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 2025-03-12.

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% 39%	109045
	Night	11% 8% 3 8% 4 4 4 3 5% 6% 42%	110162
Transparency	Day	42% 6% 13% 24% 14% 2	112685
	Night	41% 5% 13% 24% 15% 2	114662
Seeing	Day	15% 10% 30% 28% 14% 3	16244
	Night	15% 9% 33% 32% 11% 1	26307

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	6% 14% 5% 21% 8% 5% 4 3 4 5% 25%	3640
	11th to 20th	Day	5% 10% 4 12% 5% 7% 7% 6% 6% 7% 30%	4080
	21st to end	Day	10% 13% 6% 13% 6% 5% 5% 3 4 5% 31%	4488
February	1st to 10th	Day	10% 15% 5% 9% 6% 6% 6% 3 5% 7% 28%	1800
	11th to 20th	Day	11% 11% 4 9% 6% 5% 5% 4 5% 5% 36%	1754
	21st to end	Day	14% 10% 3 9% 5% 5% 4 4 4 6% 36%	1590
March	1st to 10th	Day	16% 9% 3 7% 4 4 4 3 3 5% 43%	3546
	11th to 20th	Day	11% 7% 3 8% 4 3 4 4 5% 6% 45%	3491
	21st to end	Day	23% 14% 6% 9% 5% 4 5% 3 4 5% 22%	3814
April	1st to 10th	Day	17% 11% 3 6% 4 4 4 4 6% 6% 35%	2254
	11th to 20th	Day	18% 9% 3 7% 4 4 3 4 5% 6% 36%	2254
	21st to end	Day	22% 8% 3 6% 4 4 3 4 5% 6% 35%	2446
May	1st to 10th	Day	19% 8% 3 7% 4 4 5% 4 6% 8% 31%	4082
	11th to 20th	Day	14% 7% 2 7% 5% 4 4 4 6% 7% 40%	4298
	21st to end	Day	14% 7% 2 6% 5% 4 4 4 5% 7% 42%	4824
June	1st to 10th	Day	10% 5% 2 6% 4 5% 4 4 6% 8% 45%	2660
	11th to 20th	Day	10% 4 2 5% 5% 5% 4 5% 7% 10% 44%	2660
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 4 6% 9% 42%	2660
July	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 5% 8% 11% 37%	4440
	11th to 20th	Day	5% 3 1 4 3 4 4 3 6% 7% 58%	4360
	21st to end	Day	5% 4 1 5% 5% 5% 6% 5% 8% 11% 46%	4465
August	1st to 10th	Day	8% 5% 2 6% 4 4 4 4 7% 10% 46%	4104
	11th to 20th	Day	14% 7% 2 6% 4 4 5% 4 7% 8% 39%	4041
	21st to end	Day	7% 4 2 7% 5% 5% 4 4 6% 8% 48%	4290
September	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 5% 6% 53%	2280
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 6% 7% 49%	2192
	21st to end	Day	12% 5% 2 4 3 4 4 3 5% 6% 51%	2033
October	1st to 10th	Day	15% 6% 2 5% 4 3 2 3 4 7% 48%	1900
	11th to 20th	Day	15% 7% 2 6% 4 3 4 2 4 6% 47%	1900
	21st to end	Day	14% 9% 3 6% 4 3 4 3 5% 6% 41%	2090
November	1st to 10th	Day	11% 7% 3 5% 4 3 5% 4 6% 7% 45%	1809
	11th to 20th	Day	13% 10% 3 6% 6% 3 3 4 5% 7% 39%	1600
	21st to end	Day	14% 10% 4 7% 4 4 5% 3 5% 6% 39%	1600
December	1st to 10th	Day	7% 7% 3 7% 4 4 4 4 5% 7% 48%	2610
	11th to 20th	Day	13% 10% 4 13% 7% 6% 5% 3 6% 6% 27%	3008
	21st to end	Day	21% 16% 7% 14% 5% 4 3 3 4 5% 19%	3982
January	1st to 10th	Night	9% 11% 5% 21% 7% 5% 4 3 5% 5% 26%	6320
	11th to 20th	Night	8% 11% 4 9% 6% 5% 7% 4 8% 6% 32%	5900
	21st to end	Night	11% 12% 5% 12% 5% 4 4 4 5% 6% 33%	6490
February	1st to 10th	Night	11% 12% 4 11% 7% 4 4 3 6% 6% 32%	2600
	11th to 20th	Night	11% 10% 3 8% 4 5% 4 4 5% 6% 39%	2533
	21st to end	Night	11% 9% 3 8% 5% 4 4 3 4 5% 43%	2055
