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 2025-02-21.

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%	109102
	Night	16% 10% 4 8% 5% 4 4 3 5% 6% 35%	109489
Transparency	Day	47% 5% 11% 22% 13% 1	112771
	Night	48% 5% 10% 22% 14% 2	113959
Seeing	Day	19% 13% 28% 21% 13% 6%	15708
	Night	20% 10% 27% 28% 14% 2	25538

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% 16% 9% 13% 5% 4 3 2 4 4 22%	3617
	11th to 20th	Day	14% 16% 6% 13% 7% 7% 6% 2 3 3 22%	3910
	21st to end	Day	21% 14% 8% 9% 6% 5% 4 3 3 4 22%	4466
February	1st to 10th	Day	20% 14% 6% 10% 5% 5% 4 3 4 6% 24%	1870
	11th to 20th	Day	16% 12% 4 12% 7% 5% 5% 3 4 5% 26%	1948
	21st to end	Day	19% 14% 5% 10% 5% 4 3 3 4 5% 30%	1570
March	1st to 10th	Day	22% 17% 5% 10% 5% 3 3 2 4 4 24%	3169
	11th to 20th	Day	13% 9% 3 8% 5% 4 4 3 5% 7% 39%	3480
	21st to end	Day	18% 11% 4 9% 5% 4 4 4 5% 7% 31%	3815
April	1st to 10th	Day	14% 13% 3 8% 5% 4 3 4 5% 7% 34%	2228
	11th to 20th	Day	16% 9% 3 7% 5% 4 4 3 4 6% 38%	2328
	21st to end	Day	18% 8% 3 7% 5% 4 5% 3 6% 7% 34%	2470
May	1st to 10th	Day	22% 10% 3 7% 4 4 4 4 6% 7% 29%	4082
	11th to 20th	Day	21% 8% 2 6% 3 3 4 4 5% 8% 36%	4081
	21st to end	Day	12% 7% 3 7% 5% 5% 6% 5% 7% 11% 33%	4476
June	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 4 7% 8% 38%	2486
	11th to 20th	Day	10% 5% 2 7% 5% 5% 6% 5% 6% 9% 40%	2660
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 4 7% 9% 39%	2660
July	1st to 10th	Day	12% 6% 2 7% 6% 6% 6% 5% 7% 10% 34%	4440
	11th to 20th	Day	8% 4 1 6% 4 5% 6% 5% 7% 10% 44%	4297
	21st to end	Day	10% 5% 2 8% 6% 5% 7% 5% 8% 9% 35%	4466
August	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 42%	4104
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 7% 11% 40%	4044
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 9% 50%	4262
September	1st to 10th	Day	11% 5% 2 4 5% 3 5% 3 6% 7% 48%	2157
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 49%	2090
	21st to end	Day	15% 7% 3 6% 4 3 4 3 6% 6% 44%	2090
October	1st to 10th	Day	11% 6% 3 6% 4 4 5% 4 5% 7% 47%	2090
	11th to 20th	Day	14% 7% 2 5% 4 3 4 3 5% 7% 46%	1911
	21st to end	Day	21% 8% 3 7% 4 5% 3 3 5% 7% 35%	1951
November	1st to 10th	Day	11% 6% 2 6% 4 4 3 3 5% 6% 49%	1762
	11th to 20th	Day	15% 12% 5% 7% 5% 4 4 4 5% 6% 34%	1800
	21st to end	Day	19% 12% 4 9% 5% 3 4 3 4 5% 32%	1800
December	1st to 10th	Day	18% 11% 5% 8% 5% 4 4 3 4 5% 35%	2930
	11th to 20th	Day	20% 15% 5% 10% 5% 4 4 3 4 5% 23%	3373
	21st to end	Day	24% 19% 6% 10% 5% 4 4 3 4 5% 15%	4219
January	1st to 10th	Night	16% 17% 7% 14% 6% 5% 4 3 4 4 19%	6348
	11th to 20th	Night	14% 19% 6% 13% 8% 6% 5% 3 4 5% 19%	6023
	21st to end	Night	22% 14% 5% 9% 5% 4 4 2 3 5% 27%	6490
February	1st to 10th	Night	22% 13% 4 8% 5% 5% 4 3 4 5% 28%	2525
	11th to 20th	Night	17% 11% 4 10% 6% 5% 4 4 4 6% 30%	2338
