Schreder Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Schreder Planetarium clear sky chart from 2005-11-06 to 2025-04-11.

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% 3 1 3 2 2 2 2 4 5% 63%	117638
	Night	14% 4 1 3 2 2 3 2 4 6% 58%	119506
Transparency	Day	25% 4 7% 17% 23% 24%	117392
	Night	29% 4 8% 18% 21% 19%	119341
Seeing	Day	12% 9% 22% 30% 20% 7%	15554
	Night	14% 5% 20% 35% 23% 3	24855

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	21% 7% 3 4 3 3 4 3 4 7% 38%	3639
	11th to 20th	Day	23% 6% 1 4 2 2 1 1 2 2 55%	3990
	21st to end	Day	23% 5% 2 3 2 2 2 2 3 5% 50%	4510
February	1st to 10th	Day	20% 5% 2 4 3 2 4 4 6% 5% 46%	1800
	11th to 20th	Day	19% 4 1 3 3 3 3 2 5% 6% 50%	1770
	21st to end	Day	19% 4 2 4 3 3 3 3 5% 8% 47%	1650
March	1st to 10th	Day	23% 9% 3 6% 4 3 3 2 4 6% 39%	4820
	11th to 20th	Day	20% 7% 2 4 3 3 3 2 4 7% 46%	5000
	21st to end	Day	20% 7% 2 6% 3 4 4 3 5% 7% 39%	5573
April	1st to 10th	Day	16% 6% 2 4 3 3 3 3 5% 7% 48%	2400
	11th to 20th	Day	13% 4 1 4 2 3 3 3 5% 6% 56%	2251
	21st to end	Day	5% 3 1 4 3 2 3 3 5% 7% 62%	2293
May	1st to 10th	Day	6% 3 1 2 2 3 3 2 4 6% 68%	4110
	11th to 20th	Day	4 2 1 2 1 1 1 2 3 6% 77%	4367
	21st to end	Day	4 2 1 2 2 2 2 2 4 6% 74%	4813
June	1st to 10th	Day	6% 3 1 3 3 3 3 4 5% 7% 62%	2660
	11th to 20th	Day	2 1 1 1 1 2 2 4 5% 79%	2660
	21st to end	Day	4 1 1 2 1 1 1 2 3 3 81%	2660
July	1st to 10th	Day	1 1 1 1 1 2 2 91%	4420
	11th to 20th	Day	2 1 1 1 1 1 2 1 2 3 84%	4420
	21st to end	Day	1 1 1 1 1 2 3 90%	4459
August	1st to 10th	Day	2 2 1 2 1 1 2 2 3 5% 79%	4091
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 88%	3966
	21st to end	Day	2 1 1 1 1 1 1 1 2 3 87%	4180
September	1st to 10th	Day	1 1 1 1 1 1 2 4 89%	2280
	11th to 20th	Day	3 2 3 2 2 2 2 4 6% 75%	2280
	21st to end	Day	2 1 2 2 2 1 2 3 5% 79%	2006
October	1st to 10th	Day	3 1 1 1 1 1 2 2 3 4 80%	3180
	11th to 20th	Day	5% 2 1 2 2 2 3 2 5% 7% 69%	3161
	21st to end	Day	11% 3 1 5% 4 2 4 3 6% 6% 55%	3448
November	1st to 10th	Day	14% 4 2 3 3 3 4 3 5% 7% 54%	1834
	11th to 20th	Day	15% 4 1 4 2 3 4 4 6% 8% 48%	1695
	21st to end	Day	14% 4 2 4 3 3 3 3 4 7% 55%	1600
December	1st to 10th	Day	14% 3 1 3 3 3 3 3 4 5% 58%	2620
	11th to 20th	Day	33% 5% 2 5% 4 4 4 3 5% 8% 26%	3028
	21st to end	Day	34% 6% 2 4 3 3 3 3 4 5% 33%	4004
January	1st to 10th	Night	21% 6% 2 5% 3 4 4 3 6% 8% 38%	6306
	11th to 20th	Night	21% 4 1 4 2 2 2 2 3 5% 53%	5968
	21st to end	Night	21% 6% 2 5% 3 3 4 3 3 4 47%	6468
February	1st to 10th	Night	21% 4 1 4 3 3 3 3 5% 5% 48%	2600
	11th to 20th	Night	20% 6% 1 4 3 3 3 3 4 6% 48%	2517
	21st to end	Night	16% 6% 1 4 3 4 3 3 4 8% 48%	1980
March	1st to 10th	Night	20% 7% 3 7% 4 3 3 3 4 7% 39%	5071
	11th to 20th	Night	21% 5% 2 4 3 3 3 2 4 7% 47%	5000
