Schoonover Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Schoonover Observatory clear sky chart from 2005-11-06 to 2026-06-16.

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	14% 10% 4 8% 5% 5% 5% 4 5% 7% 33%	137279
	Night	15% 11% 4 9% 5% 4 4 3 5% 6% 33%	134844
Transparency	Day	50% 4 11% 21% 12% 1	140878
	Night	50% 4 10% 21% 13% 2	139317
Seeing	Day	18% 10% 27% 23% 15% 6%	17665
	Night	19% 9% 29% 29% 13% 1	27481

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% 18% 8% 16% 6% 5% 4 3 4 5% 17%	4691
	11th to 20th	Day	11% 16% 7% 15% 9% 7% 6% 4 3 3 19%	4804
	21st to end	Day	18% 15% 7% 14% 8% 5% 5% 4 4 4 15%	5780
February	1st to 10th	Day	17% 16% 6% 13% 7% 4 3 4 4 5% 21%	1927
	11th to 20th	Day	15% 14% 6% 15% 7% 4 4 3 4 5% 23%	2048
	21st to end	Day	15% 15% 7% 10% 4 4 4 3 5% 7% 27%	1730
March	1st to 10th	Day	18% 16% 7% 11% 5% 4 4 3 3 4 26%	4641
	11th to 20th	Day	12% 12% 3 7% 5% 4 4 4 5% 6% 39%	5090
	21st to end	Day	18% 15% 5% 10% 5% 5% 4 3 5% 5% 26%	5586
April	1st to 10th	Day	16% 14% 4 8% 5% 5% 4 4 5% 6% 30%	2469
	11th to 20th	Day	17% 10% 3 7% 5% 4 4 3 5% 7% 35%	2598
	21st to end	Day	18% 9% 2 8% 5% 5% 6% 3 5% 7% 33%	2730
May	1st to 10th	Day	21% 9% 3 8% 5% 5% 4 4 5% 7% 29%	7616
	11th to 20th	Day	15% 7% 3 6% 5% 5% 5% 4 7% 8% 35%	7626
	21st to end	Day	16% 7% 3 7% 4 4 5% 4 6% 8% 37%	8391
June	1st to 10th	Day	12% 6% 2 7% 4 5% 5% 4 6% 8% 40%	2843
	11th to 20th	Day	11% 6% 2 5% 5% 4 6% 4 7% 9% 40%	2871
	21st to end	Day	10% 5% 2 5% 5% 6% 6% 5% 8% 10% 38%	2800
July	1st to 10th	Day	10% 5% 3 7% 5% 5% 5% 4 7% 10% 41%	6360
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 5% 7% 11% 40%	6325
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	6424
August	1st to 10th	Day	9% 5% 2 5% 4 4 5% 5% 7% 10% 44%	4234
	11th to 20th	Day	8% 5% 2 6% 4 5% 6% 5% 8% 10% 41%	4174
	21st to end	Day	8% 4 2 5% 5% 5% 5% 4 6% 10% 46%	4459
September	1st to 10th	Day	12% 6% 2 5% 4 4 4 3 4 7% 48%	2275
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 6% 9% 46%	2200
	21st to end	Day	17% 7% 2 5% 4 3 3 3 5% 6% 44%	2200
October	1st to 10th	Day	12% 7% 3 6% 4 4 5% 3 5% 6% 45%	2195
	11th to 20th	Day	15% 7% 2 7% 4 4 4 4 5% 6% 41%	2000
	21st to end	Day	19% 9% 3 7% 5% 4 5% 4 6% 7% 32%	2035
November	1st to 10th	Day	10% 10% 3 7% 3 3 3 4 5% 6% 47%	1852
	11th to 20th	Day	17% 14% 4 7% 5% 5% 4 3 4 5% 32%	1890
	21st to end	Day	19% 17% 5% 8% 4 4 3 3 4 5% 28%	1890
December	1st to 10th	Day	15% 15% 6% 12% 5% 4 4 4 4 5% 27%	3020
	11th to 20th	Day	16% 18% 7% 11% 5% 4 5% 3 4 6% 20%	3435
	21st to end	Day	23% 22% 8% 11% 6% 4 4 2 3 4 13%	4070
January	1st to 10th	Night	14% 18% 7% 17% 6% 4 4 3 4 4 19%	8232
	11th to 20th	Night	9% 17% 9% 17% 8% 6% 6% 4 3 4 17%	8164
	21st to end	Night	18% 14% 5% 9% 5% 5% 5% 4 5% 6% 23%	8401
February	1st to 10th	Night	18% 14% 5% 11% 7% 5% 4 3 3 5% 25%	2689
	11th to 20th	Night	14% 14% 5% 11% 5% 5% 5% 3 5% 6% 28%	2458
