Ballreich Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ballreich Observatory clear sky chart from 2005-11-06 to 2025-02-06.

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	14% 11% 4 9% 5% 5% 5% 4 5% 7% 31%	108929
	Night	14% 11% 4 9% 5% 4 4 4 5% 6% 32%	109231
Transparency	Day	50% 5% 12% 21% 12% 1	112585
	Night	50% 4 11% 21% 12% 1	113714
Seeing	Day	18% 10% 27% 24% 15% 6%	15699
	Night	19% 9% 28% 29% 13% 1	25583

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	14% 19% 8% 19% 6% 5% 4 3 4 5% 12%	3617
	11th to 20th	Day	14% 19% 6% 15% 8% 5% 7% 3 4 3 15%	3942
	21st to end	Day	21% 17% 9% 14% 6% 6% 4 3 3 3 14%	4466
February	1st to 10th	Day	17% 16% 6% 12% 6% 5% 4 4 4 4 21%	1755
	11th to 20th	Day	14% 13% 5% 12% 7% 6% 5% 4 4 5% 24%	1811
	21st to end	Day	16% 14% 4 12% 6% 4 3 4 5% 6% 25%	1570
March	1st to 10th	Day	20% 17% 5% 11% 5% 4 3 3 4 5% 23%	3234
	11th to 20th	Day	12% 14% 4 10% 5% 5% 4 3 5% 6% 34%	3480
	21st to end	Day	20% 13% 5% 11% 5% 5% 4 3 4 5% 26%	3815
April	1st to 10th	Day	14% 12% 4 9% 6% 5% 5% 4 6% 6% 29%	2172
	11th to 20th	Day	16% 10% 3 7% 5% 5% 5% 4 5% 7% 34%	2400
	21st to end	Day	19% 10% 3 7% 5% 4 4 4 5% 7% 33%	2470
May	1st to 10th	Day	18% 9% 4 8% 6% 4 5% 4 6% 7% 29%	4082
	11th to 20th	Day	17% 8% 3 7% 6% 5% 4 4 6% 7% 33%	4081
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 6% 9% 40%	4476
June	1st to 10th	Day	12% 7% 3 7% 5% 5% 4 4 6% 9% 38%	2498
	11th to 20th	Day	10% 6% 3 8% 5% 5% 5% 4 7% 9% 40%	2660
	21st to end	Day	11% 6% 2 7% 6% 5% 5% 6% 7% 9% 38%	2660
July	1st to 10th	Day	9% 7% 3 7% 6% 5% 5% 4 6% 10% 37%	4440
	11th to 20th	Day	6% 5% 2 5% 5% 4 5% 5% 7% 11% 45%	4294
	21st to end	Day	8% 6% 3 7% 5% 5% 6% 5% 7% 9% 40%	4466
August	1st to 10th	Day	10% 6% 2 5% 5% 4 5% 5% 7% 10% 40%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 8% 12% 37%	4044
	21st to end	Day	8% 5% 2 6% 4 6% 5% 3 7% 10% 43%	4470
September	1st to 10th	Day	13% 6% 2 5% 4 5% 5% 4 5% 7% 45%	2123
	11th to 20th	Day	9% 5% 2 6% 5% 4 5% 4 7% 8% 45%	2090
	21st to end	Day	17% 7% 2 7% 4 4 4 3 5% 6% 40%	2090
October	1st to 10th	Day	12% 8% 3 8% 5% 3 4 3 6% 6% 42%	2038
	11th to 20th	Day	15% 8% 3 7% 5% 4 5% 4 5% 6% 38%	1900
	21st to end	Day	17% 11% 4 8% 5% 4 5% 4 5% 7% 30%	1986
November	1st to 10th	Day	12% 9% 4 6% 5% 4 3 4 6% 7% 40%	1762
	11th to 20th	Day	17% 13% 3 7% 5% 4 5% 3 4 6% 32%	1800
	21st to end	Day	17% 15% 5% 9% 5% 4 4 3 5% 6% 26%	1800
December	1st to 10th	Day	15% 15% 7% 15% 6% 4 4 3 4 5% 21%	2785
	11th to 20th	Day	18% 19% 8% 11% 5% 4 3 3 4 5% 20%	3373
	21st to end	Day	22% 22% 7% 13% 6% 5% 3 3 3 4 14%	4175
January	1st to 10th	Night	15% 18% 7% 18% 6% 4 4 3 4 4 16%	6348
	11th to 20th	Night	10% 20% 8% 17% 8% 6% 6% 5% 3 4 13%	6017
	21st to end	Night	21% 16% 7% 12% 5% 4 4 3 3 4 21%	6490
February	1st to 10th	Night	19% 14% 5% 11% 6% 6% 4 3 4 5% 22%	2536
	11th to 20th	Night	14% 15% 4 10% 6% 5% 5% 4 4 5% 27%	2252
