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 2025-03-27.

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% 11% 4 9% 5% 4 4 4 5% 7% 33%	108784
	Night	15% 13% 5% 10% 5% 4 4 3 5% 6% 30%	110726
Transparency	Day	49% 6% 12% 21% 12% 1	112368
	Night	54% 6% 10% 18% 11% 1	115283
Seeing	Day	19% 14% 29% 22% 12% 4	16211
	Night	21% 11% 28% 27% 11% 1	26232

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% 20% 12% 21% 5% 4 3 2 3 4 14%	3617
	11th to 20th	Day	12% 17% 9% 17% 12% 8% 9% 3 2 3 8%	3620
	21st to end	Day	20% 19% 7% 14% 5% 3 4 4 4 4 17%	3982
February	1st to 10th	Day	14% 16% 7% 14% 9% 5% 4 4 5% 4 18%	1903
	11th to 20th	Day	15% 13% 6% 16% 9% 5% 4 2 4 5% 21%	1948
	21st to end	Day	16% 16% 6% 12% 4 5% 5% 3 4 5% 23%	1650
March	1st to 10th	Day	18% 14% 6% 8% 6% 4 4 3 5% 6% 28%	3220
	11th to 20th	Day	11% 9% 7% 9% 6% 4 4 4 6% 8% 32%	3443
	21st to end	Day	19% 12% 6% 10% 6% 5% 4 3 5% 5% 24%	4097
April	1st to 10th	Day	16% 14% 4 8% 4 4 4 3 5% 6% 32%	2280
	11th to 20th	Day	16% 11% 3 6% 4 3 4 3 5% 7% 38%	2257
	21st to end	Day	19% 9% 3 7% 5% 4 4 3 5% 7% 34%	2470
May	1st to 10th	Day	17% 8% 2 6% 5% 4 5% 4 6% 8% 35%	4082
	11th to 20th	Day	14% 8% 3 6% 4 4 4 3 6% 8% 39%	4081
	21st to end	Day	10% 6% 2 6% 4 4 4 4 5% 9% 46%	4823
June	1st to 10th	Day	10% 5% 3 6% 5% 4 5% 3 6% 7% 46%	2660
	11th to 20th	Day	9% 5% 2 6% 5% 5% 4 4 6% 8% 46%	2660
	21st to end	Day	11% 7% 2 5% 4 5% 4 4 6% 9% 43%	2660
July	1st to 10th	Day	11% 7% 3 7% 5% 5% 6% 4 6% 8% 37%	4440
	11th to 20th	Day	7% 4 1 5% 4 4 4 4 7% 11% 49%	4440
	21st to end	Day	7% 6% 2 7% 5% 5% 5% 5% 6% 8% 44%	4813
August	1st to 10th	Day	9% 6% 2 6% 4 4 4 4 6% 8% 48%	4149
	11th to 20th	Day	9% 6% 2 6% 4 4 4 4 6% 8% 46%	3957
	21st to end	Day	7% 4 2 6% 4 4 5% 4 6% 10% 47%	4180
September	1st to 10th	Day	10% 5% 2 5% 4 4 5% 4 6% 8% 46%	2274
	11th to 20th	Day	12% 5% 1 5% 3 5% 5% 4 6% 9% 46%	2090
	21st to end	Day	14% 7% 2 6% 4 3 4 4 6% 8% 40%	2090
October	1st to 10th	Day	14% 7% 3 6% 5% 3 4 3 5% 6% 43%	2090
	11th to 20th	Day	20% 9% 2 7% 4 4 5% 4 5% 7% 32%	1869
	21st to end	Day	22% 13% 3 8% 5% 4 5% 4 5% 6% 25%	1881
November	1st to 10th	Day	14% 12% 3 7% 4 4 4 4 6% 7% 36%	1762
	11th to 20th	Day	16% 19% 5% 10% 6% 4 3 4 5% 4 24%	1800
	21st to end	Day	20% 19% 5% 10% 4 4 4 3 3 5% 23%	1800
December	1st to 10th	Day	10% 19% 9% 18% 5% 5% 4 2 3 5% 20%	2706
	11th to 20th	Day	15% 22% 11% 15% 7% 4 3 3 4 4 13%	3008
	21st to end	Day	24% 23% 8% 15% 6% 4 3 2 3 3 10%	3982
January	1st to 10th	Night	14% 21% 10% 21% 6% 4 4 3 4 4 10%	6348
	11th to 20th	Night	13% 20% 9% 20% 9% 7% 7% 2 3 3 8%	6360
	21st to end	Night	19% 17% 9% 12% 6% 5% 5% 3 3 4 17%	6996
February	1st to 10th	Night	16% 15% 5% 11% 9% 5% 4 3 4 4 22%	2493
	11th to 20th	Night	14% 15% 6% 14% 7% 5% 4 3 5% 5% 23%	2338
	21st to end	Night	18% 15% 5% 12% 6% 4 3 3 4 5% 25%	1980
