BGSU Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the BGSU Observatory clear sky chart from 2005-11-06 to 2026-05-17.

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	14% 10% 4 9% 5% 5% 5% 4 6% 7% 32%	131833
	Night	14% 11% 4 9% 5% 4 4 4 5% 7% 33%	131066
Transparency	Day	49% 5% 11% 21% 13% 1	135432
	Night	49% 5% 11% 21% 13% 1	135537
Seeing	Day	18% 10% 28% 24% 14% 6%	17572
	Night	19% 9% 28% 29% 13% 1	27439

By Month

Percentage Cloud Cover SE (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	15% 18% 7% 16% 6% 5% 5% 4 5% 5% 15%	4691
	11th to 20th	Day	11% 17% 6% 14% 10% 6% 7% 3 3 4 18%	4807
	21st to end	Day	19% 15% 7% 12% 7% 6% 6% 4 5% 4 16%	5780
February	1st to 10th	Day	15% 16% 5% 12% 8% 5% 5% 3 4 5% 22%	1890
	11th to 20th	Day	15% 12% 5% 11% 8% 6% 6% 4 4 6% 23%	2035
	21st to end	Day	16% 14% 5% 10% 5% 4 5% 3 5% 7% 27%	1730
March	1st to 10th	Day	17% 13% 6% 11% 5% 5% 4 3 4 5% 26%	4674
	11th to 20th	Day	12% 11% 3 8% 5% 4 4 4 5% 6% 39%	5090
	21st to end	Day	17% 13% 5% 10% 5% 5% 5% 3 5% 6% 25%	5586
April	1st to 10th	Day	15% 12% 4 8% 6% 5% 5% 4 6% 7% 29%	2442
	11th to 20th	Day	16% 9% 3 7% 5% 4 5% 4 6% 7% 34%	2634
	21st to end	Day	17% 9% 3 7% 5% 4 5% 4 4 7% 34%	2730
May	1st to 10th	Day	21% 10% 3 7% 5% 5% 4 4 5% 6% 29%	5992
	11th to 20th	Day	16% 8% 3 7% 4 5% 5% 4 6% 8% 34%	5939
	21st to end	Day	16% 5% 2 6% 5% 4 5% 4 6% 8% 38%	6433
June	1st to 10th	Day	13% 6% 2 6% 6% 5% 6% 5% 6% 8% 40%	2712
	11th to 20th	Day	9% 6% 2 7% 6% 5% 5% 5% 6% 8% 42%	2800
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 5% 6% 10% 38%	2800
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 5% 4 7% 11% 40%	6360
	11th to 20th	Day	7% 5% 2 7% 5% 5% 6% 5% 8% 11% 40%	6324
	21st to end	Day	9% 6% 2 8% 5% 5% 5% 4 7% 10% 39%	6424
August	1st to 10th	Day	9% 6% 2 6% 4 5% 6% 4 7% 9% 42%	4234
	11th to 20th	Day	8% 6% 2 6% 5% 5% 6% 5% 9% 11% 38%	4174
	21st to end	Day	7% 5% 2 6% 5% 4 6% 5% 7% 10% 42%	4552
September	1st to 10th	Day	12% 7% 2 5% 3 4 5% 4 5% 8% 45%	2260
	11th to 20th	Day	8% 6% 2 6% 4 3 4 4 6% 8% 49%	2200
	21st to end	Day	15% 8% 3 6% 3 4 4 4 5% 7% 42%	2200
October	1st to 10th	Day	11% 7% 2 7% 4 5% 4 4 5% 7% 45%	2167
	11th to 20th	Day	16% 8% 2 7% 5% 5% 4 3 5% 6% 39%	2000
	21st to end	Day	17% 9% 3 7% 5% 4 5% 4 6% 7% 32%	2050
November	1st to 10th	Day	11% 10% 3 6% 4 4 4 3 5% 8% 41%	1852
	11th to 20th	Day	17% 13% 3 8% 5% 5% 3 3 4 5% 33%	1890
