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 2024-11-25.

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% 38%	101400
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 39%	98090
Transparency	Day	45% 3 11% 24% 15% 2	104938
	Night	45% 3 11% 23% 16% 2	102628
Seeing	Day	22% 16% 33% 20% 7% 2	15109
	Night	22% 13% 32% 24% 8% 1	23992

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	15% 7% 2 7% 3 3 4 3 4 6% 45%	2517
	11th to 20th	Day	17% 6% 3 8% 4 3 4 3 5% 6% 42%	2520
	21st to end	Day	20% 11% 3 7% 4 4 4 3 4 5% 35%	2772
February	1st to 10th	Day	19% 7% 3 6% 4 4 4 5% 6% 6% 36%	1761
	11th to 20th	Day	14% 8% 2 6% 4 5% 5% 4 5% 7% 39%	1848
	21st to end	Day	17% 10% 3 6% 4 5% 4 4 4 6% 36%	1570
March	1st to 10th	Day	26% 13% 3 6% 4 4 3 3 4 5% 30%	3116
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 6% 7% 40%	3350
	21st to end	Day	24% 10% 2 6% 4 3 4 4 6% 6% 33%	3999
April	1st to 10th	Day	19% 10% 3 7% 4 4 4 3 5% 6% 37%	2280
	11th to 20th	Day	18% 7% 2 5% 5% 4 5% 4 6% 7% 38%	2283
	21st to end	Day	20% 7% 3 6% 5% 4 4 3 5% 7% 36%	2470
May	1st to 10th	Day	22% 12% 3 9% 5% 4 4 3 5% 6% 28%	4106
	11th to 20th	Day	22% 9% 3 8% 5% 4 4 3 5% 6% 32%	4134
	21st to end	Day	14% 5% 2 5% 4 4 4 3 5% 8% 45%	4837
June	1st to 10th	Day	20% 6% 2 5% 4 6% 5% 4 6% 7% 35%	2660
	11th to 20th	Day	16% 6% 2 5% 5% 4 4 4 6% 8% 39%	2660
	21st to end	Day	18% 5% 2 7% 5% 5% 4 4 6% 9% 35%	2660
July	1st to 10th	Day	14% 7% 2 6% 5% 4 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 4 6% 10% 40%	4440
	21st to end	Day	17% 6% 3 7% 5% 4 5% 4 7% 8% 34%	4814
August	1st to 10th	Day	15% 6% 3 7% 4 5% 6% 5% 7% 9% 33%	4139
	11th to 20th	Day	14% 7% 3 7% 4 4 5% 4 6% 8% 38%	4027
	21st to end	Day	7% 4 2 5% 4 4 6% 5% 7% 10% 45%	4180
September	1st to 10th	Day	13% 6% 2 5% 3 4 4 4 5% 7% 47%	2266
	11th to 20th	Day	15% 6% 2 4 4 2 3 2 4 6% 51%	2090
	21st to end	Day	17% 6% 2 6% 4 4 4 2 5% 6% 44%	2090
October	1st to 10th	Day	23% 5% 2 6% 3 4 3 3 5% 6% 40%	2090
	11th to 20th	Day	15% 6% 2 5% 3 4 4 3 5% 7% 47%	1855
	21st to end	Day	20% 6% 2 6% 4 4 4 3 5% 6% 40%	1881
November	1st to 10th	Day	16% 6% 2 6% 4 3 3 3 3 5% 50%	1761
	11th to 20th	Day	18% 6% 2 5% 3 3 3 3 4 5% 48%	1800
	21st to end	Day	19% 7% 2 5% 3 4 4 3 4 6% 43%	1746
December	1st to 10th	Day	19% 7% 3 6% 4 4 4 3 5% 6% 40%	1560
	11th to 20th	Day	22% 7% 2 4 4 3 3 3 4 5% 44%	1906
	21st to end	Day	22% 10% 3 6% 5% 4 4 3 5% 6% 34%	2772
January	1st to 10th	Night	18% 7% 2 4 3 3 3 3 4 6% 46%	4429
	11th to 20th	Night	15% 8% 3 9% 5% 4 4 3 4 5% 40%	4440
	21st to end	Night	21% 13% 3 8% 5% 4 4 3 4 5% 30%	4884
February	1st to 10th	Night	16% 10% 3 6% 4 4 4 4 5% 6% 38%	2415
	11th to 20th	Night	14% 10% 3 6% 4 5% 3 4 5% 6% 40%	2218
	21st to end	Night	19% 8% 2 5% 4 3 3 4 4 6% 42%	1884
March	1st to 10th	Night	29% 10% 2 5% 3 3 3 3 4 5% 32%	3724
