Sandusky
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sandusky 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 5% 7% 33%	131688
	Night	14% 11% 4 9% 5% 5% 4 4 5% 7% 32%	131139
Transparency	Day	32% 38% 8% 14% 8% 1	135299
	Night	34% 37% 7% 13% 8% 1	135598
Seeing	Day	16% 5% 19% 31% 22% 7%	17198
	Night	19% 7% 24% 30% 17% 3	27191

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% 17% 7% 19% 6% 4 4 3 6% 5% 13%	4705
	11th to 20th	Day	12% 17% 7% 16% 10% 6% 6% 3 4 4 15%	5280
	21st to end	Day	18% 15% 8% 14% 7% 6% 6% 3 4 5% 15%	5780
February	1st to 10th	Day	16% 16% 5% 12% 7% 5% 4 4 4 6% 21%	1890
	11th to 20th	Day	14% 13% 6% 13% 8% 5% 5% 4 4 5% 23%	1972
	21st to end	Day	17% 12% 4 11% 6% 4 5% 4 5% 6% 26%	1730
March	1st to 10th	Day	17% 12% 6% 12% 5% 4 4 3 4 5% 29%	4786
	11th to 20th	Day	10% 11% 3 9% 5% 4 5% 3 5% 7% 37%	5090
	21st to end	Day	16% 13% 5% 10% 5% 5% 5% 3 5% 6% 27%	5586
April	1st to 10th	Day	14% 11% 4 9% 6% 5% 4 4 6% 6% 31%	2371
	11th to 20th	Day	16% 9% 3 8% 6% 5% 4 4 5% 7% 35%	2685
	21st to end	Day	18% 10% 2 7% 5% 3 4 4 5% 7% 35%	2730
May	1st to 10th	Day	21% 9% 3 8% 5% 5% 4 3 5% 6% 32%	5992
	11th to 20th	Day	17% 9% 2 7% 5% 5% 5% 4 6% 7% 35%	5939
	21st to end	Day	15% 6% 2 6% 5% 4 5% 4 6% 8% 38%	6433
June	1st to 10th	Day	12% 6% 3 6% 5% 5% 5% 4 6% 8% 40%	2600
	11th to 20th	Day	10% 6% 2 6% 5% 5% 6% 4 6% 8% 42%	2797
	21st to end	Day	9% 5% 2 6% 4 5% 6% 4 7% 10% 41%	2800
July	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 7% 9% 44%	6360
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 7% 10% 43%	6089
	21st to end	Day	9% 6% 2 7% 5% 4 5% 4 6% 10% 43%	6424
August	1st to 10th	Day	10% 6% 2 5% 4 4 5% 4 6% 9% 44%	4234
	11th to 20th	Day	9% 5% 2 5% 4 5% 6% 5% 8% 10% 40%	4174
	21st to end	Day	9% 5% 2 7% 4 4 6% 4 7% 10% 42%	4675
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 5% 7% 47%	2220
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 3 6% 9% 46%	2200
	21st to end	Day	17% 7% 2 7% 3 4 4 3 5% 7% 40%	2200
October	1st to 10th	Day	12% 7% 2 7% 4 4 4 3 6% 8% 43%	2120
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 4 5% 6% 38%	2000
	21st to end	Day	19% 9% 3 7% 5% 4 6% 4 6% 7% 30%	2111
November	1st to 10th	Day	11% 10% 4 8% 5% 4 4 4 6% 7% 37%	1852
	11th to 20th	Day	16% 14% 4 8% 5% 4 4 3 4 6% 31%	1890
	21st to end	Day	17% 15% 6% 10% 5% 4 4 5% 6% 6% 22%	1799
December	1st to 10th	Day	15% 15% 7% 13% 7% 5% 4 4 5% 6% 21%	2680
	11th to 20th	Day	19% 19% 6% 11% 5% 4 4 3 4 6% 18%	3094
	21st to end	Day	24% 19% 7% 12% 7% 5% 4 3 3 4 13%	4400
January	1st to 10th	Night	15% 16% 7% 19% 7% 5% 4 3 4 5% 16%	8193
	11th to 20th	Night	9% 16% 8% 17% 8% 6% 6% 4 5% 5% 17%	7680
	21st to end	Night	18% 15% 6% 11% 5% 4 4 4 4 6% 23%	8401
February	1st to 10th	Night	18% 14% 4 12% 7% 5% 5% 4 5% 5% 24%	2730
	11th to 20th	Night	15% 14% 5% 12% 6% 5% 5% 4 5% 6% 23%	2529
