Columbia Scientific Balloon Facility
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Columbia Scientific Balloon Facility 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	12% 6% 2 6% 4 4 4 4 5% 7% 46%	131891
	Night	12% 6% 2 5% 3 3 3 3 5% 7% 51%	130568
Transparency	Day	35% 6% 11% 22% 19% 7%	135556
	Night	33% 5% 10% 20% 21% 10%	134967
Seeing	Day	13% 7% 21% 26% 24% 9%	16888
	Night	14% 6% 25% 34% 18% 2	26865

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	14% 8% 2 5% 3 3 3 3 4 7% 49%	5289
	11th to 20th	Day	11% 5% 2 4 3 3 3 3 5% 7% 55%	5310
	21st to end	Day	25% 9% 3 7% 4 2 2 2 3 4 39%	5812
February	1st to 10th	Day	21% 9% 3 5% 4 3 3 2 3 6% 42%	1953
	11th to 20th	Day	22% 8% 2 5% 3 4 4 3 4 5% 40%	2049
	21st to end	Day	22% 6% 2 5% 3 3 3 2 3 4 47%	1859
March	1st to 10th	Day	17% 10% 2 7% 4 4 3 3 5% 6% 40%	5046
	11th to 20th	Day	13% 6% 2 5% 4 4 4 2 4 6% 50%	5090
	21st to end	Day	17% 8% 3 6% 4 4 3 3 5% 6% 42%	5583
April	1st to 10th	Day	16% 7% 2 7% 5% 4 4 3 5% 8% 40%	2310
	11th to 20th	Day	15% 7% 3 6% 5% 4 4 4 6% 6% 39%	2406
	21st to end	Day	12% 7% 2 6% 5% 4 4 4 6% 7% 44%	2400
May	1st to 10th	Day	18% 8% 3 7% 4 4 4 4 5% 7% 35%	5808
	11th to 20th	Day	13% 7% 3 7% 5% 5% 5% 4 5% 6% 40%	5862
	21st to end	Day	11% 6% 3 7% 5% 5% 6% 5% 7% 9% 36%	6434
June	1st to 10th	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 11% 43%	2600
	11th to 20th	Day	5% 5% 1 5% 4 5% 5% 5% 7% 11% 47%	2600
	21st to end	Day	5% 4 2 5% 5% 6% 6% 5% 7% 10% 45%	2600
July	1st to 10th	Day	8% 5% 2 7% 4 6% 6% 5% 9% 12% 35%	5900
	11th to 20th	Day	4 3 1 4 4 5% 4 4 6% 10% 54%	5900
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 6% 8% 44%	6422
August	1st to 10th	Day	2 1 1 2 2 2 2 3 5% 9% 70%	4234
	11th to 20th	Day	4 2 1 3 3 3 4 4 6% 10% 60%	4117
	21st to end	Day	5% 3 2 5% 5% 5% 6% 6% 8% 11% 44%	4255
September	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 3 5% 7% 48%	2200
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 6% 6% 47%	2200
	21st to end	Day	6% 4 1 4 4 3 3 4 5% 8% 56%	2200
October	1st to 10th	Day	6% 3 1 4 3 3 3 4 4 6% 64%	2085
	11th to 20th	Day	12% 5% 1 4 3 3 3 2 4 5% 59%	2000
	21st to end	Day	13% 5% 2 4 3 3 3 2 3 4 58%	2200
November	1st to 10th	Day	13% 6% 2 5% 3 3 2 3 4 6% 52%	2058
	11th to 20th	Day	12% 5% 2 4 4 3 4 3 4 5% 54%	2100
	21st to end	Day	17% 7% 3 6% 4 3 3 3 4 5% 45%	1911
December	1st to 10th	Day	20% 5% 2 5% 3 3 3 2 4 5% 48%	3030
	11th to 20th	Day	20% 9% 3 5% 3 4 3 3 5% 5% 40%	3481
	21st to end	Day	15% 9% 3 7% 4 3 3 3 4 5% 44%	4587
January	1st to 10th	Night	14% 5% 2 6% 3 3 3 2 4 5% 53%	7634
	11th to 20th	Night	10% 5% 1 3 2 2 3 2 5% 6% 61%	7680
	21st to end	Night	25% 9% 3 6% 4 3 3 2 4 5% 37%	8402
February	1st to 10th	Night	18% 6% 2 5% 3 3 3 3 4 4 48%	2683
	11th to 20th	Night	21% 7% 3 5% 3 3 2 2 4 5% 45%	2458
	21st to end	Night	19% 6% 2 5% 3 2 3 3 4 5% 48%	1945
