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 2024-11-03.

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% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	101003
	Night	14% 9% 3 7% 4 4 4 4 6% 7% 38%	97951
Transparency	Day	24% 49% 6% 12% 7% 1	100815
	Night	24% 50% 6% 11% 7% 2	97808
Seeing	Day	18% 12% 23% 24% 17% 6%	14861
	Night	18% 9% 21% 29% 19% 3	24877

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	16% 13% 5% 9% 4 4 4 4 6% 6% 29%	2836
	11th to 20th	Day	16% 13% 6% 8% 5% 5% 4 3 4 4 30%	2840
	21st to end	Day	20% 16% 3 7% 3 3 3 2 4 5% 32%	3124
February	1st to 10th	Day	19% 13% 3 8% 4 4 4 3 5% 5% 32%	1890
	11th to 20th	Day	22% 12% 4 8% 3 3 3 3 4 6% 32%	1848
	21st to end	Day	21% 11% 3 6% 4 5% 3 3 5% 4 35%	1570
March	1st to 10th	Day	22% 12% 3 6% 4 3 4 3 4 6% 33%	3234
	11th to 20th	Day	15% 8% 3 6% 4 3 3 3 4 5% 47%	3480
	21st to end	Day	18% 10% 3 6% 5% 4 4 3 5% 6% 37%	3815
April	1st to 10th	Day	11% 7% 3 7% 4 5% 6% 4 7% 6% 40%	2142
	11th to 20th	Day	15% 7% 2 5% 5% 4 4 4 6% 7% 42%	2270
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 5% 7% 40%	2470
May	1st to 10th	Day	14% 8% 2 8% 6% 5% 6% 4 7% 7% 33%	4082
	11th to 20th	Day	17% 9% 3 8% 6% 6% 5% 4 5% 6% 31%	4081
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 10% 36%	4476
June	1st to 10th	Day	10% 7% 3 7% 6% 6% 6% 6% 7% 9% 34%	2470
	11th to 20th	Day	5% 5% 2 7% 6% 7% 5% 6% 8% 11% 37%	2470
	21st to end	Day	8% 6% 3 8% 5% 6% 5% 6% 8% 10% 35%	2470
July	1st to 10th	Day	6% 6% 2 7% 6% 6% 7% 6% 9% 12% 32%	4120
	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% 6% 2 5% 2 3 3 3 5% 5% 54%	1690
	11th to 20th	Day	11% 9% 3 6% 4 3 3 4 5% 7% 46%	1710
	21st to end	Day	14% 8% 3 5% 4 3 4 4 5% 5% 43%	1710
December	1st to 10th	Day	19% 11% 4 5% 5% 5% 4 4 5% 5% 32%	1710
	11th to 20th	Day	16% 13% 2 7% 3 4 4 3 5% 6% 36%	2153
	21st to end	Day	14% 16% 4 7% 4 5% 4 3 5% 5% 33%	3124
January	1st to 10th	Night	18% 15% 5% 8% 4 4 4 3 3 5% 31%	4109
	11th to 20th	Night	21% 10% 3 7% 6% 4 3 3 4 5% 33%	4120
	21st to end	Night	21% 14% 4 7% 4 3 3 3 3 4 34%	4532
February	1st to 10th	Night	17% 11% 3 7% 4 4 4 4 5% 6% 35%	2285
	11th to 20th	Night	22% 12% 4 6% 4 4 4 3 4 4 33%	2218
	21st to end	Night	22% 11% 3 6% 4 4 4 3 5% 5% 31%	1884
March	1st to 10th	Night	24% 12% 4 6% 4 4 3 3 4 7% 30%	3619
	11th to 20th	Night	15% 6% 2 5% 4 3 4 3 5% 8% 45%	3480
	21st to end	Night	15% 9% 3 6% 5% 4 4 4 5% 6% 40%	3817
April	1st to 10th	Night	14% 9% 2 5% 4 3 4 3 5% 7% 44%	2052
	11th to 20th	Night	14% 8% 2 5% 4 3 3 3 5% 7% 45%	1857
	21st to end	Night	15% 6% 2 5% 5% 3 4 3 6% 7% 43%	1710
May	1st to 10th	Night	13% 7% 3 8% 5% 5% 5% 4 7% 8% 34%	2813
	11th to 20th	Night	18% 8% 3 7% 4 4 4 4 6% 7% 35%	2812
	21st to end	Night	7% 7% 2 7% 5% 5% 6% 5% 7% 10% 38%	3079
June	1st to 10th	Night	8% 7% 2 6% 5% 6% 6% 6% 8% 11% 37%	1710
	11th to 20th	Night	4 4 2 4 4 5% 5% 6% 9% 13% 44%	1710
	21st to end	Night	7% 6% 2 6% 5% 6% 5% 5% 7% 9% 41%	1710
July	1st to 10th	Night	9% 5% 3 8% 5% 6% 7% 5% 9% 10% 33%	2840
	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 5% 3 3 3 3 5% 6% 52%	2513
November	1st to 10th	Night	13% 7% 2 6% 3 3 3 3 4 5% 51%	2433
	11th to 20th	Night	14% 8% 2 5% 3 3 4 3 4 6% 46%	2470
	21st to end	Night	15% 8% 3 6% 4 4 4 3 4 7% 44%	2470
December	1st to 10th	Night	20% 13% 3 7% 4 4 4 3 5% 6% 32%	2470
	11th to 20th	Night	17% 12% 4 9% 4 3 3 3 4 5% 37%	3042
	21st to end	Night	16% 14% 4 8% 5% 5% 5% 4 6% 7% 26%	4532

