Big Springs
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Springs clear sky chart from 2005-11-06 to 2025-12-03.

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	7% 5% 2 5% 3 3 4 3 5% 7% 55%	135494
	Night	7% 6% 2 6% 4 4 4 3 5% 7% 52%	132597
Transparency	Day	28% 5% 13% 28% 21% 5%	130370
	Night	31% 5% 13% 26% 20% 5%	128728
Seeing	Day	9% 7% 28% 32% 18% 5%	17213
	Night	10% 7% 35% 38% 9%	27171

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	5% 10% 3 8% 3 3 3 3 4 6% 51%	3638
	11th to 20th	Day	4 8% 3 9% 4 4 4 3 5% 7% 49%	3640
	21st to end	Day	3 5% 3 8% 4 3 4 3 5% 7% 56%	4032
February	1st to 10th	Day	6% 9% 4 8% 5% 5% 4 4 5% 6% 44%	1944
	11th to 20th	Day	5% 8% 3 7% 5% 4 4 4 5% 6% 49%	1949
	21st to end	Day	4 8% 2 5% 3 3 4 3 5% 6% 56%	1650
March	1st to 10th	Day	8% 7% 3 5% 3 2 3 3 4 5% 56%	4500
	11th to 20th	Day	8% 5% 2 3 3 3 3 3 5% 7% 60%	4711
	21st to end	Day	7% 7% 2 5% 3 3 4 4 7% 9% 50%	5831
April	1st to 10th	Day	9% 7% 2 4 4 3 2 3 5% 7% 53%	2400
	11th to 20th	Day	13% 6% 2 5% 4 4 4 4 5% 8% 46%	2371
	21st to end	Day	11% 6% 3 5% 4 4 4 4 5% 7% 46%	2547
May	1st to 10th	Day	7% 4 2 5% 4 4 4 4 6% 8% 51%	5900
	11th to 20th	Day	8% 4 2 5% 3 3 4 3 5% 8% 54%	5893
	21st to end	Day	15% 6% 2 5% 3 3 4 3 5% 6% 47%	6925
June	1st to 10th	Day	6% 3 1 4 3 3 3 4 6% 10% 56%	2800
	11th to 20th	Day	6% 4 1 4 3 3 4 4 6% 8% 57%	2800
	21st to end	Day	3 4 1 2 3 3 4 4 6% 8% 62%	2800
July	1st to 10th	Day	5% 4 1 4 3 3 4 3 6% 8% 58%	6339
	11th to 20th	Day	5% 3 1 3 3 3 4 4 7% 10% 55%	6340
	21st to end	Day	5% 3 1 4 3 4 4 4 6% 10% 55%	6903
August	1st to 10th	Day	10% 4 2 4 3 3 4 4 6% 9% 52%	5893
	11th to 20th	Day	6% 4 2 4 4 3 4 3 5% 8% 57%	5501
	21st to end	Day	8% 6% 2 5% 3 3 5% 4 6% 7% 51%	5984
September	1st to 10th	Day	7% 4 2 3 3 3 3 2 5% 6% 62%	2400
	11th to 20th	Day	7% 3 1 4 3 3 3 3 6% 7% 61%	2240
	21st to end	Day	8% 3 1 3 2 2 3 2 4 7% 64%	2200
October	1st to 10th	Day	7% 3 1 2 2 1 2 2 3 4 74%	3590
	11th to 20th	Day	6% 4 1 4 3 3 3 3 4 6% 64%	3203
	21st to end	Day	7% 6% 1 4 2 3 3 2 5% 7% 59%	3190
November	1st to 10th	Day	5% 4 1 4 3 3 4 3 6% 7% 59%	1853
	11th to 20th	Day	5% 5% 1 4 3 3 3 3 4 5% 64%	1890
	21st to end	Day	6% 6% 2 4 3 3 3 3 5% 7% 57%	1890
December	1st to 10th	Day	3 4 2 5% 2 2 2 2 4 6% 68%	2717
	11th to 20th	Day	3 3 1 4 3 3 3 3 5% 7% 64%	3026
	21st to end	Day	7% 10% 3 7% 4 4 3 3 5% 7% 48%	4004
January	1st to 10th	Night	5% 9% 4 9% 4 3 4 3 4 6% 48%	6327
	11th to 20th	Night	2 5% 3 7% 6% 5% 5% 3 5% 7% 52%	6340
	21st to end	Night	3 5% 4 8% 5% 4 4 3 4 5% 56%	6974
February	1st to 10th	Night	7% 9% 3 8% 4 4 4 4 6% 7% 44%	2455
	11th to 20th	Night	5% 9% 3 8% 5% 4 4 4 5% 8% 45%	2338
	21st to end	Night	4 7% 2 6% 4 4 4 4 4 6% 54%	1980
March	1st to 10th	Night	8% 7% 2 5% 3 3 3 3 4 5% 58%	5374
	11th to 20th	Night	8% 8% 2 5% 4 3 3 3 4 6% 55%	5260