	21st to end	Night	19% 13% 4 11% 6% 5% 4 3 4 6% 26%	2076
March	1st to 10th	Night	18% 12% 4 7% 4 4 3 3 4 6% 34%	5273
	11th to 20th	Night	11% 8% 2 5% 5% 5% 5% 4 6% 8% 41%	5090
	21st to end	Night	15% 10% 3 9% 5% 5% 4 3 5% 6% 34%	5588
April	1st to 10th	Night	16% 13% 3 7% 6% 4 4 4 5% 7% 32%	2267
	11th to 20th	Night	14% 10% 2 8% 4 4 4 5% 5% 6% 36%	1883
	21st to end	Night	16% 8% 3 7% 5% 4 4 5% 6% 6% 36%	1890
May	1st to 10th	Night	20% 10% 4 9% 6% 4 5% 4 4 7% 28%	4123
	11th to 20th	Night	15% 7% 3 7% 4 4 4 4 5% 8% 37%	4086
	21st to end	Night	14% 6% 2 6% 4 5% 5% 4 6% 8% 40%	4421
June	1st to 10th	Night	10% 6% 3 6% 4 4 5% 4 6% 7% 45%	1797
	11th to 20th	Night	9% 6% 2 6% 5% 4 4 5% 8% 10% 41%	1600
	21st to end	Night	10% 5% 2 5% 4 4 5% 4 6% 11% 45%	1600
July	1st to 10th	Night	8% 5% 2 6% 5% 5% 5% 4 6% 10% 44%	3618
	11th to 20th	Night	9% 5% 2 6% 5% 4 5% 5% 7% 9% 43%	3873
	21st to end	Night	8% 5% 2 7% 4 4 5% 4 6% 9% 47%	4427
August	1st to 10th	Night	12% 5% 3 7% 5% 4 4 3 6% 9% 41%	2915
	11th to 20th	Night	9% 6% 2 6% 4 5% 4 4 6% 7% 47%	2875
	21st to end	Night	6% 4 2 6% 5% 6% 6% 4 7% 7% 46%	3223
September	1st to 10th	Night	11% 6% 1 6% 4 4 4 3 5% 7% 48%	2156
	11th to 20th	Night	9% 5% 2 5% 4 5% 4 3 5% 7% 52%	2200
	21st to end	Night	14% 7% 3 7% 5% 4 4 3 5% 7% 41%	2200
October	1st to 10th	Night	12% 6% 3 6% 4 3 4 4 5% 7% 46%	2279
	11th to 20th	Night	18% 9% 2 7% 5% 4 4 3 5% 7% 37%	2400
	21st to end	Night	22% 8% 2 7% 5% 4 4 4 5% 5% 33%	2725
November	1st to 10th	Night	13% 10% 4 7% 5% 4 4 3 5% 6% 39%	2666
	11th to 20th	Night	16% 13% 4 9% 5% 4 4 4 5% 7% 29%	2730
	21st to end	Night	21% 14% 5% 8% 5% 4 5% 3 5% 6% 23%	2815
December	1st to 10th	Night	13% 15% 7% 12% 7% 6% 5% 4 5% 5% 22%	4720
	11th to 20th	Night	17% 18% 7% 11% 5% 4 4 4 5% 5% 21%	5298
	21st to end	Night	24% 19% 6% 11% 6% 4 4 3 5% 6% 13%	6792

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	57% 25% 8% 8% 2	4706
	11th to 20th	Day	58% 21% 8% 5% 8% 1	5280
	21st to end	Day	53% 25% 7% 10% 4	5780
February	1st to 10th	Day	26% 60% 4 7% 2	1890
	11th to 20th	Day	25% 58% 5% 9% 3	1981
	21st to end	Day	21% 60% 7% 8% 4 1	1730
March	1st to 10th	Day	40% 30% 7% 15% 7%	4786
	11th to 20th	Day	31% 31% 13% 20% 5% 1	5090
	21st to end	Day	38% 32% 9% 12% 9%	5586
April	1st to 10th	Day	23% 60% 5% 7% 4	2371
	11th to 20th	Day	20% 60% 5% 8% 5% 1	2685
	21st to end	Day	20% 59% 6% 9% 5% 1	2730
May	1st to 10th	Day	39% 31% 7% 13% 10% 1	6027
	11th to 20th	Day	34% 32% 12% 16% 6% 1	5943
	21st to end	Day	31% 32% 7% 16% 11% 3	6447
June	1st to 10th	Day	17% 62% 4 11% 5% 1	2600
	11th to 20th	Day	17% 63% 5% 8% 5% 1	2797
	21st to end	Day	13% 61% 8% 11% 6% 1	2800
July	1st to 10th	Day	27% 28% 9% 23% 12% 1	6291
	11th to 20th	Day	25% 28% 13% 21% 13% 1	6015
	21st to end	Day	27% 28% 10% 17% 16% 2	6240
August	1st to 10th	Day	23% 38% 11% 17% 10%	4221
