Casitas de Gila Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Casitas de Gila Observatory clear sky chart from 2005-11-06 to 2024-06-30.

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 4 1 4 3 3 4 3 5% 7% 62%	89756
	Night	5% 4 1 3 3 3 3 3 5% 7% 63%	89578
Transparency	Day	21% 4 7% 15% 27% 25%	89482
	Night	20% 4 8% 17% 28% 22%	89373
Seeing	Day	7% 9% 21% 31% 22% 10%	14067
	Night	6% 3 18% 42% 28% 4	24139

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	4 9% 1 3 3 4 3 3 4 5% 60%	2858
	11th to 20th	Day	4 6% 1 2 2 2 3 3 4 6% 67%	2860
	21st to end	Day	11% 7% 2 4 3 3 3 4 6% 8% 50%	3146
February	1st to 10th	Day	5% 6% 1 4 3 3 3 2 5% 6% 64%	1710
	11th to 20th	Day	7% 5% 1 3 3 3 3 3 4 6% 62%	1764
	21st to end	Day	7% 5% 1 4 3 2 3 2 4 6% 63%	1727
March	1st to 10th	Day	3 4 1 3 3 3 4 3 4 7% 64%	3444
	11th to 20th	Day	4 5% 2 4 3 3 4 3 5% 7% 60%	3490
	21st to end	Day	3 6% 1 4 4 4 4 4 6% 7% 56%	3825
April	1st to 10th	Day	1 3 1 3 2 3 4 3 5% 6% 70%	2204
	11th to 20th	Day	2 3 1 3 2 2 3 2 3 5% 75%	2251
	21st to end	Day	2 2 1 2 2 1 2 2 4 5% 77%	2280
May	1st to 10th	Day	1 1 1 1 1 2 2 3 4 84%	3800
	11th to 20th	Day	2 1 1 2 2 3 3 4 5% 7% 71%	4057
	21st to end	Day	1 1 1 1 1 1 2 2 3 86%	4477
June	1st to 10th	Day	2 2 1 2 2 2 3 3 5% 8% 69%	2470
	11th to 20th	Day	2 2 1 2 2 1 2 2 3 6% 76%	2470
	21st to end	Day	3 3 2 5% 4 5% 5% 5% 7% 7% 54%	2458
July	1st to 10th	Day	5% 4 2 6% 6% 5% 7% 6% 9% 9% 41%	2340
	11th to 20th	Day	3 4 2 7% 6% 7% 8% 7% 11% 9% 34%	2340
	21st to end	Day	6% 5% 2 8% 8% 7% 9% 7% 10% 11% 28%	2545
August	1st to 10th	Day	5% 5% 2 6% 6% 5% 8% 6% 8% 11% 39%	2328
	11th to 20th	Day	5% 5% 2 6% 5% 7% 6% 6% 8% 11% 40%	2156
	21st to end	Day	4 5% 2 7% 5% 6% 6% 6% 8% 10% 41%	2376
September	1st to 10th	Day	8% 4 2 5% 5% 5% 5% 5% 7% 8% 45%	2160
	11th to 20th	Day	5% 4 1 3 3 3 4 4 6% 7% 59%	2045
	21st to end	Day	3 3 1 4 1 2 3 3 5% 6% 68%	1949
October	1st to 10th	Day	3 3 1 4 3 3 4 4 5% 6% 64%	1800
	11th to 20th	Day	4 2 1 2 1 2 3 2 3 5% 76%	1800
	21st to end	Day	2 1 1 2 2 2 2 3 3 6% 76%	1980
November	1st to 10th	Day	2 2 1 2 2 3 3 3 4 5% 74%	1859
	11th to 20th	Day	2 2 1 3 3 3 3 3 4 6% 71%	1900
	21st to end	Day	6% 5% 1 4 3 3 3 3 4 7% 61%	1862
December	1st to 10th	Day	7% 3 1 4 2 3 3 3 5% 7% 63%	1710
	11th to 20th	Day	8% 8% 2 6% 4 3 3 2 4 8% 54%	2169
	21st to end	Day	5% 6% 2 4 3 4 4 3 5% 5% 60%	3146
January	1st to 10th	Night	6% 7% 3 4 3 3 3 3 4 6% 58%	4097
	11th to 20th	Night	5% 2 1 2 2 3 2 2 3 5% 73%	4110
	21st to end	Night	12% 11% 2 4 3 3 3 3 5% 7% 46%	4521
February	1st to 10th	Night	6% 5% 1 2 2 3 3 3 5% 6% 65%	2470
	11th to 20th	Night	8% 6% 1 3 2 2 3 3 5% 5% 62%	2295
	21st to end	Night	7% 6% 1 2 2 2 3 3 4 5% 66%	1727
March	1st to 10th	Night	3 3 1 3 2 3 2 3 5% 7% 69%	3430
