Black Hills State University
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Hills State University clear sky chart from 2005-11-06 to 2024-11-28.

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	7% 7% 2 5% 4 4 4 4 6% 8% 50%	105476
	Night	7% 7% 3 6% 4 4 4 4 6% 7% 49%	102758
Transparency	Day	31% 7% 14% 26% 18% 4	105220
	Night	32% 7% 13% 26% 18% 4	102603
Seeing	Day	13% 16% 33% 25% 10% 2	16005
	Night	12% 15% 32% 30% 10% 1	26014

By Month

Percentage Cloud Cover SW (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	3 9% 4 8% 4 3 4 3 7% 8% 47%	2538
	11th to 20th	Day	3 10% 4 8% 5% 7% 5% 4 6% 8% 40%	2540
	21st to end	Day	3 7% 4 7% 4 4 4 3 6% 7% 51%	2794
February	1st to 10th	Day	5% 16% 5% 9% 7% 7% 5% 3 4 5% 34%	1710
	11th to 20th	Day	6% 14% 6% 9% 5% 4 4 3 6% 7% 38%	1780
	21st to end	Day	4 12% 4 9% 6% 4 5% 5% 5% 8% 39%	1570
March	1st to 10th	Day	3 9% 3 6% 4 5% 4 3 5% 8% 52%	3130
	11th to 20th	Day	7% 8% 3 5% 4 3 3 3 6% 9% 50%	3284
	21st to end	Day	11% 14% 4 10% 5% 4 4 4 5% 8% 32%	4157
April	1st to 10th	Day	11% 11% 3 6% 5% 3 4 3 6% 8% 40%	2280
	11th to 20th	Day	13% 12% 4 8% 5% 4 4 4 6% 7% 33%	2251
	21st to end	Day	15% 12% 3 5% 4 5% 5% 4 5% 8% 35%	2404
May	1st to 10th	Day	14% 12% 3 8% 5% 5% 4 4 5% 7% 33%	4296
	11th to 20th	Day	12% 7% 2 5% 4 4 4 4 7% 9% 42%	4388
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 7% 9% 40%	4825
June	1st to 10th	Day	7% 5% 2 5% 3 4 5% 4 8% 10% 47%	2660
	11th to 20th	Day	8% 4 2 4 3 4 5% 5% 8% 9% 48%	2660
	21st to end	Day	5% 4 1 3 3 4 3 4 6% 8% 59%	2660
July	1st to 10th	Day	6% 3 2 4 4 4 4 4 7% 8% 53%	4430
	11th to 20th	Day	3 1 1 3 2 3 4 3 6% 8% 65%	4430
	21st to end	Day	3 2 1 3 2 3 3 4 7% 10% 63%	4802
August	1st to 10th	Day	7% 3 1 5% 4 4 5% 4 6% 9% 52%	4411
	11th to 20th	Day	7% 3 1 4 3 4 4 5% 6% 9% 53%	3898
	21st to end	Day	4 2 1 3 2 3 3 3 5% 7% 68%	4180
September	1st to 10th	Day	7% 4 1 4 2 3 3 3 4 6% 64%	2280
	11th to 20th	Day	9% 3 1 2 2 3 3 3 5% 6% 62%	2218
	21st to end	Day	10% 4 1 3 3 3 3 3 4 7% 59%	2090
October	1st to 10th	Day	6% 5% 1 3 2 2 2 2 4 5% 69%	3266
	11th to 20th	Day	10% 5% 2 3 2 2 2 2 3 6% 61%	3119
	21st to end	Day	10% 8% 2 4 3 3 4 3 5% 9% 48%	3091
November	1st to 10th	Day	7% 7% 3 5% 4 4 4 4 7% 7% 48%	1763
	11th to 20th	Day	5% 9% 3 7% 4 4 3 4 5% 8% 49%	1755
