Ohatchee's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ohatchee's Observatory clear sky chart from 2005-11-06 to 2025-11-18.

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	9% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	126107
	Night	10% 6% 2 6% 4 4 4 4 6% 8% 46%	124275
Transparency	Day	34% 8% 14% 19% 16% 8%	129978
	Night	34% 7% 14% 18% 18% 8%	128477
Seeing	Day	11% 6% 19% 24% 24% 15%	15800
	Night	11% 5% 18% 30% 27% 9%	25692

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	12% 6% 2 6% 3 3 4 3 4 6% 52%	4378
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 5% 6% 50%	4520
	21st to end	Day	19% 8% 3 6% 4 4 4 3 5% 7% 37%	4972
February	1st to 10th	Day	15% 8% 3 7% 4 4 3 4 4 6% 43%	2000
	11th to 20th	Day	15% 6% 2 5% 3 4 5% 3 6% 7% 43%	1948
	21st to end	Day	13% 7% 3 6% 4 4 5% 4 6% 7% 39%	1650
March	1st to 10th	Day	13% 8% 3 8% 4 4 4 4 6% 7% 39%	4480
	11th to 20th	Day	8% 4 2 5% 3 4 4 3 6% 8% 53%	4681
	21st to end	Day	15% 7% 3 6% 4 4 4 3 4 6% 44%	5967
April	1st to 10th	Day	10% 6% 3 6% 4 4 5% 4 5% 7% 46%	2400
	11th to 20th	Day	11% 6% 2 5% 4 5% 4 4 7% 8% 46%	2374
	21st to end	Day	7% 4 1 5% 3 3 4 4 5% 8% 54%	2400
May	1st to 10th	Day	11% 6% 2 6% 4 4 5% 4 7% 10% 40%	5405
	11th to 20th	Day	10% 4 2 5% 4 4 5% 4 7% 10% 45%	5677
	21st to end	Day	5% 4 2 5% 4 4 5% 5% 8% 11% 46%	6433
June	1st to 10th	Day	7% 6% 3 7% 5% 6% 7% 6% 10% 11% 33%	2600
	11th to 20th	Day	4 4 2 5% 6% 6% 8% 6% 10% 12% 37%	2600
	21st to end	Day	7% 5% 2 7% 6% 6% 7% 7% 9% 13% 31%	2600
July	1st to 10th	Day	4 4 2 7% 6% 7% 8% 7% 11% 14% 31%	5900
	11th to 20th	Day	3 4 2 6% 6% 6% 7% 6% 9% 14% 36%	5446
	21st to end	Day	3 4 2 7% 6% 7% 9% 7% 12% 16% 28%	5922
August	1st to 10th	Day	4 3 2 4 4 6% 6% 6% 9% 13% 43%	3905
	11th to 20th	Day	5% 4 2 6% 6% 5% 6% 6% 8% 12% 42%	3849
	21st to end	Day	6% 5% 2 8% 8% 7% 8% 6% 8% 10% 33%	4312
September	1st to 10th	Day	9% 5% 2 7% 5% 6% 7% 6% 8% 10% 35%	2392
	11th to 20th	Day	9% 7% 3 7% 5% 6% 6% 4 7% 7% 40%	2200
	21st to end	Day	7% 4 2 6% 4 5% 5% 4 6% 8% 50%	2200
October	1st to 10th	Day	7% 4 2 6% 4 4 3 4 5% 8% 52%	2200
	11th to 20th	Day	7% 3 1 3 3 3 3 3 6% 7% 60%	2192
	21st to end	Day	8% 5% 1 6% 4 3 4 4 5% 6% 54%	2200
November	1st to 10th	Day	8% 5% 2 4 4 4 4 3 5% 7% 56%	1872
	11th to 20th	Day	10% 4 1 4 3 2 3 3 5% 7% 57%	1863
	21st to end	Day	10% 5% 2 6% 4 4 3 3 6% 7% 49%	1800
December	1st to 10th	Day	14% 6% 2 6% 4 3 4 2 5% 7% 48%	2930
	11th to 20th	Day	8% 6% 2 6% 4 4 4 3 5% 6% 52%	3373
	21st to end	Day	15% 8% 3 6% 4 3 3 3 4 6% 45%	4466
January	1st to 10th	Night	13% 6% 2 5% 4 5% 5% 3 5% 5% 47%	5549
	11th to 20th	Night	17% 9% 3 6% 3 3 3 2 3 5% 46%	5440
	21st to end	Night	17% 9% 3 6% 4 4 4 3 5% 6% 39%	5984
February	1st to 10th	Night	14% 8% 2 6% 4 3 4 4 5% 6% 46%	2400
	11th to 20th	Night	17% 7% 2 6% 4 3 4 4 5% 5% 43%	2338
	21st to end	Night	15% 8% 3 7% 4 4 5% 3 6% 6% 40%	1980
