Nininger Bluffs Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nininger Bluffs Observatory clear sky chart from 2005-11-06 to 2024-03-06.

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	13% 8% 4 7% 6% 3 5% 5% 5% 7% 36%	78478
	Night	13% 9% 4 7% 6% 3 5% 4 5% 6% 38%	81096
Transparency	Day	32% 37% 9% 15% 7% 1	78179
	Night	33% 35% 9% 15% 7% 1	80915
Seeing	Day	16% 10% 30% 27% 13% 3	14988
	Night	16% 8% 33% 31% 11% 1	25099

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	13% 16% 7% 16% 7% 4 5% 3 5% 5% 20%	2527
	11th to 20th	Day	6% 13% 6% 11% 10% 6% 8% 9% 6% 5% 20%	2531
	21st to end	Day	10% 19% 7% 12% 7% 3 5% 4 5% 6% 23%	3135
February	1st to 10th	Day	9% 9% 5% 10% 8% 5% 7% 6% 5% 6% 30%	1710
	11th to 20th	Day	9% 9% 7% 9% 6% 3 6% 5% 5% 6% 35%	1664
	21st to end	Day	13% 10% 4 9% 6% 4 6% 5% 5% 7% 31%	1489
March	1st to 10th	Day	14% 12% 4 9% 7% 2 5% 3 5% 6% 33%	1968
	11th to 20th	Day	14% 10% 4 6% 6% 3 4 4 4 8% 36%	1980
	21st to end	Day	21% 9% 4 6% 5% 3 5% 5% 5% 6% 31%	2213
April	1st to 10th	Day	18% 9% 4 5% 5% 3 5% 4 5% 7% 35%	2160
	11th to 20th	Day	21% 11% 3 6% 6% 2 4 5% 4 6% 33%	2134
	21st to end	Day	21% 10% 3 5% 6% 3 5% 5% 6% 6% 29%	2324
May	1st to 10th	Day	18% 6% 4 6% 6% 3 6% 5% 5% 8% 33%	2448
	11th to 20th	Day	17% 6% 3 6% 5% 3 5% 4 4 8% 39%	2479
	21st to end	Day	14% 6% 3 6% 6% 4 6% 5% 5% 7% 39%	2725
June	1st to 10th	Day	12% 4 2 4 4 3 4 5% 6% 8% 47%	2520
	11th to 20th	Day	13% 5% 3 5% 6% 3 5% 5% 5% 10% 39%	2520
	21st to end	Day	11% 4 2 4 6% 4 6% 6% 8% 8% 41%	2520
July	1st to 10th	Day	7% 4 2 4 4 3 4 5% 7% 10% 49%	2520
	11th to 20th	Day	8% 3 2 4 4 3 5% 5% 6% 8% 52%	2520
	21st to end	Day	6% 3 2 4 5% 4 5% 6% 7% 10% 48%	2730
August	1st to 10th	Day	9% 4 3 5% 6% 4 6% 6% 7% 9% 41%	2328
	11th to 20th	Day	13% 5% 2 4 5% 3 4 5% 6% 8% 44%	2301
	21st to end	Day	10% 4 2 4 4 2 3 4 6% 7% 52%	2446
September	1st to 10th	Day	12% 6% 2 4 5% 3 4 4 5% 7% 46%	2160
	11th to 20th	Day	14% 4 2 4 4 3 4 5% 5% 7% 48%	2156
	21st to end	Day	15% 6% 2 5% 5% 3 4 5% 5% 8% 42%	1881
October	1st to 10th	Day	17% 6% 2 4 5% 3 4 5% 5% 6% 43%	1800
	11th to 20th	Day	15% 9% 3 5% 5% 3 4 4 5% 7% 39%	1800
	21st to end	Day	19% 10% 3 6% 5% 2 4 4 4 5% 36%	1944
November	1st to 10th	Day	11% 10% 4 8% 7% 3 5% 3 5% 7% 37%	1584
	11th to 20th	Day	13% 11% 7% 10% 7% 4 5% 5% 5% 7% 28%	1520
	21st to end	Day	14% 10% 4 7% 6% 3 4 4 5% 6% 37%	1520
December	1st to 10th	Day	13% 12% 5% 11% 9% 4 7% 5% 4 6% 26%	1520
	11th to 20th	Day	11% 11% 7% 9% 8% 4 6% 4 5% 7% 28%	1918
	21st to end	Day	22% 14% 8% 14% 7% 3 3 3 4 5% 18%	2783
January	1st to 10th	Night	10% 15% 9% 14% 8% 3 4 3 4 4 26%	4428
	11th to 20th	Night	8% 11% 5% 12% 9% 5% 8% 9% 6% 5% 21%	4436
	21st to end	Night	12% 20% 7% 10% 6% 3 4 4 4 4 26%	4532
February	1st to 10th	Night	7% 10% 6% 10% 7% 4 6% 4 4 6% 34%	2470
	11th to 20th	Night	7% 8% 4 7% 7% 4 6% 5% 5% 6% 39%	2403