	21st to end	Night	16% 8% 2 7% 4 4 4 3 6% 8% 37%	5402
April	1st to 10th	Night	16% 6% 2 5% 4 3 3 3 4 7% 48%	2000
	11th to 20th	Night	11% 4 2 4 3 3 3 3 5% 7% 56%	1883
	21st to end	Night	8% 4 1 3 2 2 2 2 6% 8% 62%	1883
May	1st to 10th	Night	8% 3 1 3 2 2 2 2 3 5% 69%	2860
	11th to 20th	Night	4 2 1 2 1 1 2 2 3 4 77%	2526
	21st to end	Night	4 3 1 3 2 2 3 2 4 6% 72%	2762
June	1st to 10th	Night	5% 4 2 4 3 3 3 4 6% 7% 58%	1520
	11th to 20th	Night	3 2 1 2 2 1 2 2 3 5% 78%	1520
	21st to end	Night	2 1 1 2 1 1 2 2 3 3 81%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 2 91%	2540
	11th to 20th	Night	1 2 1 2 1 1 2 1 3 3 83%	2540
	21st to end	Night	1 1 1 1 2 2 91%	3100
August	1st to 10th	Night	3 2 1 2 1 2 2 2 3 3 79%	2848
	11th to 20th	Night	1 1 1 1 1 2 3 89%	2872
	21st to end	Night	4 2 1 1 1 1 1 1 2 2 85%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 3 88%	1900
	11th to 20th	Night	3 1 2 2 1 2 2 3 6% 77%	1900
	21st to end	Night	4 1 1 2 1 2 2 2 3 5% 78%	2169
October	1st to 10th	Night	3 1 1 1 1 2 2 2 3 4 80%	3800
	11th to 20th	Night	5% 2 1 2 2 2 3 2 4 6% 72%	3777
	21st to end	Night	8% 2 1 2 2 2 3 3 6% 10% 62%	4121
November	1st to 10th	Night	13% 4 1 3 3 3 3 3 5% 7% 53%	2464
	11th to 20th	Night	15% 4 1 4 3 3 4 4 6% 9% 48%	2703
	21st to end	Night	16% 4 1 3 3 3 3 2 4 6% 55%	2800
December	1st to 10th	Night	14% 3 1 2 2 2 2 3 5% 6% 60%	4560
	11th to 20th	Night	35% 6% 2 4 3 3 4 4 5% 7% 27%	5176
	21st to end	Night	37% 6% 1 4 3 3 3 2 4 5% 34%	6952

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% 8% 12% 20% 12% 3	3639
	11th to 20th	Day	39% 3 6% 19% 22% 11%	3990
	21st to end	Day	39% 5% 9% 11% 20% 16%	4510
February	1st to 10th	Day	39% 6% 11% 17% 19% 9%	1800
	11th to 20th	Day	37% 4 9% 20% 24% 6%	1779
	21st to end	Day	37% 4 10% 23% 19% 7%	1650
March	1st to 10th	Day	48% 6% 7% 17% 19% 4	4820
	11th to 20th	Day	41% 4 9% 21% 19% 6%	5000
	21st to end	Day	44% 8% 11% 25% 11% 2	5573
April	1st to 10th	Day	36% 5% 12% 21% 20% 5%	2400
	11th to 20th	Day	29% 6% 11% 22% 21% 11%	2254
	21st to end	Day	21% 5% 12% 26% 28% 9%	2293
May	1st to 10th	Day	16% 6% 11% 20% 28% 20%	4110
	11th to 20th	Day	12% 3 5% 15% 32% 33%	4370
	21st to end	Day	12% 4 11% 29% 32% 13%	4814
June	1st to 10th	Day	21% 6% 10% 20% 26% 17%	2660
	11th to 20th	Day	9% 3 8% 18% 32% 29%	2660
	21st to end	Day	10% 1 4 13% 28% 43%	2660
July	1st to 10th	Day	3 1 2 6% 15% 72%	4351
	11th to 20th	Day	8% 1 3 7% 20% 61%	4345
	21st to end	Day	4 1 2 10% 29% 54%	4318
August	1st to 10th	Day	10% 2 3 10% 24% 53%	4076
	11th to 20th	Day	5% 1 2 15% 36% 41%	4005
	21st to end	Day	7% 1 4 17% 33% 38%	4179
September	1st to 10th	Day	5% 1 3 9% 22% 59%	2280
	11th to 20th	Day	12% 3 7% 19% 34% 25%	2280
	21st to end	Day	11% 3 5% 16% 31% 34%	2006
October	1st to 10th	Day	11% 2 4 13% 23% 48%	3180
