Harmony Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harmony Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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 4 4 4 6% 8% 44%	127362
	Night	13% 6% 2 5% 3 3 3 3 5% 7% 49%	124585
Transparency	Day	35% 7% 11% 20% 18% 8%	131066
	Night	33% 6% 11% 20% 19% 11%	128931
Seeing	Day	13% 6% 20% 26% 25% 10%	16443
	Night	14% 7% 25% 35% 18% 2	26407

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% 9% 3 5% 4 3 3 3 4 5% 43%	4167
	11th to 20th	Day	14% 5% 2 5% 3 3 3 3 5% 7% 51%	4134
	21st to end	Day	27% 10% 3 6% 2 2 2 2 3 5% 38%	4488
February	1st to 10th	Day	22% 7% 3 7% 3 3 3 3 4 5% 40%	1990
	11th to 20th	Day	20% 9% 2 7% 3 3 3 2 4 4 42%	1949
	21st to end	Day	18% 8% 3 6% 4 3 3 3 4 6% 42%	1725
March	1st to 10th	Day	14% 7% 3 7% 4 4 4 3 4 7% 43%	4936
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 4 6% 48%	4980
	21st to end	Day	17% 8% 3 7% 4 4 4 3 4 6% 41%	5462
April	1st to 10th	Day	14% 9% 3 7% 4 4 4 3 6% 6% 40%	2200
	11th to 20th	Day	14% 9% 3 6% 5% 4 5% 3 6% 6% 40%	2248
	21st to end	Day	12% 7% 2 7% 4 4 5% 4 5% 6% 44%	2425
May	1st to 10th	Day	17% 7% 3 8% 5% 5% 4 4 6% 7% 33%	5862
	11th to 20th	Day	10% 6% 2 7% 4 5% 5% 4 6% 8% 44%	5862
	21st to end	Day	10% 6% 3 8% 5% 6% 5% 5% 7% 10% 35%	6434
June	1st to 10th	Day	4 4 2 5% 4 6% 6% 6% 8% 10% 45%	2600
	11th to 20th	Day	6% 4 2 5% 5% 5% 6% 5% 8% 10% 46%	2600
	21st to end	Day	5% 5% 2 6% 7% 5% 7% 7% 9% 10% 37%	2600
July	1st to 10th	Day	8% 6% 2 7% 5% 5% 6% 5% 8% 12% 38%	5900
	11th to 20th	Day	5% 4 2 6% 5% 5% 5% 5% 8% 13% 41%	5900
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 5% 8% 11% 40%	6422
August	1st to 10th	Day	1 2 1 3 2 3 3 3 5% 8% 69%	4234
	11th to 20th	Day	3 2 1 4 3 4 5% 5% 8% 12% 55%	4171
	21st to end	Day	4 4 2 6% 5% 6% 5% 5% 8% 10% 45%	3974
September	1st to 10th	Day	5% 6% 2 7% 5% 6% 6% 5% 6% 7% 45%	2200
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 4 7% 7% 43%	2200
	21st to end	Day	5% 4 1 5% 5% 5% 5% 4 7% 7% 50%	2200
October	1st to 10th	Day	5% 3 1 4 3 4 4 3 6% 8% 60%	2158
	11th to 20th	Day	12% 5% 2 5% 3 3 3 3 4 4 56%	2000
	21st to end	Day	13% 4 2 4 3 3 3 2 3 5% 57%	2200
November	1st to 10th	Day	11% 7% 2 5% 3 4 4 3 5% 6% 49%	2058
	11th to 20th	Day	11% 7% 3 5% 3 3 3 3 5% 5% 54%	2095
	21st to end	Day	17% 7% 2 6% 5% 4 4 3 4 5% 43%	1890
December	1st to 10th	Day	22% 7% 2 6% 3 3 3 3 4 6% 39%	3030
	11th to 20th	Day	19% 7% 3 5% 4 4 4 3 4 5% 42%	3481
	21st to end	Day	14% 8% 2 6% 3 3 3 3 4 5% 49%	4587
January	1st to 10th	Night	19% 6% 2 4 2 2 3 2 4 5% 49%	6018
	11th to 20th	Night	13% 5% 2 3 2 2 3 3 4 5% 58%	5979
	21st to end	Night	29% 8% 2 5% 3 2 3 2 3 4 39%	6490
February	1st to 10th	Night	18% 9% 2 6% 3 3 3 2 4 6% 45%	2425
	11th to 20th	Night	21% 8% 2 5% 3 3 3 2 3 5% 46%	2338
	21st to end	Night	20% 8% 2 5% 3 3 3 2 5% 5% 44%	1903
