A & O Farm
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the A & O Farm clear sky chart from 2005-11-06 to 2025-08-05.

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% 10% 3 8% 5% 5% 4 4 6% 7% 33%	125296
	Night	16% 10% 4 8% 5% 4 4 3 5% 7% 34%	122745
Transparency	Day	47% 6% 10% 22% 13% 2	128941
	Night	48% 5% 10% 21% 13% 2	127169
Seeing	Day	22% 13% 26% 22% 13% 5%	15858
	Night	21% 10% 24% 28% 14% 2	26089

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	17% 22% 8% 15% 6% 3 3 2 3 5% 17%	4056
	11th to 20th	Day	16% 20% 8% 12% 7% 4 4 2 3 3 20%	4060
	21st to end	Day	20% 17% 5% 11% 7% 5% 4 3 3 4 22%	4466
February	1st to 10th	Day	23% 13% 4 10% 5% 4 3 2 4 5% 27%	1800
	11th to 20th	Day	20% 16% 3 11% 4 3 4 3 5% 6% 25%	1851
	21st to end	Day	21% 13% 3 8% 5% 4 3 3 5% 5% 30%	1650
March	1st to 10th	Day	17% 16% 4 7% 5% 4 4 3 4 5% 32%	4883
	11th to 20th	Day	13% 7% 3 6% 5% 4 4 3 5% 7% 43%	4980
	21st to end	Day	18% 9% 3 8% 4 5% 5% 4 5% 7% 31%	5465
April	1st to 10th	Day	15% 11% 2 8% 5% 4 4 3 6% 7% 33%	2220
	11th to 20th	Day	16% 9% 3 6% 5% 4 4 3 4 7% 39%	2482
	21st to end	Day	18% 8% 2 7% 5% 4 5% 4 6% 7% 34%	2600
May	1st to 10th	Day	19% 9% 3 8% 6% 6% 5% 5% 7% 7% 26%	5862
	11th to 20th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 8% 30%	5861
	21st to end	Day	15% 7% 2 7% 5% 4 5% 4 6% 9% 34%	6433
June	1st to 10th	Day	12% 7% 3 6% 5% 5% 4 4 7% 8% 39%	2600
	11th to 20th	Day	11% 6% 3 7% 5% 5% 5% 5% 7% 10% 36%	2600
	21st to end	Day	11% 6% 2 6% 5% 4 6% 5% 6% 10% 38%	2600
July	1st to 10th	Day	8% 6% 2 7% 5% 5% 6% 4 6% 8% 42%	5900
	11th to 20th	Day	11% 7% 2 8% 5% 6% 6% 5% 7% 9% 34%	5900
	21st to end	Day	12% 8% 3 8% 5% 6% 6% 5% 6% 8% 34%	6424
August	1st to 10th	Day	9% 6% 3 7% 6% 6% 5% 5% 8% 9% 35%	4156
	11th to 20th	Day	9% 6% 3 7% 5% 5% 6% 5% 8% 9% 39%	4044
	21st to end	Day	6% 4 2 5% 5% 5% 5% 5% 6% 9% 49%	4404
September	1st to 10th	Day	14% 5% 2 5% 4 4 4 3 5% 6% 48%	2154
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 5% 8% 46%	2090
	21st to end	Day	19% 9% 2 6% 3 4 3 3 4 6% 40%	2090
October	1st to 10th	Day	14% 6% 2 5% 4 4 3 3 6% 9% 44%	1971
	11th to 20th	Day	16% 7% 2 6% 4 4 4 3 4 6% 42%	1900
	21st to end	Day	21% 7% 3 6% 4 4 3 3 4 6% 39%	2090
November	1st to 10th	Day	12% 6% 2 6% 3 4 4 4 4 6% 49%	1826
	11th to 20th	Day	16% 13% 3 6% 5% 3 3 4 6% 6% 35%	1800
	21st to end	Day	17% 12% 4 7% 5% 4 5% 2 5% 5% 34%	1777
December	1st to 10th	Day	21% 12% 4 13% 6% 4 3 2 4 4 27%	2600
	11th to 20th	Day	25% 15% 5% 9% 5% 3 3 3 5% 5% 23%	3235
	21st to end	Day	20% 16% 5% 10% 6% 5% 5% 4 5% 5% 18%	4466
January	1st to 10th	Night	16% 17% 7% 17% 5% 4 4 3 4 4 20%	5889
	11th to 20th	Night	18% 17% 6% 12% 7% 6% 3 3 4 4 21%	5900
	21st to end	Night	22% 13% 4 10% 5% 4 4 2 4 4 29%	6490
February	1st to 10th	Night	21% 13% 4 9% 5% 3 4 3 4 5% 28%	2600
	11th to 20th	Night	22% 13% 4 8% 5% 5% 4 3 5% 5% 26%	2433
