Bismarck
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bismarck clear sky chart from 2005-11-06 to 2024-11-04.

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	10% 7% 3 7% 5% 4 5% 4 6% 8% 42%	105190
	Night	8% 8% 3 7% 5% 5% 5% 4 6% 7% 43%	102495
Transparency	Day	39% 7% 14% 27% 12% 1	104933
	Night	39% 6% 14% 27% 13% 1	102342
Seeing	Day	14% 9% 30% 30% 14% 3	16086
	Night	12% 7% 31% 37% 12% 1	26010

By Month

Percentage Cloud Cover SW (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	4 10% 5% 17% 10% 6% 5% 3 7% 7% 26%	2538
	11th to 20th	Day	3 7% 3 12% 8% 7% 10% 11% 11% 8% 19%	2540
	21st to end	Day	6% 11% 5% 13% 8% 6% 6% 4 6% 6% 30%	2794
February	1st to 10th	Day	7% 15% 5% 10% 8% 8% 5% 3 5% 7% 27%	1543
	11th to 20th	Day	5% 13% 4 11% 7% 7% 5% 5% 7% 6% 29%	1815
	21st to end	Day	6% 12% 4 12% 7% 6% 5% 4 5% 7% 31%	1570
March	1st to 10th	Day	8% 10% 4 10% 6% 5% 4 3 6% 8% 36%	3130
	11th to 20th	Day	6% 8% 3 9% 6% 6% 6% 5% 6% 9% 34%	3354
	21st to end	Day	17% 16% 4 10% 6% 4 4 3 5% 6% 25%	3988
April	1st to 10th	Day	10% 10% 3 6% 5% 5% 5% 4 6% 8% 38%	2280
	11th to 20th	Day	16% 11% 3 9% 4 4 5% 4 5% 6% 34%	2363
	21st to end	Day	17% 10% 3 6% 4 4 4 4 5% 7% 37%	2470
May	1st to 10th	Day	17% 7% 2 5% 4 4 4 3 5% 7% 40%	4141
	11th to 20th	Day	12% 5% 2 7% 4 4 4 3 6% 7% 44%	4388
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 4 6% 7% 41%	4950
June	1st to 10th	Day	13% 5% 2 5% 3 4 4 4 5% 9% 45%	2850
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 3 8% 8% 44%	2850
	21st to end	Day	8% 4 2 5% 3 4 4 4 6% 9% 50%	2850
July	1st to 10th	Day	8% 4 1 5% 5% 6% 6% 5% 8% 9% 43%	4566
	11th to 20th	Day	5% 3 1 4 3 3 4 3 5% 8% 62%	4430
	21st to end	Day	4 3 1 5% 4 4 5% 4 7% 8% 54%	4802
August	1st to 10th	Day	10% 4 2 5% 3 4 4 3 5% 8% 51%	4381
	11th to 20th	Day	13% 5% 2 6% 5% 4 5% 4 6% 8% 41%	4041
	21st to end	Day	7% 5% 2 5% 3 3 4 3 4 7% 57%	4378
September	1st to 10th	Day	10% 4 1 4 3 3 3 3 4 6% 58%	2280
	11th to 20th	Day	10% 4 1 5% 3 4 4 4 6% 7% 53%	2110
	21st to end	Day	12% 6% 2 4 3 3 4 3 4 6% 54%	2090
October	1st to 10th	Day	10% 4 1 4 2 3 4 3 4 6% 58%	3480
	11th to 20th	Day	10% 5% 2 5% 3 2 3 2 4 8% 54%	2875
	21st to end	Day	10% 8% 3 8% 4 4 5% 4 6% 7% 42%	3091
November	1st to 10th	Day	11% 10% 4 8% 5% 4 4 4 5% 8% 38%	1700
	11th to 20th	Day	8% 10% 4 10% 6% 5% 5% 4 5% 6% 37%	1706
	21st to end	Day	5% 11% 4 9% 6% 4 5% 4 7% 7% 37%	1359
December	1st to 10th	Day	5% 12% 4 11% 8% 7% 5% 4 6% 10% 29%	1330
	11th to 20th	Day	7% 12% 6% 9% 6% 5% 5% 4 6% 8% 32%	1683
	21st to end	Day	11% 11% 3 11% 5% 5% 5% 3 5% 6% 35%	2474
January	1st to 10th	Night	5% 11% 4 14% 7% 6% 5% 5% 6% 7% 29%	4417
	11th to 20th	Night	4 8% 3 10% 7% 9% 11% 6% 9% 8% 25%	4430
	21st to end	Night	4 11% 4 12% 7% 8% 6% 4 5% 6% 32%	4873
February	1st to 10th	Night	7% 13% 5% 10% 6% 6% 5% 5% 6% 7% 29%	2636