March	1st to 10th	Night	17% 8% 3 6% 3 3 3 3 5% 7% 42%	4919
	11th to 20th	Night	15% 7% 3 5% 4 3 3 3 4 5% 48%	4980
	21st to end	Night	18% 9% 3 6% 4 3 3 3 4 5% 43%	5467
April	1st to 10th	Night	12% 7% 2 6% 4 4 3 3 6% 6% 47%	2200
	11th to 20th	Night	14% 6% 2 5% 4 3 3 4 6% 7% 45%	2100
	21st to end	Night	14% 7% 2 5% 4 4 3 2 6% 7% 46%	1970
May	1st to 10th	Night	21% 9% 3 7% 4 3 4 4 5% 8% 32%	4053
	11th to 20th	Night	9% 6% 2 7% 4 4 5% 5% 7% 8% 45%	4053
	21st to end	Night	10% 7% 3 7% 5% 5% 5% 5% 7% 9% 38%	4443
June	1st to 10th	Night	4 4 1 4 3 3 3 3 7% 10% 57%	1800
	11th to 20th	Night	4 3 1 3 2 3 4 4 7% 10% 59%	1800
	21st to end	Night	4 4 2 5% 4 4 5% 5% 7% 11% 50%	1800
July	1st to 10th	Night	6% 6% 2 6% 5% 5% 5% 4 8% 11% 42%	4078
	11th to 20th	Night	3 3 2 5% 3 4 4 4 7% 12% 53%	4077
	21st to end	Night	6% 5% 2 6% 4 4 5% 4 7% 10% 46%	4449
August	1st to 10th	Night	1 1 2 2 2 2 2 5% 10% 74%	2926
	11th to 20th	Night	2 2 1 3 3 3 4 4 7% 13% 58%	2888
	21st to end	Night	3 3 2 4 3 4 5% 5% 7% 11% 53%	3900
September	1st to 10th	Night	5% 5% 1 5% 3 4 5% 4 6% 9% 52%	2200
	11th to 20th	Night	9% 6% 2 7% 4 4 5% 4 6% 7% 48%	2200
	21st to end	Night	7% 3 1 5% 3 3 4 4 6% 9% 55%	2200
October	1st to 10th	Night	4 3 1 3 3 3 4 3 4 7% 65%	2220
	11th to 20th	Night	10% 4 2 3 3 3 3 2 4 6% 61%	2400
	21st to end	Night	12% 5% 2 4 3 3 3 3 3 4 60%	2640
November	1st to 10th	Night	12% 5% 2 4 3 3 3 3 4 5% 55%	2460
	11th to 20th	Night	9% 7% 2 5% 4 4 3 3 4 6% 54%	2520
	21st to end	Night	15% 6% 2 5% 4 4 3 3 4 6% 46%	2730
December	1st to 10th	Night	22% 9% 3 6% 4 3 3 3 4 5% 39%	4380
	11th to 20th	Night	17% 10% 3 5% 3 3 3 3 3 5% 46%	4946
	21st to end	Night	15% 7% 2 4 3 3 2 2 3 4 55%	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	43% 5% 6% 22% 17% 8%	4168
	11th to 20th	Day	34% 3 5% 20% 26% 12%	4134
	21st to end	Day	51% 3 3 10% 18% 15%	4488
February	1st to 10th	Day	47% 4 5% 12% 19% 12%	1990
	11th to 20th	Day	47% 4 7% 15% 18% 9%	1959
	21st to end	Day	44% 5% 7% 15% 17% 12%	1725
March	1st to 10th	Day	40% 6% 6% 16% 18% 13%	4936
	11th to 20th	Day	37% 6% 7% 9% 17% 24%	4980
	21st to end	Day	43% 6% 7% 19% 18% 6%	5464
April	1st to 10th	Day	44% 7% 8% 16% 14% 12%	2200
	11th to 20th	Day	43% 7% 8% 13% 19% 10%	2248
	21st to end	Day	39% 7% 8% 18% 21% 7%	2425
May	1st to 10th	Day	45% 9% 10% 20% 12% 3	5900
	11th to 20th	Day	35% 8% 13% 18% 22% 4	5866
	21st to end	Day	39% 10% 12% 24% 12% 2	6447
June	1st to 10th	Day	30% 10% 15% 26% 17% 2	2600
	11th to 20th	Day	29% 10% 15% 24% 18% 4	2600
	21st to end	Day	35% 12% 16% 23% 12% 2	2600
July	1st to 10th	Day	36% 9% 24% 27% 3	5836
	11th to 20th	Day	30% 10% 21% 27% 11% 1	5831
	21st to end	Day	34% 10% 17% 26% 12% 1	6240
August	1st to 10th	Day	13% 6% 13% 40% 27% 1	4220
	11th to 20th	Day	19% 8% 27% 35% 9% 2	4210
	21st to end	Day	29% 14% 18% 23% 14% 2	3973
