Rich Neck Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rich Neck Observatory clear sky chart from 2005-11-06 to 2026-05-17.

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% 5% 2 5% 4 4 4 4 6% 8% 45%	131933
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 44%	130903
Transparency	Day	37% 5% 13% 25% 17% 3	135522
	Night	39% 5% 11% 24% 18% 4	135384
Seeing	Day	16% 7% 21% 29% 20% 6%	16991
	Night	17% 8% 27% 31% 16% 2	26523

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	14% 4 2 5% 4 4 5% 4 5% 6% 48%	4661
	11th to 20th	Day	15% 8% 3 7% 3 3 3 2 3 4 51%	5220
	21st to end	Day	14% 5% 2 5% 3 4 4 3 5% 6% 48%	5780
February	1st to 10th	Day	15% 6% 2 5% 4 5% 5% 3 6% 8% 40%	1890
	11th to 20th	Day	19% 7% 2 5% 3 4 3 3 6% 7% 42%	1965
	21st to end	Day	18% 8% 2 6% 4 4 3 4 5% 6% 41%	1730
March	1st to 10th	Day	19% 5% 2 4 3 3 4 3 5% 8% 45%	4803
	11th to 20th	Day	11% 7% 3 5% 3 3 4 3 4 6% 51%	5090
	21st to end	Day	17% 6% 2 5% 4 4 4 3 5% 7% 43%	5791
April	1st to 10th	Day	14% 6% 2 5% 3 4 4 3 5% 7% 45%	2520
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 5% 7% 48%	2494
	21st to end	Day	16% 6% 2 4 4 3 4 3 5% 8% 44%	2520
May	1st to 10th	Day	20% 6% 3 6% 4 4 4 4 6% 9% 35%	5701
	11th to 20th	Day	19% 5% 2 6% 4 4 4 4 7% 9% 36%	6401
	21st to end	Day	16% 5% 2 5% 4 4 4 4 5% 8% 42%	6934
June	1st to 10th	Day	10% 4 2 5% 4 4 5% 4 7% 10% 45%	2800
	11th to 20th	Day	11% 4 2 4 4 4 5% 5% 7% 9% 46%	2800
	21st to end	Day	8% 4 1 4 3 3 5% 5% 7% 11% 49%	2800
July	1st to 10th	Day	7% 4 2 6% 4 4 5% 5% 7% 10% 46%	6360
	11th to 20th	Day	10% 5% 2 7% 4 5% 6% 5% 9% 11% 35%	6360
	21st to end	Day	8% 5% 2 5% 4 5% 5% 5% 7% 11% 43%	6428
August	1st to 10th	Day	15% 6% 2 5% 3 4 4 4 7% 11% 37%	4234
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 7% 9% 45%	3892
	21st to end	Day	8% 4 2 5% 4 4 4 4 7% 8% 51%	4312
September	1st to 10th	Day	13% 4 2 4 4 4 4 3 6% 7% 49%	2400
	11th to 20th	Day	13% 5% 2 5% 3 3 3 3 4 7% 51%	2400
	21st to end	Day	19% 9% 2 7% 4 3 4 3 5% 6% 39%	2138
October	1st to 10th	Day	15% 5% 2 5% 3 3 3 4 4 7% 49%	2000
	11th to 20th	Day	18% 4 2 4 3 2 2 3 4 6% 52%	2000
	21st to end	Day	13% 5% 2 5% 4 3 3 2 5% 5% 51%	2200
November	1st to 10th	Day	13% 5% 1 3 3 4 3 3 5% 7% 52%	1883
	11th to 20th	Day	13% 5% 2 4 3 4 4 4 5% 7% 49%	1890
	21st to end	Day	14% 7% 1 5% 3 3 3 3 5% 6% 49%	1738
December	1st to 10th	Day	12% 5% 2 6% 3 3 4 3 5% 7% 49%	2680
	11th to 20th	Day	19% 7% 2 6% 3 3 3 3 4 6% 45%	3070
	21st to end	Day	13% 7% 3 6% 4 4 4 4 5% 7% 43%	4048
January	1st to 10th	Night	12% 7% 2 5% 4 4 4 4 6% 7% 44%	8233
	11th to 20th	Night	14% 6% 2 5% 4 3 3 2 4 5% 52%	7722
	21st to end	Night	14% 7% 2 6% 3 3 3 3 4 6% 48%	8401
February	1st to 10th	Night	15% 7% 3 6% 4 4 4 4 5% 6% 42%	2730
	11th to 20th	Night	20% 7% 2 5% 4 4 3 3 5% 6% 42%	2540
	21st to end	Night	16% 8% 3 5% 4 4 3 3 5% 6% 43%	2076
