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 2026-10-29.

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% 8% 36%	148991
	Night	14% 9% 3 7% 4 4 4 4 6% 7% 37%	143098
Transparency	Day	29% 36% 9% 15% 9% 2	152741
	Night	29% 36% 9% 14% 10% 3	147419
Seeing	Day	19% 12% 24% 23% 16% 6%	17508
	Night	18% 10% 22% 29% 18% 3	27485

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	19% 14% 3 7% 3 3 3 3 5% 5% 34%	5258
	11th to 20th	Day	12% 12% 6% 9% 4 4 3 2 3 4 41%	5280
	21st to end	Day	20% 13% 4 8% 4 3 3 2 4 5% 33%	5780
February	1st to 10th	Day	18% 13% 4 8% 4 4 4 3 5% 5% 33%	2090
	11th to 20th	Day	23% 12% 4 8% 3 3 3 3 4 6% 31%	2048
	21st to end	Day	20% 10% 4 7% 4 5% 3 3 5% 4 36%	1730
March	1st to 10th	Day	19% 12% 4 6% 4 4 4 3 4 6% 34%	4739
	11th to 20th	Day	13% 8% 3 6% 4 3 3 3 4 6% 46%	5090
	21st to end	Day	17% 8% 2 6% 4 4 4 3 5% 6% 41%	5586
April	1st to 10th	Day	12% 6% 3 7% 4 5% 6% 4 8% 6% 41%	2368
	11th to 20th	Day	14% 7% 2 5% 5% 4 4 4 6% 7% 44%	2512
	21st to end	Day	15% 7% 2 6% 4 4 4 4 5% 8% 40%	2730
May	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 7% 8% 32%	7616
	11th to 20th	Day	13% 8% 3 8% 6% 6% 6% 5% 6% 7% 32%	7626
	21st to end	Day	15% 10% 4 10% 6% 6% 6% 5% 6% 8% 24%	8391
June	1st to 10th	Day	10% 7% 3 7% 6% 6% 6% 6% 7% 9% 35%	2730
	11th to 20th	Day	5% 5% 2 7% 6% 7% 6% 6% 8% 11% 36%	2730
	21st to end	Day	8% 6% 2 8% 5% 6% 5% 6% 8% 11% 35%	2730
July	1st to 10th	Day	6% 5% 2 7% 5% 6% 7% 6% 9% 12% 36%	7680
	11th to 20th	Day	11% 7% 3 9% 6% 6% 7% 6% 9% 10% 27%	7680
	21st to end	Day	12% 8% 3 9% 7% 7% 8% 6% 8% 11% 22%	8340
August	1st to 10th	Day	9% 7% 3 9% 6% 7% 7% 6% 9% 11% 28%	6014
	11th to 20th	Day	7% 5% 2 6% 5% 5% 5% 5% 8% 12% 39%	5815
	21st to end	Day	5% 4 2 5% 4 4 5% 5% 7% 9% 51%	6080
September	1st to 10th	Day	11% 5% 3 6% 5% 5% 5% 4 7% 8% 41%	2318
	11th to 20th	Day	13% 6% 2 8% 5% 5% 4 3 5% 8% 40%	2310
	21st to end	Day	14% 5% 2 6% 4 4 4 4 6% 7% 43%	2310
October	1st to 10th	Day	11% 5% 2 5% 4 3 4 3 5% 5% 53%	2310
	11th to 20th	Day	13% 6% 1 4 3 2 3 3 4 6% 53%	2148
	21st to end	Day	14% 6% 2 4 3 3 3 3 5% 6% 50%	2272
November	1st to 10th	Day	12% 6% 2 5% 2 3 3 3 5% 5% 53%	1852
	11th to 20th	Day	11% 8% 2 6% 4 3 3 4 6% 7% 46%	1890
	21st to end	Day	14% 9% 3 5% 4 3 4 4 6% 5% 42%	1890
December	1st to 10th	Day	15% 9% 3 5% 4 4 4 4 5% 5% 40%	3020
	11th to 20th	Day	18% 15% 4 8% 4 4 4 3 4 5% 30%	3463
	21st to end	Day	13% 14% 5% 7% 4 4 5% 3 5% 7% 33%	4565
January	1st to 10th	Night	18% 12% 4 8% 3 3 3 3 4 6% 36%	7635
	11th to 20th	Night	19% 10% 3 7% 5% 3 3 2 4 5% 40%	7680
	21st to end	Night	18% 12% 4 8% 4 4 4 3 4 4 36%	8401
February	1st to 10th	Night	17% 11% 3 7% 4 4 4 4 5% 6% 35%	2525
	11th to 20th	Night	23% 12% 4 7% 4 4 3 3 4 4 33%	2458
	21st to end	Night	21% 11% 3 7% 4 5% 4 3 5% 5% 32%	2076
March	1st to 10th	Night	21% 12% 3 6% 4 3 3 3 4 7% 34%	5320
