Richfield Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Richfield Observatory clear sky chart from 2005-11-06 to 2026-07-16.

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	12% 9% 3 8% 5% 4 5% 4 6% 7% 38%	138084
	Night	12% 9% 4 8% 5% 4 4 4 5% 6% 38%	134915
Transparency	Day	44% 5% 12% 25% 14% 1	141570
	Night	45% 4 11% 23% 15% 2	139493
Seeing	Day	17% 12% 30% 25% 12% 4	18238
	Night	17% 10% 31% 28% 12% 1	28078

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	10% 13% 5% 13% 7% 6% 6% 4 5% 6% 26%	4691
	11th to 20th	Day	6% 11% 7% 13% 5% 4 6% 6% 6% 7% 30%	4710
	21st to end	Day	10% 12% 6% 10% 5% 4 5% 3 4 6% 35%	5195
February	1st to 10th	Day	9% 14% 6% 11% 5% 4 5% 4 6% 7% 30%	1890
	11th to 20th	Day	12% 11% 4 9% 5% 5% 5% 3 4 6% 36%	2036
	21st to end	Day	11% 15% 4 11% 5% 5% 5% 4 4 6% 30%	1730
March	1st to 10th	Day	14% 8% 3 6% 4 4 4 4 5% 6% 43%	4580
	11th to 20th	Day	11% 7% 2 8% 5% 4 5% 4 6% 7% 42%	4791
	21st to end	Day	21% 12% 4 9% 5% 4 4 3 4 5% 29%	6099
April	1st to 10th	Day	18% 13% 4 7% 5% 5% 4 4 5% 7% 29%	2520
	11th to 20th	Day	15% 10% 3 7% 6% 5% 5% 4 5% 6% 33%	2494
	21st to end	Day	17% 10% 3 7% 4 4 5% 4 5% 7% 33%	2656
May	1st to 10th	Day	12% 8% 3 6% 4 4 4 4 7% 8% 40%	7670
	11th to 20th	Day	11% 6% 2 7% 5% 4 5% 4 6% 8% 42%	8222
	21st to end	Day	14% 7% 2 6% 4 4 5% 4 6% 8% 39%	9047
June	1st to 10th	Day	9% 6% 3 6% 5% 5% 4 4 6% 9% 44%	2940
	11th to 20th	Day	11% 6% 2 6% 5% 5% 4 5% 6% 9% 41%	2940
	21st to end	Day	11% 6% 2 5% 4 5% 5% 5% 7% 9% 41%	2940
July	1st to 10th	Day	11% 6% 3 7% 4 5% 5% 5% 7% 9% 38%	6500
	11th to 20th	Day	6% 5% 2 6% 4 5% 5% 5% 7% 9% 46%	6431
	21st to end	Day	8% 6% 3 6% 4 4 5% 4 6% 9% 44%	6924
August	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 8% 41%	4563
	11th to 20th	Day	12% 6% 2 5% 5% 5% 5% 4 6% 8% 42%	3925
	21st to end	Day	10% 5% 3 7% 4 4 5% 4 6% 8% 44%	4312
September	1st to 10th	Day	10% 6% 2 7% 4 4 5% 4 5% 6% 45%	2400
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 6% 8% 48%	2288
	21st to end	Day	12% 7% 2 7% 4 4 5% 4 4 7% 44%	2200
October	1st to 10th	Day	13% 6% 3 6% 4 4 4 3 5% 7% 45%	2115
	11th to 20th	Day	18% 10% 3 8% 5% 4 4 3 5% 6% 33%	1973
	21st to end	Day	17% 9% 4 7% 4 4 4 4 5% 5% 37%	1980
November	1st to 10th	Day	11% 10% 4 7% 4 4 4 3 5% 6% 42%	1852
	11th to 20th	Day	11% 12% 4 10% 6% 5% 4 4 6% 8% 31%	1890
	21st to end	Day	15% 13% 4 8% 5% 4 4 3 4 6% 34%	1732
December	1st to 10th	Day	7% 9% 4 10% 6% 5% 6% 4 7% 9% 34%	2690
	11th to 20th	Day	11% 16% 5% 9% 6% 5% 5% 4 6% 7% 25%	3088
	21st to end	Day	18% 21% 8% 13% 4 3 3 3 4 5% 15%	4070
January	1st to 10th	Night	11% 11% 6% 13% 6% 4 4 3 4 5% 33%	8232
	11th to 20th	Night	9% 13% 6% 14% 7% 6% 6% 4 6% 6% 23%	8280
	21st to end	Night	9% 12% 5% 10% 6% 6% 6% 4 6% 6% 31%	9016
February	1st to 10th	Night	11% 14% 4 9% 5% 4 4 4 5% 5% 34%	2730
	11th to 20th	Night	11% 10% 3 8% 5% 5% 5% 3 4 6% 40%	2468
