Onekama-DS-Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Onekama-DS-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	14% 11% 5% 10% 5% 4 4 3 5% 6% 33%	127370
	Night	14% 14% 5% 12% 6% 4 4 3 4 5% 28%	124544
Transparency	Day	51% 5% 11% 21% 11% 1	130857
	Night	57% 5% 10% 17% 9% 1	129131
Seeing	Day	21% 14% 31% 22% 9% 3	17549
	Night	22% 12% 28% 27% 10% 1	27499

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	10% 24% 13% 29% 7% 4 2 2 2 2 5%	3697
	11th to 20th	Day	11% 17% 9% 27% 14% 9% 4 1 2 2 3	3668
	21st to end	Day	13% 19% 12% 19% 9% 4 6% 2 2 2 10%	3982
February	1st to 10th	Day	10% 17% 7% 19% 15% 5% 4 2 3 3 14%	1732
	11th to 20th	Day	12% 16% 7% 16% 12% 7% 5% 3 4 3 14%	1948
	21st to end	Day	12% 18% 6% 15% 9% 5% 5% 3 3 5% 19%	1650
March	1st to 10th	Day	12% 11% 4 12% 7% 4 4 3 5% 6% 31%	4480
	11th to 20th	Day	11% 11% 7% 12% 5% 4 4 4 6% 7% 30%	4768
	21st to end	Day	23% 12% 8% 13% 4 3 3 3 4 4 23%	5778
April	1st to 10th	Day	17% 14% 4 9% 4 4 4 4 4 6% 30%	2400
	11th to 20th	Day	20% 12% 3 6% 3 4 3 3 5% 6% 34%	2429
	21st to end	Day	16% 11% 4 6% 5% 5% 4 3 6% 7% 33%	2600
May	1st to 10th	Day	14% 8% 2 6% 4 3 4 4 5% 7% 43%	5862
	11th to 20th	Day	12% 9% 3 6% 5% 4 4 3 5% 7% 43%	6151
	21st to end	Day	14% 7% 3 6% 4 4 4 4 5% 7% 44%	6935
June	1st to 10th	Day	12% 5% 2 5% 4 4 4 5% 5% 7% 46%	2800
	11th to 20th	Day	11% 5% 3 6% 5% 4 4 4 6% 9% 43%	2800
	21st to end	Day	13% 5% 2 6% 4 3 4 4 7% 10% 43%	2800
July	1st to 10th	Day	14% 6% 2 5% 3 3 3 3 6% 10% 43%	6360
	11th to 20th	Day	9% 4 1 4 3 4 4 4 5% 8% 53%	6360
	21st to end	Day	9% 5% 2 5% 3 4 4 4 6% 10% 48%	6924
August	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 4 7% 8% 44%	4434
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 5% 7% 50%	4174
	21st to end	Day	11% 6% 2 6% 4 4 4 3 6% 7% 45%	4360
September	1st to 10th	Day	14% 5% 2 6% 5% 5% 4 4 5% 6% 45%	2400
	11th to 20th	Day	12% 5% 2 6% 3 3 4 4 6% 9% 47%	2205
	21st to end	Day	15% 6% 3 7% 4 4 5% 4 7% 8% 39%	2200
October	1st to 10th	Day	16% 7% 3 7% 4 4 4 3 5% 7% 40%	2200
	11th to 20th	Day	22% 15% 4 9% 4 5% 4 4 5% 6% 22%	1892
	21st to end	Day	24% 14% 4 10% 6% 4 3 4 5% 4 22%	1980
November	1st to 10th	Day	18% 18% 4 6% 4 4 4 2 5% 7% 28%	1852
	11th to 20th	Day	15% 24% 6% 12% 5% 4 4 3 4 6% 16%	1890
	21st to end	Day	19% 24% 9% 11% 5% 4 4 2 3 4 15%	1811
December	1st to 10th	Day	11% 32% 13% 19% 4 4 3 2 1 2 7%	2690
	11th to 20th	Day	12% 25% 12% 20% 9% 4 3 2 3 3 5%	3088
	21st to end	Day	21% 21% 10% 14% 7% 5% 3 3 3 3 9%	4070
January	1st to 10th	Night	11% 23% 9% 28% 7% 4 3 2 2 3 8%	6488
	11th to 20th	Night	10% 18% 10% 25% 14% 10% 3 1 2 2 5%	6445
	21st to end	Night	11% 21% 11% 20% 8% 6% 6% 2 2 3 9%	6996
February	1st to 10th	Night	10% 19% 7% 17% 13% 6% 4 2 4 4 13%	2662
	11th to 20th	Night	12% 16% 6% 18% 11% 6% 5% 3 4 4 16%	2338