	21st to end	Night	21% 14% 5% 8% 5% 3 3 3 4 4 29%	1885
March	1st to 10th	Night	22% 12% 3 6% 4 3 4 3 4 5% 33%	3684
	11th to 20th	Night	12% 8% 3 7% 4 4 4 3 5% 7% 43%	3480
	21st to end	Night	18% 9% 2 7% 4 4 4 3 4 6% 39%	3817
April	1st to 10th	Night	15% 9% 2 7% 5% 5% 4 4 5% 8% 37%	1967
	11th to 20th	Night	16% 8% 2 6% 4 4 4 4 6% 7% 39%	1801
	21st to end	Night	18% 7% 3 6% 4 4 5% 4 7% 6% 38%	1710
May	1st to 10th	Night	23% 11% 3 7% 4 4 4 4 5% 7% 27%	2813
	11th to 20th	Night	19% 6% 2 6% 4 4 4 3 5% 7% 39%	2812
	21st to end	Night	9% 4 2 6% 4 5% 5% 4 7% 10% 43%	3079
June	1st to 10th	Night	8% 6% 2 5% 4 5% 5% 3 5% 8% 47%	1688
	11th to 20th	Night	8% 4 2 6% 4 4 4 3 7% 10% 48%	1520
	21st to end	Night	6% 5% 2 5% 5% 5% 5% 5% 7% 10% 46%	1520
July	1st to 10th	Night	12% 5% 2 6% 5% 4 4 4 5% 8% 47%	2530
	11th to 20th	Night	7% 4 1 4 3 4 5% 5% 6% 8% 53%	2653
	21st to end	Night	10% 5% 3 6% 5% 4 5% 5% 7% 9% 40%	3087
August	1st to 10th	Night	11% 6% 2 7% 4 4 6% 4 6% 8% 43%	2825
	11th to 20th	Night	8% 7% 3 6% 4 4 4 4 5% 7% 48%	2785
	21st to end	Night	4 3 1 5% 4 5% 6% 4 7% 9% 53%	3377
September	1st to 10th	Night	13% 5% 2 4 4 3 3 4 4 7% 51%	2004
	11th to 20th	Night	8% 5% 2 4 4 3 4 3 5% 7% 56%	2090
	21st to end	Night	15% 6% 2 6% 3 3 4 3 4 5% 49%	2090
October	1st to 10th	Night	9% 5% 2 5% 4 4 3 3 4 7% 52%	2090
	11th to 20th	Night	16% 7% 3 6% 3 4 3 3 4 5% 45%	2267
	21st to end	Night	18% 9% 3 6% 4 3 4 3 5% 5% 39%	2645
November	1st to 10th	Night	13% 7% 2 6% 4 3 4 4 5% 7% 46%	2536
	11th to 20th	Night	18% 9% 3 7% 4 3 4 3 5% 7% 38%	2600
	21st to end	Night	19% 13% 4 7% 5% 4 5% 3 5% 6% 28%	2600
December	1st to 10th	Night	18% 10% 4 9% 5% 4 3 3 5% 6% 34%	4250
	11th to 20th	Night	20% 16% 6% 9% 4 4 4 3 4 5% 24%	4822
	21st to end	Night	26% 19% 6% 10% 5% 4 3 3 4 5% 16%	6738

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	66% 3 7% 17% 6%	3618
	11th to 20th	Day	68% 4 8% 10% 9% 1	3910
	21st to end	Day	68% 4 10% 11% 7% 1	4466
February	1st to 10th	Day	64% 3 9% 13% 10% 1	1870
	11th to 20th	Day	61% 4 10% 17% 8%	1958
	21st to end	Day	58% 3 10% 19% 8% 1	1570
March	1st to 10th	Day	65% 4 7% 17% 7%	3169
	11th to 20th	Day	44% 5% 9% 26% 14% 1	3480
	21st to end	Day	52% 6% 11% 22% 9% 1	3815
April	1st to 10th	Day	50% 5% 11% 22% 12% 1	2228
	11th to 20th	Day	47% 5% 11% 21% 13% 3	2328
	21st to end	Day	49% 5% 12% 21% 11% 2	2470
May	1st to 10th	Day	53% 6% 12% 21% 7% 1	4120
	11th to 20th	Day	47% 6% 14% 23% 10% 1	4085
	21st to end	Day	41% 9% 14% 20% 14% 2	4489
June	1st to 10th	Day	41% 6% 12% 23% 15% 3	2486
	11th to 20th	Day	38% 7% 13% 23% 17% 1	2660
	21st to end	Day	38% 8% 15% 21% 15% 4	2660
July	1st to 10th	Day	44% 6% 11% 21% 17% 2	4371
	11th to 20th	Day	33% 7% 11% 30% 19% 1	4222
	21st to end	Day	42% 7% 14% 18% 15% 4	4324
August	1st to 10th	Day	36% 7% 16% 28% 13% 1	4091
	11th to 20th	Day	36% 6% 11% 30% 16% 1	4083
