977
	21st to end	Night	19% 5% 6% 16% 33% 20%	2000
May	1st to 10th	Night	24% 8% 8% 17% 22% 21%	4537
	11th to 20th	Night	21% 4 8% 14% 26% 26%	4264
	21st to end	Night	16% 5% 6% 11% 15% 46%	4044
June	1st to 10th	Night	21% 6% 10% 16% 21% 25%	1596
	11th to 20th	Night	16% 3 5% 11% 22% 43%	1520
	21st to end	Night	27% 7% 11% 14% 15% 26%	1520
July	1st to 10th	Night	25% 6% 11% 15% 13% 30%	2680
	11th to 20th	Night	31% 8% 17% 28% 11% 5%	2806
	21st to end	Night	36% 10% 17% 27% 9% 1	3011
August	1st to 10th	Night	39% 10% 16% 16% 11% 6%	2896
	11th to 20th	Night	29% 7% 16% 16% 17% 15%	3143
	21st to end	Night	36% 10% 19% 19% 13% 5%	3487
September	1st to 10th	Night	29% 5% 13% 18% 20% 14%	1900
	11th to 20th	Night	23% 5% 11% 17% 21% 23%	1900
	21st to end	Night	19% 3 7% 16% 28% 26%	2127
October	1st to 10th	Night	15% 2 5% 12% 31% 34%	3800
	11th to 20th	Night	18% 8% 6% 14% 26% 28%	3778
	21st to end	Night	11% 2 3 22% 41% 22%	4120
November	1st to 10th	Night	14% 2 4 21% 41% 18%	2340
	11th to 20th	Night	14% 3 4 22% 40% 17%	2583
	21st to end	Night	25% 2 4 19% 34% 17%	2600
December	1st to 10th	Night	12% 3 5% 36% 30% 14%	4555
	11th to 20th	Night	17% 4 5% 32% 35% 8%	5182
	21st to end	Night	22% 3 6% 30% 33% 7%	6951

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	4 10% 38% 37% 10%	300
	11th to 20th	Day	10% 15% 28% 35% 12% 1	300
	21st to end	Day	3 12% 38% 32% 14% 1	330
February	1st to 10th	Day	5% 17% 33% 34% 10% 1	300
	11th to 20th	Day	9% 16% 42% 29% 5%	300
	21st to end	Day	8% 25% 38% 26% 4	249
March	1st to 10th	Day	7% 26% 32% 25% 9%	444
	11th to 20th	Day	12% 24% 30% 24% 10%	500
	21st to end	Day	13% 30% 31% 18% 8%	550
April	1st to 10th	Day	11% 23% 37% 18% 10% 1	500
	11th to 20th	Day	10% 28% 36% 21% 5% 1	492
	21st to end	Day	6% 27% 38% 22% 6% 1	500
May	1st to 10th	Day	6% 23% 40% 24% 8% 1	503
	11th to 20th	Day	5% 18% 34% 28% 13% 2	528
	21st to end	Day	3 16% 32% 34% 14% 1	751
June	1st to 10th	Day	2 6% 22% 43% 25% 2	726
	11th to 20th	Day	2 9% 23% 39% 26% 2	680
	21st to end	Day	5% 5% 21% 36% 29% 4	680
July	1st to 10th	Day	2 3 16% 39% 35% 5%	561
	11th to 20th	Day	2 2 7% 31% 41% 17%	484
	21st to end	Day	4 1 6% 32% 46% 12%	531
August	1st to 10th	Day	4 1 9% 34% 43% 9%	487
	11th to 20th	Day	4 2 13% 36% 37% 8%	477
	21st to end	Day	3 3 15% 37% 36% 7%	539
September	1st to 10th	Day	4 3 16% 36% 34% 7%	490
	11th to 20th	Day	2 4 25% 39% 24% 6%	490
	21st to end	Day	3 8% 22% 36% 25% 6%	346
October	1st to 10th	Day	4 11% 23% 27% 28% 7%	300
	11th to 20th	Day	7% 9% 24% 33% 24% 5%	300
	21st to end	Day	9% 11% 18% 35% 22% 4	330
November	1st to 10th	Day	6% 14% 32% 33% 15% 1	300
	11th to 20th	Day	3 9% 27% 39% 20% 2	300
	21st to end	Day	7% 19% 26% 33% 14% 2	300
December	1st to 10th	Day	6% 11% 31% 36% 16%	300
	11th to 20th	Day	8% 10% 29% 39% 13% 1	300
	21st to end	Day	10% 16% 36% 29% 8% 1	330
January	1st to 10th	Night	4 6% 32% 43% 14% 1	800
	11th to 20th	Night	6% 8% 29% 42% 15% 1	800
	21st to end	Night	7% 7% 33% 39% 14% 1	880
February	1st to 10th	Night	5% 9% 35% 39% 11% 1	800
	11th to 20th	Night	8% 10% 38% 37% 7%	784
	21st to end	Night	7% 11% 41% 36% 4	660
March	1st to 10th	Night	6% 14% 35% 35% 10%	800
	11th to 20th	Night	8% 12% 31% 39% 11%	800
	21st to end	Night	7% 14% 32% 40% 8%	825
April	1st to 10th	Night	6% 17% 37% 34% 6%	600
	11th to 20th	Night	6% 19% 35% 33% 7%	593
	21st to end	Night	6% 14% 38% 35% 6% 1	600
May	1st to 10th	Night	4 13% 35% 38% 10%	600
	11th to 20th	Night	7% 11% 31% 37% 13% 1	591
	21st to end	Night	5% 9% 33% 43% 11%	650
June	1st to 10th	Night	3 5% 27% 49% 15% 1	599
	11th to 20th	Night	2 6% 27% 49% 15% 1	570
	21st to end	Night	3 5% 22% 45% 24% 1	570
July	1st to 10th	Night	3 2 14% 48% 31% 2	555
	11th to 20th	Night	3 1 12% 39% 42% 4	552
	21st to end	Night	2 2 7% 37% 45% 6%	624
August	1st to 10th	Night	4 1 8% 33% 48% 7%	567
	11th to 20th	Night	6% 2 12% 45% 33% 4	564
	21st to end	Night	3 1 9% 43% 39% 4	627
September	1st to 10th	Night	4 2 15% 46% 31% 2	570
	11th to 20th	Night	5% 2 16% 50% 26% 2	570
	21st to end	Night	5% 2 20% 46% 26% 1	655
October	1st to 10th	Night	6% 4 24% 46% 19% 2	760
	11th to 20th	Night	4 5% 23% 47% 19% 2	760
	21st to end	Night	5% 6% 24% 41% 21% 3	836
November	1st to 10th	Night	3 5% 26% 44% 20% 1	780
	11th to 20th	Night	3 6% 28% 44% 17% 2	983
	21st to end	Night	8% 11% 24% 37% 19% 2	1000
December	1st to 10th	Night	5% 7% 30% 43% 14% 1	1000
	11th to 20th	Night	6% 9% 31% 42% 12% 1	1000
	21st to end	Night	8% 10% 32% 40% 9% 1	1090

Page generated at 2025-06-07 08:28:15. Version ac07

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