Bergen
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bergen clear sky chart from 2005-11-06 to 2026-06-16.

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	9% 9% 3 8% 5% 5% 5% 4 7% 8% 36%	142024
	Night	7% 9% 4 9% 6% 5% 5% 4 6% 8% 37%	138730
Transparency	Day	43% 7% 15% 23% 10% 2	141727
	Night	43% 7% 15% 22% 11% 2	138610
Seeing	Day	14% 9% 29% 29% 15% 4	17392
	Night	11% 6% 33% 34% 13% 2	26465

By Month

Percentage Cloud Cover NW (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	2 7% 6% 12% 7% 6% 7% 4 7% 9% 33%	4125
	11th to 20th	Day	2 8% 3 10% 5% 6% 6% 4 7% 7% 42%	4216
	21st to end	Day	2 7% 4 10% 5% 4 4 4 6% 10% 42%	5186
February	1st to 10th	Day	4 12% 5% 11% 8% 6% 5% 5% 7% 8% 30%	1680
	11th to 20th	Day	3 12% 4 12% 7% 5% 7% 5% 6% 7% 31%	1788
	21st to end	Day	3 11% 5% 10% 8% 5% 6% 6% 6% 8% 32%	1700
March	1st to 10th	Day	2 8% 4 11% 6% 4 6% 4 6% 12% 37%	4618
	11th to 20th	Day	4 11% 5% 9% 5% 4 4 4 6% 9% 39%	5005
	21st to end	Day	8% 20% 6% 11% 5% 5% 5% 4 6% 5% 23%	5775
April	1st to 10th	Day	8% 15% 4 11% 7% 6% 6% 5% 6% 7% 25%	2562
	11th to 20th	Day	10% 17% 6% 8% 5% 4 5% 4 6% 7% 27%	2700
	21st to end	Day	11% 13% 4 10% 5% 5% 5% 5% 5% 7% 30%	2730
May	1st to 10th	Day	13% 11% 3 7% 5% 5% 5% 4 5% 7% 37%	8189
	11th to 20th	Day	13% 10% 4 10% 6% 6% 6% 5% 7% 8% 24%	8755
	21st to end	Day	14% 10% 3 8% 6% 5% 5% 4 7% 8% 31%	9649
June	1st to 10th	Day	18% 8% 3 8% 6% 6% 6% 4 7% 7% 27%	3150
	11th to 20th	Day	21% 10% 3 8% 7% 5% 7% 4 7% 6% 23%	3076
	21st to end	Day	12% 7% 2 6% 6% 5% 6% 6% 7% 9% 34%	3000
July	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 10% 42%	6780
	11th to 20th	Day	12% 4 2 4 4 4 6% 6% 8% 9% 40%	6780
	21st to end	Day	12% 5% 2 5% 4 4 5% 4 6% 9% 44%	7201
August	1st to 10th	Day	11% 5% 2 6% 4 5% 6% 5% 7% 8% 41%	4541
	11th to 20th	Day	9% 5% 2 5% 4 5% 6% 5% 8% 10% 41%	4266
	21st to end	Day	11% 4 2 5% 3 4 4 4 6% 8% 49%	4664
September	1st to 10th	Day	13% 7% 3 5% 4 4 3 4 6% 6% 46%	2472
	11th to 20th	Day	14% 8% 2 5% 4 4 4 4 5% 6% 45%	2212
	21st to end	Day	10% 8% 2 7% 5% 5% 4 3 6% 8% 43%	2200
October	1st to 10th	Day	8% 6% 2 6% 4 4 5% 4 7% 10% 44%	3481
	11th to 20th	Day	7% 7% 2 7% 5% 5% 6% 5% 8% 10% 37%	2940
	21st to end	Day	6% 7% 4 6% 6% 5% 5% 4 5% 8% 44%	3200
November	1st to 10th	Day	7% 14% 4 10% 7% 6% 5% 3 6% 6% 33%	1728
