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 2025-07-06.

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	12% 9% 4 9% 6% 5% 5% 4 6% 7% 35%	120030
	Night	10% 11% 4 10% 6% 5% 5% 4 6% 6% 32%	118981
Transparency	Day	48% 4 13% 25% 10% 1	123568
	Night	51% 3 12% 22% 10% 1	123612
Seeing	Day	16% 11% 31% 26% 12% 3	17060
	Night	15% 10% 33% 30% 11% 1	26993

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	5% 11% 5% 17% 9% 8% 7% 4 5% 7% 22%	3178
	11th to 20th	Day	6% 10% 6% 15% 9% 9% 8% 9% 9% 6% 13%	3152
	21st to end	Day	5% 13% 11% 18% 8% 6% 5% 4 5% 6% 19%	4355
February	1st to 10th	Day	9% 13% 5% 13% 8% 5% 6% 5% 7% 6% 24%	1800
	11th to 20th	Day	7% 12% 4 9% 7% 7% 6% 3 7% 7% 30%	1754
	21st to end	Day	6% 12% 4 11% 8% 8% 5% 4 6% 7% 29%	1490
March	1st to 10th	Day	10% 9% 3 7% 5% 4 5% 4 6% 8% 38%	4847
	11th to 20th	Day	9% 9% 4 12% 6% 5% 4 4 6% 8% 34%	4980
	21st to end	Day	17% 15% 5% 10% 5% 3 4 3 4 5% 30%	5464
April	1st to 10th	Day	15% 12% 3 9% 6% 5% 5% 3 6% 5% 31%	2375
	11th to 20th	Day	16% 12% 4 8% 5% 5% 4 4 5% 6% 30%	2539
	21st to end	Day	20% 11% 3 8% 5% 4 5% 4 5% 6% 31%	2600
May	1st to 10th	Day	15% 8% 2 5% 3 3 4 3 5% 5% 47%	6155
	11th to 20th	Day	15% 10% 3 6% 4 4 4 4 5% 6% 38%	6319
	21st to end	Day	15% 7% 3 6% 4 4 4 3 5% 6% 42%	7098
June	1st to 10th	Day	11% 6% 3 6% 5% 5% 6% 4 7% 9% 38%	3000
	11th to 20th	Day	14% 7% 3 7% 6% 5% 4 4 5% 8% 38%	3000
	21st to end	Day	11% 6% 3 6% 6% 5% 6% 4 8% 10% 36%	3000
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 10% 42%	4826
	11th to 20th	Day	7% 4 2 5% 3 4 5% 5% 7% 11% 48%	4750
	21st to end	Day	7% 5% 2 6% 4 4 5% 5% 7% 9% 46%	4912
August	1st to 10th	Day	10% 5% 3 6% 5% 5% 5% 5% 7% 9% 42%	4104
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 4 6% 8% 43%	4041
	21st to end	Day	15% 6% 2 6% 4 4 4 4 5% 7% 44%	4509
September	1st to 10th	Day	12% 6% 3 6% 4 3 3 3 5% 8% 47%	2280
	11th to 20th	Day	12% 7% 3 7% 5% 4 4 3 6% 6% 42%	2169
	21st to end	Day	16% 9% 3 6% 4 4 4 3 4 7% 40%	2053
October	1st to 10th	Day	18% 10% 3 6% 5% 4 4 3 5% 6% 37%	1900
	11th to 20th	Day	18% 14% 4 6% 3 4 3 3 4 6% 35%	1900
	21st to end	Day	17% 15% 4 9% 6% 3 4 3 5% 6% 27%	1998
November	1st to 10th	Day	12% 16% 6% 9% 6% 4 4 4 4 5% 30%	1567
	11th to 20th	Day	12% 18% 5% 16% 7% 5% 3 2 4 4 24%	1600
	21st to end	Day	11% 13% 6% 14% 9% 6% 5% 4 5% 6% 21%	1600
December	1st to 10th	Day	11% 13% 5% 13% 14% 10% 4 4 5% 6% 15%	2578
	11th to 20th	Day	9% 16% 7% 14% 6% 4 6% 4 7% 4 25%	2639
	21st to end	Day	15% 17% 6% 17% 8% 5% 4 3 3 5% 15%	3498
January	1st to 10th	Night	4 10% 5% 18% 10% 7% 7% 4 6% 6% 22%	6787
	11th to 20th	Night	5% 12% 6% 12% 8% 8% 11% 10% 11% 5% 12%	6753
	21st to end	Night	6% 15% 10% 16% 8% 5% 6% 4 6% 7% 17%	6616
February	1st to 10th	Night	7% 11% 4 10% 6% 7% 6% 6% 8% 7% 27%	2600
	11th to 20th	Night	5% 11% 4 10% 6% 6% 7% 6% 8% 8% 30%	2533