	21st to end	Night	19% 14% 4 11% 5% 4 4 3 4 5% 27%	2076
March	1st to 10th	Night	17% 14% 4 7% 4 4 3 3 3 5% 35%	5430
	11th to 20th	Night	11% 8% 3 6% 5% 4 4 4 6% 8% 41%	5090
	21st to end	Night	18% 10% 4 8% 4 4 4 3 4 5% 36%	5588
April	1st to 10th	Night	16% 12% 4 7% 4 4 4 4 5% 6% 34%	2168
	11th to 20th	Night	16% 8% 3 6% 5% 5% 4 4 6% 7% 35%	1969
	21st to end	Night	17% 9% 3 8% 5% 4 4 3 4 7% 36%	1890
May	1st to 10th	Night	22% 9% 3 9% 5% 5% 4 4 5% 5% 29%	5237
	11th to 20th	Night	17% 6% 3 6% 4 4 4 3 6% 9% 39%	5234
	21st to end	Night	14% 7% 2 6% 4 4 5% 3 6% 8% 40%	5761
June	1st to 10th	Night	10% 6% 2 6% 4 5% 5% 4 5% 7% 46%	1771
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 3 7% 9% 46%	1640
	21st to end	Night	9% 5% 3 5% 5% 5% 4 4 7% 9% 45%	1600
July	1st to 10th	Night	9% 5% 2 6% 4 4 5% 4 7% 9% 46%	3618
	11th to 20th	Night	8% 5% 2 7% 5% 4 4 4 7% 9% 45%	3634
	21st to end	Night	9% 6% 2 7% 5% 4 5% 4 6% 8% 44%	4427
August	1st to 10th	Night	12% 7% 2 5% 4 5% 4 4 6% 9% 41%	2915
	11th to 20th	Night	9% 7% 2 6% 4 4 4 3 6% 8% 46%	2875
	21st to end	Night	5% 4 2 7% 5% 4 5% 4 6% 8% 50%	3435
September	1st to 10th	Night	11% 5% 2 5% 3 4 4 3 4 7% 52%	2105
	11th to 20th	Night	10% 5% 1 4 3 3 4 3 5% 7% 56%	2200
	21st to end	Night	13% 6% 2 7% 4 4 4 4 4 5% 46%	2200
October	1st to 10th	Night	11% 4 2 6% 4 4 4 3 4 7% 51%	2203
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 5% 6% 41%	2400
	21st to end	Night	20% 8% 2 6% 4 3 4 4 5% 7% 37%	2802
November	1st to 10th	Night	12% 9% 3 6% 4 4 3 3 5% 6% 44%	2666
	11th to 20th	Night	15% 12% 4 7% 4 4 3 3 5% 7% 35%	2730
	21st to end	Night	19% 15% 5% 8% 5% 4 4 3 4 6% 27%	2730
December	1st to 10th	Night	13% 13% 6% 10% 6% 5% 5% 4 6% 7% 26%	4380
	11th to 20th	Night	18% 18% 7% 12% 5% 4 4 3 4 4 21%	4976
	21st to end	Night	24% 21% 6% 10% 5% 4 4 3 4 5% 14%	7150

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	72% 2 10% 11% 4	4692
	11th to 20th	Day	72% 2 7% 7% 11% 1	4804
	21st to end	Day	74% 1 7% 11% 6%	5780
February	1st to 10th	Day	66% 4 10% 14% 6% 1	1927
	11th to 20th	Day	65% 4 7% 16% 7%	2058
	21st to end	Day	57% 5% 13% 16% 8% 2	1730
March	1st to 10th	Day	63% 4 6% 19% 8% 1	4641
	11th to 20th	Day	45% 4 11% 29% 10% 1	5090
	21st to end	Day	60% 4 11% 17% 6% 1	5586
April	1st to 10th	Day	54% 5% 11% 17% 12%	2469
	11th to 20th	Day	49% 5% 11% 21% 11% 2	2598
	21st to end	Day	50% 6% 11% 22% 10% 2	2730
May	1st to 10th	Day	55% 4 10% 19% 12%	7651
	11th to 20th	Day	46% 5% 13% 24% 13% 1	7630
	21st to end	Day	45% 5% 10% 21% 15% 5%	8405
June	1st to 10th	Day	42% 5% 11% 24% 16% 2	2843
	11th to 20th	Day	39% 6% 14% 24% 16% 2	2871
	21st to end	Day	38% 9% 15% 20% 15% 4	2800
July	1st to 10th	Day	39% 4 9% 28% 17% 2	6291
	11th to 20th	Day	39% 4 16% 25% 15% 1	6250
	21st to end	Day	41% 5% 12% 22% 18% 2	6240
August	1st to 10th	Day	35% 5% 16% 27% 16% 1	4221
