Bemidji State University
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bemidji State University clear sky chart from 2005-11-06 to 2026-10-29.

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	11% 9% 3 8% 5% 5% 5% 4 6% 7% 36%	150500
	Night	10% 10% 4 10% 6% 5% 5% 4 6% 7% 33%	141946
Transparency	Day	46% 4 13% 26% 10% 1	153993
	Night	50% 4 12% 23% 10% 1	146550
Seeing	Day	16% 12% 32% 26% 12% 3	18932
	Night	16% 10% 33% 30% 10% 1	28743

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	6% 11% 5% 19% 10% 7% 7% 4 5% 6% 19%	4124
	11th to 20th	Day	5% 12% 6% 15% 8% 9% 9% 8% 8% 5% 14%	4112
	21st to end	Day	3 10% 9% 15% 8% 6% 6% 6% 8% 8% 19%	5653
February	1st to 10th	Day	8% 13% 5% 13% 8% 6% 6% 5% 7% 6% 23%	1890
	11th to 20th	Day	7% 12% 4 9% 7% 7% 6% 3 7% 7% 30%	1844
	21st to end	Day	6% 12% 4 11% 8% 8% 5% 4 6% 7% 29%	1562
March	1st to 10th	Day	10% 9% 3 7% 5% 4 5% 4 6% 8% 37%	4955
	11th to 20th	Day	9% 9% 4 12% 6% 5% 4 4 6% 9% 33%	5090
	21st to end	Day	17% 15% 5% 10% 5% 3 4 3 4 6% 30%	5585
April	1st to 10th	Day	16% 12% 3 9% 6% 5% 5% 3 6% 5% 30%	2494
	11th to 20th	Day	16% 12% 4 8% 5% 5% 4 4 5% 6% 30%	2667
	21st to end	Day	20% 10% 3 8% 5% 4 5% 4 5% 6% 31%	2730
May	1st to 10th	Day	13% 8% 2 5% 4 4 4 3 5% 6% 46%	7978
	11th to 20th	Day	15% 10% 3 6% 4 4 4 4 5% 6% 40%	8222
	21st to end	Day	13% 7% 2 6% 4 4 4 4 5% 7% 43%	9249
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 4 7% 9% 37%	3150
	11th to 20th	Day	14% 7% 3 6% 6% 5% 4 4 5% 8% 38%	3150
	21st to end	Day	11% 6% 3 6% 6% 5% 6% 4 8% 10% 36%	3150
July	1st to 10th	Day	8% 5% 2 6% 4 5% 5% 5% 7% 10% 43%	8849
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 7% 10% 46%	8850
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 46%	9163
August	1st to 10th	Day	8% 5% 2 5% 4 4 4 4 7% 9% 47%	6014
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 6% 8% 42%	5948
	21st to end	Day	15% 6% 2 5% 4 4 4 4 5% 7% 45%	6555
September	1st to 10th	Day	12% 6% 3 6% 4 3 3 3 5% 9% 46%	2520
	11th to 20th	Day	13% 8% 3 7% 5% 4 4 4 6% 6% 40%	2397
	21st to end	Day	16% 9% 2 6% 4 3 4 3 4 7% 41%	2269
October	1st to 10th	Day	17% 9% 3 6% 4 4 4 3 5% 6% 38%	2100
	11th to 20th	Day	19% 14% 4 6% 3 4 3 3 3 6% 35%	2100
	21st to end	Day	17% 15% 4 9% 6% 3 4 3 5% 7% 27%	2182
November	1st to 10th	Day	12% 16% 7% 9% 6% 4 4 4 4 5% 29%	1647
	11th to 20th	Day	11% 17% 5% 16% 7% 5% 3 2 4 4 26%	1680
	21st to end	Day	11% 13% 6% 14% 9% 6% 4 4 5% 6% 22%	1680
December	1st to 10th	Day	11% 13% 5% 13% 14% 10% 4 4 5% 6% 15%	2657
	11th to 20th	Day	9% 16% 7% 14% 6% 4 6% 4 7% 4 24%	2709
	21st to end	Day	15% 17% 6% 17% 8% 5% 4 3 4 5% 15%	3575
January	1st to 10th	Night	5% 11% 5% 18% 10% 7% 7% 5% 6% 6% 19%	8800
	11th to 20th	Night	5% 13% 6% 13% 8% 7% 10% 10% 9% 5% 14%	8803
	21st to end	Night	5% 11% 8% 13% 7% 6% 7% 6% 7% 10% 20%	8554
February	1st to 10th	Night	7% 12% 4 11% 6% 7% 6% 6% 8% 7% 26%	2730
