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 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	15% 10% 4 8% 5% 4 5% 4 5% 7% 34%	95519
	Night	15% 10% 4 8% 5% 4 4 3 5% 7% 36%	93529
Transparency	Day	48% 5% 11% 21% 13% 2	95283
	Night	48% 5% 10% 22% 13% 2	93371
Seeing	Day	17% 9% 26% 24% 16% 7%	15229
	Night	18% 9% 28% 29% 15% 2	24999

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% 16% 9% 9% 5% 4 5% 3 5% 6% 22%	2527
	11th to 20th	Day	16% 15% 7% 13% 5% 8% 7% 4 4 4 17%	2534
	21st to end	Day	27% 19% 9% 11% 4 3 3 2 3 4 15%	3124
February	1st to 10th	Day	17% 17% 6% 10% 6% 4 4 4 3 4 25%	1819
	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 7% 5% 6% 5% 5% 8% 9% 43%	2457
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 6% 7% 9% 39%	2433
	21st to end	Day	7% 6% 2 6% 4 5% 5% 4 6% 9% 46%	2486
September	1st to 10th	Day	12% 6% 2 6% 4 5% 4 3 5% 7% 46%	2075
	11th to 20th	Day	10% 5% 2 6% 5% 4 4 3 7% 8% 46%	1980
	21st to end	Day	14% 6% 2 6% 4 3 4 3 4 7% 48%	1980
October	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 3 5% 6% 46%	1980
	11th to 20th	Day	15% 7% 2 5% 3 4 5% 4 5% 7% 44%	1844
	21st to end	Day	20% 10% 2 9% 5% 4 4 3 5% 6% 33%	1800
November	1st to 10th	Day	10% 7% 2 5% 4 4 3 3 5% 6% 51%	1672
	11th to 20th	Day	15% 12% 4 8% 5% 4 4 3 5% 6% 34%	1710
	21st to end	Day	19% 12% 5% 8% 4 3 3 3 4 6% 32%	1710
December	1st to 10th	Day	19% 15% 7% 12% 5% 3 4 3 5% 4 23%	1710
	11th to 20th	Day	16% 15% 7% 11% 4 5% 4 3 4 5% 25%	2118
	21st to end	Day	20% 23% 9% 11% 5% 4 3 3 4 5% 14%	2783
January	1st to 10th	Night	16% 17% 8% 12% 5% 5% 4 3 4 4 21%	4428
	11th to 20th	Night	14% 18% 7% 15% 6% 6% 5% 3 4 5% 18%	4432
	21st to end	Night	25% 19% 7% 9% 4 4 3 2 3 4 19%	4532
February	1st to 10th	Night	20% 14% 5% 8% 6% 4 3 3 4 5% 27%	2356
	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	7% 3 2 7% 4 4 5% 4 7% 10% 47%	1701
	11th to 20th	Night	6% 5% 2 6% 5% 4 4 4 6% 9% 49%	1688
	21st to end	Night	5% 4 2 6% 4 4 5% 4 6% 9% 52%	2075
September	1st to 10th	Night	12% 6% 1 5% 4 4 4 3 6% 7% 48%	1867
	11th to 20th	Night	9% 5% 2 5% 3 3 3 4 5% 8% 54%	1980
	21st to end	Night	13% 4 2 5% 3 4 4 3 4 6% 51%	1980
October	1st to 10th	Night	9% 5% 2 6% 4 4 3 3 5% 7% 52%	1980
	11th to 20th	Night	15% 8% 3 7% 4 3 3 3 5% 6% 42%	2114
	21st to end	Night	19% 9% 2 6% 4 3 4 3 4 6% 39%	2551
November	1st to 10th	Night	12% 8% 3 5% 4 3 4 4 5% 7% 46%	2406
	11th to 20th	Night	16% 9% 4 6% 5% 3 4 3 6% 7% 37%	2470
	21st to end	Night	18% 13% 4 7% 6% 4 4 3 5% 6% 29%	2470
December	1st to 10th	Night	19% 14% 4 9% 5% 4 4 4 5% 6% 26%	2470
	11th to 20th	Night	19% 13% 6% 9% 4 4 4 4 4 6% 27%	3074
	21st to end	Night	22% 19% 7% 11% 5% 4 4 3 4 4 16%	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	62% 4 7% 17% 9%	2528
	11th to 20th	Day	70% 4 9% 12% 4	2534
	21st to end	Day	75% 3 7% 12% 3 1	3124
February	1st to 10th	Day	61% 4 10% 14% 10% 1	1819
	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	35% 7% 14% 28% 14% 2	2444
	11th to 20th	Day	38% 6% 13% 26% 15% 1	2433
	21st to end	Day	33% 7% 13% 26% 17% 6%	2486
September	1st to 10th	Day	37% 5% 12% 23% 18% 5%	2075
	11th to 20th	Day	35% 5% 10% 27% 21% 2	1980
