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 2025-01-22.

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% 6% 2 5% 4 4 4 4 6% 8% 44%	104968
	Night	15% 6% 2 6% 4 4 4 3 5% 7% 43%	104356
Transparency	Day	36% 6% 13% 25% 16% 3	108601
	Night	39% 5% 11% 24% 17% 3	108862
Seeing	Day	16% 6% 21% 30% 21% 6%	15249
	Night	17% 8% 26% 31% 16% 2	24788

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	16% 5% 2 5% 4 3 4 3 5% 7% 48%	2597
	11th to 20th	Day	15% 9% 3 8% 5% 4 4 3 4 5% 41%	2897
	21st to end	Day	18% 7% 3 6% 3 4 4 3 6% 6% 40%	3133
February	1st to 10th	Day	15% 6% 2 5% 4 5% 5% 3 6% 8% 39%	1710
	11th to 20th	Day	19% 7% 2 4 3 3 3 3 6% 7% 43%	1773
	21st to end	Day	18% 8% 2 6% 4 4 3 4 5% 6% 40%	1570
March	1st to 10th	Day	22% 5% 2 4 4 3 3 4 5% 8% 39%	3269
	11th to 20th	Day	10% 4 2 4 3 4 4 3 5% 7% 52%	3480
	21st to end	Day	21% 7% 2 5% 4 3 3 3 4 6% 42%	3960
April	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 6% 7% 45%	2280
	11th to 20th	Day	12% 5% 2 4 4 4 4 3 5% 7% 49%	2254
	21st to end	Day	16% 6% 2 4 4 4 4 3 5% 8% 44%	2280
May	1st to 10th	Day	23% 7% 3 6% 4 4 4 3 6% 8% 33%	3882
	11th to 20th	Day	20% 6% 2 6% 4 4 4 4 6% 8% 35%	4397
	21st to end	Day	10% 4 2 5% 4 4 4 4 6% 10% 48%	4823
June	1st to 10th	Day	10% 4 1 4 4 4 5% 4 7% 10% 45%	2660
	11th to 20th	Day	10% 4 2 4 4 4 5% 5% 7% 9% 46%	2660
	21st to end	Day	8% 4 1 5% 3 3 5% 5% 7% 11% 48%	2660
July	1st to 10th	Day	5% 4 2 6% 4 4 6% 6% 8% 11% 44%	4440
	11th to 20th	Day	10% 5% 2 5% 3 4 5% 5% 8% 11% 42%	4440
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 5% 7% 10% 38%	4470
August	1st to 10th	Day	15% 6% 2 6% 3 5% 4 4 7% 12% 37%	4104
	11th to 20th	Day	9% 5% 2 6% 4 4 4 4 7% 9% 45%	3771
	21st to end	Day	8% 4 2 5% 4 4 4 4 7% 9% 51%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 3 6% 7% 48%	2280
	11th to 20th	Day	12% 5% 2 6% 3 3 3 3 4 8% 51%	2280
	21st to end	Day	19% 8% 2 7% 4 3 4 3 5% 6% 39%	2031
October	1st to 10th	Day	16% 5% 2 5% 3 3 3 4 4 7% 48%	1900
	11th to 20th	Day	17% 4 2 4 3 2 2 3 4 6% 53%	1900
	21st to end	Day	14% 5% 2 5% 4 3 3 2 5% 5% 51%	2090
November	1st to 10th	Day	13% 5% 1 3 3 4 4 3 6% 6% 52%	1792
	11th to 20th	Day	13% 5% 2 4 3 4 4 4 5% 8% 49%	1800
	21st to end	Day	14% 7% 1 5% 3 3 3 3 5% 6% 49%	1655
December	1st to 10th	Day	12% 5% 2 6% 3 3 4 3 5% 7% 50%	2600
	11th to 20th	Day	19% 7% 2 6% 2 3 3 3 4 6% 45%	2990
	21st to end	Day	13% 7% 3 6% 4 4 4 4 5% 7% 43%	3960
January	1st to 10th	Night	15% 8% 2 6% 4 4 4 3 5% 7% 42%	4569
	11th to 20th	Night	17% 7% 2 6% 4 3 3 3 4 5% 46%	4278
	21st to end	Night	19% 9% 3 7% 4 3 3 2 4 5% 41%	4546
February	1st to 10th	Night	15% 7% 3 6% 4 4 4 4 5% 6% 42%	2470
	11th to 20th	Night	19% 7% 2 5% 4 4 3 3 5% 6% 42%	2292
	21st to end	Night	17% 8% 2 5% 3 4 3 3 5% 6% 43%	1884
March	1st to 10th	Night	21% 8% 3 6% 4 4 3 3 3 6% 39%	3580