	11th to 20th	Day	35% 5% 13% 32% 14% 1	4213
	21st to end	Day	33% 5% 13% 34% 13% 3	4458
September	1st to 10th	Day	35% 6% 12% 24% 19% 4	2275
	11th to 20th	Day	34% 7% 9% 26% 22% 3	2200
	21st to end	Day	41% 6% 10% 22% 21% 1	2200
October	1st to 10th	Day	28% 3 11% 35% 21% 1	3572
	11th to 20th	Day	38% 3 11% 26% 22% 1	3240
	21st to end	Day	43% 4 9% 24% 19% 1	3259
November	1st to 10th	Day	38% 5% 11% 26% 18% 1	1852
	11th to 20th	Day	54% 3 9% 21% 11% 2	1890
	21st to end	Day	59% 4 10% 18% 8% 1	1890
December	1st to 10th	Day	62% 3 12% 19% 4	3020
	11th to 20th	Day	66% 3 12% 14% 4	3432
	21st to end	Day	77% 3 6% 9% 4	4070
January	1st to 10th	Night	70% 3 7% 15% 4	8233
	11th to 20th	Night	73% 2 7% 9% 8% 1	8164
	21st to end	Night	63% 2 12% 16% 7% 1	8401
February	1st to 10th	Night	63% 4 9% 15% 7% 1	2689
	11th to 20th	Night	57% 5% 11% 17% 9% 1	2459
	21st to end	Night	60% 4 10% 15% 10% 1	2076
March	1st to 10th	Night	53% 3 8% 26% 9% 1	5430
	11th to 20th	Night	40% 5% 13% 28% 13% 1	5090
	21st to end	Night	51% 4 9% 23% 13% 1	5588
April	1st to 10th	Night	50% 5% 11% 20% 13% 1	2168
	11th to 20th	Night	47% 5% 12% 16% 17% 2	1969
	21st to end	Night	48% 6% 11% 20% 14% 2	1890
May	1st to 10th	Night	56% 5% 8% 17% 12% 2	5264
	11th to 20th	Night	43% 5% 11% 25% 15% 1	5235
	21st to end	Night	41% 4 12% 23% 14% 5%	5771
June	1st to 10th	Night	36% 6% 11% 24% 20% 3	1771
	11th to 20th	Night	34% 7% 15% 24% 17% 3	1640
	21st to end	Night	34% 6% 16% 23% 18% 3	1600
July	1st to 10th	Night	36% 4 11% 27% 18% 4	3580
	11th to 20th	Night	36% 4 15% 27% 17% 1	3589
	21st to end	Night	38% 4 15% 21% 19% 4	4297
August	1st to 10th	Night	40% 5% 14% 26% 14% 1	2904
	11th to 20th	Night	36% 4 11% 32% 17% 1	2902
	21st to end	Night	32% 5% 13% 29% 18% 3	3435
September	1st to 10th	Night	32% 5% 13% 26% 19% 6%	2105
	11th to 20th	Night	28% 5% 10% 28% 26% 3	2200
	21st to end	Night	40% 5% 10% 22% 21% 3	2200
October	1st to 10th	Night	24% 3 8% 30% 34% 1	3606
	11th to 20th	Night	35% 3 10% 27% 24% 1	3899
	21st to end	Night	35% 3 7% 31% 20% 3	4528
November	1st to 10th	Night	41% 4 10% 25% 18% 2	2666
	11th to 20th	Night	50% 3 10% 21% 14% 2	2730
	21st to end	Night	59% 5% 10% 19% 7%	2730
December	1st to 10th	Night	59% 3 12% 20% 6% 1	4380
	11th to 20th	Night	67% 3 12% 11% 6% 1	4978
	21st to end	Night	74% 3 9% 11% 3	7150

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	25% 18% 35% 16% 5% 1	330
	11th to 20th	Day	26% 20% 38% 11% 4 1	330
	21st to end	Day	28% 18% 33% 16% 4 1	363
February	1st to 10th	Day	27% 16% 37% 15% 4 1	330
	11th to 20th	Day	23% 19% 36% 17% 5%	330
	21st to end	Day	23% 19% 46% 10% 2	273
March	1st to 10th	Day	23% 18% 41% 14% 4	352
	11th to 20th	Day	29% 14% 30% 21% 6% 1	540
	21st to end	Day	29% 15% 34% 17% 5%	594
April	1st to 10th	Day	23% 16% 31% 22% 6% 2	540
	11th to 20th	Day	20% 20% 29% 18% 9% 3	532
	21st to end	Day	23% 12% 29% 26% 8% 2	540
