Berne
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Berne clear sky chart from 2005-11-06 to 2026-06-01.

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% 10% 4 9% 5% 5% 5% 4 6% 7% 33%	131688
	Night	14% 10% 4 8% 5% 4 4 4 5% 6% 34%	131614
Transparency	Day	48% 5% 12% 21% 13% 1	135289
	Night	48% 4 11% 21% 13% 1	136074
Seeing	Day	17% 10% 27% 24% 16% 7%	17661
	Night	19% 10% 28% 29% 13% 1	27538

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% 16% 8% 17% 6% 5% 4 3 4 5% 18%	4691
	11th to 20th	Day	11% 15% 8% 14% 8% 8% 7% 4 4 3 19%	4710
	21st to end	Day	19% 16% 8% 13% 6% 5% 5% 4 4 5% 17%	5590
February	1st to 10th	Day	16% 15% 6% 13% 6% 5% 4 3 5% 5% 21%	1988
	11th to 20th	Day	14% 13% 4 14% 7% 5% 5% 3 4 6% 24%	2048
	21st to end	Day	15% 14% 5% 12% 4 4 3 3 4 7% 28%	1730
March	1st to 10th	Day	18% 15% 7% 9% 5% 3 4 2 3 5% 28%	4580
	11th to 20th	Day	11% 11% 3 7% 4 4 4 3 6% 7% 40%	5043
	21st to end	Day	17% 12% 5% 11% 6% 5% 4 4 6% 7% 25%	5626
April	1st to 10th	Day	15% 12% 4 9% 5% 5% 4 4 6% 6% 29%	2520
	11th to 20th	Day	17% 9% 3 8% 5% 5% 4 4 5% 7% 35%	2550
	21st to end	Day	18% 7% 3 7% 4 5% 4 4 6% 8% 34%	2730
May	1st to 10th	Day	21% 10% 3 8% 5% 5% 5% 4 6% 6% 28%	5992
	11th to 20th	Day	18% 7% 2 6% 4 5% 5% 3 6% 8% 37%	5991
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 5% 7% 9% 36%	6576
June	1st to 10th	Day	12% 5% 2 7% 5% 4 6% 4 6% 8% 42%	2798
	11th to 20th	Day	10% 5% 3 6% 4 5% 5% 5% 7% 9% 41%	2800
	21st to end	Day	10% 5% 2 6% 6% 6% 5% 4 6% 10% 39%	2800
July	1st to 10th	Day	10% 6% 2 7% 4 5% 5% 4 7% 10% 40%	6360
	11th to 20th	Day	7% 5% 3 6% 5% 5% 6% 5% 7% 11% 39%	6360
	21st to end	Day	8% 6% 3 8% 5% 5% 6% 5% 7% 9% 36%	6573
August	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 4 7% 11% 43%	4234
	11th to 20th	Day	8% 6% 2 6% 4 4 5% 5% 7% 9% 44%	4174
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 10% 48%	4347
September	1st to 10th	Day	11% 6% 2 5% 5% 3 4 4 5% 7% 49%	2315
	11th to 20th	Day	9% 5% 3 5% 4 4 5% 3 5% 8% 49%	2200
	21st to end	Day	16% 6% 2 6% 4 4 4 3 5% 7% 43%	2200
October	1st to 10th	Day	11% 6% 2 7% 5% 4 4 4 5% 6% 46%	2200
	11th to 20th	Day	15% 6% 2 6% 4 4 5% 3 5% 7% 43%	2035
	21st to end	Day	18% 10% 3 8% 5% 4 5% 3 5% 7% 31%	1980
November	1st to 10th	Day	10% 7% 2 6% 5% 3 4 3 5% 6% 49%	1852
	11th to 20th	Day	16% 13% 4 8% 4 5% 4 3 5% 6% 32%	1890
	21st to end	Day	19% 13% 5% 10% 5% 4 4 2 4 5% 28%	1890
December	1st to 10th	Day	12% 15% 5% 10% 5% 4 5% 3 4 6% 31%	3020
	11th to 20th	Day	16% 17% 6% 12% 6% 4 4 4 4 5% 23%	3225
	21st to end	Day	25% 19% 8% 12% 6% 5% 3 3 4 5% 12%	4070
January	1st to 10th	Night	14% 16% 7% 15% 6% 5% 4 3 4 5% 21%	8232
	11th to 20th	Night	9% 17% 9% 16% 8% 6% 6% 4 4 4 19%	8280
	21st to end	Night	18% 12% 5% 8% 5% 5% 5% 4 5% 6% 26%	8585
February	1st to 10th	Night	18% 14% 6% 10% 6% 5% 4 3 4 5% 25%	2630
	11th to 20th	Night	13% 13% 4 10% 8% 5% 4 4 4 5% 30%	2458
