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 2025-03-12.

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% 37%	108766
	Night	12% 10% 4 8% 5% 4 4 4 5% 6% 38%	110446
Transparency	Day	44% 5% 12% 24% 14% 1	112297
	Night	45% 4 11% 23% 15% 2	115043
Seeing	Day	17% 11% 30% 25% 12% 4	16285
	Night	18% 10% 31% 28% 12% 1	26337

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	8% 11% 6% 14% 7% 6% 6% 4 5% 6% 28%	3617
	11th to 20th	Day	8% 11% 7% 13% 5% 4 5% 6% 6% 6% 30%	3620
	21st to end	Day	13% 14% 7% 9% 4 4 3 3 4 7% 33%	4007
February	1st to 10th	Day	9% 14% 6% 11% 5% 4 5% 4 5% 7% 30%	1800
	11th to 20th	Day	12% 11% 4 9% 5% 5% 5% 4 5% 6% 35%	1936
	21st to end	Day	11% 15% 4 11% 5% 5% 5% 4 4 6% 30%	1650
March	1st to 10th	Day	13% 9% 3 6% 4 4 4 4 5% 5% 42%	3220
	11th to 20th	Day	10% 7% 2 8% 6% 4 5% 4 6% 6% 43%	3282
	21st to end	Day	22% 13% 3 9% 5% 4 3 3 4 5% 29%	4165
April	1st to 10th	Day	18% 13% 4 7% 5% 5% 4 4 5% 7% 29%	2280
	11th to 20th	Day	16% 11% 3 7% 5% 5% 5% 3 5% 6% 34%	2254
	21st to end	Day	18% 10% 3 7% 4 4 5% 4 5% 7% 33%	2403
May	1st to 10th	Day	15% 8% 3 7% 5% 4 4 4 6% 7% 38%	4109
	11th to 20th	Day	13% 7% 2 6% 5% 4 4 4 5% 8% 43%	4399
	21st to end	Day	12% 8% 2 7% 4 4 5% 4 7% 8% 38%	4824
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 4 4 6% 9% 44%	2660
	11th to 20th	Day	11% 6% 2 6% 5% 4 4 4 6% 9% 42%	2660
	21st to end	Day	10% 6% 2 5% 5% 5% 5% 5% 7% 9% 41%	2660
July	1st to 10th	Day	12% 7% 4 7% 5% 5% 6% 5% 7% 9% 33%	4440
	11th to 20th	Day	4 4 1 5% 4 5% 5% 5% 7% 10% 49%	4440
	21st to end	Day	8% 6% 3 6% 5% 5% 5% 4 6% 9% 44%	4813
August	1st to 10th	Day	10% 5% 2 7% 5% 5% 6% 5% 7% 8% 40%	4423
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	3803
	21st to end	Day	10% 6% 3 7% 4 4 5% 4 6% 8% 44%	4180
September	1st to 10th	Day	11% 6% 2 7% 4 4 5% 4 6% 6% 44%	2280
	11th to 20th	Day	11% 6% 2 5% 4 4 4 3 6% 8% 48%	2174
	21st to end	Day	12% 7% 2 7% 4 4 5% 4 4 7% 43%	2090
October	1st to 10th	Day	14% 7% 3 6% 4 4 4 3 5% 7% 45%	2009
	11th to 20th	Day	18% 10% 3 7% 5% 4 4 3 6% 6% 33%	1875
	21st to end	Day	17% 9% 4 7% 4 4 4 4 5% 5% 36%	1881
November	1st to 10th	Day	11% 10% 4 7% 4 4 4 3 5% 6% 42%	1762
	11th to 20th	Day	11% 12% 4 10% 7% 5% 5% 4 6% 8% 30%	1800
	21st to end	Day	16% 13% 3 8% 5% 4 3 3 4 6% 35%	1650
December	1st to 10th	Day	7% 9% 4 10% 6% 5% 6% 4 7% 9% 34%	2610
	11th to 20th	Day	11% 16% 5% 10% 6% 5% 5% 4 6% 7% 24%	3008
	21st to end	Day	18% 22% 8% 13% 4 3 3 3 4 5% 15%	3982
January	1st to 10th	Night	9% 11% 5% 12% 7% 5% 4 3 4 5% 34%	6348
	11th to 20th	Night	10% 12% 6% 14% 7% 6% 6% 5% 7% 6% 24%	6360
	21st to end	Night	11% 13% 6% 11% 5% 5% 5% 3 5% 5% 31%	6968
February	1st to 10th	Night	11% 13% 4 9% 6% 4 5% 4 5% 5% 34%	2600
	11th to 20th	Night	11% 10% 3 8% 5% 5% 5% 3 4 6% 39%	2348
	21st to end	Night	15% 12% 4 8% 4 4 4 3 6% 5% 35%	1980
