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 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 5% 7% 33%	105002
	Night	15% 11% 4 8% 5% 4 4 4 5% 7% 32%	104309
Transparency	Day	27% 46% 7% 12% 7% 1	108657
	Night	29% 45% 6% 12% 6% 1	108793
Seeing	Day	16% 5% 19% 30% 22% 7%	15443
	Night	20% 7% 23% 30% 17% 3	25445

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	19% 17% 8% 14% 6% 5% 4 3 6% 5% 13%	2609
	11th to 20th	Day	15% 20% 8% 15% 7% 6% 7% 3 4 4 12%	2930
	21st to end	Day	26% 19% 10% 12% 6% 5% 3 2 4 3 10%	3133
February	1st to 10th	Day	16% 16% 5% 11% 7% 5% 4 4 4 6% 21%	1710
	11th to 20th	Day	14% 12% 5% 13% 8% 5% 5% 4 4 5% 24%	1779
	21st to end	Day	18% 12% 3 10% 6% 4 5% 4 5% 6% 26%	1570
March	1st to 10th	Day	21% 14% 5% 10% 5% 4 3 3 4 5% 27%	3266
	11th to 20th	Day	12% 12% 4 9% 6% 5% 5% 3 5% 6% 35%	3480
	21st to end	Day	19% 12% 5% 10% 5% 4 4 3 5% 5% 28%	3815
April	1st to 10th	Day	12% 11% 4 9% 6% 6% 4 4 6% 6% 31%	2145
	11th to 20th	Day	17% 9% 3 7% 6% 5% 4 4 5% 7% 35%	2427
	21st to end	Day	19% 10% 2 7% 5% 3 3 4 5% 7% 35%	2470
May	1st to 10th	Day	18% 8% 3 8% 6% 5% 5% 4 5% 6% 33%	4082
	11th to 20th	Day	17% 8% 2 6% 5% 4 5% 4 6% 7% 35%	4081
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 5% 7% 8% 42%	4476
June	1st to 10th	Day	12% 6% 3 7% 5% 5% 6% 5% 6% 8% 40%	2470
	11th to 20th	Day	10% 5% 2 5% 5% 5% 6% 4 7% 8% 43%	2657
	21st to end	Day	10% 5% 2 6% 4 5% 6% 4 7% 10% 41%	2660
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 7% 9% 41%	4440
	11th to 20th	Day	7% 4 1 5% 4 4 5% 5% 7% 10% 48%	4253
	21st to end	Day	7% 6% 2 7% 5% 5% 6% 4 6% 9% 43%	4466
August	1st to 10th	Day	10% 7% 2 5% 4 4 5% 4 6% 9% 44%	4104
	11th to 20th	Day	9% 5% 2 5% 4 5% 6% 5% 8% 10% 40%	4044
	21st to end	Day	9% 5% 2 7% 4 4 6% 4 7% 10% 42%	4532
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 4 5% 7% 46%	2109
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 3 6% 9% 45%	2090
	21st to end	Day	18% 7% 2 7% 4 4 4 3 5% 7% 39%	2090
October	1st to 10th	Day	13% 7% 2 7% 4 4 4 3 6% 8% 42%	2014
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 4 5% 6% 37%	1900
	21st to end	Day	19% 10% 3 7% 5% 4 6% 3 6% 7% 29%	2006
November	1st to 10th	Day	11% 10% 3 8% 5% 4 5% 4 6% 7% 38%	1762
	11th to 20th	Day	16% 15% 4 8% 5% 4 4 3 5% 6% 31%	1800
	21st to end	Day	17% 15% 5% 10% 5% 4 4 5% 6% 6% 22%	1714
December	1st to 10th	Day	15% 15% 6% 13% 7% 5% 4 4 5% 6% 21%	2600
	11th to 20th	Day	19% 19% 6% 11% 5% 4 4 3 4 6% 18%	3013
	21st to end	Day	24% 19% 7% 12% 7% 5% 4 3 3 4 13%	4305
January	1st to 10th	Night	17% 19% 7% 12% 6% 4 4 3 4 5% 19%	4556
	11th to 20th	Night	14% 19% 8% 16% 6% 5% 6% 5% 5% 4 12%	4250
	21st to end	Night	27% 19% 8% 11% 5% 4 3 3 3 3 14%	4546
February	1st to 10th	Night	18% 14% 4 11% 7% 5% 4 4 5% 5% 23%	2470
	11th to 20th	Night	15% 15% 5% 11% 5% 5% 5% 4 4 6% 25%	2283
