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 2025-01-22.

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 8% 5% 5% 5% 4 6% 7% 33%	105290
	Night	15% 11% 4 8% 5% 4 4 4 5% 7% 34%	104052
Transparency	Day	48% 5% 12% 21% 12% 1	108933
	Night	48% 5% 11% 21% 13% 2	108548
Seeing	Day	18% 9% 27% 24% 15% 6%	15789
	Night	19% 8% 28% 30% 13% 1	25684

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	17% 19% 6% 13% 6% 4 4 4 4 5% 17%	2607
	11th to 20th	Day	15% 21% 6% 12% 7% 6% 9% 4 3 5% 13%	2657
	21st to end	Day	27% 19% 9% 11% 5% 4 4 2 3 3 12%	3133
February	1st to 10th	Day	15% 16% 4 12% 8% 5% 5% 4 4 5% 21%	1710
	11th to 20th	Day	15% 12% 5% 10% 8% 6% 6% 3 4 6% 24%	1835
	21st to end	Day	17% 15% 4 9% 5% 4 4 3 5% 7% 27%	1570
March	1st to 10th	Day	20% 17% 5% 10% 5% 4 4 3 5% 5% 23%	3184
	11th to 20th	Day	13% 11% 4 8% 5% 4 5% 4 5% 6% 35%	3480
	21st to end	Day	20% 12% 4 10% 5% 4 5% 3 5% 6% 26%	3815
April	1st to 10th	Day	13% 12% 4 8% 6% 5% 5% 5% 6% 7% 29%	2209
	11th to 20th	Day	17% 9% 3 7% 4 4 4 4 6% 7% 34%	2380
	21st to end	Day	18% 9% 2 7% 5% 4 5% 4 4 7% 34%	2470
May	1st to 10th	Day	18% 9% 3 7% 6% 5% 5% 4 6% 7% 30%	4082
	11th to 20th	Day	17% 8% 3 6% 5% 5% 5% 4 6% 8% 33%	4081
	21st to end	Day	10% 5% 2 7% 5% 5% 6% 4 6% 8% 42%	4476
June	1st to 10th	Day	12% 6% 2 6% 6% 5% 6% 5% 6% 8% 39%	2576
	11th to 20th	Day	9% 6% 2 7% 6% 5% 5% 5% 6% 8% 43%	2660
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 5% 6% 10% 37%	2660
July	1st to 10th	Day	11% 6% 3 7% 5% 5% 5% 5% 6% 11% 37%	4440
	11th to 20th	Day	6% 4 2 6% 4 5% 5% 5% 8% 11% 44%	4418
	21st to end	Day	7% 6% 2 8% 6% 5% 6% 5% 7% 9% 39%	4466
August	1st to 10th	Day	10% 6% 2 6% 4 5% 6% 4 7% 9% 42%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 9% 11% 38%	4044
	21st to end	Day	7% 6% 2 6% 5% 4 6% 5% 7% 10% 42%	4413
September	1st to 10th	Day	13% 7% 2 5% 4 4 5% 4 5% 7% 44%	2147
	11th to 20th	Day	8% 6% 2 7% 4 3 4 4 6% 8% 48%	2090
	21st to end	Day	16% 8% 2 6% 3 4 4 4 5% 7% 41%	2090
October	1st to 10th	Day	11% 7% 2 7% 4 5% 4 4 5% 7% 44%	2059
	11th to 20th	Day	16% 9% 2 7% 5% 5% 4 3 5% 6% 38%	1900
	21st to end	Day	18% 9% 3 7% 5% 4 5% 4 6% 6% 32%	1948
November	1st to 10th	Day	11% 10% 3 6% 4 4 4 3 5% 8% 42%	1762
	11th to 20th	Day	17% 13% 3 8% 5% 5% 4 3 4 6% 33%	1800
	21st to end	Day	19% 15% 4 9% 5% 3 4 3 6% 7% 26%	1800
December	1st to 10th	Day	14% 15% 6% 12% 7% 5% 5% 3 4 7% 23%	2930
	11th to 20th	Day	18% 17% 7% 10% 5% 5% 4 4 4 5% 21%	3312
	21st to end	Day	25% 21% 7% 12% 6% 4 3 3 3 4 14%	3982
January	1st to 10th	Night	17% 17% 7% 11% 6% 5% 4 3 4 5% 22%	4568
	11th to 20th	Night	15% 19% 8% 13% 6% 4 6% 5% 5% 5% 15%	4514
	21st to end	Night	26% 18% 8% 11% 5% 4 3 2 3 4 15%	4546
February	1st to 10th	Night	18% 15% 5% 10% 6% 5% 4 3 5% 6% 24%	2470
	11th to 20th	Night	14% 14% 4 9% 6% 5% 5% 5% 5% 6% 28%	2228
