Oronoko Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oronoko Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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	13% 10% 4 9% 5% 5% 4 4 5% 7% 33%	137804
	Night	14% 12% 5% 11% 5% 5% 4 3 5% 6% 30%	135460
Transparency	Day	49% 5% 11% 21% 12% 1	141343
	Night	54% 5% 10% 18% 11% 1	139998
Seeing	Day	20% 14% 29% 22% 11% 4	18167
	Night	21% 12% 29% 27% 11% 1	27959

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	12% 21% 11% 23% 5% 4 3 2 3 4 12%	4691
	11th to 20th	Day	10% 15% 10% 18% 13% 10% 8% 3 2 3 9%	4710
	21st to end	Day	16% 17% 6% 15% 7% 8% 5% 3 3 3 15%	5156
February	1st to 10th	Day	14% 16% 7% 14% 9% 5% 4 4 5% 4 18%	1998
	11th to 20th	Day	14% 13% 6% 16% 8% 5% 4 2 5% 5% 21%	2048
	21st to end	Day	15% 16% 7% 12% 4 5% 5% 4 4 5% 23%	1730
March	1st to 10th	Day	17% 12% 6% 11% 5% 3 3 3 4 5% 31%	4580
	11th to 20th	Day	9% 10% 6% 8% 5% 3 4 4 6% 9% 35%	4873
	21st to end	Day	18% 15% 7% 10% 6% 5% 4 3 5% 4 22%	5903
April	1st to 10th	Day	17% 14% 4 8% 4 4 4 3 5% 6% 31%	2520
	11th to 20th	Day	15% 11% 3 6% 5% 4 4 3 5% 7% 37%	2497
	21st to end	Day	17% 9% 3 7% 5% 4 4 4 5% 8% 34%	2730
May	1st to 10th	Day	16% 9% 3 7% 5% 4 5% 4 5% 7% 36%	7616
	11th to 20th	Day	12% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	7626
	21st to end	Day	14% 7% 2 6% 4 4 4 3 5% 9% 43%	9046
June	1st to 10th	Day	11% 5% 3 6% 5% 5% 5% 3 6% 7% 45%	2940
	11th to 20th	Day	9% 5% 2 6% 4 5% 4 4 6% 8% 45%	2940
	21st to end	Day	10% 6% 2 5% 4 5% 4 4 6% 9% 43%	2940
July	1st to 10th	Day	10% 6% 3 7% 4 5% 5% 5% 6% 10% 40%	6500
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 5% 7% 11% 43%	6500
	21st to end	Day	8% 6% 2 6% 4 4 5% 5% 6% 10% 43%	7065
August	1st to 10th	Day	9% 5% 2 6% 4 4 4 4 6% 8% 49%	4280
	11th to 20th	Day	9% 6% 2 6% 4 4 5% 4 6% 8% 46%	4084
	21st to end	Day	7% 4 2 6% 4 4 5% 5% 6% 10% 46%	4312
September	1st to 10th	Day	10% 5% 2 5% 4 4 5% 4 6% 8% 46%	2393
	11th to 20th	Day	12% 5% 1 5% 3 5% 5% 4 6% 8% 47%	2200
	21st to end	Day	14% 7% 3 6% 4 3 4 4 6% 8% 41%	2200
October	1st to 10th	Day	14% 7% 3 6% 5% 3 4 3 5% 7% 43%	2200
	11th to 20th	Day	20% 9% 2 7% 4 4 5% 4 5% 7% 33%	1967
	21st to end	Day	21% 12% 3 8% 5% 4 5% 4 5% 6% 26%	1980
November	1st to 10th	Day	13% 12% 3 7% 4 4 4 4 6% 7% 36%	1852
	11th to 20th	Day	16% 18% 5% 10% 6% 4 3 4 5% 4 25%	1890
	21st to end	Day	19% 20% 6% 10% 4 4 4 3 3 5% 22%	1890
December	1st to 10th	Day	10% 19% 9% 18% 6% 5% 4 2 3 5% 20%	2789
	11th to 20th	Day	15% 21% 10% 15% 7% 4 3 3 4 4 13%	3088
	21st to end	Day	24% 23% 8% 15% 6% 4 3 2 3 3 10%	4070
January	1st to 10th	Night	13% 21% 10% 21% 6% 5% 4 3 4 4 11%	8232
	11th to 20th	Night	11% 18% 9% 22% 10% 8% 6% 2 3 3 9%	8280
	21st to end	Night	15% 16% 8% 14% 9% 7% 6% 3 3 4 15%	9058
February	1st to 10th	Night	16% 15% 6% 11% 9% 5% 4 3 4 5% 23%	2618
