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 2024-12-09.

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	21% 11% 4 8% 5% 5% 5% 4 5% 7% 25%	101874
	Night	23% 12% 4 8% 5% 5% 4 4 5% 6% 25%	98032
Transparency	Day	57% 7% 12% 16% 7% 1	105353
	Night	58% 6% 13% 17% 7%	102652
Seeing	Day	27% 12% 28% 23% 9% 2	17783
	Night	28% 10% 28% 25% 8% 1	25157

By Month

Percentage Cloud Cover NE (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	14% 11% 5% 14% 7% 6% 6% 5% 6% 7% 19%	2526
	11th to 20th	Day	14% 12% 4 11% 7% 7% 6% 4 5% 6% 23%	2530
	21st to end	Day	15% 11% 6% 11% 7% 6% 6% 5% 5% 7% 21%	2823
February	1st to 10th	Day	21% 9% 3 13% 6% 6% 5% 6% 7% 8% 16%	1710
	11th to 20th	Day	17% 11% 3 9% 7% 7% 7% 5% 7% 8% 20%	1686
	21st to end	Day	12% 11% 4 9% 7% 6% 5% 4 6% 6% 29%	1570
March	1st to 10th	Day	24% 10% 3 6% 5% 5% 4 3 5% 5% 29%	3114
	11th to 20th	Day	15% 14% 5% 9% 6% 7% 6% 4 6% 7% 22%	3416
	21st to end	Day	29% 12% 5% 8% 5% 5% 5% 3 4 5% 18%	4066
April	1st to 10th	Day	23% 11% 3 8% 5% 4 5% 4 4 7% 26%	2280
	11th to 20th	Day	24% 11% 4 7% 3 4 3 3 4 6% 31%	2254
	21st to end	Day	25% 12% 3 5% 5% 4 3 3 4 6% 30%	2422
May	1st to 10th	Day	27% 15% 4 7% 4 4 4 3 5% 5% 23%	4425
	11th to 20th	Day	24% 14% 3 8% 5% 4 4 3 4 6% 26%	4398
	21st to end	Day	23% 11% 4 7% 6% 4 4 4 6% 7% 24%	4836
June	1st to 10th	Day	31% 10% 4 8% 4 5% 4 3 5% 6% 19%	2660
	11th to 20th	Day	22% 11% 3 6% 5% 4 5% 4 5% 7% 27%	2660
	21st to end	Day	33% 15% 4 6% 5% 4 4 3 4 5% 17%	2660
July	1st to 10th	Day	26% 13% 4 11% 5% 4 4 3 4 5% 21%	4440
	11th to 20th	Day	20% 14% 4 8% 5% 6% 6% 4 5% 6% 21%	4440
	21st to end	Day	19% 10% 3 8% 5% 5% 4 4 5% 7% 31%	4815
August	1st to 10th	Day	21% 12% 3 9% 5% 4 5% 4 6% 7% 24%	4424
	11th to 20th	Day	19% 8% 3 7% 5% 5% 5% 4 7% 9% 28%	3972
	21st to end	Day	13% 8% 3 6% 4 4 4 4 5% 8% 41%	4180
September	1st to 10th	Day	19% 8% 3 6% 4 5% 4 4 6% 7% 35%	2280
	11th to 20th	Day	19% 8% 2 6% 5% 4 5% 4 5% 8% 34%	2260
	21st to end	Day	22% 8% 3 6% 4 3 4 3 6% 7% 35%	2062
October	1st to 10th	Day	18% 8% 2 8% 4 4 5% 5% 6% 8% 32%	1900
	11th to 20th	Day	20% 8% 3 8% 5% 5% 5% 4 6% 9% 27%	1900
	21st to end	Day	21% 12% 3 9% 5% 6% 4 3 5% 7% 24%	1905
November	1st to 10th	Day	23% 10% 4 6% 5% 5% 5% 5% 4 8% 26%	1760
	11th to 20th	Day	23% 13% 3 9% 6% 6% 5% 4 5% 6% 19%	1627
	21st to end	Day	18% 11% 5% 9% 7% 6% 6% 5% 7% 7% 19%	1600
December	1st to 10th	Day	22% 13% 4 11% 7% 5% 6% 4 6% 7% 15%	1584
	11th to 20th	Day	27% 15% 5% 12% 6% 5% 5% 4 6% 6% 10%	1906
	21st to end	Day	21% 11% 5% 11% 8% 6% 6% 4 5% 5% 17%	2783
January	1st to 10th	Night	14% 12% 5% 11% 6% 5% 6% 4 6% 8% 21%	4429
	11th to 20th	Night	21% 11% 4 12% 7% 5% 5% 4 6% 6% 17%	4440
	21st to end	Night	15% 10% 4 11% 7% 6% 6% 5% 7% 9% 20%	4839
February	1st to 10th	Night	21% 10% 4 11% 6% 6% 6% 6% 6% 6% 17%	2470