March	1st to 10th	Night	20% 9% 2 5% 4 3 3 3 4 5% 41%	5029
	11th to 20th	Night	13% 6% 2 4 3 3 3 3 5% 6% 51%	5090
	21st to end	Night	14% 7% 3 6% 4 3 3 3 5% 5% 46%	5588
April	1st to 10th	Night	12% 5% 2 5% 4 4 5% 3 5% 7% 49%	2310
	11th to 20th	Night	13% 6% 2 5% 3 4 4 4 6% 7% 46%	2073
	21st to end	Night	11% 6% 2 5% 4 3 3 3 5% 7% 52%	2000
May	1st to 10th	Night	16% 10% 3 7% 4 4 3 3 5% 8% 36%	4099
	11th to 20th	Night	10% 6% 2 7% 4 5% 5% 4 6% 7% 43%	4053
	21st to end	Night	9% 5% 2 5% 4 5% 5% 4 6% 10% 44%	4443
June	1st to 10th	Night	6% 2 1 3 3 3 4 5% 7% 9% 56%	1800
	11th to 20th	Night	4 2 1 4 2 3 3 3 5% 10% 63%	1800
	21st to end	Night	5% 3 1 4 4 3 4 5% 6% 10% 54%	1800
July	1st to 10th	Night	5% 4 2 6% 5% 4 6% 5% 8% 13% 41%	4078
	11th to 20th	Night	2 2 1 4 3 3 4 4 6% 11% 60%	4077
	21st to end	Night	6% 6% 2 5% 4 4 4 4 7% 10% 49%	4449
August	1st to 10th	Night	1 1 2 1 1 2 2 4 8% 77%	2926
	11th to 20th	Night	3 2 1 3 2 3 3 4 5% 12% 62%	2937
	21st to end	Night	4 3 1 4 3 4 5% 4 7% 11% 53%	3638
September	1st to 10th	Night	6% 5% 1 4 5% 4 4 4 6% 8% 52%	2200
	11th to 20th	Night	9% 5% 2 5% 4 4 4 3 5% 7% 53%	2200
	21st to end	Night	6% 4 1 5% 3 2 4 3 4 7% 62%	2200
October	1st to 10th	Night	5% 2 1 4 2 2 3 3 4 7% 66%	2293
	11th to 20th	Night	12% 4 1 3 2 2 3 3 4 5% 62%	2400
	21st to end	Night	13% 4 1 4 3 2 2 2 3 4 62%	2640
November	1st to 10th	Night	11% 5% 2 4 3 3 2 2 4 5% 58%	2460
	11th to 20th	Night	9% 4 2 5% 4 4 4 3 5% 5% 57%	2520
	21st to end	Night	16% 6% 2 5% 4 3 3 2 5% 5% 49%	2704
December	1st to 10th	Night	19% 6% 2 5% 3 3 2 2 4 4 48%	4380
	11th to 20th	Night	18% 9% 3 7% 4 3 3 2 3 4 45%	4946
	21st to end	Night	15% 8% 2 5% 3 3 2 3 3 4 51%	6633

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	36% 3 7% 26% 24% 3	5290
	11th to 20th	Day	29% 3 5% 22% 29% 11%	5310
	21st to end	Day	51% 3 4 13% 18% 11%	5812
February	1st to 10th	Day	46% 2 5% 15% 21% 10%	1953
	11th to 20th	Day	48% 4 7% 16% 17% 8%	2059
	21st to end	Day	42% 4 6% 16% 20% 12%	1859
March	1st to 10th	Day	44% 5% 7% 13% 20% 12%	5046
	11th to 20th	Day	35% 5% 6% 15% 18% 21%	5090
	21st to end	Day	42% 5% 8% 21% 18% 5%	5585
April	1st to 10th	Day	42% 6% 10% 19% 15% 9%	2310
	11th to 20th	Day	42% 7% 11% 13% 19% 8%	2406
	21st to end	Day	38% 6% 9% 19% 23% 5%	2400
May	1st to 10th	Day	45% 7% 12% 22% 11% 2	5846
	11th to 20th	Day	42% 6% 10% 17% 22% 2	5866
	21st to end	Day	39% 10% 13% 20% 16% 2	6447
June	1st to 10th	Day	32% 9% 17% 28% 13% 2	2600
	11th to 20th	Day	28% 9% 16% 28% 16% 4	2600
	21st to end	Day	31% 10% 15% 28% 15% 2	2600
July	1st to 10th	Day	35% 10% 26% 23% 5%	5836
	11th to 20th	Day	24% 7% 20% 34% 14% 1	5831
	21st to end	Day	35% 9% 15% 30% 12% 1	6240
August	1st to 10th	Day	12% 5% 13% 38% 29% 2	4220
	11th to 20th	Day	19% 7% 19% 42% 12% 1	4156
	21st to end	Day	30% 11% 21% 25% 12% 1	4254