	11th to 20th	Night	12% 9% 3 8% 4 5% 5% 4 5% 6% 38%	3608
	21st to end	Night	25% 8% 3 6% 4 4 4 4 5% 4 33%	3630
April	1st to 10th	Night	20% 8% 2 6% 5% 5% 5% 4 5% 6% 35%	1900
	11th to 20th	Night	20% 8% 2 5% 4 4 4 3 4 7% 40%	1845
	21st to end	Night	21% 6% 2 6% 4 4 3 3 5% 6% 38%	1710
May	1st to 10th	Night	24% 12% 3 7% 5% 5% 4 3 5% 6% 27%	2834
	11th to 20th	Night	21% 9% 2 7% 5% 5% 6% 4 6% 8% 27%	2786
	21st to end	Night	18% 6% 3 6% 4 3 4 3 5% 7% 41%	2738
June	1st to 10th	Night	18% 9% 2 6% 4 5% 5% 4 4 6% 37%	1520
	11th to 20th	Night	17% 9% 2 7% 3 3 3 3 6% 9% 37%	1520
	21st to end	Night	17% 6% 2 5% 4 4 5% 3 7% 9% 37%	1520
July	1st to 10th	Night	12% 7% 2 7% 6% 5% 5% 4 7% 9% 35%	2520
	11th to 20th	Night	10% 7% 3 7% 5% 5% 4 5% 6% 9% 39%	2520
	21st to end	Night	16% 9% 3 7% 5% 4 4 3 5% 7% 36%	2739
August	1st to 10th	Night	19% 6% 3 8% 4 5% 5% 5% 6% 8% 32%	2757
	11th to 20th	Night	10% 7% 3 8% 6% 6% 6% 5% 8% 7% 35%	2796
	21st to end	Night	8% 4 1 4 4 4 4 4 5% 9% 52%	3476
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 7% 48%	1914
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 5% 53%	2090
	21st to end	Night	17% 6% 2 6% 4 4 3 3 5% 6% 43%	2090
October	1st to 10th	Night	21% 6% 2 6% 4 4 3 3 5% 5% 41%	2090
	11th to 20th	Night	15% 5% 2 5% 4 3 4 3 5% 7% 46%	2321
	21st to end	Night	21% 6% 2 6% 3 3 4 3 5% 6% 39%	2717
November	1st to 10th	Night	14% 5% 2 6% 4 3 4 3 4 6% 49%	2537
	11th to 20th	Night	17% 7% 2 5% 3 3 4 3 4 6% 47%	2600
	21st to end	Night	16% 7% 2 5% 4 4 4 3 5% 6% 43%	2529
December	1st to 10th	Night	19% 9% 3 7% 4 4 4 3 5% 5% 39%	2617
	11th to 20th	Night	20% 6% 2 5% 3 3 4 4 5% 6% 41%	3288
	21st to end	Night	21% 9% 3 6% 4 4 4 3 4 5% 36%	4884

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% 1 8% 34% 13% 1	2518
	11th to 20th	Day	45% 3 10% 26% 14% 2	2520
	21st to end	Day	53% 2 9% 24% 10% 2	2772
February	1st to 10th	Day	48% 2 12% 21% 14% 3	1761
	11th to 20th	Day	45% 4 11% 22% 16% 3	1857
	21st to end	Day	49% 2 10% 21% 15% 3	1570
March	1st to 10th	Day	59% 1 9% 16% 12% 3	3119
	11th to 20th	Day	43% 1 12% 24% 16% 3	3350
	21st to end	Day	53% 1 4 17% 15% 8%	3999
April	1st to 10th	Day	50% 2 8% 18% 17% 4	2280
	11th to 20th	Day	46% 2 10% 23% 16% 3	2283
	21st to end	Day	49% 3 7% 21% 18% 4	2470
May	1st to 10th	Day	59% 2 10% 18% 10% 1	4120
	11th to 20th	Day	54% 2 14% 18% 11% 2	4138
	21st to end	Day	40% 2 12% 25% 19% 2	4837
June	1st to 10th	Day	48% 4 12% 23% 12% 1	2660
	11th to 20th	Day	43% 3 13% 22% 17% 2	2660
	21st to end	Day	46% 4 12% 24% 13% 1	2660
July	1st to 10th	Day	44% 5% 12% 23% 15% 1	4370
	11th to 20th	Day	39% 5% 15% 27% 14% 1	4365
	21st to end	Day	47% 4 12% 22% 13% 2	4661
August	1st to 10th	Day	46% 6% 15% 24% 8% 1	4125
	11th to 20th	Day	43% 5% 14% 27% 10% 1	4066
	21st to end	Day	32% 5% 13% 31% 18% 2	4180
