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 2024-11-05.

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% 8% 3 7% 4 4 4 3 5% 6% 35%	105506
	Night	26% 9% 3 7% 4 4 4 3 4 6% 31%	102124
Transparency	Day	51% 8% 14% 17% 8% 1	105255
	Night	55% 7% 13% 16% 8% 1	102021
Seeing	Day	22% 5% 16% 26% 23% 7%	15378
	Night	29% 6% 13% 24% 22% 6%	23531

By Month

Percentage Cloud Cover NW (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	42% 11% 3 9% 6% 4 4 3 5% 5% 9%	2219
	11th to 20th	Day	30% 12% 4 7% 4 4 4 2 2 7% 23%	2199
	21st to end	Day	55% 12% 3 6% 3 3 3 2 3 2 9%	2804
February	1st to 10th	Day	33% 12% 4 7% 5% 5% 4 4 6% 6% 15%	1710
	11th to 20th	Day	30% 9% 3 8% 6% 6% 4 2 4 5% 22%	1665
	21st to end	Day	25% 12% 4 8% 6% 4 5% 4 5% 5% 23%	1430
March	1st to 10th	Day	23% 14% 4 9% 6% 5% 5% 4 6% 6% 17%	3248
	11th to 20th	Day	22% 9% 3 7% 4 4 4 3 5% 7% 33%	3490
	21st to end	Day	25% 13% 4 9% 5% 4 4 3 4 6% 23%	3931
April	1st to 10th	Day	26% 10% 3 8% 5% 5% 6% 4 6% 6% 20%	2280
	11th to 20th	Day	20% 10% 3 8% 5% 5% 5% 4 5% 6% 28%	2344
	21st to end	Day	22% 10% 3 8% 5% 4 4 4 5% 6% 28%	2525
May	1st to 10th	Day	14% 9% 2 6% 4 4 4 4 4 6% 44%	4420
	11th to 20th	Day	11% 6% 2 7% 4 4 5% 5% 6% 10% 40%	4377
	21st to end	Day	25% 9% 3 8% 5% 4 5% 4 6% 7% 25%	4899
June	1st to 10th	Day	20% 7% 2 7% 6% 5% 5% 4 5% 7% 32%	2850
	11th to 20th	Day	18% 8% 3 8% 6% 4 5% 4 6% 8% 29%	2850
	21st to end	Day	12% 7% 3 6% 5% 5% 5% 4 7% 7% 39%	2850
July	1st to 10th	Day	7% 3 2 4 3 3 3 3 4 5% 64%	4740
	11th to 20th	Day	5% 3 1 3 2 2 2 2 3 5% 71%	4740
	21st to end	Day	11% 4 2 5% 3 3 3 3 5% 7% 56%	4865
August	1st to 10th	Day	5% 3 1 3 3 2 2 2 4 6% 69%	4356
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 5% 7% 49%	4026
	21st to end	Day	14% 7% 3 6% 4 4 4 3 5% 7% 43%	4411
September	1st to 10th	Day	13% 6% 2 6% 4 3 4 4 5% 7% 47%	2280
	11th to 20th	Day	17% 8% 3 7% 4 3 4 4 5% 6% 39%	2280
	21st to end	Day	24% 6% 3 6% 4 5% 4 4 4 6% 35%	1999
October	1st to 10th	Day	22% 7% 3 8% 6% 5% 5% 4 6% 7% 29%	3180
	11th to 20th	Day	35% 7% 2 6% 4 4 4 3 4 7% 23%	3161
	21st to end	Day	30% 12% 4 9% 5% 4 4 4 5% 6% 17%	3184
November	1st to 10th	Day	39% 9% 3 8% 4 5% 4 3 4 4 17%	1520
	11th to 20th	Day	36% 10% 3 7% 4 4 4 3 4 4 21%	1520
	21st to end	Day	38% 10% 3 7% 5% 4 4 2 5% 4 18%	1520
