Garvey Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Garvey Ranch Observatory 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 4 1 4 2 2 3 2 4 6% 67%	109161
	Night	5% 5% 2 4 3 2 3 2 4 6% 63%	108631
Transparency	Day	21% 2 5% 18% 27% 27%	108923
	Night	25% 2 6% 20% 26% 22%	108458
Seeing	Day	7% 7% 24% 35% 19% 7%	15828
	Night	7% 3 10% 37% 35% 8%	25756

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	6% 2 1 3 3 3 3 2 4 6% 67%	2587
	11th to 20th	Day	9% 4 1 4 2 3 3 3 5% 9% 57%	2847
	21st to end	Day	14% 6% 2 5% 3 2 3 3 4 6% 53%	3498
February	1st to 10th	Day	9% 5% 1 4 3 2 2 2 4 5% 63%	1900
	11th to 20th	Day	9% 4 1 3 3 2 3 2 4 7% 62%	1850
	21st to end	Day	8% 5% 2 4 3 3 3 3 5% 7% 57%	1570
March	1st to 10th	Day	9% 5% 2 5% 5% 5% 5% 5% 6% 8% 45%	3138
	11th to 20th	Day	4 4 2 4 3 3 3 3 5% 8% 62%	3279
	21st to end	Day	10% 4 2 4 3 4 4 4 5% 9% 51%	4165
April	1st to 10th	Day	5% 5% 1 4 3 3 2 4 4 8% 61%	2280
	11th to 20th	Day	4 4 2 4 2 2 3 2 4 6% 66%	2249
	21st to end	Day	4 4 1 4 3 2 2 2 3 7% 68%	2280
May	1st to 10th	Day	3 4 1 3 2 2 3 2 3 5% 71%	3909
	11th to 20th	Day	4 8% 3 7% 2 2 2 2 3 5% 60%	4071
	21st to end	Day	4 6% 3 7% 3 3 2 2 3 5% 62%	4477
June	1st to 10th	Day	4 7% 2 5% 2 3 2 2 4 8% 61%	2470
	11th to 20th	Day	4 5% 1 3 2 2 2 1 3 5% 72%	2658
	21st to end	Day	2 3 1 4 2 2 2 2 3 5% 74%	2660
July	1st to 10th	Day	1 2 1 3 1 2 2 1 2 4 80%	4420
	11th to 20th	Day	1 2 1 4 3 3 2 2 3 6% 72%	4341
	21st to end	Day	1 1 1 2 2 2 2 2 3 6% 79%	4159
August	1st to 10th	Day	1 2 1 2 1 2 2 1 2 4 82%	3783
	11th to 20th	Day	1 1 1 2 1 2 1 2 4 85%	3724
	21st to end	Day	1 1 1 3 3 2 1 2 2 4 80%	4180
September	1st to 10th	Day	3 2 1 2 1 2 2 2 3 5% 77%	2280
	11th to 20th	Day	2 3 1 2 2 2 2 1 3 5% 78%	2138
	21st to end	Day	1 2 1 2 2 2 2 2 5% 5% 76%	2090
October	1st to 10th	Day	2 2 1 2 2 2 2 2 2 4 79%	3490
	11th to 20th	Day	3 4 1 3 2 2 2 2 3 6% 73%	3268
	21st to end	Day	2 2 1 4 2 2 3 4 5% 7% 68%	3369
November	1st to 10th	Day	2 3 1 3 2 2 3 2 4 6% 72%	1764
	11th to 20th	Day	4 3 1 3 2 2 3 2 4 6% 71%	1800
	21st to end	Day	5% 3 1 4 3 4 3 3 4 7% 63%	1800
December	1st to 10th	Day	4 2 1 4 3 3 3 3 5% 7% 64%	2950
	11th to 20th	Day	9% 4 2 4 3 3 4 4 6% 9% 52%	3409
	21st to end	Day	9% 5% 2 5% 4 3 4 3 6% 8% 49%	4308
January	1st to 10th	Night	7% 4 1 3 2 2 3 2 3 5% 67%	4490
	11th to 20th	Night	8% 5% 2 5% 3 3 3 3 4 7% 57%	4097
	21st to end	Night	14% 6% 2 5% 2 2 3 3 4 5% 51%	4180
February	1st to 10th	Night	8% 5% 1 5% 3 2 3 2 4 4 62%	2280
	11th to 20th	Night	9% 5% 2 4 3 2 2 3 4 5% 61%	2218
	21st to end	Night	10% 4 1 5% 3 3 4 3 4 5% 57%	1884
March	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 6% 9% 50%	3736
	11th to 20th	Night	5% 5% 2 5% 3 2 3 3 5% 8% 59%	3697
	21st to end	Night	10% 5% 2 7% 3 3 3 3 5% 8% 52%	3488
