Oberlin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oberlin clear sky chart from 2005-11-06 to 2026-06-16.

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	15% 11% 4 9% 5% 5% 5% 4 5% 7% 32%	137728
	Night	15% 11% 4 9% 5% 5% 4 4 5% 6% 31%	134280
Transparency	Day	51% 5% 11% 20% 11% 1	141345
	Night	52% 5% 11% 19% 11% 1	138723
Seeing	Day	20% 14% 28% 22% 12% 4	17118
	Night	21% 11% 28% 27% 12% 1	26710

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	16% 19% 7% 21% 5% 4 4 2 4 5% 13%	5258
	11th to 20th	Day	12% 20% 8% 16% 9% 6% 5% 3 3 3 14%	5280
	21st to end	Day	19% 17% 8% 13% 8% 6% 5% 4 3 3 13%	5780
February	1st to 10th	Day	16% 17% 5% 13% 6% 5% 4 3 4 4 22%	1890
	11th to 20th	Day	14% 14% 7% 15% 9% 5% 4 3 4 5% 20%	1947
	21st to end	Day	17% 14% 4 13% 5% 5% 5% 4 5% 6% 24%	1730
March	1st to 10th	Day	18% 13% 6% 11% 5% 4 4 3 4 5% 28%	4852
	11th to 20th	Day	11% 12% 4 10% 5% 4 4 3 4 5% 36%	5090
	21st to end	Day	18% 13% 5% 10% 5% 4 5% 3 4 6% 27%	5586
April	1st to 10th	Day	15% 13% 4 9% 6% 4 5% 4 5% 6% 30%	2335
	11th to 20th	Day	17% 10% 3 8% 5% 5% 5% 3 4 6% 34%	2702
	21st to end	Day	18% 10% 2 8% 5% 4 4 3 5% 6% 35%	2730
May	1st to 10th	Day	20% 10% 3 8% 5% 5% 4 3 5% 6% 31%	7616
	11th to 20th	Day	15% 8% 2 7% 5% 5% 5% 4 6% 8% 35%	7626
	21st to end	Day	16% 7% 3 6% 4 4 4 4 5% 7% 37%	8391
June	1st to 10th	Day	13% 7% 3 6% 5% 5% 5% 4 6% 8% 40%	2835
	11th to 20th	Day	11% 7% 2 7% 5% 5% 5% 5% 6% 8% 39%	2959
	21st to end	Day	10% 5% 1 5% 5% 5% 5% 5% 7% 10% 41%	2847
July	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 4 6% 10% 43%	6318
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 11% 40%	5900
	21st to end	Day	11% 6% 2 7% 5% 4 5% 4 6% 9% 41%	6424
August	1st to 10th	Day	11% 7% 2 7% 4 5% 5% 3 6% 8% 41%	4234
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 5% 7% 10% 39%	4174
	21st to end	Day	9% 5% 2 7% 4 5% 5% 4 7% 10% 42%	4652
September	1st to 10th	Day	13% 5% 2 5% 4 5% 4 4 6% 7% 45%	2240
	11th to 20th	Day	10% 6% 3 6% 5% 4 5% 3 5% 9% 45%	2200
	21st to end	Day	18% 7% 2 6% 4 5% 4 4 5% 7% 39%	2200
October	1st to 10th	Day	12% 8% 2 6% 4 5% 4 4 6% 7% 41%	2099
	11th to 20th	Day	17% 8% 3 7% 3 5% 4 3 5% 6% 38%	2000
	21st to end	Day	20% 11% 3 8% 4 4 4 4 5% 7% 30%	2150
November	1st to 10th	Day	13% 11% 4 7% 4 5% 4 4 5% 7% 37%	1852
	11th to 20th	Day	16% 16% 4 7% 5% 4 4 3 4 6% 30%	1890
	21st to end	Day	16% 19% 5% 9% 5% 5% 5% 4 6% 6% 20%	1738
December	1st to 10th	Day	17% 15% 5% 13% 6% 5% 5% 4 5% 6% 20%	2680
	11th to 20th	Day	20% 20% 7% 11% 5% 4 3 3 4 5% 18%	3070
	21st to end	Day	23% 22% 7% 11% 6% 5% 4 3 4 3 11%	4453
January	1st to 10th	Night	15% 18% 8% 20% 6% 5% 4 3 4 3 14%	7635
	11th to 20th	Night	9% 19% 9% 17% 7% 6% 6% 4 4 4 14%	7680
	21st to end	Night	18% 15% 6% 12% 5% 5% 4 4 4 6% 21%	8401
February	1st to 10th	Night	19% 14% 5% 12% 7% 5% 3 4 4 5% 23%	2730
