Erwin W. Fick Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Erwin W. Fick Observatory clear sky chart from 2005-11-06 to 2026-07-16.

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	12% 8% 3 8% 5% 4 4 4 6% 7% 40%	138415
	Night	11% 8% 3 8% 4 4 4 3 5% 7% 43%	134587
Transparency	Day	42% 5% 13% 25% 14% 1	142016
	Night	41% 4 13% 25% 16% 2	139065
Seeing	Day	15% 10% 30% 27% 14% 3	18200
	Night	15% 9% 33% 32% 10% 1	28039

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	7% 13% 5% 19% 8% 6% 4 3 4 5% 26%	4728
	11th to 20th	Day	5% 9% 4 12% 6% 7% 7% 5% 6% 7% 32%	5310
	21st to end	Day	8% 11% 6% 13% 7% 6% 6% 3 5% 5% 31%	5812
February	1st to 10th	Day	9% 15% 5% 9% 6% 6% 6% 3 5% 7% 28%	1890
	11th to 20th	Day	11% 11% 4 9% 6% 5% 5% 4 5% 6% 36%	1844
	21st to end	Day	13% 11% 3 9% 5% 5% 4 3 4 6% 37%	1667
March	1st to 10th	Day	16% 9% 3 6% 3 3 3 2 3 5% 46%	5046
	11th to 20th	Day	11% 7% 2 6% 3 3 3 4 5% 8% 47%	5090
	21st to end	Day	21% 13% 5% 8% 4 4 4 3 5% 6% 26%	5583
April	1st to 10th	Day	17% 11% 3 6% 4 4 4 4 6% 6% 34%	2492
	11th to 20th	Day	18% 9% 3 7% 4 4 3 4 5% 6% 36%	2494
	21st to end	Day	21% 8% 3 6% 4 4 3 4 5% 6% 35%	2704
May	1st to 10th	Day	13% 6% 2 7% 4 4 5% 4 6% 7% 41%	7617
	11th to 20th	Day	14% 7% 2 7% 4 3 4 3 5% 6% 45%	8039
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	9047
June	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 4 6% 8% 44%	2940
	11th to 20th	Day	10% 4 2 5% 4 5% 4 5% 7% 10% 44%	2940
	21st to end	Day	10% 5% 2 6% 5% 5% 6% 4 6% 9% 41%	2940
July	1st to 10th	Day	9% 6% 2 6% 4 4 5% 5% 7% 11% 41%	6500
	11th to 20th	Day	8% 5% 2 6% 4 4 4 3 6% 7% 51%	6323
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 4 7% 10% 43%	6422
August	1st to 10th	Day	8% 5% 2 6% 4 4 4 4 7% 10% 45%	4234
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 4 7% 7% 39%	4171
	21st to end	Day	7% 4 2 7% 5% 5% 4 4 6% 8% 48%	4426
September	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 6% 6% 53%	2400
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 6% 8% 48%	2307
	21st to end	Day	11% 5% 2 4 3 4 4 3 5% 7% 51%	2140
October	1st to 10th	Day	14% 6% 2 5% 4 3 3 4 4 7% 49%	2000
	11th to 20th	Day	15% 7% 2 6% 4 3 4 2 5% 6% 46%	2000
	21st to end	Day	14% 9% 3 6% 4 3 4 3 5% 6% 41%	2200
November	1st to 10th	Day	11% 7% 2 5% 4 3 5% 4 6% 7% 45%	1901
	11th to 20th	Day	13% 9% 3 6% 6% 3 3 4 5% 7% 40%	1680
	21st to end	Day	14% 10% 4 7% 4 4 4 3 5% 6% 39%	1680
December	1st to 10th	Day	7% 7% 3 8% 4 4 4 4 5% 6% 47%	2690
	11th to 20th	Day	13% 10% 4 13% 7% 6% 5% 3 6% 6% 27%	3088
	21st to end	Day	21% 16% 7% 14% 5% 4 3 3 4 5% 19%	4070
January	1st to 10th	Night	9% 12% 5% 18% 6% 5% 4 3 5% 5% 27%	8190
	11th to 20th	Night	6% 9% 3 8% 6% 6% 7% 4 8% 7% 36%	7680
	21st to end	Night	9% 11% 5% 11% 5% 5% 4 3 5% 6% 36%	8402
February	1st to 10th	Night	10% 12% 5% 11% 7% 5% 4 3 6% 6% 32%	2730
