The BD Software Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The BD Software Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	17% 7% 2 6% 4 4 4 4 5% 7% 39%	126969
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 40%	124407
Transparency	Day	45% 3 11% 23% 15% 3	130489
	Night	45% 3 11% 22% 17% 3	128961
Seeing	Day	23% 17% 33% 19% 7% 2	16476
	Night	22% 13% 32% 24% 8% 1	25403

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	12% 6% 2 9% 5% 4 5% 4 6% 7% 41%	3605
	11th to 20th	Day	14% 7% 2 6% 3 3 3 3 5% 6% 48%	3570
	21st to end	Day	16% 9% 2 6% 3 3 4 3 4 5% 44%	3960
February	1st to 10th	Day	19% 7% 3 6% 4 4 4 5% 6% 6% 37%	1854
	11th to 20th	Day	14% 8% 2 6% 4 5% 5% 4 5% 7% 39%	1948
	21st to end	Day	17% 10% 3 6% 4 4 4 4 4 6% 37%	1650
March	1st to 10th	Day	22% 10% 2 6% 4 4 4 3 5% 6% 35%	4476
	11th to 20th	Day	16% 9% 3 7% 4 4 4 4 6% 6% 38%	4794
	21st to end	Day	27% 9% 2 5% 4 3 4 4 5% 6% 30%	5733
April	1st to 10th	Day	19% 10% 3 7% 4 4 4 3 5% 6% 37%	2400
	11th to 20th	Day	18% 7% 2 5% 5% 4 5% 4 5% 7% 38%	2405
	21st to end	Day	20% 7% 3 6% 5% 4 4 3 5% 7% 37%	2600
May	1st to 10th	Day	29% 11% 3 7% 4 4 4 3 5% 6% 24%	5886
	11th to 20th	Day	19% 9% 3 8% 5% 4 4 4 5% 7% 31%	5942
	21st to end	Day	19% 7% 3 6% 4 4 5% 3 5% 8% 36%	6949
June	1st to 10th	Day	20% 6% 2 5% 4 6% 5% 4 6% 7% 35%	2800
	11th to 20th	Day	17% 6% 2 5% 5% 4 4 4 6% 8% 38%	2800
	21st to end	Day	18% 5% 2 6% 5% 5% 4 4 6% 9% 36%	2800
July	1st to 10th	Day	17% 7% 2 6% 4 4 6% 4 6% 9% 33%	6360
	11th to 20th	Day	9% 6% 3 7% 5% 5% 5% 4 7% 11% 39%	6360
	21st to end	Day	15% 6% 3 6% 4 4 4 3 6% 8% 43%	6926
August	1st to 10th	Day	15% 6% 3 7% 4 5% 6% 5% 7% 9% 34%	4270
	11th to 20th	Day	14% 7% 3 7% 4 4 5% 4 6% 8% 38%	4157
	21st to end	Day	7% 4 2 5% 4 4 6% 5% 7% 10% 46%	4312
September	1st to 10th	Day	13% 6% 2 5% 3 4 4 4 5% 7% 47%	2385
	11th to 20th	Day	14% 6% 2 4 4 2 3 2 4 6% 52%	2200
	21st to end	Day	17% 6% 2 6% 4 4 4 2 5% 6% 43%	2200
October	1st to 10th	Day	22% 5% 2 5% 3 4 3 3 5% 5% 42%	2200
	11th to 20th	Day	16% 6% 2 5% 3 4 4 3 5% 7% 46%	1952
	21st to end	Day	20% 6% 2 6% 4 4 4 3 5% 6% 41%	1980
November	1st to 10th	Day	15% 6% 2 6% 4 3 3 3 4 5% 49%	1851
	11th to 20th	Day	18% 6% 2 5% 3 4 4 3 4 5% 47%	1890
	21st to end	Day	18% 7% 2 6% 3 3 4 3 4 6% 43%	1890
December	1st to 10th	Day	14% 9% 2 5% 3 3 3 3 4 6% 48%	2750
	11th to 20th	Day	20% 6% 2 4 4 3 3 3 4 5% 47%	3066
	21st to end	Day	20% 10% 3 6% 4 4 4 3 4 5% 37%	4048
January	1st to 10th	Night	14% 6% 2 5% 3 4 4 3 5% 6% 48%	6364
	11th to 20th	Night	14% 8% 3 9% 5% 5% 4 4 4 5% 40%	6315
	21st to end	Night	15% 10% 3 7% 5% 5% 4 3 5% 5% 38%	6996
February	1st to 10th	Night	16% 10% 3 6% 4 4 4 4 5% 6% 38%	2541
	11th to 20th	Night	15% 9% 2 6% 4 5% 4 4 5% 7% 40%	2338
	21st to end	Night	18% 9% 2 6% 4 3 4 3 4 6% 41%	1980
