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 2024-08-30.

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%	95686
	Night	15% 7% 2 6% 4 4 4 4 5% 7% 42%	93318
Transparency	Day	37% 6% 13% 25% 15% 3	95444
	Night	41% 5% 11% 24% 16% 3	93164
Seeing	Day	16% 6% 21% 30% 21% 6%	14801
	Night	17% 8% 26% 31% 16% 2	24211

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%	2517
	11th to 20th	Day	15% 9% 3 8% 5% 4 4 3 4 5% 40%	2808
	21st to end	Day	18% 7% 3 5% 3 4 4 3 6% 6% 41%	3124
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	10% 5% 2 6% 3 5% 4 4 7% 11% 43%	2457
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 45%	2275
	21st to end	Day	9% 4 2 6% 4 4 5% 4 7% 9% 46%	2486
September	1st to 10th	Day	13% 5% 2 4 4 4 4 3 6% 7% 48%	2160
	11th to 20th	Day	12% 5% 2 5% 3 3 3 2 4 7% 51%	2160
	21st to end	Day	17% 7% 2 7% 4 3 4 3 5% 6% 41%	1925
October	1st to 10th	Day	16% 5% 2 5% 3 3 3 4 4 7% 48%	1800
	11th to 20th	Day	18% 4 2 4 3 2 2 3 5% 6% 51%	1800
	21st to end	Day	14% 5% 2 5% 4 3 4 3 5% 6% 49%	1980
November	1st to 10th	Day	14% 5% 1 3 3 4 4 3 5% 6% 52%	1701
	11th to 20th	Day	14% 5% 2 4 3 4 4 4 5% 8% 48%	1710
	21st to end	Day	14% 7% 1 5% 3 3 3 3 5% 7% 48%	1573
December	1st to 10th	Day	16% 6% 2 6% 3 4 4 3 5% 7% 43%	1520
	11th to 20th	Day	16% 8% 2 5% 3 3 3 3 4 6% 46%	1910
	21st to end	Day	15% 7% 3 6% 4 4 5% 3 6% 7% 40%	2772
January	1st to 10th	Night	15% 8% 2 6% 4 4 4 3 5% 7% 42%	4429
	11th to 20th	Night	17% 8% 2 6% 4 3 3 3 4 5% 45%	4148
	21st to end	Night	19% 9% 3 7% 4 3 3 2 4 5% 41%	4532
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	9% 5% 2 7% 6% 6% 5% 4 7% 10% 40%	1701
	11th to 20th	Night	9% 7% 2 7% 5% 5% 7% 5% 6% 9% 38%	1825
	21st to end	Night	10% 5% 2 7% 4 4 5% 5% 6% 8% 43%	2080
September	1st to 10th	Night	15% 6% 2 5% 3 4 4 3 6% 7% 45%	1800
	11th to 20th	Night	10% 6% 1 5% 4 4 4 3 6% 8% 50%	1800
	21st to end	Night	18% 7% 2 6% 4 4 4 4 5% 7% 40%	2029
October	1st to 10th	Night	19% 6% 2 5% 3 4 4 3 4 6% 45%	2160
	11th to 20th	Night	17% 5% 2 5% 3 3 3 2 4 6% 50%	2160
	21st to end	Night	16% 6% 2 5% 3 3 3 3 5% 6% 47%	2376
November	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 5% 5% 52%	2375
	11th to 20th	Night	16% 7% 2 4 4 4 3 3 4 6% 47%	2470
	21st to end	Night	13% 5% 1 4 4 4 4 4 6% 6% 48%	2604
December	1st to 10th	Night	19% 7% 3 6% 4 3 4 4 6% 6% 40%	2660
	11th to 20th	Night	17% 6% 2 6% 4 4 4 3 6% 7% 42%	3285
	21st to end	Night	15% 7% 2 7% 5% 4 5% 4 6% 7% 38%	4884