	21st to end	Night	7% 8% 3 7% 5% 5% 5% 4 6% 8% 40%	5099
April	1st to 10th	Night	11% 8% 2 5% 4 4 4 4 5% 7% 47%	2000
	11th to 20th	Night	12% 7% 2 5% 4 3 4 3 6% 7% 47%	1977
	21st to end	Night	14% 7% 2 5% 4 5% 3 4 6% 6% 44%	1850
May	1st to 10th	Night	11% 7% 2 6% 5% 4 5% 4 5% 6% 45%	4080
	11th to 20th	Night	10% 4 1 5% 4 4 4 3 5% 8% 51%	4019
	21st to end	Night	18% 8% 2 6% 3 3 4 3 5% 6% 42%	3972
June	1st to 10th	Night	8% 3 2 5% 4 4 3 5% 6% 9% 51%	1600
	11th to 20th	Night	8% 3 2 5% 3 4 5% 4 7% 9% 49%	1600
	21st to end	Night	4 3 2 5% 5% 5% 7% 6% 8% 10% 45%	1600
July	1st to 10th	Night	6% 4 1 4 4 4 5% 5% 6% 8% 54%	3640
	11th to 20th	Night	6% 4 2 5% 4 5% 5% 5% 9% 10% 47%	3640
	21st to end	Night	5% 5% 2 6% 5% 5% 5% 5% 7% 9% 47%	3970
August	1st to 10th	Night	9% 6% 3 7% 6% 5% 6% 4 7% 9% 37%	3916
	11th to 20th	Night	6% 5% 2 6% 4 5% 5% 4 7% 8% 46%	4344
	21st to end	Night	8% 8% 2 6% 4 5% 4 4 6% 8% 45%	4993
September	1st to 10th	Night	7% 4 1 3 3 3 3 3 6% 7% 60%	2000
	11th to 20th	Night	7% 3 1 4 3 3 4 4 6% 8% 57%	2160
	21st to end	Night	7% 4 2 5% 4 3 3 2 4 6% 62%	2200
October	1st to 10th	Night	7% 3 3 2 2 1 2 2 4 74%	3590
	11th to 20th	Night	8% 3 1 3 2 3 3 3 4 6% 64%	3908
	21st to end	Night	6% 5% 2 4 3 3 3 3 5% 6% 59%	4610
November	1st to 10th	Night	5% 5% 2 5% 2 3 4 3 5% 7% 61%	2665
	11th to 20th	Night	5% 6% 1 4 4 3 4 3 5% 7% 58%	2730
	21st to end	Night	6% 6% 2 5% 4 4 3 3 4 6% 56%	2730
December	1st to 10th	Night	3 4 2 5% 3 3 3 3 4 5% 65%	4501
	11th to 20th	Night	3 5% 2 5% 4 3 4 3 6% 7% 57%	5181
	21st to end	Night	10% 9% 3 6% 3 4 4 4 5% 7% 45%	6974

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	35% 3 10% 33% 18% 2	3639
	11th to 20th	Day	34% 5% 12% 25% 20% 4	3640
	21st to end	Day	28% 5% 15% 27% 22% 4	4032
February	1st to 10th	Day	39% 5% 15% 22% 15% 4	1944
	11th to 20th	Day	35% 6% 12% 25% 18% 4	1959
	21st to end	Day	28% 5% 12% 28% 21% 6%	1650
March	1st to 10th	Day	30% 3 7% 23% 29% 7%	4500
	11th to 20th	Day	26% 4 9% 26% 33% 2	4711
	21st to end	Day	30% 6% 19% 30% 13% 1	5831
April	1st to 10th	Day	31% 5% 13% 31% 17% 4	2400
	11th to 20th	Day	35% 6% 15% 22% 18% 4	2374
	21st to end	Day	36% 5% 12% 27% 18% 2	2547
May	1st to 10th	Day	28% 6% 13% 29% 20% 4	5900
	11th to 20th	Day	27% 6% 13% 30% 22% 2	5897
	21st to end	Day	36% 6% 14% 28% 14% 2	6926
June	1st to 10th	Day	23% 7% 20% 32% 17% 2	2800
	11th to 20th	Day	24% 6% 14% 28% 20% 7%	2800
	21st to end	Day	19% 5% 13% 29% 27% 7%	2800
July	1st to 10th	Day	25% 4 9% 27% 29% 6%	6271
	11th to 20th	Day	24% 4 16% 32% 18% 5%	6265
	21st to end	Day	24% 5% 15% 23% 22% 11%	6705
August	1st to 10th	Day	29% 6% 14% 28% 17% 5%	4286
	11th to 20th	Day	31% 5% 13% 23% 24% 4	3981
	21st to end	Day	23% 4 15% 22% 22% 14%	4311
September	1st to 10th	Day	23% 3 9% 27% 24% 13%	2400
