Look Rock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Look Rock clear sky chart from 2005-11-06 to 2025-07-06.

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	13% 9% 3 7% 5% 5% 5% 4 6% 7% 36%	119987
	Night	14% 9% 3 7% 4 4 4 4 5% 7% 38%	118814
Transparency	Day	27% 41% 7% 13% 9% 2	123779
	Night	27% 41% 7% 13% 10% 3	123158
Seeing	Day	19% 12% 23% 23% 16% 6%	15716
	Night	18% 10% 22% 29% 18% 3	25768

By Month

Percentage Cloud Cover SE (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	17% 16% 4 7% 4 3 3 3 5% 5% 33%	4056
	11th to 20th	Day	14% 12% 6% 8% 4 5% 4 3 3 4 37%	4060
	21st to end	Day	19% 13% 3 7% 3 3 3 2 4 5% 36%	4466
February	1st to 10th	Day	18% 13% 3 8% 4 4 4 3 5% 5% 32%	1990
	11th to 20th	Day	23% 12% 4 8% 3 3 3 3 4 6% 31%	1948
	21st to end	Day	20% 10% 3 6% 4 5% 3 3 5% 4 36%	1650
March	1st to 10th	Day	19% 12% 4 6% 4 4 4 3 4 6% 34%	4636
	11th to 20th	Day	13% 8% 3 6% 4 3 3 3 5% 6% 46%	4980
	21st to end	Day	17% 9% 2 6% 4 4 4 3 4 6% 41%	5465
April	1st to 10th	Day	12% 6% 3 6% 4 5% 5% 4 8% 6% 40%	2255
	11th to 20th	Day	15% 7% 2 5% 5% 4 4 4 6% 7% 42%	2391
	21st to end	Day	15% 7% 2 6% 4 4 4 4 5% 8% 39%	2600
May	1st to 10th	Day	15% 9% 3 9% 5% 5% 6% 4 7% 8% 29%	5862
	11th to 20th	Day	15% 10% 4 9% 6% 7% 6% 5% 6% 6% 26%	5861
	21st to end	Day	14% 9% 3 8% 5% 5% 6% 5% 7% 9% 31%	6433
June	1st to 10th	Day	10% 7% 3 7% 6% 6% 6% 6% 7% 9% 34%	2600
	11th to 20th	Day	5% 5% 2 7% 6% 7% 6% 6% 8% 11% 36%	2600
	21st to end	Day	8% 6% 2 8% 5% 6% 5% 6% 8% 11% 36%	2600
July	1st to 10th	Day	6% 6% 2 7% 6% 6% 7% 6% 9% 12% 33%	4185
	11th to 20th	Day	11% 7% 2 7% 6% 5% 6% 5% 8% 9% 36%	4120
	21st to end	Day	15% 10% 5% 11% 8% 8% 8% 5% 6% 7% 18%	4466
August	1st to 10th	Day	8% 5% 2 7% 6% 6% 6% 5% 8% 11% 36%	4104
	11th to 20th	Day	9% 6% 2 7% 5% 6% 6% 5% 8% 10% 36%	3953
	21st to end	Day	6% 4 2 5% 5% 4 6% 5% 7% 8% 47%	4180
September	1st to 10th	Day	12% 6% 3 6% 5% 5% 5% 4 6% 8% 40%	2098
	11th to 20th	Day	14% 7% 3 8% 5% 5% 4 3 5% 8% 37%	2090
	21st to end	Day	15% 5% 2 6% 4 4 4 4 7% 7% 43%	2090
October	1st to 10th	Day	11% 5% 2 5% 4 3 4 3 5% 5% 53%	2090
	11th to 20th	Day	14% 6% 1 4 3 2 3 3 5% 6% 51%	1944
	21st to end	Day	14% 6% 2 4 3 3 3 3 5% 6% 50%	2083
November	1st to 10th	Day	13% 5% 2 5% 2 3 4 4 5% 5% 53%	1762
	11th to 20th	Day	12% 9% 2 6% 4 3 3 4 5% 7% 45%	1800
