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 2026-06-01.

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	11% 6% 2 6% 4 5% 5% 4 6% 8% 43%	132239
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	130913
Transparency	Day	36% 8% 12% 19% 18% 7%	136002
	Night	36% 7% 11% 18% 19% 8%	135220
Seeing	Day	15% 10% 23% 24% 19% 9%	17131
	Night	14% 9% 23% 31% 20% 3	27197

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	14% 5% 2 6% 3 4 4 3 5% 7% 48%	5258
	11th to 20th	Day	12% 5% 2 4 2 2 2 2 4 7% 58%	5280
	21st to end	Day	17% 8% 3 6% 4 4 4 3 5% 6% 40%	5900
February	1st to 10th	Day	14% 8% 3 6% 4 4 5% 3 6% 5% 41%	2100
	11th to 20th	Day	18% 7% 2 5% 3 4 4 3 5% 6% 43%	2048
	21st to end	Day	15% 7% 2 5% 4 4 4 3 5% 7% 42%	1730
March	1st to 10th	Day	19% 8% 2 6% 4 3 4 3 5% 6% 39%	4898
	11th to 20th	Day	8% 4 2 5% 3 4 4 3 5% 7% 54%	5090
	21st to end	Day	15% 7% 2 6% 4 4 4 3 4 5% 47%	5586
April	1st to 10th	Day	11% 5% 2 6% 5% 4 3 4 5% 6% 49%	2310
	11th to 20th	Day	10% 5% 1 5% 4 4 4 3 6% 7% 50%	2417
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 8% 51%	2730
May	1st to 10th	Day	11% 6% 3 7% 5% 5% 5% 3 6% 9% 42%	5992
	11th to 20th	Day	16% 6% 2 6% 5% 5% 5% 5% 7% 9% 34%	5991
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	6576
June	1st to 10th	Day	11% 6% 2 7% 6% 5% 5% 6% 8% 9% 34%	2600
	11th to 20th	Day	5% 4 2 6% 6% 6% 6% 6% 7% 13% 40%	2600
	21st to end	Day	5% 5% 2 7% 6% 7% 7% 6% 9% 10% 37%	2600
July	1st to 10th	Day	9% 7% 2 8% 7% 8% 7% 7% 9% 11% 25%	5900
	11th to 20th	Day	3 3 2 6% 5% 6% 7% 6% 10% 15% 37%	5900
	21st to end	Day	6% 6% 3 8% 6% 7% 8% 7% 10% 13% 26%	6424
August	1st to 10th	Day	14% 6% 2 6% 5% 6% 7% 6% 8% 13% 28%	4234
	11th to 20th	Day	6% 5% 2 5% 4 5% 6% 4 7% 10% 45%	4018
	21st to end	Day	8% 5% 1 6% 4 4 5% 4 7% 10% 45%	4190
September	1st to 10th	Day	10% 6% 2 7% 5% 6% 5% 5% 7% 9% 39%	2200
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 4 7% 7% 40%	2200
	21st to end	Day	12% 7% 3 6% 4 4 4 3 6% 7% 43%	2200
October	1st to 10th	Day	12% 6% 2 5% 4 4 3 3 5% 6% 50%	2200
	11th to 20th	Day	11% 4 1 3 3 3 3 3 5% 6% 58%	2040
	21st to end	Day	11% 5% 2 4 3 3 4 3 4 5% 57%	2200
November	1st to 10th	Day	12% 6% 3 5% 3 3 3 4 5% 5% 52%	1999
	11th to 20th	Day	13% 5% 2 4 3 3 3 2 4 6% 55%	1890
	21st to end	Day	13% 6% 2 5% 4 4 4 4 5% 8% 47%	1890
December	1st to 10th	Day	11% 7% 2 6% 5% 3 4 3 4 6% 49%	3020
	11th to 20th	Day	14% 6% 2 6% 3 4 3 4 4 6% 49%	3463
	21st to end	Day	20% 7% 2 6% 3 3 3 3 4 6% 44%	4565
January	1st to 10th	Night	12% 6% 2 5% 4 4 4 3 5% 6% 48%	7635
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 5% 50%	7680
	21st to end	Night	17% 9% 3 7% 4 3 4 3 4 6% 40%	8263
February	1st to 10th	Night	14% 8% 3 6% 3 3 4 3 5% 6% 46%	2520
	11th to 20th	Night	18% 7% 2 5% 4 4 3 3 4 5% 45%	2458
	21st to end	Night	13% 8% 2 6% 4 4 4 4 5% 6% 44%	2076
March	1st to 10th	Night	20% 7% 2 6% 4 4 4 3 4 6% 40%	5174
