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 2024-11-04.

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	13% 6% 2 6% 4 4 4 4 6% 8% 42%	101029
	Night	15% 6% 2 6% 4 4 4 3 5% 7% 43%	97946
Transparency	Day	38% 6% 12% 23% 17% 4	104672
	Night	38% 6% 11% 22% 18% 5%	102442
Seeing	Day	18% 10% 27% 25% 15% 5%	15137
	Night	17% 10% 28% 30% 13% 1	24779

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	17% 5% 1 4 3 3 3 3 4 5% 52%	2772
	11th to 20th	Day	14% 8% 2 5% 4 4 4 4 6% 5% 45%	2840
	21st to end	Day	16% 10% 3 6% 5% 4 4 3 5% 5% 39%	3124
February	1st to 10th	Day	13% 7% 3 8% 4 5% 4 4 6% 7% 40%	1710
	11th to 20th	Day	21% 6% 2 3 4 2 4 3 6% 6% 43%	1729
	21st to end	Day	18% 7% 3 7% 6% 4 5% 3 5% 6% 37%	1572
March	1st to 10th	Day	20% 10% 3 7% 4 3 3 3 5% 6% 36%	3435
	11th to 20th	Day	10% 4 2 5% 3 3 4 4 6% 6% 53%	3480
	21st to end	Day	21% 6% 2 6% 4 4 4 3 5% 6% 40%	3841
April	1st to 10th	Day	11% 5% 2 5% 4 3 4 3 5% 7% 52%	2280
	11th to 20th	Day	11% 6% 2 5% 5% 3 4 3 5% 7% 49%	2254
	21st to end	Day	15% 6% 2 6% 4 4 4 4 5% 7% 43%	2280
May	1st to 10th	Day	15% 8% 2 7% 5% 5% 5% 5% 7% 8% 32%	3952
	11th to 20th	Day	20% 7% 2 6% 5% 4 4 4 7% 9% 32%	4107
	21st to end	Day	9% 4 2 5% 4 4 5% 4 7% 10% 46%	4823
June	1st to 10th	Day	11% 4 2 5% 4 5% 5% 4 7% 10% 42%	2660
	11th to 20th	Day	10% 4 2 6% 5% 4 5% 6% 7% 10% 42%	2660
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 5% 8% 11% 42%	2660
July	1st to 10th	Day	5% 5% 2 6% 5% 5% 6% 6% 8% 13% 39%	4386
	11th to 20th	Day	12% 5% 2 7% 5% 6% 5% 4 8% 12% 35%	4120
	21st to end	Day	10% 6% 3 7% 6% 6% 6% 5% 7% 9% 34%	4466
August	1st to 10th	Day	15% 8% 3 8% 5% 5% 6% 5% 7% 11% 28%	4104
	11th to 20th	Day	9% 6% 2 8% 5% 5% 5% 5% 7% 10% 38%	3835
	21st to end	Day	8% 4 2 5% 3 3 4 4 7% 11% 49%	4180
September	1st to 10th	Day	13% 5% 2 5% 3 4 4 4 6% 7% 45%	2280
	11th to 20th	Day	11% 8% 3 6% 5% 3 3 3 5% 8% 46%	2280
	21st to end	Day	20% 7% 2 8% 4 4 4 3 4 7% 37%	1986
October	1st to 10th	Day	16% 6% 2 5% 4 4 4 3 3 6% 48%	1900
	11th to 20th	Day	15% 5% 2 4 2 3 3 3 5% 5% 53%	1900
	21st to end	Day	12% 5% 1 5% 3 3 3 2 4 6% 54%	2090
November	1st to 10th	Day	13% 5% 1 5% 3 3 4 3 4 5% 54%	1867
	11th to 20th	Day	13% 7% 2 4 3 4 3 3 4 6% 50%	1710
	21st to end	Day	14% 5% 2 5% 3 3 4 3 4 5% 52%	1544
December	1st to 10th	Day	17% 7% 2 5% 4 3 4 4 6% 8% 42%	1520
	11th to 20th	Day	16% 6% 2 5% 2 3 3 3 4 5% 52%	1910
	21st to end	Day	17% 7% 2 7% 4 4 4 3 5% 7% 41%	2772
January	1st to 10th	Night	15% 7% 2 6% 3 3 4 3 5% 6% 47%	4169
	11th to 20th	Night	16% 8% 2 6% 3 3 3 3 4 5% 46%	4120
	21st to end	Night	21% 9% 2 6% 3 3 3 3 4 4 44%	4532
February	1st to 10th	Night	16% 6% 3 6% 4 3 4 4 5% 6% 43%	2470
	11th to 20th	Night	19% 7% 2 6% 4 3 4 3 4 6% 42%	2336
	21st to end	Night	17% 6% 2 6% 5% 3 3 2 4 6% 45%	1879
March	1st to 10th	Night	22% 7% 2 6% 4 4 3 4 5% 6% 37%	3418