	21st to end	Day	4 9% 2 5% 4 3 3 4 5% 10% 49%	1576
December	1st to 10th	Day	3 10% 5% 9% 5% 5% 5% 4 6% 7% 42%	1520
	11th to 20th	Day	4 7% 3 5% 4 4 4 3 6% 10% 51%	1926
	21st to end	Day	7% 10% 4 8% 4 3 4 3 5% 7% 46%	2794
January	1st to 10th	Night	2 11% 4 8% 4 5% 4 4 6% 5% 46%	4417
	11th to 20th	Night	4 9% 4 9% 8% 6% 5% 4 5% 7% 40%	4430
	21st to end	Night	3 9% 3 6% 4 4 4 4 5% 7% 51%	4873
February	1st to 10th	Night	7% 15% 5% 8% 5% 4 4 4 5% 6% 36%	2485
	11th to 20th	Night	5% 13% 5% 9% 6% 4 4 4 6% 6% 39%	2287
	21st to end	Night	4 10% 4 9% 5% 5% 4 4 7% 6% 41%	1884
March	1st to 10th	Night	4 10% 3 7% 4 4 5% 4 5% 8% 47%	3734
	11th to 20th	Night	7% 8% 2 6% 5% 3 4 3 6% 9% 48%	3688
	21st to end	Night	8% 11% 4 10% 6% 5% 6% 4 7% 8% 31%	3484
April	1st to 10th	Night	12% 11% 3 5% 4 4 3 4 6% 7% 40%	1900
	11th to 20th	Night	12% 9% 4 7% 4 4 4 4 5% 6% 41%	1877
	21st to end	Night	12% 9% 3 5% 5% 4 4 4 5% 8% 41%	1775
May	1st to 10th	Night	15% 11% 3 6% 3 4 3 3 5% 6% 41%	2671
	11th to 20th	Night	10% 7% 2 6% 3 4 4 3 7% 9% 45%	2517
	21st to end	Night	14% 8% 2 6% 4 4 5% 3 6% 8% 41%	2762
June	1st to 10th	Night	9% 4 1 5% 4 4 4 4 6% 11% 48%	1520
	11th to 20th	Night	8% 4 2 5% 4 5% 5% 5% 8% 10% 45%	1520
	21st to end	Night	6% 3 2 5% 4 3 4 3 6% 7% 57%	1520
July	1st to 10th	Night	5% 3 1 3 4 3 3 3 6% 9% 59%	2540
	11th to 20th	Night	3 2 1 3 3 3 4 3 8% 10% 59%	2540
	21st to end	Night	3 3 1 4 3 4 4 4 7% 9% 59%	2761
August	1st to 10th	Night	7% 4 2 5% 4 4 5% 5% 7% 9% 49%	2528
	11th to 20th	Night	5% 3 2 4 3 3 4 4 7% 11% 54%	2923
	21st to end	Night	3 2 1 4 3 3 4 4 5% 7% 64%	3487
September	1st to 10th	Night	6% 3 1 4 3 3 3 3 4 8% 62%	1900
	11th to 20th	Night	8% 4 1 4 3 2 3 3 5% 7% 59%	1961
	21st to end	Night	10% 3 1 4 2 3 3 3 4 5% 61%	2090
October	1st to 10th	Night	8% 4 1 2 2 2 2 2 3 4 70%	3698
	11th to 20th	Night	9% 5% 2 3 3 3 4 4 5% 7% 56%	3778
	21st to end	Night	8% 6% 2 4 3 3 4 3 6% 8% 52%	4467
November	1st to 10th	Night	7% 7% 3 6% 4 4 4 4 6% 8% 46%	2535
	11th to 20th	Night	6% 9% 3 7% 4 4 3 3 6% 6% 48%	2643
	21st to end	Night	5% 8% 2 6% 3 3 4 4 6% 8% 51%	2759
December	1st to 10th	Night	4 10% 5% 11% 5% 5% 4 3 5% 6% 42%	2660
	11th to 20th	Night	3 7% 3 6% 4 4 4 4 6% 9% 49%	3271
	21st to end	Night	7% 13% 3 5% 4 4 4 4 5% 6% 45%	4873

