Richmond
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Richmond clear sky chart from 2005-11-06 to 2025-02-06.

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% 9% 4 8% 5% 4 4 4 5% 7% 35%	108583
	Night	15% 10% 4 8% 5% 4 4 3 5% 6% 35%	109765
Transparency	Day	47% 5% 11% 22% 14% 2	112253
	Night	47% 4 10% 22% 14% 2	114235
Seeing	Day	17% 10% 26% 24% 16% 7%	15761
	Night	18% 9% 28% 29% 15% 2	25660

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	15% 15% 9% 13% 6% 4 4 3 4 5% 22%	3617
	11th to 20th	Day	13% 14% 7% 14% 8% 7% 6% 4 3 3 22%	3637
	21st to end	Day	21% 15% 8% 12% 5% 4 3 3 3 4 22%	4466
February	1st to 10th	Day	17% 16% 6% 10% 6% 4 4 4 3 5% 25%	1865
	11th to 20th	Day	15% 11% 5% 12% 8% 4 5% 3 4 6% 27%	1848
	21st to end	Day	19% 13% 5% 11% 4 4 3 3 4 5% 29%	1570
March	1st to 10th	Day	22% 18% 6% 9% 4 3 3 3 3 5% 23%	3120
	11th to 20th	Day	13% 10% 3 7% 4 3 4 3 5% 7% 40%	3468
	21st to end	Day	18% 10% 4 7% 5% 5% 4 4 5% 6% 30%	3830
April	1st to 10th	Day	15% 12% 3 8% 6% 4 4 3 4 7% 33%	2280
	11th to 20th	Day	17% 10% 4 6% 4 3 4 3 5% 6% 38%	2294
	21st to end	Day	19% 8% 3 7% 4 4 4 3 5% 7% 33%	2470
May	1st to 10th	Day	21% 10% 3 7% 6% 4 4 4 5% 7% 29%	4082
	11th to 20th	Day	20% 7% 2 7% 4 4 4 3 5% 6% 38%	4081
	21st to end	Day	11% 7% 3 8% 5% 5% 6% 5% 8% 10% 33%	4476
June	1st to 10th	Day	12% 5% 3 6% 5% 5% 5% 4 7% 8% 41%	2582
	11th to 20th	Day	10% 6% 3 6% 4 5% 5% 4 7% 9% 43%	2660
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 8% 39%	2660
July	1st to 10th	Day	13% 6% 3 8% 6% 5% 5% 5% 7% 9% 33%	4440
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 5% 7% 11% 46%	4440
	21st to end	Day	9% 7% 3 7% 6% 5% 6% 5% 7% 9% 36%	4476
August	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 4 7% 10% 45%	4104
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 10% 40%	4044
	21st to end	Day	7% 5% 2 5% 4 4 4 3 6% 9% 52%	4181
September	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 3 5% 7% 47%	2190
	11th to 20th	Day	10% 5% 2 6% 5% 4 4 3 6% 8% 48%	2090
	21st to end	Day	15% 6% 2 6% 4 3 3 3 4 6% 46%	2090
October	1st to 10th	Day	12% 5% 2 6% 4 3 5% 3 5% 6% 48%	2090
	11th to 20th	Day	14% 7% 2 5% 3 4 5% 4 5% 6% 45%	1946
	21st to end	Day	19% 9% 2 8% 5% 4 4 3 5% 6% 34%	1900
November	1st to 10th	Day	10% 7% 2 5% 4 4 3 3 5% 6% 50%	1762
	11th to 20th	Day	16% 12% 4 8% 5% 4 4 4 5% 6% 33%	1800
	21st to end	Day	19% 13% 5% 9% 4 3 3 3 4 6% 31%	1800
December	1st to 10th	Day	16% 13% 5% 8% 3 3 3 3 4 5% 38%	2930
	11th to 20th	Day	19% 14% 7% 11% 4 5% 5% 3 4 5% 23%	3312
	21st to end	Day	23% 21% 7% 10% 5% 4 3 3 4 5% 15%	3982
January	1st to 10th	Night	15% 16% 8% 15% 7% 5% 4 3 4 4 19%	6348
	11th to 20th	Night	12% 18% 8% 15% 6% 7% 5% 3 4 4 18%	6338
	21st to end	Night	20% 14% 6% 8% 4 4 4 3 4 6% 27%	6490
February	1st to 10th	Night	20% 13% 5% 8% 6% 4 3 3 4 5% 27%	2421