April	1st to 10th	Night	7% 7% 2 5% 3 3 3 2 3 6% 59%	1900
	11th to 20th	Night	4 6% 2 4 3 2 3 2 3 5% 65%	1879
	21st to end	Night	4 6% 3 4 3 2 3 2 4 7% 63%	1900
May	1st to 10th	Night	4 7% 2 5% 2 2 2 1 3 6% 66%	3066
	11th to 20th	Night	3 9% 5% 9% 3 2 2 2 4 6% 55%	2834
	21st to end	Night	3 9% 2 5% 2 1 2 1 3 6% 65%	3110
June	1st to 10th	Night	2 8% 3 6% 3 2 3 3 5% 7% 59%	1705
	11th to 20th	Night	2 8% 1 3 1 2 2 2 3 7% 68%	1520
	21st to end	Night	2 6% 3 6% 2 2 2 2 4 7% 65%	1520
July	1st to 10th	Night	1 3 1 4 1 1 1 1 3 6% 78%	2540
	11th to 20th	Night	1 2 1 4 3 3 3 3 4 6% 71%	2604
	21st to end	Night	2 2 1 2 3 3 2 2 3 6% 74%	3412
August	1st to 10th	Night	2 2 1 3 2 2 2 2 3 6% 76%	3166
	11th to 20th	Night	1 2 1 2 3 2 2 1 3 6% 77%	3126
	21st to end	Night	1 2 1 5% 4 3 2 2 3 6% 72%	3498
September	1st to 10th	Night	4 5% 1 4 2 1 2 2 4 6% 70%	1900
	11th to 20th	Night	3 3 2 3 1 1 2 1 2 5% 76%	2041
	21st to end	Night	1 3 1 3 2 2 2 2 4 7% 73%	2090
October	1st to 10th	Night	2 2 1 3 3 3 2 2 3 4 75%	3490
	11th to 20th	Night	3 10% 2 4 3 2 2 2 4 7% 62%	3653
	21st to end	Night	2 3 1 3 2 2 3 2 3 4 75%	4194
November	1st to 10th	Night	3 4 1 3 2 2 2 2 4 7% 69%	2535
	11th to 20th	Night	3 3 2 5% 2 2 2 2 4 5% 70%	2600
	21st to end	Night	5% 4 2 4 3 4 4 4 6% 7% 59%	2600
December	1st to 10th	Night	5% 3 1 4 4 3 3 3 4 6% 64%	4240
	11th to 20th	Night	10% 4 2 5% 3 3 4 3 6% 7% 53%	4811
	21st to end	Night	9% 5% 2 6% 3 4 4 4 6% 9% 46%	6627

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	21% 2 4 24% 30% 19%	2587
	11th to 20th	Day	28% 2 14% 21% 16% 18%	2847
	21st to end	Day	36% 2 4 20% 22% 17%	3498
February	1st to 10th	Day	27% 2 4 14% 26% 26%	1900
	11th to 20th	Day	25% 2 4 18% 27% 24%	1860
	21st to end	Day	27% 3 6% 22% 24% 19%	1570
March	1st to 10th	Day	34% 3 7% 25% 18% 14%	3138
	11th to 20th	Day	22% 3 10% 35% 16% 15%	3279
	21st to end	Day	31% 2 11% 30% 17% 9%	4165
April	1st to 10th	Day	23% 3 10% 26% 24% 14%	2280
	11th to 20th	Day	20% 2 6% 24% 29% 18%	2252
	21st to end	Day	19% 2 6% 28% 32% 13%	2280
May	1st to 10th	Day	18% 2 6% 20% 38% 16%	3909
	11th to 20th	Day	29% 2 4 21% 36% 9%	4074
	21st to end	Day	26% 2 4 27% 35% 6%	4477
June	1st to 10th	Day	26% 2 6% 22% 30% 13%	2470
	11th to 20th	Day	19% 2 3 16% 34% 27%	2658
	21st to end	Day	18% 2 2 9% 32% 38%	2660
July	1st to 10th	Day	12% 1 1 6% 15% 65%	4351
	11th to 20th	Day	17% 2 2 11% 30% 37%	4266
	21st to end	Day	11% 2 4 19% 30% 34%	4028
August	1st to 10th	Day	11% 1 1 16% 39% 33%	3770
	11th to 20th	Day	8% 1 13% 31% 47%	3760
	21st to end	Day	12% 2 1 8% 30% 47%	4179
September	1st to 10th	Day	13% 2 2 10% 35% 39%	2280
	11th to 20th	Day	13% 2 1 13% 36% 35%	2138
	21st to end	Day	13% 1 1 18% 33% 34%	2090
October	1st to 10th	Day	13% 1 2 11% 19% 53%	3490