	11th to 20th	Night	17% 12% 4 10% 7% 6% 6% 5% 6% 7% 19%	2379
	21st to end	Night	12% 12% 5% 11% 7% 5% 4 4 6% 6% 29%	1884
March	1st to 10th	Night	21% 13% 4 8% 5% 5% 4 3 4 6% 27%	3726
	11th to 20th	Night	21% 16% 5% 8% 5% 5% 4 4 5% 6% 23%	3527
	21st to end	Night	30% 11% 6% 10% 5% 5% 4 2 3 3 20%	3566
April	1st to 10th	Night	25% 11% 3 7% 4 4 4 4 5% 6% 27%	1900
	11th to 20th	Night	22% 10% 4 8% 5% 3 3 3 5% 6% 32%	1876
	21st to end	Night	26% 12% 3 7% 4 3 3 3 4 5% 31%	1751
May	1st to 10th	Night	31% 12% 3 6% 4 3 3 3 4 5% 26%	2525
	11th to 20th	Night	23% 13% 3 6% 3 3 3 3 4 6% 32%	2506
	21st to end	Night	21% 17% 4 8% 4 4 3 3 4 7% 25%	2749
June	1st to 10th	Night	34% 13% 4 8% 4 3 3 2 4 5% 19%	1520
	11th to 20th	Night	26% 12% 2 6% 4 3 3 3 5% 5% 31%	1520
	21st to end	Night	36% 17% 3 7% 3 3 3 2 4 5% 18%	1520
July	1st to 10th	Night	32% 16% 5% 8% 4 3 3 2 4 5% 18%	2530
	11th to 20th	Night	29% 15% 4 7% 4 4 4 3 4 6% 21%	2530
	21st to end	Night	25% 13% 3 7% 4 3 4 3 4 5% 29%	2750
August	1st to 10th	Night	24% 13% 4 7% 4 4 4 3 5% 6% 26%	2516
	11th to 20th	Night	20% 10% 3 8% 5% 5% 4 4 7% 8% 27%	2851
	21st to end	Night	17% 8% 2 4 3 3 4 4 5% 8% 42%	3476
September	1st to 10th	Night	18% 6% 4 5% 4 4 4 3 5% 7% 38%	1900
	11th to 20th	Night	22% 8% 2 5% 4 4 3 4 5% 7% 38%	1919
	21st to end	Night	21% 10% 3 6% 3 5% 3 3 4 6% 36%	2116
October	1st to 10th	Night	19% 7% 2 6% 4 4 5% 3 6% 7% 38%	2280
	11th to 20th	Night	21% 8% 2 7% 4 4 4 3 5% 7% 35%	2280
	21st to end	Night	24% 10% 3 8% 4 5% 4 3 5% 6% 29%	2693
November	1st to 10th	Night	21% 11% 3 7% 4 5% 4 4 6% 8% 28%	2538
	11th to 20th	Night	25% 13% 3 7% 5% 6% 4 4 5% 6% 22%	2770
	21st to end	Night	22% 11% 4 8% 6% 6% 5% 5% 7% 7% 20%	2800
December	1st to 10th	Night	23% 12% 4 8% 6% 5% 5% 5% 6% 6% 18%	2779
	11th to 20th	Night	29% 11% 4 12% 6% 6% 5% 4 5% 5% 15%	3293
	21st to end	Night	27% 12% 4 9% 6% 5% 5% 3 4 5% 19%	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% 7% 14% 15% 2	2527
	11th to 20th	Day	59% 8% 11% 16% 5%	2530
	21st to end	Day	62% 5% 10% 14% 7% 1	2823
February	1st to 10th	Day	63% 6% 12% 13% 6%	1710
	11th to 20th	Day	58% 8% 13% 14% 6% 1	1694
	21st to end	Day	53% 7% 11% 16% 11% 2	1570
March	1st to 10th	Day	57% 6% 8% 19% 10% 1	3118
	11th to 20th	Day	61% 11% 6% 15% 6% 1	3416
	21st to end	Day	67% 7% 8% 10% 6% 1	4066
April	1st to 10th	Day	58% 7% 8% 15% 9% 3	2280
	11th to 20th	Day	54% 6% 8% 19% 12% 2	2254
	21st to end	Day	56% 7% 10% 15% 12% 1	2422
May	1st to 10th	Day	65% 5% 10% 13% 6% 1	4440
	11th to 20th	Day	58% 7% 13% 16% 6%	4402
	21st to end	Day	56% 9% 12% 17% 6%	4836
June	1st to 10th	Day	65% 6% 9% 15% 5%	2660
	11th to 20th	Day	54% 7% 12% 18% 9% 1	2660
	21st to end	Day	69% 6% 9% 11% 6%	2660
July	1st to 10th	Day	65% 6% 10% 10% 8%	4370
	11th to 20th	Day	59% 9% 14% 12% 6%	4364
	21st to end	Day	50% 7% 17% 19% 7%	4662
August	1st to 10th	Day	58% 9% 13% 16% 5%	4410
