Krause's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Krause's Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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	8% 5% 2 7% 5% 5% 5% 5% 7% 10% 41%	126956
	Night	9% 6% 2 6% 5% 4 5% 4 6% 9% 44%	124050
Transparency	Day	37% 8% 16% 20% 14% 5%	130680
	Night	36% 8% 15% 20% 15% 6%	128395
Seeing	Day	9% 4 16% 25% 26% 20%	17013
	Night	10% 4 18% 34% 27% 8%	27067

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	8% 5% 2 5% 4 3 3 3 4 7% 54%	4056
	11th to 20th	Day	19% 10% 3 8% 4 4 4 3 4 6% 34%	4060
	21st to end	Day	12% 5% 2 5% 4 3 3 3 6% 8% 48%	4627
February	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 7% 7% 43%	2000
	11th to 20th	Day	9% 5% 2 6% 4 4 4 3 5% 6% 52%	1948
	21st to end	Day	9% 6% 3 5% 4 4 4 4 5% 8% 49%	1730
March	1st to 10th	Day	8% 6% 2 7% 4 4 5% 4 7% 9% 43%	4935
	11th to 20th	Day	5% 4 2 5% 4 3 3 3 5% 8% 58%	4980
	21st to end	Day	9% 6% 2 6% 4 4 4 4 6% 9% 49%	5465
April	1st to 10th	Day	6% 4 2 4 4 4 5% 4 6% 9% 52%	2200
	11th to 20th	Day	7% 4 2 6% 5% 4 5% 5% 7% 8% 47%	2201
	21st to end	Day	4 4 1 4 4 4 4 4 8% 9% 54%	2407
May	1st to 10th	Day	3 3 1 5% 5% 5% 5% 4 8% 11% 50%	5862
	11th to 20th	Day	8% 4 2 6% 5% 5% 5% 4 5% 9% 46%	5861
	21st to end	Day	4 4 1 5% 4 5% 5% 5% 7% 12% 48%	6433
June	1st to 10th	Day	9% 7% 3 8% 7% 7% 8% 6% 8% 10% 27%	2600
	11th to 20th	Day	6% 5% 2 8% 8% 9% 8% 6% 8% 11% 28%	2600
	21st to end	Day	8% 6% 3 8% 8% 6% 7% 6% 8% 10% 29%	2600
July	1st to 10th	Day	7% 6% 3 9% 7% 8% 8% 8% 11% 14% 19%	5900
	11th to 20th	Day	4 4 2 7% 6% 6% 7% 7% 10% 16% 30%	5900
	21st to end	Day	6% 5% 2 7% 6% 6% 7% 6% 9% 15% 31%	6424
August	1st to 10th	Day	6% 7% 3 8% 6% 7% 7% 6% 9% 13% 29%	4234
	11th to 20th	Day	5% 5% 2 7% 6% 6% 8% 5% 8% 12% 36%	3978
	21st to end	Day	8% 6% 3 9% 7% 7% 9% 6% 8% 10% 25%	3949
September	1st to 10th	Day	7% 7% 3 11% 9% 7% 9% 6% 10% 10% 21%	2200
	11th to 20th	Day	9% 7% 3 10% 8% 7% 8% 6% 8% 9% 25%	2200
	21st to end	Day	8% 7% 3 9% 7% 7% 6% 5% 8% 9% 32%	2200
October	1st to 10th	Day	11% 6% 3 9% 7% 6% 6% 4 6% 9% 34%	2190
	11th to 20th	Day	6% 5% 2 6% 5% 4 4 4 6% 8% 52%	2000
	21st to end	Day	8% 5% 2 5% 5% 5% 5% 4 5% 8% 50%	2200
November	1st to 10th	Day	8% 5% 3 5% 5% 4 4 4 5% 9% 49%	2057
	11th to 20th	Day	8% 6% 2 6% 5% 5% 5% 3 5% 6% 48%	2100
	21st to end	Day	9% 6% 2 5% 4 5% 4 4 6% 8% 46%	1937
December	1st to 10th	Day	6% 4 1 5% 3 4 5% 4 6% 8% 56%	3020
	11th to 20th	Day	10% 6% 2 7% 4 5% 5% 5% 6% 9% 42%	3436
	21st to end	Day	11% 8% 3 7% 5% 5% 5% 3 5% 8% 43%	4466
January	1st to 10th	Night	9% 5% 2 4 3 3 3 3 5% 7% 55%	5889
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 4 5% 8% 31%	5900
	21st to end	Night	15% 6% 2 6% 4 3 4 3 6% 8% 42%	6324
February	1st to 10th	Night	12% 7% 2 6% 4 4 3 3 6% 7% 46%	2400
	11th to 20th	Night	10% 5% 2 6% 4 5% 4 4 5% 7% 48%	2338