September	1st to 10th	Day	35% 6% 13% 19% 18% 9%	2200
	11th to 20th	Day	35% 8% 13% 20% 16% 8%	2200
	21st to end	Day	25% 7% 10% 22% 22% 13%	2200
October	1st to 10th	Day	14% 3 6% 13% 23% 41%	3397
	11th to 20th	Day	19% 2 4 22% 30% 23%	3240
	21st to end	Day	25% 4 5% 22% 34% 10%	3538
November	1st to 10th	Day	33% 5% 8% 19% 25% 9%	2058
	11th to 20th	Day	33% 4 8% 19% 24% 13%	2100
	21st to end	Day	42% 5% 6% 18% 20% 9%	1911
December	1st to 10th	Day	40% 3 7% 18% 25% 7%	3030
	11th to 20th	Day	44% 4 7% 11% 23% 11%	3479
	21st to end	Day	42% 4 6% 16% 26% 6%	4587
January	1st to 10th	Night	34% 4 7% 20% 27% 7%	7635
	11th to 20th	Night	25% 3 6% 17% 35% 14%	7680
	21st to end	Night	52% 3 4 13% 16% 12%	8402
February	1st to 10th	Night	40% 4 7% 15% 20% 15%	2683
	11th to 20th	Night	44% 3 7% 15% 21% 10%	2458
	21st to end	Night	40% 3 7% 14% 19% 16%	1945
March	1st to 10th	Night	45% 4 6% 12% 21% 14%	5029
	11th to 20th	Night	33% 5% 7% 15% 18% 22%	5090
	21st to end	Night	40% 5% 9% 18% 21% 8%	5588
April	1st to 10th	Night	36% 6% 10% 19% 18% 12%	2310
	11th to 20th	Night	35% 6% 12% 17% 18% 12%	2073
	21st to end	Night	33% 5% 12% 19% 25% 7%	2000
May	1st to 10th	Night	45% 7% 12% 22% 12% 3	4126
	11th to 20th	Night	38% 7% 14% 17% 21% 2	4054
	21st to end	Night	33% 8% 16% 27% 11% 4	4452
June	1st to 10th	Night	22% 8% 17% 32% 19% 2	1800
	11th to 20th	Night	17% 6% 18% 34% 20% 5%	1800
	21st to end	Night	25% 8% 16% 28% 21% 3	1800
July	1st to 10th	Night	32% 9% 26% 28% 5%	4035
	11th to 20th	Night	18% 7% 25% 34% 15% 1	4026
	21st to end	Night	30% 9% 18% 29% 12% 2	4320
August	1st to 10th	Night	8% 4 15% 33% 34% 5%	2916
	11th to 20th	Night	16% 6% 21% 43% 11% 3	2964
	21st to end	Night	24% 8% 22% 28% 16% 2	3638
September	1st to 10th	Night	30% 7% 14% 22% 17% 10%	2200
	11th to 20th	Night	31% 7% 14% 20% 19% 8%	2200
	21st to end	Night	23% 5% 12% 22% 26% 13%	2200
October	1st to 10th	Night	12% 2 7% 15% 20% 44%	3748
	11th to 20th	Night	16% 2 4 19% 33% 26%	3899
	21st to end	Night	22% 4 4 18% 35% 17%	4252
November	1st to 10th	Night	30% 4 8% 19% 26% 13%	2460
	11th to 20th	Night	30% 5% 8% 19% 24% 14%	2520
	21st to end	Night	38% 4 8% 17% 23% 11%	2704
December	1st to 10th	Night	41% 4 5% 16% 27% 7%	4380
	11th to 20th	Night	44% 3 6% 11% 23% 12%	4947
	21st to end	Night	37% 4 5% 15% 28% 10%	6633

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% 14% 35% 22% 7% 1	330
	11th to 20th	Day	19% 16% 35% 21% 8% 1	330
	21st to end	Day	23% 12% 42% 17% 6%	363
February	1st to 10th	Day	24% 15% 35% 21% 5%	330
	11th to 20th	Day	33% 18% 30% 15% 4 1	330
	21st to end	Day	29% 15% 40% 13% 3	273
March	1st to 10th	Day	24% 14% 37% 17% 8%	330
	11th to 20th	Day	21% 16% 40% 18% 4 1	330
	21st to end	Day	18% 12% 42% 21% 5% 1	363
April	1st to 10th	Day	24% 12% 39% 21% 4	330
	11th to 20th	Day	22% 15% 30% 23% 9% 1	476