	21st to end	Day	14% 9% 3 5% 4 3 4 4 5% 5% 43%	1800
December	1st to 10th	Day	15% 9% 3 5% 5% 4 4 4 5% 5% 40%	2930
	11th to 20th	Day	18% 15% 4 8% 4 4 4 3 4 5% 29%	3373
	21st to end	Day	13% 14% 5% 7% 4 4 5% 3 5% 7% 32%	4466
January	1st to 10th	Night	17% 13% 4 9% 4 3 3 3 4 6% 35%	5889
	11th to 20th	Night	20% 10% 3 7% 5% 4 3 3 4 5% 36%	5900
	21st to end	Night	16% 11% 4 7% 4 4 4 3 4 5% 39%	6490
February	1st to 10th	Night	18% 11% 3 7% 4 4 4 4 5% 6% 35%	2405
	11th to 20th	Night	23% 11% 4 7% 4 4 4 3 4 4 33%	2338
	21st to end	Night	21% 11% 3 6% 4 4 4 3 5% 5% 33%	1980
March	1st to 10th	Night	21% 12% 3 6% 3 3 3 3 4 6% 34%	5203
	11th to 20th	Night	14% 5% 2 5% 3 3 4 3 6% 8% 47%	4980
	21st to end	Night	12% 9% 3 7% 5% 4 4 3 5% 7% 41%	5467
April	1st to 10th	Night	14% 8% 2 5% 4 3 4 3 6% 7% 44%	2160
	11th to 20th	Night	13% 8% 2 5% 4 3 3 3 5% 7% 46%	1956
	21st to end	Night	15% 6% 2 5% 4 4 5% 3 6% 7% 43%	1800
May	1st to 10th	Night	14% 8% 3 8% 6% 5% 6% 5% 7% 9% 29%	4033
	11th to 20th	Night	19% 10% 3 9% 5% 5% 5% 4 6% 7% 27%	4032
	21st to end	Night	13% 9% 3 8% 5% 5% 5% 4 6% 9% 33%	4421
June	1st to 10th	Night	8% 7% 2 6% 5% 6% 6% 6% 8% 10% 38%	1800
	11th to 20th	Night	5% 4 2 5% 4 5% 5% 6% 8% 13% 43%	1800
	21st to end	Night	7% 6% 2 6% 5% 6% 6% 5% 7% 9% 41%	1800
July	1st to 10th	Night	9% 5% 3 8% 5% 6% 7% 5% 9% 10% 33%	2885
	11th to 20th	Night	9% 5% 3 5% 5% 5% 5% 5% 8% 12% 40%	2840
	21st to end	Night	12% 10% 4 10% 7% 7% 7% 5% 7% 8% 21%	3087
August	1st to 10th	Night	8% 6% 2 7% 5% 5% 6% 4 7% 11% 40%	2825
	11th to 20th	Night	11% 6% 2 7% 5% 4 5% 4 7% 8% 40%	2871
	21st to end	Night	6% 4 2 6% 5% 5% 5% 5% 7% 10% 46%	3476
September	1st to 10th	Night	11% 6% 2 7% 5% 5% 4 4 7% 7% 41%	2061
	11th to 20th	Night	12% 7% 3 7% 5% 4 5% 3 6% 7% 41%	2090
	21st to end	Night	12% 6% 3 5% 4 5% 4 3 6% 7% 45%	2090
October	1st to 10th	Night	14% 5% 2 5% 3 3 2 2 4 6% 54%	2090
	11th to 20th	Night	15% 5% 2 5% 3 4 3 2 4 4 52%	2234
	21st to end	Night	13% 6% 2 4 3 3 3 3 5% 6% 52%	2513
November	1st to 10th	Night	13% 7% 2 6% 3 3 3 3 4 5% 50%	2536
	11th to 20th	Night	15% 8% 2 5% 3 3 4 3 4 6% 46%	2600
	21st to end	Night	15% 9% 2 6% 4 4 4 3 4 7% 44%	2600
December	1st to 10th	Night	18% 13% 3 7% 4 3 3 3 4 5% 37%	4250
	11th to 20th	Night	20% 12% 5% 9% 4 3 4 3 4 5% 31%	4822
	21st to end	Night	14% 13% 4 8% 4 5% 4 4 5% 7% 31%	6490