	11th to 20th	Day	22% 4 10% 27% 28% 9%	2240
	21st to end	Day	22% 4 7% 27% 32% 8%	2200
October	1st to 10th	Day	17% 3 6% 21% 33% 21%	3590
	11th to 20th	Day	25% 3 8% 37% 21% 6%	3203
	21st to end	Day	26% 3 11% 32% 22% 6%	3190
November	1st to 10th	Day	24% 4 14% 28% 22% 7%	1853
	11th to 20th	Day	23% 3 10% 32% 26% 5%	1890
	21st to end	Day	26% 4 13% 29% 23% 5%	1890
December	1st to 10th	Day	20% 3 12% 35% 27% 4	2717
	11th to 20th	Day	20% 3 15% 42% 18% 3	3024
	21st to end	Day	37% 4 9% 35% 13% 2	4004
January	1st to 10th	Night	37% 5% 13% 27% 14% 3	6327
	11th to 20th	Night	30% 6% 16% 23% 22% 3	6340
	21st to end	Night	31% 4 11% 27% 22% 5%	6974
February	1st to 10th	Night	38% 5% 14% 23% 17% 3	2455
	11th to 20th	Night	37% 6% 13% 27% 14% 3	2338
	21st to end	Night	30% 5% 10% 27% 22% 6%	1980
March	1st to 10th	Night	30% 4 7% 22% 31% 6%	5374
	11th to 20th	Night	32% 4 8% 20% 30% 6%	5260
	21st to end	Night	37% 8% 19% 22% 12% 1	5099
April	1st to 10th	Night	36% 5% 14% 24% 16% 5%	2000
	11th to 20th	Night	37% 5% 14% 24% 17% 3	1977
	21st to end	Night	39% 6% 13% 26% 15% 2	1850
May	1st to 10th	Night	38% 6% 15% 25% 14% 2	4080
	11th to 20th	Night	29% 7% 16% 29% 18% 1	4020
	21st to end	Night	42% 7% 15% 24% 12% 1	3972
June	1st to 10th	Night	28% 8% 24% 25% 12% 3	1600
	11th to 20th	Night	30% 8% 17% 24% 14% 7%	1600
	21st to end	Night	29% 9% 13% 24% 21% 3	1600
July	1st to 10th	Night	28% 5% 13% 27% 25% 2	3600
	11th to 20th	Night	31% 5% 20% 26% 15% 3	3592
	21st to end	Night	32% 6% 17% 18% 17% 9%	3856
August	1st to 10th	Night	39% 6% 17% 23% 13% 3	2847
	11th to 20th	Night	37% 8% 12% 23% 16% 3	3140
	21st to end	Night	27% 6% 15% 23% 18% 11%	3597
September	1st to 10th	Night	23% 5% 11% 25% 26% 10%	2000
	11th to 20th	Night	24% 6% 13% 27% 21% 10%	2160
	21st to end	Night	25% 4 7% 27% 29% 9%	2200
October	1st to 10th	Night	17% 2 5% 20% 38% 17%	3590
	11th to 20th	Night	23% 3 8% 33% 25% 6%	3908
	21st to end	Night	27% 3 11% 28% 23% 7%	4610
November	1st to 10th	Night	24% 4 12% 29% 24% 8%	2665
	11th to 20th	Night	24% 5% 11% 29% 24% 7%	2730
	21st to end	Night	30% 4 10% 29% 23% 5%	2730
December	1st to 10th	Night	22% 3 13% 35% 24% 4	4501
	11th to 20th	Night	26% 4 10% 39% 19% 3	5182
	21st to end	Night	38% 4 10% 32% 15% 1	6974

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	10% 6% 38% 31% 12% 4	300
	11th to 20th	Day	10% 11% 39% 35% 5% 1	300
	21st to end	Day	8% 8% 49% 24% 9% 2	330
February	1st to 10th	Day	12% 8% 49% 27% 4	300
	11th to 20th	Day	8% 11% 46% 26% 8% 2	300
	21st to end	Day	9% 15% 41% 27% 8%	249
March	1st to 10th	Day	10% 10% 35% 29% 14% 2	300
	11th to 20th	Day	10% 7% 36% 30% 16% 1	300
	21st to end	Day	16% 12% 35% 26% 9% 2	490
April	1st to 10th	Day	11% 16% 35% 28% 9% 1	500
	11th to 20th	Day	16% 17% 34% 23% 9% 1	492
	21st to end	Day	16% 12% 30% 26% 14% 2	647