	21st to end	Day	37% 3 10% 25% 23% 2	1980
October	1st to 10th	Day	38% 5% 10% 24% 21% 2	1980
	11th to 20th	Day	39% 4 9% 27% 19% 3	1844
	21st to end	Day	51% 3 10% 21% 12% 2	1800
November	1st to 10th	Day	33% 5% 11% 29% 19% 3	1672
	11th to 20th	Day	50% 4 10% 20% 13% 3	1710
	21st to end	Day	54% 3 10% 21% 11% 1	1710
December	1st to 10th	Day	64% 3 10% 16% 6% 1	1710
	11th to 20th	Day	60% 4 8% 19% 8%	2115
	21st to end	Day	74% 3 7% 10% 6%	2783
January	1st to 10th	Night	65% 4 8% 14% 8%	4428
	11th to 20th	Night	69% 4 8% 14% 5%	4432
	21st to end	Night	69% 3 7% 14% 6%	4532
February	1st to 10th	Night	60% 4 10% 18% 8% 1	2356
	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	31% 6% 16% 30% 15% 2	1690
	11th to 20th	Night	31% 6% 15% 28% 19% 1	1688
	21st to end	Night	27% 7% 14% 25% 22% 5%	2075
September	1st to 10th	Night	33% 5% 13% 24% 17% 7%	1867
	11th to 20th	Night	29% 4 10% 28% 26% 3	1980
	21st to end	Night	34% 4 10% 25% 25% 3	1980
October	1st to 10th	Night	31% 5% 10% 27% 23% 3	1980
	11th to 20th	Night	42% 4 8% 25% 20% 2	2114
	21st to end	Night	47% 3 8% 24% 15% 2	2551
November	1st to 10th	Night	38% 4 8% 24% 22% 3	2406
	11th to 20th	Night	45% 4 8% 23% 17% 3	2470
	21st to end	Night	54% 4 10% 21% 10% 1	2470
December	1st to 10th	Night	58% 4 10% 19% 9% 1	2470
	11th to 20th	Night	57% 4 8% 21% 9% 1	3076
	21st to end	Night	71% 4 8% 12% 5%	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	24% 15% 37% 18% 5% 1	270
	11th to 20th	Day	26% 17% 37% 15% 4	270
	21st to end	Day	33% 15% 31% 17% 4	297
February	1st to 10th	Day	27% 15% 34% 17% 6%	270
	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%	532
September	1st to 10th	Day	12% 4 16% 25% 30% 14%	450
	11th to 20th	Day	11% 3 14% 24% 32% 16%	450
	21st to end	Day	16% 9% 19% 24% 23% 10%	450
October	1st to 10th	Day	12% 6% 26% 28% 19% 10%	450
	11th to 20th	Day	16% 14% 29% 26% 13% 1	450
	21st to end	Day	29% 12% 35% 21% 4	315
November	1st to 10th	Day	14% 13% 33% 24% 13% 4	270
	11th to 20th	Day	23% 19% 26% 18% 11% 3	270
	21st to end	Day	26% 11% 36% 21% 6%	270
December	1st to 10th	Day	19% 21% 34% 19% 6% 1	270
	11th to 20th	Day	24% 13% 37% 19% 6% 1	270
	21st to end	Day	27% 19% 33% 16% 5%	297
January	1st to 10th	Night	22% 16% 36% 22% 5%	950
	11th to 20th	Night	25% 14% 37% 20% 4	942
	21st to end	Night	23% 12% 39% 22% 4	836
February	1st to 10th	Night	26% 12% 36% 24% 2	760
	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	5% 3 12% 35% 38% 7%	624
September	1st to 10th	Night	13% 3 12% 34% 31% 6%	607
	11th to 20th	Night	10% 4 12% 33% 35% 6%	720
	21st to end	Night	14% 4 22% 33% 24% 4	720
October	1st to 10th	Night	12% 6% 25% 31% 21% 5%	720
	11th to 20th	Night	19% 10% 28% 29% 13% 1	720
	21st to end	Night	23% 10% 33% 25% 8%	792
November	1st to 10th	Night	14% 10% 33% 27% 15% 1	740
	11th to 20th	Night	19% 16% 30% 24% 9% 1	760
	21st to end	Night	23% 13% 30% 28% 6% 1	760
December	1st to 10th	Night	24% 11% 36% 23% 5% 1	760
	11th to 20th	Night	26% 9% 33% 25% 5% 1	779
	21st to end	Night	28% 13% 34% 21% 4	1045

Page generated at 2024-08-27 09:49:38. Version ac07

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