	21st to end	Night	22% 14% 3 8% 5% 4 4 3 4 5% 28%	1980
March	1st to 10th	Night	21% 13% 3 6% 4 3 3 3 4 6% 36%	4968
	11th to 20th	Night	12% 9% 3 6% 4 3 4 3 5% 8% 42%	4980
	21st to end	Night	17% 10% 3 7% 5% 5% 4 3 5% 6% 34%	5467
April	1st to 10th	Night	18% 11% 3 7% 5% 3 4 3 5% 6% 34%	2180
	11th to 20th	Night	16% 8% 3 6% 5% 4 4 3 6% 8% 39%	1882
	21st to end	Night	15% 7% 3 8% 4 4 4 3 5% 7% 40%	1800
May	1st to 10th	Night	23% 10% 4 9% 5% 4 4 4 5% 6% 26%	4033
	11th to 20th	Night	16% 8% 3 7% 5% 4 5% 4 6% 8% 34%	4032
	21st to end	Night	17% 8% 2 7% 4 5% 5% 3 5% 8% 35%	4421
June	1st to 10th	Night	10% 6% 2 5% 5% 4 5% 4 6% 9% 45%	1800
	11th to 20th	Night	9% 6% 3 7% 5% 5% 6% 4 6% 9% 41%	1800
	21st to end	Night	11% 4 2 5% 4 4 5% 5% 7% 11% 43%	1800
July	1st to 10th	Night	9% 7% 3 7% 4 5% 4 3 6% 8% 43%	4058
	11th to 20th	Night	10% 7% 3 8% 5% 5% 5% 4 6% 10% 35%	4057
	21st to end	Night	9% 8% 3 8% 5% 5% 5% 5% 7% 8% 37%	4427
August	1st to 10th	Night	10% 8% 3 8% 5% 5% 5% 4 7% 10% 35%	2861
	11th to 20th	Night	11% 7% 3 8% 5% 4 4 4 6% 6% 43%	2785
	21st to end	Night	6% 4 2 6% 4 5% 5% 4 7% 10% 48%	3220
September	1st to 10th	Night	12% 4 2 4 4 4 4 3 4 7% 51%	2023
	11th to 20th	Night	10% 4 2 4 4 4 4 4 5% 6% 53%	2090
	21st to end	Night	16% 6% 3 6% 4 4 4 3 5% 6% 43%	2090
October	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 5% 7% 48%	2209
	11th to 20th	Night	16% 6% 3 6% 4 3 3 3 4 6% 46%	2280
	21st to end	Night	21% 7% 2 5% 4 3 4 2 4 6% 42%	2508
November	1st to 10th	Night	13% 7% 2 5% 4 4 3 3 5% 5% 49%	2469
	11th to 20th	Night	17% 11% 3 7% 4 4 4 4 6% 6% 35%	2600
	21st to end	Night	19% 11% 4 7% 5% 4 4 3 4 6% 34%	2612
December	1st to 10th	Night	19% 13% 5% 12% 5% 3 4 3 5% 6% 26%	4580
	11th to 20th	Night	18% 16% 7% 9% 5% 4 4 3 4 5% 25%	4931
	21st to end	Night	19% 17% 5% 9% 5% 5% 4 3 5% 6% 21%	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	70% 4 10% 12% 4	4057
	11th to 20th	Day	70% 3 7% 12% 8% 1	4060
	21st to end	Day	66% 4 8% 15% 7% 1	4466
February	1st to 10th	Day	60% 3 10% 18% 8% 1	1800
	11th to 20th	Day	60% 4 9% 16% 9% 1	1860
	21st to end	Day	56% 3 10% 19% 10% 1	1650
March	1st to 10th	Day	54% 4 7% 23% 10% 3	4883
	11th to 20th	Day	39% 5% 8% 30% 15% 3	4980
	21st to end	Day	50% 5% 9% 22% 12% 2	5465
April	1st to 10th	Day	50% 5% 10% 19% 13% 3	2220
	11th to 20th	Day	45% 4 11% 19% 17% 4	2482
	21st to end	Day	47% 6% 11% 21% 12% 2	2600
May	1st to 10th	Day	53% 7% 11% 17% 9% 2	5897
	11th to 20th	Day	51% 6% 10% 21% 11% 1	5865
	21st to end	Day	43% 8% 13% 21% 13% 3	6447
June	1st to 10th	Day	40% 6% 14% 22% 16% 2	2600
	11th to 20th	Day	41% 8% 14% 20% 15% 1	2600
	21st to end	Day	39% 8% 15% 23% 14% 2	2600
July	1st to 10th	Day	39% 7% 11% 24% 18% 2	5835
	11th to 20th	Day	42% 9% 12% 25% 11% 1	5831
	21st to end	Day	44% 8% 11% 18% 16% 2	6240
August	1st to 10th	Day	40% 9% 13% 27% 10%	4143
