Melinda Heights Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Melinda Heights Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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	4 3 1 3 2 2 3 3 4 6% 68%	136288
	Night	5% 5% 2 4 3 3 3 3 5% 6% 62%	132367
Transparency	Day	18% 4 7% 17% 27% 28%	131380
	Night	22% 5% 8% 15% 22% 28%	128248
Seeing	Day	6% 6% 21% 36% 23% 8%	17313
	Night	6% 2 10% 33% 38% 10%	27264

By Month

Percentage Cloud Cover SW (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	5% 4 1 3 2 2 2 2 3 5% 70%	4098
	11th to 20th	Day	6% 3 1 3 2 2 3 3 5% 5% 67%	4401
	21st to end	Day	10% 5% 2 5% 3 4 4 4 6% 8% 49%	5016
February	1st to 10th	Day	11% 5% 1 5% 3 3 2 3 5% 5% 57%	2000
	11th to 20th	Day	10% 4 1 4 3 2 3 3 5% 6% 57%	1950
	21st to end	Day	10% 7% 2 5% 4 3 3 3 5% 5% 53%	1650
March	1st to 10th	Day	10% 7% 2 6% 4 4 4 4 6% 7% 45%	4518
	11th to 20th	Day	10% 5% 2 5% 3 3 3 3 5% 7% 54%	4690
	21st to end	Day	8% 5% 2 4 3 3 4 3 5% 8% 54%	5916
April	1st to 10th	Day	6% 6% 1 4 4 3 4 3 5% 7% 58%	2400
	11th to 20th	Day	4 6% 2 4 3 3 3 3 4 6% 63%	2369
	21st to end	Day	6% 4 1 3 3 3 3 2 5% 7% 64%	2400
May	1st to 10th	Day	5% 5% 1 4 2 2 2 2 4 5% 67%	5650
	11th to 20th	Day	2 4 2 5% 3 3 3 4 5% 7% 62%	5841
	21st to end	Day	2 4 1 4 2 3 3 3 5% 8% 64%	6423
June	1st to 10th	Day	4 5% 2 4 3 2 3 3 6% 8% 62%	2600
	11th to 20th	Day	2 3 1 3 2 2 2 2 4 6% 73%	2631
	21st to end	Day	1 2 1 2 2 2 2 2 3 5% 78%	2800
July	1st to 10th	Day	1 1 1 1 1 1 1 2 3 89%	6319
	11th to 20th	Day	1 1 1 2 1 1 2 3 4 5% 79%	5885
	21st to end	Day	1 1 1 1 1 1 2 2 3 5% 82%	6055
August	1st to 10th	Day	1 1 1 1 1 1 1 2 4 86%	5346
	11th to 20th	Day	1 1 1 1 2 3 90%	5364
	21st to end	Day	1 1 1 1 1 2 2 2 3 3 82%	5984
September	1st to 10th	Day	2 1 1 2 1 2 2 2 3 5% 79%	2400
	11th to 20th	Day	2 2 1 2 1 1 2 2 4 4 78%	2220
	21st to end	Day	1 2 1 2 2 2 2 2 4 5% 77%	2200
October	1st to 10th	Day	3 2 1 2 2 2 2 2 3 4 79%	3600
	11th to 20th	Day	3 3 1 3 2 3 4 3 4 7% 67%	3467
	21st to end	Day	3 3 1 2 2 3 4 3 6% 5% 68%	3439
November	1st to 10th	Day	4 3 1 3 2 2 2 2 4 6% 71%	1854
	11th to 20th	Day	5% 3 2 4 2 2 3 3 4 6% 66%	1890
	21st to end	Day	6% 4 1 5% 4 3 3 3 6% 8% 58%	1890
December	1st to 10th	Day	5% 3 1 3 2 3 3 3 5% 7% 66%	3040
	11th to 20th	Day	8% 5% 2 4 3 4 6% 4 6% 7% 50%	3472
	21st to end	Day	8% 6% 3 6% 5% 5% 5% 4 6% 8% 44%	4510
January	1st to 10th	Night	6% 4 1 4 2 2 2 2 4 6% 67%	5867
	11th to 20th	Night	4 5% 2 5% 3 3 3 3 5% 6% 62%	5589
	21st to end	Night	12% 7% 2 5% 3 3 4 4 5% 6% 49%	5984
February	1st to 10th	Night	10% 6% 2 5% 3 3 3 2 4 6% 58%	2400
	11th to 20th	Night	10% 6% 1 4 4 4 3 3 4 5% 58%	2338
	21st to end	Night	11% 7% 2 5% 4 3 4 3 4 4 53%	1980
March	1st to 10th	Night	11% 14% 2 6% 3 4 3 3 5% 6% 42%	5376