	21st to end	Night	21% 12% 4 8% 5% 5% 4 3 5% 5% 28%	1884
March	1st to 10th	Night	18% 14% 3 7% 4 3 3 2 4 5% 35%	3655
	11th to 20th	Night	11% 7% 3 6% 5% 5% 5% 4 5% 7% 43%	3480
	21st to end	Night	17% 10% 4 8% 5% 4 4 3 5% 6% 35%	3817
April	1st to 10th	Night	15% 11% 2 7% 5% 4 5% 3 6% 7% 34%	1986
	11th to 20th	Night	18% 8% 2 7% 4 5% 4 4 5% 6% 37%	1748
	21st to end	Night	17% 9% 3 6% 4 4 4 3 6% 7% 37%	1710
May	1st to 10th	Night	17% 8% 4 8% 6% 5% 5% 4 5% 7% 31%	2813
	11th to 20th	Night	17% 7% 3 6% 4 4 4 3 5% 7% 40%	2812
	21st to end	Night	10% 5% 2 6% 4 4 5% 4 6% 9% 45%	3079
June	1st to 10th	Night	12% 5% 2 5% 4 5% 6% 4 5% 8% 45%	1598
	11th to 20th	Night	9% 5% 2 7% 4 4 5% 4 7% 9% 44%	1520
	21st to end	Night	9% 5% 2 5% 4 4 5% 4 7% 9% 44%	1520
July	1st to 10th	Night	9% 5% 1 5% 4 3 4 4 7% 9% 48%	2530
	11th to 20th	Night	7% 4 2 5% 4 4 4 4 7% 10% 49%	2547
	21st to end	Night	6% 5% 2 7% 5% 4 6% 4 7% 9% 45%	3087
August	1st to 10th	Night	11% 7% 2 6% 5% 4 4 4 5% 9% 42%	2825
	11th to 20th	Night	8% 6% 2 6% 4 4 5% 5% 7% 8% 46%	2785
	21st to end	Night	7% 5% 2 6% 4 5% 5% 4 6% 8% 48%	3240
September	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 5% 7% 49%	2014
	11th to 20th	Night	9% 5% 2 6% 4 3 2 3 5% 7% 54%	2090
	21st to end	Night	13% 8% 3 6% 4 4 4 3 4 6% 44%	2090
October	1st to 10th	Night	12% 5% 3 6% 5% 3 3 3 5% 6% 49%	2120
	11th to 20th	Night	16% 9% 3 7% 4 4 4 2 5% 6% 39%	2280
	21st to end	Night	20% 8% 3 7% 4 4 4 4 5% 7% 36%	2646
November	1st to 10th	Night	13% 8% 3 6% 4 4 4 4 5% 6% 43%	2536
	11th to 20th	Night	15% 11% 3 7% 5% 4 4 4 6% 7% 33%	2600
	21st to end	Night	19% 14% 4 8% 6% 3 5% 3 4 7% 26%	2600
December	1st to 10th	Night	13% 12% 6% 12% 7% 5% 5% 4 5% 7% 25%	4250
	11th to 20th	Night	16% 18% 7% 11% 5% 4 4 4 4 5% 22%	4868
	21st to end	Night	25% 19% 6% 10% 5% 4 4 3 4 5% 14%	6996

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	70% 4 10% 12% 4	2608
	11th to 20th	Day	75% 4 8% 8% 5%	2657
	21st to end	Day	80% 3 6% 7% 4	3133
February	1st to 10th	Day	65% 4 10% 13% 6% 1	1710
	11th to 20th	Day	61% 4 9% 17% 8%	1845
	21st to end	Day	56% 5% 13% 17% 7% 2	1570
March	1st to 10th	Day	63% 4 9% 18% 5%	3184
	11th to 20th	Day	49% 5% 14% 23% 9% 1	3480
	21st to end	Day	58% 5% 12% 17% 7%	3815
April	1st to 10th	Day	52% 6% 11% 18% 12% 1	2209
	11th to 20th	Day	47% 6% 12% 21% 12% 2	2380
	21st to end	Day	50% 4 11% 22% 11% 2	2470
May	1st to 10th	Day	50% 7% 11% 22% 9% 1	4120
	11th to 20th	Day	46% 6% 12% 24% 10% 1	4085
	21st to end	Day	38% 6% 11% 20% 20% 4	4489
June	1st to 10th	Day	40% 6% 11% 26% 14% 3	2576
	11th to 20th	Day	38% 6% 13% 22% 17% 3	2660
	21st to end	Day	40% 7% 14% 21% 14% 4	2660
July	1st to 10th	Day	41% 5% 12% 22% 17% 3	4371
	11th to 20th	Day	30% 7% 13% 29% 20% 1	4343
	21st to end	Day	37% 7% 13% 18% 21% 3	4324
August	1st to 10th	Day	36% 7% 15% 26% 16% 1	4091
	11th to 20th	Day	35% 7% 14% 30% 13% 1	4083