	11th to 20th	Night	5% 12% 4 9% 6% 6% 5% 4 6% 6% 38%	2267
	21st to end	Night	7% 10% 4 8% 6% 5% 4 4 6% 9% 38%	1884
March	1st to 10th	Night	8% 9% 4 9% 5% 4 5% 4 7% 8% 38%	3734
	11th to 20th	Night	7% 8% 2 7% 5% 4 5% 4 6% 9% 43%	3609
	21st to end	Night	16% 16% 5% 9% 5% 4 4 3 4 6% 28%	3646
April	1st to 10th	Night	7% 9% 3 7% 5% 4 5% 5% 6% 8% 41%	1900
	11th to 20th	Night	12% 8% 4 7% 5% 5% 5% 5% 7% 6% 36%	1765
	21st to end	Night	15% 8% 2 5% 5% 3 4 4 5% 7% 42%	1710
May	1st to 10th	Night	12% 7% 2 6% 4 4 4 4 6% 6% 45%	2826
	11th to 20th	Night	11% 6% 3 6% 5% 4 5% 4 6% 8% 43%	2517
	21st to end	Night	12% 5% 2 6% 4 4 4 4 7% 9% 43%	2634
June	1st to 10th	Night	9% 3 1 4 3 4 5% 3 6% 9% 51%	1330
	11th to 20th	Night	9% 5% 2 5% 5% 4 4 4 6% 8% 48%	1330
	21st to end	Night	5% 3 1 4 3 3 4 4 6% 10% 58%	1330
July	1st to 10th	Night	4 4 2 4 4 4 5% 5% 7% 9% 51%	2400
	11th to 20th	Night	4 2 1 4 3 3 4 3 6% 9% 61%	2540
	21st to end	Night	3 3 2 5% 4 4 4 4 7% 9% 56%	2761
August	1st to 10th	Night	5% 3 2 4 3 3 3 4 5% 8% 60%	2556
	11th to 20th	Night	7% 5% 2 5% 4 4 4 4 4 8% 53%	2798
	21st to end	Night	7% 4 1 4 3 3 3 3 5% 7% 59%	3285
September	1st to 10th	Night	7% 3 1 3 2 3 3 2 4 6% 64%	1900
	11th to 20th	Night	8% 4 1 4 4 4 5% 3 5% 7% 56%	2068
	21st to end	Night	12% 5% 2 4 4 3 3 3 5% 6% 54%	2090
October	1st to 10th	Night	9% 4 1 4 3 3 3 2 4 6% 60%	3480
	11th to 20th	Night	9% 6% 2 6% 4 4 3 3 6% 8% 49%	4018
	21st to end	Night	11% 7% 2 6% 4 4 4 3 5% 7% 47%	4467
November	1st to 10th	Night	8% 8% 2 6% 5% 5% 5% 4 7% 7% 41%	2451
	11th to 20th	Night	7% 10% 4 11% 5% 4 4 4 6% 6% 39%	2473
	21st to end	Night	6% 7% 3 8% 5% 5% 5% 4 7% 8% 42%	2817
December	1st to 10th	Night	7% 12% 5% 11% 6% 6% 6% 5% 6% 6% 31%	2850
	11th to 20th	Night	7% 11% 4 10% 5% 5% 5% 4 7% 7% 35%	3514
	21st to end	Night	12% 12% 3 10% 6% 5% 4 4 5% 6% 33%	5189

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	54% 8% 16% 17% 5%	2539
	11th to 20th	Day	52% 8% 14% 17% 8%	2540
	21st to end	Day	51% 8% 13% 22% 6%	2794
February	1st to 10th	Day	55% 7% 12% 17% 7% 1	1543
	11th to 20th	Day	51% 7% 13% 21% 7% 1	1825
	21st to end	Day	52% 7% 14% 19% 9%	1570
March	1st to 10th	Day	46% 6% 13% 26% 9%	3130
	11th to 20th	Day	42% 9% 17% 25% 6%	3354
	21st to end	Day	59% 6% 14% 14% 7%	3988
April	1st to 10th	Day	44% 6% 16% 23% 11% 1	2280
	11th to 20th	Day	50% 5% 12% 21% 11% 1	2366
	21st to end	Day	47% 6% 13% 25% 9% 1	2470
May	1st to 10th	Day	41% 6% 12% 27% 12% 1	4141
	11th to 20th	Day	36% 7% 13% 30% 12% 2	4392
	21st to end	Day	39% 9% 14% 31% 7%	4950
June	1st to 10th	Day	36% 7% 16% 29% 11% 2	2850
	11th to 20th	Day	36% 7% 16% 27% 13% 2	2850
	21st to end	Day	29% 8% 19% 29% 14% 1	2850
July	1st to 10th	Day	32% 10% 16% 30% 9% 2	4497
	11th to 20th	Day	20% 6% 12% 38% 21% 3	4355
	21st to end	Day	24% 8% 17% 33% 16% 2	4651
August	1st to 10th	Day	31% 6% 13% 30% 17% 3	4366