December	1st to 10th	Day	31% 14% 3 6% 6% 4 4 3 4 3 22%	1506
	11th to 20th	Day	35% 14% 5% 9% 5% 5% 4 3 4 4 12%	1685
	21st to end	Day	39% 14% 5% 10% 5% 4 4 3 3 3 11%	2442
January	1st to 10th	Night	38% 12% 3 9% 5% 4 5% 3 4 4 13%	4726
	11th to 20th	Night	33% 9% 2 6% 4 3 4 3 6% 8% 23%	4699
	21st to end	Night	51% 11% 3 6% 3 3 3 2 3 4 11%	4848
February	1st to 10th	Night	33% 12% 3 8% 5% 3 4 3 4 6% 19%	2470
	11th to 20th	Night	29% 12% 2 8% 4 4 3 3 4 5% 25%	2402
	21st to end	Night	29% 11% 3 6% 4 5% 3 3 5% 5% 26%	2023
March	1st to 10th	Night	28% 15% 4 8% 4 4 4 3 5% 5% 20%	3623
	11th to 20th	Night	22% 7% 3 6% 3 4 4 4 7% 8% 31%	3489
	21st to end	Night	30% 14% 5% 9% 5% 4 3 3 4 4 21%	3721
April	1st to 10th	Night	26% 9% 3 8% 6% 5% 4 3 5% 6% 23%	1900
	11th to 20th	Night	21% 10% 3 7% 6% 5% 4 4 5% 7% 29%	1784
	21st to end	Night	22% 9% 4 9% 5% 5% 5% 4 6% 6% 26%	1653
May	1st to 10th	Night	16% 8% 3 6% 3 3 3 3 4 5% 46%	2540
	11th to 20th	Night	10% 5% 2 6% 4 4 4 5% 7% 8% 46%	2516
	21st to end	Night	20% 10% 4 9% 5% 5% 5% 3 4 6% 29%	2671
June	1st to 10th	Night	20% 9% 3 7% 5% 4 4 3 5% 7% 34%	1330
	11th to 20th	Night	15% 10% 4 8% 6% 4 5% 5% 5% 7% 30%	1330
	21st to end	Night	10% 6% 3 6% 6% 5% 4 5% 6% 7% 42%	1330
July	1st to 10th	Night	6% 3 1 3 3 2 3 3 4 6% 67%	2220
	11th to 20th	Night	4 3 1 2 2 2 2 2 3 5% 75%	2220
	21st to end	Night	7% 5% 2 4 3 4 3 4 5% 6% 57%	2685
August	1st to 10th	Night	4 3 1 2 2 2 2 2 4 6% 72%	2560
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 4 7% 52%	2812
	21st to end	Night	12% 5% 2 6% 4 4 4 4 6% 8% 44%	3260
September	1st to 10th	Night	9% 3 1 4 4 3 4 4 6% 7% 56%	1900
	11th to 20th	Night	18% 6% 2 6% 5% 3 5% 3 4 6% 43%	1900
	21st to end	Night	20% 6% 3 7% 5% 4 4 3 4 6% 39%	2179
October	1st to 10th	Night	19% 7% 3 8% 5% 5% 5% 4 6% 7% 31%	3800
	11th to 20th	Night	30% 9% 3 6% 3 4 4 3 5% 6% 28%	3777
	21st to end	Night	31% 10% 3 7% 4 4 3 3 5% 5% 25%	4375
November	1st to 10th	Night	37% 10% 3 7% 5% 4 4 3 4 4 18%	2658
	11th to 20th	Night	36% 9% 2 5% 4 4 4 4 4 5% 23%	2660
	21st to end	Night	35% 10% 3 8% 6% 4 4 2 3 4 20%	2660
December	1st to 10th	Night	32% 10% 3 6% 6% 4 4 3 3 5% 24%	2669
	11th to 20th	Night	42% 14% 4 8% 4 3 3 3 3 4 11%	3520
	21st to end	Night	40% 14% 4 8% 4 3 3 2 3 4 16%	5214

