Heritage Farms Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heritage Farms Observatory clear sky chart from 2005-11-06 to 2025-02-06.

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	12% 6% 2 6% 4 5% 5% 4 6% 8% 43%	108889
	Night	12% 6% 2 6% 4 4 4 4 6% 7% 45%	109369
Transparency	Day	36% 8% 12% 19% 19% 7%	112696
	Night	35% 7% 11% 18% 20% 8%	113701
Seeing	Day	15% 9% 23% 24% 20% 9%	15354
	Night	14% 9% 23% 30% 20% 3	25460

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	15% 4 2 5% 3 3 3 2 4 5% 54%	4056
	11th to 20th	Day	13% 6% 2 4 2 2 3 2 4 7% 55%	4060
	21st to end	Day	17% 7% 2 6% 4 4 4 3 5% 6% 44%	4558
February	1st to 10th	Day	15% 8% 3 6% 5% 4 5% 3 6% 5% 40%	1950
	11th to 20th	Day	18% 7% 2 5% 3 4 4 3 5% 6% 44%	1848
	21st to end	Day	16% 8% 2 5% 4 4 4 3 5% 8% 41%	1570
March	1st to 10th	Day	22% 9% 3 7% 4 3 4 3 5% 5% 37%	3334
	11th to 20th	Day	9% 5% 2 5% 3 4 4 3 5% 8% 50%	3480
	21st to end	Day	18% 6% 2 6% 5% 4 4 3 5% 5% 43%	3815
April	1st to 10th	Day	11% 5% 2 6% 5% 4 3 4 5% 6% 49%	2090
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 6% 7% 48%	2185
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 7% 53%	2470
May	1st to 10th	Day	8% 6% 2 6% 5% 5% 4 3 5% 8% 47%	4082
	11th to 20th	Day	16% 7% 2 6% 5% 4 4 4 6% 7% 37%	4081
	21st to end	Day	6% 3 2 5% 5% 5% 5% 4 7% 9% 48%	4476
June	1st to 10th	Day	11% 6% 2 7% 6% 5% 5% 6% 8% 9% 34%	2470
	11th to 20th	Day	5% 4 1 6% 6% 5% 6% 6% 7% 13% 41%	2470
	21st to end	Day	5% 5% 2 7% 6% 7% 7% 6% 9% 10% 37%	2470
July	1st to 10th	Day	12% 7% 3 8% 7% 8% 7% 6% 9% 11% 22%	4120
	11th to 20th	Day	4 5% 2 7% 6% 7% 7% 6% 10% 13% 32%	4120
	21st to end	Day	7% 7% 3 9% 7% 8% 8% 7% 10% 12% 20%	4466
August	1st to 10th	Day	13% 5% 2 6% 5% 6% 7% 6% 9% 13% 28%	4104
	11th to 20th	Day	6% 5% 2 5% 4 5% 6% 4 7% 10% 45%	3893
	21st to end	Day	7% 5% 1 6% 4 4 5% 4 7% 10% 45%	4062
September	1st to 10th	Day	11% 7% 2 7% 5% 6% 5% 5% 7% 8% 37%	2090
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 4 8% 7% 38%	2090
	21st to end	Day	12% 7% 3 6% 4 4 4 3 6% 7% 43%	2090
October	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 5% 5% 52%	2090
	11th to 20th	Day	11% 4 1 3 3 3 3 3 5% 7% 57%	1938
	21st to end	Day	10% 4 2 4 3 3 4 3 5% 5% 57%	2090
November	1st to 10th	Day	12% 6% 3 5% 3 3 3 4 5% 5% 51%	1902
	11th to 20th	Day	13% 5% 2 4 3 3 3 2 4 6% 54%	1800
	21st to end	Day	13% 6% 2 5% 4 4 4 3 5% 8% 47%	1800
December	1st to 10th	Day	11% 7% 2 6% 5% 3 4 3 4 6% 50%	2930
	11th to 20th	Day	14% 6% 2 6% 3 4 3 4 5% 6% 48%	3373
	21st to end	Day	20% 7% 2 6% 3 3 3 3 4 6% 43%	4466
January	1st to 10th	Night	14% 5% 2 4 3 4 3 3 4 6% 53%	5889
	11th to 20th	Night	12% 5% 2 5% 4 4 4 4 5% 6% 48%	5900
	21st to end	Night	16% 8% 2 6% 4 3 3 3 5% 6% 43%	6380
February	1st to 10th	Night	14% 8% 3 5% 3 3 4 3 5% 6% 45%	2341
	11th to 20th	Night	19% 6% 2 5% 4 4 3 3 4 5% 46%	2218
