Dayton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dayton clear sky chart from 2005-11-06 to 2026-07-01.

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% 9% 4 8% 5% 5% 5% 4 5% 7% 34%	137765
	Night	16% 10% 4 8% 5% 4 4 3 5% 6% 35%	134621
Transparency	Day	48% 5% 11% 22% 13% 1	141390
	Night	48% 4 10% 22% 13% 2	139068
Seeing	Day	19% 14% 28% 21% 13% 5%	17593
	Night	20% 10% 27% 28% 14% 2	27294

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% 14% 7% 12% 5% 5% 3 3 5% 5% 23%	4691
	11th to 20th	Day	12% 15% 6% 15% 8% 7% 5% 2 3 3 23%	5091
	21st to end	Day	19% 13% 7% 11% 6% 6% 6% 3 4 5% 19%	5780
February	1st to 10th	Day	19% 14% 6% 10% 5% 5% 4 3 4 5% 25%	1964
	11th to 20th	Day	16% 12% 4 12% 7% 5% 5% 3 4 5% 27%	2048
	21st to end	Day	17% 13% 5% 11% 5% 4 3 3 4 5% 31%	1730
March	1st to 10th	Day	18% 15% 7% 9% 5% 3 4 2 4 4 28%	4644
	11th to 20th	Day	12% 9% 3 8% 4 4 4 3 5% 7% 40%	5090
	21st to end	Day	18% 11% 4 9% 5% 4 4 4 5% 6% 31%	5586
April	1st to 10th	Day	15% 12% 3 8% 5% 4 3 4 5% 7% 33%	2462
	11th to 20th	Day	15% 9% 3 7% 5% 4 5% 3 4 6% 38%	2576
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 3 6% 7% 35%	2730
May	1st to 10th	Day	20% 8% 2 7% 5% 5% 5% 4 6% 7% 30%	7616
	11th to 20th	Day	19% 7% 2 6% 4 4 4 4 5% 8% 37%	7626
	21st to end	Day	19% 7% 3 7% 5% 5% 5% 4 6% 9% 30%	8391
June	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 4 7% 8% 39%	2748
	11th to 20th	Day	10% 5% 2 7% 5% 5% 6% 5% 6% 9% 40%	2940
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 4 7% 9% 39%	2940
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 4 7% 9% 39%	6361
	11th to 20th	Day	11% 5% 2 7% 5% 5% 6% 5% 7% 10% 37%	6161
	21st to end	Day	11% 5% 2 8% 6% 6% 6% 5% 7% 9% 35%	6424
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 9% 42%	4234
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 7% 11% 40%	4174
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 9% 50%	4397
September	1st to 10th	Day	11% 5% 2 4 5% 3 5% 3 6% 7% 49%	2270
	11th to 20th	Day	9% 5% 2 5% 4 3 4 4 6% 8% 50%	2200
	21st to end	Day	15% 7% 3 6% 4 4 4 3 6% 6% 44%	2200
October	1st to 10th	Day	11% 6% 3 6% 4 4 5% 4 5% 7% 48%	2200
	11th to 20th	Day	14% 7% 2 5% 4 3 4 3 4 7% 47%	2011
	21st to end	Day	21% 8% 3 7% 4 4 3 3 5% 7% 36%	2053
November	1st to 10th	Day	11% 7% 2 7% 4 4 4 3 4 6% 48%	1852
	11th to 20th	Day	15% 12% 4 7% 5% 4 4 4 5% 5% 35%	1890
	21st to end	Day	19% 12% 5% 9% 5% 3 4 3 4 5% 32%	1890
December	1st to 10th	Day	17% 11% 5% 8% 5% 4 4 3 4 5% 35%	3020
	11th to 20th	Day	20% 15% 5% 11% 5% 5% 4 3 4 5% 23%	3463
	21st to end	Day	23% 20% 6% 10% 6% 4 4 3 4 5% 15%	4312
January	1st to 10th	Night	15% 16% 7% 13% 6% 6% 5% 4 5% 5% 19%	8232
	11th to 20th	Night	12% 17% 7% 15% 7% 6% 4 3 4 4 21%	7845
	21st to end	Night	19% 13% 5% 8% 6% 5% 4 3 4 6% 28%	8401
February	1st to 10th	Night	21% 13% 4 8% 6% 5% 4 3 4 5% 28%	2651