	11th to 20th	Day	49% 8% 17% 21% 4	4011
	21st to end	Day	41% 6% 14% 28% 11%	4180
September	1st to 10th	Day	46% 8% 13% 22% 10% 1	2280
	11th to 20th	Day	47% 8% 12% 23% 9% 1	2260
	21st to end	Day	47% 6% 10% 26% 10% 1	2062
October	1st to 10th	Day	53% 7% 13% 19% 7%	3160
	11th to 20th	Day	41% 8% 13% 26% 11%	3140
	21st to end	Day	52% 6% 15% 19% 8%	3127
November	1st to 10th	Day	55% 8% 13% 18% 6%	1760
	11th to 20th	Day	64% 6% 12% 13% 4	1627
	21st to end	Day	60% 9% 13% 13% 5%	1600
December	1st to 10th	Day	66% 6% 13% 11% 3	1584
	11th to 20th	Day	74% 5% 8% 10% 3	1905
	21st to end	Day	67% 7% 15% 9% 2 1	2783
January	1st to 10th	Night	58% 7% 17% 16% 2	4429
	11th to 20th	Night	65% 8% 11% 12% 4	4440
	21st to end	Night	57% 7% 14% 17% 5%	4839
February	1st to 10th	Night	64% 5% 13% 11% 6% 1	2470
	11th to 20th	Night	63% 4 13% 14% 5% 1	2382
	21st to end	Night	55% 5% 11% 15% 11% 1	1884
March	1st to 10th	Night	59% 4 7% 19% 10%	3735
	11th to 20th	Night	61% 7% 10% 15% 6% 1	3528
	21st to end	Night	69% 4 6% 14% 5% 2	3566
April	1st to 10th	Night	56% 6% 10% 17% 9% 1	1900
	11th to 20th	Night	53% 5% 9% 19% 12% 1	1876
	21st to end	Night	56% 4 8% 19% 11% 1	1751
May	1st to 10th	Night	60% 5% 14% 14% 6% 1	2530
	11th to 20th	Night	54% 5% 11% 22% 8% 1	2507
	21st to end	Night	60% 6% 12% 17% 6%	2750
June	1st to 10th	Night	68% 4 8% 14% 6% 1	1520
	11th to 20th	Night	55% 5% 10% 20% 10% 1	1520
	21st to end	Night	69% 4 8% 13% 6% 1	1520
July	1st to 10th	Night	70% 4 8% 11% 7%	2491
	11th to 20th	Night	64% 5% 9% 13% 9%	2482
	21st to end	Night	56% 5% 13% 20% 6% 1	2663
August	1st to 10th	Night	59% 4 14% 20% 3	2505
	11th to 20th	Night	52% 8% 19% 19% 3	2878
	21st to end	Night	39% 6% 17% 31% 7%	3475
September	1st to 10th	Night	44% 7% 13% 23% 12%	1900
	11th to 20th	Night	46% 5% 14% 23% 11% 1	1919
	21st to end	Night	50% 4 10% 24% 11% 1	2116
October	1st to 10th	Night	48% 8% 13% 20% 11%	3800
	11th to 20th	Night	39% 6% 14% 31% 9%	3779
	21st to end	Night	48% 6% 18% 20% 9%	4431
November	1st to 10th	Night	53% 8% 15% 17% 7%	2538
	11th to 20th	Night	61% 6% 14% 13% 6%	2770
	21st to end	Night	61% 7% 14% 13% 4	2800
December	1st to 10th	Night	63% 7% 13% 14% 3	2779
	11th to 20th	Night	70% 4 12% 9% 4	3295
	21st to end	Night	69% 4 14% 11% 2	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	29% 20% 32% 15% 4 1	370
	11th to 20th	Day	29% 16% 33% 15% 7% 1	370
	21st to end	Day	23% 14% 37% 21% 4	407
February	1st to 10th	Day	29% 19% 30% 19% 2	370
	11th to 20th	Day	25% 24% 30% 17% 4 1	366
	21st to end	Day	18% 19% 38% 20% 6%	307
March	1st to 10th	Day	23% 19% 35% 17% 6%	370
	11th to 20th	Day	18% 20% 32% 21% 8% 1	442
	21st to end	Day	28% 21% 29% 16% 5% 2	506
April	1st to 10th	Day	29% 21% 32% 12% 5%	460
	11th to 20th	Day	29% 15% 31% 18% 6%	452
	21st to end	Day	30% 12% 29% 23% 5% 1	545