March	1st to 10th	Night	14% 8% 2 6% 3 3 3 2 5% 6% 49%	3529
	11th to 20th	Night	10% 7% 2 5% 4 3 3 3 4 7% 51%	3497
	21st to end	Night	22% 12% 4 12% 6% 4 4 3 4 6% 23%	3817
April	1st to 10th	Night	14% 9% 2 6% 5% 5% 4 3 5% 7% 42%	1925
	11th to 20th	Night	15% 9% 3 7% 5% 4 3 3 5% 5% 41%	1875
	21st to end	Night	16% 7% 3 7% 4 3 4 3 4 7% 41%	1730
May	1st to 10th	Night	19% 6% 3 6% 3 4 4 4 5% 6% 40%	2823
	11th to 20th	Night	12% 7% 2 6% 4 3 3 3 5% 7% 48%	2603
	21st to end	Night	13% 6% 2 6% 4 4 4 4 5% 7% 45%	2743
June	1st to 10th	Night	6% 4 2 6% 4 4 5% 4 5% 7% 52%	1520
	11th to 20th	Night	7% 6% 2 6% 3 4 4 4 6% 9% 49%	1520
	21st to end	Night	8% 5% 2 4 4 4 4 4 6% 8% 51%	1520
July	1st to 10th	Night	8% 5% 2 5% 4 5% 4 4 6% 9% 48%	2530
	11th to 20th	Night	4 3 1 4 3 3 4 3 6% 8% 62%	2593
	21st to end	Night	5% 3 1 5% 4 5% 5% 5% 8% 11% 49%	3098
August	1st to 10th	Night	5% 4 2 5% 4 4 4 3 6% 8% 54%	2836
	11th to 20th	Night	9% 5% 2 5% 3 3 4 3 4 6% 55%	2798
	21st to end	Night	9% 5% 1 5% 3 3 3 3 5% 8% 56%	3368
September	1st to 10th	Night	10% 3 2 6% 3 3 3 2 4 6% 58%	1900
	11th to 20th	Night	10% 5% 2 5% 2 3 3 3 5% 6% 56%	1985
	21st to end	Night	9% 4 1 4 3 3 3 3 5% 7% 58%	2128
October	1st to 10th	Night	12% 6% 2 4 3 3 3 3 5% 5% 54%	2280
	11th to 20th	Night	15% 6% 2 6% 4 3 3 3 4 6% 50%	2280
	21st to end	Night	15% 9% 3 5% 4 3 3 3 4 6% 45%	2508
November	1st to 10th	Night	11% 6% 2 5% 3 3 4 3 4 7% 52%	2483
	11th to 20th	Night	12% 8% 3 7% 4 3 4 4 5% 6% 44%	2800
	21st to end	Night	13% 8% 4 7% 4 3 4 3 4 7% 43%	2800
December	1st to 10th	Night	6% 8% 3 7% 5% 4 5% 4 6% 7% 46%	4580
	11th to 20th	Night	11% 10% 4 11% 6% 4 5% 4 5% 6% 35%	5199
	21st to end	Night	20% 15% 7% 14% 5% 4 3 3 3 4 21%	6996

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% 6% 12% 15% 7%	3641
	11th to 20th	Day	52% 3 11% 18% 13% 1	4080
	21st to end	Day	56% 5% 12% 21% 6%	4488
February	1st to 10th	Day	55% 5% 13% 18% 9% 1	1800
	11th to 20th	Day	49% 6% 11% 20% 12% 2	1763
	21st to end	Day	49% 4 14% 18% 11% 3	1590
March	1st to 10th	Day	44% 5% 10% 25% 14% 2	3546
	11th to 20th	Day	38% 7% 13% 26% 14% 2	3491
	21st to end	Day	63% 7% 11% 14% 4 1	3814
April	1st to 10th	Day	47% 6% 11% 24% 10% 1	2254
	11th to 20th	Day	48% 6% 11% 20% 13% 1	2254
	21st to end	Day	48% 6% 12% 22% 12% 1	2446
May	1st to 10th	Day	47% 10% 13% 17% 12% 1	4120
	11th to 20th	Day	41% 8% 11% 27% 12% 1	4302
	21st to end	Day	39% 8% 13% 23% 17% 1	4837
June	1st to 10th	Day	35% 9% 16% 23% 16% 2	2660
	11th to 20th	Day	33% 7% 15% 24% 19% 2	2660
	21st to end	Day	37% 9% 14% 24% 14% 2	2660
July	1st to 10th	Day	40% 6% 17% 28% 8% 2	4371
	11th to 20th	Day	25% 5% 15% 32% 20% 2	4285
	21st to end	Day	30% 7% 20% 26% 16% 2	4325
August	1st to 10th	Day	33% 6% 16% 28% 16% 1	4090
	11th to 20th	Day	43% 5% 13% 26% 13% 1	4080
	21st to end	Day	34% 5% 17% 26% 16% 3	4289