	11th to 20th	Night	14% 11% 4 9% 7% 4 4 4 5% 7% 31%	2218
	21st to end	Night	19% 14% 4 9% 5% 4 3 3 5% 6% 28%	1884
March	1st to 10th	Night	20% 14% 3 6% 4 4 3 3 4 5% 34%	3733
	11th to 20th	Night	12% 8% 3 6% 4 4 4 3 4 6% 45%	3492
	21st to end	Night	17% 9% 3 7% 5% 5% 3 3 4 6% 39%	3817
April	1st to 10th	Night	15% 10% 3 6% 5% 3 4 4 5% 8% 36%	1914
	11th to 20th	Night	16% 9% 2 5% 4 4 4 4 6% 7% 39%	1833
	21st to end	Night	16% 8% 2 7% 5% 5% 5% 4 6% 6% 37%	1710
May	1st to 10th	Night	20% 12% 4 8% 5% 5% 4 4 4 6% 28%	2813
	11th to 20th	Night	19% 7% 2 6% 4 4 4 3 5% 7% 39%	2812
	21st to end	Night	10% 5% 2 6% 4 4 4 4 7% 9% 44%	3079
June	1st to 10th	Night	10% 5% 2 7% 4 5% 4 4 5% 8% 47%	1592
	11th to 20th	Night	9% 5% 2 5% 4 4 4 3 6% 11% 47%	1520
	21st to end	Night	6% 5% 2 6% 4 4 5% 4 7% 10% 47%	1520
July	1st to 10th	Night	11% 5% 3 6% 4 4 5% 3 5% 7% 46%	2530
	11th to 20th	Night	7% 3 2 4 4 3 4 4 6% 9% 55%	2530
	21st to end	Night	11% 6% 2 5% 4 4 5% 5% 7% 10% 40%	3074
August	1st to 10th	Night	9% 6% 2 7% 4 4 4 4 6% 9% 45%	2825
	11th to 20th	Night	7% 7% 3 6% 4 4 4 4 5% 8% 47%	2785
	21st to end	Night	4 3 2 6% 4 4 5% 4 7% 9% 53%	3471
September	1st to 10th	Night	11% 5% 1 5% 4 4 4 3 6% 7% 50%	1971
	11th to 20th	Night	9% 5% 2 5% 3 3 3 4 5% 8% 55%	2090
	21st to end	Night	14% 5% 2 5% 3 4 5% 3 4 6% 49%	2090
October	1st to 10th	Night	9% 5% 2 6% 3 4 3 3 5% 7% 53%	2090
	11th to 20th	Night	15% 7% 3 6% 4 3 3 3 5% 6% 44%	2232
	21st to end	Night	18% 8% 2 6% 4 3 4 3 4 7% 40%	2693
November	1st to 10th	Night	12% 7% 2 5% 4 4 4 4 5% 7% 46%	2536
	11th to 20th	Night	17% 9% 4 6% 5% 4 4 3 5% 7% 37%	2600
	21st to end	Night	18% 14% 4 8% 6% 4 4 3 5% 5% 28%	2600
December	1st to 10th	Night	17% 11% 3 9% 5% 4 4 3 4 5% 35%	4250
	11th to 20th	Night	20% 16% 7% 11% 4 3 4 3 4 5% 23%	4868
	21st to end	Night	25% 18% 7% 10% 5% 4 4 3 4 4 16%	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	65% 3 7% 18% 7%	3618
	11th to 20th	Day	68% 3 8% 11% 9% 2	3637
	21st to end	Day	66% 3 9% 13% 7% 3	4466
February	1st to 10th	Day	61% 4 10% 14% 9% 1	1865
	11th to 20th	Day	59% 3 9% 20% 9% 1	1858
	21st to end	Day	57% 4 9% 20% 8% 1	1570
March	1st to 10th	Day	64% 3 7% 17% 8%	3120
	11th to 20th	Day	44% 4 10% 28% 14% 1	3468
	21st to end	Day	52% 6% 12% 23% 7% 1	3830
April	1st to 10th	Day	50% 5% 11% 21% 13% 1	2280
	11th to 20th	Day	48% 4 11% 22% 13% 3	2294
	21st to end	Day	50% 5% 11% 21% 11% 2	2470
May	1st to 10th	Day	53% 6% 12% 21% 8% 1	4120
	11th to 20th	Day	47% 5% 13% 24% 11%	4085
	21st to end	Day	42% 8% 13% 21% 15% 2	4489
June	1st to 10th	Day	39% 6% 11% 26% 16% 3	2582
	11th to 20th	Day	36% 6% 14% 23% 20% 2	2660
	21st to end	Day	39% 7% 14% 20% 16% 4	2660
July	1st to 10th	Day	44% 5% 11% 20% 17% 2	4371
	11th to 20th	Day	30% 6% 13% 29% 21% 1	4365
	21st to end	Day	43% 7% 14% 18% 15% 3	4334
August	1st to 10th	Day	32% 7% 15% 31% 14% 1	4091
	11th to 20th	Day	36% 6% 12% 31% 15% 1	4083