	11th to 20th	Night	13% 14% 6% 14% 7% 5% 4 3 5% 5% 23%	2458
	21st to end	Night	18% 15% 6% 12% 6% 4 3 3 4 5% 26%	2076
March	1st to 10th	Night	15% 12% 5% 11% 4 4 4 2 4 5% 33%	5493
	11th to 20th	Night	11% 9% 4 7% 5% 4 4 4 5% 6% 41%	5292
	21st to end	Night	18% 13% 5% 9% 4 4 4 3 4 5% 30%	5312
April	1st to 10th	Night	16% 11% 3 7% 4 4 5% 4 5% 7% 33%	2100
	11th to 20th	Night	19% 10% 2 6% 5% 4 4 4 5% 6% 36%	2070
	21st to end	Night	17% 9% 3 6% 5% 4 3 4 6% 5% 38%	1890
May	1st to 10th	Night	16% 9% 3 8% 4 5% 4 3 5% 6% 37%	5237
	11th to 20th	Night	13% 7% 2 6% 4 4 4 3 6% 9% 43%	5220
	21st to end	Night	16% 7% 2 7% 4 4 4 3 5% 8% 42%	5139
June	1st to 10th	Night	9% 6% 2 6% 3 3 4 4 6% 9% 47%	1680
	11th to 20th	Night	10% 6% 2 5% 5% 5% 5% 5% 6% 9% 43%	1680
	21st to end	Night	9% 5% 2 7% 5% 4 5% 4 9% 11% 41%	1680
July	1st to 10th	Night	9% 5% 2 7% 5% 5% 4 4 7% 9% 43%	3698
	11th to 20th	Night	7% 5% 2 5% 4 4 4 4 6% 8% 49%	3697
	21st to end	Night	8% 7% 2 7% 4 5% 5% 4 7% 8% 44%	4027
August	1st to 10th	Night	8% 6% 3 6% 4 4 5% 4 6% 9% 45%	2869
	11th to 20th	Night	9% 5% 2 5% 4 4 5% 4 6% 8% 49%	2962
	21st to end	Night	8% 6% 2 6% 4 4 5% 4 5% 7% 49%	3586
September	1st to 10th	Night	9% 7% 2 6% 4 4 4 3 5% 7% 49%	2000
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 4 9% 55%	2185
	21st to end	Night	13% 6% 3 7% 4 4 4 3 5% 8% 43%	2200
October	1st to 10th	Night	15% 6% 2 5% 4 3 4 3 5% 7% 46%	2200
	11th to 20th	Night	19% 10% 3 8% 4 4 4 3 4 6% 36%	2431
	21st to end	Night	23% 9% 3 7% 5% 4 4 3 4 5% 33%	2860
November	1st to 10th	Night	14% 13% 3 8% 4 4 4 3 5% 5% 37%	2666
	11th to 20th	Night	15% 18% 4 11% 6% 4 4 3 5% 5% 26%	2730
	21st to end	Night	19% 19% 6% 9% 5% 4 4 2 4 5% 24%	2730
December	1st to 10th	Night	12% 17% 8% 16% 7% 5% 5% 4 4 6% 17%	4615
	11th to 20th	Night	16% 22% 9% 16% 8% 5% 4 3 3 4 12%	5339
	21st to end	Night	24% 22% 7% 12% 5% 4 4 3 4 4 11%	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	78% 4 9% 8% 1	4692
	11th to 20th	Day	82% 5% 6% 5% 2	4710
	21st to end	Day	75% 4 9% 10% 3	5156
February	1st to 10th	Day	67% 6% 10% 11% 5% 1	1998
	11th to 20th	Day	64% 5% 10% 13% 7%	2058
	21st to end	Day	62% 6% 11% 13% 7% 1	1730
March	1st to 10th	Day	55% 5% 10% 21% 8%	4580
	11th to 20th	Day	45% 5% 14% 28% 7% 1	4873
	21st to end	Day	64% 6% 9% 15% 6%	5905
April	1st to 10th	Day	53% 6% 11% 20% 11%	2520
	11th to 20th	Day	46% 6% 11% 22% 13% 3	2497
	21st to end	Day	47% 6% 12% 21% 12% 2	2730
May	1st to 10th	Day	45% 6% 10% 24% 14% 1	7651
	11th to 20th	Day	43% 6% 12% 23% 14% 1	7630
	21st to end	Day	38% 5% 10% 24% 19% 4	9060
June	1st to 10th	Day	36% 6% 11% 25% 20% 1	2940
	11th to 20th	Day	35% 7% 12% 25% 19% 2	2940
	21st to end	Day	36% 8% 15% 23% 16% 3	2940
July	1st to 10th	Day	39% 4 12% 25% 17% 2	6431
	11th to 20th	Day	34% 5% 15% 30% 15% 1	6425
	21st to end	Day	36% 6% 15% 24% 18% 2	6869
August	1st to 10th	Day	33% 6% 14% 30% 15% 1	4265