	11th to 20th	Night	8% 10% 2 5% 4 4 3 3 5% 6% 50%	5308
	21st to end	Night	7% 12% 4 7% 4 3 3 4 4 5% 48%	5055
April	1st to 10th	Night	7% 7% 3 5% 3 3 3 3 5% 7% 54%	2000
	11th to 20th	Night	5% 6% 2 5% 4 4 3 4 4 5% 59%	1979
	21st to end	Night	5% 6% 2 5% 4 3 3 4 5% 6% 57%	2000
May	1st to 10th	Night	5% 8% 2 6% 4 3 3 3 4 5% 58%	4336
	11th to 20th	Night	2 7% 4 9% 4 3 3 6% 7% 7% 48%	4074
	21st to end	Night	2 8% 3 5% 3 3 3 4 6% 5% 58%	4474
June	1st to 10th	Night	2 7% 3 5% 5% 4 4 3 7% 8% 53%	1800
	11th to 20th	Night	1 3 1 4 2 3 3 3 7% 7% 65%	1758
	21st to end	Night	2 2 1 1 2 2 2 4 5% 8% 72%	1600
July	1st to 10th	Night	1 1 1 1 1 2 4 4 84%	3640
	11th to 20th	Night	1 1 1 1 2 2 4 8% 7% 73%	4072
	21st to end	Night	1 1 1 2 2 1 2 3 4 5% 77%	4830
August	1st to 10th	Night	1 1 1 1 1 2 3 4 85%	4486
	11th to 20th	Night	1 1 1 1 2 2 5% 6% 82%	4506
	21st to end	Night	1 1 1 2 1 2 2 2 4 5% 79%	5015
September	1st to 10th	Night	2 3 1 3 2 2 2 2 4 6% 73%	2000
	11th to 20th	Night	2 3 1 2 2 2 2 3 3 4 76%	2180
	21st to end	Night	2 3 1 2 2 1 1 2 3 4 78%	2200
October	1st to 10th	Night	2 2 1 2 2 2 2 2 3 4 80%	3600
	11th to 20th	Night	3 6% 2 8% 3 2 3 2 4 5% 61%	3687
	21st to end	Night	2 3 1 4 3 2 3 2 3 5% 72%	4368
November	1st to 10th	Night	4 4 1 3 2 3 2 2 4 6% 69%	2665
	11th to 20th	Night	5% 4 2 3 3 3 3 3 3 6% 66%	2730
	21st to end	Night	7% 4 1 5% 3 3 4 3 5% 7% 56%	2730
December	1st to 10th	Night	5% 3 1 3 3 2 3 2 4 6% 67%	4370
	11th to 20th	Night	8% 6% 2 5% 4 5% 4 5% 5% 7% 49%	4902
	21st to end	Night	7% 7% 2 6% 4 5% 5% 4 7% 11% 42%	6468

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	18% 2 5% 22% 27% 25%	4099
	11th to 20th	Day	19% 5% 10% 16% 18% 32%	4401
	21st to end	Day	30% 5% 5% 15% 25% 21%	5016
February	1st to 10th	Day	29% 4 6% 13% 25% 24%	2000
	11th to 20th	Day	26% 3 8% 18% 26% 20%	1960
	21st to end	Day	32% 4 8% 16% 23% 19%	1650
March	1st to 10th	Day	31% 5% 10% 19% 19% 15%	4518
	11th to 20th	Day	27% 6% 12% 25% 19% 11%	4690
	21st to end	Day	25% 6% 13% 30% 16% 10%	5916
April	1st to 10th	Day	25% 4 11% 25% 23% 12%	2400
	11th to 20th	Day	23% 5% 7% 20% 27% 18%	2372
	21st to end	Day	19% 5% 9% 27% 29% 11%	2400
May	1st to 10th	Day	20% 3 9% 23% 34% 11%	5650
	11th to 20th	Day	21% 7% 8% 20% 34% 9%	5844
	21st to end	Day	18% 6% 8% 24% 33% 11%	6424
June	1st to 10th	Day	21% 6% 9% 22% 27% 14%	2600
	11th to 20th	Day	15% 3 6% 13% 31% 32%	2631
	21st to end	Day	12% 3 6% 10% 25% 45%	2800
July	1st to 10th	Day	5% 1 4 5% 17% 68%	6251
	11th to 20th	Day	8% 2 4 13% 36% 36%	5815
	21st to end	Day	7% 2 4 19% 31% 37%	5881
August	1st to 10th	Day	8% 2 3 14% 43% 30%	3890
	11th to 20th	Day	4 2 3 14% 26% 50%	3880
	21st to end	Day	7% 2 3 9% 28% 52%	4311
September	1st to 10th	Day	10% 3 6% 9% 34% 38%	2400
	11th to 20th	Day	10% 3 6% 10% 36% 35%	2220