	11th to 20th	Day	17% 3 7% 22% 33% 18%	3161
	21st to end	Day	30% 4 7% 18% 27% 14%	3448
November	1st to 10th	Day	31% 6% 7% 25% 18% 13%	1834
	11th to 20th	Day	34% 6% 12% 22% 16% 9%	1695
	21st to end	Day	32% 4 9% 20% 23% 12%	1600
December	1st to 10th	Day	30% 3 5% 18% 32% 13%	2620
	11th to 20th	Day	58% 5% 12% 13% 9% 3	3028
	21st to end	Day	54% 5% 9% 18% 11% 2	4004
January	1st to 10th	Night	44% 8% 14% 17% 15% 3	6306
	11th to 20th	Night	37% 4 7% 20% 21% 11%	5968
	21st to end	Night	43% 5% 6% 9% 20% 18%	6468
February	1st to 10th	Night	39% 5% 7% 22% 18% 9%	2600
	11th to 20th	Night	38% 5% 10% 19% 22% 7%	2519
	21st to end	Night	36% 4 10% 22% 21% 6%	1980
March	1st to 10th	Night	45% 6% 11% 20% 13% 5%	5071
	11th to 20th	Night	37% 5% 11% 23% 17% 7%	5000
	21st to end	Night	42% 8% 15% 25% 9% 2	5402
April	1st to 10th	Night	37% 5% 14% 21% 16% 7%	2000
	11th to 20th	Night	28% 6% 14% 22% 20% 10%	1883
	21st to end	Night	22% 5% 14% 29% 24% 7%	1883
May	1st to 10th	Night	19% 6% 8% 20% 31% 16%	2860
	11th to 20th	Night	13% 4 6% 15% 36% 26%	2526
	21st to end	Night	15% 6% 11% 33% 26% 10%	2762
June	1st to 10th	Night	24% 6% 10% 23% 27% 9%	1520
	11th to 20th	Night	11% 3 8% 19% 33% 26%	1520
	21st to end	Night	10% 2 4 13% 35% 35%	1520
July	1st to 10th	Night	4 1 2 7% 18% 68%	2500
	11th to 20th	Night	9% 2 3 5% 19% 63%	2492
	21st to end	Night	3 1 3 10% 29% 54%	3003
August	1st to 10th	Night	13% 1 3 10% 25% 48%	2839
	11th to 20th	Night	3 2 3 14% 42% 36%	2899
	21st to end	Night	9% 1 2 17% 35% 37%	3498
September	1st to 10th	Night	5% 1 3 8% 24% 58%	1900
	11th to 20th	Night	11% 3 6% 20% 34% 25%	1900
	21st to end	Night	11% 3 6% 18% 26% 36%	2169
October	1st to 10th	Night	12% 2 4 11% 22% 50%	3800
	11th to 20th	Night	16% 3 7% 31% 26% 17%	3777
	21st to end	Night	20% 3 8% 27% 26% 16%	4121
November	1st to 10th	Night	31% 6% 11% 24% 17% 12%	2464
	11th to 20th	Night	34% 6% 13% 22% 16% 9%	2703
	21st to end	Night	32% 4 10% 20% 22% 12%	2800
December	1st to 10th	Night	26% 3 7% 23% 27% 15%	4560
	11th to 20th	Night	58% 5% 7% 15% 13% 2	5176
	21st to end	Night	55% 5% 10% 16% 12% 2	6952

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	40% 7% 20% 22% 10% 3	200
	11th to 20th	Day	27% 9% 22% 22% 15% 6%	355
	21st to end	Day	23% 9% 20% 25% 16% 7%	440
February	1st to 10th	Day	25% 9% 24% 22% 18% 2	400
	11th to 20th	Day	23% 11% 28% 25% 11% 2	402
	21st to end	Day	19% 10% 27% 29% 13% 3	414
March	1st to 10th	Day	31% 13% 24% 21% 9% 3	500
	11th to 20th	Day	26% 11% 22% 25% 14% 4	500
	21st to end	Day	25% 13% 23% 23% 12% 2	550
April	1st to 10th	Day	20% 15% 22% 27% 13% 3	500
	11th to 20th	Day	18% 14% 24% 24% 15% 4	453
	21st to end	Day	6% 14% 34% 25% 16% 5%	460
May	1st to 10th	Day	11% 17% 32% 22% 14% 5%	463
	11th to 20th	Day	10% 9% 29% 26% 19% 6%	488