March	1st to 10th	Night	16% 9% 3 5% 4 3 4 3 4 5% 42%	3853
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 7% 8% 44%	3736
	21st to end	Night	20% 12% 4 10% 5% 4 3 3 4 5% 30%	3466
April	1st to 10th	Night	17% 10% 3 7% 5% 4 4 4 6% 6% 35%	1900
	11th to 20th	Night	20% 9% 2 7% 4 4 4 3 5% 5% 38%	1875
	21st to end	Night	17% 9% 3 5% 4 4 4 4 5% 7% 38%	1776
May	1st to 10th	Night	14% 7% 3 7% 4 4 5% 4 6% 7% 37%	2783
	11th to 20th	Night	13% 7% 2 6% 5% 5% 5% 5% 5% 7% 42%	2506
	21st to end	Night	12% 9% 3 6% 5% 4 4 4 5% 7% 41%	2743
June	1st to 10th	Night	9% 5% 2 5% 5% 5% 4 4 6% 9% 47%	1520
	11th to 20th	Night	10% 5% 3 5% 3 4 4 4 7% 8% 46%	1520
	21st to end	Night	9% 8% 2 6% 4 4 4 3 5% 7% 48%	1520
July	1st to 10th	Night	13% 7% 3 6% 5% 4 4 4 5% 8% 41%	2530
	11th to 20th	Night	3 3 1 5% 4 4 5% 4 6% 8% 57%	2530
	21st to end	Night	6% 4 1 5% 5% 5% 6% 5% 6% 9% 48%	2750
August	1st to 10th	Night	10% 4 2 6% 4 3 5% 4 6% 8% 48%	2517
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 6% 8% 48%	3021
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 8% 50%	3476
September	1st to 10th	Night	9% 5% 2 5% 3 4 3 3 5% 7% 55%	1900
	11th to 20th	Night	11% 4 2 5% 3 4 4 4 5% 7% 53%	1986
	21st to end	Night	11% 7% 3 6% 4 5% 3 3 4 6% 48%	2090
October	1st to 10th	Night	12% 7% 2 6% 4 4 4 3 5% 5% 49%	2166
	11th to 20th	Night	16% 8% 3 6% 4 3 4 3 4 7% 42%	2304
	21st to end	Night	18% 10% 3 6% 4 4 4 3 5% 7% 36%	2717
November	1st to 10th	Night	13% 7% 3 6% 4 4 3 3 5% 6% 45%	2536
	11th to 20th	Night	13% 11% 4 8% 5% 5% 4 4 5% 7% 34%	2600
	21st to end	Night	16% 10% 4 7% 5% 4 4 3 5% 6% 36%	2746
December	1st to 10th	Night	9% 9% 3 7% 4 4 4 3 6% 7% 43%	4580
	11th to 20th	Night	15% 16% 6% 10% 6% 4 4 3 4 4 28%	5199
	21st to end	Night	19% 20% 5% 12% 5% 5% 4 3 4 5% 19%	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	57% 4 13% 19% 7%	3618
	11th to 20th	Day	53% 3 10% 15% 16% 2	3620
	21st to end	Day	52% 3 10% 21% 13%	4007
February	1st to 10th	Day	53% 4 12% 20% 10% 1	1800
	11th to 20th	Day	50% 4 10% 23% 11% 2	1946
	21st to end	Day	55% 3 10% 19% 11% 3	1650
March	1st to 10th	Day	43% 4 9% 26% 13% 4	3220
	11th to 20th	Day	41% 5% 10% 27% 15% 2	3282
	21st to end	Day	58% 4 11% 18% 8% 1	4165
April	1st to 10th	Day	54% 5% 11% 19% 11%	2280
	11th to 20th	Day	50% 5% 9% 20% 13% 3	2254
	21st to end	Day	49% 6% 12% 18% 12% 1	2403
May	1st to 10th	Day	45% 5% 10% 24% 16% 1	4147
	11th to 20th	Day	39% 5% 11% 30% 14% 1	4403
	21st to end	Day	41% 6% 11% 22% 16% 4	4837
June	1st to 10th	Day	35% 6% 13% 28% 16% 2	2660
	11th to 20th	Day	37% 5% 14% 25% 17% 1	2660
	21st to end	Day	37% 7% 15% 24% 15% 2	2660
July	1st to 10th	Day	45% 6% 12% 25% 10% 2	4371
	11th to 20th	Day	27% 6% 17% 31% 17% 1	4365
	21st to end	Day	36% 7% 15% 21% 20% 2	4662
August	1st to 10th	Day	39% 6% 15% 29% 11% 1	4408
	11th to 20th	Day	39% 5% 12% 31% 12% 1	3841