September	1st to 10th	Day	35% 10% 12% 19% 17% 7%	2200
	11th to 20th	Day	38% 9% 12% 18% 19% 4	2200
	21st to end	Day	30% 7% 11% 21% 17% 14%	2200
October	1st to 10th	Day	14% 4 7% 13% 22% 40%	3509
	11th to 20th	Day	19% 4 8% 17% 35% 18%	3240
	21st to end	Day	25% 5% 5% 20% 30% 15%	3538
November	1st to 10th	Day	35% 7% 8% 16% 23% 11%	2058
	11th to 20th	Day	33% 5% 8% 18% 22% 14%	2095
	21st to end	Day	43% 4 7% 15% 19% 10%	1890
December	1st to 10th	Day	46% 4 7% 15% 19% 8%	3030
	11th to 20th	Day	42% 7% 6% 10% 23% 11%	3479
	21st to end	Day	38% 5% 5% 14% 27% 11%	4587
January	1st to 10th	Night	37% 4 6% 21% 21% 10%	6018
	11th to 20th	Night	30% 3 4 19% 30% 14%	5979
	21st to end	Night	50% 4 4 11% 18% 14%	6490
February	1st to 10th	Night	43% 4 6% 12% 20% 16%	2425
	11th to 20th	Night	43% 4 6% 16% 18% 13%	2338
	21st to end	Night	44% 4 8% 13% 17% 15%	1903
March	1st to 10th	Night	41% 6% 7% 15% 20% 12%	4919
	11th to 20th	Night	38% 6% 7% 14% 14% 22%	4980
	21st to end	Night	43% 6% 7% 16% 19% 9%	5467
April	1st to 10th	Night	36% 7% 10% 18% 17% 13%	2200
	11th to 20th	Night	37% 7% 10% 16% 17% 14%	2100
	21st to end	Night	37% 6% 10% 20% 20% 7%	1970
May	1st to 10th	Night	48% 7% 10% 21% 10% 4	4080
	11th to 20th	Night	34% 8% 13% 21% 18% 5%	4054
	21st to end	Night	38% 9% 13% 27% 12% 1	4452
June	1st to 10th	Night	21% 7% 19% 30% 21% 2	1800
	11th to 20th	Night	19% 8% 17% 32% 18% 5%	1800
	21st to end	Night	25% 9% 20% 29% 16% 2	1800
July	1st to 10th	Night	33% 10% 28% 25% 4	4035
	11th to 20th	Night	23% 9% 22% 36% 10%	4026
	21st to end	Night	31% 10% 21% 25% 11% 2	4320
August	1st to 10th	Night	8% 6% 16% 42% 27% 2	2916
	11th to 20th	Night	17% 8% 31% 33% 11% 1	2915
	21st to end	Night	22% 13% 22% 28% 13% 1	3900
September	1st to 10th	Night	27% 10% 17% 23% 16% 8%	2200
	11th to 20th	Night	34% 8% 14% 23% 15% 6%	2200
	21st to end	Night	25% 7% 15% 22% 18% 14%	2200
October	1st to 10th	Night	13% 4 7% 16% 19% 41%	3623
	11th to 20th	Night	16% 3 6% 18% 34% 23%	3899
	21st to end	Night	21% 4 5% 22% 31% 17%	4252
November	1st to 10th	Night	31% 7% 8% 19% 23% 12%	2460
	11th to 20th	Night	32% 5% 9% 18% 21% 15%	2520
	21st to end	Night	39% 5% 8% 17% 19% 13%	2730
December	1st to 10th	Night	48% 4 5% 15% 20% 8%	4380
	11th to 20th	Night	41% 5% 8% 9% 22% 15%	4947
	21st to end	Night	34% 4 4 16% 30% 12%	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	23% 9% 34% 24% 9% 2	330
	11th to 20th	Day	22% 13% 30% 26% 9% 1	318
	21st to end	Day	22% 14% 34% 22% 7% 1	330
February	1st to 10th	Day	31% 11% 29% 20% 8%	300
	11th to 20th	Day	31% 15% 29% 18% 7%	300
	21st to end	Day	26% 15% 36% 18% 5%	249
March	1st to 10th	Day	20% 16% 33% 24% 8%	300
	11th to 20th	Day	15% 18% 43% 17% 6% 1	300
	21st to end	Day	18% 11% 42% 21% 7% 1	330
April	1st to 10th	Day	17% 19% 39% 19% 6%	300
	11th to 20th	Day	22% 13% 32% 24% 8% 1	366
