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 2026-08-15.

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	9% 3 1 3 2 2 2 2 4 5% 66%	152800
	Night	13% 4 1 3 2 2 3 2 4 6% 60%	146523
Transparency	Day	23% 3 7% 18% 25% 25%	147668
	Night	28% 4 8% 19% 23% 19%	142648
Seeing	Day	12% 8% 22% 29% 21% 8%	17352
	Night	14% 5% 20% 35% 24% 3	26457

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	25% 8% 3 5% 3 3 4 3 4 7% 35%	4722
	11th to 20th	Day	17% 5% 1 3 2 1 2 1 2 3 62%	5202
	21st to end	Day	18% 5% 2 4 3 3 3 3 5% 7% 48%	5843
February	1st to 10th	Day	20% 5% 2 4 3 2 4 4 6% 6% 46%	1890
	11th to 20th	Day	20% 5% 2 3 3 3 3 2 5% 6% 48%	1861
	21st to end	Day	20% 4 2 4 3 3 3 3 5% 8% 46%	1730
March	1st to 10th	Day	22% 8% 3 6% 4 3 3 2 4 6% 40%	4927
	11th to 20th	Day	20% 6% 2 4 3 3 3 2 4 7% 47%	5110
	21st to end	Day	19% 7% 2 6% 3 4 4 3 5% 7% 39%	5696
April	1st to 10th	Day	16% 6% 2 4 3 3 3 3 5% 7% 48%	2520
	11th to 20th	Day	12% 4 1 4 3 3 3 3 5% 6% 56%	2489
	21st to end	Day	5% 4 1 4 3 2 3 3 5% 7% 62%	2535
May	1st to 10th	Day	5% 3 1 3 2 3 3 2 5% 7% 65%	7627
	11th to 20th	Day	2 1 1 2 1 1 2 2 3 6% 79%	8138
	21st to end	Day	4 2 1 2 2 2 2 2 4 6% 75%	8992
June	1st to 10th	Day	6% 3 1 3 2 3 3 3 5% 7% 64%	2940
	11th to 20th	Day	2 1 1 1 1 1 2 2 3 5% 79%	2940
	21st to end	Day	4 1 1 2 1 1 1 1 3 3 81%	2940
July	1st to 10th	Day	1 1 1 1 1 2 3 90%	8219
	11th to 20th	Day	2 2 1 2 2 2 2 1 2 3 81%	8220
	21st to end	Day	1 1 1 1 1 1 2 3 4 84%	8308
August	1st to 10th	Day	1 1 1 1 1 1 1 2 3 4 83%	5907
	11th to 20th	Day	1 1 1 1 1 1 2 3 88%	5763
	21st to end	Day	1 1 1 1 1 1 2 1 2 4 85%	5984
September	1st to 10th	Day	1 1 1 1 1 1 2 4 87%	2400
	11th to 20th	Day	3 2 3 2 2 2 2 4 6% 75%	2400
	21st to end	Day	3 2 1 2 2 2 1 2 3 5% 79%	2111
October	1st to 10th	Day	3 1 1 1 1 1 2 2 3 4 79%	3280
	11th to 20th	Day	5% 2 1 2 2 2 3 2 5% 7% 69%	3261
	21st to end	Day	11% 3 1 5% 4 2 4 3 6% 6% 55%	3558
November	1st to 10th	Day	15% 4 2 3 3 3 3 3 5% 8% 53%	1927
	11th to 20th	Day	17% 4 1 4 2 3 4 4 6% 8% 47%	1780
	21st to end	Day	13% 3 1 3 3 3 3 3 4 7% 56%	1680
December	1st to 10th	Day	14% 3 1 3 3 3 3 3 4 5% 58%	2700
	11th to 20th	Day	33% 5% 2 5% 4 4 4 3 5% 8% 26%	3108
	21st to end	Day	34% 6% 2 4 3 3 3 3 4 5% 33%	4092
January	1st to 10th	Night	28% 6% 2 4 3 3 3 3 5% 7% 35%	8172
	11th to 20th	Night	16% 3 1 4 2 2 2 2 3 5% 59%	7764
	21st to end	Night	18% 6% 2 6% 4 3 4 3 4 5% 44%	8371
February	1st to 10th	Night	20% 4 1 4 3 3 4 3 5% 5% 48%	2730
	11th to 20th	Night	20% 6% 1 4 3 3 3 3 4 6% 46%	2646
	21st to end	Night	18% 6% 1 4 3 4 3 3 4 8% 47%	2076
March	1st to 10th	Night	20% 7% 3 7% 4 3 3 3 4 7% 40%	5184
	11th to 20th	Night	20% 5% 2 4 3 3 2 2 4 7% 48%	5110
	21st to end	Night	16% 8% 2 7% 4 4 4 4 6% 8% 38%	5521
