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 2024-03-23.

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	14% 8% 3 6% 6% 3 5% 5% 6% 7% 36%	79077
	Night	15% 8% 3 6% 5% 3 4 5% 5% 7% 39%	80817
Transparency	Day	46% 7% 10% 19% 15% 3	78800
	Night	45% 7% 10% 19% 16% 3	80613
Seeing	Day	19% 12% 23% 24% 17% 6%	13964
	Night	18% 9% 21% 29% 19% 3	24123

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% 12% 5% 8% 6% 3 4 4 6% 6% 29%	2836
	11th to 20th	Day	17% 12% 7% 8% 6% 4 4 4 4 4 30%	2840
	21st to end	Day	20% 16% 4 6% 4 2 3 3 4 5% 32%	3124
February	1st to 10th	Day	19% 12% 4 7% 5% 3 4 4 5% 5% 32%	1890
	11th to 20th	Day	22% 11% 5% 8% 3 3 3 3 3 7% 32%	1848
	21st to end	Day	22% 10% 3 6% 5% 3 4 4 5% 4 35%	1570
March	1st to 10th	Day	17% 10% 4 4 5% 2 4 4 4 6% 38%	1962
	11th to 20th	Day	18% 9% 4 6% 5% 3 5% 5% 5% 6% 34%	2090
	21st to end	Day	17% 11% 3 6% 5% 3 5% 4 5% 6% 34%	2200
April	1st to 10th	Day	11% 5% 3 6% 5% 4 5% 6% 7% 7% 42%	2029
	11th to 20th	Day	15% 7% 2 4 5% 3 4 5% 5% 7% 42%	2149
	21st to end	Day	15% 6% 3 5% 5% 4 4 5% 5% 8% 40%	2340
May	1st to 10th	Day	12% 6% 2 6% 5% 4 6% 6% 6% 6% 40%	2340
	11th to 20th	Day	15% 7% 3 6% 7% 4 7% 5% 5% 8% 34%	2301
	21st to end	Day	11% 6% 3 7% 7% 4 6% 6% 8% 9% 33%	2531
June	1st to 10th	Day	10% 6% 3 6% 6% 5% 7% 7% 7% 9% 35%	2340
	11th to 20th	Day	5% 5% 3 6% 7% 5% 6% 7% 8% 10% 38%	2340
	21st to end	Day	8% 6% 3 7% 6% 4 6% 7% 7% 11% 35%	2340
July	1st to 10th	Day	9% 7% 3 7% 7% 4 8% 7% 8% 10% 28%	2340
	11th to 20th	Day	11% 6% 3 5% 7% 5% 7% 7% 9% 10% 29%	2340
	21st to end	Day	9% 6% 3 7% 8% 5% 8% 8% 7% 10% 29%	2547
August	1st to 10th	Day	11% 6% 2 6% 7% 4 7% 8% 8% 10% 31%	2327
	11th to 20th	Day	11% 6% 3 6% 8% 5% 7% 7% 7% 9% 30%	2254
	21st to end	Day	11% 6% 3 6% 7% 4 7% 7% 7% 10% 31%	2376
September	1st to 10th	Day	12% 6% 3 5% 6% 4 5% 5% 6% 8% 39%	1988
	11th to 20th	Day	14% 7% 3 7% 6% 4 5% 4 5% 8% 37%	1980
	21st to end	Day	14% 5% 2 5% 5% 3 4 5% 7% 7% 44%	1980
October	1st to 10th	Day	12% 5% 2 4 4 3 4 4 5% 5% 52%	1980
	11th to 20th	Day	15% 6% 2 4 4 2 3 4 5% 7% 49%	1842
	21st to end	Day	15% 6% 2 4 4 2 3 4 5% 6% 49%	1974
November	1st to 10th	Day	13% 5% 2 5% 3 2 3 4 4 6% 54%	1672
	11th to 20th	Day	11% 8% 3 5% 5% 2 4 4 5% 7% 46%	1710
	21st to end	Day	14% 8% 4 5% 5% 2 4 5% 5% 6% 43%	1710
December	1st to 10th	Day	19% 11% 5% 5% 5% 3 4 5% 5% 6% 32%	1710
	11th to 20th	Day	16% 13% 2 6% 4 2 5% 5% 5% 6% 36%	2153
	21st to end	Day	14% 15% 4 6% 5% 3 4 4 5% 6% 33%	3124
January	1st to 10th	Night	19% 14% 5% 7% 5% 2 4 4 3 5% 31%	4109
	11th to 20th	Night	22% 10% 3 6% 7% 3 3 4 4 5% 33%	4120
