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 2026-07-16.

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	10% 6% 2 4 3 3 3 3 4 7% 57%	146821
	Night	12% 8% 2 5% 3 3 3 3 4 6% 50%	143374
Transparency	Day	28% 4 7% 20% 23% 17%	141686
	Night	35% 5% 7% 17% 20% 16%	139505
Seeing	Day	16% 12% 28% 26% 14% 4	17571
	Night	17% 8% 17% 29% 23% 6%	26759

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	23% 11% 3 6% 4 4 5% 3 5% 6% 31%	5178
	11th to 20th	Day	16% 7% 2 4 3 3 3 2 3 5% 52%	5340
	21st to end	Day	17% 8% 3 6% 4 4 4 3 5% 6% 40%	5843
February	1st to 10th	Day	21% 9% 3 6% 4 3 3 3 4 4 39%	1890
	11th to 20th	Day	18% 10% 3 6% 4 3 5% 4 5% 7% 34%	1845
	21st to end	Day	21% 10% 2 6% 4 3 3 3 5% 6% 37%	1753
March	1st to 10th	Day	24% 14% 2 5% 4 3 3 3 4 7% 31%	5062
	11th to 20th	Day	19% 9% 2 4 3 3 4 3 5% 6% 42%	5110
	21st to end	Day	22% 12% 2 6% 4 5% 5% 4 7% 8% 25%	5607
April	1st to 10th	Day	16% 9% 3 5% 4 4 4 4 6% 7% 37%	2488
	11th to 20th	Day	14% 8% 3 6% 4 4 3 3 5% 7% 43%	2489
	21st to end	Day	10% 8% 2 4 3 3 3 4 6% 10% 48%	2570
May	1st to 10th	Day	6% 6% 2 4 2 3 3 3 4 7% 61%	7627
	11th to 20th	Day	3 2 1 2 2 2 3 2 4 7% 72%	7594
	21st to end	Day	3 3 1 3 2 2 3 3 4 8% 68%	8984
June	1st to 10th	Day	7% 5% 2 4 4 3 3 4 4 7% 56%	2940
	11th to 20th	Day	3 3 1 2 2 1 2 3 4 7% 72%	2940
	21st to end	Day	3 2 1 2 2 1 2 2 3 6% 75%	2940
July	1st to 10th	Day	1 1 1 1 1 2 1 2 3 86%	6353
	11th to 20th	Day	1 1 1 3 2 2 1 1 2 5% 82%	5946
	21st to end	Day	2 1 2 2 2 2 2 3 8% 76%	6402
August	1st to 10th	Day	1 1 2 1 2 2 2 4 5% 79%	5777
	11th to 20th	Day	1 3 1 2 1 2 1 1 3 5% 80%	5762
	21st to end	Day	1 2 1 2 2 2 3 3 4 7% 74%	5984
September	1st to 10th	Day	2 2 1 2 1 1 2 2 3 6% 77%	2400
	11th to 20th	Day	4 3 2 4 2 2 3 2 5% 7% 65%	2318
	21st to end	Day	4 3 1 2 2 2 3 2 4 7% 73%	2147
October	1st to 10th	Day	5% 2 1 2 2 2 3 2 4 6% 71%	3280
	11th to 20th	Day	9% 4 2 4 2 2 4 3 5% 7% 59%	3261
	21st to end	Day	9% 7% 2 6% 4 4 5% 4 5% 8% 46%	3558
November	1st to 10th	Day	13% 7% 2 5% 3 4 4 3 6% 8% 45%	2059
	11th to 20th	Day	18% 8% 2 7% 4 3 3 3 6% 7% 40%	1794
	21st to end	Day	13% 5% 2 5% 4 4 5% 3 4 7% 48%	1680
December	1st to 10th	Day	11% 6% 2 4 3 3 4 4 7% 9% 47%	2700
	11th to 20th	Day	31% 9% 3 6% 4 4 5% 4 6% 7% 21%	3108
	21st to end	Day	28% 11% 3 7% 5% 4 4 4 5% 6% 22%	4092
January	1st to 10th	Night	25% 11% 3 6% 4 4 4 4 5% 6% 28%	7735
	11th to 20th	Night	13% 8% 2 6% 4 3 3 3 3 5% 49%	7650
	21st to end	Night	19% 11% 3 7% 5% 4 4 3 4 6% 36%	8371
February	1st to 10th	Night	19% 8% 2 5% 4 3 4 3 5% 6% 41%	2730
	11th to 20th	Night	18% 11% 4 7% 4 4 4 4 6% 6% 32%	2662
	21st to end	Night	18% 9% 2 5% 4 3 4 3 4 6% 42%	2049
March	1st to 10th	Night	21% 22% 3 5% 3 3 3 2 4 6% 29%	5052
	11th to 20th	Night	19% 10% 2 5% 3 4 3 3 3 5% 42%	5110
	21st to end	Night	21% 18% 4 6% 3 4 4 3 5% 6% 27%	5610