	21st to end	Night	15% 12% 4 9% 4 4 4 3 6% 5% 36%	2076
March	1st to 10th	Night	15% 8% 2 6% 4 3 4 3 4 6% 43%	5493
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 6% 9% 45%	5432
	21st to end	Night	18% 12% 5% 9% 5% 4 4 3 4 5% 31%	5072
April	1st to 10th	Night	18% 10% 4 8% 4 4 4 4 6% 6% 35%	2100
	11th to 20th	Night	20% 10% 2 7% 4 4 4 3 5% 5% 37%	2075
	21st to end	Night	16% 9% 3 6% 5% 4 4 4 5% 7% 38%	1962
May	1st to 10th	Night	13% 6% 3 7% 4 4 4 4 6% 7% 42%	5182
	11th to 20th	Night	9% 5% 2 7% 5% 5% 5% 4 5% 8% 43%	4670
	21st to end	Night	13% 8% 2 7% 5% 4 4 3 5% 7% 41%	5139
June	1st to 10th	Night	10% 5% 2 5% 5% 4 4 4 6% 8% 47%	1680
	11th to 20th	Night	10% 5% 3 5% 4 4 4 5% 7% 8% 44%	1680
	21st to end	Night	9% 8% 2 6% 4 4 5% 3 5% 8% 47%	1680
July	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 5% 9% 44%	3698
	11th to 20th	Night	6% 5% 2 5% 4 4 4 3 6% 7% 54%	3657
	21st to end	Night	6% 4 2 5% 4 5% 5% 4 6% 8% 50%	3947
August	1st to 10th	Night	10% 4 2 6% 4 3 5% 4 6% 8% 48%	2597
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 6% 8% 47%	3118
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 8% 51%	3586
September	1st to 10th	Night	8% 5% 2 5% 3 4 3 3 5% 7% 54%	2000
	11th to 20th	Night	10% 4 2 5% 4 4 3 4 4 7% 53%	2091
	21st to end	Night	11% 7% 3 6% 4 5% 4 3 4 6% 49%	2200
October	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 5% 5% 49%	2280
	11th to 20th	Night	16% 8% 3 6% 4 3 4 3 4 7% 41%	2425
	21st to end	Night	17% 9% 3 6% 4 4 4 3 5% 7% 36%	2860
November	1st to 10th	Night	12% 8% 3 6% 4 3 3 3 5% 6% 45%	2666
	11th to 20th	Night	13% 11% 4 8% 5% 5% 4 3 5% 7% 35%	2730
	21st to end	Night	15% 10% 4 7% 5% 4 4 3 5% 6% 35%	2884
December	1st to 10th	Night	9% 10% 3 7% 4 4 4 3 6% 7% 42%	4720
	11th to 20th	Night	14% 16% 6% 10% 6% 5% 4 3 4 4 28%	5339
	21st to end	Night	19% 20% 5% 11% 5% 5% 4 3 4 5% 19%	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	59% 4 14% 16% 6%	4692
	11th to 20th	Day	51% 3 9% 19% 15% 1	4710
	21st to end	Day	51% 3 10% 23% 14%	5195
February	1st to 10th	Day	53% 4 12% 20% 10% 1	1890
	11th to 20th	Day	49% 4 9% 24% 11% 3	2046
	21st to end	Day	55% 3 10% 19% 11% 2	1730
March	1st to 10th	Day	42% 3 11% 26% 13% 6%	4580
	11th to 20th	Day	41% 4 13% 25% 15% 2	4791
	21st to end	Day	58% 4 11% 15% 11% 1	6101
April	1st to 10th	Day	54% 5% 10% 19% 11%	2520
	11th to 20th	Day	50% 5% 11% 20% 12% 2	2494
	21st to end	Day	49% 6% 12% 20% 11% 1	2656
May	1st to 10th	Day	40% 5% 9% 28% 16% 1	7705
	11th to 20th	Day	39% 6% 12% 27% 17% 1	8226
	21st to end	Day	42% 5% 10% 23% 16% 4	9061
June	1st to 10th	Day	36% 6% 13% 27% 16% 2	2940
	11th to 20th	Day	38% 5% 14% 25% 17% 1	2940
	21st to end	Day	37% 7% 15% 24% 15% 2	2940
July	1st to 10th	Day	40% 6% 12% 30% 10% 1	6431
	11th to 20th	Day	32% 6% 14% 32% 15% 1	6356
	21st to end	Day	35% 6% 16% 23% 18% 2	6728
August	1st to 10th	Day	38% 6% 15% 29% 12% 1	4548