	21st to end	Night	21% 13% 4 7% 5% 2 4 3 3 4 34%	4532
February	1st to 10th	Night	17% 10% 3 6% 5% 3 4 5% 5% 6% 35%	2285
	11th to 20th	Night	23% 11% 4 6% 5% 3 4 3 4 4 34%	2218
	21st to end	Night	22% 11% 4 6% 5% 3 5% 4 5% 5% 31%	1884
March	1st to 10th	Night	17% 11% 4 6% 4 2 4 4 4 6% 38%	2218
	11th to 20th	Night	19% 8% 4 6% 5% 3 4 4 5% 7% 36%	2090
	21st to end	Night	16% 10% 3 5% 5% 3 4 5% 5% 7% 36%	2201
April	1st to 10th	Night	14% 7% 3 4 4 2 4 4 5% 7% 46%	1944
	11th to 20th	Night	14% 7% 3 4 5% 2 4 4 5% 8% 46%	1758
	21st to end	Night	16% 6% 2 5% 5% 2 5% 4 5% 8% 43%	1620
May	1st to 10th	Night	13% 5% 3 6% 5% 3 5% 5% 7% 9% 40%	1620
	11th to 20th	Night	13% 7% 3 6% 5% 3 5% 5% 7% 8% 38%	1592
	21st to end	Night	7% 7% 3 6% 6% 4 6% 6% 6% 10% 39%	1744
June	1st to 10th	Night	7% 6% 3 5% 5% 4 6% 7% 7% 11% 38%	1620
	11th to 20th	Night	4 4 2 3 4 3 6% 7% 8% 13% 44%	1620
	21st to end	Night	7% 6% 3 5% 5% 4 6% 6% 6% 10% 42%	1620
July	1st to 10th	Night	9% 6% 4 7% 6% 4 7% 7% 8% 10% 33%	1620
	11th to 20th	Night	9% 4 3 5% 6% 4 5% 7% 8% 14% 36%	1620
	21st to end	Night	7% 6% 2 7% 5% 5% 7% 8% 9% 12% 34%	1771
August	1st to 10th	Night	8% 5% 2 6% 5% 3 6% 5% 8% 11% 40%	1611
	11th to 20th	Night	10% 6% 2 7% 7% 4 7% 6% 8% 9% 36%	1642
	21st to end	Night	10% 6% 3 6% 6% 4 6% 6% 7% 10% 36%	1980
September	1st to 10th	Night	11% 6% 2 5% 6% 3 5% 5% 6% 8% 42%	1952
	11th to 20th	Night	13% 6% 3 5% 5% 3 4 5% 6% 7% 42%	1980
	21st to end	Night	12% 5% 2 4 5% 3 5% 4 6% 7% 47%	1980
October	1st to 10th	Night	14% 5% 2 4 3 2 2 3 4 6% 54%	1980
	11th to 20th	Night	16% 5% 2 5% 4 3 3 3 4 4 50%	2116
	21st to end	Night	14% 5% 2 4 3 2 4 3 5% 6% 51%	2380
November	1st to 10th	Night	14% 7% 3 5% 4 2 3 3 4 5% 51%	2406
	11th to 20th	Night	15% 7% 3 5% 4 2 4 4 4 6% 46%	2470
	21st to end	Night	15% 7% 3 5% 4 3 4 4 4 7% 44%	2470
December	1st to 10th	Night	20% 12% 4 7% 4 3 4 4 4 6% 32%	2470
	11th to 20th	Night	17% 12% 4 8% 4 2 4 3 4 5% 37%	3042
	21st to end	Night	16% 14% 4 7% 6% 4 5% 5% 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	52% 8% 6% 13% 19% 3	2837
	11th to 20th	Day	56% 5% 5% 13% 18% 3	2840
	21st to end	Day	55% 3 7% 17% 17% 1	3124
February	1st to 10th	Day	55% 5% 6% 16% 16% 2	1890
	11th to 20th	Day	56% 4 5% 17% 15% 3	1858
	21st to end	Day	53% 4 7% 14% 17% 6%	1570
March	1st to 10th	Day	48% 5% 7% 17% 18% 6%	1962
	11th to 20th	Day	51% 6% 10% 16% 13% 3	2090
	21st to end	Day	50% 6% 11% 20% 12% 1	2200
April	1st to 10th	Day	40% 8% 9% 24% 16% 2	2029
	11th to 20th	Day	42% 5% 8% 18% 23% 4	2149
	21st to end	Day	45% 5% 10% 25% 13% 2	2340