March	1st to 10th	Night	16% 12% 5% 10% 4 5% 4 3 4 5% 32%	3853
	11th to 20th	Night	10% 8% 4 7% 5% 5% 5% 4 5% 6% 41%	3735
	21st to end	Night	19% 13% 5% 10% 4 3 4 3 4 6% 28%	3702
April	1st to 10th	Night	15% 11% 3 7% 4 5% 5% 4 5% 7% 34%	1900
	11th to 20th	Night	19% 11% 2 6% 4 4 3 4 5% 5% 36%	1870
	21st to end	Night	18% 8% 3 6% 5% 4 4 4 6% 5% 36%	1710
May	1st to 10th	Night	15% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	2813
	11th to 20th	Night	18% 8% 3 6% 4 4 3 3 5% 8% 39%	2798
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 7% 42%	2743
June	1st to 10th	Night	8% 6% 2 5% 3 3 4 4 6% 10% 48%	1520
	11th to 20th	Night	9% 6% 2 5% 5% 5% 5% 4 6% 9% 44%	1520
	21st to end	Night	9% 5% 2 7% 5% 4 5% 4 8% 10% 40%	1520
July	1st to 10th	Night	9% 4 2 7% 5% 5% 5% 4 7% 9% 42%	2530
	11th to 20th	Night	7% 4 2 4 4 3 4 3 6% 8% 55%	2530
	21st to end	Night	6% 6% 2 6% 4 5% 5% 5% 7% 9% 45%	2750
August	1st to 10th	Night	8% 6% 3 6% 4 4 5% 4 6% 9% 44%	2781
	11th to 20th	Night	9% 4 2 5% 4 4 6% 4 6% 8% 49%	2869
	21st to end	Night	8% 6% 2 6% 4 4 5% 4 5% 7% 49%	3476
September	1st to 10th	Night	10% 7% 2 6% 4 4 4 3 5% 7% 49%	1900
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 4 9% 54%	2076
	21st to end	Night	13% 6% 3 7% 4 4 4 3 5% 8% 42%	2090
October	1st to 10th	Night	15% 7% 2 5% 4 3 4 3 5% 6% 46%	2090
	11th to 20th	Night	19% 10% 3 8% 4 4 4 3 4 6% 36%	2309
	21st to end	Night	24% 10% 3 7% 5% 4 4 3 4 5% 32%	2717
November	1st to 10th	Night	15% 13% 3 8% 4 4 4 3 5% 5% 37%	2536
	11th to 20th	Night	15% 18% 4 11% 6% 4 4 3 5% 5% 25%	2600
	21st to end	Night	18% 19% 6% 9% 5% 4 4 2 4 5% 24%	2600
December	1st to 10th	Night	12% 17% 8% 16% 7% 5% 5% 4 4 6% 17%	4478
	11th to 20th	Night	16% 22% 9% 16% 8% 5% 4 3 3 4 12%	5199
	21st to end	Night	24% 22% 7% 12% 6% 4 4 3 4 4 10%	6996

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	75% 5% 9% 9% 2	3618
	11th to 20th	Day	82% 6% 7% 3 2	3620
	21st to end	Day	71% 4 10% 11% 3	3982
February	1st to 10th	Day	68% 6% 9% 10% 5% 1	1903
	11th to 20th	Day	65% 5% 10% 13% 6%	1958
	21st to end	Day	62% 6% 11% 13% 7% 1	1650
March	1st to 10th	Day	55% 7% 11% 19% 8%	3220
	11th to 20th	Day	47% 7% 14% 25% 6% 1	3443
	21st to end	Day	60% 8% 10% 17% 4	4097
April	1st to 10th	Day	51% 6% 11% 20% 11%	2280
	11th to 20th	Day	45% 7% 10% 22% 13% 3	2257
	21st to end	Day	47% 7% 12% 19% 13% 2	2470
May	1st to 10th	Day	43% 9% 12% 25% 10% 1	4120
	11th to 20th	Day	39% 8% 14% 27% 11% 1	4085
	21st to end	Day	33% 8% 11% 23% 23% 1	4836
June	1st to 10th	Day	36% 7% 11% 25% 19% 2	2660
	11th to 20th	Day	34% 7% 13% 24% 19% 3	2660
	21st to end	Day	37% 9% 14% 22% 16% 3	2660
July	1st to 10th	Day	44% 5% 13% 20% 16% 3	4371
	11th to 20th	Day	28% 6% 17% 33% 16% 1	4365
	21st to end	Day	35% 7% 16% 19% 20% 3	4662
August	1st to 10th	Day	34% 6% 14% 30% 15% 1	4134
	11th to 20th	Day	33% 7% 13% 31% 15% 1	3996