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% 33% 16% 3	2518
	11th to 20th	Day	46% 5% 9% 21% 15% 5%	2808
	21st to end	Day	43% 5% 12% 26% 11% 2	3124
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	34% 8% 17% 28% 11% 1	2444
	11th to 20th	Day	34% 9% 16% 26% 14% 1	2275
	21st to end	Day	32% 7% 16% 24% 16% 4	2486
September	1st to 10th	Day	34% 7% 15% 23% 17% 4	2160
	11th to 20th	Day	33% 5% 11% 26% 21% 4	2160
	21st to end	Day	43% 7% 9% 22% 17% 3	1925
October	1st to 10th	Day	36% 5% 13% 26% 17% 3	1800
	11th to 20th	Day	35% 3 9% 29% 21% 3	1800
	21st to end	Day	36% 5% 7% 28% 21% 3	1980
November	1st to 10th	Day	33% 4 10% 29% 21% 3	1701
	11th to 20th	Day	36% 3 10% 26% 21% 4	1710
	21st to end	Day	36% 3 10% 30% 18% 3	1573
December	1st to 10th	Day	40% 6% 15% 25% 12% 3	1520
	11th to 20th	Day	40% 3 9% 33% 11% 3	1906
	21st to end	Day	44% 5% 14% 25% 12% 1	2772
January	1st to 10th	Night	41% 4 9% 26% 17% 3	4429
	11th to 20th	Night	41% 4 9% 27% 17% 3	4148
	21st to end	Night	46% 4 7% 26% 16% 1	4532
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	37% 8% 17% 24% 13%	1690
	11th to 20th	Night	41% 8% 14% 23% 13% 1	1825
	21st to end	Night	36% 8% 14% 23% 16% 3	2080
September	1st to 10th	Night	38% 6% 13% 22% 16% 5%	1800
	11th to 20th	Night	32% 6% 10% 26% 22% 4	1800
	21st to end	Night	44% 6% 9% 21% 17% 3	2029
October	1st to 10th	Night	41% 5% 10% 23% 18% 3	2160
	11th to 20th	Night	37% 4 9% 26% 20% 4	2160
	21st to end	Night	38% 4 8% 26% 20% 3	2376
November	1st to 10th	Night	34% 5% 9% 27% 20% 6%	2375
	11th to 20th	Night	40% 4 8% 21% 21% 6%	2470
	21st to end	Night	34% 4 12% 27% 20% 4	2604
December	1st to 10th	Night	43% 5% 11% 25% 13% 3	2660
	11th to 20th	Night	41% 4 11% 23% 18% 4	3288
	21st to end	Night	43% 6% 14% 25% 10% 1	4884

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	20% 16% 31% 26% 8% 1	180
	11th to 20th	Day	16% 22% 30% 27% 5%	261
	21st to end	Day	20% 11% 33% 30% 6% 1	297
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% 30% 33% 15%	532
September	1st to 10th	Day	16% 2 11% 24% 29% 17%	450
	11th to 20th	Day	16% 1 13% 27% 28% 14%	450
	21st to end	Day	21% 7% 20% 28% 19% 5%	450
October	1st to 10th	Day	21% 3 13% 30% 24% 9%	450
	11th to 20th	Day	17% 6% 22% 29% 22% 3	450
	21st to end	Day	16% 10% 24% 35% 12% 4	495
November	1st to 10th	Day	16% 8% 25% 29% 16% 6%	379
	11th to 20th	Day	14% 13% 31% 29% 11% 2	370
	21st to end	Day	16% 15% 24% 30% 14% 1	233
December	1st to 10th	Day	19% 7% 36% 31% 7% 1	180
	11th to 20th	Day	21% 11% 31% 28% 10%	180
	21st to end	Day	21% 11% 25% 32% 11% 1	198
January	1st to 10th	Night	19% 14% 38% 24% 5%	760
	11th to 20th	Night	20% 12% 33% 28% 7%	760
	21st to end	Night	19% 12% 37% 30% 2	836
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%	832
September	1st to 10th	Night	16% 2 13% 31% 32% 6%	720
	11th to 20th	Night	11% 3 13% 33% 34% 6%	720
	21st to end	Night	20% 4 18% 33% 23% 2	720
October	1st to 10th	Night	21% 5% 17% 29% 23% 6%	720
	11th to 20th	Night	18% 8% 24% 31% 19% 1	720
	21st to end	Night	20% 10% 26% 27% 15% 2	792
November	1st to 10th	Night	15% 8% 27% 32% 15% 3	740
	11th to 20th	Night	19% 11% 30% 28% 11%	760
	21st to end	Night	14% 14% 30% 31% 10% 1	760
December	1st to 10th	Night	22% 11% 34% 22% 10% 1	760
	11th to 20th	Night	19% 10% 37% 25% 8%	760
	21st to end	Night	18% 12% 32% 32% 7%	836

Page generated at 2024-08-27 09:49:39. Version ac07

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