April	1st to 10th	Night	16% 6% 2 5% 4 3 3 3 4 7% 48%	2100
	11th to 20th	Night	11% 4 2 4 3 3 3 3 5% 7% 55%	2079
	21st to end	Night	9% 4 1 4 2 2 2 3 5% 7% 60%	2081
May	1st to 10th	Night	8% 3 1 4 2 2 3 2 4 6% 65%	5321
	11th to 20th	Night	3 2 1 3 2 2 2 2 4 6% 75%	4710
	21st to end	Night	5% 2 1 2 2 2 2 2 4 6% 72%	5181
June	1st to 10th	Night	5% 4 2 4 2 3 3 4 6% 7% 60%	1680
	11th to 20th	Night	3 2 1 2 2 1 1 1 3 5% 78%	1680
	21st to end	Night	2 1 1 2 1 1 2 2 3 3 81%	1680
July	1st to 10th	Night	1 1 1 1 2 3 3 88%	4740
	11th to 20th	Night	2 2 1 2 2 1 2 1 2 2 82%	4740
	21st to end	Night	1 1 1 1 1 2 3 4 85%	5797
August	1st to 10th	Night	2 2 1 1 1 2 2 3 3 82%	4125
	11th to 20th	Night	1 1 1 1 1 1 1 1 2 3 88%	4176
	21st to end	Night	3 1 1 2 1 1 2 1 3 3 83%	5015
September	1st to 10th	Night	1 1 1 1 1 1 1 1 3 4 86%	2000
	11th to 20th	Night	3 1 1 2 2 2 2 2 3 6% 76%	2000
	21st to end	Night	4 1 1 2 1 2 2 2 3 5% 78%	2284
October	1st to 10th	Night	3 2 1 2 1 2 2 2 3 3 79%	3920
	11th to 20th	Night	5% 2 1 2 2 2 3 2 4 6% 72%	3897
	21st to end	Night	8% 2 1 2 2 2 3 3 5% 9% 62%	4253
November	1st to 10th	Night	14% 4 1 3 3 3 3 3 6% 8% 52%	2590
	11th to 20th	Night	16% 4 1 4 3 3 4 4 5% 8% 47%	2838
	21st to end	Night	15% 4 1 3 3 3 3 2 4 7% 55%	2940
December	1st to 10th	Night	14% 3 1 2 2 2 2 3 5% 7% 60%	4700
	11th to 20th	Night	35% 6% 2 4 3 3 4 4 5% 7% 27%	5316
	21st to end	Night	37% 6% 1 4 3 3 3 2 4 4 34%	7106

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	49% 7% 10% 21% 11% 2	4723
	11th to 20th	Day	31% 2 5% 16% 22% 23%	5202
	21st to end	Day	37% 4 11% 15% 19% 14%	5843
February	1st to 10th	Day	38% 5% 10% 17% 20% 9%	1890
	11th to 20th	Day	38% 4 10% 20% 23% 5%	1870
	21st to end	Day	39% 4 10% 22% 18% 7%	1730
March	1st to 10th	Day	47% 6% 7% 17% 19% 4	4927
	11th to 20th	Day	40% 4 9% 21% 19% 7%	5110
	21st to end	Day	43% 8% 11% 25% 11% 2	5696
April	1st to 10th	Day	36% 5% 12% 21% 21% 5%	2520
	11th to 20th	Day	29% 5% 11% 21% 21% 12%	2492
	21st to end	Day	21% 5% 12% 26% 27% 9%	2535
May	1st to 10th	Day	19% 4 9% 21% 27% 20%	7627
	11th to 20th	Day	10% 2 4 19% 37% 27%	8141
	21st to end	Day	12% 2 8% 29% 36% 12%	8994
June	1st to 10th	Day	20% 5% 9% 20% 27% 18%	2940
	11th to 20th	Day	9% 3 7% 19% 32% 30%	2940
	21st to end	Day	10% 1 4 14% 30% 41%	2940
July	1st to 10th	Day	4 1 2 10% 25% 57%	8151
	11th to 20th	Day	12% 1 2 5% 20% 60%	8145
	21st to end	Day	7% 1 4 16% 27% 45%	8122
August	1st to 10th	Day	9% 1 3 10% 24% 53%	4336
	11th to 20th	Day	5% 1 2 15% 36% 40%	4186
	21st to end	Day	7% 1 3 16% 34% 38%	4311
September	1st to 10th	Day	6% 1 4 11% 22% 57%	2400
	11th to 20th	Day	13% 3 7% 19% 33% 25%	2400
	21st to end	Day	11% 3 5% 16% 31% 34%	2111
October	1st to 10th	Day	11% 2 4 13% 23% 47%	3280
	11th to 20th	Day	17% 3 7% 22% 33% 17%	3261
