Lookout Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lookout Ranch clear sky chart from 2005-11-06 to 2025-03-12.

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	11% 6% 2 4 3 3 3 3 4 6% 56%	112905
	Night	13% 8% 2 5% 3 3 3 3 4 6% 50%	114934
Transparency	Day	29% 4 7% 19% 23% 18%	112668
	Night	34% 5% 7% 17% 20% 17%	114762
Seeing	Day	15% 12% 28% 26% 15% 4	15758
	Night	16% 8% 17% 29% 23% 6%	25088

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	20% 12% 3 7% 4 3 4 3 5% 6% 33%	3984
	11th to 20th	Day	20% 9% 3 5% 3 3 2 2 2 4 48%	4100
	21st to end	Day	21% 8% 2 5% 3 3 3 3 4 5% 42%	4510
February	1st to 10th	Day	22% 9% 3 6% 4 3 3 3 4 5% 39%	1800
	11th to 20th	Day	19% 9% 3 6% 4 3 5% 4 5% 7% 35%	1755
	21st to end	Day	20% 10% 2 6% 4 2 3 3 4 7% 39%	1672
March	1st to 10th	Day	28% 16% 3 5% 4 3 3 3 3 5% 28%	3552
	11th to 20th	Day	14% 7% 2 4 3 3 3 2 4 6% 50%	3503
	21st to end	Day	24% 11% 2 6% 4 5% 5% 4 6% 7% 26%	3825
April	1st to 10th	Day	17% 10% 3 5% 4 4 4 4 5% 7% 36%	2251
	11th to 20th	Day	14% 8% 3 6% 4 4 3 3 5% 7% 43%	2249
	21st to end	Day	10% 7% 2 4 3 3 4 4 6% 10% 48%	2325
May	1st to 10th	Day	7% 5% 1 3 2 3 3 2 4 7% 63%	4110
	11th to 20th	Day	6% 3 1 2 2 2 2 2 3 6% 71%	4070
	21st to end	Day	5% 4 1 4 2 2 2 2 4 7% 69%	4805
June	1st to 10th	Day	8% 5% 3 4 4 3 3 4 4 8% 54%	2660
	11th to 20th	Day	3 3 1 2 2 2 2 3 3 7% 71%	2660
	21st to end	Day	3 2 1 2 2 2 2 2 3 6% 75%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 1 2 3 87%	4342
	11th to 20th	Day	1 1 1 2 2 2 2 1 3 5% 81%	4110
	21st to end	Day	1 1 1 1 2 2 2 3 6% 82%	4455
August	1st to 10th	Day	1 1 1 2 2 2 3 3 5% 7% 72%	4091
	11th to 20th	Day	1 3 1 2 1 2 2 1 2 5% 81%	4005
	21st to end	Day	1 2 1 3 2 2 2 2 3 6% 76%	4180
September	1st to 10th	Day	1 2 2 1 1 2 2 3 6% 79%	2280
	11th to 20th	Day	4 3 2 4 2 2 3 2 5% 8% 65%	2202
	21st to end	Day	3 3 1 2 2 2 3 2 4 7% 73%	2040
October	1st to 10th	Day	5% 2 1 2 2 2 3 2 4 6% 72%	3180
	11th to 20th	Day	9% 4 2 4 2 2 4 3 5% 7% 59%	3161
	21st to end	Day	9% 7% 2 6% 4 4 5% 4 6% 8% 46%	3448
November	1st to 10th	Day	13% 7% 2 6% 3 4 4 3 6% 8% 45%	1959
	11th to 20th	Day	17% 7% 2 7% 4 3 3 3 6% 7% 41%	1709
	21st to end	Day	13% 6% 2 5% 4 4 5% 4 4 6% 46%	1600
December	1st to 10th	Day	12% 6% 2 4 3 3 4 4 7% 9% 47%	2620
	11th to 20th	Day	30% 9% 3 7% 4 4 5% 4 6% 7% 21%	3028
	21st to end	Day	27% 11% 3 7% 5% 4 4 4 5% 6% 22%	4004
January	1st to 10th	Night	18% 11% 3 7% 4 4 5% 5% 6% 7% 30%	5972
	11th to 20th	Night	17% 11% 3 7% 4 3 2 2 3 4 43%	5880
	21st to end	Night	22% 11% 3 6% 4 4 3 2 3 4 39%	6468
February	1st to 10th	Night	20% 8% 2 5% 4 3 4 3 5% 6% 41%	2600
	11th to 20th	Night	18% 11% 3 7% 4 4 4 4 6% 6% 33%	2532
	21st to end	Night	16% 9% 2 5% 4 3 4 3 4 7% 44%	1954
March	1st to 10th	Night	24% 22% 3 6% 3 3 3 2 4 5% 26%	3542
	11th to 20th	Night	16% 6% 2 4 3 4 3 3 3 6% 48%	3505