	11th to 20th	Night	5% 11% 4 10% 6% 6% 7% 5% 8% 8% 31%	2663
	21st to end	Night	7% 11% 4 11% 8% 7% 6% 6% 5% 5% 28%	2249
March	1st to 10th	Night	8% 10% 4 8% 4 4 5% 3 5% 8% 40%	5124
	11th to 20th	Night	8% 11% 4 14% 8% 6% 5% 4 5% 5% 30%	5089
	21st to end	Night	15% 15% 6% 12% 5% 3 3 3 4 5% 29%	5588
April	1st to 10th	Night	14% 11% 3 9% 4 5% 5% 3 5% 5% 35%	2126
	11th to 20th	Night	16% 11% 4 8% 4 4 3 4 4 6% 36%	1901
	21st to end	Night	19% 9% 3 7% 5% 4 4 3 5% 5% 35%	1890
May	1st to 10th	Night	13% 8% 3 5% 3 3 3 3 5% 6% 47%	4949
	11th to 20th	Night	16% 7% 2 5% 3 3 3 3 5% 6% 47%	4670
	21st to end	Night	14% 7% 2 6% 4 4 4 3 5% 6% 45%	4944
June	1st to 10th	Night	11% 7% 3 7% 4 4 5% 4 6% 7% 42%	1470
	11th to 20th	Night	12% 6% 2 6% 4 3 4 4 6% 9% 45%	1470
	21st to end	Night	9% 5% 2 5% 5% 4 5% 4 7% 9% 44%	1470
July	1st to 10th	Night	10% 5% 1 4 3 4 5% 4 7% 10% 47%	4140
	11th to 20th	Night	6% 4 1 4 3 3 4 4 6% 9% 56%	4140
	21st to end	Night	9% 6% 2 5% 4 3 5% 3 6% 9% 48%	4929
August	1st to 10th	Night	7% 4 1 4 4 4 4 4 5% 7% 56%	4156
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 6% 8% 46%	4118
	21st to end	Night	14% 7% 2 6% 4 3 3 3 5% 7% 46%	4590
September	1st to 10th	Night	10% 5% 2 6% 3 4 4 3 6% 6% 50%	2100
	11th to 20th	Night	11% 6% 2 6% 4 3 4 3 5% 7% 48%	2221
	21st to end	Night	15% 7% 2 5% 3 3 4 3 4 6% 47%	2329
October	1st to 10th	Night	15% 8% 3 5% 4 4 4 4 6% 6% 42%	2520
	11th to 20th	Night	16% 11% 4 7% 4 4 4 3 4 5% 37%	2520
	21st to end	Night	17% 14% 4 8% 4 5% 4 4 5% 5% 30%	2830
November	1st to 10th	Night	12% 14% 5% 10% 6% 4 4 3 5% 5% 32%	2871
	11th to 20th	Night	12% 15% 6% 12% 7% 5% 4 3 6% 5% 24%	2940
	21st to end	Night	10% 12% 5% 14% 8% 6% 5% 4 6% 6% 24%	2940
December	1st to 10th	Night	6% 12% 6% 16% 15% 10% 7% 4 5% 5% 14%	4749
	11th to 20th	Night	9% 14% 6% 16% 9% 7% 5% 5% 6% 5% 19%	5718
	21st to end	Night	16% 16% 8% 16% 8% 5% 5% 3 4 5% 15%	7645

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	66% 3 9% 15% 8%	4125
	11th to 20th	Day	69% 2 6% 17% 6%	4140
	21st to end	Day	60% 3 9% 20% 8%	5653
February	1st to 10th	Day	59% 3 10% 18% 9%	1890
	11th to 20th	Day	52% 4 12% 20% 11% 1	1853
	21st to end	Day	54% 3 13% 19% 10%	1562
March	1st to 10th	Day	44% 3 15% 23% 11% 3	4957
	11th to 20th	Day	48% 3 13% 25% 10%	5090
	21st to end	Day	58% 2 9% 22% 8% 1	5585
April	1st to 10th	Day	56% 4 8% 19% 12% 2	2494
	11th to 20th	Day	55% 4 11% 20% 9% 1	2667
	21st to end	Day	54% 4 11% 22% 9% 1	2730
May	1st to 10th	Day	39% 3 10% 28% 19% 1	7989
	11th to 20th	Day	45% 3 9% 24% 15% 4	8226
	21st to end	Day	41% 3 8% 32% 15% 1	9249
June	1st to 10th	Day	42% 6% 18% 24% 10% 1	3150
	11th to 20th	Day	44% 5% 14% 26% 11% 1	3150
	21st to end	Day	42% 6% 15% 28% 8%	3150
July	1st to 10th	Day	34% 7% 22% 30% 7%	8776
	11th to 20th	Day	33% 6% 16% 33% 12% 1	8769
	21st to end	Day	34% 5% 16% 32% 12%	8961