	21st to end	Night	20% 13% 3 11% 6% 5% 4 3 4 5% 26%	1884
March	1st to 10th	Night	20% 13% 4 6% 4 4 3 3 4 5% 34%	3587
	11th to 20th	Night	12% 10% 2 5% 5% 5% 4 4 5% 7% 40%	3480
	21st to end	Night	17% 10% 3 8% 5% 4 4 3 5% 7% 34%	3817
April	1st to 10th	Night	15% 13% 3 7% 6% 4 4 4 5% 7% 33%	2051
	11th to 20th	Night	16% 10% 2 8% 4 4 4 5% 5% 6% 36%	1701
	21st to end	Night	16% 8% 3 7% 5% 4 4 5% 6% 6% 36%	1710
May	1st to 10th	Night	20% 8% 4 8% 5% 5% 4 4 4 8% 30%	2813
	11th to 20th	Night	17% 7% 3 6% 5% 4 5% 4 6% 8% 36%	2812
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 9% 47%	3079
June	1st to 10th	Night	10% 6% 3 6% 4 4 5% 4 6% 8% 45%	1707
	11th to 20th	Night	8% 6% 2 6% 5% 4 4 5% 8% 10% 42%	1520
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 11% 44%	1520
July	1st to 10th	Night	9% 5% 2 5% 5% 4 4 4 6% 10% 46%	2530
	11th to 20th	Night	8% 4 2 5% 4 4 4 5% 7% 10% 48%	2708
	21st to end	Night	6% 5% 2 7% 4 5% 6% 5% 7% 10% 45%	3087
August	1st to 10th	Night	13% 6% 3 7% 5% 4 4 3 6% 9% 41%	2825
	11th to 20th	Night	9% 6% 2 6% 4 5% 4 4 6% 7% 47%	2785
	21st to end	Night	7% 4 2 6% 5% 6% 6% 4 7% 7% 46%	3124
September	1st to 10th	Night	12% 6% 1 6% 4 4 4 3 5% 8% 47%	2048
	11th to 20th	Night	9% 5% 2 6% 4 5% 4 3 5% 7% 50%	2090
	21st to end	Night	15% 7% 2 7% 5% 4 4 3 5% 7% 40%	2090
October	1st to 10th	Night	13% 6% 3 6% 4 3 4 4 5% 7% 44%	2165
	11th to 20th	Night	19% 9% 2 7% 5% 4 3 3 4 7% 36%	2280
	21st to end	Night	22% 9% 3 7% 5% 5% 4 4 5% 5% 32%	2589
November	1st to 10th	Night	13% 10% 4 7% 4 5% 4 3 5% 6% 38%	2536
	11th to 20th	Night	16% 13% 4 9% 5% 5% 4 4 5% 7% 28%	2600
	21st to end	Night	21% 14% 5% 8% 5% 4 5% 3 5% 6% 24%	2681
December	1st to 10th	Night	13% 15% 7% 12% 7% 6% 5% 4 5% 5% 22%	4580
	11th to 20th	Night	18% 18% 7% 10% 5% 4 4 4 5% 6% 21%	5159
	21st to end	Night	25% 19% 6% 10% 6% 4 4 3 5% 6% 12%	6646

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	47% 40% 6% 6% 2	2610
	11th to 20th	Day	54% 36% 5% 3 2	2930
	21st to end	Day	50% 42% 3 3 2	3133
February	1st to 10th	Day	23% 65% 4 6% 2	1710
	11th to 20th	Day	21% 64% 4 9% 3	1788
	21st to end	Day	17% 66% 6% 7% 3 1	1570
March	1st to 10th	Day	36% 43% 5% 13% 3	3266
	11th to 20th	Day	27% 43% 11% 16% 3	3480
	21st to end	Day	31% 45% 9% 8% 6%	3815
April	1st to 10th	Day	20% 65% 5% 6% 3	2145
	11th to 20th	Day	17% 66% 5% 7% 5% 1	2427
	21st to end	Day	17% 65% 5% 7% 4 1	2470
May	1st to 10th	Day	30% 43% 7% 14% 5% 1	4120
	11th to 20th	Day	27% 43% 11% 16% 3	4085
	21st to end	Day	21% 44% 7% 11% 13% 4	4489
June	1st to 10th	Day	15% 66% 4 10% 5%	2470
	11th to 20th	Day	15% 66% 5% 7% 6% 1	2657
	21st to end	Day	12% 64% 7% 10% 6% 1	2660
July	1st to 10th	Day	26% 38% 9% 15% 10% 2	4371
	11th to 20th	Day	18% 38% 10% 21% 13% 1	4179
	21st to end	Day	23% 38% 11% 11% 15% 2	4324