	21st to end	Day	29% 6% 14% 31% 17% 3	4180
September	1st to 10th	Day	36% 5% 11% 23% 19% 5%	2190
	11th to 20th	Day	34% 5% 10% 27% 22% 3	2090
	21st to end	Day	39% 3 9% 24% 22% 2	2090
October	1st to 10th	Day	25% 3 9% 30% 31% 2	3480
	11th to 20th	Day	31% 3 9% 29% 25% 2	3212
	21st to end	Day	40% 3 10% 24% 21% 2	3112
November	1st to 10th	Day	34% 5% 11% 29% 19% 3	1762
	11th to 20th	Day	51% 4 10% 20% 13% 3	1800
	21st to end	Day	54% 3 10% 21% 11% 1	1800
December	1st to 10th	Day	51% 2 10% 27% 10%	2930
	11th to 20th	Day	63% 4 9% 17% 6%	3309
	21st to end	Day	73% 3 8% 11% 5%	3982
January	1st to 10th	Night	69% 3 6% 14% 8%	6348
	11th to 20th	Night	71% 3 7% 10% 7% 2	6338
	21st to end	Night	60% 2 10% 19% 8% 1	6490
February	1st to 10th	Night	60% 4 10% 18% 8% 1	2421
	11th to 20th	Night	52% 5% 11% 19% 12% 1	2219
	21st to end	Night	57% 3 11% 16% 10% 2	1884
March	1st to 10th	Night	54% 4 7% 24% 11% 1	3733
	11th to 20th	Night	39% 5% 11% 27% 16% 2	3492
	21st to end	Night	46% 5% 10% 29% 9% 1	3817
April	1st to 10th	Night	46% 4 11% 25% 13% 2	1914
	11th to 20th	Night	43% 4 10% 20% 18% 5%	1833
	21st to end	Night	45% 5% 12% 21% 13% 3	1710
May	1st to 10th	Night	57% 5% 9% 21% 6% 2	2840
	11th to 20th	Night	44% 6% 14% 26% 9% 1	2813
	21st to end	Night	33% 7% 16% 26% 14% 4	3087
June	1st to 10th	Night	35% 6% 9% 26% 21% 2	1592
	11th to 20th	Night	31% 6% 16% 23% 20% 4	1520
	21st to end	Night	30% 8% 16% 24% 18% 4	1520
July	1st to 10th	Night	36% 6% 11% 25% 16% 6%	2490
	11th to 20th	Night	26% 5% 15% 32% 21% 2	2482
	21st to end	Night	37% 6% 14% 24% 14% 4	2976
August	1st to 10th	Night	35% 6% 14% 31% 12% 2	2814
	11th to 20th	Night	35% 5% 13% 29% 18%	2812
	21st to end	Night	26% 6% 14% 29% 22% 3	3471
September	1st to 10th	Night	32% 5% 12% 24% 19% 7%	1971
	11th to 20th	Night	28% 4 10% 27% 27% 4	2090
	21st to end	Night	36% 4 10% 24% 24% 2	2090
October	1st to 10th	Night	21% 3 7% 31% 36% 3	3480
	11th to 20th	Night	29% 3 10% 24% 33% 1	3705
	21st to end	Night	35% 3 7% 26% 25% 4	4431
November	1st to 10th	Night	38% 4 8% 24% 22% 3	2536
	11th to 20th	Night	45% 4 8% 23% 17% 3	2600
	21st to end	Night	56% 4 9% 21% 9% 1	2600
December	1st to 10th	Night	51% 3 11% 24% 10%	4250
	11th to 20th	Night	63% 4 9% 17% 8% 1	4870
	21st to end	Night	72% 4 8% 13% 3	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	24% 17% 36% 18% 5% 1	300
	11th to 20th	Day	24% 20% 37% 15% 4	300
	21st to end	Day	30% 17% 32% 17% 4	330
February	1st to 10th	Day	27% 16% 35% 16% 5%	285
	11th to 20th	Day	24% 18% 36% 18% 4	270
	21st to end	Day	24% 16% 42% 15% 3	225
March	1st to 10th	Day	24% 19% 34% 20% 3	270
	11th to 20th	Day	23% 15% 35% 20% 6% 1	448
	21st to end	Day	27% 13% 35% 18% 7% 1	506
April	1st to 10th	Day	19% 16% 32% 21% 9% 3	460
	11th to 20th	Day	20% 14% 30% 21% 11% 4	452
	21st to end	Day	22% 12% 35% 20% 9% 2	460