April	1st to 10th	Night	13% 11% 3 8% 4 4 4 4 5% 8% 37%	2131
	11th to 20th	Night	12% 9% 3 6% 4 3 4 3 5% 8% 43%	2079
	21st to end	Night	8% 7% 2 4 3 4 3 3 5% 8% 52%	2047
May	1st to 10th	Night	8% 9% 3 5% 2 2 2 2 4 6% 58%	5321
	11th to 20th	Night	3 5% 2 3 2 2 2 2 3 6% 69%	5295
	21st to end	Night	4 6% 2 4 3 2 3 2 4 5% 66%	5185
June	1st to 10th	Night	6% 6% 1 5% 4 3 4 3 6% 8% 54%	1680
	11th to 20th	Night	3 3 1 3 2 2 2 2 5% 6% 72%	1680
	21st to end	Night	3 3 1 2 2 2 2 3 3 5% 74%	1680
July	1st to 10th	Night	1 1 1 2 1 2 1 3 4 84%	3813
	11th to 20th	Night	1 1 1 5% 4 4 4 3 3 4 72%	4145
	21st to end	Night	1 2 3 6% 3 3 4 3 5% 7% 62%	4472
August	1st to 10th	Night	1 1 1 2 2 3 3 3 4 6% 73%	4035
	11th to 20th	Night	1 3 1 4 2 2 2 2 3 4 76%	4086
	21st to end	Night	2 2 1 2 2 2 3 2 4 6% 73%	5015
September	1st to 10th	Night	1 2 1 2 2 2 1 2 3 7% 76%	2000
	11th to 20th	Night	5% 5% 1 4 3 3 4 3 5% 7% 61%	2078
	21st to end	Night	4 3 1 3 3 3 3 2 3 5% 70%	2251
October	1st to 10th	Night	3 4 1 3 2 2 2 2 2 3 75%	3920
	11th to 20th	Night	6% 7% 3 5% 3 3 3 4 5% 7% 55%	3897
	21st to end	Night	10% 7% 2 4 3 4 4 4 6% 7% 50%	4253
November	1st to 10th	Night	14% 6% 3 5% 3 4 5% 3 7% 8% 42%	2460
	11th to 20th	Night	16% 8% 2 6% 4 6% 5% 5% 5% 7% 37%	2820
	21st to end	Night	14% 6% 2 6% 4 4 3 3 5% 6% 47%	2940
December	1st to 10th	Night	12% 6% 2 5% 3 3 4 4 6% 8% 48%	4700
	11th to 20th	Night	30% 11% 2 7% 4 4 4 3 5% 6% 24%	5316
	21st to end	Night	34% 11% 3 6% 3 3 3 2 4 5% 26%	7106

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	53% 6% 11% 15% 10% 5%	5179
	11th to 20th	Day	37% 1 6% 9% 21% 26%	5340
	21st to end	Day	44% 4 7% 16% 14% 16%	5843
February	1st to 10th	Day	48% 3 7% 16% 18% 8%	1890
	11th to 20th	Day	49% 4 7% 18% 17% 4	1854
	21st to end	Day	47% 5% 10% 19% 13% 5%	1753
March	1st to 10th	Day	54% 3 6% 19% 16% 1	5062
	11th to 20th	Day	43% 4 13% 18% 14% 8%	5110
	21st to end	Day	54% 7% 11% 19% 8% 1	5607
April	1st to 10th	Day	44% 6% 11% 25% 12% 2	2488
	11th to 20th	Day	39% 5% 13% 22% 16% 5%	2492
	21st to end	Day	31% 5% 13% 29% 18% 4	2570
May	1st to 10th	Day	24% 4 10% 23% 29% 10%	7627
	11th to 20th	Day	13% 2 8% 34% 33% 10%	7597
	21st to end	Day	15% 3 7% 43% 29% 2	8986
June	1st to 10th	Day	27% 4 9% 27% 28% 6%	2940
	11th to 20th	Day	13% 4 8% 22% 38% 16%	2940
	21st to end	Day	12% 2 3 18% 38% 27%	2940
July	1st to 10th	Day	6% 2 2 11% 26% 53%	6287
	11th to 20th	Day	8% 1 3 6% 22% 59%	5877
	21st to end	Day	9% 3 7% 15% 33% 33%	6217
August	1st to 10th	Day	10% 3 4 13% 29% 41%	4206
	11th to 20th	Day	9% 2 2 19% 42% 26%	4173
	21st to end	Day	11% 3 4 19% 33% 29%	4311
September	1st to 10th	Day	10% 3 2 14% 31% 40%	2400
	11th to 20th	Day	19% 3 6% 28% 33% 11%	2318
	21st to end	Day	14% 3 4 22% 33% 23%	2147
October	1st to 10th	Day	16% 2 2 18% 22% 40%	3280