	21st to end	Night	13% 8% 2 6% 5% 4 4 4 6% 6% 43%	1884
March	1st to 10th	Night	23% 8% 2 6% 4 3 4 3 4 5% 37%	3519
	11th to 20th	Night	12% 5% 2 4 3 4 4 4 6% 7% 49%	3480
	21st to end	Night	18% 5% 2 6% 4 5% 4 3 6% 6% 41%	3817
April	1st to 10th	Night	10% 5% 2 5% 4 3 4 3 6% 7% 50%	2090
	11th to 20th	Night	12% 4 2 4 3 4 4 3 6% 8% 50%	1959
	21st to end	Night	6% 4 2 5% 5% 4 4 4 5% 7% 54%	1710
May	1st to 10th	Night	6% 5% 2 6% 4 5% 5% 4 7% 12% 44%	2813
	11th to 20th	Night	12% 6% 2 6% 5% 5% 5% 4 7% 8% 41%	2812
	21st to end	Night	7% 4 2 5% 3 4 4 4 6% 10% 51%	3079
June	1st to 10th	Night	9% 6% 2 7% 6% 5% 6% 5% 7% 10% 36%	1710
	11th to 20th	Night	5% 4 2 5% 5% 5% 6% 6% 7% 13% 44%	1710
	21st to end	Night	6% 5% 2 5% 6% 6% 6% 6% 10% 11% 37%	1710
July	1st to 10th	Night	10% 9% 3 8% 6% 6% 7% 6% 8% 11% 26%	2840
	11th to 20th	Night	4 4 2 8% 6% 6% 7% 7% 12% 14% 28%	2840
	21st to end	Night	9% 7% 3 9% 8% 7% 8% 7% 9% 11% 23%	3087
August	1st to 10th	Night	11% 6% 3 9% 6% 6% 6% 5% 9% 11% 28%	2825
	11th to 20th	Night	7% 4 2 7% 4 6% 6% 5% 7% 9% 43%	2931
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 7% 10% 49%	3562
September	1st to 10th	Night	8% 7% 2 6% 5% 5% 6% 5% 7% 9% 38%	2090
	11th to 20th	Night	13% 6% 2 7% 5% 4 4 4 5% 7% 42%	2090
	21st to end	Night	11% 6% 2 6% 4 5% 5% 4 5% 7% 46%	2090
October	1st to 10th	Night	12% 4 2 6% 4 4 3 3 4 7% 52%	2090
	11th to 20th	Night	11% 5% 2 4 2 3 3 3 4 5% 59%	2241
	21st to end	Night	10% 5% 2 4 3 4 4 2 5% 6% 57%	2508
November	1st to 10th	Night	12% 6% 2 5% 3 3 4 3 5% 6% 53%	2392
	11th to 20th	Night	14% 5% 2 4 2 3 3 3 4 7% 53%	2600
	21st to end	Night	13% 5% 2 5% 4 4 4 4 4 6% 49%	2600
December	1st to 10th	Night	12% 6% 2 5% 3 3 3 2 4 5% 55%	4250
	11th to 20th	Night	15% 5% 2 6% 4 4 3 3 4 6% 49%	4822
	21st to end	Night	18% 7% 3 6% 4 4 3 3 4 6% 42%	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	32% 4 5% 16% 32% 10%	4057
	11th to 20th	Day	31% 3 4 16% 31% 14%	4060
	21st to end	Day	41% 4 6% 17% 22% 10%	4558
February	1st to 10th	Day	43% 5% 7% 16% 20% 8%	1950
	11th to 20th	Day	41% 5% 5% 17% 24% 7%	1858
	21st to end	Day	41% 6% 9% 15% 20% 10%	1570
March	1st to 10th	Day	47% 7% 9% 13% 16% 8%	3334
	11th to 20th	Day	30% 7% 10% 17% 24% 12%	3480
	21st to end	Day	41% 6% 9% 20% 16% 8%	3815
April	1st to 10th	Day	36% 5% 11% 20% 19% 10%	2090
	11th to 20th	Day	34% 6% 9% 18% 22% 11%	2185
	21st to end	Day	28% 7% 11% 24% 26% 5%	2470
May	1st to 10th	Day	33% 10% 12% 24% 18% 3	4120
	11th to 20th	Day	42% 9% 11% 22% 14% 1	4085
	21st to end	Day	28% 11% 16% 22% 21% 2	4489
June	1st to 10th	Day	41% 11% 15% 18% 12% 2	2470
	11th to 20th	Day	32% 10% 18% 24% 15% 1	2470
	21st to end	Day	37% 13% 19% 16% 12% 3	2470
July	1st to 10th	Day	49% 14% 19% 12% 4 2	4055
	11th to 20th	Day	36% 16% 24% 19% 3 1	4051
	21st to end	Day	48% 18% 18% 12% 4	4324
August	1st to 10th	Day	43% 12% 21% 22% 3	4091
	11th to 20th	Day	31% 11% 16% 29% 12% 1	3932