	11th to 20th	Day	39% 7% 16% 28% 9% 1	4080
	21st to end	Day	26% 6% 15% 32% 18% 2	4377
September	1st to 10th	Day	28% 4 11% 35% 20% 2	2280
	11th to 20th	Day	29% 6% 15% 33% 16% 2	2110
	21st to end	Day	32% 5% 13% 31% 17% 2	2090
October	1st to 10th	Day	27% 4 10% 30% 22% 7%	3480
	11th to 20th	Day	29% 4 12% 39% 15% 1	2875
	21st to end	Day	39% 6% 13% 21% 20% 2	3091
November	1st to 10th	Day	44% 7% 14% 21% 13% 1	1700
	11th to 20th	Day	46% 7% 15% 22% 10% 1	1706
	21st to end	Day	44% 6% 19% 21% 10%	1359
December	1st to 10th	Day	50% 7% 15% 20% 7% 1	1330
	11th to 20th	Day	46% 8% 19% 21% 6%	1680
	21st to end	Day	49% 6% 10% 27% 7%	2474
January	1st to 10th	Night	51% 7% 12% 23% 6%	4417
	11th to 20th	Night	51% 7% 16% 19% 7%	4430
	21st to end	Night	51% 8% 12% 23% 6%	4873
February	1st to 10th	Night	52% 6% 12% 19% 10%	2636
	11th to 20th	Night	45% 5% 13% 25% 10% 2	2267
	21st to end	Night	43% 5% 15% 24% 12% 2	1884
March	1st to 10th	Night	41% 7% 11% 28% 13%	3734
	11th to 20th	Night	35% 7% 19% 29% 10%	3609
	21st to end	Night	57% 6% 13% 16% 8% 1	3646
April	1st to 10th	Night	39% 6% 12% 25% 14% 2	1900
	11th to 20th	Night	46% 4 11% 22% 15% 2	1765
	21st to end	Night	41% 6% 13% 26% 13% 1	1710
May	1st to 10th	Night	37% 7% 13% 27% 12% 4	2826
	11th to 20th	Night	36% 7% 14% 26% 15% 1	2518
	21st to end	Night	35% 9% 17% 28% 10%	2634
June	1st to 10th	Night	29% 6% 15% 34% 13% 2	1330
	11th to 20th	Night	33% 7% 17% 28% 13% 3	1330
	21st to end	Night	21% 7% 19% 33% 17% 2	1330
July	1st to 10th	Night	25% 10% 18% 33% 11% 2	2360
	11th to 20th	Night	18% 6% 13% 42% 17% 3	2492
	21st to end	Night	23% 7% 22% 30% 16% 2	2674
August	1st to 10th	Night	22% 6% 14% 33% 20% 4	2548
	11th to 20th	Night	30% 6% 17% 32% 14% 2	2825
	21st to end	Night	24% 6% 11% 39% 18% 3	3285
September	1st to 10th	Night	22% 4 11% 36% 24% 3	1900
	11th to 20th	Night	27% 6% 16% 31% 18% 2	2068
	21st to end	Night	30% 5% 11% 34% 18% 2	2090
October	1st to 10th	Night	26% 4 9% 26% 32% 3	3480
	11th to 20th	Night	33% 4 10% 37% 15% 2	4018
	21st to end	Night	37% 4 12% 30% 16% 1	4467
November	1st to 10th	Night	38% 6% 15% 23% 16% 2	2451
	11th to 20th	Night	44% 5% 15% 23% 11% 2	2473
	21st to end	Night	39% 7% 19% 27% 9%	2817
December	1st to 10th	Night	51% 7% 15% 19% 7%	2850
	11th to 20th	Night	46% 7% 20% 20% 7%	3516
	21st to end	Night	52% 5% 10% 24% 9% 1	5189

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	13% 9% 29% 33% 12% 4	270
	11th to 20th	Day	12% 13% 34% 28% 9% 4	270
	21st to end	Day	11% 11% 33% 27% 14% 3	297
February	1st to 10th	Day	11% 12% 41% 31% 4	270
	11th to 20th	Day	11% 10% 40% 29% 9% 1	270
	21st to end	Day	14% 8% 33% 32% 13%	225
March	1st to 10th	Day	23% 9% 35% 23% 8% 2	270
	11th to 20th	Day	13% 13% 35% 27% 9% 3	270
	21st to end	Day	18% 7% 41% 19% 12% 3	394
April	1st to 10th	Day	17% 17% 35% 24% 7%	460
	11th to 20th	Day	25% 15% 29% 21% 9% 1	564
