Heavens Gate Farm Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heavens Gate Farm Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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% 7% 3 6% 5% 3 5% 5% 5% 8% 41%	74770
	Night	12% 8% 3 6% 5% 3 4 4 5% 7% 43%	75068
Transparency	Day	42% 6% 12% 24% 14% 2	74477
	Night	41% 5% 11% 23% 16% 3	74881
Seeing	Day	15% 10% 27% 27% 16% 5%	14550
	Night	16% 10% 30% 30% 13% 1	24518

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	11% 11% 5% 10% 7% 4 4 4 5% 6% 34%	1517
	11th to 20th	Day	14% 14% 6% 10% 6% 4 4 3 5% 5% 29%	1587
	21st to end	Day	12% 12% 6% 9% 7% 3 4 4 5% 6% 32%	1782
February	1st to 10th	Day	15% 10% 5% 9% 5% 3 5% 4 4 6% 33%	1620
	11th to 20th	Day	12% 10% 4 7% 5% 4 5% 5% 5% 8% 35%	1675
	21st to end	Day	15% 11% 4 8% 6% 3 4 4 4 6% 35%	1480
March	1st to 10th	Day	14% 11% 6% 6% 6% 3 4 3 5% 6% 37%	1853
	11th to 20th	Day	15% 10% 4 6% 5% 3 4 4 5% 7% 36%	1980
	21st to end	Day	20% 10% 5% 7% 5% 3 5% 4 5% 6% 29%	2271
April	1st to 10th	Day	13% 8% 3 7% 5% 2 4 5% 4 8% 40%	2160
	11th to 20th	Day	16% 9% 4 7% 5% 2 4 3 5% 7% 38%	2134
	21st to end	Day	20% 6% 3 7% 6% 3 4 5% 5% 7% 35%	2160
May	1st to 10th	Day	15% 8% 4 6% 6% 4 5% 5% 6% 8% 34%	2272
	11th to 20th	Day	17% 6% 3 7% 5% 3 4 5% 5% 7% 38%	2479
	21st to end	Day	13% 6% 3 7% 6% 4 6% 5% 6% 9% 36%	2725
June	1st to 10th	Day	6% 4 2 6% 5% 3 5% 6% 8% 10% 45%	2520
	11th to 20th	Day	8% 4 2 5% 5% 4 5% 6% 6% 9% 46%	2520
	21st to end	Day	7% 5% 3 4 6% 3 6% 6% 8% 9% 43%	2520
July	1st to 10th	Day	8% 4 2 5% 5% 3 5% 6% 8% 10% 45%	2520
	11th to 20th	Day	6% 4 2 5% 5% 3 6% 6% 6% 10% 47%	2520
	21st to end	Day	8% 4 2 5% 4 3 5% 5% 5% 11% 47%	2625
August	1st to 10th	Day	8% 5% 2 6% 6% 4 6% 6% 7% 10% 41%	2328
	11th to 20th	Day	8% 5% 2 6% 5% 4 6% 6% 7% 9% 43%	2176
	21st to end	Day	8% 4 2 4 4 3 5% 6% 6% 9% 49%	2376
September	1st to 10th	Day	12% 5% 2 4 4 3 4 4 5% 9% 49%	2160
	11th to 20th	Day	10% 5% 2 3 4 2 3 4 6% 8% 53%	2160
	21st to end	Day	7% 4 2 5% 5% 3 5% 5% 6% 7% 52%	1931
October	1st to 10th	Day	12% 5% 2 5% 4 3 3 3 4 7% 52%	1800
	11th to 20th	Day	15% 7% 2 5% 5% 3 4 4 5% 5% 46%	1800
	21st to end	Day	17% 8% 3 5% 5% 3 3 4 4 6% 42%	1967
November	1st to 10th	Day	11% 6% 2 4 4 3 4 4 5% 7% 52%	1672
	11th to 20th	Day	15% 7% 4 5% 4 3 3 4 4 6% 44%	1710
	21st to end	Day	15% 10% 5% 6% 5% 3 4 4 4 6% 39%	1549
December	1st to 10th	Day	12% 11% 5% 7% 5% 3 5% 3 3 6% 40%	1520
	11th to 20th	Day	14% 9% 4 6% 5% 4 5% 5% 6% 6% 37%	1918
	21st to end	Day	18% 17% 6% 9% 6% 3 4 4 5% 5% 22%	2783
January	1st to 10th	Night	11% 11% 5% 7% 5% 4 4 4 5% 6% 38%	2648
	11th to 20th	Night	14% 10% 6% 8% 7% 4 4 4 4 5% 34%	2499
	21st to end	Night	12% 11% 7% 8% 5% 4 5% 5% 5% 6% 33%	2574
February	1st to 10th	Night	16% 11% 6% 7% 5% 3 5% 4 5% 6% 32%	2340
	11th to 20th	Night	14% 8% 4 7% 6% 3 4 4 4 6% 40%	2171