	21st to end	Day	6% 12% 24% 31% 18% 8%	529
June	1st to 10th	Day	6% 13% 20% 31% 23% 7%	490
	11th to 20th	Day	6% 14% 28% 31% 15% 6%	490
	21st to end	Day	2 6% 24% 33% 26% 9%	490
July	1st to 10th	Day	1 4 22% 39% 22% 12%	486
	11th to 20th	Day	2 17% 39% 28% 13%	484
	21st to end	Day	1 2 11% 41% 32% 13%	531
August	1st to 10th	Day	2 2 16% 36% 28% 15%	487
	11th to 20th	Day	2 3 18% 34% 29% 15%	477
	21st to end	Day	1 5% 17% 35% 30% 13%	539
September	1st to 10th	Day	1 3 19% 38% 29% 11%	490
	11th to 20th	Day	3 7% 21% 35% 24% 10%	490
	21st to end	Day	3 6% 24% 33% 27% 7%	490
October	1st to 10th	Day	4 10% 19% 32% 25% 9%	490
	11th to 20th	Day	8% 5% 22% 32% 23% 9%	490
	21st to end	Day	13% 9% 22% 29% 20% 7%	539
November	1st to 10th	Day	16% 9% 23% 23% 21% 8%	370
	11th to 20th	Day	20% 3 21% 30% 17% 9%	247
	21st to end	Day	17% 6% 25% 30% 18% 6%	200
December	1st to 10th	Day	23% 11% 21% 17% 21% 8%	200
	11th to 20th	Day	29% 4 19% 28% 14% 6%	200
	21st to end	Day	25% 7% 24% 27% 13% 5%	220
January	1st to 10th	Night	26% 5% 18% 30% 17% 4	800
	11th to 20th	Night	23% 8% 20% 32% 14% 3	800
	21st to end	Night	22% 5% 21% 30% 18% 4	880
February	1st to 10th	Night	22% 5% 21% 33% 17% 2	800
	11th to 20th	Night	22% 7% 24% 30% 14% 2	784
	21st to end	Night	18% 8% 26% 37% 11% 1	660
March	1st to 10th	Night	26% 7% 23% 28% 15% 2	800
	11th to 20th	Night	23% 7% 21% 30% 19% 1	800
	21st to end	Night	21% 9% 22% 34% 13% 1	880
April	1st to 10th	Night	16% 10% 26% 31% 16% 1	800
	11th to 20th	Night	12% 10% 29% 31% 16% 2	753
	21st to end	Night	9% 7% 31% 33% 19% 1	743
May	1st to 10th	Night	11% 8% 31% 31% 18% 1	570
	11th to 20th	Night	9% 5% 22% 37% 26% 2	384
	21st to end	Night	8% 9% 26% 34% 22% 1	411
June	1st to 10th	Night	7% 6% 26% 39% 22% 1	380
	11th to 20th	Night	3 9% 28% 41% 18% 1	380
	21st to end	Night	3 3 19% 50% 24% 1	380
July	1st to 10th	Night	1 1 15% 44% 37% 3	370
	11th to 20th	Night	2 1 11% 43% 38% 4	368
	21st to end	Night	1 1 6% 39% 48% 6%	615
August	1st to 10th	Night	2 1 9% 34% 46% 7%	567
	11th to 20th	Night	1 1 11% 40% 41% 6%	598
	21st to end	Night	2 1 10% 38% 44% 5%	836
September	1st to 10th	Night	2 1 15% 41% 39% 3	760
	11th to 20th	Night	4 2 12% 38% 39% 5%	760
	21st to end	Night	5% 3 18% 35% 33% 5%	760
October	1st to 10th	Night	6% 7% 18% 36% 29% 4	760
	11th to 20th	Night	8% 3 19% 36% 29% 5%	760
	21st to end	Night	12% 5% 21% 34% 23% 5%	836
November	1st to 10th	Night	13% 5% 17% 36% 26% 3	780
	11th to 20th	Night	17% 4 20% 38% 19% 2	800
	21st to end	Night	17% 6% 20% 36% 20% 2	800
December	1st to 10th	Night	26% 4 19% 31% 18% 3	800
	11th to 20th	Night	31% 4 20% 30% 14% 2	800
	21st to end	Night	26% 5% 24% 31% 13% 1	880

Page generated at 2025-04-08 06:17:27. Version ac07

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