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 2024-11-02.

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	2 3 1 4 3 3 4 4 6% 8% 61%	100834
	Night	4 4 2 5% 4 4 4 4 6% 7% 57%	98356
Transparency	Day	20% 5% 9% 22% 27% 17%	100597
	Night	25% 5% 8% 21% 26% 16%	98182
Seeing	Day	6% 13% 26% 32% 21% 3	15021
	Night	5% 8% 27% 41% 18% 1	25160

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	2 6% 3 5% 2 3 4 3 6% 7% 59%	2858
	11th to 20th	Day	2 4 1 3 3 3 3 3 5% 7% 67%	2860
	21st to end	Day	3 6% 3 6% 4 4 5% 3 6% 6% 53%	3146
February	1st to 10th	Day	3 5% 2 6% 3 4 3 4 5% 7% 59%	1710
	11th to 20th	Day	2 5% 2 5% 4 3 4 4 6% 7% 59%	1844
	21st to end	Day	1 6% 1 5% 3 3 4 3 4 7% 62%	1570
March	1st to 10th	Day	2 3 1 4 3 2 3 4 5% 7% 66%	3369
	11th to 20th	Day	4 6% 2 5% 5% 4 5% 5% 7% 8% 51%	3490
	21st to end	Day	3 5% 2 6% 3 4 3 4 6% 6% 59%	3910
April	1st to 10th	Day	2 3 1 4 2 3 3 3 4 7% 67%	2280
	11th to 20th	Day	3 3 1 4 4 3 4 3 5% 6% 65%	2251
	21st to end	Day	2 3 1 3 3 2 4 2 5% 8% 67%	2280
May	1st to 10th	Day	1 1 1 3 2 3 3 3 4 6% 72%	3800
	11th to 20th	Day	3 2 1 4 4 4 4 4 7% 9% 58%	3931
	21st to end	Day	1 1 1 2 1 2 2 2 4 5% 79%	4763
June	1st to 10th	Day	2 1 1 2 2 3 3 4 7% 9% 64%	2660
	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	5% 2 1 3 4 3 4 3 6% 6% 63%	1900
	11th to 20th	Day	2 1 1 2 2 2 2 2 4 4 76%	1900
	21st to end	Day	3 2 1 3 2 2 2 2 3 5% 74%	2090
November	1st to 10th	Day	2 2 1 3 2 2 2 3 5% 7% 73%	1865
	11th to 20th	Day	2 2 1 2 2 2 3 3 6% 5% 71%	1710
	21st to end	Day	3 4 2 4 3 3 4 2 3 6% 65%	1710
December	1st to 10th	Day	3 5% 1 4 3 3 3 2 4 8% 65%	1530
	11th to 20th	Day	4 4 2 5% 4 4 5% 4 7% 8% 54%	1926
	21st to end	Day	3 5% 2 4 3 3 3 2 5% 8% 63%	2830
January	1st to 10th	Night	2 9% 3 5% 4 3 4 4 6% 7% 55%	4097
	11th to 20th	Night	4 4 1 3 3 3 4 2 4 5% 67%	4110
	21st to end	Night	5% 7% 3 6% 4 4 4 4 6% 8% 50%	4521
February	1st to 10th	Night	2 6% 2 5% 2 3 3 3 5% 7% 62%	2470
	11th to 20th	Night	4 6% 2 5% 4 3 3 3 5% 7% 58%	2221
	21st to end	Night	4 5% 2 4 3 2 2 2 5% 5% 65%	1884
March	1st to 10th	Night	3 5% 2 4 3 3 3 2 4 5% 66%	3500
	11th to 20th	Night	10% 7% 2 6% 4 4 4 4 4 5% 49%	3490
	21st to end	Night	3 6% 1 4 4 4 4 3 4 6% 61%	3738
April	1st to 10th	Night	4 3 1 4 3 3 4 2 4 7% 64%	1900
	11th to 20th	Night	4 4 2 4 4 3 4 3 4 6% 63%	1877
	21st to end	Night	4 4 2 4 2 3 3 3 5% 6% 65%	1900
May	1st to 10th	Night	4 3 2 4 3 3 4 3 5% 6% 63%	3170
	11th to 20th	Night	5% 5% 2 6% 3 5% 5% 4 7% 7% 52%	2971
	21st to end	Night	3 2 1 3 2 3 3 3 5% 5% 70%	2806
June	1st to 10th	Night	2 2 1 4 4 4 4 5% 8% 9% 58%	1520
	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	5% 4 1 5% 3 3 4 3 4 6% 63%	2280
	11th to 20th	Night	3 1 1 2 2 2 3 3 4 4 75%	2280
	21st to end	Night	3 3 1 3 2 2 3 2 3 5% 73%	2508
November	1st to 10th	Night	2 1 1 2 2 2 2 2 4 5% 78%	2244
	11th to 20th	Night	2 3 1 2 2 2 2 2 4 5% 74%	2453
	21st to end	Night	5% 6% 2 4 3 3 2 2 4 7% 63%	2470
December	1st to 10th	Night	4 4 1 4 3 2 3 3 5% 6% 65%	2645
	11th to 20th	Night	4 4 2 5% 4 3 4 3 7% 8% 56%	3271
	21st to end	Night	4 7% 2 5% 3 3 4 3 4 6% 59%	4864