	21st to end	Day	37% 6% 13% 24% 19% 1	4179
September	1st to 10th	Day	38% 6% 10% 28% 17% 1	2280
	11th to 20th	Day	34% 4 11% 32% 17% 1	2174
	21st to end	Day	41% 4 10% 30% 14% 1	2090
October	1st to 10th	Day	25% 3 5% 40% 25% 1	3334
	11th to 20th	Day	37% 3 10% 27% 22% 1	3091
	21st to end	Day	42% 4 11% 28% 14% 2	3081
November	1st to 10th	Day	43% 4 14% 24% 14% 2	1762
	11th to 20th	Day	52% 4 13% 21% 9% 1	1800
	21st to end	Day	52% 2 13% 25% 8% 1	1650
December	1st to 10th	Day	44% 4 21% 24% 6% 1	2610
	11th to 20th	Day	57% 3 11% 18% 9% 1	3005
	21st to end	Day	72% 3 7% 11% 8%	3982
January	1st to 10th	Night	53% 3 8% 22% 14% 1	6348
	11th to 20th	Night	60% 3 9% 10% 17% 1	6360
	21st to end	Night	55% 3 13% 17% 12%	6968
February	1st to 10th	Night	52% 3 11% 19% 13% 2	2600
	11th to 20th	Night	46% 4 9% 24% 15% 2	2349
	21st to end	Night	50% 3 11% 21% 12% 3	1980
March	1st to 10th	Night	44% 4 13% 25% 11% 4	3853
	11th to 20th	Night	35% 5% 11% 27% 19% 3	3736
	21st to end	Night	58% 4 7% 18% 11% 2	3466
April	1st to 10th	Night	48% 5% 9% 21% 16% 1	1900
	11th to 20th	Night	49% 3 7% 20% 18% 3	1875
	21st to end	Night	45% 4 12% 23% 14% 2	1776
May	1st to 10th	Night	44% 6% 11% 20% 17% 3	2810
	11th to 20th	Night	40% 6% 11% 29% 13% 1	2507
	21st to end	Night	43% 5% 10% 19% 16% 8%	2751
June	1st to 10th	Night	34% 5% 14% 27% 18% 2	1520
	11th to 20th	Night	35% 5% 10% 27% 20% 2	1520
	21st to end	Night	35% 5% 16% 24% 18% 2	1520
July	1st to 10th	Night	42% 5% 14% 22% 13% 4	2490
	11th to 20th	Night	23% 5% 16% 35% 18% 3	2482
	21st to end	Night	30% 7% 15% 20% 23% 4	2662
August	1st to 10th	Night	34% 5% 15% 26% 19% 2	2508
	11th to 20th	Night	33% 5% 14% 33% 15% 1	3049
	21st to end	Night	31% 4 14% 28% 21% 3	3476
September	1st to 10th	Night	30% 5% 12% 27% 24% 2	1900
	11th to 20th	Night	32% 4 10% 34% 19% 2	1986
	21st to end	Night	38% 4 9% 31% 17% 1	2090
October	1st to 10th	Night	27% 3 6% 39% 24% 1	3608
	11th to 20th	Night	34% 3 12% 27% 21% 3	3827
	21st to end	Night	43% 4 9% 26% 17% 1	4467
November	1st to 10th	Night	39% 4 11% 27% 17% 2	2536
	11th to 20th	Night	49% 5% 12% 22% 11% 2	2600
	21st to end	Night	49% 4 14% 22% 9% 1	2746
December	1st to 10th	Night	40% 4 17% 28% 8% 3	4580
	11th to 20th	Night	59% 4 9% 15% 12% 1	5201
	21st to end	Night	68% 4 8% 13% 6%	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	18% 15% 39% 22% 5% 1	300
	11th to 20th	Day	16% 22% 34% 23% 5% 1	300
	21st to end	Day	23% 15% 38% 19% 4 1	330
February	1st to 10th	Day	14% 20% 45% 15% 5% 1	300
	11th to 20th	Day	19% 25% 37% 14% 5%	300
	21st to end	Day	20% 24% 40% 14%	249
March	1st to 10th	Day	19% 24% 40% 15% 2	300
	11th to 20th	Day	24% 20% 30% 19% 6% 1	287
	21st to end	Day	28% 13% 29% 23% 7% 1	506
April	1st to 10th	Day	27% 12% 36% 20% 5%	460
	11th to 20th	Day	23% 19% 25% 22% 8% 2	452
	21st to end	Day	23% 11% 30% 23% 12% 1	460