September	1st to 10th	Day	31% 5% 13% 27% 20% 4	2280
	11th to 20th	Day	33% 6% 14% 30% 17% 1	2192
	21st to end	Day	33% 5% 11% 30% 20% 1	2033
October	1st to 10th	Day	22% 3 7% 28% 38% 2	3160
	11th to 20th	Day	28% 3 9% 31% 24% 4	3140
	21st to end	Day	40% 3 9% 29% 16% 3	3428
November	1st to 10th	Day	37% 6% 17% 21% 17% 2	1809
	11th to 20th	Day	43% 5% 14% 21% 16% 1	1600
	21st to end	Day	46% 5% 14% 24% 11% 1	1600
December	1st to 10th	Day	36% 4 18% 33% 9% 1	2610
	11th to 20th	Day	57% 4 14% 17% 7%	3005
	21st to end	Day	70% 4 9% 13% 4 1	3982
January	1st to 10th	Night	59% 4 14% 13% 8% 1	6320
	11th to 20th	Night	49% 4 14% 14% 16% 2	5900
	21st to end	Night	52% 5% 11% 18% 13% 1	6490
February	1st to 10th	Night	52% 5% 12% 20% 10% 2	2600
	11th to 20th	Night	45% 6% 12% 23% 13% 2	2534
	21st to end	Night	43% 4 11% 21% 17% 3	2055
March	1st to 10th	Night	37% 5% 11% 28% 17% 2	3529
	11th to 20th	Night	33% 5% 11% 32% 15% 4	3497
	21st to end	Night	61% 9% 14% 10% 4 1	3817
April	1st to 10th	Night	42% 5% 12% 25% 14% 2	1925
	11th to 20th	Night	44% 6% 10% 21% 17% 3	1875
	21st to end	Night	42% 6% 13% 23% 14% 2	1730
May	1st to 10th	Night	42% 7% 12% 21% 17% 1	2850
	11th to 20th	Night	36% 6% 11% 27% 15% 5%	2604
	21st to end	Night	37% 8% 13% 22% 18% 3	2751
June	1st to 10th	Night	30% 7% 15% 28% 15% 4	1520
	11th to 20th	Night	30% 7% 13% 22% 22% 5%	1520
	21st to end	Night	30% 7% 15% 27% 18% 3	1520
July	1st to 10th	Night	32% 6% 16% 32% 13% 2	2490
	11th to 20th	Night	21% 4 19% 34% 21% 2	2545
	21st to end	Night	26% 9% 20% 26% 18% 2	2999
August	1st to 10th	Night	28% 5% 16% 33% 15% 2	2826
	11th to 20th	Night	32% 5% 16% 31% 16% 2	2825
	21st to end	Night	28% 5% 17% 29% 17% 5%	3368
September	1st to 10th	Night	28% 4 12% 27% 25% 5%	1900
	11th to 20th	Night	29% 5% 11% 34% 20% 1	1985
	21st to end	Night	27% 5% 10% 31% 24% 3	2128
October	1st to 10th	Night	21% 3 6% 24% 42% 3	3800
	11th to 20th	Night	26% 3 9% 29% 26% 7%	3779
	21st to end	Night	41% 3 10% 26% 18% 2	4120
November	1st to 10th	Night	32% 5% 16% 25% 19% 4	2483
	11th to 20th	Night	40% 5% 14% 25% 14% 2	2800
	21st to end	Night	43% 4 12% 26% 13% 1	2800
December	1st to 10th	Night	37% 4 13% 36% 9%	4580
	11th to 20th	Night	49% 5% 15% 25% 6%	5201
	21st to end	Night	67% 4 10% 14% 5%	6996

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% 34% 25% 9% 2	300
	11th to 20th	Day	17% 13% 44% 21% 4	300
	21st to end	Day	18% 13% 37% 26% 5% 1	330
February	1st to 10th	Day	16% 18% 41% 21% 3 1	300
	11th to 20th	Day	16% 18% 37% 23% 5% 1	300
	21st to end	Day	19% 18% 42% 18% 3	249
March	1st to 10th	Day	19% 15% 40% 20% 7%	300
	11th to 20th	Day	26% 12% 36% 18% 8%	273
	21st to end	Day	32% 16% 32% 15% 4	297
April	1st to 10th	Day	25% 15% 34% 20% 6%	434
	11th to 20th	Day	25% 16% 29% 21% 9%	452
	21st to end	Day	24% 14% 30% 22% 8% 2	626