	21st to end	Night	20% 19% 4 7% 3 4 3 3 4 5% 28%	3828
April	1st to 10th	Night	13% 10% 3 7% 4 4 3 3 5% 8% 38%	1929
	11th to 20th	Night	12% 8% 3 6% 4 3 4 3 6% 8% 45%	1879
	21st to end	Night	8% 6% 2 4 3 4 3 3 6% 8% 53%	1853
May	1st to 10th	Night	7% 6% 2 4 2 2 2 2 3 6% 65%	2860
	11th to 20th	Night	3 4 2 4 2 2 2 2 3 6% 70%	2833
	21st to end	Night	3 4 1 3 3 3 2 3 3 5% 70%	2766
June	1st to 10th	Night	6% 7% 2 5% 5% 3 4 3 7% 8% 52%	1520
	11th to 20th	Night	3 3 1 2 2 2 2 2 5% 6% 73%	1520
	21st to end	Night	3 2 2 2 3 2 1 3 3 5% 74%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 3 87%	2603
	11th to 20th	Night	1 1 4 3 3 3 2 3 4 76%	2860
	21st to end	Night	1 1 1 2 2 3 4 3 5% 7% 73%	3109
August	1st to 10th	Night	1 2 1 3 3 4 4 4 6% 8% 63%	2848
	11th to 20th	Night	1 2 1 2 1 1 2 1 2 4 80%	2832
	21st to end	Night	3 3 1 2 2 1 2 2 3 5% 76%	3498
September	1st to 10th	Night	1 2 1 2 2 2 1 2 3 7% 78%	1900
	11th to 20th	Night	5% 4 1 4 3 3 3 3 5% 7% 61%	1974
	21st to end	Night	4 3 1 3 3 3 3 2 3 6% 71%	2138
October	1st to 10th	Night	3 3 1 3 2 2 2 2 3 4 76%	3800
	11th to 20th	Night	6% 7% 3 5% 3 3 3 4 6% 7% 55%	3777
	21st to end	Night	10% 7% 2 4 3 4 4 4 6% 7% 50%	4121
November	1st to 10th	Night	14% 6% 3 5% 3 4 5% 3 7% 7% 43%	2340
	11th to 20th	Night	15% 8% 2 6% 4 6% 5% 5% 5% 7% 38%	2685
	21st to end	Night	14% 6% 2 6% 3 4 3 3 5% 6% 47%	2800
December	1st to 10th	Night	13% 6% 2 5% 3 3 4 4 5% 7% 48%	4560
	11th to 20th	Night	30% 11% 2 7% 4 4 4 3 5% 6% 23%	5176
	21st to end	Night	33% 12% 3 6% 3 3 3 2 4 5% 26%	6952

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	51% 6% 12% 15% 9% 7%	3984
	11th to 20th	Day	44% 2 7% 10% 21% 16%	4100
	21st to end	Day	44% 4 6% 13% 15% 18%	4510
February	1st to 10th	Day	49% 3 7% 16% 18% 8%	1800
	11th to 20th	Day	47% 4 7% 19% 18% 4	1764
	21st to end	Day	45% 5% 10% 20% 14% 5%	1672
March	1st to 10th	Day	61% 4 7% 15% 12% 1	3552
	11th to 20th	Day	36% 4 11% 21% 18% 10%	3503
	21st to end	Day	54% 7% 11% 18% 9% 2	3825
April	1st to 10th	Day	45% 6% 11% 24% 12% 2	2251
	11th to 20th	Day	40% 5% 14% 22% 16% 4	2252
	21st to end	Day	30% 5% 13% 29% 19% 4	2325
May	1st to 10th	Day	20% 6% 14% 28% 21% 11%	4110
	11th to 20th	Day	16% 3 6% 25% 36% 14%	4073
	21st to end	Day	17% 4 8% 47% 24% 1	4806
June	1st to 10th	Day	28% 5% 9% 27% 25% 5%	2660
	11th to 20th	Day	13% 4 8% 23% 38% 14%	2660
	21st to end	Day	12% 3 3 17% 38% 28%	2660
July	1st to 10th	Day	6% 2 1 7% 20% 64%	4275
	11th to 20th	Day	8% 2 3 8% 22% 56%	4041
	21st to end	Day	6% 2 2 9% 32% 48%	4315
August	1st to 10th	Day	10% 3 4 13% 28% 42%	4076
	11th to 20th	Day	9% 2 2 19% 42% 25%	4044
	21st to end	Day	11% 3 4 20% 32% 30%	4179
September	1st to 10th	Day	8% 3 2 13% 32% 42%	2280
	11th to 20th	Day	18% 3 6% 28% 34% 11%	2202
	21st to end	Day	13% 3 4 23% 32% 24%	2040