	11th to 20th	Night	16% 15% 5% 11% 6% 5% 6% 3 5% 5% 23%	2557
	21st to end	Night	18% 14% 5% 12% 6% 5% 4 3 4 5% 24%	2076
March	1st to 10th	Night	19% 13% 4 8% 4 4 4 2 4 6% 33%	5219
	11th to 20th	Night	12% 9% 3 6% 4 4 4 4 6% 7% 40%	5090
	21st to end	Night	16% 11% 4 9% 5% 4 4 3 5% 6% 33%	5588
April	1st to 10th	Night	16% 13% 3 7% 6% 4 4 3 5% 6% 32%	2301
	11th to 20th	Night	16% 9% 3 8% 5% 4 5% 4 6% 7% 33%	1867
	21st to end	Night	17% 9% 3 7% 4 4 5% 3 6% 6% 37%	1890
May	1st to 10th	Night	21% 10% 4 8% 5% 5% 5% 4 5% 6% 26%	5237
	11th to 20th	Night	15% 8% 3 6% 4 4 4 3 6% 8% 39%	5234
	21st to end	Night	16% 7% 2 6% 5% 4 5% 4 5% 7% 40%	5761
June	1st to 10th	Night	11% 6% 3 6% 4 4 5% 3 6% 7% 45%	1780
	11th to 20th	Night	9% 5% 2 7% 5% 5% 5% 5% 7% 9% 41%	1543
	21st to end	Night	9% 6% 2 5% 4 5% 5% 5% 6% 9% 44%	1543
July	1st to 10th	Night	8% 4 2 6% 4 5% 5% 4 7% 10% 44%	3652
	11th to 20th	Night	9% 4 2 6% 4 5% 5% 5% 7% 10% 43%	4057
	21st to end	Night	8% 5% 3 6% 4 4 4 4 6% 8% 47%	4427
August	1st to 10th	Night	10% 6% 3 8% 4 4 4 4 6% 8% 43%	2915
	11th to 20th	Night	9% 7% 3 7% 4 4 4 4 5% 6% 47%	2875
	21st to end	Night	7% 5% 2 6% 4 5% 6% 4 6% 8% 46%	3223
September	1st to 10th	Night	10% 5% 2 6% 5% 5% 5% 3 5% 7% 48%	2145
	11th to 20th	Night	10% 4 2 5% 3 3 3 4 5% 7% 54%	2200
	21st to end	Night	15% 7% 3 6% 5% 4 5% 4 5% 6% 41%	2200
October	1st to 10th	Night	13% 6% 2 6% 4 5% 5% 4 4 6% 46%	2300
	11th to 20th	Night	19% 8% 2 6% 5% 4 4 3 5% 7% 37%	2400
	21st to end	Night	22% 10% 3 6% 4 4 4 3 5% 6% 31%	2688
November	1st to 10th	Night	14% 9% 3 7% 4 4 4 4 6% 6% 39%	2666
	11th to 20th	Night	16% 14% 4 8% 5% 5% 4 3 5% 5% 31%	2730
	21st to end	Night	21% 16% 4 9% 5% 4 4 3 5% 6% 23%	2878
December	1st to 10th	Night	15% 16% 7% 11% 5% 5% 5% 3 5% 6% 22%	4720
	11th to 20th	Night	18% 19% 7% 11% 5% 4 4 3 4 5% 20%	5345
	21st to end	Night	23% 19% 5% 12% 5% 5% 4 3 4 5% 14%	6727

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	75% 3 10% 9% 3	5259
	11th to 20th	Day	75% 4 7% 6% 7%	5280
	21st to end	Day	77% 3 6% 11% 4	5780
February	1st to 10th	Day	65% 4 11% 14% 6%	1890
	11th to 20th	Day	67% 5% 9% 14% 5% 1	1956
	21st to end	Day	59% 6% 14% 13% 6% 1	1730
March	1st to 10th	Day	59% 4 10% 20% 7%	4852
	11th to 20th	Day	49% 6% 14% 23% 7% 1	5090
	21st to end	Day	58% 5% 9% 17% 10%	5586
April	1st to 10th	Day	53% 6% 11% 17% 11% 1	2335
	11th to 20th	Day	51% 6% 12% 17% 13% 2	2702
	21st to end	Day	50% 6% 11% 21% 10% 2	2730
May	1st to 10th	Day	53% 5% 10% 20% 11% 1	7651
	11th to 20th	Day	46% 6% 13% 23% 11% 1	7630
	21st to end	Day	45% 6% 9% 19% 17% 4	8405
June	1st to 10th	Day	41% 7% 11% 25% 15% 1	2835
	11th to 20th	Day	42% 7% 14% 21% 14% 2	2959
	21st to end	Day	36% 8% 15% 22% 17% 3	2847
July	1st to 10th	Day	38% 4 11% 29% 17% 2	6249
	11th to 20th	Day	38% 4 15% 27% 15% 1	5831
	21st to end	Day	39% 4 13% 21% 20% 2	6240
August	1st to 10th	Day	41% 6% 16% 24% 13%	4221
