Hoffelder Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hoffelder 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	17% 8% 3 7% 5% 5% 5% 4 6% 7% 34%	126752
	Night	16% 9% 3 7% 5% 5% 5% 4 5% 7% 36%	124241
Transparency	Day	46% 6% 12% 21% 13% 2	130246
	Night	47% 5% 12% 21% 13% 2	128834
Seeing	Day	24% 19% 28% 18% 8% 2	16262
	Night	22% 15% 27% 26% 9% 1	25168

By Month

Percentage Cloud Cover NE (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	12% 8% 3 9% 6% 6% 6% 5% 6% 6% 32%	3597
	11th to 20th	Day	12% 8% 3 8% 5% 5% 5% 4 7% 8% 36%	3570
	21st to end	Day	10% 10% 3 8% 5% 4 5% 4 5% 6% 41%	3960
February	1st to 10th	Day	13% 10% 3 7% 6% 7% 5% 5% 6% 7% 33%	1738
	11th to 20th	Day	11% 10% 3 9% 6% 4 6% 4 6% 6% 37%	1948
	21st to end	Day	14% 11% 3 8% 6% 6% 5% 4 5% 5% 33%	1650
March	1st to 10th	Day	20% 13% 3 9% 4 4 4 3 4 5% 30%	4476
	11th to 20th	Day	17% 11% 3 8% 4 4 4 4 5% 5% 35%	4828
	21st to end	Day	21% 11% 3 7% 4 4 3 3 5% 7% 30%	5710
April	1st to 10th	Day	18% 12% 3 6% 4 5% 4 3 5% 7% 33%	2400
	11th to 20th	Day	17% 7% 2 7% 5% 5% 4 4 6% 7% 37%	2452
	21st to end	Day	22% 9% 3 6% 5% 5% 4 3 5% 6% 33%	2600
May	1st to 10th	Day	32% 11% 3 7% 5% 4 4 3 5% 5% 21%	5886
	11th to 20th	Day	18% 8% 3 10% 6% 5% 5% 4 5% 7% 28%	6106
	21st to end	Day	20% 7% 2 7% 4 5% 5% 4 7% 9% 31%	6949
June	1st to 10th	Day	23% 7% 2 6% 5% 5% 6% 5% 6% 8% 28%	2800
	11th to 20th	Day	17% 6% 2 6% 4 5% 5% 4 6% 7% 37%	2800
	21st to end	Day	22% 7% 3 7% 5% 4 5% 4 6% 7% 30%	2800
July	1st to 10th	Day	16% 7% 3 6% 5% 5% 6% 5% 9% 10% 29%	6360
	11th to 20th	Day	14% 6% 2 5% 4 5% 6% 4 8% 10% 36%	6360
	21st to end	Day	14% 5% 2 5% 4 4 5% 3 6% 8% 42%	6926
August	1st to 10th	Day	14% 6% 2 7% 5% 5% 7% 5% 7% 8% 34%	4346
	11th to 20th	Day	17% 9% 3 6% 6% 4 6% 5% 6% 8% 31%	4175
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 7% 9% 44%	4420
September	1st to 10th	Day	11% 5% 2 4 3 5% 4 5% 6% 8% 47%	2384
	11th to 20th	Day	13% 5% 2 4 4 4 3 3 4 7% 52%	2200
	21st to end	Day	16% 6% 2 5% 3 3 4 4 5% 9% 42%	2200
October	1st to 10th	Day	18% 7% 2 7% 4 4 4 3 5% 5% 40%	2200
	11th to 20th	Day	18% 6% 2 6% 4 4 4 3 5% 7% 39%	1903
	21st to end	Day	22% 10% 2 7% 4 4 4 3 4 6% 33%	1980
November	1st to 10th	Day	15% 8% 2 6% 4 3 4 3 4 8% 42%	1851
	11th to 20th	Day	17% 6% 2 5% 4 5% 5% 4 6% 7% 38%	1890
	21st to end	Day	19% 9% 2 5% 3 4 5% 4 6% 6% 36%	1851
December	1st to 10th	Day	15% 9% 3 9% 5% 5% 6% 4 7% 8% 30%	2516
	11th to 20th	Day	17% 8% 2 5% 4 4 5% 4 6% 7% 38%	2960
	21st to end	Day	18% 9% 3 7% 4 5% 5% 4 5% 6% 34%	3960
January	1st to 10th	Night	12% 11% 4 9% 5% 5% 5% 3 5% 6% 36%	6349
	11th to 20th	Night	10% 11% 5% 11% 7% 7% 6% 5% 6% 7% 24%	6315
	21st to end	Night	11% 8% 4 9% 5% 5% 6% 4 6% 7% 37%	6996
February	1st to 10th	Night	11% 10% 3 8% 6% 5% 5% 5% 6% 7% 33%	2658
	11th to 20th	Night	9% 11% 3 7% 6% 5% 5% 4 5% 7% 38%	2338