	11th to 20th	Day	37% 8% 10% 28% 16% 1	4083
	21st to end	Day	29% 7% 13% 29% 19% 2	4404
September	1st to 10th	Day	36% 5% 10% 22% 22% 5%	2154
	11th to 20th	Day	35% 6% 10% 26% 20% 3	2090
	21st to end	Day	44% 6% 8% 22% 19% 1	2090
October	1st to 10th	Day	27% 5% 8% 26% 31% 2	3270
	11th to 20th	Day	33% 5% 12% 26% 18% 5%	3140
	21st to end	Day	33% 3 11% 29% 21% 2	3428
November	1st to 10th	Day	36% 4 9% 30% 18% 3	1826
	11th to 20th	Day	49% 4 8% 21% 16% 3	1800
	21st to end	Day	52% 4 9% 21% 13% 1	1777
December	1st to 10th	Day	61% 4 10% 20% 4	2600
	11th to 20th	Day	64% 4 9% 18% 5%	3232
	21st to end	Day	66% 5% 11% 14% 4	4466
January	1st to 10th	Night	67% 4 9% 15% 5%	5889
	11th to 20th	Night	67% 4 9% 12% 6% 2	5900
	21st to end	Night	60% 3 10% 18% 8% 1	6490
February	1st to 10th	Night	58% 4 11% 18% 9% 1	2600
	11th to 20th	Night	60% 4 9% 17% 10% 1	2435
	21st to end	Night	58% 4 10% 16% 9% 3	1980
March	1st to 10th	Night	50% 3 6% 25% 13% 2	4968
	11th to 20th	Night	39% 6% 9% 28% 17% 2	4980
	21st to end	Night	50% 4 7% 22% 13% 3	5467
April	1st to 10th	Night	50% 4 9% 20% 15% 2	2180
	11th to 20th	Night	42% 5% 11% 20% 15% 5%	1882
	21st to end	Night	43% 5% 10% 22% 17% 2	1800
May	1st to 10th	Night	57% 7% 11% 13% 8% 3	4060
	11th to 20th	Night	45% 9% 12% 21% 12% 1	4033
	21st to end	Night	45% 7% 12% 23% 9% 3	4429
June	1st to 10th	Night	35% 8% 10% 26% 18% 3	1800
	11th to 20th	Night	37% 8% 14% 20% 18% 2	1800
	21st to end	Night	33% 9% 15% 23% 19% 2	1800
July	1st to 10th	Night	38% 7% 9% 24% 19% 3	4015
	11th to 20th	Night	40% 9% 17% 22% 10% 1	4006
	21st to end	Night	40% 9% 12% 19% 17% 3	4297
August	1st to 10th	Night	42% 8% 15% 25% 10% 1	2850
	11th to 20th	Night	39% 6% 10% 23% 21% 1	2812
	21st to end	Night	29% 8% 12% 29% 20% 3	3220
September	1st to 10th	Night	33% 5% 12% 21% 22% 7%	2023
	11th to 20th	Night	30% 6% 11% 26% 24% 3	2090
	21st to end	Night	41% 6% 11% 20% 21% 2	2090
October	1st to 10th	Night	30% 4 8% 27% 27% 5%	3690
	11th to 20th	Night	31% 5% 10% 24% 23% 8%	3779
	21st to end	Night	33% 3 6% 28% 26% 5%	4120
November	1st to 10th	Night	37% 4 10% 23% 21% 5%	2469
	11th to 20th	Night	48% 4 8% 20% 16% 3	2600
	21st to end	Night	53% 4 9% 21% 12% 1	2612
December	1st to 10th	Night	59% 4 11% 20% 5%	4580
	11th to 20th	Night	62% 4 11% 16% 6%	4933
	21st to end	Night	63% 5% 10% 15% 7%	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	32% 22% 32% 10% 3 1	300
	11th to 20th	Day	39% 22% 30% 8% 1	300
	21st to end	Day	35% 25% 28% 8% 3	330
February	1st to 10th	Day	35% 24% 29% 10% 3	300
	11th to 20th	Day	47% 21% 26% 4 2	300
	21st to end	Day	35% 21% 36% 7% 1	249
March	1st to 10th	Day	30% 20% 27% 19% 5%	472
	11th to 20th	Day	29% 20% 31% 13% 6% 1	500
	21st to end	Day	33% 16% 30% 18% 3	550
April	1st to 10th	Day	30% 19% 28% 15% 7% 1	500
	11th to 20th	Day	27% 17% 28% 18% 7% 3	492
	21st to end	Day	27% 17% 28% 19% 7% 2	500
