Brady
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brady clear sky chart from 2005-11-06 to 2024-12-24.

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	8% 5% 2 5% 4 3 4 3 5% 7% 55%	101436
	Night	8% 5% 2 4 3 3 3 3 5% 7% 58%	98793
Transparency	Day	28% 5% 9% 22% 23% 12%	105293
	Night	26% 4 9% 22% 24% 14%	103063
Seeing	Day	10% 7% 25% 31% 21% 6%	15082
	Night	10% 7% 32% 36% 13% 1	25083

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	9% 8% 2 4 2 3 3 2 3 4 60%	2847
	11th to 20th	Day	10% 6% 2 4 2 2 3 2 5% 6% 59%	2850
	21st to end	Day	11% 6% 2 5% 3 3 3 3 5% 5% 53%	3458
February	1st to 10th	Day	11% 6% 2 6% 3 3 2 3 5% 6% 53%	1900
	11th to 20th	Day	13% 6% 2 4 3 2 2 3 5% 6% 52%	1849
	21st to end	Day	12% 7% 2 4 3 3 2 3 3 6% 56%	1570
March	1st to 10th	Day	11% 8% 2 6% 4 3 4 3 4 6% 48%	3251
	11th to 20th	Day	16% 7% 2 6% 4 4 4 3 5% 6% 41%	3480
	21st to end	Day	7% 5% 2 5% 4 4 5% 4 6% 8% 50%	3814
April	1st to 10th	Day	8% 6% 2 5% 3 3 3 4 6% 6% 53%	2090
	11th to 20th	Day	12% 7% 2 5% 3 3 3 3 5% 7% 50%	2234
	21st to end	Day	9% 6% 2 5% 4 4 3 2 4 6% 55%	2361
May	1st to 10th	Day	12% 6% 3 6% 4 4 4 4 5% 6% 45%	4082
	11th to 20th	Day	12% 7% 3 5% 5% 4 3 3 5% 6% 47%	4082
	21st to end	Day	8% 5% 2 6% 5% 4 6% 5% 7% 7% 45%	4477
June	1st to 10th	Day	5% 4 1 4 4 3 5% 4 5% 9% 57%	2470
	11th to 20th	Day	4 2 1 4 4 4 4 4 6% 9% 59%	2470
	21st to end	Day	5% 4 1 5% 5% 3 5% 4 7% 8% 52%	2470
July	1st to 10th	Day	4 3 1 5% 5% 5% 5% 4 6% 7% 54%	4120
	11th to 20th	Day	2 1 1 3 3 3 4 4 5% 8% 65%	4120
	21st to end	Day	5% 4 1 4 4 4 4 4 6% 9% 53%	4465
August	1st to 10th	Day	1 1 1 2 2 3 3 3 5% 7% 72%	3927
	11th to 20th	Day	4 3 1 3 2 3 3 3 5% 8% 65%	3726
	21st to end	Day	4 3 1 4 5% 5% 5% 4 7% 9% 53%	4158
September	1st to 10th	Day	10% 5% 1 5% 4 4 5% 3 5% 7% 51%	2090
	11th to 20th	Day	11% 4 2 5% 5% 4 5% 3 6% 6% 49%	2090
	21st to end	Day	8% 4 2 4 3 3 3 3 5% 6% 58%	2090
October	1st to 10th	Day	5% 3 1 3 3 3 4 3 5% 7% 63%	2090
	11th to 20th	Day	8% 5% 2 3 3 3 3 3 3 5% 62%	2029
	21st to end	Day	11% 5% 1 4 2 2 2 2 3 4 63%	2090
November	1st to 10th	Day	12% 5% 2 4 3 3 3 3 4 6% 56%	1873
	11th to 20th	Day	7% 3 1 4 3 3 3 3 4 7% 61%	1800
	21st to end	Day	11% 6% 2 5% 3 3 3 3 4 6% 54%	1800
December	1st to 10th	Day	13% 6% 2 4 3 4 3 3 3 5% 55%	1800
	11th to 20th	Day	8% 6% 2 5% 3 4 4 4 5% 7% 51%	2251
	21st to end	Day	11% 5% 2 4 3 2 2 2 3 5% 61%	3162
January	1st to 10th	Night	11% 7% 3 4 2 2 2 2 3 5% 60%	4108
	11th to 20th	Night	9% 5% 1 3 2 2 2 2 3 4 68%	4120
	21st to end	Night	13% 7% 2 5% 3 3 3 3 4 7% 51%	4238
February	1st to 10th	Night	10% 7% 3 5% 3 3 3 2 4 6% 55%	2280
	11th to 20th	Night	13% 6% 2 4 3 2 2 2 4 5% 55%	2218
	21st to end	Night	11% 5% 2 4 3 3 3 3 5% 5% 56%	1884
March	1st to 10th	Night	7% 5% 2 5% 3 3 3 4 5% 6% 56%	3607