	21st to end	Night	8% 12% 4 12% 8% 7% 6% 6% 5% 5% 28%	2145
March	1st to 10th	Night	8% 10% 4 8% 4 4 5% 3 5% 8% 41%	5011
	11th to 20th	Night	8% 11% 4 15% 8% 6% 5% 4 5% 5% 30%	4979
	21st to end	Night	15% 15% 6% 12% 4 3 3 3 4 5% 30%	5467
April	1st to 10th	Night	14% 11% 3 9% 4 5% 5% 3 5% 6% 36%	2025
	11th to 20th	Night	16% 11% 4 8% 4 4 3 4 4 5% 36%	1809
	21st to end	Night	19% 9% 3 7% 5% 4 4 3 5% 5% 35%	1800
May	1st to 10th	Night	16% 9% 2 4 3 3 3 3 4 5% 48%	3805
	11th to 20th	Night	15% 9% 3 5% 4 4 4 4 5% 6% 43%	3596
	21st to end	Night	16% 8% 3 6% 4 5% 4 3 5% 5% 42%	3784
June	1st to 10th	Night	11% 7% 3 6% 4 4 6% 4 6% 6% 43%	1400
	11th to 20th	Night	12% 5% 2 6% 4 3 4 4 6% 9% 45%	1400
	21st to end	Night	9% 5% 2 5% 5% 4 5% 4 7% 9% 44%	1400
July	1st to 10th	Night	8% 4 1 4 4 4 5% 4 9% 12% 44%	2255
	11th to 20th	Night	5% 3 1 4 3 3 3 3 6% 9% 61%	2220
	21st to end	Night	6% 4 2 4 4 3 4 3 6% 10% 54%	2648
August	1st to 10th	Night	8% 5% 2 4 4 4 4 4 6% 8% 52%	2836
	11th to 20th	Night	14% 4 2 4 3 3 3 4 6% 8% 48%	2798
	21st to end	Night	11% 6% 2 6% 4 4 3 3 5% 7% 48%	3156
September	1st to 10th	Night	10% 5% 2 6% 3 5% 4 3 6% 6% 50%	1900
	11th to 20th	Night	10% 6% 2 6% 4 3 4 3 5% 7% 49%	2009
	21st to end	Night	14% 8% 2 5% 3 4 4 3 4 7% 47%	2107
October	1st to 10th	Night	16% 8% 3 5% 4 4 5% 4 5% 6% 40%	2280
	11th to 20th	Night	15% 11% 4 8% 5% 4 4 4 5% 6% 36%	2280
	21st to end	Night	17% 14% 4 9% 4 5% 5% 4 5% 5% 29%	2595
November	1st to 10th	Night	12% 14% 5% 9% 6% 4 4 3 5% 5% 32%	2731
	11th to 20th	Night	12% 16% 6% 13% 7% 5% 4 4 6% 5% 22%	2800
	21st to end	Night	10% 12% 5% 13% 8% 6% 5% 4 6% 6% 24%	2800
December	1st to 10th	Night	6% 12% 6% 16% 15% 10% 7% 4 5% 5% 13%	4608
	11th to 20th	Night	9% 14% 6% 16% 8% 7% 5% 4 6% 5% 19%	5568
	21st to end	Night	16% 16% 8% 16% 8% 5% 5% 3 4 5% 15%	7480

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	62% 3 7% 18% 10%	3179
	11th to 20th	Day	67% 2 5% 21% 4	3180
	21st to end	Day	66% 3 10% 15% 6%	4355
February	1st to 10th	Day	59% 3 10% 18% 10%	1800
	11th to 20th	Day	52% 4 11% 20% 11% 1	1763
	21st to end	Day	54% 3 13% 19% 11%	1490
March	1st to 10th	Day	44% 3 15% 24% 12% 3	4849
	11th to 20th	Day	48% 3 13% 25% 10%	4980
	21st to end	Day	58% 2 9% 22% 8% 1	5464
April	1st to 10th	Day	55% 4 8% 19% 13% 2	2375
	11th to 20th	Day	54% 3 11% 20% 10% 1	2539
	21st to end	Day	54% 4 11% 22% 9% 1	2600
May	1st to 10th	Day	40% 3 11% 27% 18% 1	6166
	11th to 20th	Day	47% 3 11% 21% 15% 3	6323
	21st to end	Day	43% 3 8% 30% 14% 1	7098
June	1st to 10th	Day	42% 6% 18% 24% 10% 1	3000
	11th to 20th	Day	45% 5% 14% 25% 11% 1	3000
	21st to end	Day	42% 6% 15% 29% 8%	3000
July	1st to 10th	Day	35% 8% 19% 29% 9%	4752
	11th to 20th	Day	28% 6% 20% 34% 11% 1	4669
	21st to end	Day	33% 6% 17% 35% 8% 1	4756
August	1st to 10th	Day	37% 5% 15% 29% 13% 1	4090
	11th to 20th	Day	38% 5% 17% 32% 8%	4080