	11th to 20th	Day	17% 1 2 17% 35% 28%	3268
	21st to end	Day	17% 2 2 10% 28% 41%	3369
November	1st to 10th	Day	16% 2 4 18% 25% 35%	1764
	11th to 20th	Day	17% 2 5% 17% 20% 39%	1800
	21st to end	Day	23% 3 7% 12% 25% 30%	1800
December	1st to 10th	Day	22% 2 4 19% 21% 33%	2950
	11th to 20th	Day	31% 2 6% 16% 27% 18%	3408
	21st to end	Day	35% 1 9% 27% 19% 9%	4308
January	1st to 10th	Night	23% 2 6% 18% 32% 19%	4490
	11th to 20th	Night	31% 2 12% 24% 14% 17%	4097
	21st to end	Night	38% 2 4 19% 20% 17%	4180
February	1st to 10th	Night	28% 2 5% 15% 22% 28%	2280
	11th to 20th	Night	26% 2 6% 18% 23% 25%	2219
	21st to end	Night	32% 2 6% 18% 22% 21%	1884
March	1st to 10th	Night	32% 2 7% 28% 20% 11%	3736
	11th to 20th	Night	26% 2 12% 30% 15% 14%	3697
	21st to end	Night	31% 3 12% 27% 18% 8%	3488
April	1st to 10th	Night	29% 2 11% 25% 19% 13%	1900
	11th to 20th	Night	24% 2 8% 25% 24% 17%	1879
	21st to end	Night	25% 3 8% 28% 25% 10%	1900
May	1st to 10th	Night	24% 2 7% 24% 35% 8%	3066
	11th to 20th	Night	34% 2 7% 28% 24% 6%	2835
	21st to end	Night	25% 1 5% 38% 26% 4	3110
June	1st to 10th	Night	29% 2 11% 23% 25% 10%	1705
	11th to 20th	Night	21% 1 5% 19% 36% 17%	1520
	21st to end	Night	24% 1 2 11% 33% 28%	1520
July	1st to 10th	Night	13% 1 1 7% 21% 58%	2500
	11th to 20th	Night	15% 4 3 13% 38% 28%	2556
	21st to end	Night	15% 2 4 26% 26% 27%	3305
August	1st to 10th	Night	14% 1 2 21% 40% 22%	3156
	11th to 20th	Night	14% 2 1 17% 34% 33%	3156
	21st to end	Night	18% 2 1 8% 41% 31%	3498
September	1st to 10th	Night	20% 2 2 9% 33% 33%	1900
	11th to 20th	Night	16% 2 2 15% 34% 32%	2041
	21st to end	Night	17% 1 2 18% 36% 27%	2090
October	1st to 10th	Night	17% 1 2 12% 23% 45%	3490
	11th to 20th	Night	25% 1 2 17% 29% 26%	3653
	21st to end	Night	16% 2 2 11% 33% 37%	4194
November	1st to 10th	Night	18% 2 4 18% 24% 34%	2535
	11th to 20th	Night	19% 2 5% 15% 20% 38%	2600
	21st to end	Night	25% 2 7% 17% 19% 30%	2600
December	1st to 10th	Night	24% 2 5% 15% 23% 31%	4240
	11th to 20th	Night	32% 1 8% 14% 25% 18%	4811
	21st to end	Night	36% 1 12% 27% 15% 9%	6627

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% 4 20% 36% 21% 6%	192
	11th to 20th	Day	12% 6% 29% 30% 18% 4	348
	21st to end	Day	10% 9% 29% 34% 15% 3	506
February	1st to 10th	Day	13% 9% 26% 31% 16% 5%	460
	11th to 20th	Day	11% 12% 31% 31% 14% 2	455
	21st to end	Day	11% 14% 30% 32% 12% 1	382
March	1st to 10th	Day	13% 14% 32% 26% 14% 2	460
	11th to 20th	Day	11% 12% 31% 32% 12% 2	460
	21st to end	Day	11% 18% 31% 27% 10% 3	506
April	1st to 10th	Day	9% 13% 33% 25% 14% 6%	460
	11th to 20th	Day	8% 17% 34% 28% 9% 5%	452
	21st to end	Day	7% 14% 32% 28% 14% 6%	460
May	1st to 10th	Day	10% 13% 30% 30% 13% 4	463