	11th to 20th	Night	14% 5% 2 5% 3 3 4 3 5% 8% 47%	5090
	21st to end	Night	12% 9% 3 7% 5% 4 4 3 5% 7% 41%	5588
April	1st to 10th	Night	13% 8% 2 5% 4 3 4 3 6% 8% 44%	2268
	11th to 20th	Night	13% 7% 2 5% 4 3 3 3 5% 7% 47%	2055
	21st to end	Night	15% 6% 2 5% 4 4 5% 3 6% 7% 43%	1890
May	1st to 10th	Night	15% 9% 3 8% 5% 5% 5% 5% 7% 9% 29%	5237
	11th to 20th	Night	15% 9% 3 8% 5% 4 4 4 6% 7% 35%	5234
	21st to end	Night	15% 10% 3 9% 6% 6% 6% 5% 6% 8% 26%	5761
June	1st to 10th	Night	8% 7% 2 6% 5% 6% 6% 5% 7% 10% 38%	1890
	11th to 20th	Night	5% 4 2 5% 4 5% 5% 6% 9% 13% 43%	1890
	21st to end	Night	8% 6% 2 6% 5% 6% 5% 5% 7% 9% 41%	1890
July	1st to 10th	Night	8% 5% 3 7% 5% 5% 6% 5% 9% 11% 34%	5278
	11th to 20th	Night	11% 7% 3 8% 6% 6% 6% 5% 8% 11% 30%	5277
	21st to end	Night	11% 9% 4 9% 6% 7% 6% 6% 8% 11% 23%	5736
August	1st to 10th	Night	8% 6% 3 9% 6% 6% 7% 5% 8% 11% 30%	4135
	11th to 20th	Night	9% 5% 2 6% 4 4 4 4 7% 11% 44%	4226
	21st to end	Night	6% 5% 2 6% 4 5% 5% 5% 7% 11% 45%	5046
September	1st to 10th	Night	10% 6% 2 6% 5% 5% 5% 4 7% 8% 42%	2279
	11th to 20th	Night	11% 6% 2 6% 5% 4 5% 3 6% 7% 43%	2310
	21st to end	Night	12% 6% 3 5% 4 5% 4 3 5% 7% 45%	2310
October	1st to 10th	Night	14% 5% 2 5% 3 3 3 2 4 6% 53%	2310
	11th to 20th	Night	15% 5% 2 5% 3 3 3 2 4 4 54%	2470
	21st to end	Night	14% 6% 2 5% 3 3 3 3 5% 6% 52%	2742
November	1st to 10th	Night	13% 7% 3 6% 3 3 3 3 4 5% 51%	2666
	11th to 20th	Night	15% 8% 2 5% 3 3 4 3 4 6% 47%	2730
	21st to end	Night	16% 9% 2 6% 4 4 3 3 4 7% 43%	2730
December	1st to 10th	Night	18% 13% 3 7% 4 3 3 3 4 5% 37%	4380
	11th to 20th	Night	20% 12% 5% 9% 4 3 4 3 4 5% 32%	4952
	21st to end	Night	14% 13% 4 8% 4 5% 4 4 5% 7% 31%	6633

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	39% 24% 7% 16% 12% 1	5259
	11th to 20th	Day	35% 23% 2 10% 25% 4	5280
	21st to end	Day	44% 22% 4 15% 12% 3	5780
February	1st to 10th	Day	23% 59% 3 8% 6% 1	2090
	11th to 20th	Day	25% 58% 2 7% 7% 1	2058
	21st to end	Day	22% 59% 2 7% 8% 2	1730
March	1st to 10th	Day	38% 30% 6% 10% 10% 7%	4739
	11th to 20th	Day	24% 29% 4 14% 18% 12%	5090
	21st to end	Day	30% 30% 5% 24% 10% 2	5586
April	1st to 10th	Day	19% 61% 5% 9% 6%	2368
	11th to 20th	Day	18% 60% 4 10% 6% 1	2512
	21st to end	Day	17% 60% 5% 11% 6% 1	2730
May	1st to 10th	Day	39% 25% 11% 19% 7%	7651
	11th to 20th	Day	37% 26% 11% 19% 6%	7630
	21st to end	Day	45% 27% 9% 11% 7% 1	8405
June	1st to 10th	Day	18% 61% 6% 9% 5%	2730
	11th to 20th	Day	16% 62% 9% 9% 4	2730
	21st to end	Day	17% 61% 8% 9% 4	2730
July	1st to 10th	Day	26% 30% 21% 17% 6%	7615
	11th to 20th	Day	36% 30% 18% 13% 1	7611
	21st to end	Day	43% 27% 13% 11% 5%	8156
August	1st to 10th	Day	34% 35% 15% 13% 3	6001
	11th to 20th	Day	20% 32% 23% 20% 5%	5854
	21st to end	Day	16% 30% 13% 32% 9%	6079
