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 2024-03-23.

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 8% 7% 4 5% 5% 5% 7% 34%	78353
	Night	11% 10% 5% 9% 7% 4 6% 5% 5% 7% 32%	81570
Transparency	Day	50% 4 13% 23% 9% 1	78045
	Night	52% 4 12% 22% 9% 1	81413
Seeing	Day	16% 11% 31% 27% 13% 3	15162
	Night	15% 10% 32% 31% 11% 1	25304

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% 12% 7% 15% 12% 5% 6% 5% 5% 7% 21%	2218
	11th to 20th	Day	5% 9% 5% 12% 15% 8% 10% 9% 6% 5% 15%	2220
	21st to end	Day	6% 12% 12% 17% 9% 4 6% 5% 4 7% 17%	3028
February	1st to 10th	Day	9% 12% 5% 11% 9% 4 6% 7% 7% 6% 25%	1710
	11th to 20th	Day	7% 12% 4 9% 8% 6% 7% 4 6% 7% 30%	1664
	21st to end	Day	7% 11% 6% 9% 9% 6% 6% 5% 5% 7% 29%	1418
March	1st to 10th	Day	12% 12% 6% 8% 7% 4 6% 5% 5% 6% 30%	2048
	11th to 20th	Day	12% 11% 5% 8% 7% 3 4 4 6% 7% 34%	2090
	21st to end	Day	15% 11% 5% 9% 7% 2 5% 4 4 6% 31%	2200
April	1st to 10th	Day	16% 10% 4 8% 7% 4 5% 4 6% 6% 30%	2137
	11th to 20th	Day	17% 11% 4 7% 6% 4 5% 4 5% 7% 30%	2281
	21st to end	Day	19% 10% 3 7% 5% 3 4 5% 4 7% 32%	2340
May	1st to 10th	Day	20% 10% 3 5% 5% 3 4 4 4 6% 36%	2438
	11th to 20th	Day	16% 7% 3 5% 6% 3 5% 5% 5% 8% 37%	2479
	21st to end	Day	17% 7% 3 5% 5% 3 5% 4 6% 7% 36%	2783
June	1st to 10th	Day	12% 6% 3 5% 6% 4 6% 6% 6% 9% 38%	2700
	11th to 20th	Day	14% 6% 3 6% 6% 4 4 5% 5% 8% 39%	2700
	21st to end	Day	11% 5% 3 5% 6% 4 5% 6% 7% 10% 37%	2700
July	1st to 10th	Day	7% 4 2 5% 5% 3 4 6% 7% 9% 49%	2700
	11th to 20th	Day	10% 5% 2 5% 5% 3 6% 5% 6% 9% 43%	2700
	21st to end	Day	7% 3 2 5% 5% 3 5% 5% 6% 9% 50%	2802
August	1st to 10th	Day	8% 6% 3 5% 5% 3 4 6% 7% 9% 43%	2328
	11th to 20th	Day	13% 5% 3 4 5% 3 5% 5% 6% 7% 44%	2301
	21st to end	Day	12% 5% 2 5% 4 3 4 4 4 6% 49%	2565
September	1st to 10th	Day	12% 6% 3 6% 5% 2 3 4 5% 8% 47%	2160
	11th to 20th	Day	13% 7% 3 7% 6% 3 4 4 6% 6% 41%	2055
	21st to end	Day	17% 9% 3 5% 5% 3 5% 4 5% 7% 39%	1945
October	1st to 10th	Day	19% 10% 3 6% 6% 2 5% 4 4 6% 36%	1800
	11th to 20th	Day	19% 13% 4 5% 4 3 3 4 4 6% 34%	1800
	21st to end	Day	18% 14% 5% 9% 6% 2 4 3 5% 7% 27%	1894
November	1st to 10th	Day	12% 14% 7% 7% 7% 2 6% 5% 5% 5% 30%	1487
	11th to 20th	Day	11% 17% 6% 15% 8% 3 5% 3 4 4 24%	1520
	21st to end	Day	12% 13% 6% 11% 11% 4 5% 5% 5% 6% 22%	1520
December	1st to 10th	Day	11% 12% 8% 12% 9% 4 5% 6% 6% 7% 20%	1501
	11th to 20th	Day	10% 15% 7% 13% 9% 4 7% 5% 5% 4 22%	1679
	21st to end	Day	19% 14% 6% 12% 10% 4 4 3 3 5% 19%	2442
January	1st to 10th	Night	6% 10% 6% 13% 12% 5% 6% 6% 7% 6% 22%	4737
	11th to 20th	Night	5% 12% 6% 13% 11% 7% 12% 9% 7% 6% 14%	4750
	21st to end	Night	8% 16% 11% 14% 8% 4 5% 5% 6% 6% 18%	4632
February	1st to 10th	Night	7% 10% 4 9% 7% 5% 6% 7% 8% 8% 28%	2470
	11th to 20th	Night	5% 10% 4 9% 7% 4 8% 6% 7% 8% 31%	2403
	21st to end	Night	8% 11% 5% 9% 9% 5% 7% 7% 5% 6% 29%	2041