	21st to end	Night	12% 10% 4 7% 8% 4 5% 4 4 5% 37%	1965
March	1st to 10th	Night	12% 9% 4 8% 6% 3 5% 4 4 7% 37%	2123
	11th to 20th	Night	14% 9% 4 7% 5% 3 5% 4 4 7% 39%	1980
	21st to end	Night	18% 10% 4 6% 6% 2 4 4 5% 6% 36%	2142
April	1st to 10th	Night	18% 10% 2 6% 4 3 4 4 5% 7% 37%	1800
	11th to 20th	Night	23% 8% 3 7% 5% 2 4 5% 3 6% 33%	1775
	21st to end	Night	18% 8% 3 7% 5% 3 4 4 4 7% 37%	1634
May	1st to 10th	Night	18% 8% 2 6% 5% 3 4 4 4 7% 39%	1510
	11th to 20th	Night	18% 5% 2 4 5% 3 4 3 5% 7% 44%	1416
	21st to end	Night	12% 6% 3 6% 6% 3 5% 5% 5% 7% 42%	1551
June	1st to 10th	Night	10% 4 2 4 4 3 4 5% 6% 9% 48%	1440
	11th to 20th	Night	11% 3 2 4 6% 3 5% 5% 6% 9% 46%	1440
	21st to end	Night	6% 3 2 5% 4 3 4 4 6% 9% 53%	1440
July	1st to 10th	Night	5% 2 2 3 3 3 4 4 8% 9% 58%	1440
	11th to 20th	Night	6% 3 1 4 4 3 4 5% 6% 10% 55%	1440
	21st to end	Night	6% 3 1 3 3 2 4 4 6% 7% 61%	1585
August	1st to 10th	Night	6% 4 3 5% 5% 3 5% 5% 7% 9% 49%	1611
	11th to 20th	Night	12% 4 1 4 4 2 4 5% 5% 7% 52%	1600
	21st to end	Night	8% 4 2 5% 4 3 4 4 5% 5% 56%	1909
September	1st to 10th	Night	11% 3 2 4 4 3 3 4 4 8% 54%	1800
	11th to 20th	Night	12% 4 2 3 3 3 4 5% 4 7% 54%	1801
	21st to end	Night	14% 5% 2 6% 3 3 3 3 5% 6% 50%	2060
October	1st to 10th	Night	16% 6% 2 5% 4 2 3 4 4 6% 49%	2160
	11th to 20th	Night	17% 8% 3 5% 5% 3 4 4 4 6% 41%	2160
	21st to end	Night	19% 10% 4 5% 4 2 4 4 4 6% 38%	2411
November	1st to 10th	Night	13% 9% 4 5% 5% 2 4 4 5% 7% 42%	2491
	11th to 20th	Night	14% 10% 5% 9% 7% 4 4 5% 5% 5% 33%	2660
	21st to end	Night	13% 9% 5% 8% 7% 3 4 3 4 6% 37%	2660
December	1st to 10th	Night	11% 11% 5% 11% 7% 3 5% 4 5% 7% 30%	2660
	11th to 20th	Night	12% 13% 6% 10% 8% 4 5% 4 5% 6% 27%	3279
	21st to end	Night	23% 14% 6% 10% 6% 3 4 4 4 5% 21%	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	55% 25% 7% 11% 1	2528
	11th to 20th	Day	50% 27% 8% 12% 3	2531
	21st to end	Day	50% 25% 12% 11% 2	3135
February	1st to 10th	Day	37% 35% 9% 14% 5%	1710
	11th to 20th	Day	32% 37% 9% 17% 4	1673
	21st to end	Day	36% 35% 10% 11% 7% 1	1489
March	1st to 10th	Day	37% 36% 11% 12% 4	1968
	11th to 20th	Day	31% 38% 12% 15% 3 1	1980
	21st to end	Day	37% 37% 8% 14% 3	2213
April	1st to 10th	Day	31% 37% 9% 15% 8% 1	2160
	11th to 20th	Day	34% 37% 6% 12% 8% 1	2134
	21st to end	Day	37% 38% 9% 12% 4	2324
May	1st to 10th	Day	34% 37% 9% 12% 6% 1	2448
	11th to 20th	Day	28% 38% 9% 15% 8% 1	2483
	21st to end	Day	30% 39% 7% 14% 8% 1	2725
June	1st to 10th	Day	26% 39% 8% 18% 8% 1	2520
	11th to 20th	Day	24% 39% 9% 16% 12% 1	2520
	21st to end	Day	24% 40% 11% 17% 7% 1	2520
July	1st to 10th	Day	20% 40% 10% 20% 9%	2451
	11th to 20th	Day	17% 39% 10% 19% 13% 3	2445
	21st to end	Day	20% 40% 11% 18% 8% 1	2578
August	1st to 10th	Day	25% 39% 8% 20% 6% 3	2314
	11th to 20th	Day	24% 38% 9% 20% 10%	2301