	11th to 20th	Night	10% 4 1 4 3 4 4 4 7% 7% 52%	5090
	21st to end	Night	14% 5% 2 5% 4 4 4 3 5% 6% 47%	5588
April	1st to 10th	Night	10% 5% 2 5% 4 4 5% 4 6% 7% 48%	2310
	11th to 20th	Night	11% 4 2 4 3 4 4 3 6% 7% 53%	2167
	21st to end	Night	6% 4 2 5% 5% 4 4 4 5% 7% 53%	1890
May	1st to 10th	Night	9% 6% 2 6% 5% 5% 5% 4 7% 11% 39%	4123
	11th to 20th	Night	15% 5% 2 5% 4 5% 5% 4 8% 9% 36%	4122
	21st to end	Night	9% 5% 2 6% 4 4 4 5% 7% 10% 45%	4520
June	1st to 10th	Night	9% 6% 2 7% 6% 5% 6% 6% 7% 10% 36%	1800
	11th to 20th	Night	5% 4 2 5% 5% 5% 6% 6% 8% 12% 43%	1800
	21st to end	Night	6% 5% 2 5% 6% 6% 6% 6% 10% 11% 38%	1800
July	1st to 10th	Night	9% 8% 3 8% 6% 7% 7% 6% 8% 11% 26%	4058
	11th to 20th	Night	3 4 2 8% 6% 6% 7% 7% 11% 14% 32%	4057
	21st to end	Night	7% 7% 3 9% 7% 7% 7% 7% 8% 11% 28%	4427
August	1st to 10th	Night	12% 6% 3 9% 6% 6% 6% 5% 9% 10% 28%	2915
	11th to 20th	Night	7% 4 2 7% 4 6% 6% 5% 7% 9% 43%	3026
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 7% 10% 49%	3675
September	1st to 10th	Night	8% 7% 2 6% 5% 5% 6% 5% 7% 10% 39%	2200
	11th to 20th	Night	13% 5% 2 7% 5% 4 4 4 6% 8% 43%	2200
	21st to end	Night	11% 6% 2 5% 4 5% 5% 4 5% 8% 46%	2200
October	1st to 10th	Night	12% 4 2 6% 4 4 3 3 4 7% 52%	2200
	11th to 20th	Night	11% 5% 2 4 2 3 3 3 4 5% 59%	2359
	21st to end	Night	10% 5% 2 4 3 4 4 2 5% 6% 56%	2640
November	1st to 10th	Night	11% 5% 2 4 3 3 3 3 4 6% 54%	2515
	11th to 20th	Night	13% 5% 2 4 2 3 3 3 4 6% 54%	2730
	21st to end	Night	12% 5% 2 6% 4 4 4 4 5% 6% 49%	2730
December	1st to 10th	Night	12% 6% 2 5% 3 3 3 2 4 5% 54%	4380
	11th to 20th	Night	15% 5% 2 5% 4 4 3 3 4 6% 49%	4952
	21st to end	Night	18% 7% 3 6% 4 4 3 3 4 6% 43%	6633

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	35% 5% 8% 19% 25% 7%	5259
	11th to 20th	Day	29% 3 4 15% 32% 17%	5280
	21st to end	Day	44% 4 6% 16% 20% 10%	5900
February	1st to 10th	Day	42% 5% 7% 17% 20% 8%	2100
	11th to 20th	Day	41% 5% 5% 18% 24% 7%	2058
	21st to end	Day	39% 5% 9% 16% 20% 11%	1730
March	1st to 10th	Day	44% 6% 8% 11% 23% 7%	4898
	11th to 20th	Day	28% 6% 9% 15% 21% 21%	5090
	21st to end	Day	40% 5% 7% 19% 18% 11%	5586
April	1st to 10th	Day	35% 5% 11% 21% 18% 9%	2310
	11th to 20th	Day	32% 6% 9% 19% 24% 11%	2417
	21st to end	Day	29% 7% 12% 23% 25% 4	2730
May	1st to 10th	Day	37% 8% 16% 21% 16% 2	6027
	11th to 20th	Day	43% 9% 17% 20% 11% 1	5995
	21st to end	Day	34% 10% 15% 19% 20% 2	6590
June	1st to 10th	Day	41% 11% 15% 19% 13% 2	2600
	11th to 20th	Day	32% 10% 19% 23% 15% 1	2600
	21st to end	Day	37% 13% 19% 17% 12% 3	2600
July	1st to 10th	Day	46% 14% 19% 16% 4 1	5835
	11th to 20th	Day	30% 15% 32% 20% 2 1	5831
	21st to end	Day	42% 16% 21% 18% 3	6240
August	1st to 10th	Day	44% 12% 20% 21% 3	4221
	11th to 20th	Day	31% 11% 17% 29% 12% 1	4057
	21st to end	Day	33% 9% 18% 26% 13% 1	4190
