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 2024-12-24.

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	5% 6% 2 3 2 2 3 2 4 5% 65%	105366
	Night	6% 6% 2 3 2 2 3 2 4 5% 65%	103496
Transparency	Day	23% 2 7% 21% 28% 19%	105114
	Night	23% 2 7% 23% 27% 18%	103338
Seeing	Day	11% 13% 35% 30% 9% 2	15411
	Night	9% 4 23% 37% 23% 3	25038

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	8% 12% 3 5% 3 3 3 2 5% 5% 51%	2539
	11th to 20th	Day	12% 7% 2 6% 4 4 5% 4 6% 7% 43%	2672
	21st to end	Day	11% 10% 4 6% 4 3 4 4 6% 8% 40%	3146
February	1st to 10th	Day	11% 9% 4 5% 2 2 3 3 4 6% 51%	1879
	11th to 20th	Day	7% 14% 3 5% 3 4 2 3 3 5% 50%	1850
	21st to end	Day	11% 15% 4 7% 3 3 2 2 4 6% 43%	1570
March	1st to 10th	Day	7% 19% 5% 6% 4 4 4 3 5% 8% 36%	3138
	11th to 20th	Day	5% 9% 2 5% 3 3 3 3 5% 8% 55%	3325
	21st to end	Day	10% 20% 5% 5% 3 3 3 3 5% 6% 37%	4152
April	1st to 10th	Day	8% 10% 3 5% 3 4 3 3 5% 7% 49%	2280
	11th to 20th	Day	9% 11% 2 5% 3 3 2 3 4 6% 51%	2249
	21st to end	Day	9% 8% 2 3 2 3 3 3 6% 8% 54%	2280
May	1st to 10th	Day	5% 6% 2 3 2 2 2 2 3 5% 68%	3972
	11th to 20th	Day	3 5% 1 2 2 2 3 2 5% 7% 69%	4071
	21st to end	Day	4 5% 1 3 2 2 2 2 3 5% 73%	4679
June	1st to 10th	Day	4 3 2 3 3 3 3 3 5% 7% 63%	2660
	11th to 20th	Day	2 2 2 2 1 2 2 3 5% 79%	2660
	21st to end	Day	1 2 2 2 2 2 2 2 4 82%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 3 88%	4420
	11th to 20th	Day	2 2 1 3 2 3 3 2 3 5% 75%	4420
	21st to end	Day	1 2 2 2 1 2 2 3 4 82%	4604
August	1st to 10th	Day	2 1 1 2 1 2 2 2 2 3 83%	3783
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 88%	3724
	21st to end	Day	2 1 1 1 1 1 1 2 3 86%	4180
September	1st to 10th	Day	1 1 2 1 2 2 1 4 4 81%	2280
	11th to 20th	Day	2 2 1 2 2 2 1 1 3 4 79%	2190
	21st to end	Day	2 3 1 2 2 2 2 2 3 5% 77%	2090
October	1st to 10th	Day	2 3 1 2 2 2 3 2 3 5% 73%	3411
	11th to 20th	Day	2 2 1 3 2 3 2 2 3 3 77%	3161
	21st to end	Day	3 4 1 3 3 3 3 2 4 6% 66%	3356
November	1st to 10th	Day	4 9% 2 3 2 2 2 3 4 8% 61%	1764
	11th to 20th	Day	6% 4 1 3 2 2 3 3 6% 6% 64%	1800
	21st to end	Day	6% 7% 3 4 3 3 3 3 5% 7% 58%	1800
December	1st to 10th	Day	10% 5% 1 3 3 3 3 2 4 7% 57%	1775
	11th to 20th	Day	14% 11% 3 5% 4 4 4 3 5% 6% 41%	2008
	21st to end	Day	8% 9% 3 6% 4 4 4 4 6% 8% 43%	2818
January	1st to 10th	Night	8% 10% 3 5% 3 2 2 2 4 5% 55%	4406
	11th to 20th	Night	14% 11% 3 5% 3 3 4 3 5% 7% 42%	4290
	21st to end	Night	11% 10% 3 5% 3 3 5% 4 6% 10% 40%	4521
February	1st to 10th	Night	11% 9% 2 4 3 3 3 2 4 6% 52%	2299
	11th to 20th	Night	8% 11% 2 4 2 2 3 2 4 7% 56%	2218
	21st to end	Night	10% 9% 4 7% 3 3 3 2 4 6% 50%	1884
March	1st to 10th	Night	8% 16% 4 7% 3 3 3 3 5% 7% 41%	3736
	11th to 20th	Night	5% 7% 2 5% 2 3 3 3 4 7% 58%	3653