September	1st to 10th	Day	16% 57% 6% 11% 9% 1	2318
	11th to 20th	Day	16% 56% 7% 13% 7%	2310
	21st to end	Day	17% 56% 7% 11% 8%	2310
October	1st to 10th	Day	15% 36% 5% 13% 22% 9%	3700
	11th to 20th	Day	13% 35% 3 17% 20% 13%	3414
	21st to end	Day	14% 36% 4 22% 15% 9%	3598
November	1st to 10th	Day	20% 53% 4 10% 10% 2	1852
	11th to 20th	Day	17% 55% 3 11% 11% 3	1890
	21st to end	Day	20% 55% 4 10% 9% 2	1890
December	1st to 10th	Day	27% 38% 4 11% 18% 2	3020
	11th to 20th	Day	39% 33% 6% 9% 11% 2	3460
	21st to end	Day	37% 28% 9% 19% 7% 1	4565
January	1st to 10th	Night	39% 24% 9% 17% 9% 2	7636
	11th to 20th	Night	35% 24% 2 12% 22% 5%	7680
	21st to end	Night	41% 23% 6% 11% 14% 5%	8401
February	1st to 10th	Night	21% 60% 3 9% 6% 2	2525
	11th to 20th	Night	26% 58% 3 7% 6% 1	2459
	21st to end	Night	21% 60% 3 8% 6% 3	2076
March	1st to 10th	Night	38% 30% 6% 13% 11% 3	5320
	11th to 20th	Night	20% 30% 5% 16% 17% 12%	5090
	21st to end	Night	30% 29% 9% 21% 10% 2	5588
April	1st to 10th	Night	17% 60% 6% 9% 6% 1	2268
	11th to 20th	Night	17% 60% 4 10% 6% 2	2055
	21st to end	Night	17% 59% 5% 12% 7%	1890
May	1st to 10th	Night	40% 26% 12% 17% 5% 1	5264
	11th to 20th	Night	37% 25% 11% 18% 9%	5235
	21st to end	Night	43% 29% 10% 13% 5%	5771
June	1st to 10th	Night	16% 61% 8% 10% 5% 1	1890
	11th to 20th	Night	12% 62% 11% 10% 4	1890
	21st to end	Night	15% 61% 8% 11% 4	1890
July	1st to 10th	Night	28% 30% 19% 20% 4	5235
	11th to 20th	Night	35% 30% 21% 14% 1	5226
	21st to end	Night	42% 29% 15% 8% 5% 1	5606
August	1st to 10th	Night	34% 34% 15% 14% 3	4124
	11th to 20th	Night	19% 30% 23% 20% 7%	4253
	21st to end	Night	19% 31% 13% 29% 8%	5046
September	1st to 10th	Night	16% 56% 8% 10% 10% 1	2279
	11th to 20th	Night	15% 57% 8% 12% 7%	2310
	21st to end	Night	18% 56% 7% 10% 8%	2310
October	1st to 10th	Night	18% 36% 5% 16% 18% 8%	3700
	11th to 20th	Night	13% 36% 3 15% 19% 14%	3943
	21st to end	Night	13% 35% 3 21% 18% 12%	4366
November	1st to 10th	Night	21% 54% 4 11% 8% 1	2666
	11th to 20th	Night	19% 55% 2 10% 11% 4	2730
	21st to end	Night	21% 55% 2 12% 9% 1	2730
December	1st to 10th	Night	34% 37% 3 9% 16% 1	4380
	11th to 20th	Night	37% 34% 5% 11% 12% 2	4954
	21st to end	Night	38% 28% 11% 14% 9% 1	6633

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	27% 28% 28% 14% 2	330
	11th to 20th	Day	30% 32% 23% 11% 4 1	330
	21st to end	Day	26% 26% 35% 11% 2	363
February	1st to 10th	Day	28% 25% 30% 15% 2	330
	11th to 20th	Day	41% 26% 24% 8% 1	330
	21st to end	Day	39% 22% 30% 8% 1	273
March	1st to 10th	Day	30% 20% 30% 14% 6%	398
	11th to 20th	Day	26% 22% 34% 14% 4	540
	21st to end	Day	27% 19% 34% 16% 4	594
April	1st to 10th	Day	21% 20% 26% 24% 9% 1	540
	11th to 20th	Day	21% 17% 30% 20% 11% 2	532
	21st to end	Day	21% 15% 29% 23% 9% 3	540
May	1st to 10th	Day	20% 18% 28% 21% 9% 3	543