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	76% 7% 8% 6% 2 1	2219
	11th to 20th	Day	63% 6% 8% 13% 6% 4	2220
	21st to end	Day	82% 5% 4 6% 2	2804
February	1st to 10th	Day	70% 6% 11% 7% 4 2	1710
	11th to 20th	Day	65% 7% 9% 11% 6% 1	1674
	21st to end	Day	64% 7% 11% 11% 5% 2	1430
March	1st to 10th	Day	63% 7% 15% 11% 4	3248
	11th to 20th	Day	52% 8% 12% 24% 3 1	3490
	21st to end	Day	62% 9% 14% 11% 3	3931
April	1st to 10th	Day	63% 10% 14% 10% 3	2280
	11th to 20th	Day	57% 8% 10% 14% 8% 2	2344
	21st to end	Day	58% 8% 13% 14% 7% 1	2525
May	1st to 10th	Day	42% 7% 17% 22% 12%	4420
	11th to 20th	Day	39% 11% 23% 22% 5%	4380
	21st to end	Day	56% 11% 18% 13% 2	4900
June	1st to 10th	Day	53% 7% 17% 16% 5% 2	2850
	11th to 20th	Day	53% 11% 18% 13% 4	2850
	21st to end	Day	44% 9% 20% 18% 8% 2	2850
July	1st to 10th	Day	23% 7% 11% 25% 24% 10%	4666
	11th to 20th	Day	18% 5% 14% 37% 23% 2	4659
	21st to end	Day	30% 7% 22% 27% 12% 3	4711
August	1st to 10th	Day	20% 6% 14% 42% 17% 1	4339
	11th to 20th	Day	36% 9% 27% 18% 8% 1	4065
	21st to end	Day	43% 8% 18% 21% 10% 1	4410
September	1st to 10th	Day	38% 9% 16% 22% 11% 4	2280
	11th to 20th	Day	46% 8% 13% 18% 13% 2	2280
	21st to end	Day	51% 8% 14% 17% 9% 1	1999
October	1st to 10th	Day	53% 8% 17% 16% 5%	3180
	11th to 20th	Day	61% 8% 13% 12% 6%	3161
	21st to end	Day	68% 9% 9% 10% 4	3184
November	1st to 10th	Day	70% 8% 9% 9% 4 1	1520
	11th to 20th	Day	69% 6% 9% 10% 4 2	1520
	21st to end	Day	69% 7% 7% 9% 7% 1	1520
December	1st to 10th	Day	67% 7% 6% 11% 8% 1	1506
	11th to 20th	Day	73% 11% 7% 6% 3 1	1688
	21st to end	Day	77% 8% 7% 6% 2 1	2442
January	1st to 10th	Night	75% 7% 6% 9% 2	4726
	11th to 20th	Night	57% 7% 9% 16% 7% 3	4740
	21st to end	Night	79% 5% 5% 8% 2 1	4848
February	1st to 10th	Night	67% 7% 10% 9% 4 3	2470
	11th to 20th	Night	63% 7% 9% 12% 7% 1	2404
	21st to end	Night	60% 6% 10% 15% 6% 2	2023
March	1st to 10th	Night	64% 8% 11% 11% 6%	3623
	11th to 20th	Night	48% 9% 17% 21% 4	3490
	21st to end	Night	68% 8% 12% 10% 2	3721
April	1st to 10th	Night	62% 7% 13% 15% 3	1900
	11th to 20th	Night	56% 7% 11% 15% 8% 3	1784
	21st to end	Night	59% 8% 13% 12% 8%	1653
May	1st to 10th	Night	41% 6% 13% 27% 11% 1	2540
	11th to 20th	Night	33% 10% 26% 22% 8%	2516
	21st to end	Night	57% 8% 18% 13% 3	2671
June	1st to 10th	Night	51% 8% 17% 16% 5% 2	1330
	11th to 20th	Night	53% 9% 18% 16% 3	1330
	21st to end	Night	41% 8% 21% 18% 9% 3	1330
July	1st to 10th	Night	20% 4 10% 33% 23% 9%	2185
	11th to 20th	Night	16% 4 11% 42% 25% 2	2178
	21st to end	Night	28% 5% 15% 30% 19% 3	2600
August	1st to 10th	Night	15% 5% 15% 38% 26% 2	2552
	11th to 20th	Night	34% 7% 27% 20% 8% 3	2839
	21st to end	Night	39% 8% 19% 23% 11%	3260
September	1st to 10th	Night	29% 9% 17% 26% 15% 4	1900
	11th to 20th	Night	44% 6% 13% 17% 15% 4	1900
	21st to end	Night	47% 7% 15% 22% 7% 2	2179
October	1st to 10th	Night	52% 10% 18% 15% 6%	3800
	11th to 20th	Night	58% 6% 12% 17% 7%	3777
	21st to end	Night	62% 8% 12% 12% 5%	4375
November	1st to 10th	Night	70% 5% 10% 10% 4 1	2658
	11th to 20th	Night	65% 8% 10% 10% 5% 2	2660
	21st to end	Night	68% 7% 8% 8% 7% 1	2660
December	1st to 10th	Night	63% 6% 11% 11% 8% 1	2669
	11th to 20th	Night	77% 7% 7% 5% 4 1	3516
	21st to end	Night	74% 5% 7% 9% 3 1	5214