	11th to 20th	Night	15% 5% 1 5% 3 3 3 3 5% 6% 51%	3480
	21st to end	Night	16% 7% 2 5% 3 3 3 2 4 5% 49%	3791
April	1st to 10th	Night	13% 7% 3 7% 5% 4 4 2 4 7% 45%	1900
	11th to 20th	Night	11% 6% 2 5% 3 3 4 3 5% 7% 50%	1875
	21st to end	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	1900
May	1st to 10th	Night	17% 8% 3 7% 4 4 4 4 6% 8% 35%	2970
	11th to 20th	Night	22% 8% 2 7% 4 4 4 3 5% 6% 34%	2785
	21st to end	Night	10% 4 2 6% 5% 5% 4 4 7% 9% 45%	2732
June	1st to 10th	Night	10% 6% 2 6% 5% 5% 6% 4 7% 8% 40%	1520
	11th to 20th	Night	9% 5% 3 6% 6% 5% 5% 4 7% 9% 41%	1520
	21st to end	Night	9% 5% 2 5% 4 4 5% 5% 8% 10% 43%	1520
July	1st to 10th	Night	8% 5% 2 6% 5% 6% 6% 5% 8% 10% 41%	2570
	11th to 20th	Night	10% 5% 3 6% 5% 5% 6% 5% 8% 11% 36%	2840
	21st to end	Night	11% 8% 3 10% 7% 6% 7% 5% 7% 7% 30%	3087
August	1st to 10th	Night	16% 7% 3 8% 5% 5% 4 4 7% 9% 31%	2825
	11th to 20th	Night	10% 6% 2 7% 5% 4 5% 6% 7% 9% 38%	2962
	21st to end	Night	9% 6% 2 5% 4 4 4 4 6% 8% 48%	3476
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	1900
	11th to 20th	Night	12% 5% 2 5% 5% 4 4 3 6% 6% 46%	1900
	21st to end	Night	21% 8% 3 6% 3 4 3 3 5% 6% 36%	2187
October	1st to 10th	Night	14% 5% 3 6% 3 4 4 3 4 6% 48%	2280
	11th to 20th	Night	15% 5% 2 5% 4 3 3 2 4 7% 49%	2280
	21st to end	Night	14% 5% 2 5% 3 3 4 3 4 6% 53%	2508
November	1st to 10th	Night	12% 7% 2 5% 4 4 4 3 4 5% 52%	2283
	11th to 20th	Night	14% 6% 3 5% 3 3 3 4 4 5% 50%	2470
	21st to end	Night	13% 5% 2 4 4 4 4 4 5% 7% 50%	2632
December	1st to 10th	Night	17% 7% 2 5% 4 4 4 3 5% 6% 42%	2660
	11th to 20th	Night	18% 6% 3 5% 3 3 3 3 4 6% 47%	3285
	21st to end	Night	16% 8% 2 6% 3 3 4 3 5% 7% 42%	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	35% 3 6% 34% 18% 4	2773
	11th to 20th	Day	39% 6% 8% 20% 23% 5%	2840
	21st to end	Day	47% 5% 9% 21% 16% 3	3124
February	1st to 10th	Day	42% 5% 11% 25% 15% 3	1710
	11th to 20th	Day	41% 4 8% 23% 20% 5%	1738
	21st to end	Day	48% 4 10% 16% 17% 5%	1572
March	1st to 10th	Day	48% 5% 8% 18% 15% 6%	3435
	11th to 20th	Day	29% 6% 9% 25% 24% 8%	3480
	21st to end	Day	44% 6% 11% 19% 17% 3	3841
April	1st to 10th	Day	32% 5% 12% 23% 20% 8%	2280
	11th to 20th	Day	35% 5% 11% 21% 22% 6%	2254
	21st to end	Day	40% 6% 11% 22% 15% 6%	2280
May	1st to 10th	Day	46% 9% 15% 19% 10% 2	3987
	11th to 20th	Day	46% 8% 12% 24% 9% 1	4111
	21st to end	Day	30% 8% 16% 25% 19% 2	4837
June	1st to 10th	Day	34% 8% 16% 26% 14% 2	2660
	11th to 20th	Day	34% 9% 16% 23% 16% 1	2660
	21st to end	Day	34% 8% 17% 24% 16% 2	2660
July	1st to 10th	Day	32% 12% 23% 17% 12% 5%	4317
	11th to 20th	Day	40% 8% 23% 21% 7% 1	4051
	21st to end	Day	43% 10% 13% 19% 15% 1	4324
August	1st to 10th	Day	47% 8% 17% 21% 6%	4091
	11th to 20th	Day	38% 9% 15% 24% 13%	3874
	21st to end	Day	29% 6% 16% 29% 19% 1	4180