	11th to 20th	Night	17% 11% 5% 10% 5% 5% 4 4 4 6% 30%	2458
	21st to end	Night	20% 13% 5% 9% 5% 3 3 3 4 4 30%	2076
March	1st to 10th	Night	21% 12% 3 6% 4 3 4 3 4 4 36%	5429
	11th to 20th	Night	12% 7% 3 7% 4 5% 4 4 5% 7% 42%	5090
	21st to end	Night	19% 9% 3 8% 4 4 4 3 5% 6% 35%	5588
April	1st to 10th	Night	16% 9% 3 6% 4 4 4 4 5% 7% 37%	2174
	11th to 20th	Night	15% 8% 2 6% 5% 4 4 4 6% 7% 39%	1993
	21st to end	Night	18% 7% 2 6% 4 4 4 3 6% 7% 39%	1890
May	1st to 10th	Night	23% 8% 3 7% 5% 4 5% 4 6% 7% 30%	5237
	11th to 20th	Night	17% 6% 2 6% 4 4 4 4 5% 8% 40%	5234
	21st to end	Night	17% 6% 2 7% 5% 5% 4 3 6% 9% 36%	5761
June	1st to 10th	Night	9% 6% 2 5% 5% 5% 5% 3 5% 8% 47%	1866
	11th to 20th	Night	9% 4 2 6% 4 4 4 3 7% 10% 47%	1680
	21st to end	Night	7% 5% 2 5% 5% 4 5% 4 7% 10% 46%	1680
July	1st to 10th	Night	11% 4 2 6% 5% 4 4 4 5% 7% 47%	3618
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 4 7% 9% 45%	3792
	21st to end	Night	9% 6% 3 6% 5% 4 5% 5% 7% 10% 41%	4427
August	1st to 10th	Night	11% 6% 2 7% 4 4 6% 4 6% 8% 43%	2915
	11th to 20th	Night	8% 6% 3 6% 4 4 3 4 5% 7% 48%	2875
	21st to end	Night	4 3 1 5% 4 5% 6% 4 7% 9% 53%	3484
September	1st to 10th	Night	12% 5% 2 4 4 3 3 4 4 7% 52%	2110
	11th to 20th	Night	8% 4 2 4 4 3 4 3 5% 7% 57%	2200
	21st to end	Night	15% 6% 2 6% 3 3 4 3 4 5% 49%	2200
October	1st to 10th	Night	9% 5% 2 5% 4 4 3 3 4 7% 53%	2200
	11th to 20th	Night	16% 7% 3 6% 3 4 3 3 4 5% 45%	2387
	21st to end	Night	17% 9% 3 6% 4 3 4 3 5% 5% 39%	2784
November	1st to 10th	Night	13% 7% 2 6% 4 3 3 4 5% 7% 46%	2666
	11th to 20th	Night	17% 9% 3 6% 4 3 4 3 5% 7% 39%	2730
	21st to end	Night	19% 14% 4 7% 5% 4 4 3 5% 6% 28%	2730
December	1st to 10th	Night	18% 10% 4 9% 5% 4 4 3 5% 6% 34%	4380
	11th to 20th	Night	20% 16% 7% 9% 4 4 4 3 4 5% 24%	4952
	21st to end	Night	26% 19% 6% 10% 5% 4 3 3 3 5% 16%	6886

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	65% 3 12% 15% 5%	4692
	11th to 20th	Day	68% 3 8% 11% 10% 1	5091
	21st to end	Day	68% 3 10% 11% 6% 1	5780
February	1st to 10th	Day	63% 3 9% 14% 9% 1	1964
	11th to 20th	Day	61% 4 10% 17% 8% 1	2058
	21st to end	Day	57% 3 12% 20% 8% 1	1730
March	1st to 10th	Day	61% 3 6% 19% 10% 1	4644
	11th to 20th	Day	44% 4 9% 28% 14% 1	5090
	21st to end	Day	53% 5% 11% 19% 10% 3	5586
April	1st to 10th	Day	50% 5% 11% 22% 12% 1	2462
	11th to 20th	Day	47% 5% 11% 21% 13% 3	2576
	21st to end	Day	48% 5% 11% 23% 10% 2	2730
May	1st to 10th	Day	52% 5% 12% 20% 11%	7651
	11th to 20th	Day	46% 5% 13% 25% 12%	7630
	21st to end	Day	49% 6% 10% 20% 12% 3	8405
June	1st to 10th	Day	41% 6% 12% 22% 16% 3	2748
	11th to 20th	Day	39% 7% 13% 23% 17% 2	2940
	21st to end	Day	39% 8% 14% 22% 14% 3	2940
July	1st to 10th	Day	40% 6% 10% 27% 17% 1	6292
	11th to 20th	Day	40% 7% 14% 25% 14% 1	6086
	21st to end	Day	43% 6% 14% 19% 15% 3	6240
August	1st to 10th	Day	36% 7% 16% 28% 13% 1	4221