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	32% 40% 3 7% 14% 3	2837
	11th to 20th	Day	36% 38% 3 7% 14% 2	2840
	21st to end	Day	37% 39% 3 9% 11% 1	3124
February	1st to 10th	Day	21% 64% 2 6% 6% 1	1890
	11th to 20th	Day	22% 64% 1 6% 7% 1	1858
	21st to end	Day	20% 65% 1 5% 6% 2	1570
March	1st to 10th	Day	36% 40% 5% 8% 6% 4	3234
	11th to 20th	Day	20% 41% 3 16% 13% 7%	3480
	21st to end	Day	28% 41% 4 18% 7% 2	3815
April	1st to 10th	Day	18% 66% 3 7% 6%	2142
	11th to 20th	Day	18% 66% 3 7% 5% 1	2270
	21st to end	Day	15% 65% 4 10% 5% 1	2470
May	1st to 10th	Day	33% 41% 7% 14% 4	4120
	11th to 20th	Day	34% 41% 6% 17% 3	4085
	21st to end	Day	25% 42% 9% 13% 10% 1	4489
June	1st to 10th	Day	17% 66% 5% 7% 4	2470
	11th to 20th	Day	14% 67% 8% 7% 4	2470
	21st to end	Day	16% 66% 7% 7% 4	2470
July	1st to 10th	Day	21% 44% 17% 14% 4	4055
	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% 62% 4 9% 9% 2	2090
	11th to 20th	Day	14% 60% 3 10% 10% 4	1944
	21st to end	Day	15% 59% 2 11% 10% 3	2083
November	1st to 10th	Day	19% 57% 3 9% 9% 2	1690
	11th to 20th	Day	16% 60% 2 9% 10% 3	1710
	21st to end	Day	18% 60% 3 9% 9% 2	1710
December	1st to 10th	Day	24% 60% 2 8% 4 2	1710
	11th to 20th	Day	25% 49% 4 6% 14% 3	2150
	21st to end	Day	36% 38% 3 15% 7% 1	3124
January	1st to 10th	Night	37% 39% 2 8% 11% 4	4109
	11th to 20th	Night	30% 42% 2 7% 14% 6%	4120
	21st to end	Night	36% 40% 4 6% 12% 2	4532
February	1st to 10th	Night	19% 66% 2 7% 5% 2	2285
	11th to 20th	Night	22% 64% 2 5% 6% 1	2219
	21st to end	Night	18% 66% 3 5% 5% 3	1884
March	1st to 10th	Night	37% 42% 6% 8% 5% 1	3619
	11th to 20th	Night	18% 42% 4 16% 11% 8%	3480
	21st to end	Night	27% 40% 5% 16% 10% 2	3817
April	1st to 10th	Night	16% 66% 4 7% 6% 1	2052
	11th to 20th	Night	17% 66% 4 7% 4 2	1857
	21st to end	Night	14% 65% 3 11% 6% 1	1710
May	1st to 10th	Night	31% 42% 9% 14% 4	2840
	11th to 20th	Night	30% 42% 8% 15% 5%	2813
	21st to end	Night	22% 45% 10% 17% 7%	3087
June	1st to 10th	Night	14% 67% 7% 8% 3 1	1710
	11th to 20th	Night	9% 68% 10% 9% 4	1710
	21st to end	Night	14% 66% 7% 9% 4	1710
July	1st to 10th	Night	26% 41% 15% 15% 3	2795
	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	13% 60% 5% 11% 8% 2	2090
	11th to 20th	Night	15% 61% 3 9% 9% 4	2234
	21st to end	Night	13% 59% 2 10% 12% 4	2513
November	1st to 10th	Night	21% 58% 3 9% 8% 1	2433
	11th to 20th	Night	17% 60% 2 8% 9% 4	2470
	21st to end	Night	18% 60% 2 10% 9% 1	2470
December	1st to 10th	Night	27% 60% 2 5% 4 2	2470
	11th to 20th	Night	26% 50% 2 6% 14% 3	3044
	21st to end	Night	38% 38% 5% 11% 6% 1	4532

