Big Meadow
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Meadow clear sky chart from 2005-11-06 to 2026-04-17.

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	4 6% 2 3 2 2 3 2 4 5% 67%	139901
	Night	5% 5% 2 4 2 2 3 2 4 5% 66%	139684
Transparency	Day	23% 2 7% 21% 28% 20%	134971
	Night	23% 2 7% 22% 27% 19%	135589
Seeing	Day	11% 14% 35% 29% 9% 2	17131
	Night	9% 5% 25% 36% 22% 3	26801

By Month

Percentage Cloud Cover SW (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	7% 10% 2 5% 3 3 3 2 5% 6% 53%	4722
	11th to 20th	Day	6% 4 1 4 3 2 3 3 4 5% 65%	4998
	21st to end	Day	6% 7% 4 6% 4 3 3 3 5% 7% 51%	5843
February	1st to 10th	Day	11% 9% 4 5% 2 2 3 3 4 5% 52%	2077
	11th to 20th	Day	6% 14% 4 5% 3 4 3 3 3 5% 49%	2050
	21st to end	Day	10% 14% 3 6% 3 3 3 2 5% 7% 45%	1730
March	1st to 10th	Day	6% 16% 5% 8% 3 3 3 3 5% 8% 39%	4618
	11th to 20th	Day	5% 12% 3 6% 4 3 3 3 5% 8% 50%	4874
	21st to end	Day	8% 17% 4 5% 3 3 3 3 4 6% 43%	6087
April	1st to 10th	Day	7% 10% 3 5% 3 3 3 3 5% 7% 50%	2520
	11th to 20th	Day	9% 11% 2 5% 3 3 2 3 5% 7% 50%	2442
	21st to end	Day	8% 8% 2 3 2 3 3 3 6% 8% 53%	2400
May	1st to 10th	Day	5% 6% 2 3 3 2 3 2 3 5% 66%	5677
	11th to 20th	Day	3 7% 2 3 2 2 2 2 4 6% 67%	5841
	21st to end	Day	3 4 1 2 2 2 2 2 3 5% 75%	6716
June	1st to 10th	Day	3 3 2 3 3 3 3 3 5% 7% 64%	2800
	11th to 20th	Day	2 2 2 1 1 2 2 3 5% 80%	2800
	21st to end	Day	1 2 1 2 2 2 2 2 2 4 82%	2800
July	1st to 10th	Day	1 1 1 1 1 2 2 90%	6319
	11th to 20th	Day	1 2 1 2 2 2 2 2 2 4 81%	6320
	21st to end	Day	1 1 1 1 1 1 1 3 4 84%	6603
August	1st to 10th	Day	1 1 1 1 2 2 1 2 3 85%	5346
	11th to 20th	Day	1 1 1 1 1 1 1 1 2 90%	5364
	21st to end	Day	2 2 1 2 2 2 2 2 3 5% 79%	5984
September	1st to 10th	Day	1 1 2 1 2 2 1 4 4 81%	2400
	11th to 20th	Day	2 2 1 3 2 2 1 2 3 4 79%	2305
	21st to end	Day	2 3 1 2 2 1 2 2 3 5% 77%	2200
October	1st to 10th	Day	2 3 1 2 2 2 3 2 3 5% 73%	3519
	11th to 20th	Day	2 2 1 3 2 3 2 2 3 3 77%	3261
	21st to end	Day	3 4 1 3 3 3 3 2 4 6% 67%	3463
November	1st to 10th	Day	4 8% 2 3 2 2 2 3 4 7% 62%	1854
	11th to 20th	Day	7% 5% 1 3 3 2 3 3 6% 6% 61%	1890