	21st to end	Night	12% 15% 3 6% 4 3 3 3 4 6% 41%	3499
April	1st to 10th	Night	7% 9% 2 3 3 3 3 2 5% 7% 55%	1900
	11th to 20th	Night	6% 7% 2 5% 3 3 3 2 5% 6% 58%	1879
	21st to end	Night	5% 7% 1 3 2 2 3 3 5% 7% 62%	1900
May	1st to 10th	Night	4 6% 1 2 1 2 2 1 3 5% 72%	3002
	11th to 20th	Night	3 4 1 2 2 1 2 1 3 5% 76%	2834
	21st to end	Night	3 3 1 2 2 1 1 1 2 3 79%	2897
June	1st to 10th	Night	4 2 2 3 2 2 2 2 4 8% 70%	1520
	11th to 20th	Night	1 1 1 2 1 2 2 2 2 5% 82%	1520
	21st to end	Night	1 1 1 1 1 2 2 2 3 86%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 91%	2540
	11th to 20th	Night	1 2 1 2 2 2 2 2 3 4 80%	2540
	21st to end	Night	1 1 1 1 1 1 1 1 3 3 85%	2951
August	1st to 10th	Night	1 1 2 1 2 2 2 3 4 82%	3166
	11th to 20th	Night	1 1 1 1 1 1 2 2 92%	3126
	21st to end	Night	1 1 1 1 1 1 1 1 2 89%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 89%	1900
	11th to 20th	Night	1 2 1 2 2 1 1 2 3 3 83%	1989
	21st to end	Night	2 1 1 2 2 2 2 2 3 4 81%	2090
October	1st to 10th	Night	2 2 2 1 1 2 2 2 4 82%	3552
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 4 79%	3777
	21st to end	Night	2 2 1 3 2 2 2 2 3 5% 75%	4208
November	1st to 10th	Night	5% 6% 2 2 2 2 3 2 4 6% 66%	2535
	11th to 20th	Night	6% 4 1 3 2 2 2 2 5% 8% 64%	2600
	21st to end	Night	7% 7% 2 4 3 3 3 3 4 6% 59%	2600
December	1st to 10th	Night	9% 6% 1 5% 4 2 3 3 4 7% 57%	2620
	11th to 20th	Night	16% 9% 2 5% 3 3 4 3 6% 7% 42%	3416
	21st to end	Night	8% 7% 2 6% 4 5% 5% 4 6% 8% 44%	4910

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	38% 1 7% 27% 22% 4	2539
	11th to 20th	Day	41% 2 10% 25% 15% 7%	2672
	21st to end	Day	43% 2 11% 24% 15% 5%	3146
February	1st to 10th	Day	37% 3 7% 24% 20% 10%	1879
	11th to 20th	Day	38% 3 7% 20% 24% 8%	1860
	21st to end	Day	45% 4 7% 24% 17% 3	1570
March	1st to 10th	Day	49% 3 8% 20% 16% 5%	3138
	11th to 20th	Day	32% 2 14% 32% 12% 8%	3325
	21st to end	Day	51% 2 11% 21% 13% 2	4152
April	1st to 10th	Day	37% 3 12% 26% 18% 4	2280
	11th to 20th	Day	36% 4 12% 25% 19% 4	2252
	21st to end	Day	31% 4 15% 33% 16% 1	2280
May	1st to 10th	Day	22% 2 11% 32% 28% 6%	3972
	11th to 20th	Day	17% 2 8% 36% 33% 3	4074
	21st to end	Day	18% 2 8% 37% 33% 2	4679
June	1st to 10th	Day	20% 2 12% 28% 30% 8%	2660
	11th to 20th	Day	11% 1 9% 25% 38% 16%	2660
	21st to end	Day	10% 1 3 17% 42% 28%	2660
July	1st to 10th	Day	6% 1 1 7% 22% 63%	4351
	11th to 20th	Day	12% 4 3 11% 29% 40%	4345
	21st to end	Day	9% 1 4 21% 27% 38%	4458
August	1st to 10th	Day	10% 2 2 14% 40% 33%	3770
	11th to 20th	Day	5% 1 1 10% 31% 51%	3760
	21st to end	Day	7% 1 2 12% 38% 41%	4179
September	1st to 10th	Day	9% 1 3 13% 39% 36%	2280
	11th to 20th	Day	12% 1 4 21% 36% 26%	2190
	21st to end	Day	12% 2 2 22% 40% 22%	2090
