BRAS Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the BRAS Dark Sky Site clear sky chart from 2005-11-06 to 2024-11-01.

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	11% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	100642
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	98323
Transparency	Day	42% 8% 12% 17% 16% 5%	100454
	Night	36% 8% 13% 18% 17% 7%	98183
Seeing	Day	14% 5% 17% 24% 25% 16%	14846
	Night	14% 4 18% 33% 25% 6%	24550

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	16% 10% 3 7% 4 5% 4 3 5% 7% 37%	2847
	11th to 20th	Day	13% 7% 2 5% 3 3 3 2 3 4 55%	2850
	21st to end	Day	23% 10% 4 6% 4 3 3 3 4 5% 34%	3135
February	1st to 10th	Day	17% 9% 3 7% 4 4 3 4 5% 6% 37%	1894
	11th to 20th	Day	17% 8% 3 6% 4 4 4 3 6% 5% 40%	1848
	21st to end	Day	16% 9% 3 8% 5% 4 4 3 5% 8% 36%	1617
March	1st to 10th	Day	22% 10% 3 8% 4 4 4 3 6% 7% 27%	3436
	11th to 20th	Day	14% 8% 3 7% 5% 5% 6% 5% 6% 9% 32%	3480
	21st to end	Day	12% 6% 2 7% 5% 4 5% 4 5% 7% 42%	3863
April	1st to 10th	Day	10% 8% 3 6% 5% 4 6% 5% 5% 7% 41%	2280
	11th to 20th	Day	14% 7% 3 7% 4 5% 4 4 7% 7% 38%	2254
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 9% 43%	2280
May	1st to 10th	Day	11% 7% 3 9% 7% 6% 6% 4 6% 7% 34%	3765
	11th to 20th	Day	11% 6% 3 8% 5% 5% 5% 4 5% 7% 43%	3764
	21st to end	Day	5% 4 2 7% 6% 7% 6% 6% 8% 9% 38%	4129
June	1st to 10th	Day	7% 5% 2 8% 7% 7% 7% 5% 8% 9% 33%	2456
	11th to 20th	Day	5% 6% 3 9% 8% 7% 7% 7% 8% 10% 32%	2470
	21st to end	Day	6% 6% 3 10% 9% 8% 8% 8% 9% 10% 24%	2470
July	1st to 10th	Day	6% 7% 3 10% 9% 8% 8% 6% 9% 10% 22%	4120
	11th to 20th	Day	6% 7% 3 10% 9% 9% 10% 7% 9% 11% 21%	4120
	21st to end	Day	12% 10% 4 10% 7% 7% 7% 5% 7% 9% 21%	4372
August	1st to 10th	Day	3 3 1 5% 4 5% 5% 5% 7% 9% 54%	3785
	11th to 20th	Day	6% 4 2 6% 5% 7% 7% 6% 9% 11% 37%	3729
	21st to end	Day	11% 7% 3 9% 7% 7% 6% 4 6% 7% 33%	4180
September	1st to 10th	Day	10% 5% 3 8% 6% 7% 6% 5% 7% 9% 34%	2280
	11th to 20th	Day	12% 6% 3 6% 5% 6% 5% 4 6% 8% 38%	2280
	21st to end	Day	9% 5% 2 6% 5% 4 4 4 6% 7% 48%	2048
October	1st to 10th	Day	6% 4 2 6% 3 3 4 4 5% 6% 56%	1900
	11th to 20th	Day	8% 4 2 5% 3 4 3 3 5% 7% 55%	1900
	21st to end	Day	10% 4 2 4 4 3 3 3 5% 6% 54%	2090
November	1st to 10th	Day	8% 6% 2 5% 4 4 4 4 5% 8% 51%	1858
	11th to 20th	Day	10% 6% 2 5% 4 4 4 3 5% 5% 52%	1900
	21st to end	Day	13% 7% 2 6% 5% 4 4 4 6% 5% 45%	1900
December	1st to 10th	Day	15% 8% 3 5% 5% 4 5% 4 5% 6% 41%	1900
	11th to 20th	Day	15% 10% 3 7% 4 5% 4 3 6% 7% 36%	2307
	21st to end	Day	16% 8% 3 6% 5% 4 4 3 6% 6% 39%	3135
January	1st to 10th	Night	17% 7% 3 5% 4 4 4 3 5% 5% 45%	4108
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 4 5% 52%	4120
	21st to end	Night	24% 8% 2 5% 3 2 3 2 4 6% 39%	4532
February	1st to 10th	Night	15% 8% 3 6% 4 4 4 3 5% 6% 42%	2281
	11th to 20th	Night	19% 7% 3 6% 3 4 3 3 4 5% 43%	2218