	11th to 20th	Day	24% 39% 8% 23% 6%	4213
	21st to end	Day	23% 38% 12% 21% 6%	4674
September	1st to 10th	Day	13% 57% 9% 13% 7% 1	2220
	11th to 20th	Day	13% 59% 4 15% 9%	2200
	21st to end	Day	18% 58% 5% 11% 8%	2200
October	1st to 10th	Day	13% 37% 11% 24% 15%	3458
	11th to 20th	Day	24% 39% 5% 16% 15%	3240
	21st to end	Day	25% 37% 8% 17% 13%	3387
November	1st to 10th	Day	25% 54% 5% 10% 4	1852
	11th to 20th	Day	25% 54% 5% 10% 4 1	1890
	21st to end	Day	31% 55% 6% 7% 2	1799
December	1st to 10th	Day	44% 37% 10% 7% 2	2680
	11th to 20th	Day	50% 32% 9% 8% 1	3090
	21st to end	Day	58% 27% 5% 6% 4	4400
January	1st to 10th	Night	59% 23% 6% 9% 3	8194
	11th to 20th	Night	55% 22% 8% 8% 7% 1	7680
	21st to end	Night	48% 23% 10% 11% 7%	8401
February	1st to 10th	Night	27% 60% 4 6% 3	2730
	11th to 20th	Night	25% 59% 4 8% 4	2531
	21st to end	Night	24% 60% 4 8% 4	2076
March	1st to 10th	Night	37% 29% 10% 15% 7% 1	5273
	11th to 20th	Night	27% 30% 12% 22% 8% 1	5090
	21st to end	Night	34% 30% 8% 15% 12% 1	5588
April	1st to 10th	Night	25% 59% 4 8% 3	2267
	11th to 20th	Night	22% 60% 4 7% 6% 1	1883
	21st to end	Night	18% 60% 5% 10% 6% 1	1890
May	1st to 10th	Night	42% 31% 6% 10% 9% 2	4150
	11th to 20th	Night	32% 32% 9% 19% 8%	4087
	21st to end	Night	30% 31% 10% 16% 12% 1	4429
June	1st to 10th	Night	15% 63% 4 10% 7%	1797
	11th to 20th	Night	17% 62% 4 10% 5% 1	1600
	21st to end	Night	14% 62% 5% 12% 7% 1	1600
July	1st to 10th	Night	25% 29% 12% 19% 11% 4	3580
	11th to 20th	Night	28% 29% 11% 20% 10% 2	3827
	21st to end	Night	25% 27% 10% 18% 18% 3	4297
August	1st to 10th	Night	28% 38% 8% 15% 10% 1	2904
	11th to 20th	Night	24% 38% 6% 23% 9%	2902
	21st to end	Night	23% 39% 8% 20% 8% 1	3223
September	1st to 10th	Night	14% 58% 7% 13% 6% 1	2156
	11th to 20th	Night	12% 57% 5% 13% 11% 1	2200
	21st to end	Night	19% 57% 4 10% 9%	2200
October	1st to 10th	Night	14% 36% 5% 23% 21%	3721
	11th to 20th	Night	25% 36% 7% 17% 14%	3899
	21st to end	Night	22% 37% 5% 21% 13% 2	4399
November	1st to 10th	Night	27% 53% 5% 9% 5% 1	2666
	11th to 20th	Night	25% 55% 4 9% 6% 1	2730
	21st to end	Night	31% 55% 6% 7% 2	2815
December	1st to 10th	Night	43% 37% 8% 10% 3	4720
	11th to 20th	Night	46% 33% 10% 9% 2	5301
	21st to end	Night	55% 28% 8% 7% 2	6792

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	21% 11% 28% 31% 8% 1	330
	11th to 20th	Day	23% 11% 38% 22% 6%	330
	21st to end	Day	24% 7% 32% 27% 9% 1	363
February	1st to 10th	Day	22% 5% 31% 33% 8% 1	330
	11th to 20th	Day	20% 8% 35% 29% 8%	330
	21st to end	Day	18% 7% 40% 30% 5%	273
March	1st to 10th	Day	20% 5% 29% 35% 11%	419
	11th to 20th	Day	18% 8% 32% 32% 9% 2	540
	21st to end	Day	23% 6% 28% 34% 8% 1	594
April	1st to 10th	Day	18% 6% 26% 38% 11% 1	540
	11th to 20th	Day	20% 5% 27% 33% 12% 4	532
	21st to end	Day	20% 5% 24% 33% 17% 2	540