	21st to end	Night	19% 12% 5% 10% 5% 4 4 3 4 6% 28%	2076
March	1st to 10th	Night	17% 14% 4 7% 3 3 4 3 3 5% 36%	5493
	11th to 20th	Night	11% 7% 2 6% 4 4 5% 4 6% 8% 43%	5137
	21st to end	Night	17% 9% 4 9% 5% 4 4 3 5% 6% 35%	5588
April	1st to 10th	Night	16% 10% 4 7% 5% 4 5% 4 6% 7% 35%	2100
	11th to 20th	Night	16% 8% 3 6% 5% 4 5% 4 5% 8% 36%	2019
	21st to end	Night	17% 10% 3 6% 4 4 4 3 5% 6% 37%	1890
May	1st to 10th	Night	20% 11% 4 8% 5% 5% 4 4 5% 6% 29%	4123
	11th to 20th	Night	17% 7% 3 7% 4 4 4 3 5% 9% 38%	4122
	21st to end	Night	13% 7% 2 6% 4 4 5% 4 6% 9% 40%	4506
June	1st to 10th	Night	10% 4 2 6% 5% 4 4 4 6% 9% 47%	1600
	11th to 20th	Night	8% 6% 2 6% 5% 5% 5% 4 7% 7% 47%	1600
	21st to end	Night	8% 6% 2 6% 5% 4 4 4 7% 9% 46%	1600
July	1st to 10th	Night	8% 4 1 6% 4 4 5% 4 6% 9% 48%	3618
	11th to 20th	Night	7% 5% 2 6% 4 4 5% 4 6% 10% 47%	3617
	21st to end	Night	9% 7% 3 7% 5% 5% 4 3 6% 9% 42%	4270
August	1st to 10th	Night	11% 5% 2 6% 5% 4 5% 3 6% 9% 43%	2915
	11th to 20th	Night	7% 6% 3 5% 4 4 5% 3 6% 8% 49%	2875
	21st to end	Night	6% 4 2 6% 4 5% 5% 4 6% 9% 50%	3547
September	1st to 10th	Night	12% 5% 1 5% 3 3 4 3 5% 7% 52%	2065
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 6% 7% 56%	2200
	21st to end	Night	12% 7% 2 5% 4 4 4 3 5% 5% 49%	2200
October	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 6% 6% 53%	2200
	11th to 20th	Night	16% 8% 2 6% 4 4 3 3 5% 6% 42%	2359
	21st to end	Night	19% 7% 2 6% 5% 4 4 5% 5% 7% 37%	2860
November	1st to 10th	Night	12% 8% 3 6% 4 4 3 4 5% 6% 46%	2666
	11th to 20th	Night	15% 11% 4 8% 5% 4 3 3 5% 7% 36%	2730
	21st to end	Night	18% 14% 5% 10% 5% 4 4 3 4 6% 28%	2730
December	1st to 10th	Night	13% 12% 4 9% 5% 5% 6% 4 7% 7% 29%	4380
	11th to 20th	Night	17% 17% 9% 12% 4 4 4 3 4 4 21%	5193
	21st to end	Night	26% 19% 7% 10% 6% 4 4 3 4 4 13%	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	70% 4 11% 13% 3	4692
	11th to 20th	Day	71% 3 8% 9% 8% 1	4710
	21st to end	Day	72% 2 8% 11% 6%	5590
February	1st to 10th	Day	65% 3 10% 14% 7% 1	1988
	11th to 20th	Day	61% 4 9% 19% 7% 1	2058
	21st to end	Day	58% 3 13% 17% 7% 2	1730
March	1st to 10th	Day	60% 4 7% 21% 9%	4580
	11th to 20th	Day	43% 4 10% 32% 10% 1	5043
	21st to end	Day	58% 5% 14% 16% 6% 1	5628
April	1st to 10th	Day	54% 5% 11% 19% 11%	2520
	11th to 20th	Day	49% 5% 11% 22% 12% 3	2550
	21st to end	Day	48% 5% 13% 22% 11% 2	2730
May	1st to 10th	Day	55% 6% 11% 17% 12%	6027
	11th to 20th	Day	46% 5% 13% 23% 12% 1	5995
	21st to end	Day	41% 7% 12% 23% 15% 1	6590
June	1st to 10th	Day	39% 6% 11% 25% 16% 2	2798
	11th to 20th	Day	37% 6% 13% 25% 16% 2	2800
	21st to end	Day	39% 7% 15% 21% 15% 3	2800
July	1st to 10th	Day	38% 5% 11% 26% 18% 2	6291
	11th to 20th	Day	37% 6% 16% 25% 16% 1	6285
	21st to end	Day	41% 7% 14% 20% 16% 3	6386
August	1st to 10th	Day	33% 6% 19% 27% 15% 1	4221