	21st to end	Night	20% 9% 2 6% 3 3 3 3 5% 6% 40%	1852
March	1st to 10th	Night	24% 12% 4 8% 4 3 4 3 4 6% 29%	3419
	11th to 20th	Night	16% 9% 4 7% 5% 5% 4 4 5% 7% 35%	3480
	21st to end	Night	13% 8% 2 6% 3 4 4 4 6% 7% 43%	3765
April	1st to 10th	Night	12% 6% 3 5% 4 4 4 4 6% 8% 44%	1900
	11th to 20th	Night	12% 7% 2 6% 4 4 5% 3 5% 6% 46%	1875
	21st to end	Night	7% 5% 3 5% 4 3 4 4 7% 7% 52%	1900
May	1st to 10th	Night	14% 7% 3 6% 5% 4 4 4 6% 8% 38%	3130
	11th to 20th	Night	15% 7% 2 6% 5% 4 4 3 6% 7% 41%	3129
	21st to end	Night	8% 5% 2 6% 4 5% 4 5% 8% 12% 41%	3426
June	1st to 10th	Night	5% 4 2 5% 3 4 5% 5% 9% 11% 45%	1718
	11th to 20th	Night	3 4 2 5% 4 4 7% 5% 9% 12% 45%	1710
	21st to end	Night	7% 4 2 7% 6% 6% 7% 5% 8% 10% 39%	1710
July	1st to 10th	Night	3 5% 3 6% 6% 6% 7% 6% 10% 14% 33%	2850
	11th to 20th	Night	4 5% 2 5% 5% 5% 6% 6% 10% 13% 38%	2850
	21st to end	Night	5% 6% 2 8% 6% 6% 7% 5% 8% 13% 31%	3184
August	1st to 10th	Night	2 2 1 4 3 3 4 4 6% 11% 61%	3144
	11th to 20th	Night	3 2 1 5% 4 5% 5% 5% 9% 15% 46%	3100
	21st to end	Night	6% 7% 3 7% 5% 6% 6% 4 7% 9% 41%	3476
September	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 4 7% 10% 42%	1900
	11th to 20th	Night	10% 7% 2 7% 4 5% 6% 4 7% 8% 40%	1900
	21st to end	Night	7% 4 2 6% 4 4 5% 4 6% 8% 50%	2107
October	1st to 10th	Night	5% 5% 2 4 3 3 3 4 4 7% 59%	2280
	11th to 20th	Night	7% 4 2 5% 3 3 3 3 5% 6% 59%	2280
	21st to end	Night	10% 5% 2 5% 3 4 4 3 4 5% 57%	2508
November	1st to 10th	Night	8% 5% 2 5% 3 3 3 3 4 6% 57%	2227
	11th to 20th	Night	12% 5% 2 5% 3 3 4 3 4 5% 54%	2280
	21st to end	Night	15% 6% 2 6% 3 4 3 3 5% 6% 47%	2280
December	1st to 10th	Night	15% 7% 2 6% 4 3 3 4 5% 5% 45%	2280
	11th to 20th	Night	13% 10% 3 6% 4 4 4 3 5% 6% 42%	2872
	21st to end	Night	17% 10% 3 7% 4 3 3 3 4 6% 40%	4532

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	45% 6% 7% 13% 22% 8%	2848
	11th to 20th	Day	33% 4 6% 18% 30% 9%	2850
	21st to end	Day	52% 4 5% 12% 19% 7%	3135
February	1st to 10th	Day	48% 6% 8% 13% 17% 9%	1894
	11th to 20th	Day	45% 5% 7% 14% 19% 10%	1858
	21st to end	Day	47% 6% 8% 16% 16% 8%	1617
March	1st to 10th	Day	54% 8% 11% 13% 10% 4	3436
	11th to 20th	Day	44% 9% 11% 16% 15% 4	3480
	21st to end	Day	39% 7% 9% 16% 22% 6%	3863
April	1st to 10th	Day	40% 8% 10% 15% 18% 9%	2280
	11th to 20th	Day	43% 6% 10% 18% 15% 8%	2254
	21st to end	Day	35% 8% 11% 19% 23% 5%	2280
May	1st to 10th	Day	43% 11% 12% 20% 11% 4	3800
	11th to 20th	Day	39% 8% 9% 18% 23% 3	3768
	21st to end	Day	34% 11% 15% 29% 10% 1	4141
June	1st to 10th	Day	43% 10% 13% 22% 11% 1	2456
	11th to 20th	Day	42% 11% 15% 19% 12% 1	2470
	21st to end	Day	48% 13% 18% 16% 6%	2470
July	1st to 10th	Day	53% 9% 20% 15% 2	4056
	11th to 20th	Day	51% 13% 25% 9% 2	4051
	21st to end	Day	57% 10% 15% 14% 3	4234
August	1st to 10th	Day	25% 8% 13% 31% 22%	3773
	11th to 20th	Day	36% 9% 23% 26% 6% 1	3765