	21st to end	Night	18% 15% 5% 9% 6% 5% 4 3 4 6% 25%	1884
March	1st to 10th	Night	18% 15% 5% 7% 5% 3 3 3 3 5% 34%	3619
	11th to 20th	Night	12% 8% 2 6% 5% 4 5% 4 6% 7% 41%	3480
	21st to end	Night	17% 10% 4 8% 5% 4 4 3 5% 6% 35%	3817
April	1st to 10th	Night	15% 12% 3 7% 6% 4 4 4 5% 5% 34%	2024
	11th to 20th	Night	17% 8% 2 8% 5% 4 4 4 6% 6% 37%	1727
	21st to end	Night	17% 9% 2 7% 5% 4 4 3 5% 7% 37%	1710
May	1st to 10th	Night	19% 9% 3 9% 6% 5% 4 4 5% 6% 29%	2813
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 5% 7% 39%	2812
	21st to end	Night	9% 6% 2 5% 4 4 4 4 5% 9% 47%	3079
June	1st to 10th	Night	10% 7% 3 5% 4 5% 4 4 6% 7% 45%	1677
	11th to 20th	Night	9% 5% 2 5% 4 5% 5% 5% 8% 9% 43%	1520
	21st to end	Night	9% 4 3 5% 5% 4 5% 5% 7% 10% 45%	1520
July	1st to 10th	Night	9% 5% 2 5% 5% 4 5% 4 7% 9% 45%	2530
	11th to 20th	Night	8% 4 1 4 4 4 4 4 7% 10% 50%	2654
	21st to end	Night	6% 6% 2 6% 4 4 6% 5% 7% 9% 45%	3087
August	1st to 10th	Night	10% 7% 3 7% 4 5% 5% 4 6% 9% 41%	2825
	11th to 20th	Night	9% 6% 3 8% 5% 4 4 3 5% 7% 45%	2785
	21st to end	Night	6% 4 2 7% 5% 5% 5% 4 6% 9% 47%	3182
September	1st to 10th	Night	10% 6% 2 5% 4 3 4 4 5% 8% 49%	2038
	11th to 20th	Night	9% 5% 2 5% 4 4 4 3 4 7% 54%	2090
	21st to end	Night	13% 7% 3 7% 4 4 5% 3 5% 6% 45%	2090
October	1st to 10th	Night	12% 6% 3 6% 5% 4 4 3 5% 7% 47%	2142
	11th to 20th	Night	17% 10% 2 7% 4 3 4 3 5% 7% 38%	2280
	21st to end	Night	20% 8% 3 7% 4 4 4 3 5% 7% 35%	2611
November	1st to 10th	Night	13% 9% 3 7% 4 3 4 4 5% 6% 42%	2536
	11th to 20th	Night	15% 12% 4 8% 5% 4 4 3 6% 6% 33%	2600
	21st to end	Night	19% 14% 4 9% 5% 4 4 3 5% 5% 27%	2600
December	1st to 10th	Night	13% 14% 6% 13% 7% 6% 5% 4 5% 5% 24%	4250
	11th to 20th	Night	18% 17% 7% 11% 5% 4 4 3 4 5% 22%	4822
	21st to end	Night	24% 19% 7% 10% 5% 4 4 3 5% 5% 13%	6784

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	74% 3 9% 11% 2	3618
	11th to 20th	Day	75% 3 8% 6% 8%	3942
	21st to end	Day	76% 2 5% 10% 6%	4466
February	1st to 10th	Day	66% 4 11% 13% 6% 1	1755
	11th to 20th	Day	62% 4 9% 17% 7% 1	1821
	21st to end	Day	59% 4 13% 15% 6% 2	1570
March	1st to 10th	Day	65% 4 9% 18% 5%	3234
	11th to 20th	Day	50% 5% 14% 22% 8% 1	3480
	21st to end	Day	60% 5% 13% 16% 7%	3815
April	1st to 10th	Day	53% 6% 11% 17% 11% 1	2172
	11th to 20th	Day	49% 6% 12% 19% 12% 2	2400
	21st to end	Day	49% 5% 11% 21% 11% 2	2470
May	1st to 10th	Day	52% 7% 10% 21% 9% 1	4120
	11th to 20th	Day	47% 7% 12% 23% 9% 1	4085
	21st to end	Day	39% 7% 12% 20% 18% 5%	4489
June	1st to 10th	Day	42% 6% 11% 26% 13% 3	2498
	11th to 20th	Day	40% 6% 13% 23% 16% 2	2660
	21st to end	Day	39% 7% 15% 20% 15% 4	2660
July	1st to 10th	Day	42% 4 12% 22% 17% 3	4371
	11th to 20th	Day	32% 5% 13% 30% 18% 2	4219
	21st to end	Day	39% 5% 14% 19% 20% 3	4324
August	1st to 10th	Day	36% 5% 17% 27% 14% 1	4091