September	1st to 10th	Day	36% 3 11% 26% 22% 1	2266
	11th to 20th	Day	37% 2 7% 29% 23% 3	2090
	21st to end	Day	42% 2 8% 24% 22% 2	2090
October	1st to 10th	Day	42% 4 10% 24% 18% 2	3480
	11th to 20th	Day	32% 2 7% 31% 25% 4	3045
	21st to end	Day	34% 3 9% 31% 21% 3	3081
November	1st to 10th	Day	39% 2 11% 27% 17% 2	1761
	11th to 20th	Day	41% 2 7% 23% 24% 3	1800
	21st to end	Day	43% 3 13% 23% 15% 2	1746
December	1st to 10th	Day	47% 3 14% 17% 18% 1	1560
	11th to 20th	Day	46% 2 11% 18% 17% 6%	1906
	21st to end	Day	54% 2 10% 22% 11% 1	2772
January	1st to 10th	Night	41% 2 11% 30% 13% 3	4429
	11th to 20th	Night	48% 3 10% 23% 14% 3	4440
	21st to end	Night	58% 2 8% 19% 11% 2	4884
February	1st to 10th	Night	48% 3 12% 21% 14% 3	2415
	11th to 20th	Night	45% 3 9% 22% 17% 4	2220
	21st to end	Night	44% 2 8% 26% 16% 4	1884
March	1st to 10th	Night	57% 1 8% 19% 12% 4	3734
	11th to 20th	Night	49% 2 11% 18% 18% 3	3609
	21st to end	Night	55% 1 4 15% 18% 7%	3630
April	1st to 10th	Night	50% 2 9% 18% 17% 3	1900
	11th to 20th	Night	47% 2 7% 22% 19% 3	1845
	21st to end	Night	49% 2 9% 19% 17% 3	1710
May	1st to 10th	Night	59% 2 11% 18% 8% 2	2840
	11th to 20th	Night	56% 2 15% 16% 9% 2	2787
	21st to end	Night	45% 2 14% 22% 16% 1	2739
June	1st to 10th	Night	49% 3 11% 24% 13% 1	1520
	11th to 20th	Night	44% 3 13% 22% 16% 2	1520
	21st to end	Night	43% 5% 13% 23% 14% 1	1520
July	1st to 10th	Night	44% 5% 13% 22% 15% 1	2480
	11th to 20th	Night	41% 5% 15% 23% 15% 1	2472
	21st to end	Night	47% 5% 11% 21% 14% 1	2651
August	1st to 10th	Night	51% 5% 12% 20% 11% 1	2747
	11th to 20th	Night	45% 7% 14% 23% 11%	2823
	21st to end	Night	29% 4 14% 29% 23% 1	3476
September	1st to 10th	Night	37% 3 11% 27% 20% 1	1914
	11th to 20th	Night	35% 2 9% 26% 26% 2	2090
	21st to end	Night	42% 3 7% 25% 20% 2	2090
October	1st to 10th	Night	42% 3 13% 24% 15% 2	3480
	11th to 20th	Night	28% 2 10% 29% 29% 3	3857
	21st to end	Night	35% 2 10% 31% 19% 2	4467
November	1st to 10th	Night	38% 3 11% 25% 20% 3	2537
	11th to 20th	Night	41% 2 9% 23% 22% 4	2600
	21st to end	Night	42% 3 13% 26% 15% 2	2529
December	1st to 10th	Night	48% 2 11% 23% 14% 1	2617
	11th to 20th	Night	45% 2 13% 18% 21% 1	3288
	21st to end	Night	52% 2 7% 26% 13% 1	4884

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	26% 24% 27% 19% 3	180
	11th to 20th	Day	24% 29% 31% 13% 2 1	180
	21st to end	Day	22% 28% 34% 12% 4	198
February	1st to 10th	Day	29% 22% 35% 13% 1	371
	11th to 20th	Day	27% 26% 35% 11% 2	456
	21st to end	Day	26% 20% 35% 14% 4	382
March	1st to 10th	Day	27% 19% 37% 13% 3	460
	11th to 20th	Day	27% 25% 33% 11% 3 1	460
	21st to end	Day	31% 21% 30% 11% 6% 2	506
April	1st to 10th	Day	28% 27% 24% 15% 5% 1	460
	11th to 20th	Day	28% 23% 31% 14% 4	452
	21st to end	Day	27% 17% 35% 17% 2 1	460