October	1st to 10th	Day	16% 2 2 18% 22% 41%	3180
	11th to 20th	Day	25% 3 7% 23% 31% 11%	3161
	21st to end	Day	34% 5% 8% 22% 20% 11%	3448
November	1st to 10th	Day	35% 5% 7% 27% 16% 10%	1959
	11th to 20th	Day	42% 4 11% 20% 14% 8%	1709
	21st to end	Day	37% 5% 10% 17% 20% 11%	1600
December	1st to 10th	Day	33% 4 7% 21% 27% 8%	2620
	11th to 20th	Day	62% 4 7% 14% 10% 2	3028
	21st to end	Day	60% 6% 8% 16% 7% 2	4004
January	1st to 10th	Night	51% 7% 16% 10% 12% 5%	5972
	11th to 20th	Night	46% 4 6% 15% 18% 12%	5880
	21st to end	Night	50% 4 5% 7% 16% 19%	6468
February	1st to 10th	Night	43% 5% 8% 17% 18% 9%	2600
	11th to 20th	Night	49% 6% 5% 19% 17% 5%	2534
	21st to end	Night	41% 5% 11% 22% 17% 4	1954
March	1st to 10th	Night	60% 6% 8% 14% 11% 2	3542
	11th to 20th	Night	35% 7% 8% 21% 19% 10%	3505
	21st to end	Night	56% 7% 11% 16% 8% 2	3828
April	1st to 10th	Night	43% 6% 12% 22% 13% 3	1929
	11th to 20th	Night	36% 6% 12% 25% 17% 5%	1879
	21st to end	Night	28% 5% 12% 32% 19% 5%	1853
May	1st to 10th	Night	19% 7% 9% 28% 24% 12%	2860
	11th to 20th	Night	16% 4 5% 20% 31% 24%	2834
	21st to end	Night	17% 4 7% 43% 27% 2	2766
June	1st to 10th	Night	28% 5% 8% 25% 24% 9%	1520
	11th to 20th	Night	12% 3 8% 22% 39% 15%	1520
	21st to end	Night	13% 4 4 14% 34% 32%	1520
July	1st to 10th	Night	5% 2 1 6% 20% 67%	2562
	11th to 20th	Night	11% 3 4 8% 18% 57%	2806
	21st to end	Night	6% 7% 3 6% 24% 54%	3011
August	1st to 10th	Night	12% 8% 4 10% 25% 40%	2839
	11th to 20th	Night	9% 3 3 14% 40% 31%	2859
	21st to end	Night	13% 3 3 17% 29% 35%	3498
September	1st to 10th	Night	8% 3 1 13% 30% 45%	1900
	11th to 20th	Night	18% 6% 5% 19% 37% 14%	1974
	21st to end	Night	16% 4 4 20% 27% 30%	2138
October	1st to 10th	Night	16% 2 3 13% 22% 44%	3800
	11th to 20th	Night	27% 7% 6% 17% 32% 12%	3777
	21st to end	Night	32% 4 5% 25% 19% 15%	4121
November	1st to 10th	Night	37% 7% 10% 19% 16% 11%	2340
	11th to 20th	Night	42% 7% 11% 18% 15% 7%	2685
	21st to end	Night	37% 4 8% 19% 19% 12%	2800
December	1st to 10th	Night	34% 4 7% 21% 23% 11%	4560
	11th to 20th	Night	61% 5% 5% 13% 13% 3	5176
	21st to end	Night	62% 4 8% 16% 8% 3	6952

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	39% 15% 19% 17% 10% 1	350
	11th to 20th	Day	28% 13% 25% 19% 14% 3	400
	21st to end	Day	24% 13% 23% 22% 15% 3	440
February	1st to 10th	Day	29% 14% 23% 20% 11% 3	400
	11th to 20th	Day	29% 20% 22% 19% 10% 1	395
	21st to end	Day	24% 19% 26% 20% 10% 2	403
March	1st to 10th	Day	36% 17% 23% 17% 6% 1	500
	11th to 20th	Day	31% 14% 28% 18% 8% 1	465
	21st to end	Day	25% 23% 28% 16% 6% 1	506
April	1st to 10th	Day	25% 16% 33% 17% 7% 2	460
	11th to 20th	Day	22% 19% 29% 21% 8% 2	452
	21st to end	Day	15% 25% 33% 17% 8% 3	460
May	1st to 10th	Day	16% 15% 36% 21% 10% 2	463
	11th to 20th	Day	19% 14% 31% 23% 10% 3	488