March	1st to 10th	Night	20% 9% 3 7% 3 3 3 3 5% 7% 36%	5373
	11th to 20th	Night	13% 7% 2 5% 4 3 4 3 6% 7% 48%	5312
	21st to end	Night	13% 7% 2 5% 3 4 3 3 5% 6% 48%	4967
April	1st to 10th	Night	12% 6% 2 7% 5% 4 4 3 5% 6% 45%	2000
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 6% 7% 49%	1975
	21st to end	Night	6% 4 2 4 3 3 4 3 6% 8% 60%	2000
May	1st to 10th	Night	11% 7% 3 8% 5% 5% 5% 4 7% 9% 37%	4490
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 6% 10% 46%	4198
	21st to end	Night	5% 3 2 5% 4 5% 6% 4 7% 13% 47%	4421
June	1st to 10th	Night	7% 4 2 5% 5% 5% 5% 4 8% 13% 41%	1800
	11th to 20th	Night	3 3 2 5% 4 4 5% 6% 9% 12% 46%	1800
	21st to end	Night	6% 5% 1 5% 6% 6% 6% 5% 9% 12% 39%	1800
July	1st to 10th	Night	3 4 2 7% 5% 6% 7% 6% 9% 15% 36%	4058
	11th to 20th	Night	2 3 1 5% 4 5% 5% 5% 10% 13% 48%	4505
	21st to end	Night	2 3 1 7% 6% 6% 7% 7% 11% 15% 35%	4929
August	1st to 10th	Night	2 2 1 5% 4 5% 6% 5% 9% 14% 47%	3244
	11th to 20th	Night	3 3 1 6% 4 4 5% 5% 8% 12% 49%	3200
	21st to end	Night	4 4 2 6% 5% 6% 6% 5% 9% 11% 42%	3586
September	1st to 10th	Night	7% 6% 2 6% 4 5% 6% 5% 8% 11% 40%	2000
	11th to 20th	Night	8% 5% 3 7% 5% 5% 4 4 7% 8% 45%	2186
	21st to end	Night	6% 5% 2 6% 4 4 4 4 6% 8% 51%	2200
October	1st to 10th	Night	5% 5% 2 6% 4 4 4 3 5% 8% 54%	2200
	11th to 20th	Night	6% 5% 1 3 3 3 3 3 4 6% 64%	2202
	21st to end	Night	9% 5% 1 5% 3 4 3 3 4 5% 57%	2640
November	1st to 10th	Night	7% 5% 1 5% 3 4 4 3 5% 6% 57%	2644
	11th to 20th	Night	10% 5% 2 6% 3 3 3 3 4 5% 55%	2692
	21st to end	Night	10% 6% 2 5% 4 4 4 4 6% 8% 49%	2600
December	1st to 10th	Night	11% 6% 2 6% 4 3 4 3 6% 6% 47%	4250
	11th to 20th	Night	12% 5% 2 5% 3 3 4 4 5% 7% 52%	4822
	21st to end	Night	16% 8% 3 8% 3 4 3 2 4 4 45%	6490

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	34% 5% 6% 18% 27% 11%	4379
	11th to 20th	Day	35% 4 6% 17% 28% 10%	4520
	21st to end	Day	47% 5% 7% 14% 16% 11%	4972
February	1st to 10th	Day	43% 4 8% 14% 19% 11%	2000
	11th to 20th	Day	39% 7% 8% 16% 20% 9%	1958
	21st to end	Day	41% 7% 10% 16% 16% 9%	1650
March	1st to 10th	Day	43% 5% 8% 18% 17% 8%	4480
	11th to 20th	Day	28% 6% 10% 17% 23% 15%	4681
	21st to end	Day	41% 5% 11% 18% 15% 9%	5969
April	1st to 10th	Day	37% 6% 11% 17% 19% 9%	2400
	11th to 20th	Day	35% 6% 10% 20% 20% 9%	2374
	21st to end	Day	27% 7% 11% 24% 22% 9%	2400
May	1st to 10th	Day	35% 10% 16% 23% 13% 3	5440
	11th to 20th	Day	32% 7% 19% 27% 13% 1	5681
	21st to end	Day	27% 9% 17% 31% 13% 2	6447
June	1st to 10th	Day	39% 12% 17% 22% 9% 1	2600
	11th to 20th	Day	32% 13% 18% 24% 11% 2	2600
	21st to end	Day	38% 14% 22% 17% 9% 1	2600
July	1st to 10th	Day	36% 16% 31% 15% 3	5835
	11th to 20th	Day	34% 16% 36% 12% 1	5382
	21st to end	Day	38% 18% 26% 16% 1	5752
August	1st to 10th	Day	27% 12% 19% 26% 15% 1	3893
	11th to 20th	Day	31% 12% 20% 22% 13% 1	3885