	21st to end	Day	34% 6% 12% 33% 13% 2	4412
September	1st to 10th	Day	39% 5% 12% 23% 18% 3	2147
	11th to 20th	Day	34% 4 11% 28% 21% 2	2090
	21st to end	Day	42% 5% 11% 23% 17% 1	2090
October	1st to 10th	Day	28% 4 13% 34% 20% 1	3423
	11th to 20th	Day	39% 4 10% 27% 20% 1	3140
	21st to end	Day	42% 3 12% 25% 18% 1	3185
November	1st to 10th	Day	41% 6% 10% 26% 17% 1	1762
	11th to 20th	Day	54% 3 12% 19% 12% 1	1800
	21st to end	Day	57% 3 13% 19% 8%	1800
December	1st to 10th	Day	62% 4 15% 15% 3	2930
	11th to 20th	Day	66% 4 9% 16% 5%	3309
	21st to end	Day	76% 3 7% 9% 4	3982
January	1st to 10th	Night	65% 4 9% 15% 6%	4568
	11th to 20th	Night	72% 4 9% 11% 4	4514
	21st to end	Night	74% 3 8% 10% 4	4546
February	1st to 10th	Night	61% 5% 11% 16% 5% 1	2470
	11th to 20th	Night	55% 5% 9% 20% 9% 1	2229
	21st to end	Night	58% 4 10% 17% 9% 2	1884
March	1st to 10th	Night	52% 4 10% 25% 8% 1	3655
	11th to 20th	Night	38% 7% 15% 23% 16% 1	3480
	21st to end	Night	50% 5% 10% 25% 8% 1	3817
April	1st to 10th	Night	49% 5% 11% 20% 14% 2	1986
	11th to 20th	Night	47% 4 10% 19% 17% 2	1748
	21st to end	Night	46% 4 11% 22% 15% 3	1710
May	1st to 10th	Night	52% 6% 9% 18% 13% 2	2840
	11th to 20th	Night	44% 5% 12% 25% 12% 1	2813
	21st to end	Night	33% 6% 11% 27% 19% 3	3087
June	1st to 10th	Night	37% 5% 11% 26% 18% 3	1598
	11th to 20th	Night	34% 7% 13% 27% 16% 3	1520
	21st to end	Night	34% 6% 14% 26% 17% 2	1520
July	1st to 10th	Night	32% 6% 12% 27% 17% 6%	2490
	11th to 20th	Night	27% 6% 17% 29% 19% 2	2499
	21st to end	Night	33% 8% 16% 20% 18% 5%	2988
August	1st to 10th	Night	38% 7% 12% 27% 15% 2	2814
	11th to 20th	Night	33% 6% 13% 28% 18% 1	2812
	21st to end	Night	32% 6% 13% 29% 18% 2	3240
September	1st to 10th	Night	35% 5% 11% 26% 18% 5%	2014
	11th to 20th	Night	30% 4 10% 27% 26% 2	2090
	21st to end	Night	41% 4 10% 24% 18% 2	2090
October	1st to 10th	Night	25% 3 9% 31% 32% 1	3536
	11th to 20th	Night	37% 3 10% 28% 21% 1	3779
	21st to end	Night	36% 3 8% 34% 16% 3	4359
November	1st to 10th	Night	41% 4 11% 25% 17% 2	2536
	11th to 20th	Night	50% 4 11% 21% 12% 2	2600
	21st to end	Night	58% 4 12% 19% 7%	2600
December	1st to 10th	Night	58% 4 13% 18% 6%	4250
	11th to 20th	Night	64% 4 13% 12% 6% 1	4870
	21st to end	Night	72% 4 10% 9% 5%	6996

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% 17% 32% 22% 5% 1	300
	11th to 20th	Day	23% 17% 43% 13% 4 1	300
	21st to end	Day	28% 12% 31% 23% 4 1	300
February	1st to 10th	Day	26% 17% 37% 15% 3 1	270
	11th to 20th	Day	22% 17% 37% 20% 4	270
	21st to end	Day	28% 16% 41% 12% 2	225
March	1st to 10th	Day	25% 15% 35% 18% 7% 1	308
	11th to 20th	Day	25% 10% 36% 20% 7% 1	460
	21st to end	Day	31% 12% 32% 18% 7%	506
April	1st to 10th	Day	20% 13% 32% 22% 12% 1	460
	11th to 20th	Day	20% 16% 32% 19% 9% 4	452
	21st to end	Day	25% 9% 32% 23% 8% 2	460