	11th to 20th	Day	36% 6% 13% 32% 11% 1	4083
	21st to end	Day	36% 5% 13% 31% 12% 2	4469
September	1st to 10th	Day	37% 6% 12% 24% 17% 4	2123
	11th to 20th	Day	34% 6% 11% 27% 20% 2	2090
	21st to end	Day	44% 4 11% 22% 18%	2090
October	1st to 10th	Day	29% 4 13% 31% 21% 1	3389
	11th to 20th	Day	40% 4 10% 26% 20% 1	3140
	21st to end	Day	43% 4 11% 23% 18% 1	3249
November	1st to 10th	Day	42% 4 11% 25% 15% 1	1762
	11th to 20th	Day	53% 4 11% 19% 12% 1	1800
	21st to end	Day	59% 4 12% 18% 8%	1800
December	1st to 10th	Day	65% 3 15% 13% 3	2785
	11th to 20th	Day	67% 3 10% 16% 4	3370
	21st to end	Day	77% 3 7% 9% 4	4175
January	1st to 10th	Night	71% 3 7% 16% 4	6348
	11th to 20th	Night	76% 2 7% 9% 5%	6017
	21st to end	Night	68% 2 12% 10% 7%	6490
February	1st to 10th	Night	64% 4 11% 14% 6% 1	2536
	11th to 20th	Night	58% 4 9% 19% 8% 1	2253
	21st to end	Night	59% 4 10% 16% 9% 2	1884
March	1st to 10th	Night	54% 4 11% 23% 8% 1	3619
	11th to 20th	Night	40% 6% 15% 23% 14% 1	3480
	21st to end	Night	49% 4 11% 26% 9% 1	3817
April	1st to 10th	Night	50% 5% 12% 18% 13% 2	2024
	11th to 20th	Night	46% 6% 12% 18% 17% 2	1727
	21st to end	Night	47% 4 10% 22% 14% 3	1710
May	1st to 10th	Night	54% 5% 10% 18% 11% 2	2840
	11th to 20th	Night	44% 7% 12% 23% 13% 1	2813
	21st to end	Night	32% 7% 12% 28% 19% 2	3087
June	1st to 10th	Night	36% 6% 11% 27% 16% 3	1677
	11th to 20th	Night	34% 8% 14% 25% 17% 3	1520
	21st to end	Night	33% 7% 14% 27% 16% 3	1520
July	1st to 10th	Night	36% 5% 11% 26% 17% 5%	2490
	11th to 20th	Night	28% 5% 16% 31% 18% 2	2606
	21st to end	Night	34% 5% 17% 21% 20% 4	2988
August	1st to 10th	Night	39% 5% 13% 26% 15% 2	2814
	11th to 20th	Night	37% 5% 11% 29% 16% 1	2812
	21st to end	Night	33% 5% 13% 29% 17% 2	3182
September	1st to 10th	Night	33% 6% 13% 25% 18% 5%	2038
	11th to 20th	Night	30% 5% 10% 27% 25% 2	2090
	21st to end	Night	40% 5% 11% 24% 19% 2	2090
October	1st to 10th	Night	27% 3 8% 31% 30% 1	3571
	11th to 20th	Night	38% 3 10% 28% 21% 1	3779
	21st to end	Night	37% 3 9% 31% 17% 3	4298
November	1st to 10th	Night	42% 4 11% 24% 16% 2	2536
	11th to 20th	Night	51% 4 10% 22% 12% 2	2600
	21st to end	Night	59% 4 12% 18% 7% 1	2600
December	1st to 10th	Night	61% 3 12% 17% 6%	4250
	11th to 20th	Night	65% 3 12% 14% 6% 1	4824
	21st to end	Night	72% 4 10% 10% 4	6784

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	22% 22% 29% 20% 6% 1	300
	11th to 20th	Day	27% 17% 39% 12% 4 1	300
	21st to end	Day	29% 15% 30% 21% 5%	330
February	1st to 10th	Day	30% 16% 39% 13% 2 1	285
	11th to 20th	Day	24% 17% 34% 20% 4	270
	21st to end	Day	24% 21% 40% 11% 3	225
March	1st to 10th	Day	24% 16% 34% 19% 7%	332
	11th to 20th	Day	23% 14% 35% 21% 6% 1	460
	21st to end	Day	31% 12% 30% 19% 6% 1	506
April	1st to 10th	Day	19% 15% 32% 23% 10% 1	460
	11th to 20th	Day	23% 15% 31% 18% 10% 4	452
	21st to end	Day	24% 11% 32% 23% 9% 2	460