May	1st to 10th	Day	32% 12% 31% 17% 6% 2	653
	11th to 20th	Day	25% 9% 27% 26% 10% 3	674
	21st to end	Day	28% 8% 32% 24% 7% 1	735
June	1st to 10th	Day	36% 9% 22% 24% 9% 1	680
	11th to 20th	Day	29% 6% 27% 28% 9% 2	680
	21st to end	Day	43% 6% 18% 23% 9% 2	680
July	1st to 10th	Day	29% 5% 22% 29% 13% 2	670
	11th to 20th	Day	29% 4 23% 29% 14% 1	668
	21st to end	Day	31% 6% 20% 28% 13% 2	740
August	1st to 10th	Day	22% 5% 23% 31% 17% 3	675
	11th to 20th	Day	27% 7% 20% 28% 15% 3	490
	21st to end	Day	22% 6% 24% 30% 14% 3	539
September	1st to 10th	Day	18% 9% 29% 31% 10% 3	490
	11th to 20th	Day	23% 11% 25% 24% 14% 3	479
	21st to end	Day	28% 7% 23% 26% 13% 3	390
October	1st to 10th	Day	21% 9% 29% 26% 12% 3	390
	11th to 20th	Day	24% 10% 29% 23% 12% 3	390
	21st to end	Day	27% 13% 32% 18% 10%	429
November	1st to 10th	Day	24% 15% 31% 21% 8% 2	395
	11th to 20th	Day	31% 18% 29% 18% 4 1	400
	21st to end	Day	28% 19% 29% 19% 4 1	400
December	1st to 10th	Day	26% 15% 32% 21% 5%	394
	11th to 20th	Day	29% 22% 33% 13% 3	370
	21st to end	Day	21% 20% 37% 14% 7% 1	407
January	1st to 10th	Night	27% 16% 32% 20% 4	850
	11th to 20th	Night	28% 16% 36% 17% 3	850
	21st to end	Night	23% 14% 36% 23% 5%	920
February	1st to 10th	Night	27% 12% 32% 25% 3	760
	11th to 20th	Night	24% 19% 36% 18% 3 1	743
	21st to end	Night	18% 14% 34% 26% 8%	628
March	1st to 10th	Night	25% 12% 35% 23% 5%	760
	11th to 20th	Night	23% 12% 30% 25% 9% 1	760
	21st to end	Night	28% 11% 28% 26% 6% 1	689
April	1st to 10th	Night	30% 10% 30% 25% 5%	570
	11th to 20th	Night	26% 7% 31% 26% 9%	564
	21st to end	Night	33% 8% 26% 23% 9% 1	570
May	1st to 10th	Night	36% 5% 27% 21% 8% 3	570
	11th to 20th	Night	30% 5% 26% 27% 11% 1	562
	21st to end	Night	28% 5% 30% 28% 8% 1	616
June	1st to 10th	Night	41% 5% 20% 25% 8%	570
	11th to 20th	Night	32% 5% 19% 31% 11% 1	570
	21st to end	Night	42% 5% 16% 29% 7% 1	570
July	1st to 10th	Night	32% 3 22% 30% 12% 1	556
	11th to 20th	Night	33% 5% 16% 34% 13%	552
	21st to end	Night	38% 4 16% 30% 12% 1	623
August	1st to 10th	Night	29% 3 16% 35% 15% 1	568
	11th to 20th	Night	26% 4 16% 36% 16% 3	562
	21st to end	Night	24% 4 17% 33% 21% 1	627
September	1st to 10th	Night	21% 4 21% 37% 14% 3	570
	11th to 20th	Night	26% 5% 25% 28% 14% 3	570
	21st to end	Night	27% 6% 28% 27% 11% 2	596
October	1st to 10th	Night	22% 7% 27% 32% 11% 1	760
	11th to 20th	Night	24% 7% 30% 27% 11% 2	760
	21st to end	Night	27% 11% 31% 24% 7% 1	933
November	1st to 10th	Night	27% 11% 31% 24% 7% 1	880
	11th to 20th	Night	31% 15% 27% 20% 6% 1	900
	21st to end	Night	30% 14% 33% 18% 4 1	900
December	1st to 10th	Night	30% 12% 33% 19% 5%	893
	11th to 20th	Night	31% 15% 34% 16% 3	850
	21st to end	Night	27% 16% 33% 19% 4 1	935

Page generated at 2024-12-06 04:54:46. Version ac07

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