September	1st to 10th	Day	36% 8% 14% 16% 21% 4	2280
	11th to 20th	Day	37% 6% 9% 24% 20% 3	2280
	21st to end	Day	48% 5% 9% 20% 15% 3	1986
October	1st to 10th	Day	36% 5% 7% 19% 27% 5%	3160
	11th to 20th	Day	24% 3 5% 20% 34% 13%	3140
	21st to end	Day	21% 3 8% 29% 26% 13%	3428
November	1st to 10th	Day	32% 4 9% 25% 25% 4	1867
	11th to 20th	Day	36% 4 9% 22% 22% 7%	1710
	21st to end	Day	34% 3 7% 26% 24% 5%	1544
December	1st to 10th	Day	39% 5% 11% 25% 15% 4	1520
	11th to 20th	Day	36% 4 7% 29% 17% 6%	1906
	21st to end	Day	42% 5% 8% 30% 14% 2	2772
January	1st to 10th	Night	38% 4 8% 24% 20% 5%	4169
	11th to 20th	Night	41% 4 7% 22% 22% 4	4120
	21st to end	Night	45% 4 6% 23% 17% 5%	4532
February	1st to 10th	Night	40% 4 11% 24% 17% 3	2470
	11th to 20th	Night	44% 3 7% 20% 19% 6%	2338
	21st to end	Night	41% 4 9% 22% 18% 7%	1879
March	1st to 10th	Night	47% 5% 7% 20% 18% 2	3418
	11th to 20th	Night	33% 5% 6% 22% 25% 9%	3480
	21st to end	Night	39% 4 8% 23% 21% 5%	3791
April	1st to 10th	Night	39% 6% 9% 17% 22% 6%	1900
	11th to 20th	Night	33% 5% 11% 23% 22% 6%	1875
	21st to end	Night	39% 6% 12% 23% 16% 5%	1900
May	1st to 10th	Night	45% 8% 16% 19% 11% 2	3000
	11th to 20th	Night	48% 8% 11% 23% 9% 1	2786
	21st to end	Night	32% 10% 16% 25% 15% 1	2739
June	1st to 10th	Night	38% 8% 14% 24% 15% 1	1520
	11th to 20th	Night	36% 10% 17% 20% 16% 2	1520
	21st to end	Night	33% 9% 14% 23% 18% 4	1520
July	1st to 10th	Night	36% 13% 18% 18% 12% 3	2529
	11th to 20th	Night	39% 10% 23% 21% 6% 1	2786
	21st to end	Night	51% 8% 12% 16% 12%	2988
August	1st to 10th	Night	48% 8% 17% 21% 6%	2814
	11th to 20th	Night	37% 9% 18% 23% 12%	2989
	21st to end	Night	32% 8% 11% 28% 20% 1	3476
September	1st to 10th	Night	37% 9% 14% 18% 16% 6%	1900
	11th to 20th	Night	36% 7% 10% 24% 21% 2	1900
	21st to end	Night	48% 6% 9% 18% 16% 4	2187
October	1st to 10th	Night	38% 6% 11% 18% 22% 5%	3800
	11th to 20th	Night	24% 3 6% 22% 31% 13%	3779
	21st to end	Night	21% 3 5% 31% 26% 13%	4120
November	1st to 10th	Night	35% 4 9% 22% 24% 6%	2283
	11th to 20th	Night	36% 5% 8% 19% 23% 9%	2470
	21st to end	Night	33% 4 9% 26% 23% 5%	2632
December	1st to 10th	Night	43% 4 9% 23% 17% 4	2660
	11th to 20th	Night	39% 4 10% 21% 20% 6%	3288
	21st to end	Night	40% 5% 10% 26% 17% 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	26% 22% 33% 15% 5%	252
	11th to 20th	Day	28% 30% 28% 11% 3	270
	21st to end	Day	25% 21% 41% 12% 1	297
February	1st to 10th	Day	23% 23% 38% 12% 4	270
	11th to 20th	Day	34% 21% 33% 10% 2	336
	21st to end	Day	29% 16% 32% 19% 4	382
March	1st to 10th	Day	24% 19% 33% 19% 5%	460
	11th to 20th	Day	23% 21% 35% 16% 5% 1	460
	21st to end	Day	24% 15% 37% 17% 6% 1	506
April	1st to 10th	Day	23% 16% 34% 18% 7% 1	460
	11th to 20th	Day	17% 12% 33% 25% 8% 4	452
	21st to end	Day	23% 13% 32% 22% 8% 1	460