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% 8% 21% 27% 11% 1	2539
	11th to 20th	Day	35% 11% 16% 25% 10% 4	2540
	21st to end	Day	30% 7% 18% 30% 13% 2	2794
February	1st to 10th	Day	52% 5% 12% 19% 9% 3	1710
	11th to 20th	Day	44% 7% 14% 19% 12% 4	1789
	21st to end	Day	42% 7% 12% 22% 13% 4	1570
March	1st to 10th	Day	27% 8% 13% 25% 24% 2	3130
	11th to 20th	Day	29% 7% 20% 31% 13% 1	3284
	21st to end	Day	49% 9% 17% 20% 5%	4157
April	1st to 10th	Day	43% 6% 16% 24% 9% 2	2280
	11th to 20th	Day	49% 7% 13% 19% 10% 2	2254
	21st to end	Day	46% 7% 15% 23% 8%	2404
May	1st to 10th	Day	49% 8% 12% 22% 9% 2	4296
	11th to 20th	Day	35% 9% 14% 28% 12% 2	4392
	21st to end	Day	36% 10% 15% 29% 9% 1	4825
June	1st to 10th	Day	31% 9% 21% 25% 11% 2	2660
	11th to 20th	Day	28% 9% 19% 27% 14% 3	2660
	21st to end	Day	21% 7% 15% 30% 22% 5%	2660
July	1st to 10th	Day	26% 6% 13% 30% 23% 2	4361
	11th to 20th	Day	15% 5% 11% 30% 29% 9%	4355
	21st to end	Day	15% 5% 12% 27% 27% 14%	4651
August	1st to 10th	Day	26% 7% 15% 24% 18% 10%	4396
	11th to 20th	Day	26% 6% 15% 29% 21% 3	3938
	21st to end	Day	16% 5% 10% 26% 32% 10%	4179
September	1st to 10th	Day	22% 4 10% 27% 27% 10%	2280
	11th to 20th	Day	23% 5% 12% 28% 26% 7%	2218
	21st to end	Day	26% 4 10% 32% 24% 3	2090
October	1st to 10th	Day	20% 3 9% 21% 34% 14%	3266
	11th to 20th	Day	26% 3 12% 31% 23% 4	3119
	21st to end	Day	34% 4 14% 29% 15% 4	3091
November	1st to 10th	Day	32% 8% 12% 24% 21% 4	1763
	11th to 20th	Day	32% 5% 13% 26% 19% 4	1755
	21st to end	Day	30% 6% 16% 28% 16% 3	1576
December	1st to 10th	Day	40% 7% 13% 23% 15% 2	1520
	11th to 20th	Day	27% 7% 20% 33% 11% 2	1924
	21st to end	Day	38% 6% 9% 26% 20% 3	2794
January	1st to 10th	Night	35% 7% 12% 30% 13% 2	4417
	11th to 20th	Night	38% 10% 13% 24% 13% 2	4430
	21st to end	Night	30% 8% 18% 28% 14% 2	4873
February	1st to 10th	Night	46% 7% 15% 19% 11% 2	2485
	11th to 20th	Night	44% 6% 13% 21% 13% 3	2288
	21st to end	Night	40% 7% 13% 21% 14% 5%	1884
March	1st to 10th	Night	31% 9% 12% 25% 22% 2	3734
	11th to 20th	Night	31% 7% 22% 22% 16% 2	3688
	21st to end	Night	42% 15% 17% 19% 7%	3484
April	1st to 10th	Night	41% 7% 15% 22% 12% 3	1900
	11th to 20th	Night	43% 6% 13% 24% 13% 2	1877
	21st to end	Night	41% 5% 14% 28% 11% 1	1775
May	1st to 10th	Night	42% 7% 11% 21% 18% 1	2671
	11th to 20th	Night	32% 8% 15% 32% 12% 1	2518
	21st to end	Night	39% 8% 13% 31% 8%	2762
June	1st to 10th	Night	29% 8% 21% 28% 12% 1	1520
	11th to 20th	Night	31% 7% 20% 24% 15% 3	1520
	21st to end	Night	24% 7% 14% 26% 24% 5%	1520
July	1st to 10th	Night	21% 5% 13% 31% 27% 3	2500
	11th to 20th	Night	19% 5% 12% 32% 26% 6%	2492
	21st to end	Night	20% 5% 12% 29% 25% 9%	2674
August	1st to 10th	Night	29% 6% 13% 22% 20% 9%	2520
	11th to 20th	Night	23% 6% 17% 28% 21% 4	2948
	21st to end	Night	19% 5% 11% 22% 32% 11%	3487
September	1st to 10th	Night	22% 4 7% 27% 27% 13%	1900
	11th to 20th	Night	23% 6% 11% 26% 25% 9%	1961
	21st to end	Night	26% 4 9% 29% 24% 7%	2090
October	1st to 10th	Night	21% 3 9% 23% 30% 15%	3698
	11th to 20th	Night	28% 5% 10% 27% 26% 5%	3778
	21st to end	Night	30% 5% 13% 30% 16% 7%	4467
November	1st to 10th	Night	34% 7% 14% 21% 19% 5%	2535
	11th to 20th	Night	36% 5% 12% 25% 19% 4	2643
	21st to end	Night	30% 6% 16% 26% 18% 4	2759
December	1st to 10th	Night	41% 6% 12% 24% 14% 3	2660
	11th to 20th	Night	30% 7% 14% 34% 13% 1	3272
	21st to end	Night	37% 7% 10% 28% 15% 3	4873