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	23% 7% 6% 35% 25% 3	2859
	11th to 20th	Day	18% 4 14% 37% 23% 3	2860
	21st to end	Day	31% 5% 8% 25% 26% 5%	3146
February	1st to 10th	Day	24% 5% 9% 26% 26% 10%	1710
	11th to 20th	Day	25% 4 7% 26% 28% 11%	1854
	21st to end	Day	23% 3 4 19% 31% 19%	1570
March	1st to 10th	Day	17% 5% 3 19% 38% 18%	3369
	11th to 20th	Day	28% 7% 10% 23% 25% 8%	3490
	21st to end	Day	23% 6% 4 20% 35% 12%	3910
April	1st to 10th	Day	18% 4 4 17% 36% 20%	2280
	11th to 20th	Day	20% 4 4 17% 31% 24%	2254
	21st to end	Day	17% 5% 5% 20% 35% 18%	2280
May	1st to 10th	Day	12% 4 4 16% 36% 28%	3800
	11th to 20th	Day	20% 6% 7% 20% 30% 16%	3934
	21st to end	Day	9% 3 4 11% 23% 49%	4763
June	1st to 10th	Day	15% 5% 8% 20% 27% 27%	2660
	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	22% 5% 7% 20% 25% 22%	1900
	11th to 20th	Day	13% 3 3 14% 37% 28%	1900
	21st to end	Day	15% 4 6% 21% 37% 18%	2090
November	1st to 10th	Day	13% 2 5% 23% 40% 17%	1865
	11th to 20th	Day	14% 4 6% 25% 39% 11%	1710
	21st to end	Day	24% 3 4 23% 34% 13%	1710
December	1st to 10th	Day	22% 3 9% 33% 24% 10%	1530
	11th to 20th	Day	27% 5% 10% 25% 26% 5%	1924
	21st to end	Day	22% 3 8% 24% 30% 13%	2830
January	1st to 10th	Night	28% 7% 7% 29% 24% 5%	4097
	11th to 20th	Night	21% 4 8% 38% 24% 6%	4110
	21st to end	Night	31% 3 9% 26% 26% 5%	4521
February	1st to 10th	Night	22% 4 9% 24% 30% 11%	2470
	11th to 20th	Night	26% 6% 5% 23% 27% 13%	2221
	21st to end	Night	22% 3 3 18% 36% 19%	1884
March	1st to 10th	Night	21% 6% 2 16% 38% 17%	3500
	11th to 20th	Night	35% 4 9% 19% 24% 10%	3490
	21st to end	Night	20% 8% 4 23% 33% 11%	3738
April	1st to 10th	Night	22% 3 3 17% 34% 22%	1900
	11th to 20th	Night	24% 4 4 15% 28% 26%	1877
	21st to end	Night	20% 5% 6% 16% 34% 19%	1900
May	1st to 10th	Night	17% 7% 5% 13% 29% 29%	3170
	11th to 20th	Night	28% 5% 11% 20% 20% 16%	2972
	21st to end	Night	15% 5% 4 9% 18% 49%	2806
June	1st to 10th	Night	21% 6% 10% 17% 21% 26%	1520
	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	24% 4 8% 17% 23% 24%	2280
	11th to 20th	Night	13% 4 4 14% 31% 33%	2280
	21st to end	Night	17% 3 4 18% 38% 20%	2508
November	1st to 10th	Night	13% 2 4 22% 41% 19%	2244
	11th to 20th	Night	14% 3 4 23% 40% 16%	2453
	21st to end	Night	25% 2 4 19% 34% 16%	2470
December	1st to 10th	Night	20% 4 7% 31% 30% 8%	2645
	11th to 20th	Night	25% 5% 8% 26% 29% 7%	3272
	21st to end	Night	26% 4 6% 23% 31% 9%	4864