	11th to 20th	Day	4 13% 4 9% 5% 4 4 4 7% 8% 38%	1538
	21st to end	Day	4 14% 4 9% 5% 4 5% 4 6% 9% 35%	1470
December	1st to 10th	Day	4 10% 5% 10% 6% 8% 7% 6% 7% 8% 29%	2360
	11th to 20th	Day	3 10% 4 10% 7% 5% 6% 4 6% 9% 34%	2712
	21st to end	Day	2 12% 4 9% 5% 4 5% 5% 6% 8% 40%	3575
January	1st to 10th	Night	2 12% 6% 14% 7% 6% 7% 5% 6% 7% 28%	8768
	11th to 20th	Night	2 8% 4 11% 7% 5% 6% 5% 7% 7% 39%	8741
	21st to end	Night	2 9% 4 11% 5% 5% 5% 4 6% 9% 38%	8994
February	1st to 10th	Night	5% 10% 4 14% 8% 7% 6% 4 7% 8% 29%	2940
	11th to 20th	Night	4 12% 4 11% 7% 6% 7% 5% 6% 7% 30%	2719
	21st to end	Night	2 10% 5% 11% 7% 5% 5% 4 6% 8% 36%	2102
March	1st to 10th	Night	2 9% 4 11% 6% 5% 6% 5% 7% 9% 37%	5496
	11th to 20th	Night	4 10% 4 10% 5% 5% 5% 4 8% 9% 35%	5214
	21st to end	Night	7% 16% 6% 11% 6% 5% 5% 4 6% 7% 26%	5438
April	1st to 10th	Night	7% 14% 4 9% 6% 6% 6% 4 5% 8% 31%	2058
	11th to 20th	Night	10% 14% 5% 11% 6% 5% 5% 3 6% 7% 29%	1871
	21st to end	Night	10% 11% 4 9% 7% 6% 6% 4 6% 7% 31%	1890
May	1st to 10th	Night	15% 11% 3 8% 4 3 4 3 5% 6% 38%	4732
	11th to 20th	Night	14% 10% 3 8% 5% 5% 5% 4 8% 9% 29%	4105
	21st to end	Night	10% 7% 3 7% 6% 6% 6% 4 7% 9% 36%	4522
June	1st to 10th	Night	18% 9% 3 6% 6% 4 5% 4 5% 7% 33%	1470
	11th to 20th	Night	18% 8% 3 8% 8% 5% 6% 5% 5% 8% 26%	1435
	21st to end	Night	10% 6% 2 6% 5% 5% 6% 5% 7% 9% 39%	1400
July	1st to 10th	Night	10% 5% 3 7% 5% 5% 5% 4 6% 7% 43%	3180
	11th to 20th	Night	11% 4 2 5% 4 4 4 4 6% 8% 48%	3180
	21st to end	Night	11% 6% 2 5% 3 3 4 3 5% 9% 49%	3639
August	1st to 10th	Night	12% 5% 2 7% 4 4 4 4 5% 8% 44%	2609
	11th to 20th	Night	11% 4 2 6% 3 4 4 5% 7% 11% 41%	2788
	21st to end	Night	10% 5% 2 5% 4 4 4 3 5% 8% 50%	3245
September	1st to 10th	Night	12% 6% 2 6% 4 3 3 3 5% 7% 49%	1925
	11th to 20th	Night	15% 8% 2 5% 3 3 4 3 6% 7% 44%	2187
	21st to end	Night	10% 8% 2 5% 3 4 4 4 6% 8% 46%	2200
October	1st to 10th	Night	8% 7% 2 6% 4 4 4 4 6% 8% 47%	3714
	11th to 20th	Night	6% 7% 2 7% 4 5% 5% 3 6% 8% 47%	4206
	21st to end	Night	6% 9% 3 8% 4 4 5% 4 6% 7% 44%	4600
November	1st to 10th	Night	7% 15% 4 9% 6% 4 5% 4 6% 7% 33%	2770
	11th to 20th	Night	4 11% 3 9% 6% 5% 5% 4 7% 8% 36%	3079
	21st to end	Night	4 11% 4 9% 6% 6% 5% 5% 6% 9% 36%	3150
December	1st to 10th	Night	5% 12% 4 10% 6% 6% 6% 5% 7% 9% 31%	5040