	21st to end	Day	18% 15% 4 9% 5% 3 4 3 6% 7% 26%	1890
December	1st to 10th	Day	14% 15% 6% 12% 7% 5% 5% 3 4 6% 22%	3020
	11th to 20th	Day	18% 17% 7% 10% 5% 5% 4 4 4 5% 21%	3401
	21st to end	Day	24% 21% 7% 12% 6% 4 3 3 3 4 14%	4070
January	1st to 10th	Night	15% 15% 6% 15% 7% 6% 5% 3 4 4 20%	8232
	11th to 20th	Night	10% 17% 8% 14% 7% 5% 5% 4 5% 5% 19%	8160
	21st to end	Night	17% 14% 6% 10% 5% 5% 5% 4 5% 6% 23%	8401
February	1st to 10th	Night	17% 15% 4 10% 6% 5% 4 4 5% 5% 24%	2730
	11th to 20th	Night	14% 13% 4 9% 6% 5% 5% 5% 5% 6% 27%	2468
	21st to end	Night	19% 13% 4 9% 5% 5% 4 3 5% 5% 28%	2076
March	1st to 10th	Night	17% 12% 3 8% 4 4 4 3 4 5% 36%	5385
	11th to 20th	Night	10% 7% 3 6% 5% 5% 5% 4 5% 7% 43%	5090
	21st to end	Night	16% 10% 4 9% 5% 4 4 3 5% 6% 35%	5588
April	1st to 10th	Night	17% 10% 2 7% 5% 4 5% 3 6% 7% 33%	2195
	11th to 20th	Night	16% 8% 2 8% 5% 5% 4 3 5% 6% 37%	1934
	21st to end	Night	17% 9% 3 7% 4 4 4 3 5% 7% 37%	1890
May	1st to 10th	Night	20% 10% 4 9% 6% 5% 5% 3 5% 5% 28%	4123
	11th to 20th	Night	17% 7% 3 7% 4 4 4 3 5% 7% 38%	4086
	21st to end	Night	13% 6% 3 6% 5% 4 4 4 6% 8% 41%	4421
June	1st to 10th	Night	12% 5% 2 5% 4 5% 6% 4 5% 8% 45%	1682
	11th to 20th	Night	9% 5% 2 7% 4 4 5% 4 7% 9% 44%	1600
	21st to end	Night	9% 5% 2 5% 4 4 5% 5% 7% 9% 45%	1600
July	1st to 10th	Night	8% 5% 1 6% 5% 4 4 4 7% 9% 46%	3618
	11th to 20th	Night	8% 5% 2 6% 4 4 5% 4 7% 10% 44%	3634
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 6% 9% 46%	4427
August	1st to 10th	Night	11% 6% 2 6% 5% 4 4 4 6% 9% 43%	2915
	11th to 20th	Night	8% 6% 2 6% 4 4 5% 5% 7% 8% 46%	2875
	21st to end	Night	7% 5% 2 6% 4 5% 5% 4 6% 8% 48%	3343
September	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 5% 7% 50%	2120
	11th to 20th	Night	8% 4 2 6% 4 3 2 3 5% 7% 55%	2200
	21st to end	Night	13% 8% 3 6% 4 4 5% 4 4 6% 45%	2200
October	1st to 10th	Night	12% 5% 2 6% 5% 3 3 3 5% 6% 49%	2232
	11th to 20th	Night	16% 9% 3 7% 4 4 4 2 5% 6% 39%	2400
	21st to end	Night	20% 7% 3 7% 4 4 4 4 5% 7% 37%	2786
November	1st to 10th	Night	13% 8% 3 6% 4 4 4 4 5% 6% 44%	2666
	11th to 20th	Night	15% 11% 3 7% 6% 4 4 4 5% 7% 33%	2730
	21st to end	Night	19% 14% 4 8% 6% 3 5% 3 4 7% 26%	2730
December	1st to 10th	Night	13% 12% 5% 12% 7% 5% 5% 4 5% 7% 25%	4380
	11th to 20th	Night	16% 18% 7% 11% 5% 4 4 4 4 5% 22%	4999
	21st to end	Night	25% 19% 6% 10% 5% 4 4 3 4 5% 14%	7150