	11th to 20th	Day	34% 7% 13% 31% 15% 1	4123
	21st to end	Day	32% 6% 13% 27% 19% 2	4311
September	1st to 10th	Day	34% 7% 15% 25% 16% 3	2393
	11th to 20th	Day	33% 6% 12% 30% 19% 2	2200
	21st to end	Day	40% 7% 12% 24% 17% 1	2200
October	1st to 10th	Day	30% 4 9% 35% 21% 1	3590
	11th to 20th	Day	40% 5% 11% 21% 23%	3170
	21st to end	Day	50% 5% 9% 24% 11% 1	3180
November	1st to 10th	Day	47% 7% 11% 21% 13% 1	1852
	11th to 20th	Day	61% 6% 9% 17% 6% 1	1890
	21st to end	Day	67% 5% 10% 15% 4	1890
December	1st to 10th	Day	70% 4 15% 10% 2	2789
	11th to 20th	Day	75% 5% 10% 8% 1	3085
	21st to end	Day	80% 4 6% 8% 2	4070
January	1st to 10th	Night	76% 5% 7% 10% 2	8233
	11th to 20th	Night	83% 4 7% 5% 1	8280
	21st to end	Night	75% 4 11% 8% 3	9058
February	1st to 10th	Night	65% 5% 11% 13% 6% 1	2618
	11th to 20th	Night	62% 5% 9% 16% 6%	2459
	21st to end	Night	62% 5% 9% 16% 6% 2	2076
March	1st to 10th	Night	53% 6% 11% 24% 7% 1	5493
	11th to 20th	Night	43% 6% 12% 28% 10% 2	5292
	21st to end	Night	56% 6% 10% 19% 10% 1	5312
April	1st to 10th	Night	49% 7% 12% 20% 12% 1	2100
	11th to 20th	Night	48% 6% 9% 19% 16% 3	2070
	21st to end	Night	46% 7% 11% 21% 13% 2	1890
May	1st to 10th	Night	47% 5% 10% 22% 13% 3	5264
	11th to 20th	Night	38% 6% 14% 21% 20% 2	5221
	21st to end	Night	41% 5% 9% 18% 23% 4	5149
June	1st to 10th	Night	33% 6% 12% 28% 18% 3	1680
	11th to 20th	Night	37% 7% 14% 22% 19% 2	1680
	21st to end	Night	35% 8% 17% 23% 14% 2	1680
July	1st to 10th	Night	37% 5% 11% 29% 14% 4	3660
	11th to 20th	Night	32% 5% 14% 23% 24% 2	3652
	21st to end	Night	36% 6% 14% 22% 20% 2	3912
August	1st to 10th	Night	35% 6% 13% 29% 16% 1	2860
	11th to 20th	Night	32% 7% 11% 29% 20% 1	2989
	21st to end	Night	34% 5% 10% 29% 20% 3	3586
September	1st to 10th	Night	35% 6% 12% 24% 18% 5%	2000
	11th to 20th	Night	28% 5% 8% 31% 25% 2	2185
	21st to end	Night	40% 6% 11% 25% 18% 2	2200
October	1st to 10th	Night	27% 4 9% 32% 26% 1	3590
	11th to 20th	Night	43% 4 9% 21% 22% 1	3967
	21st to end	Night	44% 5% 8% 27% 16% 1	4610
November	1st to 10th	Night	50% 6% 9% 21% 14% 1	2666
	11th to 20th	Night	60% 5% 11% 15% 7% 1	2730
	21st to end	Night	64% 5% 10% 16% 5%	2730
December	1st to 10th	Night	69% 4 12% 11% 3	4615
	11th to 20th	Night	78% 5% 8% 7% 2	5341
	21st to end	Night	77% 5% 9% 7% 2	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	24% 20% 36% 14% 4 1	330
	11th to 20th	Day	26% 24% 34% 12% 4 1	330
	21st to end	Day	29% 20% 34% 14% 2	363
February	1st to 10th	Day	29% 22% 31% 14% 4	330
	11th to 20th	Day	29% 25% 32% 14%	330
	21st to end	Day	29% 30% 33% 7% 1	273
March	1st to 10th	Day	27% 25% 35% 12% 2	330
	11th to 20th	Day	31% 18% 31% 15% 4 1	440
	21st to end	Day	31% 19% 30% 14% 5% 1	594
April	1st to 10th	Day	29% 21% 30% 17% 3 1	540
	11th to 20th	Day	26% 23% 27% 16% 6% 2	532
	21st to end	Day	26% 15% 31% 18% 7% 2	540
