Starburst Meadows Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starburst Meadows Observatory clear sky chart from 2005-11-06 to 2025-11-18.

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	19% 8% 2 6% 4 4 4 3 5% 7% 38%	126037
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 38%	124329
Transparency	Day	29% 39% 7% 14% 9% 2	129557
	Night	30% 38% 7% 14% 9% 2	128897
Seeing	Day	21% 14% 33% 22% 8% 2	16304
	Night	22% 12% 31% 26% 9% 1	25232

By Month

Percentage Cloud Cover NE (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	14% 7% 3 7% 6% 5% 5% 3 5% 7% 39%	3597
	11th to 20th	Day	14% 7% 3 6% 3 4 4 4 4 7% 45%	3570
	21st to end	Day	14% 10% 2 5% 3 4 4 3 4 5% 47%	3960
February	1st to 10th	Day	17% 9% 3 6% 5% 4 4 4 6% 6% 37%	1775
	11th to 20th	Day	13% 9% 3 6% 5% 5% 5% 4 5% 5% 39%	1948
	21st to end	Day	16% 11% 3 6% 5% 4 4 4 5% 6% 37%	1650
March	1st to 10th	Day	23% 11% 2 6% 5% 5% 4 3 4 4 33%	4476
	11th to 20th	Day	18% 11% 2 6% 4 4 4 3 4 6% 37%	4888
	21st to end	Day	28% 8% 2 6% 3 3 4 3 5% 5% 33%	5592
April	1st to 10th	Day	20% 10% 3 6% 5% 3 4 4 5% 6% 35%	2400
	11th to 20th	Day	19% 6% 2 5% 4 5% 4 4 5% 7% 39%	2480
	21st to end	Day	23% 8% 2 5% 5% 4 4 3 5% 5% 36%	2600
May	1st to 10th	Day	33% 11% 3 6% 4 3 4 3 4 5% 23%	5886
	11th to 20th	Day	19% 9% 3 8% 5% 4 5% 4 6% 7% 30%	5923
	21st to end	Day	21% 6% 2 7% 4 4 5% 4 6% 8% 33%	6949
June	1st to 10th	Day	23% 7% 2 6% 5% 4 5% 4 5% 8% 33%	2800
	11th to 20th	Day	17% 7% 2 6% 5% 4 4 4 4 8% 39%	2800
	21st to end	Day	22% 7% 2 6% 5% 4 5% 4 6% 7% 33%	2800
July	1st to 10th	Day	18% 8% 3 6% 5% 5% 5% 4 6% 9% 31%	6360
	11th to 20th	Day	14% 8% 2 6% 4 4 4 4 6% 9% 37%	6360
	21st to end	Day	17% 5% 2 5% 3 3 4 4 6% 8% 44%	6926
August	1st to 10th	Day	15% 6% 3 7% 4 4 5% 3 6% 8% 37%	4242
	11th to 20th	Day	17% 7% 3 7% 4 4 4 4 6% 8% 35%	4175
	21st to end	Day	9% 4 1 5% 4 5% 5% 5% 7% 9% 47%	4487
September	1st to 10th	Day	13% 4 2 4 4 4 4 3 5% 7% 50%	2348
	11th to 20th	Day	12% 5% 2 5% 3 3 3 3 4 6% 55%	2200
	21st to end	Day	17% 6% 2 5% 3 3 4 4 5% 7% 45%	2200
October	1st to 10th	Day	18% 6% 3 6% 4 4 4 2 5% 6% 42%	2200
	11th to 20th	Day	18% 6% 2 6% 4 4 4 2 3 6% 43%	1931
	21st to end	Day	21% 8% 2 5% 3 3 3 3 4 6% 41%	1980
November	1st to 10th	Day	17% 6% 3 4 4 3 3 3 5% 6% 47%	1851
	11th to 20th	Day	20% 4 2 5% 4 3 3 4 5% 6% 45%	1863