	21st to end	Night	14% 16% 5% 16% 7% 5% 4 3 5% 5% 19%	1980
March	1st to 10th	Night	16% 10% 3 11% 5% 3 3 3 5% 6% 34%	5373
	11th to 20th	Night	11% 11% 3 9% 5% 4 4 4 5% 8% 36%	5178
	21st to end	Night	19% 13% 4 11% 4 4 4 3 4 5% 28%	5192
April	1st to 10th	Night	18% 11% 4 9% 4 4 4 3 5% 6% 31%	2000
	11th to 20th	Night	21% 9% 3 7% 5% 4 4 3 4 6% 35%	1918
	21st to end	Night	17% 9% 4 7% 5% 4 4 4 4 6% 37%	1800
May	1st to 10th	Night	14% 7% 3 6% 4 4 5% 3 6% 8% 40%	4033
	11th to 20th	Night	11% 7% 3 8% 4 5% 4 4 6% 7% 40%	3742
	21st to end	Night	20% 7% 2 5% 3 3 3 3 4 6% 44%	3942
June	1st to 10th	Night	13% 7% 2 7% 4 4 4 4 6% 8% 42%	1600
	11th to 20th	Night	11% 7% 2 7% 5% 4 5% 5% 7% 8% 41%	1600
	21st to end	Night	12% 6% 2 7% 4 4 4 4 5% 8% 44%	1600
July	1st to 10th	Night	13% 7% 2 6% 4 5% 4 4 6% 8% 42%	3618
	11th to 20th	Night	8% 5% 2 5% 3 4 4 3 5% 7% 55%	3617
	21st to end	Night	6% 6% 2 6% 4 4 4 4 6% 7% 50%	3947
August	1st to 10th	Night	11% 5% 2 7% 4 5% 5% 3 6% 8% 43%	2719
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 5% 7% 50%	2875
	21st to end	Night	9% 6% 2 7% 4 5% 4 3 5% 6% 49%	3534
September	1st to 10th	Night	11% 6% 2 5% 4 4 4 3 6% 6% 48%	2000
	11th to 20th	Night	11% 6% 2 4 3 3 4 4 6% 8% 49%	2175
	21st to end	Night	15% 7% 2 7% 5% 5% 4 5% 5% 7% 39%	2200
October	1st to 10th	Night	18% 7% 3 6% 5% 3 3 2 5% 6% 42%	2200
	11th to 20th	Night	24% 12% 4 7% 4 4 3 3 4 6% 27%	2503
	21st to end	Night	25% 13% 4 8% 4 4 4 3 4 5% 26%	2860
November	1st to 10th	Night	16% 17% 4 9% 5% 3 3 3 5% 6% 29%	2666
	11th to 20th	Night	15% 23% 7% 11% 5% 4 4 3 3 4 20%	2730
	21st to end	Night	18% 24% 9% 12% 4 3 3 3 3 5% 15%	2804
December	1st to 10th	Night	12% 26% 14% 19% 6% 3 3 2 2 3 10%	4720
	11th to 20th	Night	14% 26% 10% 19% 9% 3 2 2 3 3 8%	5339
	21st to end	Night	22% 21% 8% 13% 6% 4 3 3 3 4 12%	7150

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	89% 3 4 4 1	3698
	11th to 20th	Day	93% 3 2 2 1	3668
	21st to end	Day	82% 4 6% 6% 1	3982
February	1st to 10th	Day	76% 5% 7% 11% 1	1732
	11th to 20th	Day	75% 5% 8% 9% 4	1958
	21st to end	Day	69% 5% 9% 13% 4 1	1650
March	1st to 10th	Day	54% 5% 14% 17% 9% 1	4480
	11th to 20th	Day	51% 5% 15% 18% 9% 1	4768
	21st to end	Day	64% 5% 9% 14% 7%	5780
April	1st to 10th	Day	54% 6% 10% 20% 11%	2400
	11th to 20th	Day	50% 5% 8% 21% 14% 2	2429
	21st to end	Day	48% 6% 12% 18% 14% 2	2600
May	1st to 10th	Day	40% 5% 10% 24% 17% 3	5897
	11th to 20th	Day	41% 5% 10% 25% 18% 2	6155
	21st to end	Day	39% 6% 10% 24% 20% 1	6949
June	1st to 10th	Day	36% 7% 12% 28% 16% 2	2800
	11th to 20th	Day	36% 6% 14% 25% 17% 1	2800
	21st to end	Day	35% 7% 16% 26% 15% 1	2800
July	1st to 10th	Day	36% 5% 14% 30% 13% 1	6291
	11th to 20th	Day	28% 6% 14% 34% 16% 1	6285
	21st to end	Day	31% 6% 15% 30% 17% 1	6728
August	1st to 10th	Day	35% 6% 14% 31% 13% 1	4419