March	1st to 10th	Night	16% 7% 2 5% 3 4 3 3 4 5% 48%	5265
	11th to 20th	Night	10% 6% 2 5% 3 3 4 3 5% 7% 51%	5090
	21st to end	Night	14% 7% 2 7% 4 4 4 3 4 6% 45%	5383
April	1st to 10th	Night	16% 7% 3 6% 4 4 4 3 5% 7% 42%	2100
	11th to 20th	Night	12% 6% 2 6% 4 4 3 3 6% 7% 47%	2075
	21st to end	Night	17% 5% 2 4 3 4 4 4 5% 8% 44%	2100
May	1st to 10th	Night	17% 8% 3 7% 5% 5% 5% 5% 6% 9% 31%	4457
	11th to 20th	Night	22% 7% 2 6% 4 4 4 3 6% 8% 32%	3623
	21st to end	Night	18% 6% 2 7% 4 4 4 4 7% 9% 36%	3920
June	1st to 10th	Night	11% 4 2 5% 5% 4 5% 4 6% 10% 44%	1600
	11th to 20th	Night	12% 5% 2 6% 6% 5% 4 4 6% 9% 42%	1600
	21st to end	Night	9% 5% 2 5% 5% 5% 5% 5% 8% 11% 41%	1600
July	1st to 10th	Night	10% 5% 2 7% 5% 4 6% 4 7% 11% 39%	3598
	11th to 20th	Night	12% 6% 3 7% 5% 5% 5% 5% 7% 11% 33%	3597
	21st to end	Night	10% 6% 2 7% 5% 5% 5% 5% 6% 9% 41%	4418
August	1st to 10th	Night	16% 6% 2 7% 5% 5% 5% 4 6% 10% 34%	2915
	11th to 20th	Night	13% 6% 2 7% 5% 5% 6% 5% 6% 9% 35%	3121
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 6% 8% 48%	3586
September	1st to 10th	Night	14% 6% 2 5% 3 4 4 3 5% 7% 46%	2000
	11th to 20th	Night	11% 6% 1 5% 3 4 4 3 5% 8% 49%	2000
	21st to end	Night	20% 7% 2 6% 4 4 4 4 5% 6% 37%	2256
October	1st to 10th	Night	17% 6% 2 5% 3 4 4 3 4 6% 46%	2400
	11th to 20th	Night	17% 5% 2 4 3 3 3 2 4 6% 51%	2400
	21st to end	Night	15% 5% 2 5% 3 3 3 3 5% 6% 49%	2640
November	1st to 10th	Night	11% 5% 2 5% 3 3 3 3 5% 5% 53%	2633
	11th to 20th	Night	16% 7% 2 5% 4 4 3 3 4 6% 47%	2730
	21st to end	Night	13% 5% 1 5% 4 4 4 4 6% 6% 48%	2879
December	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 5% 7% 51%	4720
	11th to 20th	Night	20% 6% 3 5% 4 4 4 3 5% 6% 40%	5345
	21st to end	Night	15% 7% 2 6% 4 4 4 4 6% 7% 41%	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	38% 3 7% 28% 21% 4	4662
	11th to 20th	Day	39% 3 5% 21% 24% 8%	5220
	21st to end	Day	37% 3 10% 34% 13% 2	5780
February	1st to 10th	Day	42% 5% 12% 26% 13% 2	1890
	11th to 20th	Day	42% 3 10% 26% 17% 2	1974
	21st to end	Day	44% 4 12% 21% 15% 4	1730
March	1st to 10th	Day	38% 4 9% 22% 19% 8%	4803
	11th to 20th	Day	33% 4 10% 26% 21% 6%	5090
	21st to end	Day	42% 4 10% 20% 19% 6%	5791
April	1st to 10th	Day	37% 5% 14% 21% 18% 5%	2520
	11th to 20th	Day	35% 5% 12% 24% 19% 6%	2494
	21st to end	Day	38% 5% 12% 24% 17% 4	2520
May	1st to 10th	Day	45% 6% 16% 21% 11% 1	5733
	11th to 20th	Day	43% 7% 13% 26% 10% 1	6405
	21st to end	Day	39% 6% 13% 24% 16% 2	6949
June	1st to 10th	Day	32% 9% 16% 25% 16% 2	2800
	11th to 20th	Day	32% 9% 16% 24% 16% 2	2800
	21st to end	Day	28% 9% 17% 26% 19% 1	2800
July	1st to 10th	Day	32% 8% 23% 20% 13% 4	6290
	11th to 20th	Day	41% 9% 21% 22% 6% 1	6285
	21st to end	Day	33% 8% 14% 21% 22% 1	6243
August	1st to 10th	Day	41% 6% 18% 27% 8%	4221
	11th to 20th	Day	35% 7% 14% 31% 13% 1	3929