	21st to end	Day	49% 8% 14% 13% 15% 2	4179
September	1st to 10th	Day	44% 11% 15% 15% 11% 4	2280
	11th to 20th	Day	41% 8% 15% 15% 15% 6%	2280
	21st to end	Day	34% 7% 11% 22% 17% 9%	2048
October	1st to 10th	Day	28% 6% 9% 20% 22% 15%	1900
	11th to 20th	Day	29% 5% 8% 16% 28% 15%	1900
	21st to end	Day	30% 5% 7% 15% 28% 15%	2090
November	1st to 10th	Day	32% 4 9% 19% 26% 10%	1858
	11th to 20th	Day	33% 5% 8% 17% 26% 12%	1900
	21st to end	Day	39% 6% 7% 17% 22% 9%	1900
December	1st to 10th	Day	40% 7% 10% 19% 16% 8%	1900
	11th to 20th	Day	47% 5% 8% 12% 21% 7%	2305
	21st to end	Day	43% 7% 10% 14% 24% 3	3135
January	1st to 10th	Night	39% 5% 8% 14% 26% 9%	4108
	11th to 20th	Night	33% 5% 6% 18% 26% 11%	4120
	21st to end	Night	46% 4 6% 17% 18% 9%	4532
February	1st to 10th	Night	43% 6% 7% 15% 20% 9%	2281
	11th to 20th	Night	43% 5% 6% 16% 18% 12%	2219
	21st to end	Night	44% 6% 10% 14% 15% 11%	1852
March	1st to 10th	Night	54% 7% 10% 13% 11% 6%	3419
	11th to 20th	Night	45% 9% 11% 15% 15% 5%	3480
	21st to end	Night	37% 8% 11% 18% 20% 6%	3765
April	1st to 10th	Night	36% 8% 12% 17% 17% 11%	1900
	11th to 20th	Night	37% 6% 10% 18% 17% 11%	1875
	21st to end	Night	28% 8% 11% 21% 25% 7%	1900
May	1st to 10th	Night	38% 11% 14% 19% 13% 4	3160
	11th to 20th	Night	38% 8% 12% 20% 20% 2	3130
	21st to end	Night	30% 10% 20% 27% 11% 2	3435
June	1st to 10th	Night	29% 12% 20% 24% 15% 1	1718
	11th to 20th	Night	28% 11% 20% 27% 12% 2	1710
	21st to end	Night	36% 13% 20% 23% 8% 1	1710
July	1st to 10th	Night	38% 13% 31% 14% 3	2805
	11th to 20th	Night	32% 15% 38% 12% 3	2796
	21st to end	Night	40% 18% 21% 16% 4	3083
August	1st to 10th	Night	16% 9% 20% 31% 23% 1	3132
	11th to 20th	Night	26% 10% 30% 29% 5%	3130
	21st to end	Night	38% 10% 17% 18% 14% 2	3476
September	1st to 10th	Night	34% 13% 19% 20% 10% 5%	1900
	11th to 20th	Night	38% 10% 16% 17% 14% 5%	1900
	21st to end	Night	31% 7% 14% 22% 15% 11%	2107
October	1st to 10th	Night	24% 5% 11% 22% 22% 16%	2280
	11th to 20th	Night	25% 5% 8% 19% 25% 16%	2280
	21st to end	Night	28% 5% 6% 16% 26% 19%	2508
November	1st to 10th	Night	28% 5% 10% 19% 25% 13%	2227
	11th to 20th	Night	32% 5% 8% 16% 25% 15%	2280
	21st to end	Night	37% 5% 8% 18% 21% 11%	2280
December	1st to 10th	Night	40% 5% 7% 20% 20% 7%	2280
	11th to 20th	Night	42% 6% 7% 13% 19% 13%	2873
	21st to end	Night	46% 5% 9% 14% 19% 7%	4532

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	21% 13% 35% 20% 9% 3	270
	11th to 20th	Day	16% 12% 37% 25% 8% 1	270
	21st to end	Day	27% 9% 36% 24% 5%	297
February	1st to 10th	Day	24% 11% 28% 27% 9%	270
	11th to 20th	Day	25% 13% 30% 23% 9%	270
	21st to end	Day	23% 17% 38% 18% 4	225
March	1st to 10th	Day	26% 9% 32% 26% 7%	270
	11th to 20th	Day	23% 12% 35% 21% 8% 1	270
	21st to end	Day	17% 7% 38% 24% 12% 1	321
April	1st to 10th	Day	18% 8% 28% 31% 13% 2	460