	21st to end	Day	6% 7% 3 4 3 3 3 3 4 7% 59%	1890
December	1st to 10th	Day	6% 4 1 3 3 3 4 3 4 6% 63%	2988
	11th to 20th	Day	11% 9% 2 4 3 3 3 3 5% 8% 48%	3108
	21st to end	Day	11% 9% 2 5% 4 4 4 4 7% 9% 42%	4092
January	1st to 10th	Night	7% 11% 3 5% 2 3 2 2 4 5% 55%	8172
	11th to 20th	Night	7% 6% 2 3 2 2 3 2 4 6% 62%	7960
	21st to end	Night	6% 8% 3 6% 4 4 5% 3 5% 8% 48%	8371
February	1st to 10th	Night	11% 9% 2 4 3 3 3 2 4 6% 52%	2541
	11th to 20th	Night	7% 11% 2 4 2 3 3 2 4 7% 54%	2458
	21st to end	Night	9% 9% 3 7% 3 3 3 2 4 6% 51%	2076
March	1st to 10th	Night	6% 14% 5% 8% 3 3 3 3 4 6% 44%	5496
	11th to 20th	Night	4 9% 3 6% 3 4 4 4 4 6% 53%	5343
	21st to end	Night	11% 13% 3 5% 3 3 3 3 4 7% 44%	5128
April	1st to 10th	Night	7% 8% 3 3 3 3 3 2 5% 7% 55%	2100
	11th to 20th	Night	6% 8% 2 5% 3 3 3 2 5% 6% 58%	2039
	21st to end	Night	4 7% 1 4 2 2 3 3 5% 7% 61%	2000
May	1st to 10th	Night	3 6% 2 3 2 2 2 2 3 4 70%	4298
	11th to 20th	Night	2 4 1 2 2 1 2 1 3 5% 76%	4074
	21st to end	Night	2 2 1 2 1 1 1 1 2 4 82%	4163
June	1st to 10th	Night	4 2 2 2 2 1 2 2 4 8% 71%	1600
	11th to 20th	Night	1 1 1 1 1 2 2 2 2 5% 82%	1600
	21st to end	Night	1 1 1 1 1 2 2 2 3 86%	1600
July	1st to 10th	Night	1 1 1 1 2 93%	3640
	11th to 20th	Night	1 1 1 1 1 1 2 2 3 85%	3640
	21st to end	Night	1 1 1 1 1 1 1 2 4 86%	4230
August	1st to 10th	Night	1 1 1 1 1 1 2 2 4 86%	4486
	11th to 20th	Night	1 1 1 1 1 2 94%	4506
	21st to end	Night	1 1 2 2 2 2 2 2 3 83%	5015
September	1st to 10th	Night	1 1 1 1 1 2 1 2 2 88%	2000
	11th to 20th	Night	1 2 1 2 2 1 1 2 3 3 82%	2094
	21st to end	Night	2 2 1 2 2 2 2 2 3 4 79%	2200
October	1st to 10th	Night	2 2 2 1 1 2 2 2 4 82%	3664
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 4 79%	3897
	21st to end	Night	2 2 1 3 2 2 2 2 3 5% 76%	4343
November	1st to 10th	Night	4 6% 2 2 2 2 3 2 4 6% 67%	2665
	11th to 20th	Night	6% 4 2 4 2 2 3 2 5% 8% 62%	2730
	21st to end	Night	6% 7% 2 4 3 3 3 3 4 6% 59%	2730
December	1st to 10th	Night	5% 4 1 4 3 2 4 3 4 6% 64%	4403
	11th to 20th	Night	12% 7% 2 4 3 3 4 3 7% 9% 46%	5316
	21st to end	Night	9% 7% 2 6% 4 5% 5% 5% 7% 9% 41%	7106