	21st to end	Day	11% 3 6% 15% 32% 34%	2200
October	1st to 10th	Day	11% 2 3 11% 18% 55%	3600
	11th to 20th	Day	14% 3 6% 14% 29% 35%	3467
	21st to end	Day	16% 4 4 10% 31% 34%	3439
November	1st to 10th	Day	16% 3 6% 17% 25% 33%	1854
	11th to 20th	Day	19% 4 7% 16% 19% 35%	1890
	21st to end	Day	24% 4 9% 14% 22% 28%	1890
December	1st to 10th	Day	17% 4 5% 16% 23% 34%	3040
	11th to 20th	Day	30% 5% 7% 14% 25% 19%	3471
	21st to end	Day	35% 5% 10% 23% 19% 8%	4510
January	1st to 10th	Night	19% 3 5% 14% 31% 28%	5867
	11th to 20th	Night	22% 5% 10% 16% 16% 31%	5589
	21st to end	Night	33% 6% 6% 10% 21% 24%	5984
February	1st to 10th	Night	28% 4 6% 15% 21% 27%	2400
	11th to 20th	Night	29% 4 7% 15% 20% 24%	2339
	21st to end	Night	33% 5% 5% 13% 19% 25%	1980
March	1st to 10th	Night	36% 7% 10% 15% 17% 14%	5376
	11th to 20th	Night	32% 7% 9% 23% 17% 11%	5308
	21st to end	Night	34% 7% 10% 21% 18% 10%	5055
April	1st to 10th	Night	30% 6% 9% 20% 20% 14%	2000
	11th to 20th	Night	25% 7% 8% 18% 23% 19%	1979
	21st to end	Night	26% 7% 12% 20% 22% 13%	2000
May	1st to 10th	Night	28% 7% 10% 14% 29% 11%	4333
	11th to 20th	Night	31% 10% 11% 17% 23% 9%	4075
	21st to end	Night	25% 8% 8% 22% 24% 12%	4474
June	1st to 10th	Night	28% 10% 16% 14% 19% 13%	1800
	11th to 20th	Night	17% 7% 11% 14% 23% 27%	1758
	21st to end	Night	13% 6% 12% 12% 19% 38%	1600
July	1st to 10th	Night	5% 2 6% 8% 16% 63%	3600
	11th to 20th	Night	7% 3 5% 19% 23% 43%	4019
	21st to end	Night	9% 3 5% 17% 26% 39%	4692
August	1st to 10th	Night	9% 3 5% 11% 38% 34%	3256
	11th to 20th	Night	6% 3 7% 13% 24% 48%	3256
	21st to end	Night	7% 3 5% 11% 18% 57%	3608
September	1st to 10th	Night	15% 4 8% 9% 27% 38%	2000
	11th to 20th	Night	14% 5% 6% 9% 29% 38%	2180
	21st to end	Night	13% 4 6% 11% 32% 34%	2200
October	1st to 10th	Night	10% 2 5% 11% 15% 57%	3600
	11th to 20th	Night	25% 2 5% 10% 20% 38%	3687
	21st to end	Night	17% 3 3 8% 26% 43%	4368
November	1st to 10th	Night	18% 3 6% 14% 21% 38%	2665
	11th to 20th	Night	21% 3 6% 13% 18% 38%	2730
	21st to end	Night	27% 4 7% 16% 16% 30%	2730
December	1st to 10th	Night	19% 3 6% 12% 22% 39%	4370
	11th to 20th	Night	31% 6% 8% 12% 20% 24%	4902
	21st to end	Night	30% 7% 11% 22% 20% 9%	6468

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	15% 7% 17% 36% 20% 4	300
	11th to 20th	Day	12% 9% 24% 35% 16% 4	432
	21st to end	Day	12% 11% 27% 31% 17% 3	550
February	1st to 10th	Day	15% 10% 24% 28% 18% 5%	500
	11th to 20th	Day	12% 9% 31% 32% 15% 2	495
	21st to end	Day	12% 14% 29% 32% 11% 1	414
March	1st to 10th	Day	15% 14% 31% 27% 10% 3	500
	11th to 20th	Day	13% 10% 31% 28% 15% 3	500
	21st to end	Day	9% 14% 32% 32% 11% 2	550
April	1st to 10th	Day	8% 10% 30% 28% 18% 5%	500
	11th to 20th	Day	5% 11% 34% 33% 13% 4	492
	21st to end	Day	4 10% 31% 32% 15% 8%	500