May	1st to 10th	Day	24% 14% 29% 23% 8% 2	543
	11th to 20th	Day	22% 10% 26% 24% 12% 6%	567
	21st to end	Day	13% 7% 27% 25% 19% 8%	617
June	1st to 10th	Day	12% 8% 26% 29% 18% 6%	683
	11th to 20th	Day	14% 5% 26% 28% 21% 5%	756
	21st to end	Day	12% 7% 25% 30% 19% 6%	730
July	1st to 10th	Day	12% 2 19% 29% 22% 15%	721
	11th to 20th	Day	9% 3 24% 29% 22% 13%	709
	21st to end	Day	11% 3 15% 28% 28% 15%	576
August	1st to 10th	Day	10% 2 14% 30% 27% 17%	526
	11th to 20th	Day	11% 3 18% 30% 26% 11%	519
	21st to end	Day	10% 3 15% 26% 31% 15%	583
September	1st to 10th	Day	15% 3 16% 25% 28% 14%	530
	11th to 20th	Day	9% 2 14% 22% 35% 18%	530
	21st to end	Day	20% 9% 17% 25% 20% 9%	530
October	1st to 10th	Day	10% 6% 25% 30% 20% 10%	530
	11th to 20th	Day	16% 13% 30% 26% 12% 2	530
	21st to end	Day	24% 11% 37% 22% 4 1	418
November	1st to 10th	Day	17% 13% 36% 21% 10% 3	330
	11th to 20th	Day	27% 18% 30% 16% 10%	330
	21st to end	Day	29% 16% 35% 17% 2	330
December	1st to 10th	Day	22% 20% 34% 18% 5% 1	330
	11th to 20th	Day	25% 15% 38% 17% 4	330
	21st to end	Day	29% 17% 35% 16% 3	363
January	1st to 10th	Night	24% 15% 36% 21% 4	1050
	11th to 20th	Night	25% 17% 37% 16% 4	1012
	21st to end	Night	25% 16% 35% 21% 3	924
February	1st to 10th	Night	25% 12% 35% 26% 2	840
	11th to 20th	Night	22% 14% 38% 24% 2	823
	21st to end	Night	26% 14% 39% 20% 3	692
March	1st to 10th	Night	22% 13% 34% 25% 5% 1	840
	11th to 20th	Night	19% 14% 36% 25% 5%	840
	21st to end	Night	24% 13% 30% 25% 7% 1	924
April	1st to 10th	Night	21% 13% 35% 26% 5%	698
	11th to 20th	Night	20% 13% 34% 25% 8% 1	623
	21st to end	Night	19% 8% 37% 26% 10% 1	630
May	1st to 10th	Night	25% 6% 32% 30% 7% 1	630
	11th to 20th	Night	22% 5% 29% 30% 13% 1	621
	21st to end	Night	12% 3 26% 36% 21% 2	683
June	1st to 10th	Night	12% 2 25% 44% 17%	630
	11th to 20th	Night	11% 3 22% 45% 18% 1	615
	21st to end	Night	11% 2 23% 38% 25% 1	600
July	1st to 10th	Night	11% 2 15% 41% 28% 4	585
	11th to 20th	Night	8% 3 16% 40% 29% 4	582
	21st to end	Night	10% 2 12% 44% 31% 2	657
August	1st to 10th	Night	10% 1 12% 43% 30% 4	597
	11th to 20th	Night	11% 3 11% 42% 30% 4	594
	21st to end	Night	7% 2 13% 39% 34% 4	660
September	1st to 10th	Night	12% 3 16% 36% 29% 4	705
	11th to 20th	Night	10% 2 13% 38% 32% 5%	800
	21st to end	Night	15% 5% 21% 34% 23% 2	800
October	1st to 10th	Night	13% 5% 23% 35% 21% 3	800
	11th to 20th	Night	21% 11% 28% 28% 11% 1	800
	21st to end	Night	24% 11% 31% 27% 7%	880
November	1st to 10th	Night	18% 9% 35% 26% 12% 1	820
	11th to 20th	Night	22% 15% 31% 24% 7% 1	840
	21st to end	Night	26% 13% 33% 24% 5%	840
December	1st to 10th	Night	23% 14% 37% 21% 5%	840
	11th to 20th	Night	27% 12% 35% 22% 4	851
	21st to end	Night	31% 15% 33% 19% 3	1155

Page generated at 2026-06-13 02:31:44. Version ac07

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