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	34% 2 10% 25% 22% 8%	4723
	11th to 20th	Day	24% 1 5% 14% 26% 30%	4998
	21st to end	Day	33% 2 8% 18% 28% 11%	5843
February	1st to 10th	Day	36% 3 7% 23% 19% 12%	2077
	11th to 20th	Day	40% 3 7% 20% 23% 8%	2060
	21st to end	Day	42% 4 8% 25% 16% 4	1730
March	1st to 10th	Day	46% 3 7% 18% 19% 7%	4618
	11th to 20th	Day	36% 3 15% 28% 10% 8%	4874
	21st to end	Day	45% 3 11% 24% 14% 3	6087
April	1st to 10th	Day	36% 4 12% 26% 18% 4	2520
	11th to 20th	Day	35% 4 12% 25% 20% 4	2445
	21st to end	Day	31% 4 15% 32% 16% 1	2400
May	1st to 10th	Day	23% 3 10% 35% 26% 4	5677
	11th to 20th	Day	20% 3 9% 35% 30% 3	5844
	21st to end	Day	15% 2 7% 34% 38% 3	6717
June	1st to 10th	Day	20% 3 12% 29% 29% 8%	2800
	11th to 20th	Day	11% 1 9% 24% 38% 18%	2800
	21st to end	Day	10% 1 3 16% 43% 27%	2800
July	1st to 10th	Day	4 1 1 6% 23% 64%	6251
	11th to 20th	Day	9% 3 3 9% 31% 45%	6245
	21st to end	Day	7% 2 3 17% 38% 33%	6411
August	1st to 10th	Day	9% 2 3 14% 40% 33%	3890
	11th to 20th	Day	5% 1 2 10% 32% 51%	3880
	21st to end	Day	7% 1 2 12% 38% 40%	4311
September	1st to 10th	Day	8% 1 4 14% 39% 35%	2400
	11th to 20th	Day	12% 1 4 21% 37% 24%	2305
	21st to end	Day	12% 2 3 22% 40% 21%	2200
October	1st to 10th	Day	15% 2 4 14% 34% 31%	3519
	11th to 20th	Day	16% 2 3 16% 42% 21%	3261
	21st to end	Day	20% 3 5% 19% 36% 17%	3463
November	1st to 10th	Day	24% 2 6% 24% 29% 15%	1854
	11th to 20th	Day	24% 3 7% 23% 30% 13%	1890
	21st to end	Day	27% 4 5% 20% 29% 16%	1890
December	1st to 10th	Day	23% 3 6% 22% 26% 19%	2988
	11th to 20th	Day	36% 4 11% 21% 20% 8%	3108
	21st to end	Day	40% 3 8% 23% 18% 8%	4092
January	1st to 10th	Night	33% 2 9% 24% 21% 10%	8172
	11th to 20th	Night	25% 1 4 16% 27% 28%	7960
	21st to end	Night	35% 3 7% 16% 23% 16%	8371
February	1st to 10th	Night	36% 2 6% 22% 22% 13%	2541
	11th to 20th	Night	33% 3 8% 24% 24% 9%	2459
	21st to end	Night	35% 3 10% 26% 19% 8%	2076
March	1st to 10th	Night	43% 2 6% 18% 21% 10%	5496
	11th to 20th	Night	32% 3 11% 30% 15% 8%	5343
	21st to end	Night	41% 4 15% 24% 14% 3	5128
April	1st to 10th	Night	29% 3 15% 28% 18% 6%	2100
	11th to 20th	Night	28% 4 13% 28% 21% 6%	2039
	21st to end	Night	23% 3 15% 40% 18% 1	2000
May	1st to 10th	Night	20% 3 11% 42% 22% 3	4295
	11th to 20th	Night	13% 2 13% 42% 29% 2	4075
	21st to end	Night	10% 1 7% 37% 41% 3	4163
June	1st to 10th	Night	15% 2 14% 32% 33% 5%	1600
	11th to 20th	Night	9% 1 9% 25% 39% 16%	1600
	21st to end	Night	8% 1 3 18% 43% 27%	1600
July	1st to 10th	Night	3 1 7% 22% 66%	3600
	11th to 20th	Night	7% 2 3 10% 32% 46%	3592
	21st to end	Night	5% 1 4 20% 36% 34%	4111
August	1st to 10th	Night	8% 2 4 18% 40% 28%	3256
	11th to 20th	Night	3 1 2 12% 30% 52%	3256
	21st to end	Night	7% 1 1 11% 40% 40%	3608
September	1st to 10th	Night	6% 1 1 14% 38% 39%	2000
	11th to 20th	Night	10% 2 4 23% 38% 22%	2094
	21st to end	Night	11% 2 4 22% 38% 23%	2200
October	1st to 10th	Night	10% 1 4 15% 37% 33%	3664
	11th to 20th	Night	12% 2 3 14% 35% 34%	3897
	21st to end	Night	15% 2 3 16% 44% 20%	4343
November	1st to 10th	Night	21% 2 7% 24% 28% 18%	2665
	11th to 20th	Night	22% 3 7% 21% 31% 15%	2730
	21st to end	Night	27% 3 7% 19% 29% 16%	2730
December	1st to 10th	Night	23% 4 6% 22% 25% 20%	4403
	11th to 20th	Night	34% 4 11% 21% 22% 8%	5316
	21st to end	Night	40% 4 10% 19% 21% 7%	7106