	11th to 20th	Day	36% 6% 12% 30% 16% 1	4213
	21st to end	Day	31% 5% 13% 30% 18% 3	4396
September	1st to 10th	Day	33% 6% 11% 25% 22% 4	2270
	11th to 20th	Day	31% 4 12% 26% 23% 3	2200
	21st to end	Day	41% 4 9% 22% 23% 2	2200
October	1st to 10th	Day	24% 5% 9% 31% 29% 2	3590
	11th to 20th	Day	32% 3 9% 30% 24% 2	3251
	21st to end	Day	39% 3 11% 24% 21% 2	3290
November	1st to 10th	Day	37% 4 11% 28% 18% 3	1852
	11th to 20th	Day	50% 3 10% 21% 13% 2	1890
	21st to end	Day	55% 4 9% 21% 9% 1	1890
December	1st to 10th	Day	54% 3 11% 25% 7%	3020
	11th to 20th	Day	64% 4 10% 17% 5%	3460
	21st to end	Day	72% 3 9% 11% 4	4312
January	1st to 10th	Night	68% 4 10% 14% 5%	8233
	11th to 20th	Night	67% 3 7% 12% 8% 1	7845
	21st to end	Night	59% 3 11% 19% 7% 1	8401
February	1st to 10th	Night	59% 4 10% 18% 9% 1	2651
	11th to 20th	Night	55% 3 10% 20% 11% 1	2459
	21st to end	Night	59% 3 11% 16% 10% 2	2076
March	1st to 10th	Night	52% 3 6% 27% 11% 2	5429
	11th to 20th	Night	41% 4 11% 29% 13% 1	5090
	21st to end	Night	50% 4 8% 25% 11% 1	5588
April	1st to 10th	Night	45% 5% 12% 23% 12% 2	2174
	11th to 20th	Night	42% 5% 13% 19% 17% 4	1993
	21st to end	Night	44% 5% 11% 25% 13% 3	1890
May	1st to 10th	Night	53% 6% 10% 20% 8% 3	5264
	11th to 20th	Night	44% 5% 11% 25% 14% 1	5235
	21st to end	Night	44% 6% 12% 22% 11% 4	5771
June	1st to 10th	Night	35% 6% 11% 25% 23% 2	1866
	11th to 20th	Night	32% 7% 16% 24% 18% 4	1680
	21st to end	Night	31% 8% 17% 22% 17% 4	1680
July	1st to 10th	Night	36% 6% 12% 24% 19% 4	3580
	11th to 20th	Night	35% 6% 15% 28% 15% 1	3747
	21st to end	Night	38% 5% 14% 24% 17% 3	4297
August	1st to 10th	Night	38% 7% 13% 29% 12% 1	2904
	11th to 20th	Night	35% 6% 10% 29% 20%	2902
	21st to end	Night	27% 6% 15% 29% 21% 3	3484
September	1st to 10th	Night	32% 5% 12% 25% 20% 6%	2110
	11th to 20th	Night	27% 5% 9% 26% 29% 3	2200
	21st to end	Night	38% 5% 9% 21% 25% 2	2200
October	1st to 10th	Night	23% 3 7% 30% 34% 2	3590
	11th to 20th	Night	30% 3 9% 27% 29% 2	3886
	21st to end	Night	35% 3 7% 25% 26% 4	4497
November	1st to 10th	Night	38% 4 11% 24% 21% 3	2666
	11th to 20th	Night	46% 4 8% 24% 15% 3	2730
	21st to end	Night	57% 4 10% 20% 9% 1	2730
December	1st to 10th	Night	53% 3 12% 24% 8%	4380
	11th to 20th	Night	63% 3 10% 17% 6% 1	4954
	21st to end	Night	72% 3 8% 13% 3	6886

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	29% 19% 35% 12% 4	330
	11th to 20th	Day	31% 27% 31% 10% 2	330
	21st to end	Day	33% 22% 29% 12% 3	363
February	1st to 10th	Day	28% 25% 32% 14% 2	330
	11th to 20th	Day	32% 23% 35% 7% 3	330
	21st to end	Day	27% 24% 41% 6% 1	273
March	1st to 10th	Day	29% 27% 30% 12% 2	355
	11th to 20th	Day	27% 21% 31% 16% 6%	540
	21st to end	Day	31% 20% 31% 14% 4	594
April	1st to 10th	Day	24% 19% 32% 17% 8% 1	540
	11th to 20th	Day	24% 20% 28% 19% 7% 2	532
	21st to end	Day	23% 20% 30% 17% 9% 1	540