	21st to end	Day	32% 6% 13% 26% 20% 3	4179
September	1st to 10th	Day	34% 7% 16% 23% 16% 3	2274
	11th to 20th	Day	33% 6% 12% 29% 18% 2	2090
	21st to end	Day	40% 7% 12% 23% 16% 1	2090
October	1st to 10th	Day	30% 4 9% 36% 20% 1	3480
	11th to 20th	Day	40% 6% 11% 21% 23%	3072
	21st to end	Day	50% 5% 10% 24% 10% 2	3081
November	1st to 10th	Day	48% 7% 11% 20% 13% 1	1762
	11th to 20th	Day	62% 6% 9% 15% 6% 1	1800
	21st to end	Day	66% 5% 10% 15% 4	1800
December	1st to 10th	Day	69% 4 15% 10% 2	2706
	11th to 20th	Day	75% 5% 10% 8% 1	3005
	21st to end	Day	80% 4 6% 8% 2	3982
January	1st to 10th	Night	76% 6% 7% 9% 2	6348
	11th to 20th	Night	84% 5% 6% 4 2	6360
	21st to end	Night	72% 4 13% 8% 3	6996
February	1st to 10th	Night	65% 5% 10% 12% 6% 1	2493
	11th to 20th	Night	63% 6% 10% 15% 6%	2339
	21st to end	Night	62% 5% 10% 15% 6% 2	1980
March	1st to 10th	Night	52% 8% 11% 23% 7%	3853
	11th to 20th	Night	42% 8% 12% 24% 12% 2	3735
	21st to end	Night	57% 7% 12% 17% 7% 1	3702
April	1st to 10th	Night	48% 7% 12% 20% 12% 1	1900
	11th to 20th	Night	48% 6% 8% 19% 16% 3	1870
	21st to end	Night	48% 7% 10% 18% 14% 2	1710
May	1st to 10th	Night	45% 8% 12% 22% 11% 1	2840
	11th to 20th	Night	41% 7% 13% 23% 15% 1	2799
	21st to end	Night	39% 8% 10% 18% 22% 2	2751
June	1st to 10th	Night	32% 6% 13% 29% 17% 3	1520
	11th to 20th	Night	35% 7% 14% 23% 19% 2	1520
	21st to end	Night	36% 9% 17% 22% 14% 2	1520
July	1st to 10th	Night	38% 6% 14% 24% 13% 6%	2490
	11th to 20th	Night	27% 6% 14% 24% 28% 2	2482
	21st to end	Night	34% 8% 16% 17% 23% 3	2662
August	1st to 10th	Night	35% 6% 13% 29% 16% 1	2772
	11th to 20th	Night	32% 7% 11% 29% 20% 1	2896
	21st to end	Night	34% 5% 10% 29% 20% 3	3476
September	1st to 10th	Night	35% 7% 12% 23% 19% 5%	1900
	11th to 20th	Night	29% 6% 8% 30% 25% 2	2076
	21st to end	Night	40% 6% 11% 25% 17% 2	2090
October	1st to 10th	Night	27% 4 9% 32% 26% 1	3480
	11th to 20th	Night	43% 4 9% 21% 22% 1	3845
	21st to end	Night	44% 5% 8% 27% 16% 1	4467
November	1st to 10th	Night	49% 6% 9% 21% 14% 1	2536
	11th to 20th	Night	61% 5% 11% 15% 7% 1	2600
	21st to end	Night	64% 6% 10% 16% 5%	2600
December	1st to 10th	Night	69% 4 13% 11% 3	4478
	11th to 20th	Night	78% 5% 8% 7% 2	5201
	21st to end	Night	77% 5% 9% 7% 2	6996

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% 20% 36% 15% 4 1	300
	11th to 20th	Day	25% 21% 36% 13% 4 1	300
	21st to end	Day	27% 21% 34% 15% 2	330
February	1st to 10th	Day	31% 21% 30% 14% 4	300
	11th to 20th	Day	29% 25% 31% 14%	300
	21st to end	Day	28% 29% 33% 8% 2	249
March	1st to 10th	Day	27% 23% 35% 12% 2	300
	11th to 20th	Day	28% 18% 32% 17% 4 1	405
	21st to end	Day	32% 18% 28% 15% 6% 1	530
April	1st to 10th	Day	25% 21% 31% 19% 4 1	460
	11th to 20th	Day	24% 23% 27% 17% 7% 2	452
	21st to end	Day	27% 15% 31% 18% 7% 2	460