	21st to end	Day	22% 9% 2 5% 3 3 3 2 4 6% 43%	1791
December	1st to 10th	Day	15% 11% 2 4 3 3 4 4 5% 6% 43%	2346
	11th to 20th	Day	18% 8% 2 4 3 3 3 2 4 5% 48%	2723
	21st to end	Day	22% 10% 3 6% 4 4 4 3 4 5% 35%	3960
January	1st to 10th	Night	12% 8% 3 7% 4 4 4 3 6% 6% 43%	6349
	11th to 20th	Night	13% 10% 4 10% 5% 5% 4 4 5% 5% 35%	6315
	21st to end	Night	15% 10% 3 7% 4 4 4 3 4 5% 41%	6996
February	1st to 10th	Night	17% 10% 3 6% 5% 5% 4 3 5% 6% 36%	2622
	11th to 20th	Night	14% 10% 3 6% 5% 5% 4 3 5% 5% 41%	2338
	21st to end	Night	14% 10% 4 6% 4 4 4 3 5% 5% 41%	1980
March	1st to 10th	Night	26% 10% 3 7% 4 4 4 3 4 5% 31%	5364
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 4 6% 7% 33%	5056
	21st to end	Night	25% 8% 3 5% 4 4 4 4 6% 5% 32%	5336
April	1st to 10th	Night	22% 10% 2 5% 4 4 5% 2 4 6% 35%	2000
	11th to 20th	Night	20% 6% 2 6% 5% 4 5% 5% 5% 6% 37%	1868
	21st to end	Night	23% 7% 3 6% 4 4 4 3 4 6% 36%	1800
May	1st to 10th	Night	32% 9% 3 8% 4 4 4 3 5% 6% 23%	4054
	11th to 20th	Night	19% 11% 3 7% 5% 5% 5% 4 6% 7% 29%	4000
	21st to end	Night	18% 10% 4 8% 5% 4 5% 4 6% 7% 30%	3926
June	1st to 10th	Night	21% 8% 2 8% 5% 4 4 4 4 7% 32%	1600
	11th to 20th	Night	17% 8% 2 5% 5% 3 5% 3 5% 8% 39%	1600
	21st to end	Night	22% 8% 3 6% 4 4 5% 3 6% 7% 33%	1600
July	1st to 10th	Night	14% 8% 4 7% 5% 5% 5% 5% 6% 8% 34%	3600
	11th to 20th	Night	15% 10% 3 8% 5% 4 5% 3 6% 8% 34%	3600
	21st to end	Night	12% 4 2 5% 4 4 4 5% 6% 8% 45%	3926
August	1st to 10th	Night	21% 7% 2 8% 5% 4 5% 4 6% 6% 32%	2873
	11th to 20th	Night	17% 9% 2 7% 5% 4 4 4 7% 8% 33%	2872
	21st to end	Night	11% 6% 2 5% 5% 4 3 4 5% 8% 46%	3408
September	1st to 10th	Night	12% 7% 2 5% 3 4 4 3 5% 5% 49%	2051
	11th to 20th	Night	15% 7% 1 5% 2 3 3 2 4 6% 52%	2200
	21st to end	Night	15% 7% 2 5% 3 4 3 3 5% 6% 47%	2200
October	1st to 10th	Night	18% 6% 2 6% 3 4 4 3 5% 6% 42%	2200
	11th to 20th	Night	18% 5% 2 6% 4 4 4 3 5% 7% 42%	2466
	21st to end	Night	24% 6% 2 6% 4 4 3 4 4 5% 38%	2860
November	1st to 10th	Night	17% 6% 2 5% 4 4 4 3 4 5% 46%	2667
	11th to 20th	Night	18% 6% 2 4 4 5% 4 3 5% 6% 44%	2692
	21st to end	Night	17% 7% 2 6% 4 4 3 3 4 7% 42%	2602
December	1st to 10th	Night	17% 11% 2 6% 3 3 4 3 5% 6% 39%	4839
	11th to 20th	Night	24% 7% 2 5% 3 3 3 3 4 4 43%	5473
	21st to end	Night	22% 12% 3 7% 4 3 3 2 4 4 37%	6996