August	1st to 10th	Day	23% 39% 10% 17% 10%	4091
	11th to 20th	Day	23% 40% 8% 23% 6%	4083
	21st to end	Day	23% 40% 11% 20% 6% 1	4531
September	1st to 10th	Day	13% 60% 9% 11% 6% 1	2109
	11th to 20th	Day	13% 61% 4 12% 8%	2090
	21st to end	Day	17% 61% 4 10% 7%	2090
October	1st to 10th	Day	13% 38% 12% 23% 14%	3352
	11th to 20th	Day	25% 40% 5% 15% 15%	3140
	21st to end	Day	24% 38% 8% 17% 13%	3282
November	1st to 10th	Day	24% 57% 5% 9% 4	1762
	11th to 20th	Day	24% 57% 4 9% 5%	1800
	21st to end	Day	30% 57% 6% 6% 2	1714
December	1st to 10th	Day	43% 38% 10% 7% 1	2600
	11th to 20th	Day	49% 33% 9% 8% 1	3009
	21st to end	Day	57% 28% 5% 7% 3	4305
January	1st to 10th	Night	45% 39% 5% 8% 3	4556
	11th to 20th	Night	52% 37% 5% 4 1	4250
	21st to end	Night	50% 40% 4 3 2	4546
February	1st to 10th	Night	24% 66% 4 5% 2	2470
	11th to 20th	Night	21% 65% 3 8% 3	2285
	21st to end	Night	21% 66% 2 8% 3	1884
March	1st to 10th	Night	33% 41% 7% 14% 5%	3587
	11th to 20th	Night	23% 43% 13% 14% 7% 1	3480
	21st to end	Night	28% 43% 8% 16% 6%	3817
April	1st to 10th	Night	21% 65% 4 7% 3	2051
	11th to 20th	Night	18% 66% 4 6% 5% 1	1701
	21st to end	Night	15% 66% 5% 8% 5% 1	1710
May	1st to 10th	Night	31% 43% 5% 13% 7% 1	2840
	11th to 20th	Night	27% 44% 8% 16% 5%	2813
	21st to end	Night	18% 42% 8% 15% 15% 1	3087
June	1st to 10th	Night	14% 66% 3 10% 6%	1707
	11th to 20th	Night	16% 65% 3 9% 5% 1	1520
	21st to end	Night	13% 65% 4 11% 6% 1	1520
July	1st to 10th	Night	21% 38% 9% 18% 9% 5%	2490
	11th to 20th	Night	20% 39% 10% 19% 10% 3	2659
	21st to end	Night	21% 38% 11% 15% 12% 3	2988
August	1st to 10th	Night	28% 39% 8% 15% 9% 1	2814
	11th to 20th	Night	24% 40% 6% 22% 8%	2812
	21st to end	Night	23% 40% 8% 19% 8% 1	3124
September	1st to 10th	Night	14% 61% 7% 11% 6% 1	2048
	11th to 20th	Night	13% 60% 5% 11% 10% 1	2090
	21st to end	Night	18% 60% 4 10% 8%	2090
October	1st to 10th	Night	14% 37% 5% 23% 20%	3607
	11th to 20th	Night	25% 38% 7% 17% 14%	3779
	21st to end	Night	22% 38% 5% 21% 12% 2	4263
November	1st to 10th	Night	26% 56% 5% 8% 4 1	2536
	11th to 20th	Night	24% 58% 3 8% 6% 1	2600
	21st to end	Night	29% 57% 6% 7% 1	2681
December	1st to 10th	Night	42% 38% 8% 10% 3	4580
	11th to 20th	Night	45% 34% 10% 9% 2	5162
	21st to end	Night	55% 28% 8% 7% 2	6646

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	22% 11% 27% 30% 8% 1	300
	11th to 20th	Day	24% 10% 37% 23% 7%	300
	21st to end	Day	26% 7% 30% 26% 10% 1	300
February	1st to 10th	Day	24% 6% 30% 33% 8%	270
	11th to 20th	Day	20% 8% 37% 28% 7%	270
	21st to end	Day	21% 7% 38% 28% 5%	225
March	1st to 10th	Day	22% 6% 28% 33% 12%	351
	11th to 20th	Day	18% 8% 31% 32% 10% 2	460
	21st to end	Day	25% 6% 28% 32% 8% 1	506
April	1st to 10th	Day	15% 5% 26% 39% 12% 2	460
	11th to 20th	Day	21% 5% 26% 33% 11% 5%	452
	21st to end	Day	21% 5% 24% 32% 16% 2	460