	11th to 20th	Night	15% 6% 2 5% 4 4 4 4 6% 5% 44%	3480
	21st to end	Night	7% 5% 2 5% 4 3 4 4 6% 7% 54%	3817
April	1st to 10th	Night	5% 5% 1 4 3 3 4 4 7% 7% 57%	2090
	11th to 20th	Night	9% 6% 2 5% 4 4 3 3 4 7% 51%	1891
	21st to end	Night	9% 4 1 4 2 2 3 3 5% 6% 61%	1819
May	1st to 10th	Night	15% 8% 2 5% 3 3 3 3 5% 6% 49%	2823
	11th to 20th	Night	8% 6% 2 6% 4 3 3 4 5% 7% 54%	2823
	21st to end	Night	8% 4 2 5% 4 4 4 3 6% 7% 53%	3090
June	1st to 10th	Night	2 2 1 3 2 3 4 3 7% 10% 61%	1710
	11th to 20th	Night	3 2 1 2 3 2 4 3 7% 9% 65%	1710
	21st to end	Night	3 3 1 3 3 3 3 3 5% 8% 63%	1710
July	1st to 10th	Night	3 3 1 3 3 3 3 3 6% 9% 63%	2850
	11th to 20th	Night	1 1 1 2 2 2 2 3 5% 9% 73%	2850
	21st to end	Night	3 4 1 4 3 3 4 4 6% 10% 59%	3098
August	1st to 10th	Night	2 1 1 3 2 2 3 2 4 7% 74%	2995
	11th to 20th	Night	2 2 1 3 2 2 3 3 6% 11% 64%	3113
	21st to end	Night	3 2 1 3 2 3 4 4 7% 11% 59%	3505
September	1st to 10th	Night	7% 4 1 4 3 4 4 4 5% 8% 54%	2090
	11th to 20th	Night	8% 5% 1 4 3 4 4 4 6% 8% 51%	2090
	21st to end	Night	8% 3 1 4 2 3 4 4 5% 7% 59%	2090
October	1st to 10th	Night	5% 3 1 2 3 2 3 2 4 7% 68%	2090
	11th to 20th	Night	9% 4 1 4 3 4 3 3 4 4 63%	2129
	21st to end	Night	11% 6% 1 3 3 2 2 2 4 4 63%	2508
November	1st to 10th	Night	10% 5% 2 4 2 3 3 2 4 5% 60%	2423
	11th to 20th	Night	5% 4 1 3 3 3 3 3 4 6% 64%	2600
	21st to end	Night	13% 4 2 4 3 3 3 4 4 6% 54%	2600
December	1st to 10th	Night	11% 5% 2 5% 3 2 3 3 4 6% 56%	2600
	11th to 20th	Night	9% 6% 2 6% 4 4 4 4 6% 5% 51%	3166
	21st to end	Night	10% 6% 2 4 3 2 3 2 4 5% 58%	4578

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	31% 2 4 14% 29% 21%	2848
	11th to 20th	Day	27% 3 5% 16% 31% 18%	2850
	21st to end	Day	34% 3 6% 15% 29% 13%	3458
February	1st to 10th	Day	34% 3 5% 17% 20% 21%	1900
	11th to 20th	Day	33% 4 5% 21% 20% 18%	1859
	21st to end	Day	32% 3 5% 15% 24% 21%	1570
March	1st to 10th	Day	37% 4 6% 11% 21% 22%	3251
	11th to 20th	Day	44% 4 10% 13% 17% 12%	3480
	21st to end	Day	30% 4 10% 16% 24% 16%	3814
April	1st to 10th	Day	30% 5% 9% 19% 19% 18%	2090
	11th to 20th	Day	34% 4 7% 16% 23% 15%	2234
	21st to end	Day	32% 4 6% 21% 25% 13%	2361
May	1st to 10th	Day	40% 5% 10% 15% 20% 11%	4120
	11th to 20th	Day	38% 5% 7% 18% 23% 10%	4086
	21st to end	Day	35% 7% 13% 24% 14% 7%	4489
June	1st to 10th	Day	24% 6% 13% 29% 23% 5%	2470
	11th to 20th	Day	22% 5% 14% 29% 22% 8%	2470
	21st to end	Day	27% 7% 12% 25% 22% 7%	2470
July	1st to 10th	Day	26% 7% 15% 38% 12% 1	4056
	11th to 20th	Day	17% 6% 13% 36% 24% 5%	4051
	21st to end	Day	25% 6% 12% 35% 20% 2	4325
August	1st to 10th	Day	12% 4 11% 36% 34% 2	3913
	11th to 20th	Day	19% 4 15% 40% 19% 3	3762
	21st to end	Day	26% 9% 16% 25% 22% 3	4157
September	1st to 10th	Day	33% 5% 10% 21% 21% 10%	2090