August	1st to 10th	Day	33% 5% 18% 31% 13% 1	6000
	11th to 20th	Day	38% 5% 21% 29% 6%	5987
	21st to end	Day	39% 5% 15% 32% 9%	6554
September	1st to 10th	Day	37% 3 15% 34% 10%	2520
	11th to 20th	Day	43% 4 19% 27% 7%	2397
	21st to end	Day	45% 4 12% 31% 8%	2269
October	1st to 10th	Day	37% 2 14% 31% 15% 1	3360
	11th to 20th	Day	47% 3 8% 23% 18% 1	3340
	21st to end	Day	55% 3 13% 23% 6%	3451
November	1st to 10th	Day	57% 4 11% 17% 9% 1	1647
	11th to 20th	Day	64% 3 10% 15% 7% 1	1680
	21st to end	Day	63% 4 13% 13% 6% 1	1680
December	1st to 10th	Day	71% 3 11% 13% 3	2657
	11th to 20th	Day	62% 2 8% 19% 9%	2710
	21st to end	Day	73% 3 5% 15% 4	3575
January	1st to 10th	Night	65% 3 10% 13% 9%	8800
	11th to 20th	Night	66% 3 7% 15% 8%	8850
	21st to end	Night	59% 3 8% 21% 9%	8554
February	1st to 10th	Night	53% 3 12% 21% 9% 1	2730
	11th to 20th	Night	49% 5% 11% 22% 13% 1	2664
	21st to end	Night	56% 3 11% 20% 9% 1	2249
March	1st to 10th	Night	43% 3 16% 23% 13% 2	5135
	11th to 20th	Night	57% 3 8% 19% 12% 1	5090
	21st to end	Night	60% 3 9% 18% 9% 1	5588
April	1st to 10th	Night	51% 4 8% 23% 13% 1	2126
	11th to 20th	Night	51% 3 9% 22% 15% 1	1901
	21st to end	Night	50% 3 11% 23% 12% 1	1890
May	1st to 10th	Night	39% 3 10% 32% 15%	4959
	11th to 20th	Night	39% 3 9% 23% 22% 3	4671
	21st to end	Night	40% 3 9% 32% 14% 2	4945
June	1st to 10th	Night	40% 4 17% 27% 10% 1	1470
	11th to 20th	Night	37% 4 16% 27% 14% 2	1470
	21st to end	Night	36% 6% 19% 29% 9% 1	1470
July	1st to 10th	Night	31% 7% 22% 31% 9%	4105
	11th to 20th	Night	24% 5% 17% 37% 16%	4098
	21st to end	Night	33% 5% 18% 32% 11% 1	4818
August	1st to 10th	Night	28% 4 18% 36% 13% 1	4146
	11th to 20th	Night	36% 5% 21% 30% 7%	4145
	21st to end	Night	40% 4 15% 32% 8% 1	4590
September	1st to 10th	Night	35% 4 15% 34% 11% 1	2100
	11th to 20th	Night	36% 4 19% 30% 9%	2221
	21st to end	Night	39% 4 10% 35% 11%	2329
October	1st to 10th	Night	32% 3 10% 37% 15% 3	4040
	11th to 20th	Night	47% 3 10% 26% 14%	4019
	21st to end	Night	51% 3 11% 25% 8%	4516
November	1st to 10th	Night	55% 3 11% 21% 9% 1	2871
	11th to 20th	Night	61% 4 12% 16% 7% 1	2940
	21st to end	Night	59% 5% 14% 16% 6%	2940
December	1st to 10th	Night	72% 4 11% 11% 3	4749
	11th to 20th	Night	65% 3 9% 14% 9%	5716
	21st to end	Night	74% 2 7% 13% 5%	7645

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	10% 15% 36% 28% 8% 3	330
	11th to 20th	Day	18% 10% 35% 26% 9% 1	330
	21st to end	Day	11% 12% 42% 22% 10% 3	363
February	1st to 10th	Day	16% 17% 42% 18% 5% 1	330
	11th to 20th	Day	13% 18% 36% 22% 8% 4	330
	21st to end	Day	12% 13% 46% 25% 3	273
March	1st to 10th	Day	15% 17% 38% 23% 6% 1	330
	11th to 20th	Day	16% 11% 41% 19% 11% 3	330
	21st to end	Day	16% 19% 36% 20% 6% 2	363
April	1st to 10th	Day	23% 15% 32% 23% 7% 1	514
	11th to 20th	Day	23% 16% 31% 20% 9% 1	705
	21st to end	Day	24% 10% 31% 21% 13% 1	750