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% 10% 34% 21% 5% 2	220
	11th to 20th	Day	16% 12% 32% 28% 11% 2	309
	21st to end	Day	18% 12% 34% 24% 12% 1	473
February	1st to 10th	Day	21% 15% 31% 24% 7% 2	529
	11th to 20th	Day	22% 20% 33% 19% 5%	535
	21st to end	Day	19% 20% 39% 18% 4	446
March	1st to 10th	Day	21% 21% 38% 16% 4	540
	11th to 20th	Day	19% 20% 33% 21% 7%	540
	21st to end	Day	25% 20% 33% 19% 3	594
April	1st to 10th	Day	19% 20% 31% 25% 6%	540
	11th to 20th	Day	21% 18% 33% 24% 4	517
	21st to end	Day	14% 16% 35% 25% 9% 2	500
May	1st to 10th	Day	16% 20% 32% 22% 9% 1	503
	11th to 20th	Day	14% 16% 33% 26% 10% 2	528
	21st to end	Day	14% 13% 32% 28% 12% 1	573
June	1st to 10th	Day	5% 12% 32% 34% 14% 2	530
	11th to 20th	Day	6% 15% 35% 31% 12% 2	530
	21st to end	Day	2 12% 37% 33% 13% 3	530
July	1st to 10th	Day	2 7% 37% 38% 13% 4	526
	11th to 20th	Day	2 2 29% 47% 13% 8%	524
	21st to end	Day	2 3 32% 45% 10% 7%	575
August	1st to 10th	Day	3 8% 44% 32% 10% 4	527
	11th to 20th	Day	3 9% 33% 38% 10% 6%	517
	21st to end	Day	2 4 38% 41% 13% 2	583
September	1st to 10th	Day	3 8% 40% 37% 11% 1	530
	11th to 20th	Day	5% 12% 40% 34% 8% 1	530
	21st to end	Day	6% 15% 37% 34% 7% 1	530
October	1st to 10th	Day	6% 18% 31% 35% 8%	530
	11th to 20th	Day	7% 14% 38% 32% 8%	530
	21st to end	Day	8% 11% 37% 35% 9%	524
November	1st to 10th	Day	9% 15% 34% 30% 12% 1	330
	11th to 20th	Day	12% 17% 33% 25% 10% 2	330
	21st to end	Day	13% 15% 31% 29% 11% 1	330
December	1st to 10th	Day	14% 12% 34% 29% 11% 1	316
	11th to 20th	Day	14% 10% 35% 24% 15% 1	220
	21st to end	Day	24% 14% 32% 19% 8% 2	242
January	1st to 10th	Night	20% 7% 30% 24% 15% 4	840
	11th to 20th	Night	10% 10% 35% 31% 13% 1	840
	21st to end	Night	16% 8% 33% 29% 12% 2	924
February	1st to 10th	Night	18% 7% 33% 29% 13% 2	840
	11th to 20th	Night	15% 7% 32% 29% 15% 2	824
	21st to end	Night	17% 10% 33% 31% 8% 1	692
March	1st to 10th	Night	16% 10% 29% 34% 11% 1	840
	11th to 20th	Night	13% 8% 31% 29% 17% 3	840
	21st to end	Night	18% 6% 31% 34% 11% 1	924
April	1st to 10th	Night	12% 7% 29% 40% 12% 1	840
	11th to 20th	Night	11% 7% 28% 37% 17% 1	815
	21st to end	Night	7% 5% 26% 38% 22% 2	800
May	1st to 10th	Night	8% 5% 25% 40% 20% 2	694
	11th to 20th	Night	9% 4 21% 43% 21% 3	591
	21st to end	Night	7% 4 28% 36% 23% 2	521
June	1st to 10th	Night	5% 2 23% 43% 24% 4	400
	11th to 20th	Night	1 2 26% 42% 26% 4	400
	21st to end	Night	1 2 16% 45% 35% 2	400
July	1st to 10th	Night	1 1 12% 39% 45% 3	390
	11th to 20th	Night	1 8% 43% 45% 3	388
	21st to end	Night	2 13% 35% 45% 5%	546
August	1st to 10th	Night	2 1 15% 44% 35% 3	796
	11th to 20th	Night	1 1 11% 39% 45% 4	792
	21st to end	Night	2 10% 39% 45% 4	880
September	1st to 10th	Night	1 1 12% 41% 40% 4	800
	11th to 20th	Night	2 2 15% 47% 30% 4	800
	21st to end	Night	2 2 22% 39% 32% 3	800
October	1st to 10th	Night	4 3 20% 49% 22% 3	800
	11th to 20th	Night	4 3 25% 41% 25% 3	800
	21st to end	Night	5% 3 24% 35% 27% 6%	880
November	1st to 10th	Night	8% 4 21% 39% 24% 4	820
	11th to 20th	Night	8% 7% 25% 40% 17% 3	840
	21st to end	Night	10% 6% 30% 36% 15% 3	840
December	1st to 10th	Night	13% 9% 28% 36% 12% 3	840
	11th to 20th	Night	18% 6% 31% 31% 12% 2	840
	21st to end	Night	18% 10% 33% 27% 10% 2	924

Page generated at 2026-04-13 23:44:25. Version ac07

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