	21st to end	Night	12% 10% 3 7% 5% 4 5% 4 5% 7% 37%	1980
March	1st to 10th	Night	20% 11% 3 8% 5% 5% 5% 4 5% 5% 28%	5364
	11th to 20th	Night	15% 9% 4 9% 5% 6% 5% 4 5% 6% 32%	5130
	21st to end	Night	22% 10% 3 6% 3 4 4 3 5% 7% 31%	5220
April	1st to 10th	Night	18% 11% 3 6% 4 4 4 3 5% 6% 35%	2000
	11th to 20th	Night	17% 8% 2 7% 5% 5% 5% 4 5% 6% 36%	1897
	21st to end	Night	22% 8% 3 6% 5% 4 4 3 4 6% 36%	1800
May	1st to 10th	Night	32% 11% 3 7% 4 4 4 3 4 5% 22%	4054
	11th to 20th	Night	16% 9% 3 9% 6% 6% 5% 4 5% 7% 29%	3817
	21st to end	Night	18% 8% 2 6% 5% 4 4 4 5% 8% 36%	3926
June	1st to 10th	Night	20% 9% 3 5% 4 4 4 4 5% 7% 35%	1600
	11th to 20th	Night	18% 7% 1 4 4 5% 4 4 5% 9% 39%	1600
	21st to end	Night	19% 8% 3 6% 4 4 5% 4 6% 8% 35%	1600
July	1st to 10th	Night	13% 6% 2 6% 5% 4 6% 4 7% 8% 39%	3600
	11th to 20th	Night	15% 7% 3 7% 4 4 4 3 5% 7% 40%	3600
	21st to end	Night	11% 4 1 4 3 4 5% 4 7% 8% 48%	3926
August	1st to 10th	Night	20% 8% 2 7% 4 4 4 4 5% 6% 36%	2770
	11th to 20th	Night	16% 8% 3 7% 4 4 5% 3 6% 6% 37%	2872
	21st to end	Night	10% 6% 1 5% 5% 4 4 4 6% 8% 47%	3475
September	1st to 10th	Night	13% 6% 1 4 4 3 3 3 5% 8% 50%	2015
	11th to 20th	Night	15% 5% 2 4 2 3 3 3 4 7% 53%	2200
	21st to end	Night	16% 6% 2 5% 4 3 3 3 5% 7% 45%	2200
October	1st to 10th	Night	18% 7% 2 5% 4 4 4 5% 6% 6% 40%	2200
	11th to 20th	Night	16% 7% 2 6% 4 5% 5% 4 5% 8% 40%	2493
	21st to end	Night	23% 7% 2 6% 4 4 5% 3 6% 7% 33%	2860
November	1st to 10th	Night	15% 8% 2 6% 4 4 5% 4 5% 6% 41%	2667
	11th to 20th	Night	15% 8% 3 6% 5% 5% 4 4 5% 6% 40%	2730
	21st to end	Night	15% 8% 3 6% 4 5% 4 4 6% 7% 38%	2767
December	1st to 10th	Night	16% 12% 2 8% 6% 5% 5% 4 6% 7% 30%	4870
	11th to 20th	Night	21% 9% 2 5% 4 4 5% 4 4 6% 35%	5356
	21st to end	Night	18% 9% 3 7% 4 4 4 3 5% 6% 36%	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	48% 4 13% 24% 11% 1	3598
	11th to 20th	Day	43% 6% 13% 24% 11% 3	3600
	21st to end	Day	42% 5% 11% 20% 18% 5%	3960
February	1st to 10th	Day	49% 5% 11% 20% 12% 3	1738
	11th to 20th	Day	46% 4 13% 21% 12% 3	1957
	21st to end	Day	52% 3 11% 18% 13% 4	1650
March	1st to 10th	Day	58% 4 7% 11% 13% 6%	4479
	11th to 20th	Day	49% 5% 13% 18% 11% 3	4828
	21st to end	Day	52% 4 4 18% 17% 4	5710
April	1st to 10th	Day	52% 3 9% 18% 14% 4	2400
	11th to 20th	Day	47% 5% 10% 22% 14% 3	2452
	21st to end	Day	52% 4 8% 18% 13% 4	2600
May	1st to 10th	Day	64% 5% 9% 15% 6% 1	5897
	11th to 20th	Day	55% 6% 13% 17% 8% 2	6110
	21st to end	Day	46% 7% 12% 21% 12% 1	6949
June	1st to 10th	Day	52% 6% 12% 20% 9% 1	2800
	11th to 20th	Day	44% 6% 13% 21% 14% 2	2800
	21st to end	Day	52% 7% 11% 18% 11% 1	2800
July	1st to 10th	Day	45% 8% 16% 20% 10%	6290
	11th to 20th	Day	40% 8% 15% 24% 12% 1	6285
	21st to end	Day	37% 7% 12% 27% 16%	6728
August	1st to 10th	Day	45% 7% 15% 24% 8%	4332
	11th to 20th	Day	48% 7% 15% 23% 7%	4214