	21st to end	Night	16% 9% 3 6% 6% 3 4 4 4 5% 40%	1776
March	1st to 10th	Night	14% 9% 3 5% 5% 3 4 4 5% 5% 42%	2123
	11th to 20th	Night	17% 8% 3 7% 5% 3 5% 5% 5% 6% 37%	1980
	21st to end	Night	19% 11% 5% 6% 6% 3 6% 5% 5% 6% 28%	2084
April	1st to 10th	Night	13% 6% 3 6% 5% 3 4 4 5% 7% 44%	1800
	11th to 20th	Night	13% 6% 3 5% 6% 3 4 4 5% 7% 44%	1775
	21st to end	Night	17% 8% 3 6% 5% 2 4 4 4 6% 40%	1800
May	1st to 10th	Night	14% 6% 2 6% 6% 3 5% 6% 6% 8% 39%	1684
	11th to 20th	Night	14% 7% 4 6% 6% 2 4 4 5% 7% 42%	1416
	21st to end	Night	10% 7% 2 6% 5% 3 5% 6% 5% 8% 44%	1551
June	1st to 10th	Night	6% 5% 2 4 4 4 3 5% 6% 8% 54%	1440
	11th to 20th	Night	7% 5% 2 6% 5% 3 4 5% 5% 11% 48%	1440
	21st to end	Night	6% 3 2 4 5% 3 6% 5% 6% 10% 49%	1440
July	1st to 10th	Night	8% 4 2 5% 5% 3 5% 4 7% 8% 49%	1440
	11th to 20th	Night	5% 4 2 5% 4 2 5% 5% 5% 9% 56%	1440
	21st to end	Night	7% 3 2 5% 4 3 3 5% 6% 8% 54%	1690
August	1st to 10th	Night	6% 3 2 5% 4 3 3 5% 7% 10% 51%	1611
	11th to 20th	Night	7% 4 2 5% 5% 3 5% 5% 4 7% 53%	1725
	21st to end	Night	5% 3 1 4 4 3 4 5% 7% 9% 55%	1980
September	1st to 10th	Night	11% 5% 2 4 3 2 3 4 5% 6% 54%	1800
	11th to 20th	Night	8% 4 2 5% 4 3 4 4 6% 7% 53%	1800
	21st to end	Night	7% 4 2 4 4 2 5% 4 5% 8% 55%	2007
October	1st to 10th	Night	8% 5% 2 4 5% 2 4 4 4 7% 55%	2160
	11th to 20th	Night	13% 6% 2 5% 4 3 3 4 4 6% 51%	2160
	21st to end	Night	18% 7% 3 4 4 2 3 5% 4 5% 45%	2389
November	1st to 10th	Night	9% 5% 2 4 4 2 3 4 5% 7% 54%	2406
	11th to 20th	Night	12% 6% 3 6% 5% 3 4 3 5% 6% 48%	2470
	21st to end	Night	17% 8% 3 5% 4 3 3 4 4 6% 43%	2626
December	1st to 10th	Night	14% 10% 4 7% 6% 3 5% 5% 6% 6% 35%	2660
	11th to 20th	Night	15% 8% 4 7% 5% 3 4 4 4 6% 41%	3279
	21st to end	Night	19% 18% 8% 11% 7% 4 4 3 4 4 20%	4884

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	51% 4 10% 20% 14% 1	1518
	11th to 20th	Day	58% 5% 9% 20% 8%	1587
	21st to end	Day	53% 5% 12% 19% 9% 1	1782
February	1st to 10th	Day	53% 5% 11% 20% 9% 2	1620
	11th to 20th	Day	49% 5% 12% 21% 12% 1	1684
	21st to end	Day	51% 4 10% 22% 10% 2	1480
March	1st to 10th	Day	49% 5% 10% 25% 10% 2	1853
	11th to 20th	Day	49% 5% 11% 22% 11% 2	1980
	21st to end	Day	56% 6% 12% 17% 8% 1	2271
April	1st to 10th	Day	43% 5% 11% 25% 15% 1	2160
	11th to 20th	Day	46% 4 10% 25% 13% 2	2134
	21st to end	Day	48% 6% 12% 19% 14% 1	2160
May	1st to 10th	Day	48% 7% 13% 22% 10% 1	2272
	11th to 20th	Day	46% 6% 11% 22% 13% 1	2483
	21st to end	Day	44% 8% 12% 19% 15% 2	2725
June	1st to 10th	Day	30% 8% 15% 28% 16% 2	2520
	11th to 20th	Day	33% 8% 13% 23% 20% 3	2520
	21st to end	Day	34% 8% 15% 23% 17% 3	2520
July	1st to 10th	Day	31% 9% 15% 27% 14% 3	2451
	11th to 20th	Day	31% 8% 17% 26% 15% 3	2445
	21st to end	Day	31% 7% 13% 31% 15% 1	2479
August	1st to 10th	Day	35% 8% 17% 26% 12% 2	2314