May	1st to 10th	Day	24% 10% 29% 25% 8% 5%	463
	11th to 20th	Day	22% 7% 27% 23% 12% 9%	487
	21st to end	Day	10% 5% 26% 28% 17% 13%	529
June	1st to 10th	Day	12% 6% 23% 33% 20% 6%	602
	11th to 20th	Day	11% 4 25% 31% 22% 7%	680
	21st to end	Day	9% 6% 27% 30% 19% 9%	680
July	1st to 10th	Day	12% 3 17% 26% 24% 18%	671
	11th to 20th	Day	7% 3 21% 29% 25% 14%	668
	21st to end	Day	9% 4 15% 29% 27% 15%	542
August	1st to 10th	Day	8% 4 13% 27% 30% 17%	486
	11th to 20th	Day	11% 5% 16% 30% 26% 13%	479
	21st to end	Day	9% 4 10% 27% 35% 15%	539
September	1st to 10th	Day	11% 4 15% 27% 30% 13%	490
	11th to 20th	Day	10% 3 14% 25% 32% 16%	490
	21st to end	Day	18% 10% 19% 24% 21% 9%	490
October	1st to 10th	Day	11% 6% 25% 29% 19% 10%	490
	11th to 20th	Day	15% 14% 29% 25% 14% 3	490
	21st to end	Day	27% 12% 35% 21% 5%	349
November	1st to 10th	Day	13% 14% 34% 24% 12% 3	300
	11th to 20th	Day	23% 19% 28% 18% 10% 3	300
	21st to end	Day	27% 11% 37% 20% 5%	300
December	1st to 10th	Day	19% 22% 36% 17% 6% 1	300
	11th to 20th	Day	25% 14% 37% 17% 6% 1	300
	21st to end	Day	28% 18% 33% 16% 5%	330
January	1st to 10th	Night	22% 16% 36% 22% 5%	1000
	11th to 20th	Night	25% 15% 37% 20% 3	991
	21st to end	Night	22% 13% 40% 21% 4	880
February	1st to 10th	Night	26% 12% 36% 24% 2	781
	11th to 20th	Night	20% 16% 37% 25% 3	743
	21st to end	Night	26% 11% 37% 22% 4	628
March	1st to 10th	Night	22% 12% 33% 26% 6% 1	760
	11th to 20th	Night	18% 13% 36% 26% 7% 1	760
	21st to end	Night	24% 11% 31% 27% 6% 1	836
April	1st to 10th	Night	18% 11% 36% 27% 8% 1	584
	11th to 20th	Night	20% 9% 31% 28% 9% 2	563
	21st to end	Night	20% 8% 39% 21% 11% 1	570
May	1st to 10th	Night	23% 6% 30% 30% 11% 1	570
	11th to 20th	Night	20% 5% 24% 30% 18% 2	561
	21st to end	Night	11% 3 23% 35% 25% 3	617
June	1st to 10th	Night	11% 3 22% 41% 23% 1	570
	11th to 20th	Night	10% 3 20% 38% 27% 2	570
	21st to end	Night	8% 2 21% 41% 24% 3	570
July	1st to 10th	Night	11% 3 14% 33% 32% 8%	555
	11th to 20th	Night	8% 2 14% 38% 32% 6%	552
	21st to end	Night	9% 3 11% 40% 34% 3	624
August	1st to 10th	Night	8% 2 11% 38% 36% 5%	567
	11th to 20th	Night	7% 2 11% 43% 30% 6%	564
	21st to end	Night	6% 3 12% 35% 38% 7%	627
September	1st to 10th	Night	12% 3 13% 35% 31% 6%	641
	11th to 20th	Night	9% 4 12% 34% 36% 6%	760
	21st to end	Night	16% 4 21% 32% 23% 3	760
October	1st to 10th	Night	11% 6% 24% 32% 22% 5%	760
	11th to 20th	Night	18% 10% 28% 29% 14% 2	760
	21st to end	Night	22% 10% 34% 25% 9%	836
November	1st to 10th	Night	14% 10% 33% 28% 14% 1	780
	11th to 20th	Night	20% 16% 31% 24% 9% 1	800
	21st to end	Night	23% 14% 30% 27% 6% 1	800
December	1st to 10th	Night	24% 12% 37% 22% 5% 1	800
	11th to 20th	Night	26% 10% 33% 25% 5% 1	820
	21st to end	Night	29% 14% 33% 20% 4	1100

Page generated at 2025-02-03 03:05:54. Version ac07

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