	11th to 20th	Night	11% 10% 3 8% 4 5% 4 4 5% 6% 40%	2663
	21st to end	Night	11% 8% 3 8% 5% 4 4 3 4 6% 44%	2154
March	1st to 10th	Night	15% 7% 2 5% 3 3 3 2 4 5% 51%	5029
	11th to 20th	Night	9% 7% 3 5% 4 3 3 3 5% 8% 50%	5090
	21st to end	Night	18% 11% 4 11% 5% 4 4 3 4 6% 29%	5588
April	1st to 10th	Night	14% 9% 2 6% 4 4 4 3 5% 6% 41%	2127
	11th to 20th	Night	14% 8% 3 7% 5% 4 3 3 5% 5% 42%	2075
	21st to end	Night	16% 8% 3 7% 4 4 4 3 4 6% 40%	1912
May	1st to 10th	Night	12% 5% 2 5% 3 3 4 3 5% 7% 50%	5266
	11th to 20th	Night	13% 6% 2 5% 3 3 3 2 5% 6% 50%	4849
	21st to end	Night	18% 8% 3 7% 4 4 3 3 4 6% 40%	5139
June	1st to 10th	Night	6% 5% 2 6% 4 4 4 5% 5% 8% 51%	1680
	11th to 20th	Night	7% 5% 2 6% 4 3 4 4 6% 8% 49%	1680
	21st to end	Night	8% 6% 1 4 4 3 4 4 6% 8% 51%	1680
July	1st to 10th	Night	7% 5% 2 5% 4 4 4 4 6% 9% 50%	3698
	11th to 20th	Night	7% 4 2 5% 3 3 4 3 6% 8% 56%	3748
	21st to end	Night	7% 4 2 6% 4 5% 5% 5% 8% 10% 46%	4449
August	1st to 10th	Night	5% 4 2 5% 4 4 4 3 6% 8% 54%	2926
	11th to 20th	Night	9% 5% 2 5% 3 3 4 3 4 6% 54%	2888
	21st to end	Night	9% 5% 1 5% 3 3 3 3 5% 7% 56%	3474
September	1st to 10th	Night	10% 3 2 6% 3 3 3 2 4 6% 58%	2000
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 5% 6% 55%	2090
	21st to end	Night	8% 4 1 4 3 3 4 3 5% 7% 58%	2240
October	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 6% 53%	2400
	11th to 20th	Night	15% 6% 2 6% 4 3 3 3 4 6% 49%	2400
	21st to end	Night	15% 9% 3 5% 3 3 3 3 4 7% 45%	2640
November	1st to 10th	Night	11% 6% 2 5% 3 3 4 3 5% 7% 51%	2611
	11th to 20th	Night	12% 8% 3 7% 4 3 4 3 5% 6% 44%	2940
	21st to end	Night	13% 9% 4 7% 4 3 4 3 4 7% 42%	2940
December	1st to 10th	Night	6% 9% 3 7% 5% 4 5% 4 6% 7% 45%	4720
	11th to 20th	Night	11% 10% 4 11% 6% 4 4 4 5% 6% 35%	5339
	21st to end	Night	20% 15% 7% 14% 5% 4 3 3 3 4 22%	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	61% 4 12% 14% 8% 1	4729
	11th to 20th	Day	50% 3 10% 21% 15% 1	5310
	21st to end	Day	55% 4 12% 22% 6%	5812
February	1st to 10th	Day	55% 5% 14% 18% 8% 1	1890
	11th to 20th	Day	49% 6% 11% 21% 11% 2	1853
	21st to end	Day	49% 4 14% 19% 11% 3	1667
March	1st to 10th	Day	43% 4 9% 26% 17% 2	5046
	11th to 20th	Day	35% 5% 9% 30% 18% 2	5090
	21st to end	Day	59% 5% 15% 16% 4 1	5585
April	1st to 10th	Day	49% 6% 11% 25% 9% 1	2492
	11th to 20th	Day	48% 6% 12% 21% 12% 2	2494
	21st to end	Day	49% 5% 12% 22% 12% 1	2704
May	1st to 10th	Day	39% 7% 10% 27% 17% 1	7655
	11th to 20th	Day	40% 5% 9% 27% 16% 2	8043
	21st to end	Day	46% 5% 11% 22% 14% 1	9061
June	1st to 10th	Day	36% 8% 16% 24% 14% 2	2940
	11th to 20th	Day	33% 6% 15% 25% 19% 2	2940
	21st to end	Day	37% 8% 15% 24% 13% 2	2940
July	1st to 10th	Day	38% 4 16% 32% 9% 1	6431
	11th to 20th	Day	33% 4 14% 31% 17% 1	6248
	21st to end	Day	35% 5% 20% 27% 12% 1	6240
August	1st to 10th	Day	33% 6% 16% 28% 15% 1	4220