	11th to 20th	Night	12% 5% 2 5% 4 3 4 4 6% 7% 49%	3480
	21st to end	Night	16% 8% 2 7% 4 3 3 3 4 5% 46%	3672
April	1st to 10th	Night	16% 7% 3 6% 4 4 4 2 5% 7% 42%	1900
	11th to 20th	Night	12% 6% 2 6% 4 4 3 3 6% 6% 47%	1875
	21st to end	Night	18% 5% 2 4 3 4 4 4 5% 7% 44%	1900
May	1st to 10th	Night	19% 9% 3 7% 5% 5% 5% 4 5% 7% 31%	3042
	11th to 20th	Night	23% 8% 2 7% 5% 4 5% 3 5% 8% 31%	2495
	21st to end	Night	11% 5% 2 7% 4 4 4 4 7% 10% 43%	2732
June	1st to 10th	Night	11% 4 2 5% 4 4 5% 4 6% 10% 44%	1520
	11th to 20th	Night	11% 5% 2 6% 6% 4 4 4 6% 8% 43%	1520
	21st to end	Night	9% 5% 2 5% 5% 5% 5% 5% 8% 11% 41%	1520
July	1st to 10th	Night	7% 4 2 7% 5% 5% 6% 4 8% 11% 40%	2520
	11th to 20th	Night	11% 5% 2 6% 5% 5% 5% 4 6% 11% 39%	2520
	21st to end	Night	13% 7% 3 8% 6% 6% 5% 4 6% 9% 35%	3078
August	1st to 10th	Night	17% 6% 2 7% 5% 5% 5% 4 6% 10% 33%	2825
	11th to 20th	Night	13% 6% 2 7% 5% 5% 6% 5% 6% 9% 35%	3024
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 6% 7% 49%	3476
September	1st to 10th	Night	14% 6% 2 5% 3 4 4 3 6% 7% 45%	1900
	11th to 20th	Night	10% 6% 1 5% 3 4 4 3 6% 8% 49%	1900
	21st to end	Night	19% 7% 2 6% 3 4 4 4 5% 6% 38%	2143
October	1st to 10th	Night	18% 6% 2 5% 4 4 4 3 4 6% 45%	2280
	11th to 20th	Night	16% 5% 2 4 3 3 3 2 4 6% 52%	2280
	21st to end	Night	15% 5% 2 5% 3 3 3 3 5% 6% 49%	2508
November	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 5% 5% 53%	2504
	11th to 20th	Night	16% 7% 2 4 4 4 3 3 4 6% 47%	2600
	21st to end	Night	13% 5% 1 4 4 4 4 4 6% 6% 48%	2742
December	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 5% 7% 51%	4580
	11th to 20th	Night	20% 6% 3 5% 4 4 4 3 5% 6% 39%	5205
	21st to end	Night	15% 7% 2 6% 4 4 4 4 6% 7% 41%	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	37% 4 7% 32% 16% 4	2598
	11th to 20th	Day	45% 5% 9% 21% 16% 5%	2897
	21st to end	Day	43% 5% 12% 26% 11% 2	3133
February	1st to 10th	Day	42% 5% 12% 26% 13% 2	1710
	11th to 20th	Day	40% 3 10% 27% 17% 3	1782
	21st to end	Day	44% 4 13% 19% 16% 4	1570
March	1st to 10th	Day	43% 5% 11% 23% 14% 4	3269
	11th to 20th	Day	30% 5% 9% 30% 22% 4	3480
	21st to end	Day	44% 4 10% 20% 18% 3	3960
April	1st to 10th	Day	37% 5% 13% 22% 17% 5%	2280
	11th to 20th	Day	34% 5% 12% 24% 20% 6%	2254
	21st to end	Day	39% 5% 11% 22% 18% 4	2280
May	1st to 10th	Day	49% 7% 12% 22% 10% 2	3917
	11th to 20th	Day	44% 7% 16% 23% 8% 1	4401
	21st to end	Day	31% 7% 15% 27% 18% 2	4837
June	1st to 10th	Day	32% 9% 17% 25% 15% 2	2660
	11th to 20th	Day	32% 9% 16% 25% 17% 2	2660
	21st to end	Day	28% 9% 17% 26% 18% 1	2660
July	1st to 10th	Day	31% 8% 25% 19% 12% 5%	4370
	11th to 20th	Day	35% 7% 20% 27% 9% 2	4365
	21st to end	Day	38% 9% 16% 20% 17% 1	4327
August	1st to 10th	Day	41% 6% 18% 27% 7%	4091
	11th to 20th	Day	35% 7% 14% 30% 13% 1	3808
	21st to end	Day	29% 6% 16% 29% 18% 3	4180