May	1st to 10th	Day	23% 8% 33% 21% 12% 3	463
	11th to 20th	Day	20% 9% 25% 25% 14% 7%	487
	21st to end	Day	12% 6% 24% 28% 19% 11%	529
June	1st to 10th	Day	13% 7% 27% 30% 18% 6%	596
	11th to 20th	Day	12% 5% 29% 29% 20% 5%	680
	21st to end	Day	12% 7% 26% 31% 18% 6%	680
July	1st to 10th	Day	12% 3 19% 32% 21% 14%	671
	11th to 20th	Day	9% 5% 22% 31% 21% 12%	659
	21st to end	Day	10% 3 21% 26% 27% 13%	532
August	1st to 10th	Day	12% 3 13% 29% 25% 17%	486
	11th to 20th	Day	12% 3 16% 32% 25% 12%	479
	21st to end	Day	9% 3 17% 29% 28% 15%	539
September	1st to 10th	Day	16% 4 15% 29% 23% 13%	490
	11th to 20th	Day	9% 2 13% 26% 30% 19%	490
	21st to end	Day	19% 9% 21% 23% 19% 9%	490
October	1st to 10th	Day	13% 7% 23% 27% 20% 9%	490
	11th to 20th	Day	19% 13% 30% 23% 12% 3	490
	21st to end	Day	23% 11% 35% 22% 7% 1	397
November	1st to 10th	Day	13% 13% 36% 22% 12% 4	300
	11th to 20th	Day	25% 16% 31% 20% 7% 1	300
	21st to end	Day	27% 13% 37% 19% 4	300
December	1st to 10th	Day	22% 17% 35% 17% 9%	300
	11th to 20th	Day	22% 20% 35% 19% 4 1	300
	21st to end	Day	28% 16% 34% 18% 3	330
January	1st to 10th	Night	24% 14% 35% 21% 6%	1000
	11th to 20th	Night	28% 13% 36% 18% 4 1	960
	21st to end	Night	24% 13% 34% 24% 5%	841
February	1st to 10th	Night	26% 12% 34% 24% 4	760
	11th to 20th	Night	23% 12% 37% 25% 3	743
	21st to end	Night	27% 14% 37% 19% 3	628
March	1st to 10th	Night	22% 10% 32% 29% 7%	760
	11th to 20th	Night	18% 13% 36% 25% 7% 1	760
	21st to end	Night	24% 10% 31% 27% 8%	836
April	1st to 10th	Night	21% 11% 37% 26% 4 1	656
	11th to 20th	Night	23% 9% 33% 26% 8% 1	563
	21st to end	Night	22% 6% 34% 28% 9% 1	570
May	1st to 10th	Night	20% 6% 29% 34% 10% 1	570
	11th to 20th	Night	20% 6% 26% 31% 16% 1	561
	21st to end	Night	11% 3 24% 39% 21% 3	617
June	1st to 10th	Night	12% 5% 22% 44% 17%	570
	11th to 20th	Night	12% 3 22% 44% 18% 2	570
	21st to end	Night	11% 2 24% 40% 21% 2	570
July	1st to 10th	Night	10% 1 16% 41% 28% 4	555
	11th to 20th	Night	8% 3 18% 42% 24% 5%	552
	21st to end	Night	7% 3 12% 44% 32% 2	624
August	1st to 10th	Night	9% 2 12% 41% 32% 4	567
	11th to 20th	Night	11% 1 15% 38% 32% 4	564
	21st to end	Night	8% 2 12% 38% 35% 5%	627
September	1st to 10th	Night	14% 4 14% 33% 29% 5%	684
	11th to 20th	Night	9% 3 13% 35% 34% 5%	760
	21st to end	Night	16% 5% 20% 33% 22% 3	760
October	1st to 10th	Night	14% 5% 24% 33% 21% 2	760
	11th to 20th	Night	20% 11% 29% 28% 11% 1	760
	21st to end	Night	24% 10% 30% 27% 9%	836
November	1st to 10th	Night	17% 10% 33% 28% 11% 1	780
	11th to 20th	Night	24% 13% 31% 24% 7% 1	800
	21st to end	Night	26% 12% 32% 24% 6%	800
December	1st to 10th	Night	25% 13% 34% 22% 6%	800
	11th to 20th	Night	27% 11% 34% 24% 4	820
	21st to end	Night	31% 11% 31% 23% 3	1100

Page generated at 2025-01-19 03:06:50. Version ac07

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