October	1st to 10th	Day	16% 2 4 14% 34% 30%	3411
	11th to 20th	Day	15% 2 3 17% 42% 21%	3161
	21st to end	Day	20% 3 5% 19% 36% 17%	3356
November	1st to 10th	Day	25% 2 6% 23% 28% 15%	1764
	11th to 20th	Day	22% 3 7% 24% 31% 14%	1800
	21st to end	Day	28% 4 6% 19% 28% 16%	1800
December	1st to 10th	Day	29% 3 7% 19% 26% 15%	1775
	11th to 20th	Day	46% 3 8% 17% 18% 8%	2008
	21st to end	Day	41% 3 7% 22% 19% 8%	2818
January	1st to 10th	Night	34% 1 8% 30% 20% 6%	4406
	11th to 20th	Night	43% 2 6% 26% 16% 7%	4290
	21st to end	Night	42% 2 10% 23% 16% 6%	4521
February	1st to 10th	Night	36% 2 6% 23% 22% 11%	2299
	11th to 20th	Night	31% 2 8% 25% 25% 9%	2219
	21st to end	Night	36% 3 10% 25% 19% 6%	1884
March	1st to 10th	Night	44% 2 7% 21% 19% 6%	3736
	11th to 20th	Night	27% 2 13% 31% 16% 10%	3653
	21st to end	Night	46% 2 11% 26% 13% 2	3499
April	1st to 10th	Night	29% 3 15% 29% 17% 6%	1900
	11th to 20th	Night	27% 4 14% 29% 20% 6%	1879
	21st to end	Night	22% 3 15% 41% 17% 1	1900
May	1st to 10th	Night	19% 1 9% 44% 25% 3	3002
	11th to 20th	Night	14% 1 9% 44% 29% 3	2835
	21st to end	Night	13% 1 10% 41% 33% 2	2897
June	1st to 10th	Night	16% 2 14% 30% 33% 5%	1520
	11th to 20th	Night	9% 1 10% 26% 40% 14%	1520
	21st to end	Night	8% 1 4 18% 42% 28%	1520
July	1st to 10th	Night	4 2 9% 22% 63%	2500
	11th to 20th	Night	9% 2 4 12% 29% 43%	2492
	21st to end	Night	7% 2 5% 21% 28% 38%	2859
August	1st to 10th	Night	8% 2 4 18% 40% 27%	3156
	11th to 20th	Night	4 1 2 12% 30% 53%	3156
	21st to end	Night	7% 1 1 11% 40% 41%	3498
September	1st to 10th	Night	6% 1 1 13% 39% 40%	1900
	11th to 20th	Night	9% 1 4 24% 38% 24%	1989
	21st to end	Night	10% 2 3 22% 39% 24%	2090
October	1st to 10th	Night	10% 1 4 14% 37% 34%	3552
	11th to 20th	Night	12% 2 4 14% 35% 34%	3777
	21st to end	Night	15% 2 3 16% 44% 21%	4208
November	1st to 10th	Night	22% 3 7% 24% 27% 18%	2535
	11th to 20th	Night	21% 3 7% 21% 32% 16%	2600
	21st to end	Night	28% 3 7% 19% 28% 16%	2600
December	1st to 10th	Night	29% 3 8% 20% 24% 16%	2620
	11th to 20th	Night	43% 3 9% 19% 19% 8%	3416
	21st to end	Night	39% 2 8% 22% 21% 8%	4910

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	28% 7% 34% 23% 6% 2	180
	11th to 20th	Day	18% 11% 32% 25% 12% 2	260
	21st to end	Day	19% 11% 33% 25% 11% 1	407
February	1st to 10th	Day	20% 15% 31% 24% 8% 2	451
	11th to 20th	Day	20% 18% 34% 22% 6%	455
	21st to end	Day	21% 19% 37% 18% 4	382
March	1st to 10th	Day	23% 17% 38% 17% 5%	460
	11th to 20th	Day	20% 20% 32% 21% 7%	460
	21st to end	Day	26% 21% 33% 17% 3	506
April	1st to 10th	Day	20% 19% 31% 24% 6%	460
	11th to 20th	Day	21% 18% 32% 24% 5%	452
	21st to end	Day	14% 16% 34% 24% 10% 2	460
May	1st to 10th	Day	16% 20% 33% 22% 8% 1	463