	11th to 20th	Night	8% 5% 2 4 3 2 3 3 4 5% 62%	3490
	21st to end	Night	4 5% 1 3 2 3 3 3 5% 8% 62%	3828
April	1st to 10th	Night	2 2 1 2 3 2 2 3 5% 6% 72%	1976
	11th to 20th	Night	2 3 2 2 2 2 2 4 5% 74%	1877
	21st to end	Night	2 2 1 2 2 2 2 2 4 6% 77%	1900
May	1st to 10th	Night	1 1 1 1 2 2 1 3 4 83%	3170
	11th to 20th	Night	2 2 1 2 2 3 3 3 4 6% 72%	2844
	21st to end	Night	1 1 1 1 1 1 1 3 3 86%	3110
June	1st to 10th	Night	2 2 1 3 3 4 3 3 4 6% 67%	1710
	11th to 20th	Night	1 2 1 2 2 3 4 3 4 5% 73%	1710
	21st to end	Night	3 3 1 4 6% 5% 5% 5% 8% 8% 51%	1701
July	1st to 10th	Night	3 4 1 6% 4 5% 5% 6% 8% 12% 46%	1620
	11th to 20th	Night	2 3 2 7% 5% 6% 8% 7% 12% 14% 35%	1620
	21st to end	Night	4 5% 2 7% 6% 5% 7% 6% 10% 14% 34%	1773
August	1st to 10th	Night	3 3 2 5% 5% 4 6% 6% 12% 13% 41%	1611
	11th to 20th	Night	3 4 1 6% 5% 6% 7% 6% 10% 11% 40%	1744
	21st to end	Night	4 4 1 6% 6% 6% 7% 6% 9% 11% 41%	1980
September	1st to 10th	Night	5% 6% 2 5% 4 5% 5% 5% 8% 9% 46%	1800
	11th to 20th	Night	4 3 2 4 4 4 3 4 5% 7% 61%	1910
	21st to end	Night	3 2 1 4 3 2 3 3 4 5% 70%	2011
October	1st to 10th	Night	3 2 1 4 3 3 4 3 4 5% 67%	2160
	11th to 20th	Night	3 2 1 1 1 2 1 2 4 4 79%	2160
	21st to end	Night	3 2 1 2 1 2 2 2 3 5% 79%	2376
November	1st to 10th	Night	3 2 2 2 2 2 2 4 6% 75%	2220
	11th to 20th	Night	2 2 1 2 2 2 2 3 3 6% 74%	2280
	21st to end	Night	8% 4 1 3 2 2 3 2 5% 6% 64%	2315
December	1st to 10th	Night	7% 4 1 3 2 2 3 3 4 7% 63%	2470
	11th to 20th	Night	6% 5% 1 5% 4 4 4 4 5% 8% 54%	3041
	21st to end	Night	8% 6% 1 4 3 3 3 3 4 6% 60%	4521

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	26% 2 5% 15% 39% 13%	2859
	11th to 20th	Day	20% 3 7% 25% 33% 13%	2860
	21st to end	Day	29% 5% 7% 21% 27% 11%	3146
February	1st to 10th	Day	22% 3 5% 15% 28% 26%	1710
	11th to 20th	Day	24% 3 5% 16% 30% 22%	1773
	21st to end	Day	23% 2 3 12% 31% 28%	1727
March	1st to 10th	Day	19% 3 5% 13% 38% 21%	3444
	11th to 20th	Day	19% 6% 8% 20% 31% 16%	3490
	21st to end	Day	23% 4 9% 18% 31% 16%	3825
April	1st to 10th	Day	15% 3 4 13% 37% 29%	2204
	11th to 20th	Day	13% 2 2 11% 31% 40%	2254
	21st to end	Day	11% 2 3 15% 35% 35%	2280
May	1st to 10th	Day	8% 1 2 7% 30% 51%	3800
	11th to 20th	Day	10% 5% 6% 11% 29% 39%	4060
	21st to end	Day	6% 2 2 6% 19% 66%	4477
June	1st to 10th	Day	14% 3 5% 12% 30% 36%	2470
	11th to 20th	Day	11% 2 3 7% 23% 54%	2470
	21st to end	Day	25% 5% 9% 14% 18% 28%	2458
July	1st to 10th	Day	32% 8% 12% 17% 14% 17%	2276
	11th to 20th	Day	35% 12% 19% 20% 9% 5%	2271
	21st to end	Day	41% 11% 23% 16% 8% 1	2404
August	1st to 10th	Day	34% 10% 17% 20% 14% 6%	2313
	11th to 20th	Day	33% 11% 16% 18% 16% 6%	2156
	21st to end	Day	33% 9% 15% 19% 18% 6%	2376
September	1st to 10th	Day	32% 6% 12% 18% 19% 12%	2160
	11th to 20th	Day	22% 5% 7% 19% 29% 18%	2045