	21st to end	Day	16% 10% 33% 30% 10% 2	500
May	1st to 10th	Day	14% 11% 32% 32% 8% 1	675
	11th to 20th	Day	14% 7% 27% 32% 18% 4	725
	21st to end	Day	13% 5% 23% 32% 21% 5%	789
June	1st to 10th	Day	8% 3 12% 37% 28% 12%	730
	11th to 20th	Day	6% 2 14% 37% 31% 9%	730
	21st to end	Day	5% 2 12% 31% 34% 16%	730
July	1st to 10th	Day	9% 2 7% 30% 34% 18%	721
	11th to 20th	Day	4 1 6% 28% 46% 15%	718
	21st to end	Day	6% 2 5% 28% 44% 16%	794
August	1st to 10th	Day	4 3 25% 51% 17%	726
	11th to 20th	Day	6% 1 3 22% 52% 15%	687
	21st to end	Day	8% 1 5% 16% 41% 29%	552
September	1st to 10th	Day	6% 9% 26% 33% 25%	330
	11th to 20th	Day	5% 2 8% 27% 34% 24%	330
	21st to end	Day	12% 3 10% 28% 31% 17%	330
October	1st to 10th	Day	3 1 16% 34% 35% 11%	330
	11th to 20th	Day	10% 4 27% 31% 22% 7%	330
	21st to end	Day	20% 9% 25% 25% 17% 4	363
November	1st to 10th	Day	18% 6% 24% 33% 17% 2	330
	11th to 20th	Day	16% 10% 27% 32% 13% 2	330
	21st to end	Day	22% 12% 33% 20% 12% 1	330
December	1st to 10th	Day	21% 8% 38% 18% 12% 3	330
	11th to 20th	Day	28% 13% 28% 22% 8% 1	330
	21st to end	Day	19% 13% 39% 21% 7% 1	363
January	1st to 10th	Night	19% 9% 32% 32% 8%	1050
	11th to 20th	Night	21% 11% 33% 28% 7%	1050
	21st to end	Night	21% 10% 33% 32% 5%	1155
February	1st to 10th	Night	22% 10% 34% 30% 4	1003
	11th to 20th	Night	26% 12% 34% 25% 3	824
	21st to end	Night	22% 13% 39% 22% 4	561
March	1st to 10th	Night	22% 12% 34% 26% 5%	630
	11th to 20th	Night	18% 12% 37% 27% 6%	630
	21st to end	Night	14% 11% 40% 29% 6%	693
April	1st to 10th	Night	13% 9% 42% 29% 7%	630
	11th to 20th	Night	16% 12% 36% 27% 9%	611
	21st to end	Night	14% 8% 40% 28% 10% 1	600
May	1st to 10th	Night	11% 7% 38% 33% 9% 1	600
	11th to 20th	Night	13% 7% 28% 37% 15% 1	591
	21st to end	Night	8% 4 26% 41% 19% 2	650
June	1st to 10th	Night	6% 2 14% 42% 33% 4	600
	11th to 20th	Night	5% 2 16% 52% 24% 3	600
	21st to end	Night	6% 1 12% 38% 38% 6%	600
July	1st to 10th	Night	4 2 8% 42% 38% 7%	585
	11th to 20th	Night	3 1 5% 41% 44% 6%	582
	21st to end	Night	5% 1 5% 40% 44% 5%	657
August	1st to 10th	Night	2 5% 40% 47% 6%	597
	11th to 20th	Night	7% 2 5% 39% 41% 7%	594
	21st to end	Night	5% 1 5% 35% 47% 7%	660
September	1st to 10th	Night	8% 1 6% 36% 42% 7%	600
	11th to 20th	Night	10% 1 5% 34% 44% 5%	600
	21st to end	Night	8% 1 9% 38% 39% 5%	600
October	1st to 10th	Night	5% 3 12% 45% 29% 5%	693
	11th to 20th	Night	14% 3 22% 40% 19% 3	800
	21st to end	Night	15% 7% 25% 34% 17% 2	880
November	1st to 10th	Night	14% 4 25% 38% 19% 1	820
	11th to 20th	Night	11% 8% 28% 40% 13%	840
	21st to end	Night	20% 9% 27% 30% 13% 1	1024
December	1st to 10th	Night	19% 9% 28% 35% 8%	1050
	11th to 20th	Night	22% 8% 29% 35% 6%	1050
	21st to end	Night	22% 8% 30% 32% 7%	1155

Page generated at 2026-04-14 01:44:28. Version ac07

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