May	1st to 10th	Day	22% 4 20% 33% 17% 4	543
	11th to 20th	Day	16% 4 19% 32% 24% 5%	551
	21st to end	Day	12% 2 13% 31% 32% 10%	573
June	1st to 10th	Day	12% 4 13% 36% 28% 6%	530
	11th to 20th	Day	12% 2 13% 38% 29% 6%	727
	21st to end	Day	11% 4 13% 35% 31% 7%	730
July	1st to 10th	Day	10% 2 7% 32% 34% 15%	721
	11th to 20th	Day	9% 2 9% 32% 36% 12%	604
	21st to end	Day	8% 4 8% 31% 39% 11%	576
August	1st to 10th	Day	10% 2 7% 28% 38% 15%	526
	11th to 20th	Day	10% 2 8% 31% 36% 12%	519
	21st to end	Day	8% 3 7% 32% 35% 14%	583
September	1st to 10th	Day	13% 2 11% 22% 35% 16%	530
	11th to 20th	Day	10% 3 7% 23% 39% 19%	530
	21st to end	Day	20% 5% 15% 22% 28% 10%	530
October	1st to 10th	Day	12% 5% 15% 29% 28% 12%	530
	11th to 20th	Day	20% 7% 21% 32% 16% 4	530
	21st to end	Day	24% 10% 27% 26% 12% 3	494
November	1st to 10th	Day	13% 8% 26% 29% 19% 5%	330
	11th to 20th	Day	23% 16% 23% 26% 10% 2	330
	21st to end	Day	25% 9% 29% 31% 5%	281
December	1st to 10th	Day	20% 10% 33% 28% 8% 1	220
	11th to 20th	Day	20% 11% 39% 23% 6%	226
	21st to end	Day	27% 10% 29% 28% 6%	363
January	1st to 10th	Night	25% 11% 35% 22% 7%	1037
	11th to 20th	Night	26% 11% 35% 23% 5%	840
	21st to end	Night	25% 9% 33% 27% 6% 1	924
February	1st to 10th	Night	22% 8% 33% 30% 7%	840
	11th to 20th	Night	21% 8% 34% 33% 4	823
	21st to end	Night	25% 8% 36% 26% 4	692
March	1st to 10th	Night	22% 5% 32% 31% 10%	840
	11th to 20th	Night	18% 7% 35% 30% 9% 2	840
	21st to end	Night	21% 6% 27% 33% 11% 1	924
April	1st to 10th	Night	21% 9% 27% 32% 10% 1	797
	11th to 20th	Night	18% 7% 26% 35% 12% 3	623
	21st to end	Night	21% 3 23% 36% 15% 1	630
May	1st to 10th	Night	19% 5% 20% 37% 15% 3	630
	11th to 20th	Night	22% 4 16% 31% 22% 4	609
	21st to end	Night	11% 3 12% 33% 32% 9%	650
June	1st to 10th	Night	13% 3 15% 38% 28% 4	600
	11th to 20th	Night	10% 2 14% 40% 31% 4	600
	21st to end	Night	9% 3 16% 36% 31% 5%	600
July	1st to 10th	Night	10% 2 9% 36% 34% 9%	585
	11th to 20th	Night	9% 2 12% 35% 33% 9%	582
	21st to end	Night	9% 2 9% 37% 39% 4	657
August	1st to 10th	Night	10% 2 8% 38% 34% 8%	597
	11th to 20th	Night	11% 1 10% 33% 35% 9%	594
	21st to end	Night	9% 3 12% 30% 38% 9%	660
September	1st to 10th	Night	13% 4 12% 30% 33% 9%	765
	11th to 20th	Night	11% 3 11% 28% 37% 11%	800
	21st to end	Night	17% 6% 16% 31% 24% 7%	800
October	1st to 10th	Night	16% 5% 18% 30% 24% 7%	800
	11th to 20th	Night	25% 9% 24% 27% 13% 2	800
	21st to end	Night	28% 10% 25% 28% 9% 1	880
November	1st to 10th	Night	20% 10% 26% 29% 13% 2	820
	11th to 20th	Night	25% 13% 30% 22% 8% 2	840
	21st to end	Night	30% 12% 29% 24% 6%	840
December	1st to 10th	Night	26% 13% 31% 23% 6%	840
	11th to 20th	Night	25% 11% 37% 22% 5% 1	840
	21st to end	Night	30% 11% 29% 25% 5%	992

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

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