	21st to end	Day	31% 5% 13% 30% 18% 3	4261
September	1st to 10th	Day	34% 6% 11% 23% 22% 4	2157
	11th to 20th	Day	32% 4 12% 26% 22% 3	2090
	21st to end	Day	41% 4 9% 23% 22% 2	2090
October	1st to 10th	Day	25% 5% 10% 31% 29% 2	3480
	11th to 20th	Day	32% 3 9% 30% 25% 1	3151
	21st to end	Day	39% 3 11% 24% 21% 2	3188
November	1st to 10th	Day	36% 4 11% 28% 19% 3	1762
	11th to 20th	Day	51% 3 10% 21% 13% 2	1800
	21st to end	Day	55% 4 9% 21% 10% 1	1800
December	1st to 10th	Day	53% 3 11% 25% 7%	2930
	11th to 20th	Day	65% 4 10% 16% 5%	3370
	21st to end	Day	72% 3 9% 11% 4	4219
January	1st to 10th	Night	69% 4 7% 13% 6%	6348
	11th to 20th	Night	69% 4 8% 11% 7% 1	6023
	21st to end	Night	62% 3 10% 17% 7% 1	6490
February	1st to 10th	Night	60% 4 10% 18% 8% 1	2525
	11th to 20th	Night	56% 4 10% 18% 11% 1	2339
	21st to end	Night	60% 3 10% 15% 9% 2	1885
March	1st to 10th	Night	53% 4 7% 24% 11% 1	3684
	11th to 20th	Night	41% 5% 12% 28% 13% 2	3480
	21st to end	Night	47% 5% 9% 28% 10% 1	3817
April	1st to 10th	Night	44% 6% 12% 23% 13% 2	1967
	11th to 20th	Night	42% 5% 11% 18% 18% 4	1801
	21st to end	Night	45% 5% 12% 24% 12% 3	1710
May	1st to 10th	Night	56% 6% 9% 21% 7% 2	2840
	11th to 20th	Night	44% 6% 13% 27% 9% 1	2813
	21st to end	Night	32% 9% 13% 28% 13% 4	3087
June	1st to 10th	Night	34% 6% 11% 26% 21% 2	1688
	11th to 20th	Night	30% 7% 17% 24% 18% 4	1520
	21st to end	Night	31% 8% 16% 23% 17% 5%	1520
July	1st to 10th	Night	37% 6% 11% 23% 17% 6%	2490
	11th to 20th	Night	29% 5% 13% 31% 20% 2	2605
	21st to end	Night	39% 6% 13% 23% 16% 4	2988
August	1st to 10th	Night	38% 7% 13% 28% 12% 1	2814
	11th to 20th	Night	35% 6% 10% 28% 20%	2812
	21st to end	Night	27% 6% 16% 28% 21% 3	3377
September	1st to 10th	Night	32% 5% 12% 25% 19% 6%	2004
	11th to 20th	Night	28% 5% 9% 26% 28% 4	2090
	21st to end	Night	37% 5% 9% 22% 24% 2	2090
October	1st to 10th	Night	23% 3 8% 31% 33% 3	3480
	11th to 20th	Night	30% 3 9% 27% 29% 2	3766
	21st to end	Night	34% 3 8% 25% 26% 4	4358
November	1st to 10th	Night	38% 4 11% 23% 21% 3	2536
	11th to 20th	Night	47% 4 8% 23% 16% 3	2600
	21st to end	Night	56% 4 11% 20% 9% 1	2600
December	1st to 10th	Night	53% 3 12% 24% 8%	4250
	11th to 20th	Night	63% 3 10% 17% 7%	4824
	21st to end	Night	72% 3 8% 13% 3	6738

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% 20% 35% 12% 4	300
	11th to 20th	Day	29% 27% 32% 11% 2	300
	21st to end	Day	32% 22% 31% 12% 3	330
February	1st to 10th	Day	30% 26% 30% 13% 1	300
	11th to 20th	Day	32% 25% 34% 6% 3	300
	21st to end	Day	29% 23% 41% 5% 2	225
March	1st to 10th	Day	27% 29% 29% 13% 2	293
	11th to 20th	Day	26% 20% 30% 17% 6%	460
	21st to end	Day	31% 18% 31% 14% 5%	506
April	1st to 10th	Day	23% 18% 31% 18% 9% 1	460
	11th to 20th	Day	22% 20% 27% 20% 8% 2	452
	21st to end	Day	24% 20% 30% 16% 9% 2	460
May	1st to 10th	Day	28% 13% 31% 19% 6% 3	463