September	1st to 10th	Day	34% 6% 14% 23% 18% 4	2280
	11th to 20th	Day	33% 5% 11% 26% 21% 3	2280
	21st to end	Day	44% 6% 9% 21% 16% 3	2031
October	1st to 10th	Day	34% 4 9% 21% 27% 5%	3160
	11th to 20th	Day	25% 3 6% 30% 26% 9%	3140
	21st to end	Day	22% 3 8% 32% 26% 9%	3428
November	1st to 10th	Day	32% 4 11% 28% 22% 3	1792
	11th to 20th	Day	35% 3 11% 26% 21% 4	1800
	21st to end	Day	36% 4 9% 30% 18% 3	1655
December	1st to 10th	Day	34% 4 16% 28% 14% 4	2600
	11th to 20th	Day	41% 2 12% 31% 10% 2	2986
	21st to end	Day	40% 5% 14% 24% 16% 1	3960
January	1st to 10th	Night	40% 4 9% 26% 17% 3	4569
	11th to 20th	Night	41% 4 8% 27% 17% 3	4278
	21st to end	Night	46% 4 7% 26% 16% 1	4546
February	1st to 10th	Night	42% 4 12% 25% 15% 2	2470
	11th to 20th	Night	43% 3 8% 22% 19% 5%	2294
	21st to end	Night	42% 4 10% 23% 17% 5%	1884
March	1st to 10th	Night	47% 4 8% 25% 14% 2	3580
	11th to 20th	Night	32% 5% 10% 29% 20% 4	3480
	21st to end	Night	42% 4 8% 21% 20% 6%	3672
April	1st to 10th	Night	42% 5% 9% 19% 21% 4	1900
	11th to 20th	Night	37% 5% 12% 22% 19% 6%	1875
	21st to end	Night	39% 6% 11% 23% 17% 4	1900
May	1st to 10th	Night	51% 6% 11% 21% 9% 2	3072
	11th to 20th	Night	51% 7% 12% 18% 10% 1	2496
	21st to end	Night	34% 8% 16% 23% 16% 3	2739
June	1st to 10th	Night	35% 9% 12% 26% 17% 1	1520
	11th to 20th	Night	38% 7% 14% 26% 13% 3	1520
	21st to end	Night	35% 8% 16% 22% 17% 3	1520
July	1st to 10th	Night	37% 9% 23% 18% 11% 2	2480
	11th to 20th	Night	38% 6% 23% 24% 8% 1	2472
	21st to end	Night	45% 8% 12% 22% 12%	2980
August	1st to 10th	Night	45% 7% 17% 22% 8%	2814
	11th to 20th	Night	44% 7% 13% 26% 10% 1	3053
	21st to end	Night	32% 7% 11% 29% 19% 2	3476
September	1st to 10th	Night	38% 5% 12% 21% 18% 5%	1900
	11th to 20th	Night	33% 6% 10% 26% 21% 4	1900
	21st to end	Night	46% 6% 9% 20% 16% 3	2143
October	1st to 10th	Night	41% 4 10% 21% 20% 5%	3800
	11th to 20th	Night	24% 3 12% 21% 32% 8%	3779
	21st to end	Night	23% 3 9% 32% 25% 7%	4120
November	1st to 10th	Night	34% 5% 9% 26% 21% 5%	2504
	11th to 20th	Night	40% 4 8% 22% 20% 6%	2600
	21st to end	Night	34% 4 12% 26% 20% 3	2742
December	1st to 10th	Night	33% 4 13% 28% 20% 3	4580
	11th to 20th	Night	46% 3 12% 20% 14% 5%	5208
	21st to end	Night	42% 5% 13% 23% 16% 1	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	19% 20% 30% 24% 7% 1	200
	11th to 20th	Day	16% 22% 31% 27% 4	290
	21st to end	Day	19% 11% 33% 29% 6% 1	300
February	1st to 10th	Day	17% 9% 36% 28% 10%	270
	11th to 20th	Day	24% 13% 38% 21% 4	381
	21st to end	Day	25% 9% 34% 25% 7%	382
March	1st to 10th	Day	17% 12% 34% 28% 7% 1	460
	11th to 20th	Day	17% 9% 35% 29% 8% 2	460
	21st to end	Day	20% 8% 30% 33% 7% 1	506
April	1st to 10th	Day	20% 8% 31% 31% 9% 2	460
	11th to 20th	Day	13% 9% 25% 35% 14% 4	452
	21st to end	Day	18% 8% 25% 32% 15% 1	460