May	1st to 10th	Day	21% 5% 19% 33% 18% 4	463
	11th to 20th	Day	17% 4 18% 31% 24% 6%	487
	21st to end	Day	11% 2 12% 30% 34% 11%	529
June	1st to 10th	Day	12% 4 13% 36% 29% 7%	490
	11th to 20th	Day	11% 3 12% 38% 30% 7%	677
	21st to end	Day	11% 4 13% 35% 30% 6%	680
July	1st to 10th	Day	11% 1 8% 31% 34% 15%	671
	11th to 20th	Day	9% 2 9% 32% 36% 13%	560
	21st to end	Day	8% 3 8% 32% 38% 11%	532
August	1st to 10th	Day	11% 2 8% 28% 36% 15%	486
	11th to 20th	Day	10% 3 8% 33% 35% 12%	479
	21st to end	Day	9% 4 7% 31% 35% 14%	539
September	1st to 10th	Day	14% 2 11% 23% 36% 14%	490
	11th to 20th	Day	10% 3 8% 24% 38% 18%	490
	21st to end	Day	21% 5% 16% 23% 26% 9%	490
October	1st to 10th	Day	12% 5% 16% 29% 27% 11%	490
	11th to 20th	Day	21% 8% 21% 30% 16% 4	490
	21st to end	Day	25% 9% 25% 25% 13% 3	455
November	1st to 10th	Day	12% 8% 26% 29% 20% 6%	300
	11th to 20th	Day	23% 14% 24% 26% 10% 2	300
	21st to end	Day	27% 7% 30% 30% 5%	256
December	1st to 10th	Day	19% 12% 33% 27% 9% 1	200
	11th to 20th	Day	20% 11% 38% 24% 6%	205
	21st to end	Day	26% 10% 29% 28% 7%	330
January	1st to 10th	Night	25% 11% 35% 22% 7%	988
	11th to 20th	Night	27% 11% 33% 24% 5%	800
	21st to end	Night	26% 9% 30% 27% 6% 1	841
February	1st to 10th	Night	23% 8% 34% 29% 6% 1	760
	11th to 20th	Night	21% 8% 34% 32% 5%	743
	21st to end	Night	26% 8% 35% 26% 5%	628
March	1st to 10th	Night	22% 5% 31% 31% 10% 1	760
	11th to 20th	Night	18% 6% 34% 30% 9% 2	760
	21st to end	Night	22% 6% 26% 33% 12% 1	836
April	1st to 10th	Night	20% 8% 27% 33% 10% 1	721
	11th to 20th	Night	19% 7% 25% 34% 12% 3	563
	21st to end	Night	21% 3 24% 36% 15% 2	570
May	1st to 10th	Night	19% 5% 19% 38% 16% 3	570
	11th to 20th	Night	22% 4 15% 31% 23% 5%	561
	21st to end	Night	10% 3 12% 32% 33% 9%	617
June	1st to 10th	Night	13% 3 15% 37% 28% 4	570
	11th to 20th	Night	10% 2 14% 40% 31% 4	570
	21st to end	Night	9% 3 17% 36% 30% 4	570
July	1st to 10th	Night	10% 3 9% 35% 34% 10%	555
	11th to 20th	Night	9% 3 12% 34% 34% 8%	552
	21st to end	Night	8% 2 9% 38% 40% 4	624
August	1st to 10th	Night	10% 2 7% 39% 33% 8%	567
	11th to 20th	Night	11% 1 11% 34% 34% 9%	564
	21st to end	Night	9% 3 12% 29% 38% 9%	627
September	1st to 10th	Night	13% 4 12% 30% 32% 9%	727
	11th to 20th	Night	11% 3 11% 29% 35% 10%	760
	21st to end	Night	17% 6% 16% 31% 23% 7%	760
October	1st to 10th	Night	17% 5% 19% 29% 24% 7%	760
	11th to 20th	Night	26% 9% 24% 26% 13% 2	760
	21st to end	Night	28% 10% 24% 28% 9% 1	836
November	1st to 10th	Night	20% 10% 26% 29% 13% 2	780
	11th to 20th	Night	25% 13% 30% 22% 8% 2	800
	21st to end	Night	30% 11% 29% 24% 6%	800
December	1st to 10th	Night	26% 13% 31% 23% 7%	800
	11th to 20th	Night	25% 11% 36% 23% 5% 1	800
	21st to end	Night	30% 11% 28% 25% 5%	945

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