	11th to 20th	Day	21% 11% 28% 22% 11% 6%	487
	21st to end	Day	14% 8% 28% 27% 13% 10%	529
June	1st to 10th	Day	14% 9% 24% 31% 17% 6%	506
	11th to 20th	Day	11% 8% 28% 31% 17% 6%	680
	21st to end	Day	10% 9% 32% 29% 14% 6%	680
July	1st to 10th	Day	13% 4 21% 25% 23% 14%	671
	11th to 20th	Day	9% 5% 28% 27% 20% 11%	590
	21st to end	Day	10% 3 22% 30% 21% 14%	532
August	1st to 10th	Day	12% 5% 16% 28% 25% 15%	486
	11th to 20th	Day	13% 5% 22% 27% 22% 10%	479
	21st to end	Day	8% 6% 17% 29% 27% 12%	539
September	1st to 10th	Day	12% 5% 17% 29% 29% 9%	490
	11th to 20th	Day	9% 4 17% 27% 30% 13%	490
	21st to end	Day	20% 9% 21% 24% 18% 8%	490
October	1st to 10th	Day	12% 6% 28% 29% 18% 8%	490
	11th to 20th	Day	16% 18% 32% 19% 12% 3	490
	21st to end	Day	24% 16% 38% 16% 6% 1	400
November	1st to 10th	Day	15% 19% 34% 21% 7% 3	300
	11th to 20th	Day	28% 17% 30% 15% 9% 1	300
	21st to end	Day	29% 16% 40% 11% 4	300
December	1st to 10th	Day	23% 25% 32% 14% 6%	300
	11th to 20th	Day	25% 24% 35% 11% 5%	300
	21st to end	Day	34% 18% 32% 11% 4 1	330
January	1st to 10th	Night	25% 16% 33% 22% 4 1	1000
	11th to 20th	Night	31% 16% 33% 17% 3	858
	21st to end	Night	25% 15% 32% 24% 3	880
February	1st to 10th	Night	29% 13% 32% 25% 2	800
	11th to 20th	Night	25% 18% 34% 21% 2	783
	21st to end	Night	28% 14% 35% 19% 3	629
March	1st to 10th	Night	24% 15% 31% 25% 6%	760
	11th to 20th	Night	22% 15% 34% 23% 6% 1	760
	21st to end	Night	28% 11% 29% 26% 6%	836
April	1st to 10th	Night	21% 11% 35% 26% 6%	637
	11th to 20th	Night	21% 12% 31% 25% 10% 1	563
	21st to end	Night	20% 10% 38% 23% 8% 1	570
May	1st to 10th	Night	24% 8% 32% 24% 11% 1	570
	11th to 20th	Night	19% 5% 27% 30% 17% 2	561
	21st to end	Night	10% 5% 24% 34% 25% 3	617
June	1st to 10th	Night	11% 4 25% 40% 19% 1	570
	11th to 20th	Night	9% 4 23% 39% 23% 2	570
	21st to end	Night	7% 4 25% 37% 24% 2	570
July	1st to 10th	Night	10% 4 14% 35% 30% 7%	555
	11th to 20th	Night	7% 3 16% 38% 30% 6%	552
	21st to end	Night	10% 3 14% 38% 32% 2	624
August	1st to 10th	Night	9% 1 13% 39% 35% 3	567
	11th to 20th	Night	7% 2 14% 42% 29% 5%	564
	21st to end	Night	7% 2 16% 30% 40% 6%	627
September	1st to 10th	Night	15% 4 16% 34% 28% 4	674
	11th to 20th	Night	11% 3 17% 32% 34% 4	760
	21st to end	Night	16% 7% 21% 31% 23% 2	760
October	1st to 10th	Night	12% 5% 27% 30% 22% 4	760
	11th to 20th	Night	21% 10% 27% 28% 13% 1	760
	21st to end	Night	22% 12% 32% 24% 10%	836
November	1st to 10th	Night	18% 9% 31% 27% 14% 1	780
	11th to 20th	Night	23% 16% 28% 25% 8% 1	800
	21st to end	Night	26% 13% 28% 26% 6% 1	800
December	1st to 10th	Night	28% 12% 32% 22% 5%	800
	11th to 20th	Night	27% 13% 31% 23% 5% 1	800
	21st to end	Night	31% 14% 30% 22% 3	985

Page generated at 2025-02-18 03:26:29. Version ac07

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