	21st to end	Night	8% 7% 2 6% 5% 3 4 4 6% 6% 49%	1897
March	1st to 10th	Night	13% 8% 3 7% 4 4 4 3 5% 5% 45%	4918
	11th to 20th	Night	6% 4 2 5% 3 3 3 4 6% 9% 55%	4980
	21st to end	Night	9% 6% 2 6% 4 4 4 3 5% 8% 50%	5467
April	1st to 10th	Night	6% 5% 2 4 4 3 4 4 6% 9% 52%	2200
	11th to 20th	Night	6% 6% 2 5% 4 3 3 3 6% 8% 53%	2144
	21st to end	Night	6% 3 2 4 4 5% 5% 3 5% 8% 57%	2000
May	1st to 10th	Night	4 4 2 7% 4 5% 4 4 6% 10% 50%	4041
	11th to 20th	Night	8% 5% 2 6% 4 3 4 3 6% 10% 48%	4032
	21st to end	Night	3 3 1 4 4 4 4 4 6% 11% 55%	4421
June	1st to 10th	Night	10% 6% 2 6% 5% 6% 6% 6% 7% 10% 37%	1800
	11th to 20th	Night	6% 5% 2 7% 7% 6% 7% 7% 8% 12% 33%	1800
	21st to end	Night	6% 8% 3 9% 5% 6% 5% 5% 9% 10% 34%	1800
July	1st to 10th	Night	8% 7% 3 10% 7% 7% 7% 6% 11% 12% 21%	4058
	11th to 20th	Night	4 5% 2 8% 7% 7% 8% 7% 9% 13% 30%	4057
	21st to end	Night	7% 6% 2 9% 7% 7% 7% 6% 9% 10% 29%	4427
August	1st to 10th	Night	6% 5% 2 9% 6% 7% 6% 6% 8% 11% 34%	2915
	11th to 20th	Night	4 4 2 5% 5% 5% 6% 5% 9% 15% 40%	3001
	21st to end	Night	7% 6% 3 9% 6% 6% 6% 6% 8% 12% 31%	3949
September	1st to 10th	Night	9% 8% 2 9% 6% 6% 6% 5% 8% 10% 31%	2200
	11th to 20th	Night	10% 7% 3 9% 6% 6% 6% 6% 8% 11% 29%	2200
	21st to end	Night	7% 7% 3 7% 5% 5% 7% 5% 6% 10% 38%	2200
October	1st to 10th	Night	10% 7% 3 6% 5% 5% 5% 4 7% 8% 40%	2208
	11th to 20th	Night	5% 4 2 5% 3 5% 4 4 6% 8% 55%	2400
	21st to end	Night	8% 5% 2 6% 4 4 4 3 6% 7% 52%	2640
November	1st to 10th	Night	8% 5% 2 6% 4 3 4 3 7% 7% 50%	2461
	11th to 20th	Night	7% 7% 2 7% 5% 4 4 3 5% 7% 49%	2520
	21st to end	Night	8% 6% 3 7% 4 5% 5% 3 6% 8% 47%	2679
December	1st to 10th	Night	6% 4 2 5% 4 3 4 3 5% 7% 56%	4380
	11th to 20th	Night	9% 7% 2 5% 4 4 4 4 4 6% 50%	4914
	21st to end	Night	14% 7% 2 7% 4 5% 5% 3 5% 7% 40%	6490

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	30% 4 8% 15% 28% 14%	4057
	11th to 20th	Day	53% 3 5% 14% 17% 8%	4060
	21st to end	Day	34% 5% 8% 27% 18% 9%	4627
February	1st to 10th	Day	39% 5% 10% 15% 20% 11%	2000
	11th to 20th	Day	33% 4 8% 19% 25% 11%	1958
	21st to end	Day	34% 5% 10% 18% 23% 11%	1730
March	1st to 10th	Day	35% 7% 12% 18% 20% 8%	4935
	11th to 20th	Day	24% 4 9% 22% 22% 18%	4980
	21st to end	Day	32% 4 10% 28% 18% 9%	5465
April	1st to 10th	Day	28% 7% 13% 22% 22% 9%	2200
	11th to 20th	Day	33% 6% 11% 19% 22% 9%	2201
	21st to end	Day	24% 6% 13% 25% 25% 8%	2407
May	1st to 10th	Day	24% 7% 22% 29% 14% 4	5897
	11th to 20th	Day	33% 8% 14% 33% 11% 1	5865
	21st to end	Day	26% 7% 18% 33% 15% 1	6447
June	1st to 10th	Day	47% 11% 19% 16% 6%	2600
	11th to 20th	Day	45% 11% 20% 21% 3	2600
	21st to end	Day	46% 12% 23% 15% 4	2600
July	1st to 10th	Day	49% 13% 30% 8% 1	5835
	11th to 20th	Day	38% 12% 39% 11%	5831
	21st to end	Day	38% 14% 27% 20% 1	6240
August	1st to 10th	Day	43% 12% 30% 13% 3	4221
	11th to 20th	Day	37% 12% 25% 21% 5%	4017