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	37% 30% 3 13% 15% 2	4057
	11th to 20th	Day	36% 28% 3 10% 21% 2	4060
	21st to end	Day	38% 28% 4 15% 13% 2	4466
February	1st to 10th	Day	22% 61% 3 8% 6% 1	1990
	11th to 20th	Day	24% 61% 2 6% 6% 1	1958
	21st to end	Day	20% 62% 1 6% 8% 3	1650
March	1st to 10th	Day	38% 30% 5% 10% 10% 7%	4636
	11th to 20th	Day	24% 29% 3 14% 18% 12%	4980
	21st to end	Day	30% 30% 4 24% 10% 2	5465
April	1st to 10th	Day	18% 63% 4 8% 6%	2255
	11th to 20th	Day	19% 63% 4 8% 6% 1	2391
	21st to end	Day	16% 63% 5% 10% 5% 1	2600
May	1st to 10th	Day	38% 32% 10% 16% 4	5897
	11th to 20th	Day	41% 32% 10% 14% 3	5865
	21st to end	Day	35% 31% 9% 14% 9% 1	6447
June	1st to 10th	Day	18% 63% 6% 8% 5%	2600
	11th to 20th	Day	15% 65% 9% 8% 4	2600
	21st to end	Day	16% 64% 8% 8% 4	2600
July	1st to 10th	Day	21% 44% 17% 15% 4	4120
	11th to 20th	Day	26% 40% 14% 18% 2	4051
	21st to end	Day	46% 40% 6% 5% 2	4324
August	1st to 10th	Day	24% 40% 14% 17% 5%	4091
	11th to 20th	Day	20% 42% 17% 15% 7% 1	3992
	21st to end	Day	15% 40% 9% 29% 7% 1	4179
September	1st to 10th	Day	15% 62% 5% 9% 8% 2	2098
	11th to 20th	Day	17% 62% 5% 10% 7%	2090
	21st to end	Day	16% 61% 6% 10% 7%	2090
October	1st to 10th	Day	14% 38% 4 12% 22% 9%	3480
	11th to 20th	Day	13% 37% 3 16% 19% 13%	3210
	21st to end	Day	13% 37% 5% 21% 15% 9%	3409
November	1st to 10th	Day	19% 56% 4 10% 10% 2	1762
	11th to 20th	Day	17% 58% 2 10% 11% 3	1800
	21st to end	Day	19% 58% 3 10% 9% 2	1800
December	1st to 10th	Day	26% 39% 4 11% 18% 2	2930
	11th to 20th	Day	39% 34% 5% 9% 10% 2	3370
	21st to end	Day	37% 28% 9% 18% 7% 1	4466
January	1st to 10th	Night	38% 29% 4 14% 12% 3	5889
	11th to 20th	Night	34% 31% 2 11% 16% 6%	5900
	21st to end	Night	34% 29% 5% 12% 16% 4	6490
February	1st to 10th	Night	20% 62% 2 8% 6% 2	2405
	11th to 20th	Night	25% 61% 3 6% 5% 1	2339
	21st to end	Night	18% 63% 3 7% 6% 3	1980
March	1st to 10th	Night	38% 31% 5% 12% 11% 3	5203
	11th to 20th	Night	19% 31% 5% 16% 17% 12%	4980
	21st to end	Night	30% 29% 8% 21% 10% 2	5467
April	1st to 10th	Night	17% 63% 5% 8% 6% 1	2160
	11th to 20th	Night	17% 63% 4 8% 6% 2	1956
	21st to end	Night	16% 62% 5% 11% 6% 1	1800
May	1st to 10th	Night	36% 32% 13% 15% 4	4060
	11th to 20th	Night	42% 32% 10% 13% 4	4033
	21st to end	Night	34% 34% 10% 16% 7%	4429
June	1st to 10th	Night	15% 64% 8% 9% 4 1	1800
	11th to 20th	Night	11% 65% 10% 9% 4	1800
	21st to end	Night	14% 64% 8% 10% 4	1800
July	1st to 10th	Night	27% 40% 15% 15% 3	2840
	11th to 20th	Night	20% 39% 18% 19% 3 1	2786
	21st to end	Night	42% 41% 9% 6% 3	2988
August	1st to 10th	Night	23% 41% 13% 18% 5%	2814
	11th to 20th	Night	21% 40% 16% 16% 6%	2898
	21st to end	Night	14% 40% 10% 27% 8%	3476
September	1st to 10th	Night	14% 61% 7% 9% 8% 1	2061
	11th to 20th	Night	15% 62% 7% 9% 7%	2090
	21st to end	Night	16% 61% 7% 9% 7%	2090
October	1st to 10th	Night	16% 38% 5% 15% 18% 8%	3480
	11th to 20th	Night	13% 38% 3 15% 18% 13%	3707
	21st to end	Night	11% 37% 3 21% 18% 11%	4137
November	1st to 10th	Night	21% 57% 4 10% 8% 1	2536
	11th to 20th	Night	18% 58% 2 9% 10% 4	2600
	21st to end	Night	19% 57% 2 11% 9% 1	2600
December	1st to 10th	Night	33% 38% 3 9% 17% 1	4250
	11th to 20th	Night	37% 35% 4 11% 11% 2	4824
	21st to end	Night	38% 29% 11% 14% 9% 1	6490