	11th to 20th	Day	25% 3 7% 24% 30% 11%	3261
	21st to end	Day	34% 5% 8% 22% 20% 10%	3558
November	1st to 10th	Day	35% 5% 8% 26% 17% 9%	2059
	11th to 20th	Day	43% 4 11% 19% 15% 8%	1794
	21st to end	Day	36% 5% 9% 18% 20% 12%	1680
December	1st to 10th	Day	32% 4 7% 21% 27% 8%	2700
	11th to 20th	Day	61% 4 7% 14% 10% 3	3108
	21st to end	Day	60% 6% 8% 16% 7% 2	4092
January	1st to 10th	Night	55% 6% 13% 11% 11% 4	7735
	11th to 20th	Night	38% 3 6% 12% 18% 23%	7650
	21st to end	Night	50% 4 6% 10% 14% 16%	8371
February	1st to 10th	Night	43% 5% 8% 17% 18% 10%	2730
	11th to 20th	Night	50% 6% 5% 18% 16% 5%	2664
	21st to end	Night	43% 5% 11% 21% 16% 4	2049
March	1st to 10th	Night	57% 5% 7% 18% 11% 3	5052
	11th to 20th	Night	43% 6% 7% 20% 16% 8%	5110
	21st to end	Night	56% 7% 10% 17% 9% 2	5610
April	1st to 10th	Night	44% 6% 11% 21% 14% 3	2131
	11th to 20th	Night	37% 6% 12% 24% 16% 5%	2079
	21st to end	Night	30% 5% 11% 31% 19% 4	2047
May	1st to 10th	Night	26% 6% 8% 19% 29% 13%	5319
	11th to 20th	Night	18% 3 5% 30% 29% 16%	5296
	21st to end	Night	20% 4 7% 37% 30% 2	5186
June	1st to 10th	Night	27% 5% 8% 24% 27% 9%	1680
	11th to 20th	Night	12% 3 9% 21% 38% 17%	1680
	21st to end	Night	13% 4 4 14% 33% 31%	1680
July	1st to 10th	Night	6% 3 1 11% 22% 56%	3772
	11th to 20th	Night	13% 3 4 8% 15% 58%	4091
	21st to end	Night	17% 6% 6% 10% 23% 38%	4345
August	1st to 10th	Night	11% 8% 4 11% 26% 39%	2929
	11th to 20th	Night	9% 3 3 14% 39% 32%	2950
	21st to end	Night	13% 3 3 17% 29% 35%	3608
September	1st to 10th	Night	9% 3 2 13% 30% 43%	2000
	11th to 20th	Night	19% 6% 4 19% 36% 14%	2078
	21st to end	Night	17% 4 4 19% 27% 29%	2251
October	1st to 10th	Night	16% 2 3 13% 22% 43%	3920
	11th to 20th	Night	27% 7% 6% 17% 31% 12%	3897
	21st to end	Night	32% 4 5% 25% 19% 14%	4253
November	1st to 10th	Night	38% 7% 10% 18% 16% 11%	2460
	11th to 20th	Night	44% 7% 10% 18% 15% 6%	2820
	21st to end	Night	37% 4 8% 19% 20% 12%	2940
December	1st to 10th	Night	34% 4 7% 21% 23% 11%	4700
	11th to 20th	Night	61% 5% 5% 13% 12% 4	5316
	21st to end	Night	62% 4 8% 15% 8% 2	7106

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	40% 15% 19% 16% 10% 1	378
	11th to 20th	Day	26% 12% 23% 19% 16% 4	430
	21st to end	Day	22% 12% 25% 23% 14% 3	473
February	1st to 10th	Day	28% 14% 23% 20% 12% 2	430
	11th to 20th	Day	30% 20% 22% 18% 9% 1	425
	21st to end	Day	26% 18% 26% 19% 9% 2	434
March	1st to 10th	Day	35% 17% 23% 18% 6% 1	540
	11th to 20th	Day	31% 13% 27% 19% 9% 1	540
	21st to end	Day	25% 23% 28% 15% 7% 2	594
April	1st to 10th	Day	24% 16% 33% 17% 9% 2	540
	11th to 20th	Day	22% 18% 30% 20% 8% 2	532
	21st to end	Day	16% 22% 33% 17% 9% 3	540
May	1st to 10th	Day	16% 15% 36% 21% 10% 3	543
	11th to 20th	Day	19% 15% 32% 20% 10% 3	568
	21st to end	Day	13% 15% 34% 25% 10% 3	617