May	1st to 10th	Day	31% 23% 28% 13% 4 1	463
	11th to 20th	Day	22% 18% 37% 19% 4 1	487
	21st to end	Day	19% 15% 37% 22% 6% 1	529
June	1st to 10th	Day	22% 11% 37% 20% 9% 1	490
	11th to 20th	Day	16% 18% 36% 22% 7% 2	490
	21st to end	Day	20% 13% 37% 23% 6% 2	490
July	1st to 10th	Day	18% 8% 34% 28% 10% 3	485
	11th to 20th	Day	15% 8% 32% 31% 11% 2	484
	21st to end	Day	14% 6% 37% 33% 8% 1	532
August	1st to 10th	Day	12% 10% 35% 30% 11% 2	486
	11th to 20th	Day	17% 7% 33% 27% 13% 4	479
	21st to end	Day	14% 7% 34% 27% 14% 4	539
September	1st to 10th	Day	18% 11% 32% 24% 12% 4	490
	11th to 20th	Day	22% 10% 28% 20% 12% 9%	490
	21st to end	Day	20% 12% 33% 23% 8% 5%	490
October	1st to 10th	Day	26% 12% 27% 22% 10% 3	490
	11th to 20th	Day	20% 18% 27% 22% 10% 2	426
	21st to end	Day	26% 15% 34% 17% 8% 1	429
November	1st to 10th	Day	19% 15% 37% 18% 9% 2	395
	11th to 20th	Day	27% 21% 32% 16% 5% 1	400
	21st to end	Day	27% 19% 31% 16% 6% 1	382
December	1st to 10th	Day	25% 25% 31% 15% 3	220
	11th to 20th	Day	31% 22% 37% 8% 2	180
	21st to end	Day	23% 26% 30% 15% 5% 2	198
January	1st to 10th	Night	22% 20% 37% 19% 3	760
	11th to 20th	Night	27% 20% 33% 18% 2	760
	21st to end	Night	21% 20% 35% 20% 4 1	836
February	1st to 10th	Night	23% 18% 35% 22% 2	760
	11th to 20th	Night	23% 18% 39% 17% 3	743
	21st to end	Night	26% 17% 33% 19% 4	628
March	1st to 10th	Night	26% 17% 35% 19% 4	760
	11th to 20th	Night	24% 17% 38% 17% 4	760
	21st to end	Night	26% 16% 33% 19% 5%	836
April	1st to 10th	Night	26% 18% 32% 21% 4	760
	11th to 20th	Night	26% 17% 33% 19% 5%	721
	21st to end	Night	24% 15% 32% 25% 3	570
May	1st to 10th	Night	28% 12% 33% 21% 5% 1	570
	11th to 20th	Night	23% 13% 34% 24% 5%	548
	21st to end	Night	21% 7% 32% 30% 10%	411
June	1st to 10th	Night	22% 6% 33% 29% 9% 1	380
	11th to 20th	Night	21% 5% 33% 32% 8% 1	380
	21st to end	Night	22% 4 31% 33% 9%	380
July	1st to 10th	Night	16% 4 29% 39% 11% 1	370
	11th to 20th	Night	14% 4 26% 40% 16% 1	368
	21st to end	Night	15% 4 30% 40% 11%	416
August	1st to 10th	Night	13% 3 30% 40% 14% 1	525
	11th to 20th	Night	13% 4 30% 35% 17%	563
	21st to end	Night	16% 3 23% 38% 17% 3	836
September	1st to 10th	Night	15% 5% 31% 32% 15% 1	760
	11th to 20th	Night	18% 6% 27% 27% 20% 4	760
	21st to end	Night	19% 7% 27% 29% 16% 2	760
October	1st to 10th	Night	24% 9% 26% 25% 14% 2	760
	11th to 20th	Night	18% 12% 33% 24% 12% 1	760
	21st to end	Night	26% 13% 31% 22% 7%	836
November	1st to 10th	Night	17% 15% 34% 26% 8% 1	780
	11th to 20th	Night	23% 18% 32% 20% 7%	800
	21st to end	Night	22% 23% 32% 18% 5%	779
December	1st to 10th	Night	26% 17% 36% 17% 4	760
	11th to 20th	Night	22% 20% 33% 21% 4 1	760
	21st to end	Night	26% 18% 34% 20% 2	836

Page generated at 2024-11-22 08:02:26. Version ac07

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