	21st to end	Day	32% 9% 18% 26% 13% 1	4062
September	1st to 10th	Day	40% 11% 15% 16% 14% 4	2090
	11th to 20th	Day	41% 8% 11% 18% 17% 4	2090
	21st to end	Day	39% 7% 10% 20% 18% 6%	2090
October	1st to 10th	Day	31% 5% 6% 14% 31% 13%	3480
	11th to 20th	Day	16% 3 5% 17% 26% 32%	3204
	21st to end	Day	21% 4 6% 18% 37% 15%	3428
November	1st to 10th	Day	35% 5% 8% 13% 26% 14%	1902
	11th to 20th	Day	33% 3 6% 20% 24% 15%	1800
	21st to end	Day	36% 6% 8% 17% 24% 9%	1800
December	1st to 10th	Day	36% 5% 7% 17% 26% 10%	2930
	11th to 20th	Day	37% 4 8% 22% 22% 7%	3370
	21st to end	Day	42% 5% 7% 20% 23% 3	4466
January	1st to 10th	Night	31% 6% 6% 18% 31% 9%	5889
	11th to 20th	Night	35% 6% 6% 17% 27% 10%	5900
	21st to end	Night	42% 4 5% 14% 27% 8%	6380
February	1st to 10th	Night	40% 4 8% 16% 22% 10%	2341
	11th to 20th	Night	41% 5% 6% 15% 22% 11%	2219
	21st to end	Night	39% 7% 9% 15% 16% 14%	1884
March	1st to 10th	Night	48% 6% 10% 14% 13% 8%	3519
	11th to 20th	Night	31% 8% 11% 13% 26% 12%	3480
	21st to end	Night	41% 7% 8% 16% 17% 11%	3817
April	1st to 10th	Night	33% 6% 10% 19% 20% 12%	2090
	11th to 20th	Night	31% 5% 9% 22% 22% 11%	1959
	21st to end	Night	28% 6% 11% 23% 22% 8%	1710
May	1st to 10th	Night	27% 13% 16% 22% 18% 4	2840
	11th to 20th	Night	37% 10% 14% 23% 15% 1	2813
	21st to end	Night	25% 9% 15% 27% 21% 4	3087
June	1st to 10th	Night	40% 11% 18% 17% 13%	1710
	11th to 20th	Night	28% 12% 19% 25% 13% 2	1710
	21st to end	Night	34% 13% 23% 15% 11% 4	1710
July	1st to 10th	Night	47% 15% 20% 12% 3 2	2795
	11th to 20th	Night	35% 18% 28% 15% 3 1	2786
	21st to end	Night	49% 17% 18% 12% 3 1	2988
August	1st to 10th	Night	44% 13% 21% 19% 2	2814
	11th to 20th	Night	31% 12% 18% 25% 12% 1	2958
	21st to end	Night	27% 10% 21% 29% 12% 1	3562
September	1st to 10th	Night	39% 12% 17% 15% 14% 4	2090
	11th to 20th	Night	41% 9% 12% 17% 17% 4	2090
	21st to end	Night	37% 8% 12% 18% 19% 6%	2090
October	1st to 10th	Night	34% 5% 8% 12% 29% 12%	3480
	11th to 20th	Night	18% 2 5% 12% 29% 34%	3714
	21st to end	Night	20% 4 5% 19% 32% 20%	4120
November	1st to 10th	Night	33% 5% 8% 14% 26% 15%	2392
	11th to 20th	Night	33% 4 7% 15% 27% 14%	2600
	21st to end	Night	35% 5% 8% 17% 24% 11%	2600
December	1st to 10th	Night	32% 4 7% 18% 31% 8%	4250
	11th to 20th	Night	37% 5% 11% 18% 21% 8%	4824
	21st to end	Night	44% 4 6% 20% 23% 3	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	21% 23% 42% 13% 2	300
	11th to 20th	Day	24% 22% 32% 15% 6% 1	300
	21st to end	Day	25% 26% 34% 11% 4	330
February	1st to 10th	Day	25% 18% 38% 15% 4	285
	11th to 20th	Day	27% 22% 33% 17% 1	270
	21st to end	Day	27% 19% 42% 9% 3	225
March	1st to 10th	Day	18% 20% 31% 24% 7% 1	393
	11th to 20th	Day	16% 18% 36% 21% 8%	460
	21st to end	Day	19% 19% 33% 22% 7%	506
April	1st to 10th	Day	23% 15% 27% 24% 10% 1	460
	11th to 20th	Day	15% 13% 30% 25% 14% 3	452