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	69% 5% 12% 11% 3	4692
	11th to 20th	Day	70% 3 8% 7% 11%	4807
	21st to end	Day	72% 3 9% 10% 6%	5780
February	1st to 10th	Day	65% 4 10% 14% 6% 1	1890
	11th to 20th	Day	61% 4 9% 16% 8% 1	2045
	21st to end	Day	56% 5% 13% 17% 7% 1	1730
March	1st to 10th	Day	60% 4 10% 19% 8%	4674
	11th to 20th	Day	45% 4 14% 25% 10% 1	5090
	21st to end	Day	59% 4 11% 16% 9%	5586
April	1st to 10th	Day	53% 5% 11% 18% 12% 1	2442
	11th to 20th	Day	48% 6% 12% 21% 12% 2	2634
	21st to end	Day	49% 4 11% 23% 10% 2	2730
May	1st to 10th	Day	53% 6% 9% 17% 13% 1	6027
	11th to 20th	Day	46% 6% 13% 21% 12% 2	5943
	21st to end	Day	42% 6% 10% 23% 16% 3	6447
June	1st to 10th	Day	40% 6% 11% 25% 15% 3	2712
	11th to 20th	Day	39% 6% 13% 22% 17% 3	2800
	21st to end	Day	39% 7% 14% 21% 15% 4	2800
July	1st to 10th	Day	36% 6% 11% 26% 18% 2	6291
	11th to 20th	Day	35% 7% 14% 25% 17% 1	6249
	21st to end	Day	37% 7% 12% 21% 20% 2	6240
August	1st to 10th	Day	35% 7% 15% 26% 16% 1	4221
	11th to 20th	Day	35% 7% 14% 30% 12% 1	4213
	21st to end	Day	34% 6% 12% 33% 13% 2	4551
September	1st to 10th	Day	38% 5% 12% 25% 18% 3	2260
	11th to 20th	Day	33% 4 11% 30% 21% 2	2200
	21st to end	Day	42% 5% 11% 23% 18% 1	2200
October	1st to 10th	Day	28% 4 12% 33% 21% 1	3531
	11th to 20th	Day	39% 4 10% 27% 20% 1	3240
	21st to end	Day	42% 3 11% 25% 18% 1	3287
November	1st to 10th	Day	41% 6% 10% 26% 17% 1	1852
	11th to 20th	Day	53% 3 12% 20% 12% 1	1890
	21st to end	Day	58% 3 12% 19% 7%	1890
December	1st to 10th	Day	63% 4 15% 15% 4	3020
	11th to 20th	Day	66% 4 10% 16% 5%	3398
	21st to end	Day	76% 3 7% 9% 4	4070
January	1st to 10th	Night	67% 4 9% 15% 5%	8233
	11th to 20th	Night	66% 3 10% 11% 8% 1	8160
	21st to end	Night	61% 4 13% 13% 8%	8401
February	1st to 10th	Night	61% 5% 10% 17% 6% 1	2730
	11th to 20th	Night	56% 5% 10% 20% 9% 1	2469
	21st to end	Night	58% 4 11% 17% 9% 1	2076
March	1st to 10th	Night	50% 4 11% 24% 10% 1	5385
	11th to 20th	Night	38% 6% 14% 27% 14% 1	5090
	21st to end	Night	49% 4 10% 21% 14% 1	5588
April	1st to 10th	Night	50% 5% 11% 19% 13% 2	2195
	11th to 20th	Night	48% 4 10% 19% 17% 2	1934
	21st to end	Night	46% 4 11% 22% 14% 2	1890
May	1st to 10th	Night	57% 5% 8% 14% 13% 3	4150
	11th to 20th	Night	45% 5% 12% 23% 13% 1	4087
	21st to end	Night	39% 6% 11% 26% 17% 2	4429
June	1st to 10th	Night	37% 5% 10% 26% 19% 3	1682
	11th to 20th	Night	35% 7% 13% 27% 16% 3	1600
	21st to end	Night	33% 6% 15% 26% 18% 2	1600
July	1st to 10th	Night	32% 6% 13% 25% 18% 5%	3580
	11th to 20th	Night	33% 6% 17% 26% 16% 1	3589
	21st to end	Night	33% 7% 14% 22% 20% 4	4297
August	1st to 10th	Night	37% 7% 12% 27% 15% 2	2904
	11th to 20th	Night	33% 6% 13% 29% 18% 1	2902
	21st to end	Night	32% 6% 13% 29% 18% 2	3343
September	1st to 10th	Night	34% 5% 11% 27% 18% 4	2120
	11th to 20th	Night	29% 4 10% 29% 26% 2	2200
	21st to end	Night	41% 4 10% 23% 19% 2	2200
October	1st to 10th	Night	25% 3 8% 31% 32% 1	3648
	11th to 20th	Night	37% 3 10% 28% 21% 1	3899
	21st to end	Night	36% 3 8% 34% 17% 3	4499
November	1st to 10th	Night	41% 4 11% 26% 17% 2	2666
	11th to 20th	Night	49% 4 11% 22% 12% 2	2730
	21st to end	Night	58% 4 12% 19% 6%	2730
December	1st to 10th	Night	58% 4 13% 18% 6%	4380
	11th to 20th	Night	63% 4 13% 12% 6% 1	5001
	21st to end	Night	73% 4 10% 9% 5%	7150