	11th to 20th	Day	35% 8% 13% 28% 15% 1	2176
	21st to end	Day	29% 7% 13% 26% 19% 5%	2376
September	1st to 10th	Day	33% 6% 11% 26% 18% 6%	2160
	11th to 20th	Day	29% 4 10% 30% 23% 4	2160
	21st to end	Day	30% 5% 11% 29% 24% 2	1931
October	1st to 10th	Day	34% 4 10% 26% 22% 4	1800
	11th to 20th	Day	39% 5% 8% 23% 20% 3	1800
	21st to end	Day	44% 4 9% 24% 16% 3	1967
November	1st to 10th	Day	34% 4 13% 25% 20% 4	1672
	11th to 20th	Day	41% 3 10% 25% 18% 3	1710
	21st to end	Day	48% 5% 10% 24% 12%	1549
December	1st to 10th	Day	47% 5% 13% 22% 12% 1	1520
	11th to 20th	Day	46% 5% 11% 25% 11% 2	1915
	21st to end	Day	64% 4 10% 14% 6% 1	2783
January	1st to 10th	Night	47% 5% 10% 24% 14% 1	2648
	11th to 20th	Night	52% 4 10% 24% 9%	2499
	21st to end	Night	51% 5% 14% 19% 10% 1	2574
February	1st to 10th	Night	53% 5% 11% 18% 10% 2	2340
	11th to 20th	Night	45% 5% 12% 22% 14% 2	2172
	21st to end	Night	47% 4 11% 23% 12% 4	1776
March	1st to 10th	Night	44% 5% 9% 26% 14% 2	2123
	11th to 20th	Night	48% 5% 10% 21% 13% 3	1980
	21st to end	Night	56% 6% 10% 19% 7% 1	2084
April	1st to 10th	Night	39% 6% 13% 24% 15% 4	1800
	11th to 20th	Night	40% 4 11% 24% 17% 4	1775
	21st to end	Night	46% 5% 9% 21% 16% 3	1800
May	1st to 10th	Night	42% 6% 13% 23% 14% 1	1684
	11th to 20th	Night	42% 6% 10% 23% 18% 1	1417
	21st to end	Night	38% 7% 13% 20% 18% 4	1552
June	1st to 10th	Night	27% 6% 16% 29% 19% 3	1440
	11th to 20th	Night	31% 7% 11% 22% 24% 5%	1440
	21st to end	Night	29% 8% 16% 22% 21% 3	1440
July	1st to 10th	Night	33% 5% 15% 28% 15% 4	1400
	11th to 20th	Night	25% 6% 14% 32% 20% 3	1392
	21st to end	Night	26% 5% 15% 30% 21% 3	1596
August	1st to 10th	Night	27% 7% 16% 32% 16% 2	1601
	11th to 20th	Night	29% 7% 10% 32% 20% 1	1725
	21st to end	Night	23% 7% 15% 25% 22% 7%	1980
September	1st to 10th	Night	30% 5% 10% 24% 24% 6%	1800
	11th to 20th	Night	29% 5% 10% 25% 26% 5%	1800
	21st to end	Night	28% 5% 10% 26% 28% 4	2007
October	1st to 10th	Night	30% 5% 10% 25% 25% 5%	2160
	11th to 20th	Night	35% 4 8% 27% 21% 5%	2160
	21st to end	Night	42% 5% 9% 21% 21% 3	2389
November	1st to 10th	Night	30% 5% 12% 27% 20% 6%	2406
	11th to 20th	Night	38% 3 10% 26% 19% 3	2470
	21st to end	Night	44% 4 11% 26% 14% 1	2626
December	1st to 10th	Night	48% 6% 13% 22% 11% 1	2660
	11th to 20th	Night	45% 4 11% 25% 13% 1	3281
	21st to end	Night	69% 4 8% 12% 7% 1	4884

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	19% 20% 34% 21% 5% 1	270
	11th to 20th	Day	28% 21% 37% 13% 2	257
	21st to end	Day	16% 23% 39% 18% 3	264
February	1st to 10th	Day	27% 18% 38% 13% 4	240
	11th to 20th	Day	23% 25% 33% 14% 5%	240
	21st to end	Day	25% 21% 36% 16% 2	198
March	1st to 10th	Day	18% 24% 44% 12% 2	240
	11th to 20th	Day	29% 14% 34% 19% 3 1	240
	21st to end	Day	33% 16% 31% 15% 4 1	357
April	1st to 10th	Day	19% 15% 34% 24% 7% 1	420
	11th to 20th	Day	21% 16% 31% 20% 11% 1	412