May	1st to 10th	Day	43% 9% 10% 23% 12% 2	2340
	11th to 20th	Day	50% 7% 12% 19% 10% 1	2305
	21st to end	Day	45% 9% 13% 21% 11% 1	2531
June	1st to 10th	Day	46% 9% 14% 20% 10% 1	2340
	11th to 20th	Day	40% 10% 18% 19% 10% 2	2340
	21st to end	Day	42% 11% 15% 17% 11% 3	2340
July	1st to 10th	Day	48% 13% 14% 16% 9% 1	2275
	11th to 20th	Day	46% 11% 17% 13% 10% 3	2271
	21st to end	Day	47% 11% 17% 18% 7%	2405
August	1st to 10th	Day	46% 11% 17% 19% 6% 1	2314
	11th to 20th	Day	49% 11% 14% 15% 10% 1	2254
	21st to end	Day	48% 11% 12% 16% 10% 3	2376
September	1st to 10th	Day	43% 9% 11% 18% 15% 4	1988
	11th to 20th	Day	46% 8% 9% 20% 15% 2	1980
	21st to end	Day	39% 8% 9% 20% 19% 5%	1980
October	1st to 10th	Day	35% 6% 10% 23% 22% 5%	1980
	11th to 20th	Day	36% 5% 7% 24% 22% 7%	1842
	21st to end	Day	37% 4 5% 25% 23% 5%	1974
November	1st to 10th	Day	34% 4 7% 21% 28% 7%	1672
	11th to 20th	Day	38% 5% 5% 22% 24% 5%	1710
	21st to end	Day	41% 5% 6% 21% 21% 4	1710
December	1st to 10th	Day	54% 6% 7% 18% 13% 2	1710
	11th to 20th	Day	49% 4 9% 15% 19% 4	2150
	21st to end	Day	53% 4 7% 23% 12% 1	3124
January	1st to 10th	Night	55% 6% 5% 14% 16% 4	4109
	11th to 20th	Night	51% 9% 4 11% 18% 6%	4120
	21st to end	Night	56% 4 6% 13% 18% 2	4532
February	1st to 10th	Night	50% 5% 8% 17% 17% 3	2285
	11th to 20th	Night	56% 4 6% 16% 14% 4	2219
	21st to end	Night	54% 6% 7% 14% 15% 4	1884
March	1st to 10th	Night	49% 5% 8% 14% 19% 5%	2218
	11th to 20th	Night	49% 6% 9% 20% 14% 3	2090
	21st to end	Night	48% 6% 10% 22% 12% 1	2201
April	1st to 10th	Night	39% 5% 11% 23% 19% 3	1944
	11th to 20th	Night	40% 5% 9% 21% 21% 5%	1758
	21st to end	Night	41% 6% 11% 29% 13% 1	1620
May	1st to 10th	Night	41% 8% 15% 23% 12% 2	1620
	11th to 20th	Night	43% 9% 18% 20% 10% 1	1593
	21st to end	Night	40% 9% 15% 25% 9% 1	1745
June	1st to 10th	Night	40% 9% 19% 22% 10% 1	1620
	11th to 20th	Night	29% 11% 25% 25% 9% 1	1620
	21st to end	Night	37% 9% 17% 22% 10% 4	1620
July	1st to 10th	Night	45% 10% 16% 19% 10%	1575
	11th to 20th	Night	36% 11% 23% 17% 9% 3	1566
	21st to end	Night	38% 12% 21% 21% 7% 1	1672
August	1st to 10th	Night	37% 10% 22% 22% 9%	1600
	11th to 20th	Night	43% 10% 17% 17% 12% 1	1642
	21st to end	Night	41% 10% 19% 21% 9% 1	1980
September	1st to 10th	Night	40% 7% 15% 20% 15% 3	1952
	11th to 20th	Night	41% 7% 14% 18% 19%	1980
	21st to end	Night	37% 7% 9% 22% 20% 4	1980
October	1st to 10th	Night	34% 5% 9% 21% 25% 6%	1980
	11th to 20th	Night	38% 6% 8% 23% 20% 6%	2116
	21st to end	Night	35% 6% 5% 22% 25% 7%	2380