	11th to 20th	Day	38% 5% 13% 31% 12% 1	3963
	21st to end	Day	37% 6% 13% 25% 18% 1	4311
September	1st to 10th	Day	38% 6% 10% 28% 16% 1	2400
	11th to 20th	Day	34% 4 12% 33% 17% 1	2288
	21st to end	Day	41% 4 10% 31% 14% 1	2200
October	1st to 10th	Day	25% 3 5% 40% 25% 1	3440
	11th to 20th	Day	38% 3 10% 27% 21% 1	3189
	21st to end	Day	42% 4 10% 29% 13% 2	3180
November	1st to 10th	Day	42% 4 13% 24% 14% 2	1852
	11th to 20th	Day	51% 4 13% 22% 9% 1	1890
	21st to end	Day	53% 2 13% 24% 7% 1	1732
December	1st to 10th	Day	45% 4 21% 24% 6% 1	2690
	11th to 20th	Day	57% 3 11% 18% 9% 1	3085
	21st to end	Day	72% 3 7% 11% 8%	4070
January	1st to 10th	Night	54% 3 9% 22% 12% 1	8233
	11th to 20th	Night	60% 3 9% 11% 16% 1	8280
	21st to end	Night	52% 3 12% 20% 12%	9016
February	1st to 10th	Night	52% 3 10% 19% 13% 2	2730
	11th to 20th	Night	45% 4 9% 25% 15% 2	2469
	21st to end	Night	49% 3 11% 21% 12% 3	2076
March	1st to 10th	Night	43% 3 14% 24% 13% 4	5493
	11th to 20th	Night	36% 4 13% 29% 14% 4	5432
	21st to end	Night	57% 4 9% 16% 12% 2	5072
April	1st to 10th	Night	49% 5% 9% 21% 16% 1	2100
	11th to 20th	Night	49% 3 7% 21% 17% 3	2075
	21st to end	Night	45% 4 12% 24% 13% 2	1962
May	1st to 10th	Night	39% 5% 11% 24% 19% 2	5209
	11th to 20th	Night	38% 5% 13% 25% 17% 2	4671
	21st to end	Night	43% 4 8% 22% 16% 7%	5149
June	1st to 10th	Night	34% 5% 13% 27% 19% 2	1680
	11th to 20th	Night	36% 6% 10% 26% 19% 2	1680
	21st to end	Night	36% 5% 16% 24% 17% 2	1680
July	1st to 10th	Night	37% 5% 13% 32% 11% 3	3660
	11th to 20th	Night	28% 5% 14% 32% 19% 2	3612
	21st to end	Night	29% 6% 15% 24% 23% 3	3832
August	1st to 10th	Night	33% 5% 15% 26% 19% 2	2588
	11th to 20th	Night	34% 5% 14% 33% 15% 1	3146
	21st to end	Night	31% 4 14% 28% 21% 3	3586
September	1st to 10th	Night	30% 5% 12% 28% 24% 2	2000
	11th to 20th	Night	32% 4 10% 34% 19% 1	2091
	21st to end	Night	38% 4 9% 31% 17% 1	2200
October	1st to 10th	Night	27% 3 6% 40% 24% 1	3722
	11th to 20th	Night	35% 3 12% 27% 20% 3	3948
	21st to end	Night	43% 3 9% 27% 17% 1	4610
November	1st to 10th	Night	40% 4 11% 27% 17% 2	2666
	11th to 20th	Night	48% 4 12% 23% 11% 2	2730
	21st to end	Night	50% 4 13% 22% 9% 1	2884
December	1st to 10th	Night	41% 4 16% 27% 8% 3	4720
	11th to 20th	Night	59% 4 9% 15% 12% 1	5341
	21st to end	Night	68% 4 8% 14% 6%	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	18% 16% 39% 21% 5% 1	330
	11th to 20th	Day	15% 24% 34% 22% 5% 1	330
	21st to end	Day	22% 17% 39% 18% 4 1	363
February	1st to 10th	Day	13% 20% 45% 16% 5% 2	330
	11th to 20th	Day	18% 26% 36% 14% 5%	330
	21st to end	Day	21% 24% 41% 14%	273
March	1st to 10th	Day	19% 24% 40% 15% 2	330
	11th to 20th	Day	25% 21% 31% 17% 5% 1	346
	21st to end	Day	27% 15% 30% 21% 6% 1	594
April	1st to 10th	Day	28% 13% 36% 18% 4	540
	11th to 20th	Day	23% 20% 27% 20% 8% 2	532
	21st to end	Day	23% 11% 31% 24% 11% 1	540