	11th to 20th	Day	34% 5% 14% 30% 16% 1	4213
	21st to end	Day	36% 7% 15% 29% 12% 1	4359
September	1st to 10th	Day	39% 6% 13% 27% 13% 1	2400
	11th to 20th	Day	33% 8% 15% 30% 14% 1	2205
	21st to end	Day	42% 6% 15% 27% 10%	2200
October	1st to 10th	Day	31% 4 9% 37% 19% 1	3590
	11th to 20th	Day	52% 6% 11% 20% 10%	3043
	21st to end	Day	60% 5% 14% 16% 5%	3180
November	1st to 10th	Day	57% 6% 10% 20% 8%	1852
	11th to 20th	Day	69% 5% 11% 10% 4	1890
	21st to end	Day	74% 5% 10% 8% 2	1811
December	1st to 10th	Day	86% 3 4 6% 1	2690
	11th to 20th	Day	86% 4 6% 4 1	3085
	21st to end	Day	79% 5% 7% 7% 2	4070
January	1st to 10th	Night	83% 4 5% 6% 1	6488
	11th to 20th	Night	90% 3 4 3 1	6445
	21st to end	Night	82% 4 7% 7%	6996
February	1st to 10th	Night	76% 5% 6% 10% 4	2662
	11th to 20th	Night	73% 4 8% 11% 3	2339
	21st to end	Night	67% 5% 10% 14% 4	1980
March	1st to 10th	Night	51% 4 17% 20% 8%	5373
	11th to 20th	Night	47% 5% 19% 20% 8% 1	5178
	21st to end	Night	58% 5% 11% 18% 8% 1	5192
April	1st to 10th	Night	54% 6% 8% 21% 11% 1	2000
	11th to 20th	Night	51% 5% 8% 20% 13% 3	1918
	21st to end	Night	49% 4 11% 20% 13% 3	1800
May	1st to 10th	Night	41% 5% 13% 19% 19% 3	4060
	11th to 20th	Night	41% 8% 10% 23% 17% 1	3743
	21st to end	Night	42% 5% 9% 24% 15% 5%	3950
June	1st to 10th	Night	39% 7% 11% 27% 15% 2	1600
	11th to 20th	Night	38% 8% 11% 23% 18% 2	1600
	21st to end	Night	39% 7% 13% 25% 15% 2	1600
July	1st to 10th	Night	39% 6% 12% 24% 14% 4	3580
	11th to 20th	Night	29% 6% 13% 31% 19% 2	3572
	21st to end	Night	32% 6% 14% 25% 20% 2	3832
August	1st to 10th	Night	38% 7% 14% 26% 14% 2	2710
	11th to 20th	Night	34% 5% 13% 31% 17%	2902
	21st to end	Night	35% 6% 13% 24% 21% 1	3534
September	1st to 10th	Night	35% 6% 13% 25% 20% 1	2000
	11th to 20th	Night	32% 8% 13% 32% 15% 1	2175
	21st to end	Night	44% 6% 13% 25% 12% 1	2200
October	1st to 10th	Night	38% 4 9% 36% 13%	3590
	11th to 20th	Night	50% 5% 9% 25% 11%	4091
	21st to end	Night	52% 4 14% 22% 8%	4610
November	1st to 10th	Night	56% 6% 10% 18% 8% 1	2666
	11th to 20th	Night	69% 4 10% 10% 5% 1	2730
	21st to end	Night	72% 6% 11% 9% 2	2804
December	1st to 10th	Night	82% 4 7% 6% 1	4720
	11th to 20th	Night	84% 3 6% 6% 1	5341
	21st to end	Night	76% 5% 10% 6% 3	7150

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% 23% 34% 15% 5% 1	330
	11th to 20th	Day	29% 20% 36% 13% 2	318
	21st to end	Day	25% 23% 33% 18% 2 1	330
February	1st to 10th	Day	22% 31% 31% 11% 4 1	300
	11th to 20th	Day	26% 26% 34% 12% 1	300
	21st to end	Day	27% 30% 37% 5% 2	249
March	1st to 10th	Day	25% 29% 34% 11% 1	300
	11th to 20th	Day	27% 17% 30% 18% 8%	405
	21st to end	Day	31% 17% 29% 17% 5% 1	550
April	1st to 10th	Day	28% 18% 33% 16% 4 1	500
	11th to 20th	Day	30% 19% 29% 13% 6% 3	492
	21st to end	Day	25% 17% 29% 21% 8% 1	500
May	1st to 10th	Day	20% 19% 37% 17% 7% 1	503