May	1st to 10th	Day	22% 14% 33% 22% 8% 1	653
	11th to 20th	Day	21% 12% 29% 24% 10% 3	675
	21st to end	Day	16% 10% 26% 30% 14% 3	734
June	1st to 10th	Day	8% 7% 28% 29% 24% 4	680
	11th to 20th	Day	11% 6% 29% 36% 14% 4	680
	21st to end	Day	8% 7% 36% 33% 14% 3	680
July	1st to 10th	Day	7% 5% 18% 33% 25% 12%	671
	11th to 20th	Day	6% 4 25% 35% 22% 8%	668
	21st to end	Day	6% 1 21% 41% 26% 5%	739
August	1st to 10th	Day	9% 4 21% 35% 26% 5%	676
	11th to 20th	Day	14% 3 18% 35% 23% 6%	665
	21st to end	Day	10% 4 21% 37% 22% 6%	610
September	1st to 10th	Day	12% 5% 24% 30% 22% 7%	490
	11th to 20th	Day	7% 4 25% 38% 21% 5%	402
	21st to end	Day	13% 8% 26% 34% 16% 3	300
October	1st to 10th	Day	17% 6% 30% 29% 14% 4	300
	11th to 20th	Day	18% 20% 34% 20% 8% 1	300
	21st to end	Day	19% 15% 36% 21% 7% 2	330
November	1st to 10th	Day	17% 13% 39% 21% 8% 3	300
	11th to 20th	Day	19% 20% 32% 20% 7% 1	300
	21st to end	Day	22% 14% 38% 21% 5% 1	300
December	1st to 10th	Day	10% 13% 46% 22% 8% 1	300
	11th to 20th	Day	14% 17% 36% 23% 8% 1	300
	21st to end	Day	24% 15% 39% 17% 4 1	330
January	1st to 10th	Night	12% 13% 38% 30% 7%	1000
	11th to 20th	Night	15% 14% 36% 27% 7% 1	1000
	21st to end	Night	18% 11% 36% 29% 6%	1100
February	1st to 10th	Night	16% 12% 39% 29% 4	1000
	11th to 20th	Night	16% 13% 40% 26% 4	979
	21st to end	Night	15% 12% 43% 24% 4 2	735
March	1st to 10th	Night	19% 11% 36% 26% 8% 1	600
	11th to 20th	Night	18% 9% 38% 27% 8%	575
	21st to end	Night	22% 12% 39% 20% 6% 1	627
April	1st to 10th	Night	17% 15% 40% 25% 4	570
	11th to 20th	Night	18% 13% 35% 28% 5% 1	563
	21st to end	Night	19% 9% 37% 27% 7% 1	570
May	1st to 10th	Night	19% 8% 34% 31% 8%	570
	11th to 20th	Night	16% 10% 31% 32% 11% 1	561
	21st to end	Night	16% 7% 28% 35% 14%	617
June	1st to 10th	Night	8% 5% 28% 41% 19%	570
	11th to 20th	Night	9% 4 29% 46% 11%	570
	21st to end	Night	8% 5% 31% 42% 12% 1	570
July	1st to 10th	Night	6% 2 16% 44% 30% 2	555
	11th to 20th	Night	4 1 21% 45% 26% 2	552
	21st to end	Night	4 3 17% 50% 25% 1	624
August	1st to 10th	Night	8% 2 17% 49% 23% 1	567
	11th to 20th	Night	8% 2 16% 45% 26% 3	564
	21st to end	Night	9% 3 20% 43% 22% 3	627
September	1st to 10th	Night	9% 4 24% 40% 21% 2	570
	11th to 20th	Night	13% 1 24% 40% 20% 2	570
	21st to end	Night	10% 6% 29% 38% 16% 1	608
October	1st to 10th	Night	14% 7% 33% 32% 13% 1	760
	11th to 20th	Night	17% 12% 35% 28% 7%	760
	21st to end	Night	22% 10% 33% 28% 8%	836
November	1st to 10th	Night	15% 9% 37% 30% 8%	837
	11th to 20th	Night	16% 14% 42% 22% 6%	1000
	21st to end	Night	17% 13% 34% 29% 7%	1000
December	1st to 10th	Night	15% 11% 39% 28% 7%	1000
	11th to 20th	Night	19% 10% 34% 31% 5% 1	1000
	21st to end	Night	21% 12% 37% 24% 5%	1100

Page generated at 2025-03-09 07:08:42. Version ac07

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