	21st to end	Day	29% 6% 16% 29% 18% 3	4312
September	1st to 10th	Day	34% 6% 14% 23% 18% 4	2400
	11th to 20th	Day	34% 5% 11% 26% 21% 3	2400
	21st to end	Day	45% 6% 10% 20% 15% 3	2138
October	1st to 10th	Day	34% 4 9% 21% 27% 5%	3260
	11th to 20th	Day	26% 3 6% 30% 26% 9%	3240
	21st to end	Day	23% 3 8% 31% 26% 9%	3538
November	1st to 10th	Day	32% 4 10% 29% 22% 3	1883
	11th to 20th	Day	35% 3 10% 26% 21% 4	1890
	21st to end	Day	37% 3 9% 30% 18% 3	1738
December	1st to 10th	Day	35% 4 16% 28% 14% 4	2680
	11th to 20th	Day	41% 3 12% 31% 10% 3	3066
	21st to end	Day	40% 5% 14% 24% 16% 1	4048
January	1st to 10th	Night	39% 3 10% 25% 20% 4	8234
	11th to 20th	Night	36% 3 6% 25% 22% 8%	7722
	21st to end	Night	39% 3 8% 29% 19% 3	8401
February	1st to 10th	Night	43% 4 12% 24% 16% 2	2730
	11th to 20th	Night	43% 3 8% 22% 19% 4	2542
	21st to end	Night	42% 3 10% 23% 17% 5%	2076
March	1st to 10th	Night	40% 3 7% 25% 16% 9%	5265
	11th to 20th	Night	32% 4 12% 26% 20% 7%	5090
	21st to end	Night	41% 4 8% 21% 20% 6%	5383
April	1st to 10th	Night	43% 4 10% 19% 20% 4	2100
	11th to 20th	Night	37% 4 12% 22% 20% 5%	2075
	21st to end	Night	38% 6% 11% 24% 18% 4	2100
May	1st to 10th	Night	50% 5% 14% 20% 9% 2	4487
	11th to 20th	Night	49% 6% 13% 20% 12% 1	3624
	21st to end	Night	43% 6% 14% 21% 14% 2	3927
June	1st to 10th	Night	36% 8% 12% 25% 17% 2	1600
	11th to 20th	Night	39% 6% 14% 25% 13% 2	1600
	21st to end	Night	35% 8% 16% 22% 18% 3	1600
July	1st to 10th	Night	39% 9% 19% 18% 13% 2	3560
	11th to 20th	Night	44% 7% 24% 17% 6% 1	3552
	21st to end	Night	39% 7% 13% 23% 18%	4289
August	1st to 10th	Night	45% 7% 17% 23% 8%	2904
	11th to 20th	Night	44% 7% 13% 26% 10% 1	3150
	21st to end	Night	33% 7% 11% 28% 19% 2	3586
September	1st to 10th	Night	38% 5% 12% 22% 18% 5%	2000
	11th to 20th	Night	34% 6% 10% 26% 21% 4	2000
	21st to end	Night	46% 6% 10% 19% 16% 3	2256
October	1st to 10th	Night	40% 4 9% 21% 20% 5%	3920
	11th to 20th	Night	25% 3 12% 21% 32% 7%	3899
	21st to end	Night	24% 3 9% 32% 25% 7%	4252
November	1st to 10th	Night	33% 5% 9% 26% 22% 5%	2633
	11th to 20th	Night	40% 4 8% 22% 21% 6%	2730
	21st to end	Night	34% 4 12% 26% 20% 3	2879
December	1st to 10th	Night	33% 4 13% 28% 19% 3	4720
	11th to 20th	Night	45% 3 12% 20% 15% 5%	5348
	21st to end	Night	42% 5% 13% 23% 16% 1	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	19% 19% 30% 25% 8%	220
	11th to 20th	Day	17% 22% 33% 24% 4	319
	21st to end	Day	18% 11% 35% 30% 5% 1	363
February	1st to 10th	Day	18% 9% 38% 26% 9%	330
	11th to 20th	Day	25% 14% 37% 20% 3	453
	21st to end	Day	25% 9% 33% 26% 7%	446
March	1st to 10th	Day	18% 12% 35% 27% 8% 1	540
	11th to 20th	Day	18% 11% 33% 28% 8% 2	540
	21st to end	Day	19% 8% 34% 32% 6% 1	594
April	1st to 10th	Day	19% 10% 29% 30% 10% 2	540
	11th to 20th	Day	13% 9% 28% 33% 14% 4	532
	21st to end	Day	19% 8% 24% 31% 17% 1	540