May	1st to 10th	Day	27% 16% 31% 17% 7% 2	543
	11th to 20th	Day	23% 15% 28% 22% 9% 4	567
	21st to end	Day	15% 13% 31% 25% 13% 4	843
June	1st to 10th	Day	13% 11% 32% 28% 12% 4	780
	11th to 20th	Day	14% 11% 31% 29% 13% 3	780
	21st to end	Day	13% 9% 33% 28% 12% 4	780
July	1st to 10th	Day	9% 5% 28% 27% 22% 8%	771
	11th to 20th	Day	10% 7% 30% 29% 18% 6%	768
	21st to end	Day	10% 6% 26% 36% 17% 5%	845
August	1st to 10th	Day	9% 3 20% 32% 24% 11%	560
	11th to 20th	Day	11% 5% 24% 27% 26% 7%	519
	21st to end	Day	10% 5% 21% 33% 23% 7%	583
September	1st to 10th	Day	14% 7% 22% 30% 20% 7%	530
	11th to 20th	Day	10% 5% 18% 28% 27% 12%	530
	21st to end	Day	19% 11% 20% 26% 16% 8%	530
October	1st to 10th	Day	17% 10% 27% 25% 18% 2	530
	11th to 20th	Day	25% 17% 29% 24% 5%	400
	21st to end	Day	33% 17% 34% 14% 2	363
November	1st to 10th	Day	22% 18% 36% 17% 6% 2	330
	11th to 20th	Day	30% 25% 29% 13% 4	330
	21st to end	Day	35% 19% 34% 11% 1	330
December	1st to 10th	Day	25% 29% 29% 10% 6% 1	330
	11th to 20th	Day	24% 30% 32% 11% 3 1	330
	21st to end	Day	27% 28% 33% 11% 1	363
January	1st to 10th	Night	25% 18% 34% 19% 4	1050
	11th to 20th	Night	26% 18% 34% 18% 3	1050
	21st to end	Night	23% 17% 36% 21% 3	1155
February	1st to 10th	Night	26% 13% 36% 22% 3	880
	11th to 20th	Night	23% 17% 34% 23% 3	823
	21st to end	Night	27% 17% 36% 17% 3	692
March	1st to 10th	Night	22% 17% 32% 22% 6%	840
	11th to 20th	Night	21% 14% 35% 24% 5%	840
	21st to end	Night	25% 13% 29% 28% 5%	803
April	1st to 10th	Night	23% 15% 33% 23% 6% 1	630
	11th to 20th	Night	25% 13% 30% 25% 7% 1	623
	21st to end	Night	22% 10% 33% 26% 8% 1	630
May	1st to 10th	Night	20% 8% 32% 30% 9% 1	630
	11th to 20th	Night	20% 8% 27% 33% 13%	621
	21st to end	Night	15% 4 25% 39% 17% 1	683
June	1st to 10th	Night	11% 6% 24% 42% 16% 1	630
	11th to 20th	Night	14% 4 30% 37% 13% 1	630
	21st to end	Night	11% 5% 24% 39% 20% 1	630
July	1st to 10th	Night	10% 3 17% 40% 27% 3	615
	11th to 20th	Night	8% 3 20% 39% 27% 3	612
	21st to end	Night	9% 2 16% 44% 28% 2	687
August	1st to 10th	Night	8% 2 14% 46% 27% 3	597
	11th to 20th	Night	10% 3 15% 39% 29% 4	594
	21st to end	Night	9% 4 16% 39% 28% 3	660
September	1st to 10th	Night	13% 5% 17% 38% 24% 4	600
	11th to 20th	Night	12% 4 15% 38% 27% 4	785
	21st to end	Night	16% 7% 23% 30% 20% 3	800
October	1st to 10th	Night	20% 5% 26% 30% 19% 1	800
	11th to 20th	Night	25% 16% 25% 27% 6% 1	800
	21st to end	Night	30% 14% 29% 22% 5%	880
November	1st to 10th	Night	23% 14% 32% 21% 9%	820
	11th to 20th	Night	27% 20% 30% 20% 3 1	840
	21st to end	Night	30% 15% 31% 20% 4	840
December	1st to 10th	Night	26% 18% 35% 16% 3	984
	11th to 20th	Night	26% 17% 36% 17% 3	1050
	21st to end	Night	32% 17% 33% 16% 1	1155

Page generated at 2026-07-28 03:25:19. Version ac07

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