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 11% 39% 36% 10%	270
	11th to 20th	Day	10% 15% 29% 33% 12%	270
	21st to end	Day	3 12% 37% 32% 15% 1	297
February	1st to 10th	Day	5% 19% 34% 30% 10% 1	270
	11th to 20th	Day	8% 17% 43% 27% 5%	270
	21st to end	Day	8% 28% 38% 22% 4	225
March	1st to 10th	Day	7% 27% 32% 25% 8%	407
	11th to 20th	Day	13% 25% 30% 23% 10%	460
	21st to end	Day	14% 32% 31% 17% 6%	506
April	1st to 10th	Day	10% 25% 38% 17% 9% 1	460
	11th to 20th	Day	10% 29% 37% 19% 4 1	452
	21st to end	Day	7% 28% 37% 23% 5%	460
May	1st to 10th	Day	6% 24% 41% 23% 6% 1	463
	11th to 20th	Day	4 18% 34% 28% 14% 2	488
	21st to end	Day	4 16% 33% 33% 13% 1	698
June	1st to 10th	Day	2 7% 22% 43% 25% 2	680
	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% 19% 35% 22% 4	330
November	1st to 10th	Day	5% 15% 32% 34% 13% 1	273
	11th to 20th	Day	3 9% 25% 40% 20% 2	270
	21st to end	Day	8% 20% 26% 32% 13% 2	270
December	1st to 10th	Day	7% 12% 33% 35% 13%	270
	11th to 20th	Day	9% 11% 31% 37% 10% 1	270
	21st to end	Day	11% 17% 36% 29% 6%	297
January	1st to 10th	Night	4 6% 31% 43% 15% 1	760
	11th to 20th	Night	7% 8% 28% 41% 15% 1	760
	21st to end	Night	7% 8% 31% 39% 15% 1	836
February	1st to 10th	Night	6% 10% 35% 38% 11% 1	760
	11th to 20th	Night	8% 10% 37% 38% 7%	744
	21st to end	Night	8% 12% 40% 36% 4	628
March	1st to 10th	Night	6% 13% 35% 34% 11%	760
	11th to 20th	Night	8% 12% 31% 38% 12%	760
	21st to end	Night	7% 14% 32% 39% 8%	784
April	1st to 10th	Night	6% 17% 38% 33% 6%	570
	11th to 20th	Night	6% 20% 35% 32% 7%	563
	21st to end	Night	6% 15% 38% 35% 6% 1	570
May	1st to 10th	Night	4 14% 36% 38% 9%	570
	11th to 20th	Night	8% 11% 30% 37% 13% 1	561
	21st to end	Night	5% 9% 33% 42% 11%	617
June	1st to 10th	Night	2 5% 27% 49% 16% 1	570
	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	2 5% 26% 45% 21% 1	748
	11th to 20th	Night	3 6% 26% 44% 18% 2	933
	21st to end	Night	8% 11% 23% 36% 20% 2	950
December	1st to 10th	Night	5% 7% 30% 42% 14% 1	950
	11th to 20th	Night	7% 10% 30% 41% 12% 1	950
	21st to end	Night	9% 10% 31% 40% 9% 1	1036

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