	21st to end	Day	16% 4 7% 19% 31% 22%	1949
October	1st to 10th	Day	20% 5% 8% 16% 26% 25%	1800
	11th to 20th	Day	13% 3 4 11% 31% 37%	1800
	21st to end	Day	12% 2 5% 16% 36% 29%	1980
November	1st to 10th	Day	13% 3 6% 17% 34% 27%	1859
	11th to 20th	Day	15% 3 5% 17% 33% 28%	1900
	21st to end	Day	24% 3 7% 15% 31% 20%	1862
December	1st to 10th	Day	22% 2 7% 21% 30% 19%	1710
	11th to 20th	Day	32% 2 7% 21% 24% 13%	2168
	21st to end	Day	24% 4 7% 16% 34% 16%	3146
January	1st to 10th	Night	26% 3 7% 20% 33% 10%	4097
	11th to 20th	Night	16% 2 7% 26% 37% 12%	4110
	21st to end	Night	36% 4 7% 19% 25% 9%	4521
February	1st to 10th	Night	21% 3 6% 17% 29% 24%	2470
	11th to 20th	Night	24% 3 6% 17% 29% 21%	2296
	21st to end	Night	21% 3 3 16% 30% 26%	1727
March	1st to 10th	Night	14% 3 7% 20% 40% 17%	3430
	11th to 20th	Night	19% 8% 7% 19% 31% 15%	3490
	21st to end	Night	17% 5% 9% 24% 31% 13%	3828
April	1st to 10th	Night	14% 1 4 17% 40% 24%	1976
	11th to 20th	Night	12% 3 3 11% 33% 38%	1877
	21st to end	Night	11% 2 4 15% 39% 29%	1900
May	1st to 10th	Night	9% 1 2 8% 38% 42%	3170
	11th to 20th	Night	12% 5% 7% 11% 32% 33%	2845
	21st to end	Night	6% 2 2 6% 18% 66%	3110
June	1st to 10th	Night	17% 3 5% 12% 30% 33%	1710
	11th to 20th	Night	13% 3 4 7% 22% 52%	1710
	21st to end	Night	26% 5% 13% 12% 17% 27%	1701
July	1st to 10th	Night	27% 9% 16% 19% 13% 16%	1575
	11th to 20th	Night	30% 14% 21% 20% 9% 5%	1566
	21st to end	Night	34% 11% 29% 17% 7% 2	1674
August	1st to 10th	Night	27% 11% 24% 19% 11% 7%	1602
	11th to 20th	Night	31% 12% 18% 19% 15% 6%	1744
	21st to end	Night	29% 11% 19% 21% 16% 4	1980
September	1st to 10th	Night	31% 8% 12% 20% 18% 12%	1800
	11th to 20th	Night	22% 4 10% 19% 28% 17%	1910
	21st to end	Night	18% 4 7% 18% 34% 20%	2011
October	1st to 10th	Night	19% 5% 10% 15% 28% 24%	2160
	11th to 20th	Night	11% 2 4 15% 31% 37%	2160
	21st to end	Night	11% 1 4 20% 31% 32%	2376
November	1st to 10th	Night	11% 3 5% 19% 38% 25%	2220
	11th to 20th	Night	13% 2 5% 21% 30% 29%	2280
	21st to end	Night	22% 2 6% 16% 34% 19%	2315
December	1st to 10th	Night	21% 3 7% 21% 29% 19%	2470
	11th to 20th	Night	27% 4 10% 19% 28% 12%	3041
	21st to end	Night	26% 3 8% 19% 28% 16%	4521

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% 7% 18% 41% 16% 4	270
	11th to 20th	Day	14% 5% 22% 33% 20% 7%	270
	21st to end	Day	8% 6% 22% 37% 19% 7%	297
February	1st to 10th	Day	6% 10% 19% 38% 20% 7%	270
	11th to 20th	Day	14% 11% 22% 39% 12% 1	274
	21st to end	Day	14% 26% 32% 21% 6% 2	382
March	1st to 10th	Day	8% 20% 33% 27% 10% 2	460
	11th to 20th	Day	10% 19% 30% 26% 11% 4	460
	21st to end	Day	8% 26% 33% 22% 8% 2	506
April	1st to 10th	Day	5% 17% 38% 23% 13% 3	460
	11th to 20th	Day	8% 21% 34% 26% 11% 1	452