	21st to end	Day	13% 15% 33% 25% 10% 3	529
June	1st to 10th	Day	10% 14% 37% 27% 9% 2	490
	11th to 20th	Day	9% 17% 37% 26% 9% 2	490
	21st to end	Day	2 8% 36% 35% 16% 4	490
July	1st to 10th	Day	4 6% 32% 37% 16% 5%	486
	11th to 20th	Day	1 3 35% 36% 19% 5%	484
	21st to end	Day	2 24% 47% 21% 6%	531
August	1st to 10th	Day	4 3 35% 37% 17% 5%	487
	11th to 20th	Day	3 5% 30% 35% 22% 5%	477
	21st to end	Day	4 5% 26% 37% 22% 6%	539
September	1st to 10th	Day	3 6% 30% 34% 20% 6%	490
	11th to 20th	Day	6% 10% 25% 35% 19% 4	490
	21st to end	Day	5% 10% 28% 27% 23% 7%	490
October	1st to 10th	Day	7% 10% 26% 30% 20% 7%	490
	11th to 20th	Day	13% 9% 20% 27% 24% 7%	490
	21st to end	Day	14% 11% 24% 28% 17% 6%	539
November	1st to 10th	Day	16% 14% 21% 23% 21% 4	495
	11th to 20th	Day	21% 10% 17% 24% 22% 7%	269
	21st to end	Day	18% 13% 22% 22% 19% 8%	200
December	1st to 10th	Day	28% 10% 24% 15% 14% 10%	200
	11th to 20th	Day	32% 13% 21% 18% 12% 6%	200
	21st to end	Day	33% 15% 20% 18% 12% 3	220
January	1st to 10th	Night	29% 9% 14% 27% 17% 5%	800
	11th to 20th	Night	24% 7% 17% 28% 18% 6%	800
	21st to end	Night	24% 9% 11% 28% 23% 5%	880
February	1st to 10th	Night	25% 10% 15% 29% 19% 3	800
	11th to 20th	Night	25% 12% 17% 25% 16% 5%	784
	21st to end	Night	22% 13% 19% 30% 14% 2	660
March	1st to 10th	Night	30% 12% 16% 25% 14% 4	800
	11th to 20th	Night	27% 7% 16% 28% 19% 3	766
	21st to end	Night	26% 10% 21% 26% 14% 3	836
April	1st to 10th	Night	19% 14% 22% 25% 16% 4	760
	11th to 20th	Night	16% 15% 24% 24% 16% 5%	751
	21st to end	Night	15% 15% 26% 22% 18% 4	713
May	1st to 10th	Night	13% 10% 25% 29% 18% 5%	570
	11th to 20th	Night	10% 8% 24% 30% 23% 5%	561
	21st to end	Night	12% 15% 24% 30% 17% 3	415
June	1st to 10th	Night	9% 11% 28% 30% 18% 3	380
	11th to 20th	Night	6% 12% 28% 36% 16% 2	380
	21st to end	Night	3 3 26% 42% 25% 2	380
July	1st to 10th	Night	4 4 21% 34% 30% 7%	406
	11th to 20th	Night	2 1 19% 34% 34% 9%	552
	21st to end	Night	3 1 15% 31% 37% 13%	624
August	1st to 10th	Night	2 2 17% 36% 34% 9%	567
	11th to 20th	Night	3 3 15% 31% 37% 11%	571
	21st to end	Night	6% 2 13% 32% 38% 9%	836
September	1st to 10th	Night	3 4 13% 33% 35% 13%	760
	11th to 20th	Night	8% 6% 14% 32% 31% 9%	760
	21st to end	Night	6% 6% 15% 28% 32% 12%	760
October	1st to 10th	Night	8% 7% 12% 33% 31% 9%	760
	11th to 20th	Night	12% 5% 10% 30% 32% 10%	760
	21st to end	Night	15% 6% 13% 28% 28% 10%	836
November	1st to 10th	Night	16% 9% 12% 27% 28% 7%	780
	11th to 20th	Night	20% 9% 13% 31% 22% 5%	800
	21st to end	Night	17% 11% 13% 31% 22% 6%	800
December	1st to 10th	Night	24% 8% 13% 28% 20% 7%	800
	11th to 20th	Night	30% 9% 15% 27% 14% 5%	800
	21st to end	Night	33% 11% 14% 23% 14% 4	880

Page generated at 2025-03-09 05:08:48. Version ac07

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