	11th to 20th	Night	4 11% 5% 10% 8% 7% 6% 5% 7% 8% 28%	5700
	21st to end	Night	3 11% 4 10% 5% 4 5% 4 6% 7% 41%	7623

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	45% 6% 13% 21% 13% 3	4125
	11th to 20th	Day	39% 6% 14% 21% 17% 4	4237
	21st to end	Day	36% 6% 16% 31% 11% 1	5187
February	1st to 10th	Day	48% 7% 15% 17% 10% 3	1680
	11th to 20th	Day	48% 8% 14% 18% 10% 2	1797
	21st to end	Day	47% 8% 13% 19% 11% 2	1700
March	1st to 10th	Day	38% 8% 15% 23% 16% 1	4618
	11th to 20th	Day	39% 6% 15% 24% 14% 1	5006
	21st to end	Day	58% 8% 11% 15% 7% 1	5775
April	1st to 10th	Day	53% 9% 16% 14% 7%	2562
	11th to 20th	Day	53% 7% 14% 17% 8% 1	2700
	21st to end	Day	52% 9% 13% 18% 6% 1	2730
May	1st to 10th	Day	46% 5% 10% 25% 12% 2	8189
	11th to 20th	Day	52% 8% 12% 21% 6% 1	8759
	21st to end	Day	48% 8% 15% 22% 8%	9650
June	1st to 10th	Day	52% 10% 15% 16% 6% 2	3150
	11th to 20th	Day	58% 9% 14% 12% 6% 1	3076
	21st to end	Day	42% 10% 20% 20% 7% 1	3000
July	1st to 10th	Day	37% 6% 16% 24% 14% 3	6706
	11th to 20th	Day	38% 6% 20% 27% 8% 1	6699
	21st to end	Day	36% 5% 16% 26% 14% 3	6997
August	1st to 10th	Day	38% 7% 18% 29% 7%	4524
	11th to 20th	Day	36% 6% 24% 26% 7% 1	4307
	21st to end	Day	32% 6% 20% 31% 9% 2	4663
September	1st to 10th	Day	36% 8% 18% 24% 12% 3	2472
	11th to 20th	Day	39% 7% 16% 26% 11% 1	2212
	21st to end	Day	38% 7% 17% 24% 12% 3	2200
October	1st to 10th	Day	36% 6% 20% 32% 7% 1	3481
	11th to 20th	Day	39% 7% 18% 21% 12% 3	2940
	21st to end	Day	39% 5% 11% 32% 12% 1	3200
November	1st to 10th	Day	50% 8% 12% 19% 10% 2	1728
	11th to 20th	Day	41% 7% 17% 22% 10% 2	1538
	21st to end	Day	44% 8% 16% 20% 8% 4	1470
December	1st to 10th	Day	51% 6% 13% 20% 8% 2	2360
	11th to 20th	Day	44% 7% 21% 20% 7% 1	2714
	21st to end	Day	40% 6% 10% 21% 19% 4	3575
January	1st to 10th	Night	52% 7% 12% 18% 9% 2	8769
	11th to 20th	Night	43% 5% 14% 20% 13% 6%	8782
	21st to end	Night	40% 7% 17% 23% 12% 1	8994
February	1st to 10th	Night	50% 7% 11% 17% 12% 3	2940
	11th to 20th	Night	48% 8% 13% 17% 13% 2	2720
	21st to end	Night	45% 5% 12% 22% 14% 2	2102
March	1st to 10th	Night	40% 8% 16% 21% 12% 2	5496
	11th to 20th	Night	40% 8% 14% 22% 14% 1	5214
	21st to end	Night	54% 8% 12% 15% 10% 1	5438
April	1st to 10th	Night	47% 9% 13% 19% 10% 1	2058
	11th to 20th	Night	51% 7% 15% 18% 8% 1	1871