March	1st to 10th	Night	25% 8% 2 6% 4 3 3 3 4 6% 37%	5364
	11th to 20th	Night	16% 10% 3 7% 4 5% 5% 3 5% 6% 37%	5164
	21st to end	Night	26% 9% 3 6% 4 4 4 4 5% 4 32%	5196
April	1st to 10th	Night	20% 8% 3 6% 4 5% 5% 4 5% 6% 35%	2000
	11th to 20th	Night	21% 8% 2 5% 4 4 4 3 4 7% 39%	1943
	21st to end	Night	21% 6% 3 6% 4 4 3 3 5% 6% 38%	1800
May	1st to 10th	Night	32% 11% 3 6% 4 4 3 3 4 6% 25%	4054
	11th to 20th	Night	17% 9% 3 7% 5% 5% 6% 5% 6% 8% 28%	3992
	21st to end	Night	21% 9% 3 8% 5% 4 5% 3 5% 6% 32%	3926
June	1st to 10th	Night	18% 10% 2 7% 4 5% 5% 4 4 6% 38%	1600
	11th to 20th	Night	17% 9% 2 7% 3 4 3 3 6% 9% 37%	1600
	21st to end	Night	17% 6% 2 6% 4 4 5% 3 7% 9% 38%	1600
July	1st to 10th	Night	13% 8% 2 7% 5% 5% 5% 4 7% 9% 37%	3600
	11th to 20th	Night	11% 7% 3 7% 5% 5% 5% 4 6% 9% 39%	3600
	21st to end	Night	12% 7% 2 6% 4 4 4 3 5% 7% 45%	3926
August	1st to 10th	Night	19% 6% 3 8% 4 5% 5% 5% 6% 7% 33%	2845
	11th to 20th	Night	10% 7% 3 8% 6% 6% 6% 5% 8% 8% 35%	2886
	21st to end	Night	8% 4 1 4 4 4 4 4 5% 9% 52%	3586
September	1st to 10th	Night	12% 6% 2 6% 4 3 5% 3 5% 7% 48%	2015
	11th to 20th	Night	13% 5% 2 5% 4 3 3 3 4 5% 53%	2200
	21st to end	Night	17% 6% 2 7% 4 4 3 3 5% 6% 43%	2200
October	1st to 10th	Night	20% 6% 2 6% 4 4 3 3 5% 5% 43%	2200
	11th to 20th	Night	15% 5% 2 5% 4 3 5% 3 5% 7% 46%	2444
	21st to end	Night	21% 7% 2 6% 3 3 4 3 5% 6% 40%	2860
November	1st to 10th	Night	14% 5% 2 6% 4 3 4 4 4 6% 48%	2667
	11th to 20th	Night	16% 6% 2 5% 3 3 4 3 4 6% 47%	2730
	21st to end	Night	16% 7% 2 5% 4 3 4 3 5% 6% 44%	2730
December	1st to 10th	Night	18% 8% 2 6% 4 4 4 3 5% 6% 42%	4647
	11th to 20th	Night	22% 7% 2 6% 3 3 3 3 4 5% 42%	5348
	21st to end	Night	18% 9% 3 6% 4 3 4 3 4 5% 41%	7150

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	43% 2 7% 29% 18% 2	3606
	11th to 20th	Day	39% 3 11% 24% 21% 3	3600
	21st to end	Day	43% 2 9% 23% 19% 3	3960
February	1st to 10th	Day	48% 2 12% 21% 15% 2	1854
	11th to 20th	Day	45% 4 11% 22% 16% 3	1957
	21st to end	Day	48% 2 10% 22% 15% 3	1650
March	1st to 10th	Day	52% 2 9% 15% 12% 10%	4479
	11th to 20th	Day	47% 2 11% 26% 12% 2	4794
	21st to end	Day	56% 2 5% 16% 14% 7%	5733
April	1st to 10th	Day	50% 2 8% 18% 17% 4	2400
	11th to 20th	Day	46% 2 10% 22% 17% 3	2405
	21st to end	Day	48% 3 7% 21% 18% 4	2600
May	1st to 10th	Day	62% 3 11% 15% 7% 1	5897
	11th to 20th	Day	53% 3 13% 18% 10% 2	5946
	21st to end	Day	48% 3 12% 22% 14% 1	6949
June	1st to 10th	Day	48% 4 11% 23% 13% 1	2800
	11th to 20th	Day	43% 3 13% 21% 17% 2	2800
	21st to end	Day	45% 4 12% 24% 14% 1	2800
July	1st to 10th	Day	47% 5% 12% 21% 14% 1	6290
	11th to 20th	Day	39% 6% 15% 26% 13% 1	6285
	21st to end	Day	39% 4 12% 29% 15% 1	6728
August	1st to 10th	Day	45% 6% 15% 24% 9% 1	4256
	11th to 20th	Day	43% 5% 14% 27% 10% 1	4196
	21st to end	Day	31% 5% 13% 31% 18% 2	4312