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	39% 8% 18% 15% 12% 8%	180
	11th to 20th	Day	41% 13% 11% 16% 13% 6%	180
	21st to end	Day	49% 5% 12% 15% 14% 4	221
February	1st to 10th	Day	39% 6% 17% 21% 15% 2	370
	11th to 20th	Day	35% 6% 17% 23% 15% 3	365
	21st to end	Day	28% 10% 19% 27% 11% 4	316
March	1st to 10th	Day	30% 6% 18% 25% 15% 5%	460
	11th to 20th	Day	29% 7% 17% 19% 21% 6%	460
	21st to end	Day	31% 7% 22% 21% 16% 4	506
April	1st to 10th	Day	28% 10% 17% 23% 19% 3	460
	11th to 20th	Day	23% 6% 22% 27% 17% 6%	452
	21st to end	Day	23% 6% 23% 25% 18% 5%	460
May	1st to 10th	Day	15% 5% 18% 30% 27% 5%	463
	11th to 20th	Day	16% 5% 14% 27% 30% 9%	488
	21st to end	Day	17% 4 18% 30% 22% 9%	576
June	1st to 10th	Day	18% 4 18% 32% 21% 6%	680
	11th to 20th	Day	17% 6% 20% 32% 21% 4	680
	21st to end	Day	12% 5% 19% 28% 30% 7%	680
July	1st to 10th	Day	11% 3 14% 32% 32% 9%	671
	11th to 20th	Day	5% 3 16% 35% 33% 8%	668
	21st to end	Day	7% 3 11% 28% 41% 12%	580
August	1st to 10th	Day	9% 2 11% 25% 38% 14%	487
	11th to 20th	Day	7% 2 9% 31% 38% 12%	477
	21st to end	Day	12% 5% 16% 29% 29% 10%	539
September	1st to 10th	Day	14% 3 15% 33% 27% 8%	490
	11th to 20th	Day	18% 4 16% 26% 27% 8%	490
	21st to end	Day	26% 5% 16% 21% 25% 7%	490
October	1st to 10th	Day	26% 5% 16% 23% 20% 9%	490
	11th to 20th	Day	34% 5% 14% 20% 18% 10%	490
	21st to end	Day	33% 9% 17% 21% 13% 6%	403
November	1st to 10th	Day	38% 7% 18% 21% 13% 3	188
	11th to 20th	Day	36% 9% 13% 12% 19% 10%	180
	21st to end	Day	37% 9% 17% 17% 11% 9%	180
December	1st to 10th	Day	42% 7% 17% 11% 11% 12%	180
	11th to 20th	Day	41% 11% 12% 19% 16% 2	180
	21st to end	Day	41% 6% 21% 20% 10% 3	198
January	1st to 10th	Night	45% 9% 16% 16% 11% 3	850
	11th to 20th	Night	43% 7% 12% 18% 17% 3	850
	21st to end	Night	40% 6% 14% 23% 13% 3	841
February	1st to 10th	Night	38% 7% 18% 22% 12% 3	760
	11th to 20th	Night	33% 8% 18% 24% 15% 1	744
	21st to end	Night	33% 8% 18% 24% 14% 2	628
March	1st to 10th	Night	33% 8% 17% 21% 18% 3	760
	11th to 20th	Night	33% 8% 16% 22% 17% 4	760
	21st to end	Night	34% 7% 16% 22% 17% 4	836
April	1st to 10th	Night	31% 7% 13% 27% 19% 4	760
	11th to 20th	Night	23% 7% 16% 31% 17% 7%	656
	21st to end	Night	26% 5% 16% 29% 18% 5%	513
May	1st to 10th	Night	19% 3 13% 26% 34% 5%	380
	11th to 20th	Night	18% 3 6% 27% 38% 8%	374
	21st to end	Night	19% 3 9% 29% 34% 6%	411
June	1st to 10th	Night	21% 5% 11% 28% 30% 5%	380
	11th to 20th	Night	16% 6% 15% 33% 27% 4	380
	21st to end	Night	14% 2 10% 30% 36% 8%	380
July	1st to 10th	Night	12% 1 7% 28% 45% 7%	370
	11th to 20th	Night	7% 3 9% 28% 43% 10%	368
	21st to end	Night	4 2 6% 27% 48% 13%	416
August	1st to 10th	Night	9% 2 3 23% 43% 20%	396
	11th to 20th	Night	9% 1 5% 22% 47% 16%	564
	21st to end	Night	11% 3 10% 23% 41% 12%	689
September	1st to 10th	Night	11% 1 5% 34% 37% 12%	760
	11th to 20th	Night	20% 3 12% 19% 31% 15%	760
	21st to end	Night	22% 4 12% 27% 29% 7%	760
October	1st to 10th	Night	23% 4 13% 24% 26% 10%	760
	11th to 20th	Night	33% 4 13% 23% 20% 8%	760
	21st to end	Night	36% 6% 15% 24% 14% 4	836
November	1st to 10th	Night	42% 8% 15% 23% 13% 1	760
	11th to 20th	Night	39% 8% 16% 21% 13% 4	760
	21st to end	Night	37% 8% 16% 21% 14% 4	760
December	1st to 10th	Night	34% 6% 15% 27% 15% 4	764
	11th to 20th	Night	48% 8% 14% 21% 8% 1	850
	21st to end	Night	45% 8% 20% 18% 8% 1	935

Page generated at 2024-11-02 23:11:23. Version ac07

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