	11th to 20th	Day	39% 5% 13% 32% 10% 1	4213
	21st to end	Day	37% 5% 15% 29% 12% 2	4652
September	1st to 10th	Day	36% 8% 14% 21% 16% 3	2240
	11th to 20th	Day	36% 6% 14% 26% 16% 2	2200
	21st to end	Day	45% 7% 10% 20% 18%	2200
October	1st to 10th	Day	32% 5% 13% 30% 19% 1	3411
	11th to 20th	Day	44% 4 11% 21% 19% 1	3240
	21st to end	Day	42% 4 12% 24% 17% 1	3452
November	1st to 10th	Day	47% 5% 12% 23% 13% 1	1852
	11th to 20th	Day	56% 5% 10% 18% 9% 2	1890
	21st to end	Day	62% 6% 12% 14% 6%	1738
December	1st to 10th	Day	67% 4 13% 13% 3	2680
	11th to 20th	Day	70% 5% 9% 13% 4	3066
	21st to end	Day	79% 4 7% 8% 3	4453
January	1st to 10th	Night	76% 3 7% 11% 3	7636
	11th to 20th	Night	74% 3 7% 8% 6% 1	7680
	21st to end	Night	67% 3 10% 13% 7%	8401
February	1st to 10th	Night	64% 5% 11% 14% 5% 1	2730
	11th to 20th	Night	62% 6% 10% 15% 6%	2559
	21st to end	Night	62% 5% 10% 14% 7% 2	2076
March	1st to 10th	Night	55% 3 13% 20% 9%	5219
	11th to 20th	Night	41% 6% 14% 27% 10% 1	5090
	21st to end	Night	50% 6% 9% 20% 13% 1	5588
April	1st to 10th	Night	52% 6% 11% 16% 13% 2	2301
	11th to 20th	Night	48% 6% 12% 16% 15% 3	1867
	21st to end	Night	46% 6% 12% 19% 14% 3	1890
May	1st to 10th	Night	58% 5% 9% 15% 10% 3	5264
	11th to 20th	Night	43% 6% 12% 23% 15% 1	5235
	21st to end	Night	44% 5% 12% 21% 16% 3	5771
June	1st to 10th	Night	38% 6% 11% 24% 17% 4	1780
	11th to 20th	Night	36% 8% 15% 21% 18% 2	1543
	21st to end	Night	35% 8% 14% 25% 16% 2	1543
July	1st to 10th	Night	35% 4 15% 24% 17% 4	3614
	11th to 20th	Night	36% 5% 15% 27% 15% 3	4006
	21st to end	Night	34% 5% 13% 21% 25% 2	4297
August	1st to 10th	Night	39% 6% 13% 25% 15% 2	2904
	11th to 20th	Night	37% 6% 11% 31% 14% 1	2902
	21st to end	Night	34% 5% 15% 29% 14% 3	3223
September	1st to 10th	Night	35% 6% 13% 25% 16% 4	2145
	11th to 20th	Night	28% 7% 12% 29% 22% 2	2200
	21st to end	Night	43% 7% 11% 20% 18% 2	2200
October	1st to 10th	Night	32% 4 8% 30% 26% 1	3755
	11th to 20th	Night	45% 4 10% 21% 20% 1	3899
	21st to end	Night	42% 4 10% 26% 17% 2	4336
November	1st to 10th	Night	44% 6% 13% 22% 14% 2	2666
	11th to 20th	Night	55% 5% 11% 18% 9% 2	2730
	21st to end	Night	61% 5% 13% 16% 5%	2878
December	1st to 10th	Night	64% 4 11% 16% 4	4720
	11th to 20th	Night	67% 5% 11% 14% 3	5348
	21st to end	Night	73% 5% 10% 10% 2	6727

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	26% 21% 37% 11% 5% 1	330
	11th to 20th	Day	31% 29% 30% 7% 3	330
	21st to end	Day	28% 27% 29% 14% 1 1	363
February	1st to 10th	Day	30% 23% 33% 11% 3	330
	11th to 20th	Day	31% 22% 33% 12% 2	330
	21st to end	Day	27% 29% 36% 8% 1	273
March	1st to 10th	Day	26% 20% 35% 15% 4	446
	11th to 20th	Day	27% 18% 33% 17% 5%	540
	21st to end	Day	29% 17% 32% 17% 4 1	594
April	1st to 10th	Day	25% 19% 32% 17% 6% 1	540
	11th to 20th	Day	25% 20% 27% 17% 8% 3	532
	21st to end	Day	26% 14% 32% 17% 8% 2	540