September	1st to 10th	Day	39% 11% 15% 18% 14% 4	2200
	11th to 20th	Day	39% 8% 11% 20% 18% 4	2200
	21st to end	Day	40% 7% 11% 20% 17% 5%	2200
October	1st to 10th	Day	32% 4 6% 14% 30% 13%	3590
	11th to 20th	Day	17% 3 5% 17% 27% 32%	3306
	21st to end	Day	21% 4 6% 18% 37% 15%	3538
November	1st to 10th	Day	35% 4 8% 13% 27% 14%	1999
	11th to 20th	Day	32% 3 7% 20% 25% 14%	1890
	21st to end	Day	36% 6% 8% 18% 24% 8%	1890
December	1st to 10th	Day	37% 5% 7% 17% 25% 10%	3020
	11th to 20th	Day	37% 4 8% 22% 22% 8%	3460
	21st to end	Day	42% 4 7% 20% 23% 3	4565
January	1st to 10th	Night	34% 6% 8% 20% 24% 7%	7636
	11th to 20th	Night	35% 5% 5% 16% 28% 11%	7680
	21st to end	Night	46% 4 5% 14% 23% 8%	8263
February	1st to 10th	Night	39% 4 8% 17% 22% 10%	2520
	11th to 20th	Night	42% 5% 6% 16% 21% 10%	2459
	21st to end	Night	39% 7% 8% 15% 17% 15%	2076
March	1st to 10th	Night	44% 6% 9% 15% 15% 11%	5174
	11th to 20th	Night	28% 7% 10% 12% 25% 19%	5090
	21st to end	Night	37% 5% 7% 17% 20% 14%	5588
April	1st to 10th	Night	34% 6% 10% 19% 19% 11%	2310
	11th to 20th	Night	29% 5% 8% 22% 25% 11%	2167
	21st to end	Night	29% 6% 12% 23% 22% 8%	1890
May	1st to 10th	Night	34% 11% 16% 21% 15% 3	4150
	11th to 20th	Night	39% 10% 17% 22% 11% 1	4123
	21st to end	Night	30% 8% 15% 24% 19% 3	4528
June	1st to 10th	Night	40% 11% 18% 17% 14%	1800
	11th to 20th	Night	29% 12% 19% 24% 13% 2	1800
	21st to end	Night	34% 12% 23% 16% 11% 4	1800
July	1st to 10th	Night	46% 15% 20% 14% 3 1	4015
	11th to 20th	Night	33% 17% 31% 16% 2	4006
	21st to end	Night	46% 15% 20% 16% 3	4297
August	1st to 10th	Night	46% 12% 21% 19% 2	2904
	11th to 20th	Night	31% 13% 18% 25% 11% 1	3053
	21st to end	Night	28% 9% 20% 29% 12% 1	3675
September	1st to 10th	Night	38% 11% 17% 17% 14% 4	2200
	11th to 20th	Night	39% 9% 12% 18% 17% 4	2200
	21st to end	Night	37% 8% 12% 19% 19% 6%	2200
October	1st to 10th	Night	34% 5% 8% 13% 28% 12%	3590
	11th to 20th	Night	18% 2 5% 12% 30% 33%	3832
	21st to end	Night	20% 4 5% 19% 32% 20%	4252
November	1st to 10th	Night	32% 5% 8% 14% 27% 15%	2515
	11th to 20th	Night	32% 4 7% 16% 27% 14%	2730
	21st to end	Night	35% 5% 8% 17% 24% 11%	2730
December	1st to 10th	Night	33% 4 6% 18% 30% 8%	4380
	11th to 20th	Night	37% 5% 11% 18% 21% 9%	4954
	21st to end	Night	43% 4 6% 21% 23% 3	6633

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	20% 22% 42% 14% 2	330
	11th to 20th	Day	24% 23% 32% 15% 5% 1	330
	21st to end	Day	25% 26% 35% 11% 4	363
February	1st to 10th	Day	25% 17% 40% 14% 3	330
	11th to 20th	Day	29% 22% 32% 15% 1	330
	21st to end	Day	26% 20% 40% 11% 3	273
March	1st to 10th	Day	19% 19% 29% 23% 9% 1	466
	11th to 20th	Day	17% 18% 35% 21% 9% 1	540
	21st to end	Day	17% 18% 33% 23% 8%	594
April	1st to 10th	Day	21% 15% 27% 25% 11% 1	540
	11th to 20th	Day	14% 12% 28% 28% 15% 3	532
	21st to end	Day	12% 9% 25% 29% 19% 5%	540