	21st to end	Day	49% 13% 21% 15% 2	3949
September	1st to 10th	Day	51% 16% 17% 11% 4	2200
	11th to 20th	Day	50% 11% 20% 13% 5%	2200
	21st to end	Day	45% 9% 14% 17% 11% 3	2200
October	1st to 10th	Day	56% 7% 13% 12% 7% 5%	3567
	11th to 20th	Day	25% 6% 6% 21% 33% 8%	3240
	21st to end	Day	27% 5% 7% 22% 32% 8%	3538
November	1st to 10th	Day	33% 6% 10% 20% 20% 12%	2057
	11th to 20th	Day	36% 5% 8% 19% 22% 11%	2100
	21st to end	Day	36% 5% 9% 22% 21% 8%	1937
December	1st to 10th	Day	26% 4 16% 25% 19% 9%	3020
	11th to 20th	Day	37% 7% 10% 19% 18% 9%	3433
	21st to end	Day	40% 6% 10% 21% 18% 4	4466
January	1st to 10th	Night	29% 4 7% 17% 30% 13%	5889
	11th to 20th	Night	52% 5% 7% 17% 16% 4	5900
	21st to end	Night	39% 6% 10% 21% 16% 9%	6324
February	1st to 10th	Night	37% 5% 10% 17% 17% 13%	2400
	11th to 20th	Night	35% 6% 10% 18% 21% 11%	2339
	21st to end	Night	33% 5% 12% 18% 23% 9%	1897
March	1st to 10th	Night	40% 6% 9% 16% 20% 9%	4918
	11th to 20th	Night	24% 6% 14% 21% 18% 17%	4980
	21st to end	Night	33% 5% 10% 25% 20% 8%	5467
April	1st to 10th	Night	28% 6% 17% 24% 17% 9%	2200
	11th to 20th	Night	28% 6% 10% 26% 20% 9%	2144
	21st to end	Night	26% 5% 14% 26% 22% 7%	2000
May	1st to 10th	Night	27% 10% 20% 27% 12% 3	4068
	11th to 20th	Night	30% 8% 18% 29% 14% 1	4033
	21st to end	Night	23% 8% 18% 34% 17% 1	4429
June	1st to 10th	Night	40% 9% 23% 21% 6%	1800
	11th to 20th	Night	40% 13% 24% 21% 2	1800
	21st to end	Night	42% 13% 23% 17% 4 1	1800
July	1st to 10th	Night	51% 14% 28% 6% 1	4015
	11th to 20th	Night	43% 13% 35% 9% 1	4006
	21st to end	Night	45% 11% 25% 18% 1	4297
August	1st to 10th	Night	40% 12% 33% 12% 3	2904
	11th to 20th	Night	31% 12% 30% 22% 5%	3028
	21st to end	Night	42% 14% 26% 16% 2	3949
September	1st to 10th	Night	44% 15% 22% 14% 5%	2200
	11th to 20th	Night	45% 13% 20% 18% 3 1	2200
	21st to end	Night	41% 9% 19% 18% 10% 2	2200
October	1st to 10th	Night	54% 8% 12% 14% 7% 4	3611
	11th to 20th	Night	25% 6% 6% 24% 34% 5%	3899
	21st to end	Night	28% 6% 8% 19% 32% 7%	4252
November	1st to 10th	Night	31% 6% 11% 21% 19% 11%	2461
	11th to 20th	Night	35% 5% 8% 21% 20% 11%	2520
	21st to end	Night	35% 5% 9% 22% 20% 8%	2679
December	1st to 10th	Night	28% 4 14% 26% 15% 13%	4380
	11th to 20th	Night	34% 5% 11% 23% 17% 10%	4916
	21st to end	Night	43% 6% 12% 20% 15% 5%	6490

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	11% 7% 41% 26% 13% 2	300
	11th to 20th	Day	9% 12% 32% 29% 14% 4	300
	21st to end	Day	13% 13% 36% 31% 6%	330
February	1st to 10th	Day	12% 11% 24% 30% 20% 4	300
	11th to 20th	Day	12% 6% 32% 32% 14% 4	300
	21st to end	Day	11% 6% 25% 31% 22% 4	329
March	1st to 10th	Day	7% 8% 32% 35% 18% 1	500
	11th to 20th	Day	10% 8% 25% 32% 19% 5%	500
	21st to end	Day	9% 6% 26% 31% 24% 4	550
April	1st to 10th	Day	9% 8% 24% 34% 22% 3	500