March	1st to 10th	Night	10% 12% 6% 8% 7% 4 6% 5% 4 6% 32%	2132
	11th to 20th	Night	9% 10% 4 9% 6% 4 5% 5% 5% 5% 38%	2089
	21st to end	Night	15% 10% 4 9% 6% 3 5% 5% 5% 6% 33%	2200
April	1st to 10th	Night	15% 10% 4 8% 5% 4 5% 4 5% 6% 35%	1823
	11th to 20th	Night	17% 11% 5% 7% 4 3 4 4 4 6% 36%	1627
	21st to end	Night	18% 9% 4 6% 5% 3 5% 5% 5% 6% 34%	1620
May	1st to 10th	Night	15% 9% 4 6% 5% 3 4 4 4 6% 41%	1522
	11th to 20th	Night	16% 7% 3 4 5% 3 4 4 7% 7% 41%	1416
	21st to end	Night	14% 5% 2 5% 5% 4 5% 5% 6% 7% 41%	1490
June	1st to 10th	Night	11% 7% 3 6% 6% 3 6% 5% 6% 6% 42%	1260
	11th to 20th	Night	11% 4 3 5% 4 2 5% 4 6% 10% 46%	1260
	21st to end	Night	8% 4 2 5% 5% 3 5% 5% 6% 10% 45%	1260
July	1st to 10th	Night	4 3 2 3 4 3 4 4 6% 10% 57%	1260
	11th to 20th	Night	7% 3 2 3 3 2 4 4 6% 10% 55%	1260
	21st to end	Night	4 3 2 3 4 2 4 5% 6% 10% 57%	1512
August	1st to 10th	Night	5% 4 2 3 5% 4 4 5% 5% 8% 55%	1611
	11th to 20th	Night	12% 4 2 4 4 2 3 5% 5% 7% 51%	1600
	21st to end	Night	10% 4 2 4 4 2 4 4 5% 7% 54%	1790
September	1st to 10th	Night	11% 5% 2 4 4 3 5% 4 6% 6% 50%	1800
	11th to 20th	Night	11% 6% 3 5% 5% 2 4 4 5% 7% 49%	1903
	21st to end	Night	15% 7% 3 5% 3 3 4 4 4 7% 46%	1996
October	1st to 10th	Night	16% 9% 3 4 5% 3 5% 5% 5% 6% 38%	2160
	11th to 20th	Night	16% 10% 4 7% 6% 3 4 4 5% 6% 35%	2160
	21st to end	Night	17% 13% 5% 8% 5% 3 5% 5% 4 6% 29%	2457
November	1st to 10th	Night	12% 12% 6% 9% 6% 3 5% 4 5% 5% 33%	2591
	11th to 20th	Night	12% 14% 7% 12% 8% 4 5% 4 5% 6% 23%	2660
	21st to end	Night	10% 11% 6% 10% 9% 4 6% 5% 6% 7% 26%	2660
December	1st to 10th	Night	8% 12% 7% 11% 11% 6% 7% 7% 6% 7% 18%	2675
	11th to 20th	Night	10% 13% 6% 13% 10% 5% 6% 5% 5% 5% 19%	3518
	21st to end	Night	21% 12% 8% 10% 9% 4 4 4 5% 5% 18%	5225

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	63% 4 9% 19% 5%	2219
	11th to 20th	Day	69% 3 7% 17% 5%	2220
	21st to end	Day	69% 3 8% 14% 6%	3028
February	1st to 10th	Day	57% 3 11% 19% 10%	1710
	11th to 20th	Day	53% 4 12% 19% 11% 1	1673
	21st to end	Day	55% 3 12% 19% 11%	1418
March	1st to 10th	Day	55% 4 13% 22% 6%	2050
	11th to 20th	Day	51% 4 14% 22% 9%	2090
	21st to end	Day	56% 4 10% 22% 7% 1	2200
April	1st to 10th	Day	55% 4 9% 19% 12% 1	2137
	11th to 20th	Day	54% 4 11% 20% 10% 1	2281
	21st to end	Day	53% 4 12% 21% 9% 1	2340
May	1st to 10th	Day	51% 3 9% 24% 12% 1	2438
	11th to 20th	Day	46% 5% 11% 27% 10% 2	2483
	21st to end	Day	47% 4 13% 23% 11% 1	2783
June	1st to 10th	Day	42% 6% 18% 25% 9%	2700
	11th to 20th	Day	44% 5% 14% 26% 11% 1	2700
	21st to end	Day	41% 6% 15% 30% 8%	2700
July	1st to 10th	Day	31% 6% 16% 34% 13% 1	2626
	11th to 20th	Day	37% 6% 18% 26% 13% 1	2619
	21st to end	Day	31% 6% 16% 34% 12% 1	2646
August	1st to 10th	Day	36% 5% 16% 32% 9% 2	2314
	11th to 20th	Day	38% 5% 18% 29% 10% 1	2301