May	1st to 10th	Day	21% 12% 35% 22% 8% 2	559
	11th to 20th	Day	20% 13% 32% 23% 9% 3	775
	21st to end	Day	17% 8% 30% 27% 11% 5%	844
June	1st to 10th	Day	9% 9% 33% 30% 14% 4	780
	11th to 20th	Day	13% 12% 30% 29% 12% 4	780
	21st to end	Day	13% 8% 32% 29% 14% 3	780
July	1st to 10th	Day	9% 4 22% 33% 23% 9%	771
	11th to 20th	Day	8% 6% 26% 33% 19% 7%	744
	21st to end	Day	7% 3 28% 37% 18% 7%	794
August	1st to 10th	Day	8% 3 24% 36% 18% 10%	726
	11th to 20th	Day	13% 4 16% 29% 25% 13%	523
	21st to end	Day	12% 6% 19% 30% 23% 9%	583
September	1st to 10th	Day	14% 6% 25% 27% 19% 8%	530
	11th to 20th	Day	11% 3 21% 31% 24% 10%	530
	21st to end	Day	16% 11% 24% 26% 17% 6%	530
October	1st to 10th	Day	18% 9% 26% 28% 14% 6%	445
	11th to 20th	Day	23% 17% 33% 18% 8%	330
	21st to end	Day	25% 13% 39% 18% 4 1	363
November	1st to 10th	Day	18% 19% 35% 20% 7% 1	330
	11th to 20th	Day	19% 20% 35% 19% 7%	330
	21st to end	Day	24% 13% 42% 17% 4	330
December	1st to 10th	Day	19% 19% 41% 14% 6% 1	330
	11th to 20th	Day	19% 23% 35% 16% 6% 1	330
	21st to end	Day	25% 21% 35% 15% 4 1	363
January	1st to 10th	Night	17% 19% 35% 22% 6%	1050
	11th to 20th	Night	20% 17% 38% 19% 6% 1	1050
	21st to end	Night	19% 14% 38% 24% 5%	1155
February	1st to 10th	Night	19% 14% 38% 24% 5%	1050
	11th to 20th	Night	17% 18% 35% 25% 5%	833
	21st to end	Night	23% 15% 39% 18% 4	692
March	1st to 10th	Night	20% 14% 35% 24% 7% 1	840
	11th to 20th	Night	17% 15% 36% 25% 6%	808
	21st to end	Night	21% 8% 32% 31% 6% 2	693
April	1st to 10th	Night	24% 12% 35% 23% 6%	630
	11th to 20th	Night	26% 9% 31% 25% 7% 1	623
	21st to end	Night	21% 8% 32% 30% 9% 1	630
May	1st to 10th	Night	18% 7% 32% 34% 7% 1	630
	11th to 20th	Night	17% 7% 31% 31% 13% 1	621
	21st to end	Night	14% 4 26% 37% 18% 2	683
June	1st to 10th	Night	11% 4 27% 41% 17% 1	630
	11th to 20th	Night	13% 4 32% 36% 13% 1	630
	21st to end	Night	11% 5% 26% 40% 17%	630
July	1st to 10th	Night	9% 2 18% 40% 28% 3	615
	11th to 20th	Night	6% 3 22% 43% 23% 3	597
	21st to end	Night	7% 1 20% 46% 24% 2	657
August	1st to 10th	Night	7% 2 17% 46% 26% 3	597
	11th to 20th	Night	12% 1 15% 39% 28% 5%	594
	21st to end	Night	10% 3 17% 41% 26% 3	660
September	1st to 10th	Night	10% 3 22% 35% 25% 5%	600
	11th to 20th	Night	12% 3 21% 31% 28% 5%	691
	21st to end	Night	14% 8% 24% 29% 22% 4	800
October	1st to 10th	Night	16% 8% 27% 32% 17% 1	800
	11th to 20th	Night	20% 11% 33% 27% 8% 1	800
	21st to end	Night	22% 10% 31% 28% 8% 1	880
November	1st to 10th	Night	17% 12% 38% 23% 10% 1	820
	11th to 20th	Night	19% 18% 35% 22% 7%	840
	21st to end	Night	21% 14% 37% 21% 7%	994
December	1st to 10th	Night	22% 15% 37% 22% 4	1050
	11th to 20th	Night	22% 14% 37% 21% 5% 1	1050
	21st to end	Night	29% 14% 35% 18% 3	1155

Page generated at 2026-07-13 02:14:48. Version ac07

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