May	1st to 10th	Day	17% 15% 31% 24% 10% 2	463
	11th to 20th	Day	21% 8% 28% 29% 11% 3	487
	21st to end	Day	19% 4 22% 30% 19% 5%	529
June	1st to 10th	Day	12% 6% 26% 29% 23% 4	490
	11th to 20th	Day	11% 5% 23% 34% 18% 8%	490
	21st to end	Day	12% 5% 23% 34% 21% 5%	490
July	1st to 10th	Day	10% 2 17% 34% 27% 11%	485
	11th to 20th	Day	6% 2 14% 38% 30% 10%	484
	21st to end	Day	10% 2 20% 34% 24% 10%	532
August	1st to 10th	Day	14% 3 17% 31% 27% 8%	486
	11th to 20th	Day	11% 4 16% 31% 25% 12%	479
	21st to end	Day	9% 4 16% 29% 26% 17%	539
September	1st to 10th	Day	15% 3 17% 28% 22% 16%	490
	11th to 20th	Day	16% 4 17% 29% 21% 13%	490
	21st to end	Day	28% 7% 23% 26% 12% 3	490
October	1st to 10th	Day	21% 5% 22% 25% 19% 8%	490
	11th to 20th	Day	16% 12% 21% 29% 19% 3	490
	21st to end	Day	15% 10% 33% 26% 11% 5%	539
November	1st to 10th	Day	18% 9% 30% 25% 14% 4	457
	11th to 20th	Day	17% 14% 31% 24% 12% 1	370
	21st to end	Day	21% 14% 34% 19% 11% 1	204
December	1st to 10th	Day	24% 16% 38% 14% 7% 1	180
	11th to 20th	Day	23% 16% 32% 20% 9%	180
	21st to end	Day	21% 13% 36% 20% 10% 2	198
January	1st to 10th	Night	21% 17% 37% 20% 4	760
	11th to 20th	Night	21% 18% 33% 24% 4	760
	21st to end	Night	22% 15% 37% 24% 1	836
February	1st to 10th	Night	21% 14% 36% 26% 3	760
	11th to 20th	Night	24% 20% 36% 18% 2	743
	21st to end	Night	23% 19% 35% 20% 3	628
March	1st to 10th	Night	20% 16% 35% 25% 4	760
	11th to 20th	Night	24% 16% 34% 21% 5% 1	760
	21st to end	Night	18% 16% 37% 24% 4	836
April	1st to 10th	Night	17% 19% 39% 22% 3	760
	11th to 20th	Night	17% 12% 37% 26% 8%	751
	21st to end	Night	18% 9% 38% 29% 6%	760
May	1st to 10th	Night	16% 12% 35% 29% 7%	665
	11th to 20th	Night	17% 5% 30% 36% 11% 1	547
	21st to end	Night	16% 3 17% 42% 20% 2	411
June	1st to 10th	Night	11% 3 21% 42% 21% 1	380
	11th to 20th	Night	9% 3 21% 42% 22% 3	380
	21st to end	Night	9% 5% 22% 45% 18% 1	380
July	1st to 10th	Night	10% 2 18% 39% 29% 3	393
	11th to 20th	Night	5% 3 12% 41% 34% 5%	552
	21st to end	Night	8% 3 17% 43% 24% 4	624
August	1st to 10th	Night	11% 2 13% 43% 26% 4	567
	11th to 20th	Night	13% 2 13% 42% 27% 3	663
	21st to end	Night	11% 4 13% 35% 31% 5%	836
September	1st to 10th	Night	16% 2 13% 36% 27% 5%	760
	11th to 20th	Night	14% 3 14% 36% 29% 4	760
	21st to end	Night	25% 4 21% 30% 19% 1	760
October	1st to 10th	Night	17% 4 21% 30% 24% 3	760
	11th to 20th	Night	18% 9% 24% 31% 16% 1	760
	21st to end	Night	16% 10% 28% 29% 15% 1	836
November	1st to 10th	Night	16% 7% 29% 31% 14% 3	755
	11th to 20th	Night	18% 12% 30% 31% 9%	760
	21st to end	Night	14% 13% 31% 32% 10% 1	760
December	1st to 10th	Night	21% 13% 34% 23% 8%	760
	11th to 20th	Night	18% 11% 36% 30% 6%	760
	21st to end	Night	20% 14% 29% 32% 5%	836

Page generated at 2024-11-01 22:47:39. Version ac07

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