	21st to end	Day	17% 38% 9% 20% 15% 1	2446
September	1st to 10th	Day	23% 37% 9% 19% 11%	2160
	11th to 20th	Day	23% 38% 10% 23% 6%	2156
	21st to end	Day	26% 38% 9% 21% 6%	1881
October	1st to 10th	Day	25% 38% 7% 21% 9%	1800
	11th to 20th	Day	31% 38% 11% 14% 6% 1	1800
	21st to end	Day	31% 38% 9% 15% 7%	1944
November	1st to 10th	Day	28% 42% 8% 12% 8% 2	1584
	11th to 20th	Day	36% 41% 8% 9% 5%	1520
	21st to end	Day	28% 41% 12% 16% 3	1520
December	1st to 10th	Day	37% 41% 11% 8% 2	1520
	11th to 20th	Day	37% 34% 15% 11% 3	1915
	21st to end	Day	55% 27% 8% 8% 2	2783
January	1st to 10th	Night	51% 26% 8% 13% 2	4428
	11th to 20th	Night	48% 28% 9% 12% 3	4436
	21st to end	Night	51% 23% 6% 16% 3	4532
February	1st to 10th	Night	34% 35% 9% 16% 6% 1	2470
	11th to 20th	Night	28% 36% 12% 17% 6% 1	2404
	21st to end	Night	34% 35% 9% 16% 6% 1	1965
March	1st to 10th	Night	31% 37% 11% 16% 5%	2123
	11th to 20th	Night	31% 36% 9% 17% 6% 1	1980
	21st to end	Night	34% 37% 8% 15% 5%	2142
April	1st to 10th	Night	31% 37% 6% 15% 11% 1	1800
	11th to 20th	Night	35% 36% 6% 13% 9% 2	1775
	21st to end	Night	32% 38% 7% 13% 9% 1	1634
May	1st to 10th	Night	31% 38% 9% 11% 10% 1	1510
	11th to 20th	Night	24% 38% 9% 17% 11% 2	1417
	21st to end	Night	28% 39% 8% 13% 11% 1	1552
June	1st to 10th	Night	23% 39% 7% 20% 10% 1	1440
	11th to 20th	Night	21% 38% 10% 14% 15% 2	1440
	21st to end	Night	19% 38% 10% 19% 11% 3	1440
July	1st to 10th	Night	16% 40% 9% 22% 13% 1	1400
	11th to 20th	Night	15% 39% 8% 23% 13% 3	1392
	21st to end	Night	15% 39% 11% 21% 10% 4	1497
August	1st to 10th	Night	20% 39% 8% 19% 10% 4	1601
	11th to 20th	Night	20% 37% 9% 19% 13% 2	1600
	21st to end	Night	19% 37% 7% 19% 14% 4	1909
September	1st to 10th	Night	18% 37% 7% 23% 14% 1	1800
	11th to 20th	Night	21% 38% 10% 19% 12%	1801
	21st to end	Night	24% 37% 9% 21% 9%	2060
October	1st to 10th	Night	21% 37% 8% 22% 10% 2	2160
	11th to 20th	Night	31% 37% 11% 15% 7% 1	2160
	21st to end	Night	30% 37% 8% 15% 9%	2411
November	1st to 10th	Night	24% 41% 9% 14% 10% 1	2491
	11th to 20th	Night	34% 41% 7% 10% 7% 1	2660
	21st to end	Night	29% 40% 11% 15% 4 1	2660
December	1st to 10th	Night	34% 41% 10% 12% 3	2660
	11th to 20th	Night	39% 35% 9% 13% 3 1	3281
	21st to end	Night	51% 26% 9% 11% 2	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	13% 13% 33% 27% 11% 3	270
	11th to 20th	Day	18% 14% 36% 26% 6% 1	270
	21st to end	Day	15% 10% 38% 25% 9% 3	297
February	1st to 10th	Day	12% 16% 41% 24% 5% 2	270
	11th to 20th	Day	15% 16% 39% 23% 7% 1	270
	21st to end	Day	17% 14% 37% 30% 2	225
March	1st to 10th	Day	18% 13% 43% 19% 7%	255
	11th to 20th	Day	20% 10% 37% 25% 7% 1	240
	21st to end	Day	26% 18% 22% 23% 8% 3	299
April	1st to 10th	Day	23% 16% 32% 22% 6% 1	420
	11th to 20th	Day	28% 14% 22% 24% 10% 1	412
	21st to end	Day	26% 13% 29% 20% 10% 2	584