May	1st to 10th	Day	22% 6% 25% 28% 16% 2	543
	11th to 20th	Day	18% 5% 20% 33% 21% 3	551
	21st to end	Day	18% 3 14% 27% 28% 10%	573
June	1st to 10th	Day	11% 3 15% 33% 28% 10%	530
	11th to 20th	Day	12% 3 14% 31% 31% 8%	530
	21st to end	Day	10% 1 14% 32% 35% 8%	530
July	1st to 10th	Day	10% 3 6% 32% 35% 15%	525
	11th to 20th	Day	5% 1 4 31% 40% 18%	524
	21st to end	Day	9% 3 6% 31% 40% 11%	576
August	1st to 10th	Day	13% 2 7% 29% 36% 13%	526
	11th to 20th	Day	12% 3 7% 29% 37% 13%	519
	21st to end	Day	8% 2 12% 30% 33% 15%	583
September	1st to 10th	Day	16% 3 13% 25% 29% 15%	530
	11th to 20th	Day	17% 2 12% 27% 29% 13%	530
	21st to end	Day	24% 6% 18% 29% 18% 4	530
October	1st to 10th	Day	19% 3 14% 30% 24% 11%	530
	11th to 20th	Day	18% 7% 23% 28% 20% 4	530
	21st to end	Day	14% 10% 24% 35% 13% 4	583
November	1st to 10th	Day	14% 8% 28% 29% 15% 5%	441
	11th to 20th	Day	13% 14% 31% 31% 10% 2	430
	21st to end	Day	17% 17% 25% 28% 12% 1	278
December	1st to 10th	Day	19% 7% 36% 31% 5%	220
	11th to 20th	Day	20% 10% 33% 27% 10%	220
	21st to end	Day	18% 12% 29% 30% 11%	242
January	1st to 10th	Night	18% 16% 38% 24% 5%	840
	11th to 20th	Night	20% 14% 33% 27% 6%	840
	21st to end	Night	18% 14% 37% 29% 2	924
February	1st to 10th	Night	19% 10% 37% 29% 5%	840
	11th to 20th	Night	23% 15% 39% 21% 2	823
	21st to end	Night	21% 13% 34% 29% 3	692
March	1st to 10th	Night	17% 10% 37% 29% 6%	840
	11th to 20th	Night	19% 11% 34% 27% 8% 2	840
	21st to end	Night	17% 10% 36% 31% 5% 1	924
April	1st to 10th	Night	18% 10% 38% 27% 7%	840
	11th to 20th	Night	13% 8% 30% 37% 11%	831
	21st to end	Night	19% 6% 29% 33% 13% 1	840
May	1st to 10th	Night	16% 8% 26% 35% 14% 1	785
	11th to 20th	Night	17% 7% 23% 36% 17%	406
	21st to end	Night	15% 3 15% 36% 27% 3	433
June	1st to 10th	Night	12% 2 20% 37% 26% 3	400
	11th to 20th	Night	12% 3 15% 42% 26% 2	400
	21st to end	Night	10% 2 16% 43% 27% 3	400
July	1st to 10th	Night	11% 3 11% 36% 35% 4	390
	11th to 20th	Night	8% 3 6% 36% 43% 4	388
	21st to end	Night	7% 2 11% 41% 34% 5%	648
August	1st to 10th	Night	11% 2 10% 40% 34% 4	597
	11th to 20th	Night	12% 2 12% 35% 34% 5%	738
	21st to end	Night	12% 2 11% 32% 35% 8%	880
September	1st to 10th	Night	16% 2 15% 31% 31% 6%	800
	11th to 20th	Night	13% 3 13% 34% 33% 6%	800
	21st to end	Night	22% 4 18% 33% 22% 2	800
October	1st to 10th	Night	20% 5% 17% 28% 24% 6%	800
	11th to 20th	Night	17% 10% 24% 29% 18% 2	800
	21st to end	Night	18% 10% 26% 28% 15% 2	880
November	1st to 10th	Night	15% 9% 28% 32% 14% 2	820
	11th to 20th	Night	19% 12% 31% 27% 10%	840
	21st to end	Night	14% 15% 30% 30% 9% 1	840
December	1st to 10th	Night	21% 12% 35% 22% 9% 1	840
	11th to 20th	Night	19% 12% 37% 25% 8%	840
	21st to end	Night	18% 12% 32% 31% 6%	924

Page generated at 2026-05-14 01:58:59. Version ac07

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