	11th to 20th	Day	9% 8% 23% 31% 24% 5%	492
	21st to end	Day	5% 3 17% 31% 29% 14%	500
May	1st to 10th	Day	3 3 17% 31% 31% 14%	503
	11th to 20th	Day	9% 1 11% 32% 28% 19%	527
	21st to end	Day	8% 1 8% 19% 34% 30%	573
June	1st to 10th	Day	11% 2 6% 23% 33% 26%	530
	11th to 20th	Day	8% 2 7% 18% 30% 36%	530
	21st to end	Day	6% 2 5% 14% 27% 47%	530
July	1st to 10th	Day	7% 2 4 8% 29% 50%	525
	11th to 20th	Day	7% 1 2 8% 31% 51%	524
	21st to end	Day	9% 1 3 13% 29% 45%	576
August	1st to 10th	Day	6% 4 6% 13% 29% 42%	526
	11th to 20th	Day	5% 1 3 12% 28% 52%	519
	21st to end	Day	10% 2 4 16% 29% 38%	583
September	1st to 10th	Day	10% 2 6% 14% 32% 36%	530
	11th to 20th	Day	10% 2 6% 24% 33% 24%	530
	21st to end	Day	9% 2 9% 18% 33% 29%	530
October	1st to 10th	Day	14% 3 15% 32% 27% 9%	530
	11th to 20th	Day	7% 4 15% 28% 37% 9%	530
	21st to end	Day	7% 4 19% 34% 30% 6%	583
November	1st to 10th	Day	8% 6% 21% 29% 31% 6%	535
	11th to 20th	Day	14% 4 23% 33% 22% 5%	540
	21st to end	Day	8% 8% 26% 31% 23% 3	377
December	1st to 10th	Day	8% 6% 33% 30% 17% 6%	330
	11th to 20th	Day	13% 6% 31% 31% 18% 2	321
	21st to end	Day	10% 6% 28% 35% 18% 3	330
January	1st to 10th	Night	12% 8% 34% 34% 12% 1	800
	11th to 20th	Night	13% 7% 27% 37% 15% 1	800
	21st to end	Night	18% 7% 33% 34% 8%	880
February	1st to 10th	Night	15% 7% 26% 38% 14%	800
	11th to 20th	Night	12% 7% 29% 39% 12% 1	783
	21st to end	Night	12% 6% 31% 44% 7%	660
March	1st to 10th	Night	8% 7% 32% 40% 12% 1	800
	11th to 20th	Night	10% 7% 28% 39% 15% 1	800
	21st to end	Night	9% 6% 27% 43% 14% 1	880
April	1st to 10th	Night	9% 4 29% 42% 15% 1	800
	11th to 20th	Night	8% 5% 28% 41% 16% 2	791
	21st to end	Night	7% 4 23% 44% 23% 1	800
May	1st to 10th	Night	5% 2 13% 50% 28% 2	608
	11th to 20th	Night	7% 2 11% 43% 32% 5%	591
	21st to end	Night	8% 1 6% 32% 45% 7%	650
June	1st to 10th	Night	11% 2 7% 35% 38% 8%	600
	11th to 20th	Night	7% 3 6% 22% 41% 23%	600
	21st to end	Night	9% 2 4 18% 46% 22%	600
July	1st to 10th	Night	8% 1 3 14% 43% 30%	585
	11th to 20th	Night	4 1 2 10% 49% 33%	582
	21st to end	Night	7% 1 3 12% 51% 26%	657
August	1st to 10th	Night	7% 2 4 12% 47% 27%	597
	11th to 20th	Night	6% 1 2 12% 44% 35%	594
	21st to end	Night	12% 2 6% 20% 40% 21%	880
September	1st to 10th	Night	10% 3 8% 21% 39% 19%	800
	11th to 20th	Night	12% 3 7% 27% 37% 13%	800
	21st to end	Night	11% 3 10% 28% 40% 9%	800
October	1st to 10th	Night	13% 3 15% 38% 28% 4	800
	11th to 20th	Night	6% 2 13% 40% 35% 3	800
	21st to end	Night	12% 2 16% 39% 28% 3	880
November	1st to 10th	Night	10% 3 23% 36% 26% 2	820
	11th to 20th	Night	11% 5% 19% 40% 21% 3	840
	21st to end	Night	11% 3 27% 41% 18% 1	840
December	1st to 10th	Night	10% 4 24% 38% 22% 1	840
	11th to 20th	Night	11% 6% 26% 37% 19% 1	829
	21st to end	Night	13% 5% 25% 39% 17% 1	880

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