	21st to end	Night	49% 9% 13% 21% 6% 1	1890
May	1st to 10th	Night	47% 4 10% 23% 13% 2	4729
	11th to 20th	Night	46% 8% 15% 22% 9%	4105
	21st to end	Night	40% 9% 17% 27% 6% 1	4526
June	1st to 10th	Night	48% 9% 14% 19% 10% 1	1470
	11th to 20th	Night	54% 8% 14% 14% 7% 2	1435
	21st to end	Night	38% 11% 20% 23% 6% 2	1400
July	1st to 10th	Night	39% 5% 17% 25% 11% 3	3145
	11th to 20th	Night	34% 5% 23% 27% 7% 4	3138
	21st to end	Night	33% 4 21% 27% 13% 1	3538
August	1st to 10th	Night	38% 6% 14% 33% 8%	2601
	11th to 20th	Night	35% 6% 27% 25% 6% 1	2813
	21st to end	Night	33% 4 21% 31% 10% 1	3245
September	1st to 10th	Night	34% 6% 18% 26% 12% 4	1925
	11th to 20th	Night	37% 8% 15% 24% 12% 4	2187
	21st to end	Night	35% 7% 18% 24% 13% 3	2200
October	1st to 10th	Night	35% 5% 18% 25% 15% 1	3714
	11th to 20th	Night	36% 5% 18% 27% 12% 2	4206
	21st to end	Night	38% 5% 12% 30% 13% 1	4600
November	1st to 10th	Night	47% 7% 12% 20% 11% 2	2770
	11th to 20th	Night	42% 9% 16% 20% 12% 2	3079
	21st to end	Night	42% 9% 15% 21% 9% 4	3150
December	1st to 10th	Night	49% 5% 17% 19% 7% 2	5040
	11th to 20th	Night	50% 8% 16% 16% 8% 1	5697
	21st to end	Night	40% 6% 10% 23% 17% 4	7623

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	5% 8% 30% 35% 15% 6%	220
	11th to 20th	Day	5% 7% 36% 32% 15% 4	220
	21st to end	Day	8% 10% 32% 34% 14% 3	242
February	1st to 10th	Day	7% 11% 37% 29% 9% 6%	220
	11th to 20th	Day	7% 11% 34% 33% 14% 1	300
	21st to end	Day	6% 12% 35% 31% 13% 2	416
March	1st to 10th	Day	7% 13% 38% 29% 10% 3	540
	11th to 20th	Day	11% 12% 35% 29% 10% 4	540
	21st to end	Day	13% 17% 32% 24% 11% 3	594
April	1st to 10th	Day	14% 16% 34% 23% 11% 3	540
	11th to 20th	Day	16% 13% 30% 26% 11% 3	532
	21st to end	Day	17% 14% 27% 26% 12% 3	540
May	1st to 10th	Day	19% 14% 26% 26% 13% 2	583
	11th to 20th	Day	16% 9% 24% 30% 16% 5%	775
	21st to end	Day	20% 7% 20% 30% 19% 3	844
June	1st to 10th	Day	19% 10% 26% 31% 11% 3	780
	11th to 20th	Day	24% 10% 23% 28% 12% 3	756
	21st to end	Day	14% 5% 23% 32% 19% 6%	730
July	1st to 10th	Day	15% 5% 22% 31% 23% 5%	721
	11th to 20th	Day	16% 4 25% 32% 20% 4	718
	21st to end	Day	10% 5% 26% 35% 18% 6%	720
August	1st to 10th	Day	13% 5% 28% 30% 18% 7%	527
	11th to 20th	Day	11% 5% 27% 34% 18% 4	517
	21st to end	Day	11% 6% 28% 29% 20% 6%	583