	21st to end	Day	40% 5% 18% 28% 9% 1	4508
September	1st to 10th	Day	36% 3 15% 34% 11%	2280
	11th to 20th	Day	42% 3 19% 28% 7%	2169
	21st to end	Day	45% 4 13% 31% 7%	2053
October	1st to 10th	Day	38% 2 14% 30% 15% 1	3160
	11th to 20th	Day	47% 3 9% 24% 17% 1	3140
	21st to end	Day	55% 3 13% 23% 6%	3267
November	1st to 10th	Day	57% 4 12% 17% 10% 1	1567
	11th to 20th	Day	66% 3 10% 14% 7% 1	1600
	21st to end	Day	64% 4 13% 13% 6% 1	1600
December	1st to 10th	Day	71% 3 11% 13% 2	2578
	11th to 20th	Day	61% 2 8% 19% 10%	2640
	21st to end	Day	73% 3 5% 15% 4	3498
January	1st to 10th	Night	63% 3 8% 15% 11%	6787
	11th to 20th	Night	65% 3 9% 14% 8%	6800
	21st to end	Night	66% 3 10% 17% 4	6616
February	1st to 10th	Night	53% 4 12% 22% 9% 1	2600
	11th to 20th	Night	49% 5% 12% 22% 12% 1	2534
	21st to end	Night	55% 3 11% 20% 9% 1	2145
March	1st to 10th	Night	42% 3 16% 24% 13% 2	5022
	11th to 20th	Night	57% 3 8% 19% 12%	4980
	21st to end	Night	59% 3 9% 18% 10% 1	5467
April	1st to 10th	Night	50% 4 8% 24% 14% 1	2025
	11th to 20th	Night	51% 3 8% 21% 15% 1	1809
	21st to end	Night	51% 3 10% 23% 12% 1	1800
May	1st to 10th	Night	40% 3 12% 28% 17% 1	3814
	11th to 20th	Night	42% 3 11% 23% 19% 3	3597
	21st to end	Night	43% 3 9% 29% 14% 2	3785
June	1st to 10th	Night	40% 4 18% 27% 10% 1	1400
	11th to 20th	Night	36% 5% 16% 26% 15% 2	1400
	21st to end	Night	35% 6% 19% 30% 9% 1	1400
July	1st to 10th	Night	31% 7% 21% 28% 11% 1	2220
	11th to 20th	Night	21% 5% 17% 42% 15% 1	2178
	21st to end	Night	26% 5% 20% 36% 11% 1	2565
August	1st to 10th	Night	30% 5% 19% 31% 14% 1	2826
	11th to 20th	Night	33% 5% 17% 35% 9% 1	2825
	21st to end	Night	36% 4 18% 30% 11% 1	3156
September	1st to 10th	Night	34% 4 15% 34% 12% 1	1900
	11th to 20th	Night	35% 4 20% 31% 10%	2009
	21st to end	Night	39% 4 10% 36% 11%	2107
October	1st to 10th	Night	33% 3 9% 37% 15% 3	3800
	11th to 20th	Night	46% 3 11% 26% 13%	3779
	21st to end	Night	52% 3 11% 26% 8%	4281
November	1st to 10th	Night	55% 3 11% 21% 9% 1	2731
	11th to 20th	Night	63% 4 12% 15% 6% 1	2800
	21st to end	Night	59% 5% 14% 16% 6%	2800
December	1st to 10th	Night	72% 4 11% 10% 2	4608
	11th to 20th	Night	65% 3 9% 14% 9%	5566
	21st to end	Night	74% 2 7% 13% 5%	7480

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	9% 15% 34% 30% 9% 3	300
	11th to 20th	Day	19% 8% 35% 27% 10% 1	300
	21st to end	Day	12% 12% 40% 22% 11% 3	330
February	1st to 10th	Day	17% 16% 42% 20% 5% 1	300
	11th to 20th	Day	12% 19% 37% 22% 7% 3	300
	21st to end	Day	12% 13% 46% 26% 3	249
March	1st to 10th	Day	14% 17% 37% 24% 7% 1	300
	11th to 20th	Day	15% 9% 41% 20% 12% 3	300
	21st to end	Day	16% 16% 37% 22% 7% 2	330
April	1st to 10th	Day	22% 15% 32% 23% 7% 1	475
	11th to 20th	Day	23% 16% 30% 21% 9% 1	657
	21st to end	Day	24% 10% 31% 21% 13% 1	700
May	1st to 10th	Day	21% 14% 30% 23% 10% 2	703