	21st to end	Day	33% 7% 16% 25% 17% 2	4420
September	1st to 10th	Day	34% 7% 13% 28% 17% 1	2384
	11th to 20th	Day	33% 4 9% 32% 19% 2	2200
	21st to end	Day	38% 5% 13% 27% 17% 1	2200
October	1st to 10th	Day	44% 6% 12% 22% 14% 1	3590
	11th to 20th	Day	37% 5% 15% 26% 16% 1	3067
	21st to end	Day	39% 4 14% 23% 17% 4	3180
November	1st to 10th	Day	41% 5% 14% 23% 15% 2	1851
	11th to 20th	Day	42% 5% 14% 19% 16% 3	1890
	21st to end	Day	47% 4 16% 22% 10% 1	1851
December	1st to 10th	Day	48% 5% 17% 22% 7% 1	2516
	11th to 20th	Day	43% 5% 11% 18% 18% 5%	2960
	21st to end	Day	51% 5% 10% 16% 12% 6%	3960
January	1st to 10th	Night	47% 6% 13% 24% 10% 1	6349
	11th to 20th	Night	56% 6% 13% 16% 7% 2	6360
	21st to end	Night	45% 4 10% 19% 17% 5%	6996
February	1st to 10th	Night	49% 5% 13% 17% 13% 3	2658
	11th to 20th	Night	44% 6% 12% 21% 15% 2	2340
	21st to end	Night	45% 4 11% 22% 13% 4	1980
March	1st to 10th	Night	55% 4 10% 14% 12% 4	5374
	11th to 20th	Night	51% 6% 16% 17% 9% 2	5131
	21st to end	Night	52% 4 6% 16% 19% 3	5220
April	1st to 10th	Night	50% 4 9% 19% 15% 2	2000
	11th to 20th	Night	48% 4 9% 23% 15% 1	1897
	21st to end	Night	51% 4 11% 18% 14% 3	1800
May	1st to 10th	Night	64% 5% 10% 13% 7% 1	4060
	11th to 20th	Night	53% 7% 11% 19% 8% 2	3818
	21st to end	Night	46% 6% 16% 21% 10% 1	3927
June	1st to 10th	Night	50% 6% 13% 20% 11%	1600
	11th to 20th	Night	43% 6% 14% 24% 13% 2	1600
	21st to end	Night	47% 6% 15% 20% 10% 1	1600
July	1st to 10th	Night	40% 7% 20% 23% 10%	3560
	11th to 20th	Night	42% 8% 14% 24% 12%	3552
	21st to end	Night	33% 7% 16% 33% 11%	3809
August	1st to 10th	Night	50% 7% 14% 22% 7%	2760
	11th to 20th	Night	45% 8% 16% 20% 11%	2899
	21st to end	Night	34% 7% 16% 27% 15% 1	3475
September	1st to 10th	Night	33% 6% 13% 31% 16%	2015
	11th to 20th	Night	32% 5% 11% 33% 18% 1	2200
	21st to end	Night	38% 6% 12% 29% 15% 2	2200
October	1st to 10th	Night	43% 7% 14% 22% 13% 1	3590
	11th to 20th	Night	36% 5% 12% 28% 16% 2	4068
	21st to end	Night	41% 5% 11% 27% 15% 2	4610
November	1st to 10th	Night	43% 4 12% 26% 13% 1	2667
	11th to 20th	Night	43% 5% 13% 22% 15% 2	2730
	21st to end	Night	44% 5% 15% 23% 11% 1	2767
December	1st to 10th	Night	50% 5% 12% 26% 6%	4870
	11th to 20th	Night	50% 4 10% 17% 18% 2	5356
	21st to end	Night	50% 5% 11% 18% 15% 2	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	32% 20% 30% 17% 2	200
	11th to 20th	Day	28% 22% 33% 14% 4 1	200
	21st to end	Day	20% 26% 34% 16% 4	220
February	1st to 10th	Day	29% 24% 30% 15% 2	323
	11th to 20th	Day	30% 27% 29% 12% 2	496
	21st to end	Day	27% 24% 28% 17% 3	414
March	1st to 10th	Day	26% 26% 31% 13% 4	500
	11th to 20th	Day	30% 23% 30% 12% 5% 1	500
	21st to end	Day	31% 24% 25% 14% 6% 1	550
April	1st to 10th	Day	35% 22% 24% 12% 6% 1	500
	11th to 20th	Day	31% 26% 23% 13% 6% 1	492
	21st to end	Day	33% 23% 27% 10% 5% 1	500