	11th to 20th	Day	17% 9% 27% 25% 16% 5%	567
	21st to end	Day	16% 11% 22% 24% 17% 9%	617
June	1st to 10th	Day	13% 8% 23% 29% 21% 7%	570
	11th to 20th	Day	8% 5% 20% 31% 26% 11%	570
	21st to end	Day	11% 4 21% 29% 23% 11%	570
July	1st to 10th	Day	11% 4 15% 28% 28% 15%	565
	11th to 20th	Day	12% 4 13% 30% 27% 15%	564
	21st to end	Day	13% 3 13% 27% 30% 13%	620
August	1st to 10th	Day	17% 5% 16% 23% 27% 12%	566
	11th to 20th	Day	11% 3 16% 31% 30% 9%	559
	21st to end	Day	11% 3 17% 22% 32% 15%	627
September	1st to 10th	Day	10% 5% 16% 24% 34% 11%	570
	11th to 20th	Day	12% 5% 13% 28% 30% 13%	570
	21st to end	Day	16% 6% 15% 31% 26% 4	570
October	1st to 10th	Day	14% 8% 21% 29% 21% 6%	570
	11th to 20th	Day	14% 12% 25% 29% 17% 2	570
	21st to end	Day	22% 9% 22% 31% 13% 3	607
November	1st to 10th	Day	20% 11% 32% 26% 8% 2	330
	11th to 20th	Day	17% 19% 32% 25% 6%	330
	21st to end	Day	20% 16% 35% 22% 7%	330
December	1st to 10th	Day	30% 18% 34% 15% 3	330
	11th to 20th	Day	26% 16% 32% 21% 5%	330
	21st to end	Day	27% 19% 33% 16% 5%	363
January	1st to 10th	Night	25% 18% 28% 25% 4	840
	11th to 20th	Night	28% 19% 30% 20% 4	840
	21st to end	Night	23% 17% 34% 24% 2	924
February	1st to 10th	Night	25% 13% 31% 28% 4	840
	11th to 20th	Night	30% 18% 32% 17% 1	823
	21st to end	Night	32% 17% 30% 19% 2	692
March	1st to 10th	Night	25% 16% 29% 26% 4	840
	11th to 20th	Night	22% 18% 30% 23% 6% 1	840
	21st to end	Night	22% 15% 31% 24% 8%	924
April	1st to 10th	Night	19% 16% 28% 29% 8% 1	798
	11th to 20th	Night	18% 13% 31% 25% 12%	623
	21st to end	Night	17% 8% 28% 33% 12% 1	630
May	1st to 10th	Night	15% 10% 27% 31% 15% 2	630
	11th to 20th	Night	16% 6% 21% 34% 19% 3	621
	21st to end	Night	11% 3 18% 33% 30% 5%	683
June	1st to 10th	Night	11% 3 17% 36% 31% 3	630
	11th to 20th	Night	6% 4 13% 36% 32% 9%	630
	21st to end	Night	9% 2 13% 34% 36% 6%	630
July	1st to 10th	Night	10% 1 8% 29% 45% 7%	615
	11th to 20th	Night	10% 3 8% 26% 44% 9%	612
	21st to end	Night	11% 2 8% 28% 42% 8%	690
August	1st to 10th	Night	9% 2 10% 30% 41% 8%	627
	11th to 20th	Night	10% 3 9% 34% 38% 5%	624
	21st to end	Night	12% 1 11% 25% 41% 10%	693
September	1st to 10th	Night	11% 3 11% 30% 38% 7%	809
	11th to 20th	Night	14% 3 9% 33% 35% 5%	840
	21st to end	Night	14% 3 17% 35% 28% 2	840
October	1st to 10th	Night	15% 5% 18% 28% 28% 6%	840
	11th to 20th	Night	17% 8% 23% 32% 18% 2	840
	21st to end	Night	17% 8% 22% 36% 15% 2	913
November	1st to 10th	Night	17% 7% 22% 35% 17% 2	820
	11th to 20th	Night	17% 13% 27% 31% 12% 1	840
	21st to end	Night	22% 10% 25% 31% 12%	840
December	1st to 10th	Night	29% 13% 26% 27% 6%	840
	11th to 20th	Night	23% 13% 28% 29% 7%	840
	21st to end	Night	25% 16% 24% 31% 4	924

Page generated at 2026-10-26 03:37:50. Version ac07

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