September	1st to 10th	Day	15% 7% 30% 25% 16% 8%	530
	11th to 20th	Day	18% 6% 23% 31% 16% 6%	530
	21st to end	Day	15% 11% 33% 27% 11% 2	530
October	1st to 10th	Day	15% 10% 28% 27% 16% 5%	463
	11th to 20th	Day	13% 11% 35% 23% 15% 3	330
	21st to end	Day	13% 14% 37% 23% 10% 2	363
November	1st to 10th	Day	15% 10% 35% 29% 9% 2	330
	11th to 20th	Day	13% 15% 30% 31% 10% 1	256
	21st to end	Day	8% 9% 34% 30% 14% 6%	220
December	1st to 10th	Day	7% 7% 39% 31% 12% 4	220
	11th to 20th	Day	6% 10% 47% 25% 8% 4	220
	21st to end	Day	5% 7% 31% 34% 18% 5%	242
January	1st to 10th	Night	8% 10% 40% 31% 11% 1	1050
	11th to 20th	Night	8% 8% 41% 34% 8% 1	1038
	21st to end	Night	9% 11% 38% 31% 10% 1	924
February	1st to 10th	Night	9% 9% 33% 33% 13% 3	840
	11th to 20th	Night	7% 7% 37% 35% 12% 1	824
	21st to end	Night	5% 6% 34% 35% 17% 3	692
March	1st to 10th	Night	8% 4 40% 33% 12% 3	840
	11th to 20th	Night	8% 7% 40% 34% 10% 1	840
	21st to end	Night	12% 7% 35% 32% 13% 2	924
April	1st to 10th	Night	11% 7% 34% 32% 14% 1	798
	11th to 20th	Night	14% 9% 35% 33% 10%	623
	21st to end	Night	15% 10% 29% 35% 11%	630
May	1st to 10th	Night	21% 7% 25% 33% 13%	467
	11th to 20th	Night	13% 6% 25% 41% 15% 1	414
	21st to end	Night	20% 4 20% 37% 18% 1	455
June	1st to 10th	Night	21% 6% 25% 34% 13% 1	420
	11th to 20th	Night	20% 4 25% 35% 15% 1	410
	21st to end	Night	12% 3 21% 37% 25% 2	400
July	1st to 10th	Night	14% 2 16% 43% 25% 1	390
	11th to 20th	Night	15% 2 21% 41% 19% 2	388
	21st to end	Night	11% 3 16% 45% 24% 2	438
August	1st to 10th	Night	12% 3 14% 39% 29% 3	398
	11th to 20th	Night	11% 2 16% 44% 25% 2	517
	21st to end	Night	10% 3 21% 45% 20%	660
September	1st to 10th	Night	15% 3 21% 40% 19% 3	725
	11th to 20th	Night	18% 4 18% 37% 21% 2	800
	21st to end	Night	13% 5% 33% 36% 11% 2	800
October	1st to 10th	Night	17% 4 29% 34% 15% 2	800
	11th to 20th	Night	12% 4 37% 34% 11% 2	800
	21st to end	Night	10% 9% 36% 35% 8% 1	880
November	1st to 10th	Night	14% 9% 39% 28% 9% 2	925
	11th to 20th	Night	9% 10% 46% 28% 6% 1	1050
	21st to end	Night	7% 7% 41% 34% 9% 2	1050
December	1st to 10th	Night	9% 7% 42% 30% 10% 1	1050
	11th to 20th	Night	7% 8% 42% 33% 9% 2	1050
	21st to end	Night	8% 6% 39% 33% 11% 2	1155

Page generated at 2026-06-13 00:31:43. Version ac07

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