	11th to 20th	Day	13% 15% 33% 27% 11% 2	488
	21st to end	Day	15% 13% 30% 28% 13% 2	529
June	1st to 10th	Day	5% 13% 32% 33% 14% 2	490
	11th to 20th	Day	6% 14% 36% 31% 12% 2	490
	21st to end	Day	2 11% 37% 34% 13% 3	490
July	1st to 10th	Day	2 4 38% 40% 13% 3	486
	11th to 20th	Day	2 2 27% 48% 14% 7%	484
	21st to end	Day	2 3 31% 47% 10% 7%	531
August	1st to 10th	Day	2 7% 45% 33% 9% 3	487
	11th to 20th	Day	3 9% 34% 39% 10% 5%	477
	21st to end	Day	1 4 38% 41% 13% 3	539
September	1st to 10th	Day	3 7% 41% 37% 11% 1	490
	11th to 20th	Day	4 13% 40% 35% 8% 1	490
	21st to end	Day	6% 13% 37% 36% 7%	490
October	1st to 10th	Day	5% 18% 31% 37% 9%	490
	11th to 20th	Day	6% 14% 38% 34% 8%	490
	21st to end	Day	7% 12% 36% 34% 10%	483
November	1st to 10th	Day	9% 15% 33% 30% 12%	300
	11th to 20th	Day	8% 16% 35% 28% 11% 2	300
	21st to end	Day	14% 14% 29% 30% 11% 1	300
December	1st to 10th	Day	15% 10% 34% 30% 11%	287
	11th to 20th	Day	16% 10% 36% 24% 15% 1	200
	21st to end	Day	23% 13% 31% 22% 9% 2	204
January	1st to 10th	Night	19% 4 29% 27% 17% 4	760
	11th to 20th	Night	12% 7% 33% 32% 15% 2	760
	21st to end	Night	17% 6% 31% 31% 13% 2	836
February	1st to 10th	Night	17% 5% 31% 31% 14% 2	760
	11th to 20th	Night	14% 5% 31% 31% 17% 2	744
	21st to end	Night	18% 7% 31% 34% 9% 1	628
March	1st to 10th	Night	17% 7% 28% 36% 12% 1	760
	11th to 20th	Night	14% 7% 27% 31% 18% 3	760
	21st to end	Night	18% 6% 28% 35% 12% 1	836
April	1st to 10th	Night	13% 5% 28% 41% 13% 1	760
	11th to 20th	Night	10% 6% 27% 38% 18% 1	751
	21st to end	Night	7% 5% 26% 38% 22% 2	760
May	1st to 10th	Night	8% 4 25% 40% 20% 2	660
	11th to 20th	Night	9% 3 19% 44% 22% 3	561
	21st to end	Night	7% 4 26% 37% 24% 2	495
June	1st to 10th	Night	5% 2 21% 43% 25% 4	380
	11th to 20th	Night	1 1 23% 43% 28% 4	380
	21st to end	Night	1 2 14% 44% 37% 2	380
July	1st to 10th	Night	1 9% 39% 47% 3	370
	11th to 20th	Night	1 9% 40% 46% 3	368
	21st to end	Night	2 12% 33% 46% 6%	519
August	1st to 10th	Night	2 1 14% 44% 37% 3	756
	11th to 20th	Night	1 1 11% 39% 45% 4	752
	21st to end	Night	2 9% 37% 47% 4	836
September	1st to 10th	Night	1 1 12% 40% 42% 4	760
	11th to 20th	Night	1 2 15% 47% 30% 5%	760
	21st to end	Night	2 1 20% 39% 34% 3	760
October	1st to 10th	Night	4 2 19% 50% 23% 3	760
	11th to 20th	Night	3 3 24% 42% 26% 3	760
	21st to end	Night	5% 3 23% 35% 28% 6%	836
November	1st to 10th	Night	9% 4 20% 39% 24% 4	780
	11th to 20th	Night	8% 5% 25% 42% 18% 3	800
	21st to end	Night	11% 5% 28% 37% 15% 3	800
December	1st to 10th	Night	13% 8% 27% 37% 13% 3	800
	11th to 20th	Night	19% 5% 30% 32% 13% 2	800
	21st to end	Night	17% 6% 34% 30% 11% 2	850

Page generated at 2024-12-21 01:13:53. Version ac07

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