	11th to 20th	Day	8% 12% 28% 32% 13% 7%	488
	21st to end	Day	7% 10% 33% 30% 16% 4	529
June	1st to 10th	Day	6% 8% 24% 38% 18% 6%	490
	11th to 20th	Day	6% 6% 24% 38% 18% 8%	490
	21st to end	Day	3 4 22% 41% 21% 10%	490
July	1st to 10th	Day	2 1 15% 44% 26% 11%	486
	11th to 20th	Day	1 2 10% 46% 25% 16%	484
	21st to end	Day	2 1 12% 44% 26% 15%	531
August	1st to 10th	Day	4 1 15% 47% 21% 12%	487
	11th to 20th	Day	4 1 15% 43% 23% 14%	477
	21st to end	Day	3 2 16% 44% 24% 11%	539
September	1st to 10th	Day	4 2 23% 42% 18% 11%	490
	11th to 20th	Day	3 4 30% 37% 18% 8%	490
	21st to end	Day	2 7% 27% 33% 22% 10%	490
October	1st to 10th	Day	3 8% 26% 33% 22% 8%	490
	11th to 20th	Day	6% 8% 25% 33% 21% 7%	490
	21st to end	Day	5% 7% 23% 34% 20% 10%	496
November	1st to 10th	Day	6% 4 15% 35% 30% 10%	300
	11th to 20th	Day	6% 3 15% 37% 30% 9%	300
	21st to end	Day	6% 4 20% 39% 22% 9%	300
December	1st to 10th	Day	11% 1 14% 41% 27% 6%	300
	11th to 20th	Day	6% 3 18% 39% 24% 10%	300
	21st to end	Day	15% 5% 21% 40% 18% 2	287
January	1st to 10th	Night	10% 2 13% 45% 24% 5%	784
	11th to 20th	Night	10% 2 11% 45% 28% 4	760
	21st to end	Night	13% 2 15% 42% 24% 4	836
February	1st to 10th	Night	10% 3 14% 41% 26% 6%	760
	11th to 20th	Night	10% 3 15% 42% 24% 5%	744
	21st to end	Night	12% 3 16% 46% 20% 3	628
March	1st to 10th	Night	9% 4 17% 47% 19% 4	760
	11th to 20th	Night	10% 3 13% 41% 26% 7%	760
	21st to end	Night	8% 4 15% 45% 24% 3	836
April	1st to 10th	Night	9% 5% 11% 44% 27% 4	760
	11th to 20th	Night	7% 6% 13% 41% 29% 4	751
	21st to end	Night	4 7% 12% 40% 30% 7%	760
May	1st to 10th	Night	8% 5% 13% 39% 30% 5%	698
	11th to 20th	Night	7% 5% 13% 40% 30% 6%	561
	21st to end	Night	6% 5% 16% 39% 31% 4	617
June	1st to 10th	Night	4 5% 14% 36% 36% 5%	565
	11th to 20th	Night	4 4 2 28% 56% 6%	380
	21st to end	Night	6% 4 1 27% 55% 7%	380
July	1st to 10th	Night	4 2 1 9% 70% 14%	370
	11th to 20th	Night	3 2 1 15% 68% 12%	406
	21st to end	Night	4 2 2 21% 53% 18%	800
August	1st to 10th	Night	3 2 3 25% 51% 15%	756
	11th to 20th	Night	3 2 3 20% 53% 19%	752
	21st to end	Night	3 2 3 20% 52% 19%	836
September	1st to 10th	Night	8% 2 4 24% 46% 18%	760
	11th to 20th	Night	4 3 4 34% 45% 11%	760
	21st to end	Night	3 2 4 31% 49% 11%	760
October	1st to 10th	Night	5% 2 5% 40% 42% 6%	760
	11th to 20th	Night	7% 3 6% 35% 41% 9%	760
	21st to end	Night	5% 2 8% 36% 37% 11%	836
November	1st to 10th	Night	5% 1 8% 41% 34% 11%	780
	11th to 20th	Night	4 2 6% 44% 34% 10%	800
	21st to end	Night	6% 2 12% 45% 30% 6%	800
December	1st to 10th	Night	9% 3 11% 43% 30% 5%	800
	11th to 20th	Night	13% 4 11% 44% 25% 4	800
	21st to end	Night	11% 4 16% 44% 20% 5%	880

Page generated at 2025-01-04 00:23:57. Version ac07

Copyright © 2025 Attilla Danko.