September	1st to 10th	Day	36% 3 11% 26% 22% 1	2385
	11th to 20th	Day	36% 2 8% 29% 23% 3	2200
	21st to end	Day	42% 2 8% 24% 21% 2	2200
October	1st to 10th	Day	41% 3 10% 24% 19% 3	3590
	11th to 20th	Day	33% 2 7% 31% 24% 3	3142
	21st to end	Day	34% 3 9% 31% 20% 3	3180
November	1st to 10th	Day	40% 2 11% 27% 18% 2	1851
	11th to 20th	Day	41% 2 7% 23% 23% 3	1890
	21st to end	Day	44% 3 13% 25% 15% 2	1890
December	1st to 10th	Day	39% 3 14% 29% 14% 1	2750
	11th to 20th	Day	41% 2 13% 18% 20% 5%	3066
	21st to end	Day	51% 2 7% 21% 15% 4	4048
January	1st to 10th	Night	38% 2 9% 33% 16% 2	6364
	11th to 20th	Night	47% 3 11% 22% 14% 4	6360
	21st to end	Night	49% 2 8% 18% 18% 5%	6996
February	1st to 10th	Night	48% 3 11% 21% 14% 3	2541
	11th to 20th	Night	45% 3 9% 22% 17% 4	2340
	21st to end	Night	45% 2 8% 25% 16% 4	1980
March	1st to 10th	Night	51% 1 8% 16% 16% 8%	5374
	11th to 20th	Night	51% 2 14% 17% 14% 2	5165
	21st to end	Night	55% 2 4 13% 20% 6%	5196
April	1st to 10th	Night	51% 2 9% 18% 17% 3	2000
	11th to 20th	Night	47% 2 7% 21% 19% 3	1943
	21st to end	Night	48% 2 9% 19% 18% 4	1800
May	1st to 10th	Night	62% 2 12% 13% 8% 2	4060
	11th to 20th	Night	53% 4 15% 17% 10% 2	3993
	21st to end	Night	54% 3 12% 18% 11% 1	3927
June	1st to 10th	Night	49% 3 11% 23% 13% 1	1600
	11th to 20th	Night	44% 4 13% 22% 15% 2	1600
	21st to end	Night	43% 5% 13% 23% 15% 2	1600
July	1st to 10th	Night	43% 5% 12% 22% 17%	3560
	11th to 20th	Night	41% 5% 17% 21% 14% 1	3552
	21st to end	Night	39% 4 10% 31% 15% 1	3809
August	1st to 10th	Night	50% 5% 12% 21% 11% 1	2835
	11th to 20th	Night	45% 6% 14% 24% 11% 1	2913
	21st to end	Night	29% 4 14% 29% 23% 1	3586
September	1st to 10th	Night	36% 3 11% 27% 20% 1	2015
	11th to 20th	Night	34% 2 9% 26% 27% 2	2200
	21st to end	Night	42% 3 7% 25% 20% 3	2200
October	1st to 10th	Night	41% 3 13% 25% 16% 2	3590
	11th to 20th	Night	28% 2 10% 29% 28% 3	3980
	21st to end	Night	35% 2 10% 31% 19% 2	4610
November	1st to 10th	Night	38% 3 10% 25% 20% 3	2667
	11th to 20th	Night	40% 2 9% 24% 22% 4	2730
	21st to end	Night	41% 3 13% 26% 15% 2	2730
December	1st to 10th	Night	44% 3 10% 29% 13% 1	4647
	11th to 20th	Night	47% 2 13% 15% 22% 2	5348
	21st to end	Night	48% 2 7% 23% 18% 2	7150

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% 26% 27% 17% 3	202
	11th to 20th	Day	25% 29% 32% 13% 2 1	200
	21st to end	Day	24% 27% 35% 11% 3	220
February	1st to 10th	Day	29% 22% 35% 12% 1	404
	11th to 20th	Day	28% 26% 34% 10% 2	496
	21st to end	Day	26% 20% 36% 14% 4	414
March	1st to 10th	Day	28% 21% 36% 13% 3	500
	11th to 20th	Day	27% 25% 33% 11% 3 1	500
	21st to end	Day	32% 21% 29% 11% 5% 1	550
April	1st to 10th	Day	31% 27% 23% 14% 5% 1	500
	11th to 20th	Day	30% 24% 29% 13% 3	492
	21st to end	Day	28% 17% 35% 17% 2 1	500