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	10% 22% 30% 26% 9% 3	270
	11th to 20th	Day	16% 21% 28% 23% 9% 3	270
	21st to end	Day	21% 33% 25% 13% 8% 1	297
February	1st to 10th	Day	18% 23% 41% 16% 3	270
	11th to 20th	Day	17% 27% 36% 16% 3	270
	21st to end	Day	16% 24% 43% 14% 3	225
March	1st to 10th	Day	15% 28% 34% 14% 8% 1	270
	11th to 20th	Day	13% 20% 38% 20% 6% 2	332
	21st to end	Day	21% 18% 32% 21% 7% 1	506
April	1st to 10th	Day	22% 24% 36% 15% 3	460
	11th to 20th	Day	25% 27% 36% 10% 3	452
	21st to end	Day	23% 14% 30% 24% 8% 1	584
May	1st to 10th	Day	20% 19% 30% 19% 10% 2	653
	11th to 20th	Day	21% 12% 26% 25% 13% 3	675
	21st to end	Day	19% 15% 31% 21% 12% 3	734
June	1st to 10th	Day	9% 11% 30% 30% 16% 3	680
	11th to 20th	Day	12% 17% 37% 25% 8% 1	680
	21st to end	Day	9% 10% 37% 28% 14% 2	680
July	1st to 10th	Day	5% 7% 31% 36% 19% 2	671
	11th to 20th	Day	4 9% 37% 34% 14% 1	668
	21st to end	Day	4 8% 32% 36% 18% 3	739
August	1st to 10th	Day	7% 7% 33% 37% 15% 1	676
	11th to 20th	Day	8% 7% 35% 34% 14% 3	528
	21st to end	Day	4 13% 32% 37% 10% 4	539
September	1st to 10th	Day	7% 9% 37% 31% 12% 3	490
	11th to 20th	Day	9% 10% 33% 31% 14% 4	428
	21st to end	Day	14% 16% 33% 21% 11% 5%	300
October	1st to 10th	Day	16% 17% 25% 24% 14% 4	300
	11th to 20th	Day	20% 20% 34% 16% 7% 4	300
	21st to end	Day	16% 27% 30% 19% 8% 1	330
November	1st to 10th	Day	18% 23% 33% 18% 6% 2	300
	11th to 20th	Day	17% 28% 31% 18% 5% 1	300
	21st to end	Day	12% 22% 35% 24% 7%	291
December	1st to 10th	Day	14% 27% 36% 18% 4 1	270
	11th to 20th	Day	14% 27% 33% 23% 3	270
	21st to end	Day	14% 24% 38% 18% 5% 1	297
January	1st to 10th	Night	9% 24% 36% 18% 11% 1	950
	11th to 20th	Night	15% 27% 29% 20% 8% 1	950
	21st to end	Night	14% 26% 33% 20% 6%	1045
February	1st to 10th	Night	15% 24% 34% 20% 6% 1	775
	11th to 20th	Night	11% 21% 34% 26% 6% 1	744
	21st to end	Night	12% 16% 38% 26% 7% 1	628
March	1st to 10th	Night	11% 20% 35% 25% 9% 1	760
	11th to 20th	Night	9% 15% 39% 27% 8% 2	760
	21st to end	Night	16% 12% 28% 34% 9% 1	634
April	1st to 10th	Night	18% 11% 36% 29% 6%	570
	11th to 20th	Night	21% 14% 31% 28% 6% 1	563
	21st to end	Night	18% 11% 30% 32% 8% 1	570
May	1st to 10th	Night	16% 8% 29% 33% 12% 2	570
	11th to 20th	Night	17% 10% 25% 34% 14% 1	561
	21st to end	Night	17% 11% 30% 30% 11%	617
June	1st to 10th	Night	10% 11% 28% 36% 15% 1	570
	11th to 20th	Night	10% 10% 41% 32% 7%	570
	21st to end	Night	8% 6% 33% 42% 11% 1	570
July	1st to 10th	Night	6% 4 28% 41% 19% 1	555
	11th to 20th	Night	5% 5% 32% 44% 13% 1	552
	21st to end	Night	3 3 27% 52% 14%	624
August	1st to 10th	Night	6% 3 29% 47% 15%	567
	11th to 20th	Night	6% 4 25% 44% 18% 2	564
	21st to end	Night	4 5% 28% 44% 19% 1	627
September	1st to 10th	Night	7% 4 25% 45% 17% 2	570
	11th to 20th	Night	11% 9% 26% 37% 16% 2	570
	21st to end	Night	12% 10% 29% 33% 14% 2	570
October	1st to 10th	Night	17% 11% 26% 32% 12% 2	697
	11th to 20th	Night	14% 14% 30% 30% 11% 1	760
	21st to end	Night	16% 16% 33% 25% 7% 2	1045
November	1st to 10th	Night	12% 18% 35% 26% 7% 2	975
	11th to 20th	Night	13% 22% 36% 22% 6% 2	1000
	21st to end	Night	11% 22% 36% 25% 6%	986
December	1st to 10th	Night	12% 25% 36% 21% 6% 1	950
	11th to 20th	Night	11% 22% 35% 25% 7% 1	950
	21st to end	Night	16% 22% 33% 22% 6%	1045

Page generated at 2024-11-24 22:22:15. Version ac07

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