May	1st to 10th	Day	13% 9% 29% 29% 15% 4	703
	11th to 20th	Day	16% 7% 29% 29% 17% 2	725
	21st to end	Day	15% 9% 28% 27% 17% 4	789
June	1st to 10th	Day	6% 4 24% 31% 25% 9%	730
	11th to 20th	Day	5% 6% 30% 37% 18% 2	730
	21st to end	Day	5% 4 25% 40% 21% 5%	730
July	1st to 10th	Day	8% 3 18% 41% 24% 6%	721
	11th to 20th	Day	5% 2 17% 38% 33% 5%	718
	21st to end	Day	6% 2 15% 39% 30% 8%	794
August	1st to 10th	Day	7% 3 16% 38% 29% 6%	726
	11th to 20th	Day	6% 3 21% 34% 28% 7%	577
	21st to end	Day	5% 3 20% 37% 25% 10%	583
September	1st to 10th	Day	6% 3 20% 37% 25% 8%	530
	11th to 20th	Day	4 2 16% 41% 28% 10%	370
	21st to end	Day	11% 4 22% 26% 26% 11%	330
October	1st to 10th	Day	13% 6% 21% 27% 23% 10%	330
	11th to 20th	Day	8% 10% 34% 29% 13% 5%	330
	21st to end	Day	12% 10% 31% 31% 14% 3	363
November	1st to 10th	Day	8% 9% 36% 29% 14% 3	330
	11th to 20th	Day	7% 10% 32% 36% 12% 2	330
	21st to end	Day	10% 7% 35% 32% 13% 3	330
December	1st to 10th	Day	7% 7% 42% 34% 9% 1	306
	11th to 20th	Day	9% 10% 44% 28% 8% 1	300
	21st to end	Day	15% 12% 38% 28% 6% 1	330
January	1st to 10th	Night	7% 9% 42% 33% 9%	1000
	11th to 20th	Night	7% 11% 41% 33% 7% 1	1000
	21st to end	Night	8% 9% 43% 33% 7%	1100
February	1st to 10th	Night	11% 9% 46% 29% 5%	800
	11th to 20th	Night	8% 8% 46% 32% 5%	784
	21st to end	Night	9% 8% 48% 31% 3	660
March	1st to 10th	Night	10% 9% 39% 37% 5%	800
	11th to 20th	Night	11% 7% 42% 33% 7%	724
	21st to end	Night	13% 8% 40% 34% 5%	660
April	1st to 10th	Night	15% 12% 36% 33% 3	600
	11th to 20th	Night	14% 11% 41% 31% 3	593
	21st to end	Night	18% 11% 33% 31% 7%	600
May	1st to 10th	Night	13% 10% 32% 36% 10%	600
	11th to 20th	Night	16% 5% 31% 37% 11%	591
	21st to end	Night	18% 7% 33% 32% 10%	650
June	1st to 10th	Night	9% 4 30% 42% 15% 1	600
	11th to 20th	Night	11% 7% 37% 37% 9%	600
	21st to end	Night	6% 2 30% 49% 13%	600
July	1st to 10th	Night	9% 2 26% 48% 14%	585
	11th to 20th	Night	5% 1 24% 54% 15% 1	582
	21st to end	Night	6% 2 21% 53% 18%	657
August	1st to 10th	Night	7% 2 20% 53% 16% 2	597
	11th to 20th	Night	5% 3 25% 53% 14%	594
	21st to end	Night	5% 2 27% 50% 16%	660
September	1st to 10th	Night	8% 2 30% 47% 13%	600
	11th to 20th	Night	8% 4 28% 44% 15% 1	600
	21st to end	Night	9% 5% 29% 42% 15% 1	600
October	1st to 10th	Night	14% 6% 26% 41% 13% 1	600
	11th to 20th	Night	9% 8% 32% 37% 12% 1	798
	21st to end	Night	11% 8% 33% 37% 10% 1	1100
November	1st to 10th	Night	8% 6% 38% 39% 8%	1025
	11th to 20th	Night	8% 8% 40% 37% 7%	1050
	21st to end	Night	9% 7% 33% 41% 10%	1050
December	1st to 10th	Night	8% 9% 43% 33% 7%	1011
	11th to 20th	Night	8% 9% 40% 36% 7%	1000
	21st to end	Night	12% 11% 37% 35% 4	1100

Page generated at 2025-11-29 23:00:51. Version ac07

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