	21st to end	Day	41% 13% 19% 15% 10% 2	4311
September	1st to 10th	Day	39% 11% 18% 15% 12% 4	2392
	11th to 20th	Day	40% 9% 14% 15% 16% 7%	2200
	21st to end	Day	32% 7% 12% 21% 20% 8%	2200
October	1st to 10th	Day	31% 4 8% 11% 16% 29%	3590
	11th to 20th	Day	16% 3 5% 20% 23% 33%	3548
	21st to end	Day	22% 4 5% 11% 38% 19%	3538
November	1st to 10th	Day	29% 4 8% 20% 23% 15%	1872
	11th to 20th	Day	28% 5% 7% 16% 29% 14%	1863
	21st to end	Day	33% 7% 7% 18% 22% 13%	1800
December	1st to 10th	Day	38% 5% 9% 17% 24% 8%	2930
	11th to 20th	Day	33% 5% 8% 25% 19% 11%	3370
	21st to end	Day	40% 6% 6% 16% 28% 4	4466
January	1st to 10th	Night	37% 5% 6% 14% 28% 10%	5549
	11th to 20th	Night	43% 3 5% 12% 30% 8%	5440
	21st to end	Night	45% 4 8% 14% 20% 10%	5984
February	1st to 10th	Night	40% 4 7% 16% 22% 11%	2400
	11th to 20th	Night	43% 5% 6% 14% 19% 13%	2339
	21st to end	Night	43% 6% 9% 16% 13% 13%	1980
March	1st to 10th	Night	47% 5% 8% 15% 18% 8%	5373
	11th to 20th	Night	35% 6% 9% 14% 19% 16%	5312
	21st to end	Night	36% 5% 13% 21% 15% 10%	4967
April	1st to 10th	Night	38% 6% 12% 13% 19% 11%	2000
	11th to 20th	Night	33% 5% 11% 20% 22% 9%	1975
	21st to end	Night	24% 5% 12% 29% 23% 7%	2000
May	1st to 10th	Night	39% 9% 19% 18% 13% 3	4520
	11th to 20th	Night	33% 7% 18% 26% 15% 1	4199
	21st to end	Night	26% 8% 19% 33% 12% 1	4429
June	1st to 10th	Night	32% 9% 22% 26% 9% 2	1800
	11th to 20th	Night	26% 12% 25% 24% 12% 1	1800
	21st to end	Night	33% 12% 26% 18% 9% 1	1800
July	1st to 10th	Night	33% 14% 33% 17% 3	4015
	11th to 20th	Night	24% 15% 45% 14% 1	4449
	21st to end	Night	31% 20% 27% 21% 2	4785
August	1st to 10th	Night	22% 12% 27% 26% 12% 1	3232
	11th to 20th	Night	24% 11% 26% 28% 10%	3230
	21st to end	Night	34% 14% 22% 17% 11% 3	3586
September	1st to 10th	Night	34% 11% 21% 17% 12% 4	2000
	11th to 20th	Night	34% 9% 15% 19% 16% 6%	2186
	21st to end	Night	29% 7% 14% 24% 17% 9%	2200
October	1st to 10th	Night	33% 5% 8% 13% 20% 21%	3590
	11th to 20th	Night	13% 3 6% 18% 27% 32%	3585
	21st to end	Night	20% 3 5% 11% 44% 17%	4252
November	1st to 10th	Night	29% 4 8% 17% 26% 15%	2644
	11th to 20th	Night	32% 4 5% 19% 26% 14%	2692
	21st to end	Night	32% 6% 9% 18% 22% 13%	2600
December	1st to 10th	Night	36% 4 8% 18% 22% 11%	4250
	11th to 20th	Night	33% 4 8% 25% 21% 10%	4824
	21st to end	Night	42% 4 6% 17% 25% 6%	6490

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	17% 14% 40% 20% 7% 1	300
	11th to 20th	Day	15% 14% 31% 28% 11% 2	300
	21st to end	Day	21% 14% 38% 22% 5% 1	330
February	1st to 10th	Day	19% 16% 34% 23% 7% 1	300
	11th to 20th	Day	20% 18% 34% 21% 6% 1	300
	21st to end	Day	13% 20% 40% 21% 6%	249
March	1st to 10th	Day	15% 15% 40% 23% 7%	300
	11th to 20th	Day	16% 16% 36% 22% 11%	347
	21st to end	Day	15% 11% 31% 29% 12% 1	550
April	1st to 10th	Day	15% 12% 32% 25% 14% 2	500