May	1st to 10th	Day	25% 8% 33% 22% 10% 3	463
	11th to 20th	Day	22% 7% 28% 23% 13% 7%	487
	21st to end	Day	12% 7% 23% 29% 19% 11%	529
June	1st to 10th	Day	14% 5% 27% 30% 19% 5%	518
	11th to 20th	Day	12% 5% 28% 28% 21% 6%	680
	21st to end	Day	14% 7% 27% 28% 18% 5%	680
July	1st to 10th	Day	13% 3 20% 30% 21% 14%	671
	11th to 20th	Day	9% 3 22% 30% 22% 13%	587
	21st to end	Day	10% 5% 19% 27% 27% 12%	532
August	1st to 10th	Day	12% 4 14% 30% 24% 17%	486
	11th to 20th	Day	13% 2 15% 33% 25% 13%	479
	21st to end	Day	9% 4 17% 29% 25% 16%	539
September	1st to 10th	Day	16% 5% 15% 26% 24% 14%	490
	11th to 20th	Day	8% 3 16% 24% 31% 18%	490
	21st to end	Day	19% 10% 21% 24% 18% 9%	490
October	1st to 10th	Day	13% 8% 24% 25% 22% 8%	490
	11th to 20th	Day	17% 15% 30% 24% 11% 3	490
	21st to end	Day	23% 13% 36% 20% 6% 1	435
November	1st to 10th	Day	16% 13% 36% 20% 12% 4	300
	11th to 20th	Day	27% 17% 29% 16% 10% 1	300
	21st to end	Day	26% 16% 37% 19% 2	300
December	1st to 10th	Day	22% 19% 33% 17% 8% 1	253
	11th to 20th	Day	24% 20% 35% 18% 3	300
	21st to end	Day	31% 16% 33% 15% 5%	330
January	1st to 10th	Night	25% 16% 35% 20% 4 1	1000
	11th to 20th	Night	27% 14% 37% 17% 4	852
	21st to end	Night	22% 16% 35% 23% 4	880
February	1st to 10th	Night	27% 13% 33% 25% 3	781
	11th to 20th	Night	23% 12% 36% 26% 2	743
	21st to end	Night	27% 13% 38% 19% 3	628
March	1st to 10th	Night	21% 11% 34% 27% 7%	760
	11th to 20th	Night	19% 15% 35% 24% 6% 1	760
	21st to end	Night	23% 10% 31% 27% 9%	836
April	1st to 10th	Night	21% 12% 36% 26% 5%	694
	11th to 20th	Night	20% 10% 36% 23% 9% 1	563
	21st to end	Night	21% 6% 34% 29% 8% 1	570
May	1st to 10th	Night	22% 7% 28% 33% 9% 1	570
	11th to 20th	Night	21% 6% 25% 33% 13% 1	561
	21st to end	Night	11% 3 21% 42% 20% 3	617
June	1st to 10th	Night	11% 3 24% 42% 19%	570
	11th to 20th	Night	11% 3 21% 44% 20% 1	570
	21st to end	Night	11% 2 23% 39% 22% 2	570
July	1st to 10th	Night	9% 2 16% 38% 31% 3	555
	11th to 20th	Night	9% 3 17% 40% 26% 4	552
	21st to end	Night	8% 2 15% 43% 30% 2	624
August	1st to 10th	Night	8% 2 12% 45% 30% 4	567
	11th to 20th	Night	10% 3 12% 40% 29% 5%	564
	21st to end	Night	8% 3 12% 37% 36% 4	627
September	1st to 10th	Night	13% 4 15% 34% 29% 5%	708
	11th to 20th	Night	10% 3 14% 35% 33% 5%	760
	21st to end	Night	15% 7% 20% 34% 22% 2	760
October	1st to 10th	Night	14% 7% 23% 33% 20% 3	760
	11th to 20th	Night	22% 11% 28% 29% 9% 1	760
	21st to end	Night	23% 11% 31% 27% 7% 1	836
November	1st to 10th	Night	17% 10% 32% 29% 10% 1	780
	11th to 20th	Night	21% 14% 33% 23% 7% 2	800
	21st to end	Night	27% 11% 34% 23% 6%	800
December	1st to 10th	Night	26% 13% 34% 22% 5%	800
	11th to 20th	Night	26% 12% 37% 21% 4	800
	21st to end	Night	30% 13% 33% 21% 4	1005

Page generated at 2025-02-03 03:05:52. Version ac07

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