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	33% 28% 7% 21% 11%	3598
	11th to 20th	Day	28% 28% 9% 23% 11% 2	3600
	21st to end	Day	30% 29% 7% 15% 15% 5%	3960
February	1st to 10th	Day	18% 62% 5% 7% 6% 2	1775
	11th to 20th	Day	18% 61% 4 8% 7% 2	1957
	21st to end	Day	17% 62% 3 9% 7% 2	1650
March	1st to 10th	Day	42% 29% 5% 7% 10% 7%	4479
	11th to 20th	Day	36% 30% 11% 13% 8% 2	4888
	21st to end	Day	41% 29% 3 12% 11% 4	5592
April	1st to 10th	Day	21% 62% 2 7% 6% 2	2400
	11th to 20th	Day	18% 62% 4 9% 6% 2	2480
	21st to end	Day	20% 62% 2 8% 7%	2600
May	1st to 10th	Day	48% 34% 7% 9% 2	5897
	11th to 20th	Day	39% 32% 11% 13% 4 1	5927
	21st to end	Day	36% 31% 11% 14% 7%	6949
June	1st to 10th	Day	17% 62% 5% 10% 6%	2800
	11th to 20th	Day	16% 62% 5% 10% 8% 1	2800
	21st to end	Day	17% 61% 4 12% 6% 1	2800
July	1st to 10th	Day	37% 29% 9% 17% 8%	6290
	11th to 20th	Day	33% 28% 10% 18% 10% 1	6285
	21st to end	Day	29% 27% 10% 22% 12%	6728
August	1st to 10th	Day	30% 38% 10% 17% 5%	4228
	11th to 20th	Day	32% 39% 11% 14% 4	4214
	21st to end	Day	17% 39% 11% 18% 14% 1	4487
September	1st to 10th	Day	12% 58% 7% 15% 8%	2348
	11th to 20th	Day	16% 57% 4 13% 9% 1	2200
	21st to end	Day	16% 57% 3 15% 8% 1	2200
October	1st to 10th	Day	29% 38% 6% 17% 9% 1	3590
	11th to 20th	Day	18% 36% 6% 22% 18%	3121
	21st to end	Day	21% 36% 8% 19% 14% 2	3180
November	1st to 10th	Day	19% 54% 7% 11% 8% 1	1851
	11th to 20th	Day	18% 55% 3 9% 11% 3	1863
	21st to end	Day	19% 57% 6% 10% 8% 1	1791
December	1st to 10th	Day	23% 36% 11% 21% 8%	2346
	11th to 20th	Day	27% 31% 8% 13% 12% 9%	2723
	21st to end	Day	38% 29% 5% 13% 12% 3	3960
January	1st to 10th	Night	30% 27% 8% 24% 9% 2	6349
	11th to 20th	Night	36% 27% 10% 16% 9% 2	6360
	21st to end	Night	34% 29% 4 14% 13% 5%	6996
February	1st to 10th	Night	19% 62% 5% 6% 6% 2	2622
	11th to 20th	Night	17% 61% 4 8% 9% 1	2340
	21st to end	Night	19% 61% 2 9% 6% 2	1980
March	1st to 10th	Night	43% 29% 5% 7% 9% 6%	5374
	11th to 20th	Night	35% 31% 12% 13% 7% 1	5057
	21st to end	Night	41% 29% 3 9% 14% 4	5336
April	1st to 10th	Night	21% 62% 2 6% 7% 2	2000
	11th to 20th	Night	20% 63% 3 7% 7% 1	1868
	21st to end	Night	20% 62% 4 6% 6% 2	1800
May	1st to 10th	Night	48% 33% 8% 8% 3	4060
	11th to 20th	Night	39% 32% 9% 15% 5%	4001
	21st to end	Night	38% 33% 9% 14% 6% 1	3927
June	1st to 10th	Night	19% 63% 4 9% 6%	1600
	11th to 20th	Night	15% 62% 7% 9% 6% 1	1600
	21st to end	Night	18% 61% 5% 11% 5% 1	1600
July	1st to 10th	Night	34% 28% 10% 18% 10%	3560
	11th to 20th	Night	38% 28% 7% 16% 10%	3552
	21st to end	Night	26% 28% 12% 25% 9%	3809
August	1st to 10th	Night	37% 38% 9% 12% 5%	2863
	11th to 20th	Night	33% 39% 9% 13% 5%	2899
	21st to end	Night	21% 39% 10% 17% 12%	3408
September	1st to 10th	Night	14% 58% 5% 14% 8%	2051
	11th to 20th	Night	18% 57% 4 12% 9% 1	2200
	21st to end	Night	16% 57% 4 16% 7% 1	2200
October	1st to 10th	Night	26% 38% 10% 15% 10% 1	3590
	11th to 20th	Night	17% 36% 6% 21% 19% 1	4015
	21st to end	Night	22% 36% 6% 20% 13% 2	4610
November	1st to 10th	Night	20% 53% 4 13% 8% 1	2667
	11th to 20th	Night	20% 55% 4 10% 10% 2	2692
	21st to end	Night	18% 57% 6% 10% 8% 1	2602
December	1st to 10th	Night	28% 36% 5% 22% 9%	4839
	11th to 20th	Night	32% 32% 7% 11% 14% 3	5474
	21st to end	Night	39% 27% 6% 13% 14% 1	6996