	11th to 20th	Day	34% 6% 14% 30% 15% 1	4213
	21st to end	Day	31% 6% 14% 30% 16% 3	4346
September	1st to 10th	Day	35% 5% 13% 25% 19% 3	2315
	11th to 20th	Day	33% 5% 11% 26% 23% 2	2200
	21st to end	Day	41% 5% 10% 22% 21% 1	2200
October	1st to 10th	Day	27% 4 11% 32% 24% 1	3590
	11th to 20th	Day	33% 4 11% 25% 25% 1	3289
	21st to end	Day	43% 4 9% 26% 17% 2	3180
November	1st to 10th	Day	36% 4 13% 28% 18% 1	1852
	11th to 20th	Day	54% 3 10% 20% 11% 2	1890
	21st to end	Day	59% 3 10% 19% 7% 1	1890
December	1st to 10th	Day	54% 4 15% 21% 6%	3020
	11th to 20th	Day	64% 4 12% 17% 4	3222
	21st to end	Day	76% 3 8% 9% 4	4070
January	1st to 10th	Night	66% 3 9% 15% 6%	8233
	11th to 20th	Night	69% 3 7% 10% 9% 1	8280
	21st to end	Night	60% 3 12% 18% 7%	8585
February	1st to 10th	Night	61% 4 11% 16% 7% 1	2630
	11th to 20th	Night	56% 4 10% 19% 10% 1	2459
	21st to end	Night	57% 4 11% 17% 10% 1	2076
March	1st to 10th	Night	51% 4 7% 27% 10% 1	5493
	11th to 20th	Night	38% 6% 12% 28% 14% 1	5137
	21st to end	Night	50% 4 10% 25% 10% 1	5588
April	1st to 10th	Night	49% 5% 11% 21% 13% 1	2100
	11th to 20th	Night	45% 5% 12% 20% 15% 3	2019
	21st to end	Night	46% 5% 11% 22% 13% 3	1890
May	1st to 10th	Night	56% 5% 9% 17% 12% 2	4150
	11th to 20th	Night	43% 6% 12% 25% 14% 1	4123
	21st to end	Night	39% 7% 14% 23% 15% 3	4514
June	1st to 10th	Night	34% 5% 9% 28% 21% 3	1600
	11th to 20th	Night	34% 6% 12% 26% 19% 3	1600
	21st to end	Night	34% 6% 16% 24% 17% 4	1600
July	1st to 10th	Night	33% 5% 12% 27% 18% 5%	3580
	11th to 20th	Night	32% 6% 16% 26% 18% 1	3572
	21st to end	Night	38% 5% 16% 20% 18% 3	4144
August	1st to 10th	Night	35% 6% 14% 28% 14% 1	2904
	11th to 20th	Night	32% 6% 13% 30% 18% 1	2902
	21st to end	Night	30% 6% 14% 28% 20% 3	3547
September	1st to 10th	Night	31% 5% 13% 25% 20% 5%	2065
	11th to 20th	Night	27% 5% 8% 29% 28% 3	2200
	21st to end	Night	37% 5% 11% 23% 22% 3	2200
October	1st to 10th	Night	23% 4 8% 29% 35% 2	3590
	11th to 20th	Night	33% 3 11% 24% 28% 1	3832
	21st to end	Night	34% 4 8% 30% 21% 2	4610
November	1st to 10th	Night	38% 4 10% 27% 19% 2	2666
	11th to 20th	Night	49% 3 10% 21% 14% 2	2730
	21st to end	Night	59% 3 10% 20% 7%	2730
December	1st to 10th	Night	52% 4 13% 23% 6% 1	4380
	11th to 20th	Night	66% 4 12% 12% 6%	5195
	21st to end	Night	74% 4 9% 9% 3	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	21% 19% 36% 19% 4 1	330
	11th to 20th	Day	23% 20% 40% 12% 4	330
	21st to end	Day	29% 17% 33% 16% 6%	363
February	1st to 10th	Day	25% 17% 34% 18% 5%	330
	11th to 20th	Day	24% 18% 34% 18% 5% 1	330
	21st to end	Day	25% 19% 41% 14% 1	273
March	1st to 10th	Day	25% 17% 38% 16% 3	330
	11th to 20th	Day	27% 15% 30% 20% 7% 1	519
	21st to end	Day	28% 16% 32% 17% 6%	594
April	1st to 10th	Day	21% 16% 34% 21% 8% 1	540
	11th to 20th	Day	20% 20% 26% 22% 8% 3	532
	21st to end	Day	22% 12% 32% 21% 11% 2	540