	21st to end	Day	30% 4 7% 19% 27% 14%	3558
November	1st to 10th	Day	31% 6% 7% 26% 17% 12%	1927
	11th to 20th	Day	35% 6% 12% 22% 15% 9%	1780
	21st to end	Day	30% 4 9% 21% 23% 12%	1680
December	1st to 10th	Day	29% 3 5% 18% 31% 12%	2700
	11th to 20th	Day	57% 5% 12% 13% 9% 3	3108
	21st to end	Day	54% 5% 9% 18% 11% 2	4092
January	1st to 10th	Night	50% 7% 11% 19% 12% 2	8172
	11th to 20th	Night	30% 4 6% 16% 24% 21%	7764
	21st to end	Night	43% 4 8% 12% 18% 15%	8371
February	1st to 10th	Night	38% 5% 7% 22% 19% 9%	2730
	11th to 20th	Night	39% 5% 9% 19% 22% 6%	2648
	21st to end	Night	37% 4 11% 21% 20% 6%	2076
March	1st to 10th	Night	44% 6% 11% 20% 14% 5%	5184
	11th to 20th	Night	36% 5% 11% 23% 17% 7%	5110
	21st to end	Night	41% 8% 14% 25% 9% 2	5521
April	1st to 10th	Night	37% 5% 13% 21% 16% 7%	2100
	11th to 20th	Night	29% 6% 14% 21% 20% 10%	2079
	21st to end	Night	24% 5% 13% 29% 23% 6%	2081
May	1st to 10th	Night	22% 4 8% 21% 31% 15%	5319
	11th to 20th	Night	13% 4 6% 21% 37% 19%	4710
	21st to end	Night	15% 4 8% 32% 35% 7%	5182
June	1st to 10th	Night	23% 6% 10% 22% 29% 10%	1680
	11th to 20th	Night	11% 3 8% 19% 33% 26%	1680
	21st to end	Night	10% 2 4 13% 37% 34%	1680
July	1st to 10th	Night	5% 1 2 11% 28% 53%	4700
	11th to 20th	Night	12% 1 2 3 21% 61%	4692
	21st to end	Night	6% 1 5% 16% 26% 45%	5671
August	1st to 10th	Night	12% 1 2 11% 26% 48%	3019
	11th to 20th	Night	3 2 3 14% 42% 36%	3027
	21st to end	Night	9% 1 2 16% 35% 36%	3608
September	1st to 10th	Night	7% 1 3 9% 24% 56%	2000
	11th to 20th	Night	12% 3 6% 20% 34% 24%	2000
	21st to end	Night	11% 3 6% 17% 26% 36%	2284
October	1st to 10th	Night	13% 2 4 11% 22% 49%	3920
	11th to 20th	Night	16% 3 7% 31% 26% 17%	3897
	21st to end	Night	20% 4 8% 26% 26% 16%	4253
November	1st to 10th	Night	31% 5% 11% 25% 16% 11%	2590
	11th to 20th	Night	35% 6% 13% 22% 16% 9%	2838
	21st to end	Night	31% 4 11% 21% 22% 12%	2940
December	1st to 10th	Night	26% 3 7% 23% 26% 15%	4700
	11th to 20th	Night	58% 5% 7% 15% 13% 2	5316
	21st to end	Night	55% 5% 9% 16% 12% 2	7106

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	39% 8% 20% 21% 9% 3	220
	11th to 20th	Day	25% 9% 21% 22% 17% 6%	383
	21st to end	Day	21% 8% 20% 25% 19% 7%	473
February	1st to 10th	Day	24% 9% 23% 22% 20% 2	430
	11th to 20th	Day	24% 12% 27% 24% 12% 2	433
	21st to end	Day	20% 10% 26% 28% 12% 2	446
March	1st to 10th	Day	29% 13% 24% 21% 10% 3	540
	11th to 20th	Day	24% 10% 21% 26% 16% 3	540
	21st to end	Day	24% 13% 23% 25% 13% 3	594
April	1st to 10th	Day	19% 14% 22% 27% 14% 4	540
	11th to 20th	Day	17% 15% 24% 24% 16% 5%	532
	21st to end	Day	6% 12% 32% 26% 17% 5%	540
May	1st to 10th	Day	10% 15% 29% 22% 17% 7%	543
	11th to 20th	Day	10% 10% 29% 27% 18% 6%	568