May	1st to 10th	Day	33% 22% 28% 13% 4 1	503
	11th to 20th	Day	22% 18% 37% 18% 4 1	527
	21st to end	Day	19% 16% 37% 21% 6% 1	573
June	1st to 10th	Day	23% 11% 37% 19% 8% 1	530
	11th to 20th	Day	17% 18% 36% 21% 6% 2	530
	21st to end	Day	19% 13% 37% 24% 6% 2	530
July	1st to 10th	Day	19% 8% 34% 27% 9% 2	525
	11th to 20th	Day	15% 9% 32% 31% 11% 2	524
	21st to end	Day	13% 7% 37% 33% 8% 1	576
August	1st to 10th	Day	12% 9% 35% 29% 11% 3	526
	11th to 20th	Day	16% 7% 33% 28% 13% 4	519
	21st to end	Day	13% 7% 36% 26% 14% 4	583
September	1st to 10th	Day	17% 11% 33% 24% 12% 4	530
	11th to 20th	Day	20% 9% 28% 22% 12% 9%	530
	21st to end	Day	20% 12% 33% 23% 8% 5%	530
October	1st to 10th	Day	25% 12% 26% 22% 11% 4	530
	11th to 20th	Day	21% 18% 27% 22% 10% 2	459
	21st to end	Day	26% 16% 33% 17% 7% 1	462
November	1st to 10th	Day	20% 17% 36% 18% 8% 2	425
	11th to 20th	Day	26% 21% 33% 15% 4	430
	21st to end	Day	27% 21% 30% 15% 5% 1	430
December	1st to 10th	Day	26% 24% 32% 15% 3	264
	11th to 20th	Day	34% 20% 36% 7% 3	220
	21st to end	Day	25% 25% 29% 16% 4 2	242
January	1st to 10th	Night	22% 21% 37% 18% 3	805
	11th to 20th	Night	27% 20% 33% 18% 3	800
	21st to end	Night	20% 20% 36% 20% 4 1	880
February	1st to 10th	Night	23% 18% 35% 22% 2	800
	11th to 20th	Night	25% 18% 38% 16% 3	783
	21st to end	Night	25% 17% 34% 19% 4	660
March	1st to 10th	Night	26% 17% 35% 18% 4	800
	11th to 20th	Night	24% 17% 37% 17% 5%	800
	21st to end	Night	26% 16% 34% 19% 5%	880
April	1st to 10th	Night	27% 18% 32% 20% 4	800
	11th to 20th	Night	26% 17% 33% 18% 5%	759
	21st to end	Night	24% 16% 32% 25% 3	600
May	1st to 10th	Night	29% 12% 33% 21% 5% 1	600
	11th to 20th	Night	22% 13% 35% 24% 5% 1	577
	21st to end	Night	22% 7% 32% 30% 9%	433
June	1st to 10th	Night	22% 6% 34% 29% 9% 1	400
	11th to 20th	Night	20% 6% 34% 32% 8% 1	400
	21st to end	Night	22% 5% 30% 34% 10%	400
July	1st to 10th	Night	16% 5% 28% 40% 11% 1	390
	11th to 20th	Night	14% 4 27% 40% 15% 1	388
	21st to end	Night	14% 4 31% 41% 10%	438
August	1st to 10th	Night	13% 3 29% 41% 14% 1	553
	11th to 20th	Night	13% 4 29% 37% 16% 1	593
	21st to end	Night	16% 3 25% 38% 17% 3	880
September	1st to 10th	Night	15% 5% 31% 33% 15% 1	800
	11th to 20th	Night	17% 6% 26% 28% 20% 4	800
	21st to end	Night	19% 7% 27% 29% 16% 2	800
October	1st to 10th	Night	23% 9% 26% 26% 14% 2	800
	11th to 20th	Night	19% 12% 32% 25% 11% 1	800
	21st to end	Night	25% 14% 31% 23% 7%	880
November	1st to 10th	Night	18% 15% 33% 26% 8% 1	820
	11th to 20th	Night	22% 18% 33% 20% 7%	840
	21st to end	Night	22% 22% 32% 19% 5%	840
December	1st to 10th	Night	26% 17% 36% 17% 4	840
	11th to 20th	Night	23% 20% 33% 19% 4	840
	21st to end	Night	26% 18% 33% 21% 3	924

Page generated at 2025-12-30 01:14:06. Version ac07

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