	11th to 20th	Day	11% 14% 28% 26% 18% 3	492
	21st to end	Day	7% 7% 28% 32% 21% 5%	500
May	1st to 10th	Day	8% 5% 29% 29% 24% 5%	503
	11th to 20th	Day	9% 3 18% 28% 27% 14%	527
	21st to end	Day	6% 2 15% 32% 28% 18%	573
June	1st to 10th	Day	10% 2 11% 26% 32% 20%	530
	11th to 20th	Day	7% 2 12% 21% 33% 25%	530
	21st to end	Day	8% 9% 22% 33% 28%	530
July	1st to 10th	Day	8% 6% 17% 34% 35%	525
	11th to 20th	Day	6% 1 3 16% 34% 40%	524
	21st to end	Day	5% 1 4 16% 43% 31%	576
August	1st to 10th	Day	7% 3 17% 34% 38%	526
	11th to 20th	Day	10% 1 4 13% 33% 40%	519
	21st to end	Day	9% 1 8% 19% 32% 31%	583
September	1st to 10th	Day	9% 2 6% 19% 35% 28%	530
	11th to 20th	Day	12% 3 9% 22% 35% 19%	530
	21st to end	Day	9% 2 8% 29% 33% 19%	530
October	1st to 10th	Day	9% 3 18% 37% 25% 8%	530
	11th to 20th	Day	7% 5% 16% 30% 30% 12%	522
	21st to end	Day	14% 7% 20% 33% 20% 6%	363
November	1st to 10th	Day	13% 6% 22% 34% 22% 3	330
	11th to 20th	Day	14% 6% 27% 31% 18% 3	321
	21st to end	Day	11% 8% 33% 27% 17% 3	300
December	1st to 10th	Day	18% 9% 32% 26% 11% 4	300
	11th to 20th	Day	17% 12% 35% 24% 9% 2	300
	21st to end	Day	20% 14% 28% 21% 15% 1	330
January	1st to 10th	Night	16% 7% 34% 35% 8%	800
	11th to 20th	Night	16% 9% 28% 35% 12%	800
	21st to end	Night	21% 9% 32% 31% 7%	880
February	1st to 10th	Night	17% 9% 30% 35% 9%	800
	11th to 20th	Night	21% 9% 32% 28% 10%	783
	21st to end	Night	16% 12% 32% 35% 5%	660
March	1st to 10th	Night	16% 8% 31% 35% 11% 1	800
	11th to 20th	Night	13% 7% 30% 34% 15% 2	800
	21st to end	Night	12% 6% 27% 38% 17% 1	665
April	1st to 10th	Night	16% 6% 23% 37% 17% 1	600
	11th to 20th	Night	13% 5% 25% 33% 23% 1	593
	21st to end	Night	7% 4 18% 41% 29% 3	600
May	1st to 10th	Night	9% 4 16% 40% 27% 5%	600
	11th to 20th	Night	6% 3 12% 39% 34% 6%	591
	21st to end	Night	6% 2 9% 30% 44% 10%	650
June	1st to 10th	Night	9% 8% 27% 46% 10%	600
	11th to 20th	Night	4 1 4 21% 51% 20%	600
	21st to end	Night	8% 1 5% 19% 45% 22%	600
July	1st to 10th	Night	4 3 12% 50% 30%	585
	11th to 20th	Night	4 3 8% 46% 39%	582
	21st to end	Night	3 2 12% 52% 30%	657
August	1st to 10th	Night	3 3 9% 48% 38%	597
	11th to 20th	Night	7% 3 9% 48% 33%	594
	21st to end	Night	8% 1 6% 17% 45% 22%	660
September	1st to 10th	Night	9% 2 5% 19% 44% 22%	600
	11th to 20th	Night	10% 1 8% 25% 42% 13%	786
	21st to end	Night	9% 1 9% 29% 43% 9%	800
October	1st to 10th	Night	8% 2 16% 37% 32% 6%	800
	11th to 20th	Night	8% 3 15% 35% 33% 6%	800
	21st to end	Night	12% 4 18% 36% 26% 3	880
November	1st to 10th	Night	11% 5% 17% 41% 23% 3	820
	11th to 20th	Night	11% 7% 23% 38% 19% 2	829
	21st to end	Night	12% 6% 26% 36% 17% 3	800
December	1st to 10th	Night	13% 7% 28% 34% 17% 2	800
	11th to 20th	Night	19% 6% 26% 33% 15% 1	800
	21st to end	Night	22% 7% 27% 33% 10% 1	880

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