May	1st to 10th	Day	21% 14% 31% 23% 9% 2	753
	11th to 20th	Day	20% 12% 30% 26% 10% 3	775
	21st to end	Day	17% 10% 28% 32% 11% 2	844
June	1st to 10th	Day	13% 12% 29% 28% 14% 3	780
	11th to 20th	Day	15% 12% 36% 25% 10% 2	780
	21st to end	Day	14% 11% 29% 28% 14% 5%	780
July	1st to 10th	Day	8% 7% 25% 30% 22% 8%	771
	11th to 20th	Day	11% 7% 31% 27% 17% 8%	768
	21st to end	Day	8% 6% 29% 30% 20% 7%	849
August	1st to 10th	Day	9% 9% 24% 32% 21% 5%	776
	11th to 20th	Day	14% 6% 24% 33% 16% 8%	765
	21st to end	Day	13% 9% 26% 30% 19% 3	846
September	1st to 10th	Day	14% 8% 30% 29% 16% 2	570
	11th to 20th	Day	14% 12% 30% 30% 12% 2	447
	21st to end	Day	19% 12% 32% 24% 11% 2	360
October	1st to 10th	Day	17% 13% 36% 23% 8% 3	360
	11th to 20th	Day	25% 10% 38% 23% 4	360
	21st to end	Day	26% 19% 32% 16% 7% 1	387
November	1st to 10th	Day	21% 16% 30% 22% 10% 1	330
	11th to 20th	Day	24% 16% 35% 21% 3 1	330
	21st to end	Day	22% 16% 33% 26% 3	330
December	1st to 10th	Day	15% 15% 41% 23% 5% 1	330
	11th to 20th	Day	17% 18% 35% 26% 4	330
	21st to end	Day	21% 13% 36% 23% 5% 2	363
January	1st to 10th	Night	11% 13% 35% 28% 10% 2	1050
	11th to 20th	Night	14% 10% 38% 30% 7% 1	1050
	21st to end	Night	14% 12% 37% 28% 7% 1	1155
February	1st to 10th	Night	13% 14% 34% 29% 9% 1	1050
	11th to 20th	Night	11% 14% 40% 25% 8% 2	1029
	21st to end	Night	14% 12% 36% 28% 8% 2	865
March	1st to 10th	Night	16% 10% 37% 26% 10% 1	688
	11th to 20th	Night	14% 12% 39% 28% 6% 1	630
	21st to end	Night	19% 10% 31% 25% 13% 2	693
April	1st to 10th	Night	20% 11% 34% 27% 8% 1	630
	11th to 20th	Night	21% 11% 32% 27% 9% 1	623
	21st to end	Night	22% 9% 26% 31% 11%	630
May	1st to 10th	Night	19% 9% 30% 33% 9% 1	630
	11th to 20th	Night	19% 7% 31% 32% 9% 1	621
	21st to end	Night	17% 5% 28% 40% 10%	683
June	1st to 10th	Night	13% 8% 30% 34% 14%	630
	11th to 20th	Night	13% 7% 29% 42% 9%	630
	21st to end	Night	12% 6% 26% 39% 17%	630
July	1st to 10th	Night	7% 3 22% 45% 22% 2	615
	11th to 20th	Night	8% 4 28% 39% 20% 1	612
	21st to end	Night	7% 3 25% 41% 20% 3	690
August	1st to 10th	Night	8% 3 22% 46% 20% 1	627
	11th to 20th	Night	13% 5% 18% 40% 20% 3	624
	21st to end	Night	12% 7% 27% 34% 18% 1	693
September	1st to 10th	Night	12% 6% 27% 35% 18% 2	630
	11th to 20th	Night	11% 7% 31% 35% 14% 2	630
	21st to end	Night	16% 9% 32% 28% 14% 2	649
October	1st to 10th	Night	19% 10% 34% 28% 9%	840
	11th to 20th	Night	22% 10% 35% 26% 7%	840
	21st to end	Night	24% 12% 34% 25% 5%	996
November	1st to 10th	Night	18% 12% 33% 28% 8%	1025
	11th to 20th	Night	19% 14% 35% 25% 7% 1	1050
	21st to end	Night	16% 15% 40% 24% 5%	1050
December	1st to 10th	Night	14% 14% 36% 27% 9% 1	1050
	11th to 20th	Night	19% 13% 38% 24% 5% 1	1050
	21st to end	Night	23% 10% 35% 24% 7% 1	1155

Page generated at 2026-10-26 03:37:49. Version ac07

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