	21st to end	Day	16% 11% 34% 27% 10% 2	525
May	1st to 10th	Day	14% 11% 33% 32% 9%	703
	11th to 20th	Day	14% 6% 28% 33% 15% 4	725
	21st to end	Day	11% 7% 23% 36% 20% 4	789
June	1st to 10th	Day	6% 2 15% 36% 31% 10%	730
	11th to 20th	Day	6% 2 13% 38% 33% 8%	730
	21st to end	Day	8% 2 10% 28% 37% 16%	730
July	1st to 10th	Day	8% 2 8% 26% 39% 17%	721
	11th to 20th	Day	4 1 5% 24% 47% 18%	718
	21st to end	Day	5% 1 5% 22% 47% 19%	794
August	1st to 10th	Day	2 3 20% 51% 23%	726
	11th to 20th	Day	5% 3 19% 51% 21%	715
	21st to end	Day	6% 2 5% 16% 31% 39%	388
September	1st to 10th	Day	7% 1 6% 21% 35% 30%	330
	11th to 20th	Day	7% 1 5% 17% 39% 30%	330
	21st to end	Day	7% 1 8% 21% 42% 21%	330
October	1st to 10th	Day	3 1 11% 28% 41% 15%	330
	11th to 20th	Day	11% 4 18% 29% 25% 12%	330
	21st to end	Day	20% 8% 22% 21% 21% 8%	363
November	1st to 10th	Day	15% 7% 19% 30% 22% 8%	330
	11th to 20th	Day	14% 8% 26% 31% 17% 5%	330
	21st to end	Day	21% 16% 28% 21% 12% 3	330
December	1st to 10th	Day	23% 7% 28% 24% 12% 6%	330
	11th to 20th	Day	23% 14% 26% 24% 9% 3	330
	21st to end	Day	21% 9% 33% 25% 10% 2	363
January	1st to 10th	Night	21% 9% 32% 31% 7%	1050
	11th to 20th	Night	20% 11% 31% 29% 8%	1031
	21st to end	Night	21% 11% 30% 32% 6%	1100
February	1st to 10th	Night	24% 11% 32% 28% 4	825
	11th to 20th	Night	26% 11% 32% 27% 4	784
	21st to end	Night	25% 14% 38% 20% 3	583
March	1st to 10th	Night	21% 11% 39% 25% 4	600
	11th to 20th	Night	17% 12% 36% 30% 6%	600
	21st to end	Night	14% 10% 43% 27% 5%	660
April	1st to 10th	Night	15% 10% 41% 31% 3	600
	11th to 20th	Night	16% 11% 38% 29% 6%	593
	21st to end	Night	15% 10% 36% 30% 8% 1	600
May	1st to 10th	Night	13% 9% 39% 33% 5% 1	600
	11th to 20th	Night	12% 6% 33% 35% 12% 1	591
	21st to end	Night	9% 4 29% 42% 15% 1	650
June	1st to 10th	Night	5% 2 16% 49% 26% 2	600
	11th to 20th	Night	5% 2 23% 50% 20% 1	600
	21st to end	Night	4 1 11% 46% 34% 5%	600
July	1st to 10th	Night	5% 2 8% 44% 37% 4	585
	11th to 20th	Night	3 1 7% 49% 38% 2	582
	21st to end	Night	5% 1 6% 48% 37% 3	657
August	1st to 10th	Night	2 4 50% 41% 3	597
	11th to 20th	Night	4 1 5% 47% 38% 6%	594
	21st to end	Night	4 7% 33% 48% 8%	660
September	1st to 10th	Night	6% 1 9% 32% 46% 6%	600
	11th to 20th	Night	10% 2 7% 33% 42% 5%	600
	21st to end	Night	8% 1 12% 35% 39% 7%	600
October	1st to 10th	Night	5% 2 10% 43% 35% 4	620
	11th to 20th	Night	11% 3 21% 39% 24% 2	800
	21st to end	Night	12% 9% 26% 33% 19% 2	880
November	1st to 10th	Night	13% 4 23% 38% 21% 1	820
	11th to 20th	Night	12% 8% 26% 38% 15% 1	840
	21st to end	Night	17% 11% 27% 30% 15% 1	1050
December	1st to 10th	Night	20% 8% 27% 32% 12% 1	1050
	11th to 20th	Night	24% 10% 27% 32% 7%	1050
	21st to end	Night	19% 8% 30% 33% 9%	1155

Page generated at 2026-01-14 00:14:27. Version ac07

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