May	1st to 10th	Day	28% 15% 29% 17% 9% 3	503
	11th to 20th	Day	22% 11% 30% 22% 11% 4	527
	21st to end	Day	16% 10% 25% 27% 17% 6%	573
June	1st to 10th	Day	16% 7% 25% 29% 18% 5%	530
	11th to 20th	Day	14% 8% 23% 31% 17% 6%	530
	21st to end	Day	12% 8% 31% 25% 19% 6%	530
July	1st to 10th	Day	12% 5% 20% 26% 21% 15%	525
	11th to 20th	Day	9% 6% 23% 33% 19% 10%	524
	21st to end	Day	17% 4 18% 29% 21% 10%	576
August	1st to 10th	Day	11% 6% 20% 33% 22% 9%	502
	11th to 20th	Day	12% 6% 19% 32% 21% 10%	479
	21st to end	Day	11% 4 19% 28% 26% 12%	539
September	1st to 10th	Day	16% 5% 17% 29% 22% 11%	490
	11th to 20th	Day	11% 3 16% 29% 28% 13%	490
	21st to end	Day	24% 10% 22% 22% 18% 3	490
October	1st to 10th	Day	14% 9% 27% 28% 18% 5%	490
	11th to 20th	Day	21% 12% 27% 22% 14% 3	490
	21st to end	Day	25% 13% 30% 22% 9% 1	539
November	1st to 10th	Day	18% 15% 35% 21% 8% 3	364
	11th to 20th	Day	30% 15% 28% 19% 6% 1	300
	21st to end	Day	23% 22% 33% 18% 3	287
December	1st to 10th	Day	30% 19% 34% 16% 2 1	200
	11th to 20th	Day	32% 19% 30% 16% 3	257
	21st to end	Day	37% 16% 28% 15% 5%	330
January	1st to 10th	Night	28% 18% 29% 21% 4	800
	11th to 20th	Night	33% 16% 27% 20% 4	800
	21st to end	Night	27% 17% 33% 20% 3	880
February	1st to 10th	Night	27% 15% 30% 27% 2	800
	11th to 20th	Night	33% 18% 28% 19% 2	783
	21st to end	Night	30% 17% 31% 20% 2	660
March	1st to 10th	Night	27% 14% 31% 24% 5%	800
	11th to 20th	Night	27% 16% 28% 21% 7% 1	800
	21st to end	Night	27% 16% 30% 22% 5%	880
April	1st to 10th	Night	27% 15% 32% 19% 6%	800
	11th to 20th	Night	20% 13% 33% 24% 10% 1	698
	21st to end	Night	18% 8% 35% 31% 7% 1	600
May	1st to 10th	Night	20% 11% 28% 28% 13% 1	600
	11th to 20th	Night	18% 7% 28% 30% 16% 1	591
	21st to end	Night	13% 4 22% 31% 25% 4	650
June	1st to 10th	Night	13% 3 23% 37% 23% 1	600
	11th to 20th	Night	11% 4 20% 38% 25% 3	600
	21st to end	Night	12% 4 18% 37% 27% 2	600
July	1st to 10th	Night	11% 4 13% 37% 30% 5%	585
	11th to 20th	Night	10% 5% 14% 34% 32% 5%	582
	21st to end	Night	12% 3 13% 37% 30% 4	657
August	1st to 10th	Night	11% 3 10% 40% 34% 2	579
	11th to 20th	Night	10% 3 14% 37% 30% 5%	564
	21st to end	Night	11% 4 11% 35% 33% 7%	684
September	1st to 10th	Night	13% 3 14% 35% 29% 7%	760
	11th to 20th	Night	11% 3 14% 33% 35% 4	760
	21st to end	Night	19% 6% 18% 34% 20% 4	760
October	1st to 10th	Night	15% 6% 20% 33% 24% 3	760
	11th to 20th	Night	18% 8% 26% 30% 16% 1	760
	21st to end	Night	25% 9% 21% 31% 12% 1	836
November	1st to 10th	Night	17% 9% 27% 33% 14% 1	780
	11th to 20th	Night	24% 13% 27% 26% 10% 1	800
	21st to end	Night	25% 13% 26% 29% 7% 1	800
December	1st to 10th	Night	33% 14% 26% 23% 5%	800
	11th to 20th	Night	25% 15% 30% 24% 6%	800
	21st to end	Night	29% 13% 28% 28% 2	880

Page generated at 2025-08-02 01:32:27. Version ac07

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