	11th to 20th	Day	42% 5% 13% 26% 13% 1	4210
	21st to end	Day	33% 5% 16% 26% 16% 2	4425
September	1st to 10th	Day	30% 5% 15% 27% 20% 3	2400
	11th to 20th	Day	33% 6% 14% 30% 17% 1	2307
	21st to end	Day	33% 5% 11% 30% 20% 1	2140
October	1st to 10th	Day	22% 3 7% 28% 38% 2	3260
	11th to 20th	Day	28% 4 10% 30% 24% 4	3240
	21st to end	Day	40% 3 9% 29% 16% 3	3538
November	1st to 10th	Day	36% 6% 17% 22% 17% 2	1901
	11th to 20th	Day	43% 5% 14% 22% 16% 1	1680
	21st to end	Day	46% 4 14% 24% 11% 1	1680
December	1st to 10th	Day	36% 4 17% 32% 9% 1	2690
	11th to 20th	Day	57% 4 14% 18% 7%	3085
	21st to end	Day	70% 4 9% 13% 4	4070
January	1st to 10th	Night	58% 4 15% 15% 7% 1	8191
	11th to 20th	Night	44% 4 13% 18% 19% 2	7680
	21st to end	Night	49% 4 14% 21% 12% 1	8402
February	1st to 10th	Night	52% 5% 13% 20% 9% 1	2730
	11th to 20th	Night	44% 6% 12% 24% 13% 2	2664
	21st to end	Night	43% 4 11% 22% 17% 3	2154
March	1st to 10th	Night	36% 4 9% 31% 18% 2	5029
	11th to 20th	Night	33% 4 8% 33% 18% 4	5090
	21st to end	Night	55% 7% 15% 15% 6% 2	5588
April	1st to 10th	Night	42% 5% 12% 25% 14% 2	2127
	11th to 20th	Night	43% 5% 11% 22% 17% 3	2075
	21st to end	Night	43% 6% 14% 22% 13% 2	1912
May	1st to 10th	Night	34% 4 8% 27% 24% 2	5293
	11th to 20th	Night	36% 4 10% 26% 19% 6%	4850
	21st to end	Night	45% 5% 10% 22% 16% 2	5149
June	1st to 10th	Night	31% 7% 15% 29% 15% 3	1680
	11th to 20th	Night	31% 7% 13% 22% 23% 5%	1680
	21st to end	Night	31% 6% 15% 27% 18% 3	1680
July	1st to 10th	Night	30% 5% 16% 32% 15% 1	3660
	11th to 20th	Night	27% 4 17% 32% 18% 2	3703
	21st to end	Night	32% 7% 21% 26% 14% 1	4320
August	1st to 10th	Night	28% 5% 17% 33% 15% 2	2916
	11th to 20th	Night	31% 5% 16% 32% 15% 2	2915
	21st to end	Night	28% 5% 17% 29% 17% 5%	3474
September	1st to 10th	Night	28% 4 12% 27% 24% 4	2000
	11th to 20th	Night	29% 4 12% 34% 19% 1	2090
	21st to end	Night	27% 5% 10% 30% 26% 3	2240
October	1st to 10th	Night	22% 3 6% 24% 42% 3	3920
	11th to 20th	Night	27% 3 9% 28% 26% 7%	3899
	21st to end	Night	41% 3 10% 26% 18% 2	4252
November	1st to 10th	Night	32% 5% 16% 26% 18% 3	2611
	11th to 20th	Night	40% 4 14% 26% 14% 1	2940
	21st to end	Night	44% 4 12% 26% 13% 1	2940
December	1st to 10th	Night	38% 4 13% 36% 9%	4720
	11th to 20th	Night	49% 5% 14% 25% 6%	5341
	21st to end	Night	66% 4 10% 14% 5%	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	18% 13% 35% 25% 8% 2	330
	11th to 20th	Day	15% 15% 45% 21% 4	330
	21st to end	Day	16% 13% 38% 26% 5% 1	363
February	1st to 10th	Day	15% 18% 42% 21% 4 1	330
	11th to 20th	Day	17% 18% 36% 23% 5% 1	330
	21st to end	Day	18% 18% 42% 18% 4	273
March	1st to 10th	Day	19% 15% 40% 18% 7%	330
	11th to 20th	Day	27% 13% 33% 19% 8%	330
	21st to end	Day	29% 18% 33% 16% 4	363
April	1st to 10th	Day	26% 16% 35% 19% 5%	512
	11th to 20th	Day	25% 18% 30% 19% 8%	532