May	1st to 10th	Day	35% 20% 26% 15% 3 2	503
	11th to 20th	Day	24% 20% 32% 15% 6% 2	527
	21st to end	Day	24% 16% 31% 21% 6% 1	573
June	1st to 10th	Day	23% 16% 36% 16% 8% 1	530
	11th to 20th	Day	19% 18% 32% 20% 8% 2	530
	21st to end	Day	24% 15% 33% 19% 8% 2	530
July	1st to 10th	Day	19% 14% 32% 22% 10% 2	525
	11th to 20th	Day	15% 13% 33% 25% 11% 2	524
	21st to end	Day	16% 12% 35% 24% 11% 2	576
August	1st to 10th	Day	15% 9% 29% 28% 15% 4	526
	11th to 20th	Day	16% 14% 26% 24% 13% 6%	519
	21st to end	Day	13% 13% 32% 25% 14% 4	583
September	1st to 10th	Day	16% 14% 25% 26% 15% 4	530
	11th to 20th	Day	17% 12% 25% 20% 15% 10%	530
	21st to end	Day	18% 16% 24% 25% 12% 5%	530
October	1st to 10th	Day	22% 16% 24% 21% 13% 4	530
	11th to 20th	Day	26% 18% 25% 18% 12% 1	439
	21st to end	Day	35% 15% 23% 19% 7%	462
November	1st to 10th	Day	27% 20% 23% 21% 8% 1	425
	11th to 20th	Day	29% 19% 27% 17% 7% 1	430
	21st to end	Day	30% 23% 23% 18% 6%	391
December	1st to 10th	Day	25% 23% 30% 15% 6%	220
	11th to 20th	Day	36% 20% 31% 9% 4	214
	21st to end	Day	31% 22% 25% 17% 5%	220
January	1st to 10th	Night	21% 22% 31% 23% 4	800
	11th to 20th	Night	25% 19% 29% 24% 3	800
	21st to end	Night	17% 23% 35% 21% 3	880
February	1st to 10th	Night	19% 22% 33% 24% 3	800
	11th to 20th	Night	20% 26% 36% 17% 2	783
	21st to end	Night	21% 21% 30% 24% 3	660
March	1st to 10th	Night	26% 20% 33% 20% 2	800
	11th to 20th	Night	23% 22% 26% 23% 6%	800
	21st to end	Night	25% 19% 30% 21% 5% 1	880
April	1st to 10th	Night	28% 19% 28% 21% 4	800
	11th to 20th	Night	22% 18% 31% 23% 5%	713
	21st to end	Night	27% 18% 29% 21% 4 1	600
May	1st to 10th	Night	28% 13% 28% 26% 6%	600
	11th to 20th	Night	23% 11% 30% 25% 10%	506
	21st to end	Night	21% 7% 26% 36% 9% 1	433
June	1st to 10th	Night	24% 11% 26% 31% 9%	400
	11th to 20th	Night	18% 8% 27% 32% 15%	400
	21st to end	Night	20% 7% 25% 38% 10%	400
July	1st to 10th	Night	16% 4 25% 39% 15% 1	390
	11th to 20th	Night	16% 4 22% 39% 18% 2	388
	21st to end	Night	17% 4 18% 42% 19% 1	438
August	1st to 10th	Night	16% 6% 20% 38% 18% 1	504
	11th to 20th	Night	16% 6% 26% 34% 17% 2	592
	21st to end	Night	15% 7% 23% 34% 21% 2	808
September	1st to 10th	Night	15% 7% 24% 34% 17% 2	800
	11th to 20th	Night	17% 10% 22% 27% 22% 4	800
	21st to end	Night	19% 9% 23% 32% 16% 1	800
October	1st to 10th	Night	24% 10% 20% 30% 15% 1	800
	11th to 20th	Night	22% 13% 28% 23% 12% 1	800
	21st to end	Night	28% 15% 26% 26% 4	880
November	1st to 10th	Night	22% 17% 28% 24% 8% 1	820
	11th to 20th	Night	22% 19% 26% 24% 8% 1	840
	21st to end	Night	25% 18% 24% 26% 5% 1	840
December	1st to 10th	Night	25% 18% 32% 19% 6%	885
	11th to 20th	Night	25% 21% 29% 20% 4	848
	21st to end	Night	25% 21% 29% 22% 3	880

Page generated at 2025-12-15 01:13:49. Version ac07

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