	21st to end	Day	35% 4 14% 31% 14% 1	2565
September	1st to 10th	Day	37% 3 15% 33% 11%	2160
	11th to 20th	Day	43% 3 18% 28% 7%	2055
	21st to end	Day	46% 4 13% 31% 5%	1945
October	1st to 10th	Day	51% 3 15% 22% 8% 1	1800
	11th to 20th	Day	53% 3 12% 23% 10% 1	1800
	21st to end	Day	58% 3 15% 18% 5%	1894
November	1st to 10th	Day	56% 4 12% 18% 10% 1	1487
	11th to 20th	Day	66% 3 10% 13% 8% 1	1520
	21st to end	Day	63% 4 13% 13% 6% 1	1520
December	1st to 10th	Day	62% 3 14% 16% 4	1501
	11th to 20th	Day	66% 3 11% 17% 4	1680
	21st to end	Day	70% 2 5% 17% 5%	2442
January	1st to 10th	Night	61% 3 10% 20% 5%	4737
	11th to 20th	Night	69% 3 10% 12% 4	4750
	21st to end	Night	67% 3 9% 17% 5%	4632
February	1st to 10th	Night	51% 4 13% 23% 9% 1	2470
	11th to 20th	Night	49% 5% 12% 21% 12% 1	2404
	21st to end	Night	55% 3 11% 20% 10% 1	2041
March	1st to 10th	Night	53% 4 13% 21% 8% 1	2143
	11th to 20th	Night	49% 4 11% 25% 12% 1	2090
	21st to end	Night	53% 4 12% 20% 9% 2	2200
April	1st to 10th	Night	51% 4 8% 23% 13% 1	1823
	11th to 20th	Night	52% 3 9% 20% 15% 1	1627
	21st to end	Night	51% 3 11% 22% 11% 1	1620
May	1st to 10th	Night	45% 4 11% 24% 14% 1	1522
	11th to 20th	Night	42% 4 12% 25% 14% 2	1417
	21st to end	Night	42% 5% 11% 26% 14% 2	1491
June	1st to 10th	Night	41% 4 19% 26% 9% 1	1260
	11th to 20th	Night	35% 5% 16% 27% 15% 2	1260
	21st to end	Night	35% 6% 20% 29% 9% 1	1260
July	1st to 10th	Night	24% 4 18% 36% 17% 1	1225
	11th to 20th	Night	24% 6% 18% 33% 17% 1	1218
	21st to end	Night	24% 4 18% 35% 16% 2	1429
August	1st to 10th	Night	27% 4 16% 39% 12% 2	1601
	11th to 20th	Night	33% 5% 17% 34% 10% 1	1600
	21st to end	Night	30% 4 13% 35% 16% 2	1790
September	1st to 10th	Night	35% 4 15% 34% 12% 1	1800
	11th to 20th	Night	35% 4 19% 31% 10%	1903
	21st to end	Night	40% 4 11% 36% 9%	1996
October	1st to 10th	Night	46% 4 13% 26% 10% 1	2160
	11th to 20th	Night	51% 3 11% 27% 8%	2160
	21st to end	Night	57% 3 12% 22% 5%	2457
November	1st to 10th	Night	54% 3 11% 22% 9% 1	2591
	11th to 20th	Night	63% 3 12% 14% 7% 1	2660
	21st to end	Night	57% 5% 15% 17% 6%	2660
December	1st to 10th	Night	64% 4 14% 15% 4	2675
	11th to 20th	Night	65% 3 11% 15% 6% 1	3516
	21st to end	Night	69% 3 9% 13% 6%	5225

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% 14% 34% 31% 10% 2	270
	11th to 20th	Day	18% 8% 36% 26% 11% 1	270
	21st to end	Day	11% 9% 40% 24% 12% 3	297
February	1st to 10th	Day	17% 13% 43% 21% 5% 1	270
	11th to 20th	Day	13% 20% 36% 22% 6% 4	270
	21st to end	Day	12% 12% 44% 28% 4	225
March	1st to 10th	Day	14% 17% 36% 26% 6% 1	270
	11th to 20th	Day	14% 8% 42% 20% 13% 3	270
	21st to end	Day	14% 15% 36% 24% 9% 2	270
April	1st to 10th	Day	22% 15% 33% 22% 8% 1	397
	11th to 20th	Day	24% 14% 28% 23% 10% 1	559
	21st to end	Day	24% 9% 31% 23% 13% 1	600
May	1st to 10th	Day	22% 14% 31% 22% 10% 2	603