May	1st to 10th	Day	27% 17% 29% 17% 6% 3	543
	11th to 20th	Day	22% 13% 28% 21% 11% 5%	567
	21st to end	Day	17% 10% 27% 26% 11% 9%	617
June	1st to 10th	Day	14% 9% 26% 30% 16% 6%	588
	11th to 20th	Day	11% 10% 29% 29% 15% 5%	780
	21st to end	Day	11% 8% 30% 29% 16% 6%	780
July	1st to 10th	Day	13% 4 20% 26% 23% 13%	722
	11th to 20th	Day	9% 5% 28% 28% 21% 10%	636
	21st to end	Day	10% 3 21% 30% 22% 14%	576
August	1st to 10th	Day	11% 5% 16% 28% 26% 14%	526
	11th to 20th	Day	13% 5% 21% 27% 24% 11%	519
	21st to end	Day	8% 6% 18% 30% 27% 11%	583
September	1st to 10th	Day	12% 6% 16% 28% 30% 9%	530
	11th to 20th	Day	8% 4 16% 26% 31% 15%	530
	21st to end	Day	20% 9% 20% 24% 18% 8%	530
October	1st to 10th	Day	12% 6% 26% 29% 19% 8%	530
	11th to 20th	Day	16% 17% 31% 21% 12% 3	530
	21st to end	Day	24% 17% 38% 15% 6%	436
November	1st to 10th	Day	17% 19% 34% 21% 7% 2	330
	11th to 20th	Day	29% 16% 32% 13% 8% 1	330
	21st to end	Day	30% 16% 39% 11% 4	330
December	1st to 10th	Day	22% 25% 34% 14% 5%	330
	11th to 20th	Day	25% 23% 36% 11% 4	330
	21st to end	Day	34% 19% 33% 10% 3 1	363
January	1st to 10th	Night	25% 16% 33% 22% 5% 1	1050
	11th to 20th	Night	30% 17% 33% 16% 3	901
	21st to end	Night	25% 16% 32% 23% 3	924
February	1st to 10th	Night	28% 12% 33% 26% 2	840
	11th to 20th	Night	24% 18% 34% 21% 2	823
	21st to end	Night	28% 15% 36% 20% 2	692
March	1st to 10th	Night	24% 15% 31% 24% 5%	840
	11th to 20th	Night	23% 15% 34% 22% 5% 1	840
	21st to end	Night	27% 13% 29% 25% 6%	924
April	1st to 10th	Night	22% 12% 36% 24% 6%	704
	11th to 20th	Night	21% 14% 31% 24% 10% 1	623
	21st to end	Night	20% 10% 37% 23% 9% 1	630
May	1st to 10th	Night	24% 10% 32% 24% 10% 1	630
	11th to 20th	Night	19% 7% 28% 29% 16% 2	621
	21st to end	Night	11% 5% 24% 35% 23% 3	683
June	1st to 10th	Night	12% 4 26% 39% 19% 1	630
	11th to 20th	Night	10% 4 23% 40% 21% 2	630
	21st to end	Night	8% 4 25% 36% 24% 3	630
July	1st to 10th	Night	10% 3 14% 36% 30% 6%	585
	11th to 20th	Night	8% 3 16% 37% 30% 5%	582
	21st to end	Night	10% 3 14% 38% 33% 2	657
August	1st to 10th	Night	9% 2 13% 39% 34% 3	597
	11th to 20th	Night	7% 3 13% 41% 31% 5%	594
	21st to end	Night	7% 2 16% 32% 38% 5%	660
September	1st to 10th	Night	14% 3 16% 35% 28% 4	710
	11th to 20th	Night	10% 3 16% 33% 34% 4	800
	21st to end	Night	16% 7% 20% 31% 24% 2	800
October	1st to 10th	Night	12% 5% 26% 31% 22% 4	800
	11th to 20th	Night	20% 11% 26% 30% 13% 1	800
	21st to end	Night	22% 12% 33% 23% 9%	880
November	1st to 10th	Night	17% 9% 33% 26% 14% 1	820
	11th to 20th	Night	23% 16% 29% 24% 8% 1	840
	21st to end	Night	27% 13% 28% 26% 6% 1	840
December	1st to 10th	Night	28% 13% 32% 22% 5%	840
	11th to 20th	Night	27% 13% 32% 22% 5% 1	840
	21st to end	Night	31% 15% 30% 21% 3	1034

Page generated at 2026-06-28 02:10:46. Version ac07

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