May	1st to 10th	Day	20% 12% 34% 24% 9% 1	603
	11th to 20th	Day	19% 13% 30% 23% 12% 4	625
	21st to end	Day	17% 10% 26% 28% 15% 4	679
June	1st to 10th	Day	9% 8% 27% 33% 18% 4	630
	11th to 20th	Day	15% 8% 32% 31% 12% 2	630
	21st to end	Day	10% 10% 30% 31% 16% 5%	630
July	1st to 10th	Day	7% 5% 22% 31% 25% 11%	621
	11th to 20th	Day	9% 7% 25% 32% 20% 8%	618
	21st to end	Day	7% 3 26% 38% 20% 5%	684
August	1st to 10th	Day	11% 2 21% 37% 23% 6%	626
	11th to 20th	Day	15% 4 21% 31% 25% 5%	615
	21st to end	Day	10% 6% 26% 33% 20% 5%	565
September	1st to 10th	Day	15% 6% 30% 29% 14% 6%	450
	11th to 20th	Day	11% 7% 31% 28% 19% 4	446
	21st to end	Day	16% 15% 33% 21% 11% 4	270
October	1st to 10th	Day	18% 11% 28% 25% 13% 5%	270
	11th to 20th	Day	18% 17% 36% 21% 7% 1	270
	21st to end	Day	27% 14% 37% 13% 7% 1	297
November	1st to 10th	Day	17% 18% 35% 19% 10% 1	270
	11th to 20th	Day	18% 21% 37% 21% 3	270
	21st to end	Day	21% 15% 41% 19% 4	270
December	1st to 10th	Day	15% 10% 40% 27% 7% 1	270
	11th to 20th	Day	19% 14% 36% 24% 7%	270
	21st to end	Day	28% 14% 36% 18% 3	297
January	1st to 10th	Night	12% 11% 39% 30% 8%	950
	11th to 20th	Night	17% 10% 38% 29% 5% 1	950
	21st to end	Night	20% 9% 36% 29% 7%	1045
February	1st to 10th	Night	13% 10% 41% 28% 7%	950
	11th to 20th	Night	11% 12% 44% 26% 6% 1	929
	21st to end	Night	17% 11% 34% 30% 7% 1	709
March	1st to 10th	Night	15% 10% 38% 27% 9% 1	639
	11th to 20th	Night	17% 10% 38% 27% 7%	540
	21st to end	Night	21% 11% 29% 26% 11% 2	594
April	1st to 10th	Night	20% 10% 38% 27% 5%	540
	11th to 20th	Night	27% 9% 30% 27% 7%	533
	21st to end	Night	22% 10% 33% 25% 9% 2	540
May	1st to 10th	Night	20% 11% 30% 32% 6% 1	540
	11th to 20th	Night	19% 7% 29% 34% 10% 1	531
	21st to end	Night	15% 8% 24% 39% 14%	584
June	1st to 10th	Night	12% 4 29% 42% 14%	540
	11th to 20th	Night	12% 4 31% 42% 10%	540
	21st to end	Night	9% 3 24% 47% 15% 2	540
July	1st to 10th	Night	5% 2 21% 40% 29% 2	525
	11th to 20th	Night	5% 3 24% 48% 18% 2	522
	21st to end	Night	6% 3 20% 50% 20% 2	591
August	1st to 10th	Night	7% 2 18% 49% 23% 1	537
	11th to 20th	Night	13% 3 19% 37% 25% 3	534
	21st to end	Night	8% 3 26% 38% 22% 2	594
September	1st to 10th	Night	11% 4 25% 39% 16% 4	540
	11th to 20th	Night	12% 6% 29% 32% 19% 2	540
	21st to end	Night	15% 9% 33% 28% 15%	620
October	1st to 10th	Night	19% 7% 28% 30% 15% 1	720
	11th to 20th	Night	20% 10% 35% 26% 8% 1	720
	21st to end	Night	25% 10% 28% 29% 7%	792
November	1st to 10th	Night	19% 9% 36% 28% 8%	825
	11th to 20th	Night	18% 14% 36% 26% 6%	950
	21st to end	Night	18% 14% 37% 24% 7%	950
December	1st to 10th	Night	15% 9% 39% 29% 7% 1	950
	11th to 20th	Night	19% 9% 39% 26% 6% 1	950
	21st to end	Night	25% 10% 34% 27% 4	1045

Page generated at 2024-03-03 05:28:57. Version ac07

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