	21st to end	Day	24% 14% 32% 21% 7% 2	724
May	1st to 10th	Day	19% 14% 33% 23% 9% 1	753
	11th to 20th	Day	22% 13% 28% 24% 11% 3	775
	21st to end	Day	16% 10% 27% 29% 14% 3	844
June	1st to 10th	Day	9% 7% 27% 30% 23% 4	780
	11th to 20th	Day	11% 7% 30% 35% 15% 3	780
	21st to end	Day	9% 7% 37% 32% 13% 3	780
July	1st to 10th	Day	8% 5% 20% 32% 24% 11%	771
	11th to 20th	Day	6% 5% 24% 33% 23% 9%	744
	21st to end	Day	6% 1 21% 41% 26% 5%	794
August	1st to 10th	Day	9% 4 22% 35% 25% 5%	726
	11th to 20th	Day	13% 3 18% 36% 24% 7%	715
	21st to end	Day	10% 4 22% 37% 22% 6%	658
September	1st to 10th	Day	12% 6% 24% 29% 22% 7%	530
	11th to 20th	Day	7% 4 24% 39% 21% 5%	437
	21st to end	Day	12% 8% 25% 33% 17% 4	330
October	1st to 10th	Day	16% 5% 32% 28% 14% 4	330
	11th to 20th	Day	18% 20% 35% 20% 7% 1	330
	21st to end	Day	20% 15% 37% 21% 6% 2	363
November	1st to 10th	Day	17% 13% 42% 19% 7% 2	330
	11th to 20th	Day	19% 20% 33% 21% 7% 1	330
	21st to end	Day	23% 15% 37% 20% 5% 1	330
December	1st to 10th	Day	10% 14% 45% 22% 7% 1	330
	11th to 20th	Day	15% 18% 35% 23% 8% 1	330
	21st to end	Day	24% 14% 41% 17% 3 1	363
January	1st to 10th	Night	12% 13% 37% 30% 6%	1050
	11th to 20th	Night	15% 15% 36% 27% 7% 1	1050
	21st to end	Night	18% 12% 36% 29% 5%	1155
February	1st to 10th	Night	16% 12% 40% 29% 4	1050
	11th to 20th	Night	16% 13% 40% 27% 4	1029
	21st to end	Night	15% 12% 43% 24% 4 2	770
March	1st to 10th	Night	19% 11% 37% 25% 7%	630
	11th to 20th	Night	18% 10% 39% 26% 8%	630
	21st to end	Night	21% 12% 41% 19% 5% 1	693
April	1st to 10th	Night	17% 15% 40% 24% 3	630
	11th to 20th	Night	17% 14% 35% 28% 5% 1	623
	21st to end	Night	20% 9% 36% 27% 7% 1	630
May	1st to 10th	Night	18% 8% 32% 34% 8%	630
	11th to 20th	Night	17% 10% 31% 31% 11%	621
	21st to end	Night	17% 7% 28% 35% 13%	683
June	1st to 10th	Night	8% 5% 28% 41% 18%	630
	11th to 20th	Night	9% 5% 29% 47% 10%	630
	21st to end	Night	10% 5% 32% 41% 12%	630
July	1st to 10th	Night	6% 2 16% 43% 30% 2	615
	11th to 20th	Night	5% 2 20% 44% 27% 2	597
	21st to end	Night	5% 3 17% 50% 24% 1	657
August	1st to 10th	Night	8% 2 17% 49% 23% 1	597
	11th to 20th	Night	8% 2 16% 44% 26% 3	594
	21st to end	Night	9% 3 20% 43% 22% 2	660
September	1st to 10th	Night	9% 4 23% 41% 21% 2	600
	11th to 20th	Night	12% 1 24% 41% 20% 2	600
	21st to end	Night	9% 6% 28% 38% 18% 1	640
October	1st to 10th	Night	15% 7% 32% 32% 13% 1	800
	11th to 20th	Night	17% 13% 36% 28% 7%	800
	21st to end	Night	22% 10% 33% 28% 7%	880
November	1st to 10th	Night	14% 10% 38% 30% 8%	880
	11th to 20th	Night	16% 14% 42% 23% 6%	1050
	21st to end	Night	17% 13% 33% 29% 7%	1050
December	1st to 10th	Night	15% 11% 39% 28% 7%	1050
	11th to 20th	Night	19% 10% 35% 31% 5% 1	1050
	21st to end	Night	22% 12% 38% 24% 5%	1155

Page generated at 2026-07-13 02:14:54. Version ac07

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