	21st to end	Day	23% 15% 32% 23% 6% 1	420
May	1st to 10th	Day	17% 13% 36% 23% 9% 1	481
	11th to 20th	Day	19% 11% 29% 26% 13% 2	625
	21st to end	Day	14% 7% 28% 27% 16% 7%	679
June	1st to 10th	Day	7% 5% 22% 34% 24% 8%	630
	11th to 20th	Day	9% 3 25% 35% 22% 6%	630
	21st to end	Day	9% 8% 26% 35% 17% 5%	630
July	1st to 10th	Day	9% 3 14% 35% 25% 14%	621
	11th to 20th	Day	8% 3 20% 36% 27% 7%	618
	21st to end	Day	9% 2 17% 34% 30% 7%	684
August	1st to 10th	Day	6% 3 16% 40% 27% 8%	626
	11th to 20th	Day	7% 3 17% 32% 30% 11%	490
	21st to end	Day	9% 2 15% 33% 30% 11%	495
September	1st to 10th	Day	14% 3 16% 32% 27% 9%	450
	11th to 20th	Day	9% 3 17% 33% 27% 12%	450
	21st to end	Day	6% 11% 23% 32% 20% 8%	399
October	1st to 10th	Day	13% 8% 31% 32% 12% 5%	270
	11th to 20th	Day	14% 24% 36% 19% 7%	270
	21st to end	Day	27% 18% 30% 20% 4	297
November	1st to 10th	Day	10% 12% 41% 23% 10% 4	270
	11th to 20th	Day	20% 17% 34% 20% 8% 1	270
	21st to end	Day	26% 12% 36% 19% 6%	270
December	1st to 10th	Day	13% 21% 42% 15% 6% 4	270
	11th to 20th	Day	23% 13% 42% 17% 6%	270
	21st to end	Day	26% 23% 36% 13% 2	297
January	1st to 10th	Night	16% 17% 40% 22% 5%	950
	11th to 20th	Night	19% 17% 36% 22% 5%	930
	21st to end	Night	19% 15% 38% 25% 2	990
February	1st to 10th	Night	22% 13% 40% 21% 4	900
	11th to 20th	Night	18% 15% 39% 25% 3	776
	21st to end	Night	23% 17% 36% 21% 3	592
March	1st to 10th	Night	19% 15% 39% 22% 4	683
	11th to 20th	Night	21% 12% 35% 27% 6%	540
	21st to end	Night	24% 12% 33% 26% 5%	594
April	1st to 10th	Night	16% 13% 39% 26% 5%	540
	11th to 20th	Night	16% 11% 34% 29% 9%	533
	21st to end	Night	21% 8% 35% 30% 6%	540
May	1st to 10th	Night	15% 7% 35% 33% 8% 1	540
	11th to 20th	Night	17% 6% 27% 37% 13% 1	531
	21st to end	Night	14% 4 25% 34% 21% 3	584
June	1st to 10th	Night	6% 5% 19% 46% 21% 1	540
	11th to 20th	Night	9% 3 22% 44% 20% 2	540
	21st to end	Night	7% 3 24% 42% 22% 1	540
July	1st to 10th	Night	10% 2 10% 38% 36% 4	525
	11th to 20th	Night	6% 2 16% 44% 28% 3	522
	21st to end	Night	8% 1 13% 44% 34% 1	591
August	1st to 10th	Night	8% 1 9% 45% 33% 3	537
	11th to 20th	Night	8% 1 13% 39% 34% 5%	534
	21st to end	Night	5% 1 14% 36% 41% 3	594
September	1st to 10th	Night	14% 3 15% 37% 26% 5%	540
	11th to 20th	Night	10% 2 18% 36% 29% 6%	540
	21st to end	Night	8% 7% 23% 33% 24% 5%	699
October	1st to 10th	Night	11% 5% 28% 31% 23% 3	720
	11th to 20th	Night	15% 12% 33% 29% 10% 1	720
	21st to end	Night	23% 10% 34% 25% 7%	792
November	1st to 10th	Night	13% 9% 39% 30% 9% 1	740
	11th to 20th	Night	15% 14% 39% 26% 5% 1	760
	21st to end	Night	21% 14% 36% 23% 6%	916
December	1st to 10th	Night	19% 13% 38% 24% 5% 1	950
	11th to 20th	Night	22% 11% 33% 28% 6%	950
	21st to end	Night	24% 17% 35% 22% 3	1045

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