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	22% 29% 28% 17% 5%	200
	11th to 20th	Day	27% 20% 27% 21% 5% 1	200
	21st to end	Day	17% 22% 36% 18% 6%	220
February	1st to 10th	Day	25% 18% 35% 18% 3	375
	11th to 20th	Day	22% 23% 40% 14% 1	496
	21st to end	Day	22% 19% 36% 18% 4	414
March	1st to 10th	Day	24% 19% 37% 17% 3	500
	11th to 20th	Day	20% 23% 38% 15% 3 1	500
	21st to end	Day	26% 23% 31% 13% 5% 2	550
April	1st to 10th	Day	28% 22% 30% 15% 4 2	500
	11th to 20th	Day	25% 18% 34% 16% 6% 2	492
	21st to end	Day	28% 15% 34% 18% 4 2	500
May	1st to 10th	Day	29% 17% 31% 17% 5% 1	503
	11th to 20th	Day	20% 13% 41% 17% 7% 1	527
	21st to end	Day	21% 13% 35% 25% 5% 2	573
June	1st to 10th	Day	21% 12% 35% 23% 8% 2	530
	11th to 20th	Day	17% 13% 38% 22% 8% 2	530
	21st to end	Day	23% 9% 34% 23% 9% 1	530
July	1st to 10th	Day	20% 6% 34% 27% 10% 2	525
	11th to 20th	Day	17% 6% 33% 30% 12% 3	524
	21st to end	Day	16% 6% 33% 30% 12% 3	576
August	1st to 10th	Day	14% 6% 30% 33% 14% 3	526
	11th to 20th	Day	16% 6% 29% 30% 13% 6%	519
	21st to end	Day	11% 8% 32% 29% 15% 5%	583
September	1st to 10th	Day	15% 7% 31% 29% 14% 3	530
	11th to 20th	Day	15% 8% 32% 24% 14% 8%	530
	21st to end	Day	19% 9% 32% 23% 12% 5%	530
October	1st to 10th	Day	20% 13% 24% 25% 12% 5%	530
	11th to 20th	Day	21% 15% 28% 23% 10% 3	423
	21st to end	Day	28% 14% 28% 22% 8% 1	462
November	1st to 10th	Day	21% 19% 28% 22% 8% 2	425
	11th to 20th	Day	22% 20% 32% 19% 5% 1	421
	21st to end	Day	26% 19% 26% 22% 6% 1	400
December	1st to 10th	Day	24% 16% 35% 18% 7%	240
	11th to 20th	Day	26% 26% 30% 15% 5%	200
	21st to end	Day	25% 22% 29% 18% 6%	220
January	1st to 10th	Night	21% 20% 36% 20% 4	800
	11th to 20th	Night	23% 19% 35% 19% 4	800
	21st to end	Night	18% 20% 39% 20% 3	880
February	1st to 10th	Night	22% 19% 33% 22% 3	800
	11th to 20th	Night	21% 21% 37% 18% 2	783
	21st to end	Night	20% 17% 35% 23% 5%	660
March	1st to 10th	Night	24% 18% 37% 20% 2	800
	11th to 20th	Night	21% 15% 35% 21% 8%	800
	21st to end	Night	24% 15% 34% 22% 4 1	880
April	1st to 10th	Night	27% 14% 33% 21% 4	800
	11th to 20th	Night	21% 12% 35% 26% 6%	684
	21st to end	Night	26% 11% 30% 27% 6% 1	600
May	1st to 10th	Night	25% 8% 31% 27% 8% 2	600
	11th to 20th	Night	24% 8% 32% 28% 8% 1	585
	21st to end	Night	26% 5% 24% 33% 11% 1	433
June	1st to 10th	Night	26% 6% 22% 32% 12% 2	400
	11th to 20th	Night	20% 3 26% 35% 15% 1	400
	21st to end	Night	25% 4 24% 35% 12% 1	400
July	1st to 10th	Night	19% 4 18% 42% 15% 1	390
	11th to 20th	Night	19% 2 21% 37% 19% 2	388
	21st to end	Night	16% 3 18% 42% 20% 1	438
August	1st to 10th	Night	16% 3 21% 41% 18% 1	568
	11th to 20th	Night	16% 5% 19% 39% 20% 2	592
	21st to end	Night	15% 4 22% 37% 20% 2	767
September	1st to 10th	Night	14% 3 28% 34% 19% 1	800
	11th to 20th	Night	17% 5% 27% 27% 20% 3	800
	21st to end	Night	18% 6% 25% 33% 16% 3	800
October	1st to 10th	Night	22% 8% 24% 28% 18% 1	800
	11th to 20th	Night	20% 11% 31% 26% 11% 2	800
	21st to end	Night	28% 11% 29% 25% 7%	880
November	1st to 10th	Night	21% 12% 32% 27% 7% 2	820
	11th to 20th	Night	21% 16% 34% 22% 6% 1	829
	21st to end	Night	21% 18% 33% 22% 5%	802
December	1st to 10th	Night	26% 14% 36% 18% 6%	900
	11th to 20th	Night	25% 19% 33% 20% 3	873
	21st to end	Night	27% 16% 35% 19% 3	880

Page generated at 2025-11-15 00:56:01. Version ac07

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