	11th to 20th	Day	35% 6% 11% 19% 23% 6%	2090
	21st to end	Day	27% 5% 8% 23% 24% 14%	2090
October	1st to 10th	Day	13% 3 5% 14% 28% 36%	3480
	11th to 20th	Day	21% 3 5% 21% 25% 25%	3347
	21st to end	Day	20% 3 3 20% 39% 14%	3428
November	1st to 10th	Day	31% 4 6% 22% 23% 14%	1873
	11th to 20th	Day	24% 3 7% 21% 23% 21%	1800
	21st to end	Day	33% 3 4 20% 24% 16%	1800
December	1st to 10th	Day	35% 3 6% 19% 24% 13%	1800
	11th to 20th	Day	33% 4 9% 14% 24% 17%	2249
	21st to end	Day	29% 2 3 17% 30% 19%	3162
January	1st to 10th	Night	29% 2 3 15% 30% 21%	4108
	11th to 20th	Night	23% 2 4 18% 28% 25%	4120
	21st to end	Night	36% 3 5% 14% 27% 15%	4238
February	1st to 10th	Night	33% 3 6% 15% 23% 21%	2280
	11th to 20th	Night	33% 2 6% 18% 22% 19%	2218
	21st to end	Night	31% 4 5% 14% 23% 24%	1884
March	1st to 10th	Night	27% 5% 7% 15% 29% 17%	3607
	11th to 20th	Night	41% 5% 9% 17% 16% 13%	3480
	21st to end	Night	30% 4 11% 19% 23% 14%	3817
April	1st to 10th	Night	25% 5% 10% 20% 19% 20%	2090
	11th to 20th	Night	33% 5% 9% 15% 21% 17%	1891
	21st to end	Night	26% 4 10% 23% 26% 11%	1819
May	1st to 10th	Night	36% 6% 8% 20% 19% 11%	2850
	11th to 20th	Night	31% 5% 12% 23% 19% 11%	2824
	21st to end	Night	30% 6% 12% 29% 15% 8%	3099
June	1st to 10th	Night	18% 6% 15% 35% 22% 4	1710
	11th to 20th	Night	16% 5% 15% 32% 24% 8%	1710
	21st to end	Night	20% 5% 13% 29% 26% 7%	1710
July	1st to 10th	Night	19% 7% 18% 40% 15% 1	2805
	11th to 20th	Night	10% 4 16% 41% 25% 4	2796
	21st to end	Night	20% 5% 16% 38% 19% 1	2999
August	1st to 10th	Night	12% 3 11% 33% 38% 3	2985
	11th to 20th	Night	15% 4 19% 41% 17% 3	3143
	21st to end	Night	18% 9% 22% 27% 21% 3	3505
September	1st to 10th	Night	28% 6% 11% 23% 21% 11%	2090
	11th to 20th	Night	29% 9% 14% 23% 19% 7%	2090
	21st to end	Night	25% 5% 10% 23% 22% 15%	2090
October	1st to 10th	Night	11% 2 7% 16% 24% 40%	3480
	11th to 20th	Night	20% 3 7% 17% 28% 24%	3537
	21st to end	Night	20% 3 4 22% 35% 15%	4120
November	1st to 10th	Night	28% 3 7% 20% 24% 17%	2423
	11th to 20th	Night	23% 3 7% 22% 24% 21%	2600
	21st to end	Night	32% 4 7% 17% 25% 16%	2600
December	1st to 10th	Night	30% 3 8% 19% 25% 14%	2600
	11th to 20th	Night	34% 4 6% 15% 22% 19%	3167
	21st to end	Night	30% 3 4 15% 29% 19%	4578

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	11% 14% 43% 27% 4 1	270
	11th to 20th	Day	16% 17% 32% 25% 9% 1	270
	21st to end	Day	12% 15% 40% 25% 7%	297
February	1st to 10th	Day	18% 17% 38% 19% 9%	270
	11th to 20th	Day	20% 14% 44% 19% 3	270
	21st to end	Day	18% 13% 48% 17% 4	225
March	1st to 10th	Day	13% 19% 40% 22% 5%	270
	11th to 20th	Day	18% 11% 42% 23% 5% 1	270
	21st to end	Day	12% 15% 48% 20% 4 1	297
April	1st to 10th	Day	14% 17% 46% 19% 3 1	270
	11th to 20th	Day	13% 20% 45% 18% 3	432
	21st to end	Day	12% 18% 40% 23% 6%	541