May	1st to 10th	Day	27% 15% 30% 18% 8% 2	463
	11th to 20th	Day	22% 12% 28% 25% 9% 4	487
	21st to end	Day	13% 11% 32% 26% 14% 4	733
June	1st to 10th	Day	12% 11% 31% 29% 13% 4	680
	11th to 20th	Day	13% 10% 30% 30% 14% 4	680
	21st to end	Day	14% 10% 32% 27% 13% 4	680
July	1st to 10th	Day	9% 5% 27% 26% 24% 9%	671
	11th to 20th	Day	10% 7% 30% 27% 19% 6%	668
	21st to end	Day	9% 4 25% 38% 18% 6%	739
August	1st to 10th	Day	10% 3 20% 31% 24% 12%	519
	11th to 20th	Day	11% 5% 25% 26% 26% 7%	479
	21st to end	Day	10% 4 22% 33% 23% 8%	539
September	1st to 10th	Day	13% 6% 23% 31% 20% 6%	490
	11th to 20th	Day	10% 6% 19% 29% 26% 11%	490
	21st to end	Day	19% 12% 20% 25% 16% 7%	490
October	1st to 10th	Day	18% 10% 28% 24% 17% 3	490
	11th to 20th	Day	26% 18% 28% 23% 5%	367
	21st to end	Day	34% 17% 31% 15% 2	330
November	1st to 10th	Day	21% 18% 35% 18% 6% 2	300
	11th to 20th	Day	27% 26% 29% 14% 4	300
	21st to end	Day	34% 18% 36% 11% 1	300
December	1st to 10th	Day	25% 30% 28% 11% 5% 1	300
	11th to 20th	Day	22% 31% 32% 11% 3 1	300
	21st to end	Day	27% 28% 33% 12% 1	330
January	1st to 10th	Night	25% 18% 34% 19% 5%	1000
	11th to 20th	Night	26% 17% 34% 19% 3	1000
	21st to end	Night	23% 17% 36% 21% 4	1100
February	1st to 10th	Night	27% 13% 36% 22% 3	838
	11th to 20th	Night	23% 17% 33% 23% 3	783
	21st to end	Night	27% 17% 36% 17% 3	660
March	1st to 10th	Night	22% 16% 32% 23% 6% 1	800
	11th to 20th	Night	19% 14% 36% 25% 6%	800
	21st to end	Night	25% 12% 29% 28% 6%	752
April	1st to 10th	Night	21% 14% 34% 24% 6% 1	570
	11th to 20th	Night	24% 12% 31% 25% 7% 1	563
	21st to end	Night	22% 11% 33% 25% 8% 1	570
May	1st to 10th	Night	20% 8% 31% 31% 9% 1	570
	11th to 20th	Night	20% 6% 26% 34% 13% 1	561
	21st to end	Night	14% 4 24% 39% 18% 1	617
June	1st to 10th	Night	11% 6% 24% 42% 17% 1	570
	11th to 20th	Night	12% 4 29% 39% 14% 1	570
	21st to end	Night	11% 5% 24% 39% 21% 1	570
July	1st to 10th	Night	8% 3 17% 40% 28% 3	555
	11th to 20th	Night	9% 3 20% 37% 27% 4	552
	21st to end	Night	8% 2 15% 44% 29% 2	624
August	1st to 10th	Night	8% 2 13% 46% 27% 3	567
	11th to 20th	Night	9% 3 16% 39% 29% 4	564
	21st to end	Night	9% 4 16% 39% 29% 3	627
September	1st to 10th	Night	13% 4 17% 39% 23% 4	570
	11th to 20th	Night	12% 5% 15% 37% 27% 4	746
	21st to end	Night	16% 8% 24% 31% 19% 3	760
October	1st to 10th	Night	20% 6% 26% 29% 19% 1	760
	11th to 20th	Night	26% 16% 25% 27% 6% 1	760
	21st to end	Night	31% 14% 28% 21% 5%	836
November	1st to 10th	Night	23% 13% 32% 21% 10% 1	780
	11th to 20th	Night	27% 19% 30% 20% 4 1	800
	21st to end	Night	29% 15% 32% 20% 4	800
December	1st to 10th	Night	27% 18% 35% 17% 3	937
	11th to 20th	Night	26% 17% 37% 18% 3	1000
	21st to end	Night	31% 17% 34% 17% 1	1100

Page generated at 2025-03-24 09:04:31. Version ac07

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