May	1st to 10th	Day	10% 9% 29% 33% 14% 5%	503
	11th to 20th	Day	6% 7% 27% 36% 20% 5%	528
	21st to end	Day	6% 8% 26% 38% 17% 5%	573
June	1st to 10th	Day	2 5% 19% 38% 28% 8%	530
	11th to 20th	Day	2 2 24% 37% 23% 11%	530
	21st to end	Day	2 2 16% 40% 29% 11%	530
July	1st to 10th	Day	2 1 9% 40% 34% 15%	526
	11th to 20th	Day	1 6% 37% 35% 20%	524
	21st to end	Day	1 1 7% 38% 36% 18%	575
August	1st to 10th	Day	1 1 8% 43% 34% 14%	527
	11th to 20th	Day	1 1 8% 42% 31% 18%	517
	21st to end	Day	1 1 10% 37% 34% 17%	583
September	1st to 10th	Day	2 2 12% 47% 24% 13%	530
	11th to 20th	Day	3 4 18% 44% 24% 8%	530
	21st to end	Day	2 5% 22% 36% 25% 11%	530
October	1st to 10th	Day	4 4 22% 37% 26% 8%	530
	11th to 20th	Day	4 8% 21% 37% 23% 8%	530
	21st to end	Day	4 5% 21% 34% 28% 9%	513
November	1st to 10th	Day	5% 6% 16% 33% 32% 7%	330
	11th to 20th	Day	5% 8% 17% 38% 23% 8%	330
	21st to end	Day	5% 9% 22% 36% 20% 8%	330
December	1st to 10th	Day	10% 5% 17% 34% 29% 5%	330
	11th to 20th	Day	7% 4 20% 34% 27% 8%	321
	21st to end	Day	14% 10% 25% 32% 15% 4	330
January	1st to 10th	Night	11% 3 16% 38% 24% 9%	800
	11th to 20th	Night	9% 4 13% 40% 28% 8%	800
	21st to end	Night	14% 3 15% 38% 26% 5%	880
February	1st to 10th	Night	12% 3 14% 37% 27% 8%	800
	11th to 20th	Night	11% 3 15% 39% 25% 7%	784
	21st to end	Night	14% 4 15% 41% 22% 5%	660
March	1st to 10th	Night	9% 5% 16% 43% 23% 4	800
	11th to 20th	Night	11% 4 14% 37% 28% 8%	800
	21st to end	Night	8% 4 13% 40% 30% 4	880
April	1st to 10th	Night	10% 3 11% 41% 31% 5%	800
	11th to 20th	Night	6% 4 15% 39% 30% 6%	791
	21st to end	Night	7% 4 10% 37% 35% 8%	800
May	1st to 10th	Night	7% 3 13% 35% 38% 5%	706
	11th to 20th	Night	5% 3 13% 32% 39% 7%	591
	21st to end	Night	5% 2 14% 38% 36% 5%	650
June	1st to 10th	Night	3 2 13% 39% 37% 7%	600
	11th to 20th	Night	1 1 8% 35% 49% 5%	558
	21st to end	Night	2 1 5% 23% 59% 11%	400
July	1st to 10th	Night	1 4 15% 63% 17%	390
	11th to 20th	Night	1 1 18% 61% 18%	568
	21st to end	Night	2 1 2 14% 60% 21%	810
August	1st to 10th	Night	2 1 2 20% 57% 18%	796
	11th to 20th	Night	1 2 14% 61% 23%	792
	21st to end	Night	1 1 17% 61% 19%	880
September	1st to 10th	Night	2 1 4 21% 54% 18%	800
	11th to 20th	Night	3 2 4 25% 53% 13%	800
	21st to end	Night	3 1 7% 31% 45% 15%	800
October	1st to 10th	Night	3 1 6% 41% 42% 7%	800
	11th to 20th	Night	6% 2 7% 36% 38% 12%	800
	21st to end	Night	4 3 10% 34% 35% 15%	880
November	1st to 10th	Night	4 2 9% 37% 35% 13%	820
	11th to 20th	Night	7% 1 8% 40% 33% 11%	840
	21st to end	Night	7% 3 14% 39% 29% 8%	840
December	1st to 10th	Night	9% 3 11% 41% 28% 7%	840
	11th to 20th	Night	12% 3 15% 40% 25% 6%	828
	21st to end	Night	11% 5% 17% 35% 24% 8%	880

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