November	1st to 10th	Night	37% 5% 6% 20% 25% 7%	2406
	11th to 20th	Night	40% 5% 5% 21% 22% 7%	2470
	21st to end	Night	41% 5% 6% 24% 20% 4	2470
December	1st to 10th	Night	56% 5% 7% 16% 12% 3	2470
	11th to 20th	Night	50% 6% 6% 14% 21% 4	3044
	21st to end	Night	57% 5% 8% 17% 11% 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% 6%	470
April	1st to 10th	Day	20% 20% 23% 26% 10% 1	420
	11th to 20th	Day	21% 17% 27% 21% 12% 2	412
	21st to end	Day	22% 13% 26% 25% 10% 3	420
May	1st to 10th	Day	17% 16% 29% 22% 11% 4	423
	11th to 20th	Day	15% 8% 26% 27% 18% 7%	447
	21st to end	Day	15% 7% 20% 25% 21% 12%	485
June	1st to 10th	Day	13% 6% 20% 28% 23% 9%	450
	11th to 20th	Day	8% 4 16% 30% 28% 13%	450
	21st to end	Day	13% 4 21% 29% 21% 12%	450
July	1st to 10th	Day	12% 3 14% 25% 29% 16%	445
	11th to 20th	Day	12% 2 11% 30% 28% 16%	444
	21st to end	Day	10% 2 12% 29% 33% 15%	488
August	1st to 10th	Day	17% 3 14% 23% 29% 14%	446
	11th to 20th	Day	12% 3 13% 31% 30% 10%	439
	21st to end	Day	12% 3 16% 21% 32% 17%	495
September	1st to 10th	Day	10% 5% 14% 23% 36% 12%	450
	11th to 20th	Day	14% 5% 12% 25% 29% 14%	450
	21st to end	Day	15% 5% 14% 32% 28% 5%	450
October	1st to 10th	Day	15% 8% 19% 27% 24% 8%	450
	11th to 20th	Day	15% 14% 24% 28% 17% 2	450
	21st to end	Day	23% 9% 20% 32% 12% 3	489
November	1st to 10th	Day	20% 11% 29% 27% 10% 3	270
	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% 26% 9%	801
April	1st to 10th	Night	19% 15% 27% 30% 9% 1	684
	11th to 20th	Night	18% 13% 29% 25% 14% 1	533
	21st to end	Night	18% 8% 28% 32% 13% 1	540
May	1st to 10th	Night	14% 10% 25% 34% 16% 2	540
	11th to 20th	Night	16% 5% 19% 35% 22% 3	531
	21st to end	Night	9% 3 14% 34% 35% 5%	584
June	1st to 10th	Night	10% 2 16% 34% 34% 4	540
	11th to 20th	Night	5% 3 13% 34% 34% 11%	540
	21st to end	Night	9% 1 13% 33% 37% 7%	540
July	1st to 10th	Night	11% 1 8% 27% 46% 7%	525
	11th to 20th	Night	9% 2 9% 27% 43% 10%	522
	21st to end	Night	9% 1 8% 28% 46% 9%	591
August	1st to 10th	Night	8% 2 9% 28% 44% 9%	537
	11th to 20th	Night	10% 2 9% 34% 40% 6%	534
	21st to end	Night	13% 1 10% 23% 43% 11%	594
September	1st to 10th	Night	12% 2 10% 28% 40% 8%	692
	11th to 20th	Night	15% 4 10% 30% 35% 6%	720
	21st to end	Night	13% 2 17% 35% 30% 2	720
October	1st to 10th	Night	15% 5% 17% 25% 31% 7%	720
	11th to 20th	Night	18% 8% 23% 30% 19% 2	720
	21st to end	Night	18% 9% 21% 35% 16% 2	792
November	1st to 10th	Night	18% 6% 19% 36% 19% 3	740
	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

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