May	1st to 10th	Day	23% 6% 23% 29% 17% 2	463
	11th to 20th	Day	18% 5% 19% 34% 22% 3	487
	21st to end	Day	17% 2 13% 27% 30% 10%	529
June	1st to 10th	Day	11% 3 15% 32% 28% 10%	490
	11th to 20th	Day	12% 3 14% 31% 31% 8%	490
	21st to end	Day	10% 1 16% 34% 34% 7%	490
July	1st to 10th	Day	9% 2 7% 31% 35% 16%	485
	11th to 20th	Day	4 1 4 32% 41% 17%	484
	21st to end	Day	10% 3 6% 32% 39% 10%	532
August	1st to 10th	Day	13% 2 8% 29% 36% 13%	486
	11th to 20th	Day	10% 3 7% 30% 37% 13%	479
	21st to end	Day	8% 2 12% 29% 33% 15%	539
September	1st to 10th	Day	16% 3 12% 24% 30% 16%	490
	11th to 20th	Day	16% 1 12% 28% 29% 13%	490
	21st to end	Day	23% 7% 19% 29% 18% 4	490
October	1st to 10th	Day	20% 3 14% 30% 23% 9%	490
	11th to 20th	Day	16% 6% 23% 29% 21% 4	490
	21st to end	Day	14% 9% 23% 35% 14% 5%	539
November	1st to 10th	Day	15% 7% 26% 30% 16% 6%	410
	11th to 20th	Day	14% 13% 31% 30% 11% 2	400
	21st to end	Day	16% 17% 24% 29% 13% 1	255
December	1st to 10th	Day	18% 7% 37% 32% 6% 1	200
	11th to 20th	Day	21% 10% 31% 28% 10%	200
	21st to end	Day	19% 11% 25% 32% 12%	220
January	1st to 10th	Night	18% 17% 37% 23% 5%	800
	11th to 20th	Night	20% 13% 33% 28% 6%	800
	21st to end	Night	19% 13% 37% 29% 2	841
February	1st to 10th	Night	19% 9% 36% 30% 5%	760
	11th to 20th	Night	23% 14% 40% 21% 2	743
	21st to end	Night	22% 13% 34% 28% 3	628
March	1st to 10th	Night	17% 10% 38% 29% 6%	760
	11th to 20th	Night	20% 10% 34% 26% 8% 2	760
	21st to end	Night	18% 9% 34% 32% 6% 1	836
April	1st to 10th	Night	18% 10% 38% 26% 7%	760
	11th to 20th	Night	13% 8% 30% 37% 11%	751
	21st to end	Night	20% 6% 28% 32% 13% 1	760
May	1st to 10th	Night	16% 7% 25% 35% 15% 2	711
	11th to 20th	Night	17% 7% 22% 37% 17% 1	374
	21st to end	Night	14% 3 14% 37% 28% 3	411
June	1st to 10th	Night	12% 2 21% 36% 27% 3	380
	11th to 20th	Night	11% 3 15% 42% 26% 2	380
	21st to end	Night	10% 2 16% 43% 26% 3	380
July	1st to 10th	Night	11% 4 11% 35% 35% 4	370
	11th to 20th	Night	8% 2 7% 37% 43% 4	368
	21st to end	Night	8% 2 11% 41% 33% 5%	615
August	1st to 10th	Night	11% 2 10% 39% 35% 4	567
	11th to 20th	Night	11% 2 13% 36% 34% 5%	701
	21st to end	Night	12% 2 10% 32% 36% 8%	836
September	1st to 10th	Night	16% 2 14% 31% 31% 6%	760
	11th to 20th	Night	12% 3 13% 33% 33% 6%	760
	21st to end	Night	21% 4 18% 32% 23% 2	760
October	1st to 10th	Night	21% 5% 17% 28% 23% 6%	760
	11th to 20th	Night	17% 9% 25% 30% 18% 2	760
	21st to end	Night	19% 9% 26% 28% 16% 2	836
November	1st to 10th	Night	14% 8% 28% 33% 15% 3	780
	11th to 20th	Night	20% 11% 31% 28% 10%	800
	21st to end	Night	15% 15% 30% 30% 9% 1	800
December	1st to 10th	Night	21% 12% 34% 23% 9% 1	800
	11th to 20th	Night	20% 10% 37% 25% 8%	800
	21st to end	Night	18% 12% 31% 32% 7%	880

Page generated at 2025-01-19 03:06:49. Version ac07

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