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	26% 29% 28% 15% 2	300
	11th to 20th	Day	30% 32% 22% 11% 4 1	300
	21st to end	Day	25% 27% 35% 12% 2	330
February	1st to 10th	Day	28% 24% 29% 16% 2	300
	11th to 20th	Day	42% 25% 24% 9% 1	300
	21st to end	Day	39% 23% 29% 8% 1	249
March	1st to 10th	Day	29% 20% 29% 15% 6%	365
	11th to 20th	Day	25% 22% 34% 14% 5%	500
	21st to end	Day	27% 19% 33% 16% 5%	550
April	1st to 10th	Day	22% 21% 26% 23% 9% 1	500
	11th to 20th	Day	21% 17% 29% 20% 11% 2	492
	21st to end	Day	21% 14% 29% 24% 9% 3	500
May	1st to 10th	Day	19% 17% 29% 21% 10% 4	503
	11th to 20th	Day	17% 8% 27% 25% 17% 6%	527
	21st to end	Day	16% 11% 21% 25% 18% 10%	573
June	1st to 10th	Day	13% 8% 22% 29% 21% 7%	530
	11th to 20th	Day	8% 5% 18% 31% 27% 12%	530
	21st to end	Day	11% 4 21% 30% 23% 12%	530
July	1st to 10th	Day	12% 4 14% 27% 29% 15%	505
	11th to 20th	Day	12% 3 12% 31% 27% 15%	484
	21st to end	Day	12% 2 13% 28% 31% 14%	532
August	1st to 10th	Day	16% 4 16% 24% 27% 13%	486
	11th to 20th	Day	12% 4 16% 30% 28% 10%	479
	21st to end	Day	12% 3 15% 21% 33% 17%	539
September	1st to 10th	Day	10% 5% 15% 24% 35% 11%	490
	11th to 20th	Day	14% 5% 13% 26% 29% 13%	490
	21st to end	Day	17% 6% 15% 31% 26% 5%	490
October	1st to 10th	Day	14% 8% 20% 28% 23% 7%	490
	11th to 20th	Day	15% 13% 24% 29% 17% 2	490
	21st to end	Day	22% 9% 21% 33% 12% 3	532
November	1st to 10th	Day	20% 11% 30% 28% 9% 2	300
	11th to 20th	Day	17% 18% 32% 26% 6%	300
	21st to end	Day	18% 17% 34% 24% 7%	300
December	1st to 10th	Day	28% 20% 33% 16% 3	300
	11th to 20th	Day	26% 15% 32% 21% 5%	300
	21st to end	Day	27% 18% 33% 17% 5%	330
January	1st to 10th	Night	25% 17% 29% 25% 4	800
	11th to 20th	Night	27% 19% 29% 21% 4	800
	21st to end	Night	22% 17% 33% 25% 2	880
February	1st to 10th	Night	25% 13% 30% 28% 4	800
	11th to 20th	Night	30% 18% 32% 18% 1	783
	21st to end	Night	30% 18% 30% 20% 2	660
March	1st to 10th	Night	25% 16% 28% 27% 4	800
	11th to 20th	Night	22% 18% 29% 24% 6% 1	800
	21st to end	Night	23% 14% 30% 24% 8%	880
April	1st to 10th	Night	19% 17% 27% 28% 8% 1	760
	11th to 20th	Night	18% 13% 31% 24% 13% 1	593
	21st to end	Night	17% 8% 28% 33% 12% 1	600
May	1st to 10th	Night	14% 10% 27% 32% 15% 2	600
	11th to 20th	Night	17% 6% 20% 34% 20% 3	591
	21st to end	Night	10% 3 17% 33% 32% 5%	650
June	1st to 10th	Night	11% 3 17% 36% 31% 3	600
	11th to 20th	Night	6% 3 13% 36% 33% 10%	600
	21st to end	Night	9% 2 13% 34% 37% 6%	600
July	1st to 10th	Night	11% 1 8% 29% 44% 7%	570
	11th to 20th	Night	9% 2 9% 28% 43% 9%	552
	21st to end	Night	10% 1 8% 29% 44% 8%	624
August	1st to 10th	Night	8% 2 10% 29% 42% 9%	567
	11th to 20th	Night	10% 3 10% 34% 38% 5%	564
	21st to end	Night	12% 1 10% 23% 44% 11%	627
September	1st to 10th	Night	12% 3 11% 28% 39% 8%	731
	11th to 20th	Night	16% 4 10% 31% 35% 5%	760
	21st to end	Night	14% 3 17% 35% 29% 2	760
October	1st to 10th	Night	15% 5% 17% 26% 30% 7%	760
	11th to 20th	Night	18% 8% 22% 31% 18% 2	760
	21st to end	Night	17% 8% 21% 36% 16% 2	836
November	1st to 10th	Night	17% 7% 21% 35% 18% 2	780
	11th to 20th	Night	17% 12% 27% 31% 12% 1	800
	21st to end	Night	22% 10% 25% 32% 12%	800
December	1st to 10th	Night	29% 13% 25% 27% 6%	800
	11th to 20th	Night	23% 14% 26% 30% 8%	800
	21st to end	Night	25% 15% 24% 32% 5%	880

Page generated at 2025-07-03 00:30:16. Version ac07

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