	21st to end	Day	6% 12% 23% 30% 21% 9%	617
June	1st to 10th	Day	5% 12% 20% 33% 23% 7%	570
	11th to 20th	Day	5% 13% 27% 31% 17% 7%	570
	21st to end	Day	2 6% 24% 32% 26% 10%	570
July	1st to 10th	Day	1 4 22% 37% 24% 12%	566
	11th to 20th	Day	2 16% 39% 28% 14%	564
	21st to end	Day	1 2 12% 40% 32% 15%	619
August	1st to 10th	Day	2 2 14% 36% 29% 17%	567
	11th to 20th	Day	1 3 16% 34% 29% 17%	534
	21st to end	Day	1 5% 15% 33% 31% 14%	583
September	1st to 10th	Day	1 3 18% 37% 29% 11%	530
	11th to 20th	Day	3 6% 20% 34% 24% 12%	530
	21st to end	Day	4 6% 23% 33% 26% 7%	530
October	1st to 10th	Day	5% 10% 19% 32% 25% 9%	530
	11th to 20th	Day	8% 5% 23% 32% 23% 9%	530
	21st to end	Day	14% 9% 21% 28% 21% 8%	583
November	1st to 10th	Day	17% 8% 21% 24% 22% 8%	403
	11th to 20th	Day	22% 3 21% 30% 17% 8%	272
	21st to end	Day	15% 6% 23% 29% 20% 7%	220
December	1st to 10th	Day	21% 10% 20% 18% 22% 9%	220
	11th to 20th	Day	30% 4 18% 26% 15% 7%	220
	21st to end	Day	28% 7% 22% 25% 14% 5%	242
January	1st to 10th	Night	28% 5% 17% 30% 17% 4	840
	11th to 20th	Night	22% 8% 19% 33% 16% 3	840
	21st to end	Night	22% 5% 20% 31% 18% 3	924
February	1st to 10th	Night	21% 5% 21% 34% 17% 2	840
	11th to 20th	Night	23% 7% 24% 30% 13% 2	824
	21st to end	Night	19% 8% 25% 37% 10% 1	692
March	1st to 10th	Night	25% 7% 23% 29% 14% 2	840
	11th to 20th	Night	22% 6% 20% 32% 19% 1	840
	21st to end	Night	20% 9% 22% 35% 13% 1	924
April	1st to 10th	Night	16% 10% 26% 31% 16% 1	840
	11th to 20th	Night	12% 10% 29% 31% 17% 2	831
	21st to end	Night	10% 6% 30% 33% 19% 1	821
May	1st to 10th	Night	10% 8% 29% 31% 20% 1	630
	11th to 20th	Night	8% 5% 23% 38% 25% 1	424
	21st to end	Night	8% 8% 24% 35% 24% 1	455
June	1st to 10th	Night	6% 5% 25% 41% 22% 1	420
	11th to 20th	Night	3 8% 27% 42% 19%	420
	21st to end	Night	3 3 19% 49% 25% 1	420
July	1st to 10th	Night	15% 46% 35% 3	410
	11th to 20th	Night	2 1 11% 47% 36% 3	408
	21st to end	Night	1 1 6% 40% 46% 6%	681
August	1st to 10th	Night	2 1 8% 33% 48% 7%	627
	11th to 20th	Night	1 1 11% 39% 42% 6%	642
	21st to end	Night	2 1 9% 39% 44% 5%	880
September	1st to 10th	Night	2 2 15% 41% 39% 3	800
	11th to 20th	Night	4 2 11% 38% 39% 5%	800
	21st to end	Night	5% 4 18% 35% 33% 5%	800
October	1st to 10th	Night	7% 7% 18% 36% 29% 4	800
	11th to 20th	Night	8% 3 19% 36% 29% 5%	800
	21st to end	Night	12% 5% 21% 34% 23% 5%	880
November	1st to 10th	Night	14% 5% 16% 35% 27% 3	820
	11th to 20th	Night	18% 4 20% 38% 19% 2	840
	21st to end	Night	17% 5% 19% 36% 20% 2	840
December	1st to 10th	Night	24% 4 19% 32% 19% 3	840
	11th to 20th	Night	30% 4 19% 29% 15% 2	840
	21st to end	Night	28% 5% 24% 30% 12% 1	924

Page generated at 2026-08-12 00:37:13. Version ac07

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