May	1st to 10th	Day	11% 10% 43% 29% 6%	653
	11th to 20th	Day	16% 7% 35% 30% 10% 3	675
	21st to end	Day	10% 7% 32% 37% 13% 1	734
June	1st to 10th	Day	6% 2 20% 45% 21% 5%	680
	11th to 20th	Day	3 2 24% 50% 18% 3	680
	21st to end	Day	4 2 14% 43% 31% 6%	680
July	1st to 10th	Day	6% 1 8% 40% 33% 12%	671
	11th to 20th	Day	3 5% 39% 43% 9%	668
	21st to end	Day	2 1 4 37% 42% 14%	739
August	1st to 10th	Day	3 4 34% 43% 16%	577
	11th to 20th	Day	8% 1 5% 32% 39% 16%	477
	21st to end	Day	7% 1 6% 25% 41% 21%	530
September	1st to 10th	Day	10% 1 8% 20% 40% 21%	300
	11th to 20th	Day	8% 1 5% 25% 41% 19%	300
	21st to end	Day	13% 1 6% 32% 32% 16%	300
October	1st to 10th	Day	3 1 12% 39% 37% 8%	300
	11th to 20th	Day	10% 2 26% 38% 22% 2	300
	21st to end	Day	18% 9% 27% 24% 20% 2	330
November	1st to 10th	Day	19% 7% 29% 32% 11% 3	300
	11th to 20th	Day	14% 10% 27% 30% 13% 5%	300
	21st to end	Day	17% 15% 33% 24% 8% 3	300
December	1st to 10th	Day	17% 8% 33% 28% 12% 2	300
	11th to 20th	Day	8% 13% 44% 26% 8% 1	300
	21st to end	Day	17% 12% 37% 25% 9%	306
January	1st to 10th	Night	14% 9% 41% 29% 8% 1	950
	11th to 20th	Night	15% 10% 36% 32% 7%	950
	21st to end	Night	15% 11% 37% 31% 6%	868
February	1st to 10th	Night	14% 11% 41% 28% 5%	760
	11th to 20th	Night	16% 13% 43% 25% 3	744
	21st to end	Night	15% 15% 47% 21% 1	628
March	1st to 10th	Night	13% 13% 45% 26% 3	685
	11th to 20th	Night	13% 12% 43% 28% 4	570
	21st to end	Night	8% 14% 53% 22% 3	627
April	1st to 10th	Night	8% 12% 53% 24% 3	570
	11th to 20th	Night	11% 16% 49% 22% 2	563
	21st to end	Night	10% 12% 52% 19% 7%	570
May	1st to 10th	Night	9% 11% 49% 29% 2	570
	11th to 20th	Night	13% 5% 40% 32% 10% 1	561
	21st to end	Night	8% 6% 44% 35% 8%	617
June	1st to 10th	Night	2 2 32% 50% 13% 1	570
	11th to 20th	Night	3 2 35% 51% 9%	570
	21st to end	Night	3 2 22% 50% 22% 1	570
July	1st to 10th	Night	5% 1 13% 51% 28% 2	555
	11th to 20th	Night	3 11% 59% 26% 1	552
	21st to end	Night	3 8% 57% 29% 2	624
August	1st to 10th	Night	2 6% 59% 31% 1	567
	11th to 20th	Night	6% 8% 47% 38% 2	564
	21st to end	Night	5% 6% 48% 36% 4	627
September	1st to 10th	Night	8% 2 10% 46% 31% 4	570
	11th to 20th	Night	10% 1 9% 46% 32% 2	570
	21st to end	Night	10% 1 14% 45% 29% 2	570
October	1st to 10th	Night	5% 1 20% 46% 26% 2	570
	11th to 20th	Night	10% 5% 29% 40% 15% 1	609
	21st to end	Night	13% 8% 29% 34% 14% 1	836
November	1st to 10th	Night	13% 5% 31% 38% 13% 1	863
	11th to 20th	Night	8% 7% 35% 38% 11% 1	1000
	21st to end	Night	15% 10% 33% 30% 11% 1	1000
December	1st to 10th	Night	13% 9% 33% 37% 9%	1000
	11th to 20th	Night	15% 10% 35% 34% 6%	1000
	21st to end	Night	12% 9% 40% 30% 8%	1063

Page generated at 2024-12-21 03:13:50. Version ac07

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