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	25% 29% 27% 16% 3	270
	11th to 20th	Day	30% 31% 23% 11% 4 1	270
	21st to end	Day	24% 26% 35% 12% 2	297
February	1st to 10th	Day	29% 23% 29% 16% 2	270
	11th to 20th	Day	40% 24% 24% 10% 1	270
	21st to end	Day	42% 22% 27% 8%	225
March	1st to 10th	Day	27% 20% 31% 16% 7%	332
	11th to 20th	Day	24% 22% 35% 14% 5%	460
	21st to end	Day	27% 17% 32% 18% 5%	506
April	1st to 10th	Day	22% 20% 25% 24% 9% 1	460
	11th to 20th	Day	22% 17% 28% 20% 11% 2	452
	21st to end	Day	22% 14% 28% 25% 9% 3	460
May	1st to 10th	Day	17% 17% 29% 22% 10% 4	463
	11th to 20th	Day	16% 8% 27% 26% 17% 6%	487
	21st to end	Day	15% 8% 21% 26% 19% 11%	529
June	1st to 10th	Day	13% 7% 21% 29% 22% 8%	490
	11th to 20th	Day	8% 4 17% 31% 28% 12%	490
	21st to end	Day	12% 4 22% 30% 21% 11%	490
July	1st to 10th	Day	12% 4 14% 26% 29% 15%	485
	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% 29% 27% 11% 3	276
	11th to 20th	Day	16% 17% 33% 27% 7%	270
	21st to end	Day	16% 17% 34% 24% 8%	270
December	1st to 10th	Day	29% 18% 33% 17% 3	270
	11th to 20th	Day	25% 14% 33% 22% 6%	270
	21st to end	Day	27% 19% 35% 16% 4	297
January	1st to 10th	Night	25% 17% 28% 26% 4	760
	11th to 20th	Night	27% 19% 28% 21% 4	760
	21st to end	Night	23% 17% 32% 26% 3	836
February	1st to 10th	Night	24% 13% 31% 29% 4	760
	11th to 20th	Night	29% 17% 33% 19% 1	743
	21st to end	Night	32% 18% 29% 19% 2	628
March	1st to 10th	Night	24% 16% 28% 28% 4	760
	11th to 20th	Night	22% 18% 29% 24% 6% 1	760
	21st to end	Night	23% 14% 28% 25% 8%	836
April	1st to 10th	Night	19% 16% 27% 28% 9% 1	722
	11th to 20th	Night	18% 14% 29% 25% 14% 1	563
	21st to end	Night	17% 8% 29% 33% 13% 1	570
May	1st to 10th	Night	14% 9% 25% 33% 16% 2	570
	11th to 20th	Night	16% 6% 20% 35% 21% 3	561
	21st to end	Night	9% 3 16% 34% 33% 5%	617
June	1st to 10th	Night	10% 2 17% 35% 32% 4	570
	11th to 20th	Night	5% 3 13% 36% 34% 10%	570
	21st to end	Night	9% 2 13% 34% 35% 7%	570
July	1st to 10th	Night	10% 1 8% 29% 45% 7%	555
	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	18% 7% 19% 35% 19% 3	749
	11th to 20th	Night	17% 12% 27% 31% 13% 1	760
	21st to end	Night	21% 10% 24% 33% 13%	760
December	1st to 10th	Night	29% 12% 24% 28% 6%	760
	11th to 20th	Night	22% 13% 26% 30% 8%	760
	21st to end	Night	25% 15% 24% 31% 5%	836

Page generated at 2024-10-31 02:39:24. Version ac07

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