	11th to 20th	Day	18% 11% 36% 24% 8% 3	648
	21st to end	Day	15% 12% 33% 26% 11% 3	789
June	1st to 10th	Day	15% 12% 34% 26% 9% 3	730
	11th to 20th	Day	16% 11% 36% 26% 9% 2	730
	21st to end	Day	17% 9% 33% 26% 12% 2	730
July	1st to 10th	Day	9% 7% 32% 33% 15% 5%	721
	11th to 20th	Day	11% 9% 29% 33% 14% 4	718
	21st to end	Day	10% 5% 35% 32% 14% 4	794
August	1st to 10th	Day	10% 6% 27% 31% 19% 8%	649
	11th to 20th	Day	14% 7% 21% 30% 19% 9%	519
	21st to end	Day	15% 8% 26% 29% 17% 5%	583
September	1st to 10th	Day	18% 9% 25% 26% 15% 7%	530
	11th to 20th	Day	10% 7% 24% 33% 19% 7%	530
	21st to end	Day	18% 12% 23% 28% 14% 5%	530
October	1st to 10th	Day	20% 16% 25% 23% 14% 2	530
	11th to 20th	Day	30% 15% 35% 17% 3	365
	21st to end	Day	35% 17% 31% 13% 4	363
November	1st to 10th	Day	33% 16% 31% 15% 5%	330
	11th to 20th	Day	28% 24% 33% 11% 3	330
	21st to end	Day	31% 25% 29% 12% 2	330
December	1st to 10th	Day	33% 21% 29% 14% 3 1	330
	11th to 20th	Day	33% 25% 30% 9% 2	330
	21st to end	Day	37% 21% 28% 10% 3 1	363
January	1st to 10th	Night	25% 19% 33% 18% 5%	1050
	11th to 20th	Night	25% 18% 32% 19% 5%	1031
	21st to end	Night	22% 14% 35% 22% 6%	1100
February	1st to 10th	Night	21% 16% 35% 24% 4	922
	11th to 20th	Night	21% 21% 31% 22% 5%	783
	21st to end	Night	25% 18% 33% 20% 3	660
March	1st to 10th	Night	20% 14% 34% 24% 8% 1	800
	11th to 20th	Night	18% 15% 34% 25% 7%	800
	21st to end	Night	24% 11% 30% 28% 7% 1	760
April	1st to 10th	Night	25% 12% 34% 24% 5% 1	600
	11th to 20th	Night	27% 10% 31% 24% 7% 1	593
	21st to end	Night	21% 11% 31% 28% 8% 1	600
May	1st to 10th	Night	19% 7% 33% 32% 9% 1	600
	11th to 20th	Night	17% 7% 32% 29% 13% 1	591
	21st to end	Night	16% 7% 26% 34% 17% 1	650
June	1st to 10th	Night	15% 5% 29% 37% 14% 1	600
	11th to 20th	Night	13% 7% 27% 36% 15% 2	600
	21st to end	Night	14% 4 25% 39% 18% 1	600
July	1st to 10th	Night	12% 2 18% 43% 22% 2	585
	11th to 20th	Night	8% 4 21% 39% 25% 2	582
	21st to end	Night	8% 5% 21% 40% 24% 2	657
August	1st to 10th	Night	11% 2 16% 47% 22% 2	597
	11th to 20th	Night	12% 4 16% 37% 27% 4	594
	21st to end	Night	13% 4 21% 39% 22% 2	660
September	1st to 10th	Night	14% 6% 21% 32% 23% 4	600
	11th to 20th	Night	13% 7% 19% 33% 24% 4	775
	21st to end	Night	18% 9% 20% 31% 20% 3	800
October	1st to 10th	Night	21% 10% 24% 31% 14% 1	800
	11th to 20th	Night	32% 12% 23% 26% 6% 1	800
	21st to end	Night	34% 12% 25% 23% 6% 1	880
November	1st to 10th	Night	28% 14% 30% 23% 6% 1	820
	11th to 20th	Night	30% 19% 29% 18% 4	840
	21st to end	Night	31% 17% 28% 20% 3	914
December	1st to 10th	Night	30% 20% 30% 17% 3	1050
	11th to 20th	Night	31% 19% 31% 15% 4 1	1050
	21st to end	Night	31% 16% 33% 17% 2	1155

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

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