	11th to 20th	Day	22% 7% 30% 24% 15% 2	452
	21st to end	Day	11% 5% 28% 30% 21% 5%	460
May	1st to 10th	Day	12% 5% 24% 33% 22% 4	463
	11th to 20th	Day	14% 2 18% 29% 27% 11%	487
	21st to end	Day	6% 2 13% 32% 32% 16%	529
June	1st to 10th	Day	10% 2 9% 29% 33% 18%	666
	11th to 20th	Day	8% 2 11% 26% 36% 17%	680
	21st to end	Day	9% 2 8% 23% 31% 27%	680
July	1st to 10th	Day	9% 2 4 19% 34% 31%	671
	11th to 20th	Day	7% 2 2 17% 38% 34%	668
	21st to end	Day	11% 1 3 20% 35% 30%	682
August	1st to 10th	Day	5% 2 1 14% 34% 44%	486
	11th to 20th	Day	8% 1 1 10% 31% 49%	479
	21st to end	Day	13% 3 3 16% 34% 32%	539
September	1st to 10th	Day	12% 3 2 17% 37% 28%	490
	11th to 20th	Day	13% 1 5% 21% 36% 24%	490
	21st to end	Day	10% 3 8% 21% 36% 23%	424
October	1st to 10th	Day	7% 2 16% 37% 26% 12%	300
	11th to 20th	Day	8% 3 17% 37% 22% 13%	300
	21st to end	Day	15% 6% 20% 29% 21% 8%	330
November	1st to 10th	Day	14% 1 20% 31% 28% 6%	270
	11th to 20th	Day	16% 6% 24% 32% 17% 4	270
	21st to end	Day	17% 8% 30% 26% 16% 3	270
December	1st to 10th	Day	19% 7% 24% 30% 14% 6%	270
	11th to 20th	Day	23% 7% 31% 30% 8%	270
	21st to end	Day	26% 6% 30% 25% 11% 2	297
January	1st to 10th	Night	21% 7% 30% 33% 8% 1	950
	11th to 20th	Night	18% 8% 29% 35% 10% 1	950
	21st to end	Night	22% 8% 30% 33% 7%	1045
February	1st to 10th	Night	20% 8% 30% 35% 6%	761
	11th to 20th	Night	23% 10% 26% 35% 7%	743
	21st to end	Night	25% 10% 34% 29% 3	596
March	1st to 10th	Night	17% 8% 28% 38% 9%	570
	11th to 20th	Night	16% 5% 29% 38% 10%	570
	21st to end	Night	15% 5% 32% 36% 12%	627
April	1st to 10th	Night	15% 7% 30% 37% 10% 1	570
	11th to 20th	Night	15% 8% 26% 37% 13% 1	563
	21st to end	Night	9% 4 28% 43% 15% 1	570
May	1st to 10th	Night	12% 2 23% 46% 17% 1	570
	11th to 20th	Night	12% 2 16% 43% 25% 2	561
	21st to end	Night	9% 1 9% 39% 35% 7%	617
June	1st to 10th	Night	7% 1 5% 39% 41% 7%	570
	11th to 20th	Night	5% 1 7% 33% 45% 9%	570
	21st to end	Night	9% 1 6% 25% 43% 15%	570
July	1st to 10th	Night	5% 1 1 21% 51% 20%	555
	11th to 20th	Night	4 2 1 16% 52% 26%	552
	21st to end	Night	6% 1 2 18% 54% 19%	624
August	1st to 10th	Night	4 1 1 18% 52% 24%	567
	11th to 20th	Night	5% 1 1 15% 52% 26%	564
	21st to end	Night	8% 1 3 18% 49% 21%	627
September	1st to 10th	Night	11% 2 4 18% 48% 18%	570
	11th to 20th	Night	15% 2 4 20% 48% 11%	570
	21st to end	Night	9% 2 5% 29% 46% 9%	717
October	1st to 10th	Night	8% 1 12% 36% 37% 6%	760
	11th to 20th	Night	9% 3 13% 42% 30% 3	760
	21st to end	Night	13% 4 17% 39% 25% 2	836
November	1st to 10th	Night	11% 4 17% 41% 24% 3	743
	11th to 20th	Night	15% 5% 21% 39% 19% 1	760
	21st to end	Night	19% 4 24% 38% 15% 1	760
December	1st to 10th	Night	20% 8% 21% 35% 16% 1	760
	11th to 20th	Night	21% 5% 24% 37% 12%	807
	21st to end	Night	26% 7% 25% 33% 9%	1045

Page generated at 2024-10-29 10:20:46. Version ac07

Copyright © 2024 Attilla Danko.