	11th to 20th	Day	20% 11% 29% 27% 11% 3	725
	21st to end	Day	17% 10% 28% 32% 12% 2	789
June	1st to 10th	Day	12% 12% 29% 28% 15% 3	730
	11th to 20th	Day	14% 12% 36% 25% 11% 2	730
	21st to end	Day	14% 10% 29% 28% 14% 5%	730
July	1st to 10th	Day	8% 7% 24% 30% 22% 8%	697
	11th to 20th	Day	10% 7% 28% 27% 19% 9%	668
	21st to end	Day	7% 6% 27% 29% 22% 8%	739
August	1st to 10th	Day	9% 9% 23% 32% 22% 6%	676
	11th to 20th	Day	15% 5% 23% 32% 17% 8%	665
	21st to end	Day	14% 9% 26% 29% 19% 3	738
September	1st to 10th	Day	13% 8% 30% 30% 17% 2	490
	11th to 20th	Day	12% 11% 30% 31% 14% 2	379
	21st to end	Day	19% 13% 33% 24% 11%	300
October	1st to 10th	Day	20% 11% 34% 23% 9% 3	300
	11th to 20th	Day	23% 8% 38% 26% 4	300
	21st to end	Day	24% 19% 32% 16% 8% 1	330
November	1st to 10th	Day	20% 15% 31% 22% 11% 1	300
	11th to 20th	Day	25% 15% 35% 21% 3	300
	21st to end	Day	22% 16% 34% 25% 3	300
December	1st to 10th	Day	14% 15% 40% 24% 6% 1	300
	11th to 20th	Day	16% 17% 37% 27% 4	300
	21st to end	Day	21% 12% 35% 24% 5% 2	330
January	1st to 10th	Night	11% 13% 35% 28% 10% 2	1000
	11th to 20th	Night	15% 10% 37% 30% 7% 1	1000
	21st to end	Night	15% 12% 37% 28% 8% 1	1100
February	1st to 10th	Night	13% 13% 34% 30% 9% 1	1000
	11th to 20th	Night	10% 15% 40% 25% 8% 2	979
	21st to end	Night	14% 11% 36% 28% 8% 2	825
March	1st to 10th	Night	15% 10% 37% 26% 11% 1	655
	11th to 20th	Night	13% 12% 39% 29% 7% 1	600
	21st to end	Night	19% 10% 30% 26% 13% 2	660
April	1st to 10th	Night	19% 10% 34% 27% 8% 1	600
	11th to 20th	Night	21% 10% 33% 26% 9% 1	593
	21st to end	Night	22% 9% 27% 31% 11%	600
May	1st to 10th	Night	20% 9% 30% 34% 9% 1	600
	11th to 20th	Night	19% 7% 31% 32% 9% 1	591
	21st to end	Night	17% 5% 28% 39% 10%	650
June	1st to 10th	Night	12% 9% 31% 34% 14% 1	600
	11th to 20th	Night	13% 6% 29% 43% 9%	600
	21st to end	Night	12% 6% 27% 39% 17% 1	600
July	1st to 10th	Night	6% 2 22% 46% 22% 2	570
	11th to 20th	Night	8% 4 26% 40% 20% 1	552
	21st to end	Night	6% 3 25% 41% 22% 3	624
August	1st to 10th	Night	7% 3 22% 47% 20% 2	567
	11th to 20th	Night	13% 5% 19% 38% 22% 3	564
	21st to end	Night	11% 7% 28% 33% 19% 2	627
September	1st to 10th	Night	12% 6% 26% 35% 18% 2	570
	11th to 20th	Night	11% 6% 31% 35% 15% 2	570
	21st to end	Night	15% 9% 34% 28% 13% 2	587
October	1st to 10th	Night	20% 10% 32% 29% 9%	760
	11th to 20th	Night	21% 10% 36% 26% 7%	760
	21st to end	Night	24% 11% 34% 26% 5%	914
November	1st to 10th	Night	18% 12% 33% 28% 9% 1	975
	11th to 20th	Night	19% 13% 35% 25% 7% 1	1000
	21st to end	Night	16% 14% 40% 24% 5% 1	1000
December	1st to 10th	Night	14% 14% 35% 28% 9% 1	1000
	11th to 20th	Night	19% 12% 38% 25% 6% 1	1000
	21st to end	Night	23% 10% 34% 24% 8% 1	1100

Page generated at 2025-07-03 00:30:11. Version ac07

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