	11th to 20th	Day	19% 12% 28% 27% 12% 3	625
	21st to end	Day	17% 10% 28% 31% 12% 2	679
June	1st to 10th	Day	12% 10% 28% 30% 15% 4	630
	11th to 20th	Day	14% 11% 35% 26% 12% 2	630
	21st to end	Day	13% 7% 30% 29% 15% 6%	630
July	1st to 10th	Day	9% 7% 24% 31% 22% 7%	621
	11th to 20th	Day	11% 8% 29% 27% 19% 7%	618
	21st to end	Day	7% 5% 27% 30% 22% 8%	684
August	1st to 10th	Day	8% 8% 23% 32% 23% 6%	626
	11th to 20th	Day	15% 5% 24% 31% 17% 8%	615
	21st to end	Day	13% 8% 25% 29% 20% 4	684
September	1st to 10th	Day	14% 8% 29% 30% 17% 2	450
	11th to 20th	Day	13% 10% 30% 30% 13% 3	345
	21st to end	Day	20% 13% 33% 23% 11%	270
October	1st to 10th	Day	21% 10% 32% 24% 10% 3	270
	11th to 20th	Day	23% 8% 37% 27% 4	270
	21st to end	Day	25% 20% 32% 15% 7% 1	297
November	1st to 10th	Day	19% 14% 32% 22% 12% 1	270
	11th to 20th	Day	23% 16% 35% 22% 4	270
	21st to end	Day	23% 17% 33% 24% 3	270
December	1st to 10th	Day	13% 15% 41% 24% 6% 1	270
	11th to 20th	Day	15% 16% 37% 28% 4	270
	21st to end	Day	21% 12% 34% 25% 5% 3	297
January	1st to 10th	Night	12% 13% 34% 29% 10% 3	950
	11th to 20th	Night	15% 9% 38% 30% 7% 1	950
	21st to end	Night	15% 11% 36% 28% 8% 1	1045
February	1st to 10th	Night	12% 12% 34% 31% 10% 1	950
	11th to 20th	Night	11% 15% 39% 25% 9% 2	929
	21st to end	Night	14% 11% 36% 28% 9% 2	785
March	1st to 10th	Night	15% 10% 37% 25% 11% 1	623
	11th to 20th	Night	13% 12% 39% 29% 7% 1	570
	21st to end	Night	20% 10% 27% 27% 14% 2	600
April	1st to 10th	Night	19% 10% 35% 26% 9% 1	540
	11th to 20th	Night	23% 9% 32% 26% 9% 1	533
	21st to end	Night	22% 9% 27% 31% 11%	540
May	1st to 10th	Night	19% 9% 30% 32% 9% 1	540
	11th to 20th	Night	19% 6% 31% 33% 9% 2	531
	21st to end	Night	17% 5% 30% 38% 10%	584
June	1st to 10th	Night	11% 8% 31% 34% 15% 1	540
	11th to 20th	Night	12% 6% 29% 43% 10%	540
	21st to end	Night	10% 6% 26% 39% 18% 1	540
July	1st to 10th	Night	6% 2 22% 47% 22% 2	525
	11th to 20th	Night	8% 4 28% 40% 19% 1	522
	21st to end	Night	6% 3 24% 41% 22% 3	591
August	1st to 10th	Night	7% 2 21% 47% 20% 2	537
	11th to 20th	Night	13% 5% 19% 38% 21% 3	534
	21st to end	Night	11% 6% 28% 34% 20% 2	594
September	1st to 10th	Night	13% 6% 25% 36% 18% 2	540
	11th to 20th	Night	11% 6% 30% 36% 15% 2	540
	21st to end	Night	15% 9% 34% 28% 13% 2	556
October	1st to 10th	Night	20% 10% 31% 29% 10%	720
	11th to 20th	Night	21% 10% 35% 26% 7%	720
	21st to end	Night	24% 11% 33% 26% 6%	865
November	1st to 10th	Night	17% 12% 33% 29% 9% 1	925
	11th to 20th	Night	18% 13% 35% 26% 7% 1	950
	21st to end	Night	16% 14% 40% 24% 5% 1	950
December	1st to 10th	Night	14% 14% 35% 28% 9% 1	950
	11th to 20th	Night	19% 12% 38% 25% 6% 1	950
	21st to end	Night	24% 10% 34% 24% 7% 1	1045

Page generated at 2024-03-19 22:31:05. Version ac07

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