	21st to end	Day	21% 11% 31% 24% 12% 1	650
May	1st to 10th	Day	18% 11% 30% 28% 12% 2	653
	11th to 20th	Day	18% 10% 26% 31% 12% 3	675
	21st to end	Day	15% 9% 31% 24% 17% 4	734
June	1st to 10th	Day	11% 10% 25% 30% 19% 5%	680
	11th to 20th	Day	13% 10% 37% 26% 12% 2	680
	21st to end	Day	11% 8% 28% 36% 15% 2	680
July	1st to 10th	Day	6% 6% 27% 39% 19% 3	671
	11th to 20th	Day	6% 7% 32% 36% 17% 3	668
	21st to end	Day	5% 4 27% 38% 22% 4	739
August	1st to 10th	Day	8% 5% 22% 39% 22% 5%	676
	11th to 20th	Day	11% 4 21% 35% 22% 6%	665
	21st to end	Day	9% 7% 28% 31% 22% 4	659
September	1st to 10th	Day	12% 10% 29% 28% 18% 3	490
	11th to 20th	Day	11% 9% 28% 33% 16% 3	320
	21st to end	Day	18% 13% 26% 29% 12% 2	300
October	1st to 10th	Day	20% 10% 29% 23% 17% 2	300
	11th to 20th	Day	14% 16% 34% 22% 12% 2	300
	21st to end	Day	21% 12% 37% 21% 6% 2	330
November	1st to 10th	Day	21% 10% 30% 29% 10% 1	279
	11th to 20th	Day	13% 12% 35% 29% 9% 2	270
	21st to end	Day	12% 13% 31% 30% 13% 1	270
December	1st to 10th	Day	14% 7% 37% 27% 10% 4	270
	11th to 20th	Day	17% 10% 35% 31% 6% 1	270
	21st to end	Day	15% 11% 37% 25% 8% 3	297
January	1st to 10th	Night	11% 10% 35% 34% 10% 1	950
	11th to 20th	Night	13% 10% 32% 33% 11% 1	950
	21st to end	Night	10% 10% 36% 36% 9%	1045
February	1st to 10th	Night	15% 9% 30% 37% 10% 1	950
	11th to 20th	Night	11% 8% 35% 34% 11% 1	793
	21st to end	Night	11% 5% 29% 41% 11% 3	628
March	1st to 10th	Night	13% 9% 34% 33% 9% 2	760
	11th to 20th	Night	15% 7% 32% 34% 11% 1	647
	21st to end	Night	16% 6% 30% 36% 11% 1	627
April	1st to 10th	Night	10% 9% 38% 37% 6% 1	570
	11th to 20th	Night	16% 9% 33% 32% 8% 1	563
	21st to end	Night	19% 6% 29% 32% 14%	570
May	1st to 10th	Night	14% 7% 28% 37% 14%	570
	11th to 20th	Night	14% 5% 29% 39% 13% 1	561
	21st to end	Night	14% 6% 29% 38% 13%	617
June	1st to 10th	Night	11% 7% 27% 39% 15% 1	570
	11th to 20th	Night	11% 5% 38% 34% 12%	570
	21st to end	Night	6% 4 29% 45% 14% 1	570
July	1st to 10th	Night	6% 2 24% 49% 19%	555
	11th to 20th	Night	4 4 33% 44% 15%	552
	21st to end	Night	5% 2 26% 51% 14% 2	624
August	1st to 10th	Night	5% 3 25% 50% 17%	567
	11th to 20th	Night	7% 3 26% 43% 18% 2	564
	21st to end	Night	6% 5% 27% 44% 18%	627
September	1st to 10th	Night	8% 4 25% 45% 17% 2	570
	11th to 20th	Night	8% 5% 28% 42% 16% 1	570
	21st to end	Night	13% 6% 31% 37% 12% 1	570
October	1st to 10th	Night	18% 7% 28% 36% 10%	570
	11th to 20th	Night	16% 9% 28% 35% 11% 1	897
	21st to end	Night	16% 8% 35% 30% 10% 1	1045
November	1st to 10th	Night	12% 10% 34% 32% 10% 1	943
	11th to 20th	Night	11% 10% 31% 36% 10% 1	950
	21st to end	Night	9% 11% 33% 38% 8%	950
December	1st to 10th	Night	12% 7% 34% 35% 11% 1	950
	11th to 20th	Night	14% 11% 30% 34% 10% 1	950
	21st to end	Night	18% 10% 27% 34% 11%	1045

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