May	1st to 10th	Day	23% 10% 35% 23% 8% 2	477
	11th to 20th	Day	21% 11% 32% 24% 10% 3	675
	21st to end	Day	17% 8% 29% 28% 13% 5%	734
June	1st to 10th	Day	9% 10% 33% 30% 15% 4	680
	11th to 20th	Day	13% 10% 29% 30% 13% 5%	680
	21st to end	Day	14% 8% 31% 30% 14% 4	680
July	1st to 10th	Day	9% 3 21% 32% 24% 10%	671
	11th to 20th	Day	8% 6% 27% 32% 20% 7%	668
	21st to end	Day	6% 3 28% 36% 19% 8%	739
August	1st to 10th	Day	8% 3 24% 36% 18% 10%	676
	11th to 20th	Day	12% 4 16% 30% 25% 13%	483
	21st to end	Day	13% 6% 19% 30% 22% 9%	539
September	1st to 10th	Day	14% 6% 25% 28% 20% 8%	490
	11th to 20th	Day	12% 3 22% 31% 23% 10%	490
	21st to end	Day	17% 11% 24% 26% 16% 6%	490
October	1st to 10th	Day	19% 9% 26% 28% 12% 6%	409
	11th to 20th	Day	23% 17% 31% 19% 9%	300
	21st to end	Day	27% 14% 38% 17% 4 1	330
November	1st to 10th	Day	18% 17% 35% 21% 8% 1	300
	11th to 20th	Day	18% 20% 36% 19% 7%	300
	21st to end	Day	24% 11% 42% 18% 4	300
December	1st to 10th	Day	20% 19% 41% 14% 6% 1	300
	11th to 20th	Day	19% 21% 35% 17% 7% 1	300
	21st to end	Day	25% 20% 33% 16% 4 1	330
January	1st to 10th	Night	17% 19% 35% 23% 6%	1000
	11th to 20th	Night	20% 16% 38% 19% 6% 1	1000
	21st to end	Night	19% 13% 37% 25% 6%	1100
February	1st to 10th	Night	19% 15% 37% 24% 5%	1000
	11th to 20th	Night	17% 18% 35% 25% 5%	793
	21st to end	Night	24% 15% 40% 17% 4	660
March	1st to 10th	Night	20% 14% 35% 24% 7% 1	800
	11th to 20th	Night	16% 13% 37% 26% 7% 1	739
	21st to end	Night	22% 7% 30% 32% 7% 2	627
April	1st to 10th	Night	23% 11% 35% 25% 6%	570
	11th to 20th	Night	26% 9% 32% 25% 7% 1	563
	21st to end	Night	21% 8% 32% 29% 10% 1	570
May	1st to 10th	Night	19% 7% 33% 34% 7% 1	570
	11th to 20th	Night	19% 6% 29% 32% 14% 1	561
	21st to end	Night	14% 4 25% 38% 18% 2	617
June	1st to 10th	Night	11% 4 27% 41% 17% 1	570
	11th to 20th	Night	13% 3 31% 37% 15% 1	570
	21st to end	Night	11% 5% 25% 41% 17% 1	570
July	1st to 10th	Night	9% 1 17% 40% 29% 4	555
	11th to 20th	Night	6% 2 23% 42% 24% 3	552
	21st to end	Night	7% 1 20% 46% 24% 2	624
August	1st to 10th	Night	7% 2 17% 46% 26% 3	567
	11th to 20th	Night	11% 1 15% 40% 28% 5%	564
	21st to end	Night	11% 3 17% 41% 26% 3	627
September	1st to 10th	Night	10% 3 22% 35% 26% 4	570
	11th to 20th	Night	12% 3 21% 31% 27% 5%	656
	21st to end	Night	14% 8% 24% 28% 21% 4	760
October	1st to 10th	Night	16% 9% 27% 31% 17% 1	760
	11th to 20th	Night	20% 12% 33% 26% 9% 1	760
	21st to end	Night	23% 10% 31% 27% 8% 1	836
November	1st to 10th	Night	17% 12% 37% 23% 10% 1	780
	11th to 20th	Night	20% 17% 35% 22% 7% 1	800
	21st to end	Night	21% 14% 37% 21% 7%	946
December	1st to 10th	Night	22% 15% 37% 21% 4	1000
	11th to 20th	Night	22% 14% 37% 21% 6% 1	1000
	21st to end	Night	29% 14% 35% 19% 4	1100

Page generated at 2025-03-09 07:08:49. Version ac07

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