	21st to end	Day	8% 20% 32% 27% 10% 3	460
May	1st to 10th	Day	5% 17% 30% 31% 14% 4	463
	11th to 20th	Day	5% 9% 30% 33% 18% 6%	488
	21st to end	Day	4 11% 35% 33% 14% 4	529
June	1st to 10th	Day	3 5% 27% 37% 20% 9%	490
	11th to 20th	Day	2 6% 29% 35% 19% 9%	490
	21st to end	Day	4 4 17% 38% 25% 12%	487
July	1st to 10th	Day	5% 2 9% 33% 33% 19%	446
	11th to 20th	Day	6% 1 3 27% 35% 28%	444
	21st to end	Day	5% 2 5% 20% 39% 29%	487
August	1st to 10th	Day	6% 1 5% 27% 37% 24%	447
	11th to 20th	Day	6% 3 8% 27% 34% 22%	437
	21st to end	Day	6% 3 7% 26% 32% 26%	495
September	1st to 10th	Day	10% 3 9% 29% 32% 16%	450
	11th to 20th	Day	5% 2 13% 33% 33% 13%	450
	21st to end	Day	4 7% 16% 35% 27% 10%	419
October	1st to 10th	Day	4 7% 17% 31% 28% 14%	270
	11th to 20th	Day	9% 4 14% 33% 28% 13%	270
	21st to end	Day	5% 6% 16% 28% 32% 13%	297
November	1st to 10th	Day	4 8% 21% 39% 24% 4	270
	11th to 20th	Day	3 3 13% 40% 35% 6%	270
	21st to end	Day	12% 8% 21% 32% 20% 6%	270
December	1st to 10th	Day	7% 7% 19% 38% 22% 7%	270
	11th to 20th	Day	8% 8% 23% 37% 20% 4	270
	21st to end	Day	15% 9% 21% 38% 15% 3	297
January	1st to 10th	Night	9% 2 22% 45% 20% 3	760
	11th to 20th	Night	8% 1 23% 44% 21% 3	760
	21st to end	Night	12% 3 22% 42% 19% 2	836
February	1st to 10th	Night	8% 4 25% 42% 19% 2	760
	11th to 20th	Night	10% 4 25% 47% 13% 1	744
	21st to end	Night	11% 4 35% 41% 10%	628
March	1st to 10th	Night	7% 6% 30% 43% 13% 1	760
	11th to 20th	Night	7% 6% 25% 41% 20% 1	760
	21st to end	Night	5% 6% 30% 43% 16%	836
April	1st to 10th	Night	3 6% 29% 49% 12% 1	646
	11th to 20th	Night	3 6% 33% 44% 13%	563
	21st to end	Night	3 6% 30% 42% 17% 2	570
May	1st to 10th	Night	3 6% 24% 51% 15% 1	570
	11th to 20th	Night	4 2 21% 50% 20% 1	561
	21st to end	Night	2 4 19% 55% 19% 1	617
June	1st to 10th	Night	4 2 12% 54% 26% 2	570
	11th to 20th	Night	2 2 15% 53% 27% 1	570
	21st to end	Night	4 2 7% 44% 41% 2	567
July	1st to 10th	Night	6% 1 4 36% 43% 10%	525
	11th to 20th	Night	2 1 2 21% 61% 12%	522
	21st to end	Night	5% 1 3 16% 60% 15%	591
August	1st to 10th	Night	4 1 1 16% 57% 20%	537
	11th to 20th	Night	4 1 3 23% 57% 12%	534
	21st to end	Night	4 2 3 25% 55% 11%	594
September	1st to 10th	Night	7% 1 3 32% 53% 4	540
	11th to 20th	Night	6% 2 3 39% 45% 6%	650
	21st to end	Night	3 2 9% 43% 38% 5%	720
October	1st to 10th	Night	4 1 13% 47% 31% 3	720
	11th to 20th	Night	4 2 13% 49% 29% 3	720
	21st to end	Night	4 2 16% 40% 33% 5%	792
November	1st to 10th	Night	4 2 15% 46% 29% 4	740
	11th to 20th	Night	4 1 16% 49% 26% 4	760
	21st to end	Night	10% 2 21% 39% 24% 4	760
December	1st to 10th	Night	10% 2 18% 47% 20% 3	760
	11th to 20th	Night	10% 3 22% 45% 18% 2	760
	21st to end	Night	12% 3 22% 45% 15% 2	836

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