June	1st to 10th	Day	9% 14% 38% 27% 9% 3	570
	11th to 20th	Day	9% 17% 38% 26% 9% 2	570
	21st to end	Day	3 9% 35% 34% 14% 5%	570
July	1st to 10th	Day	3 6% 35% 35% 16% 4	566
	11th to 20th	Day	1 4 34% 37% 19% 5%	545
	21st to end	Day	1 2 24% 46% 21% 6%	575
August	1st to 10th	Day	4 3 36% 36% 16% 5%	527
	11th to 20th	Day	3 5% 31% 35% 21% 5%	517
	21st to end	Day	4 5% 26% 37% 22% 6%	583
September	1st to 10th	Day	4 6% 30% 35% 19% 6%	530
	11th to 20th	Day	6% 10% 25% 35% 18% 5%	530
	21st to end	Day	6% 11% 28% 27% 22% 7%	530
October	1st to 10th	Day	8% 11% 25% 30% 20% 7%	530
	11th to 20th	Day	14% 9% 21% 26% 23% 7%	530
	21st to end	Day	15% 11% 24% 28% 17% 5%	583
November	1st to 10th	Day	16% 13% 21% 24% 21% 4	535
	11th to 20th	Day	23% 10% 17% 23% 20% 6%	294
	21st to end	Day	16% 11% 23% 23% 19% 7%	220
December	1st to 10th	Day	25% 9% 25% 16% 14% 10%	220
	11th to 20th	Day	32% 12% 20% 18% 11% 7%	220
	21st to end	Day	34% 14% 20% 17% 12% 3	242
January	1st to 10th	Night	30% 8% 14% 26% 17% 4	840
	11th to 20th	Night	23% 6% 17% 29% 19% 6%	840
	21st to end	Night	23% 8% 12% 30% 22% 5%	924
February	1st to 10th	Night	25% 10% 15% 29% 19% 3	840
	11th to 20th	Night	25% 12% 18% 24% 15% 5%	824
	21st to end	Night	24% 13% 19% 29% 13% 2	692
March	1st to 10th	Night	30% 13% 15% 25% 14% 3	840
	11th to 20th	Night	27% 8% 17% 29% 17% 2	840
	21st to end	Night	26% 10% 22% 26% 13% 2	924
April	1st to 10th	Night	19% 14% 22% 25% 17% 3	840
	11th to 20th	Night	16% 15% 23% 26% 15% 5%	831
	21st to end	Night	16% 15% 27% 22% 17% 3	787
May	1st to 10th	Night	13% 9% 25% 30% 18% 5%	630
	11th to 20th	Night	10% 10% 26% 28% 21% 5%	621
	21st to end	Night	12% 15% 24% 29% 17% 3	459
June	1st to 10th	Night	9% 11% 29% 29% 19% 3	420
	11th to 20th	Night	5% 12% 30% 35% 16% 2	420
	21st to end	Night	4 4 26% 40% 24% 2	420
July	1st to 10th	Night	4 4 23% 34% 29% 7%	450
	11th to 20th	Night	2 1 20% 33% 35% 9%	597
	21st to end	Night	3 2 15% 32% 36% 12%	657
August	1st to 10th	Night	2 2 19% 35% 32% 9%	597
	11th to 20th	Night	3 3 17% 31% 36% 10%	602
	21st to end	Night	5% 2 13% 32% 38% 9%	880
September	1st to 10th	Night	3 5% 13% 34% 34% 12%	800
	11th to 20th	Night	8% 7% 14% 32% 31% 9%	800
	21st to end	Night	7% 6% 16% 28% 31% 11%	800
October	1st to 10th	Night	9% 7% 12% 33% 30% 9%	800
	11th to 20th	Night	12% 6% 11% 30% 32% 10%	800
	21st to end	Night	14% 7% 13% 28% 27% 10%	880
November	1st to 10th	Night	17% 9% 13% 27% 28% 7%	820
	11th to 20th	Night	21% 9% 13% 31% 22% 5%	840
	21st to end	Night	16% 11% 14% 33% 22% 5%	840
December	1st to 10th	Night	23% 8% 14% 29% 20% 6%	840
	11th to 20th	Night	31% 8% 15% 27% 15% 5%	840
	21st to end	Night	34% 11% 14% 23% 14% 3	924

Page generated at 2026-07-13 00:14:51. Version ac07

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