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	23% 16% 34% 22% 5% 1	330
	11th to 20th	Day	24% 19% 41% 12% 4 1	330
	21st to end	Day	25% 15% 32% 23% 4 1	363
February	1st to 10th	Day	25% 15% 40% 16% 3 2	330
	11th to 20th	Day	23% 17% 35% 22% 3	330
	21st to end	Day	25% 17% 43% 12% 2	273
March	1st to 10th	Day	23% 15% 39% 17% 6% 1	372
	11th to 20th	Day	26% 12% 35% 19% 6% 1	540
	21st to end	Day	29% 13% 33% 18% 7%	594
April	1st to 10th	Day	23% 15% 32% 20% 10% 1	540
	11th to 20th	Day	21% 17% 32% 18% 9% 3	532
	21st to end	Day	24% 10% 31% 24% 9% 2	540
May	1st to 10th	Day	24% 8% 34% 20% 11% 2	543
	11th to 20th	Day	20% 9% 27% 26% 13% 7%	551
	21st to end	Day	13% 6% 26% 26% 18% 10%	573
June	1st to 10th	Day	14% 7% 27% 29% 17% 6%	642
	11th to 20th	Day	12% 6% 29% 29% 18% 5%	730
	21st to end	Day	12% 7% 25% 32% 18% 6%	730
July	1st to 10th	Day	11% 2 20% 33% 21% 13%	721
	11th to 20th	Day	9% 5% 22% 31% 22% 11%	708
	21st to end	Day	10% 3 20% 26% 28% 13%	576
August	1st to 10th	Day	11% 3 13% 29% 27% 17%	526
	11th to 20th	Day	12% 3 16% 32% 25% 12%	519
	21st to end	Day	8% 3 17% 29% 28% 15%	583
September	1st to 10th	Day	15% 4 16% 28% 22% 14%	530
	11th to 20th	Day	8% 2 13% 27% 30% 20%	530
	21st to end	Day	18% 9% 20% 24% 19% 10%	530
October	1st to 10th	Day	13% 7% 23% 27% 21% 10%	530
	11th to 20th	Day	18% 12% 30% 25% 13% 2	530
	21st to end	Day	23% 12% 36% 21% 7% 1	433
November	1st to 10th	Day	15% 13% 34% 22% 12% 3	330
	11th to 20th	Day	26% 17% 32% 18% 6% 1	330
	21st to end	Day	28% 13% 36% 18% 4	330
December	1st to 10th	Day	22% 16% 34% 18% 9%	330
	11th to 20th	Day	22% 20% 35% 18% 4 1	330
	21st to end	Day	29% 15% 35% 18% 3	363
January	1st to 10th	Night	24% 14% 35% 21% 6%	1050
	11th to 20th	Night	26% 14% 36% 18% 4 1	1008
	21st to end	Night	23% 14% 36% 22% 4	924
February	1st to 10th	Night	24% 13% 34% 25% 4	840
	11th to 20th	Night	22% 13% 37% 25% 3	823
	21st to end	Night	26% 14% 38% 19% 3	692
March	1st to 10th	Night	22% 11% 33% 28% 7%	840
	11th to 20th	Night	19% 14% 36% 24% 7%	840
	21st to end	Night	23% 11% 32% 26% 8%	924
April	1st to 10th	Night	22% 12% 37% 25% 4 1	725
	11th to 20th	Night	21% 11% 33% 26% 8% 1	623
	21st to end	Night	22% 7% 34% 28% 9%	630
May	1st to 10th	Night	20% 7% 30% 33% 9% 1	630
	11th to 20th	Night	20% 7% 26% 31% 15% 1	609
	21st to end	Night	12% 3 24% 39% 20% 3	650
June	1st to 10th	Night	12% 5% 23% 43% 17%	600
	11th to 20th	Night	12% 3 22% 44% 18% 2	600
	21st to end	Night	11% 2 24% 40% 21% 2	600
July	1st to 10th	Night	10% 1 16% 42% 27% 4	585
	11th to 20th	Night	8% 3 18% 42% 24% 5%	582
	21st to end	Night	7% 3 12% 44% 32% 2	657
August	1st to 10th	Night	9% 2 12% 41% 32% 4	597
	11th to 20th	Night	10% 1 14% 37% 34% 4	594
	21st to end	Night	8% 2 12% 38% 34% 5%	660
September	1st to 10th	Night	14% 4 14% 33% 29% 5%	720
	11th to 20th	Night	9% 3 13% 35% 35% 5%	800
	21st to end	Night	16% 5% 20% 34% 23% 3	800
October	1st to 10th	Night	14% 5% 23% 34% 22% 3	800
	11th to 20th	Night	20% 11% 29% 29% 11% 1	800
	21st to end	Night	24% 10% 30% 28% 9%	880
November	1st to 10th	Night	17% 10% 33% 28% 10% 1	820
	11th to 20th	Night	23% 14% 31% 24% 7% 1	840
	21st to end	Night	27% 12% 32% 24% 6%	840
December	1st to 10th	Night	24% 13% 35% 22% 5%	840
	11th to 20th	Night	26% 11% 35% 24% 4	861
	21st to end	Night	31% 12% 32% 22% 3	1155

Page generated at 2026-05-14 01:59:00. Version ac07

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