May	1st to 10th	Day	23% 13% 30% 22% 8% 3	543
	11th to 20th	Day	21% 8% 28% 22% 15% 6%	567
	21st to end	Day	13% 6% 27% 27% 17% 9%	617
June	1st to 10th	Day	11% 8% 25% 30% 20% 5%	728
	11th to 20th	Day	13% 6% 25% 30% 20% 6%	730
	21st to end	Day	12% 7% 25% 27% 20% 8%	730
July	1st to 10th	Day	11% 4 17% 28% 23% 17%	721
	11th to 20th	Day	7% 3 22% 30% 24% 14%	718
	21st to end	Day	9% 1 15% 34% 29% 12%	647
August	1st to 10th	Day	7% 2 15% 29% 27% 19%	526
	11th to 20th	Day	11% 4 17% 27% 28% 13%	519
	21st to end	Day	9% 3 13% 28% 32% 15%	583
September	1st to 10th	Day	12% 5% 15% 24% 29% 14%	530
	11th to 20th	Day	8% 2 14% 25% 31% 20%	530
	21st to end	Day	20% 9% 19% 23% 21% 9%	530
October	1st to 10th	Day	10% 6% 23% 31% 20% 9%	530
	11th to 20th	Day	15% 13% 29% 28% 13% 3	525
	21st to end	Day	26% 13% 35% 21% 4 1	363
November	1st to 10th	Day	12% 16% 34% 23% 12% 3	330
	11th to 20th	Day	24% 19% 31% 15% 10% 1	330
	21st to end	Day	31% 12% 38% 15% 4	330
December	1st to 10th	Day	21% 18% 37% 19% 5%	330
	11th to 20th	Day	21% 15% 41% 16% 6% 1	330
	21st to end	Day	29% 18% 32% 17% 3	363
January	1st to 10th	Night	22% 16% 35% 22% 4	1050
	11th to 20th	Night	25% 15% 37% 19% 4	1050
	21st to end	Night	23% 16% 35% 23% 4	991
February	1st to 10th	Night	26% 12% 34% 24% 4	840
	11th to 20th	Night	20% 13% 40% 24% 2	823
	21st to end	Night	24% 14% 38% 21% 2	692
March	1st to 10th	Night	22% 14% 33% 24% 6%	840
	11th to 20th	Night	19% 13% 37% 26% 6% 1	840
	21st to end	Night	23% 13% 31% 26% 6%	924
April	1st to 10th	Night	21% 11% 34% 27% 6% 1	630
	11th to 20th	Night	20% 13% 32% 26% 8% 1	623
	21st to end	Night	20% 9% 36% 23% 10% 1	630
May	1st to 10th	Night	21% 8% 32% 31% 7% 1	630
	11th to 20th	Night	23% 5% 27% 29% 15% 1	621
	21st to end	Night	11% 2 25% 40% 19% 2	683
June	1st to 10th	Night	11% 2 25% 43% 18% 1	600
	11th to 20th	Night	11% 3 23% 42% 21% 1	600
	21st to end	Night	10% 3 23% 37% 26% 1	600
July	1st to 10th	Night	10% 2 15% 38% 31% 4	585
	11th to 20th	Night	8% 3 15% 41% 29% 4	582
	21st to end	Night	9% 3 12% 44% 31% 2	657
August	1st to 10th	Night	9% 1 11% 42% 33% 4	597
	11th to 20th	Night	9% 2 12% 41% 32% 4	594
	21st to end	Night	7% 1 12% 38% 37% 5%	660
September	1st to 10th	Night	14% 3 13% 35% 30% 4	665
	11th to 20th	Night	10% 3 12% 36% 35% 4	800
	21st to end	Night	15% 6% 22% 32% 22% 3	800
October	1st to 10th	Night	13% 5% 24% 36% 19% 4	800
	11th to 20th	Night	19% 11% 27% 30% 12% 1	800
	21st to end	Night	21% 13% 32% 27% 8%	880
November	1st to 10th	Night	16% 10% 35% 25% 13%	820
	11th to 20th	Night	20% 16% 32% 24% 7%	840
	21st to end	Night	25% 14% 31% 24% 6%	840
December	1st to 10th	Night	24% 15% 34% 22% 5%	840
	11th to 20th	Night	24% 14% 33% 22% 6%	956
	21st to end	Night	32% 15% 31% 19% 3	1155

Page generated at 2026-05-29 01:53:32. Version ac07

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