May	1st to 10th	Day	11% 14% 27% 29% 14% 6%	543
	11th to 20th	Day	13% 5% 25% 26% 21% 10%	567
	21st to end	Day	12% 7% 17% 30% 24% 11%	617
June	1st to 10th	Day	13% 3 19% 26% 27% 12%	530
	11th to 20th	Day	6% 4 17% 24% 28% 21%	530
	21st to end	Day	7% 3 12% 30% 31% 17%	530
July	1st to 10th	Day	8% 2 10% 23% 33% 25%	525
	11th to 20th	Day	7% 1 6% 22% 38% 26%	524
	21st to end	Day	5% 1 10% 26% 38% 20%	576
August	1st to 10th	Day	16% 2 12% 25% 27% 17%	526
	11th to 20th	Day	8% 1 9% 22% 39% 21%	519
	21st to end	Day	13% 2 12% 27% 28% 17%	583
September	1st to 10th	Day	12% 4 14% 28% 28% 15%	530
	11th to 20th	Day	14% 4 14% 29% 29% 11%	530
	21st to end	Day	16% 5% 16% 29% 26% 7%	530
October	1st to 10th	Day	15% 5% 25% 27% 20% 7%	530
	11th to 20th	Day	11% 8% 23% 31% 21% 6%	530
	21st to end	Day	15% 8% 25% 29% 19% 4	583
November	1st to 10th	Day	21% 6% 26% 28% 16% 3	477
	11th to 20th	Day	16% 15% 38% 21% 7% 2	330
	21st to end	Day	16% 16% 33% 25% 8% 1	330
December	1st to 10th	Day	25% 19% 33% 17% 6% 1	330
	11th to 20th	Day	25% 16% 34% 18% 6% 1	330
	21st to end	Day	25% 15% 33% 21% 6% 1	363
January	1st to 10th	Night	20% 19% 32% 24% 5%	840
	11th to 20th	Night	19% 14% 32% 26% 8%	840
	21st to end	Night	21% 17% 34% 24% 3	924
February	1st to 10th	Night	19% 14% 31% 30% 6%	840
	11th to 20th	Night	22% 18% 32% 26% 3	823
	21st to end	Night	17% 18% 34% 27% 4	692
March	1st to 10th	Night	17% 14% 31% 33% 6%	840
	11th to 20th	Night	15% 16% 31% 29% 8% 1	840
	21st to end	Night	15% 15% 33% 28% 10%	924
April	1st to 10th	Night	14% 13% 31% 30% 12%	840
	11th to 20th	Night	13% 11% 27% 34% 14% 1	721
	21st to end	Night	7% 9% 25% 39% 20% 1	630
May	1st to 10th	Night	9% 8% 26% 38% 18% 1	630
	11th to 20th	Night	10% 3 25% 35% 22% 4	621
	21st to end	Night	13% 3 17% 34% 29% 5%	683
June	1st to 10th	Night	10% 2 14% 40% 32% 3	600
	11th to 20th	Night	6% 2 15% 32% 35% 10%	600
	21st to end	Night	7% 1 11% 34% 40% 7%	600
July	1st to 10th	Night	9% 2 7% 30% 38% 15%	585
	11th to 20th	Night	7% 1 7% 25% 47% 13%	582
	21st to end	Night	7% 1 7% 30% 47% 9%	657
August	1st to 10th	Night	9% 2 8% 30% 39% 12%	597
	11th to 20th	Night	11% 2 7% 29% 43% 9%	594
	21st to end	Night	13% 1 10% 29% 36% 9%	710
September	1st to 10th	Night	10% 3 11% 32% 36% 9%	800
	11th to 20th	Night	14% 2 11% 32% 36% 5%	800
	21st to end	Night	15% 3 16% 30% 33% 3	800
October	1st to 10th	Night	14% 3 22% 33% 24% 5%	800
	11th to 20th	Night	13% 7% 22% 31% 24% 3	800
	21st to end	Night	12% 8% 24% 31% 22% 2	880
November	1st to 10th	Night	15% 7% 23% 33% 21% 2	820
	11th to 20th	Night	16% 10% 26% 32% 14% 1	840
	21st to end	Night	15% 12% 28% 31% 14%	840
December	1st to 10th	Night	18% 12% 30% 28% 11% 1	840
	11th to 20th	Night	19% 11% 29% 30% 10% 1	840
	21st to end	Night	23% 15% 22% 32% 8%	924

Page generated at 2026-05-29 01:53:27. Version ac07

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