	21st to end	Day	12% 9% 27% 29% 18% 4	460
May	1st to 10th	Day	10% 15% 26% 28% 15% 6%	463
	11th to 20th	Day	14% 5% 23% 27% 21% 10%	487
	21st to end	Day	11% 6% 16% 30% 25% 12%	529
June	1st to 10th	Day	13% 2 19% 27% 27% 12%	490
	11th to 20th	Day	6% 3 17% 23% 28% 22%	490
	21st to end	Day	7% 3 13% 31% 30% 16%	490
July	1st to 10th	Day	8% 2 10% 23% 33% 24%	485
	11th to 20th	Day	7% 1 6% 21% 38% 26%	484
	21st to end	Day	5% 1 10% 26% 39% 20%	532
August	1st to 10th	Day	14% 2 13% 24% 29% 19%	486
	11th to 20th	Day	8% 1 9% 23% 39% 20%	479
	21st to end	Day	12% 2 11% 27% 30% 18%	539
September	1st to 10th	Day	12% 4 13% 26% 29% 15%	490
	11th to 20th	Day	15% 4 14% 27% 29% 11%	490
	21st to end	Day	16% 5% 16% 29% 27% 8%	490
October	1st to 10th	Day	15% 5% 25% 27% 21% 7%	490
	11th to 20th	Day	11% 7% 24% 31% 19% 7%	490
	21st to end	Day	14% 8% 24% 29% 21% 5%	539
November	1st to 10th	Day	21% 5% 26% 27% 16% 4	440
	11th to 20th	Day	18% 16% 37% 21% 6% 2	300
	21st to end	Day	17% 15% 32% 27% 9% 1	300
December	1st to 10th	Day	21% 20% 34% 17% 7% 1	300
	11th to 20th	Day	24% 16% 36% 17% 6% 1	300
	21st to end	Day	26% 16% 32% 20% 6% 1	330
January	1st to 10th	Night	21% 19% 33% 22% 5%	800
	11th to 20th	Night	19% 14% 32% 26% 9%	800
	21st to end	Night	21% 17% 34% 25% 3	880
February	1st to 10th	Night	20% 13% 30% 31% 7%	781
	11th to 20th	Night	23% 16% 32% 27% 3	743
	21st to end	Night	17% 18% 34% 28% 3	628
March	1st to 10th	Night	16% 14% 32% 32% 6%	760
	11th to 20th	Night	16% 16% 31% 29% 9% 1	760
	21st to end	Night	15% 16% 32% 28% 10%	836
April	1st to 10th	Night	15% 13% 31% 29% 12%	760
	11th to 20th	Night	14% 12% 26% 33% 14% 1	652
	21st to end	Night	7% 9% 26% 38% 19% 1	570
May	1st to 10th	Night	8% 8% 26% 38% 19% 1	570
	11th to 20th	Night	10% 3 25% 34% 24% 4	561
	21st to end	Night	12% 2 15% 35% 30% 5%	617
June	1st to 10th	Night	10% 1 14% 40% 32% 3	570
	11th to 20th	Night	5% 2 16% 32% 35% 10%	570
	21st to end	Night	7% 1 11% 35% 39% 7%	570
July	1st to 10th	Night	9% 2 7% 30% 37% 15%	555
	11th to 20th	Night	8% 1 7% 25% 46% 13%	552
	21st to end	Night	7% 1 7% 31% 46% 9%	624
August	1st to 10th	Night	7% 2 9% 31% 40% 12%	567
	11th to 20th	Night	11% 1 7% 30% 44% 7%	564
	21st to end	Night	13% 1 10% 29% 38% 10%	674
September	1st to 10th	Night	10% 2 11% 30% 38% 9%	760
	11th to 20th	Night	15% 2 12% 32% 35% 5%	760
	21st to end	Night	14% 3 16% 31% 32% 4	760
October	1st to 10th	Night	14% 3 21% 32% 25% 5%	760
	11th to 20th	Night	13% 7% 22% 31% 24% 3	760
	21st to end	Night	12% 8% 24% 32% 23% 2	836
November	1st to 10th	Night	14% 7% 23% 32% 22% 2	780
	11th to 20th	Night	17% 11% 25% 32% 15% 1	800
	21st to end	Night	15% 12% 27% 31% 15%	800
December	1st to 10th	Night	16% 12% 31% 29% 11% 1	800
	11th to 20th	Night	20% 11% 29% 30% 10% 1	800
	21st to end	Night	24% 15% 22% 31% 8%	880

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