May	1st to 10th	Day	27% 15% 29% 21% 6% 2	543
	11th to 20th	Day	21% 10% 32% 23% 10% 4	567
	21st to end	Day	16% 9% 26% 26% 18% 4	617
June	1st to 10th	Day	12% 9% 30% 30% 15% 3	570
	11th to 20th	Day	14% 8% 29% 31% 16% 3	639
	21st to end	Day	12% 9% 29% 30% 17% 4	730
July	1st to 10th	Day	10% 5% 22% 30% 22% 10%	705
	11th to 20th	Day	13% 5% 23% 29% 22% 8%	524
	21st to end	Day	10% 4 23% 30% 23% 9%	576
August	1st to 10th	Day	10% 5% 21% 29% 25% 10%	526
	11th to 20th	Day	13% 4 22% 28% 23% 10%	519
	21st to end	Day	11% 5% 20% 29% 23% 12%	583
September	1st to 10th	Day	14% 7% 22% 21% 23% 12%	530
	11th to 20th	Day	10% 5% 16% 27% 27% 15%	530
	21st to end	Day	21% 11% 24% 22% 14% 8%	530
October	1st to 10th	Day	12% 9% 27% 25% 20% 7%	530
	11th to 20th	Day	18% 17% 32% 23% 7% 3	530
	21st to end	Day	27% 19% 31% 18% 5%	533
November	1st to 10th	Day	21% 20% 32% 17% 8% 2	330
	11th to 20th	Day	30% 22% 28% 15% 5%	330
	21st to end	Day	33% 22% 32% 12% 1	250
December	1st to 10th	Day	24% 25% 32% 14% 3 1	220
	11th to 20th	Day	25% 26% 36% 11% 2	220
	21st to end	Day	30% 24% 32% 12% 2	338
January	1st to 10th	Night	27% 19% 32% 17% 4	840
	11th to 20th	Night	30% 21% 32% 14% 4	840
	21st to end	Night	26% 17% 34% 20% 3	924
February	1st to 10th	Night	26% 17% 32% 22% 3	840
	11th to 20th	Night	24% 18% 33% 22% 3	823
	21st to end	Night	28% 17% 35% 18% 3	692
March	1st to 10th	Night	25% 14% 34% 22% 6%	840
	11th to 20th	Night	21% 16% 33% 23% 6% 1	840
	21st to end	Night	25% 12% 31% 25% 8%	924
April	1st to 10th	Night	22% 15% 33% 25% 4	838
	11th to 20th	Night	21% 12% 33% 25% 8% 1	623
	21st to end	Night	21% 7% 34% 31% 6% 1	630
May	1st to 10th	Night	21% 9% 29% 33% 8% 1	630
	11th to 20th	Night	19% 7% 27% 32% 13% 1	621
	21st to end	Night	13% 5% 22% 37% 21% 2	683
June	1st to 10th	Night	13% 4 26% 42% 15% 1	520
	11th to 20th	Night	10% 3 28% 44% 15%	410
	21st to end	Night	11% 4 24% 39% 21% 1	543
July	1st to 10th	Night	10% 2 15% 42% 29% 2	585
	11th to 20th	Night	9% 4 17% 42% 24% 3	582
	21st to end	Night	10% 2 16% 41% 29% 2	657
August	1st to 10th	Night	10% 2 14% 44% 28% 4	597
	11th to 20th	Night	11% 3 15% 39% 29% 4	594
	21st to end	Night	9% 3 19% 34% 31% 4	660
September	1st to 10th	Night	13% 5% 17% 36% 26% 4	790
	11th to 20th	Night	11% 4 13% 34% 33% 5%	800
	21st to end	Night	17% 9% 21% 30% 21% 3	800
October	1st to 10th	Night	16% 8% 23% 32% 19% 3	800
	11th to 20th	Night	22% 13% 29% 26% 9% 1	800
	21st to end	Night	27% 15% 30% 22% 5%	880
November	1st to 10th	Night	21% 12% 33% 25% 9% 1	820
	11th to 20th	Night	26% 14% 33% 19% 6% 1	840
	21st to end	Night	31% 15% 29% 19% 5%	840
December	1st to 10th	Night	28% 18% 31% 18% 5%	840
	11th to 20th	Night	27% 17% 37% 17% 3	840
	21st to end	Night	29% 18% 32% 19% 2	924

Page generated at 2026-06-13 02:31:40. Version ac07

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