Rutland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rutland clear sky chart from 2005-11-06 to 2025-07-06.

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	18% 11% 4 9% 5% 4 4 4 5% 6% 29%	119815
	Night	18% 13% 4 10% 5% 4 4 3 5% 5% 28%	118980
Transparency	Day	54% 6% 11% 18% 9% 1	123341
	Night	57% 6% 10% 16% 9% 1	123615
Seeing	Day	28% 20% 28% 15% 6% 2	15600
	Night	26% 19% 25% 21% 8% 1	24595

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	13% 16% 7% 19% 7% 4 4 2 4 4 20%	3597
	11th to 20th	Day	10% 15% 6% 19% 9% 5% 4 3 4 5% 21%	3570
	21st to end	Day	13% 17% 8% 12% 6% 5% 5% 3 4 4 24%	3960
February	1st to 10th	Day	14% 16% 4 11% 7% 6% 4 4 5% 6% 23%	1780
	11th to 20th	Day	13% 15% 5% 15% 7% 5% 4 4 4 5% 23%	1944
	21st to end	Day	16% 15% 6% 12% 7% 4 3 3 4 6% 25%	1650
March	1st to 10th	Day	21% 15% 6% 12% 5% 5% 3 3 4 4 22%	4476
	11th to 20th	Day	14% 16% 5% 8% 4 3 4 3 5% 6% 31%	4666
	21st to end	Day	22% 10% 4 10% 5% 4 4 3 3 5% 29%	5970
April	1st to 10th	Day	21% 16% 3 8% 4 4 3 3 5% 5% 30%	2400
	11th to 20th	Day	17% 13% 3 7% 5% 4 4 3 4 6% 33%	2374
	21st to end	Day	22% 13% 4 7% 4 4 3 3 5% 6% 30%	2555
May	1st to 10th	Day	33% 12% 3 7% 4 4 4 3 5% 5% 20%	5966
	11th to 20th	Day	18% 12% 3 7% 5% 5% 5% 4 6% 6% 28%	6318
	21st to end	Day	20% 9% 3 7% 5% 4 5% 4 6% 7% 30%	6949
June	1st to 10th	Day	22% 8% 3 7% 5% 6% 6% 4 6% 7% 27%	2800
	11th to 20th	Day	20% 7% 2 6% 5% 4 5% 4 6% 8% 32%	2800
	21st to end	Day	20% 9% 3 7% 5% 5% 4 4 6% 7% 29%	2800
July	1st to 10th	Day	14% 7% 2 6% 5% 4 6% 4 7% 11% 34%	4510
	11th to 20th	Day	13% 6% 3 7% 6% 5% 5% 5% 8% 9% 33%	4440
	21st to end	Day	16% 6% 3 7% 5% 5% 5% 5% 6% 8% 36%	4814
August	1st to 10th	Day	16% 8% 3 7% 5% 5% 6% 4 7% 8% 31%	4377
	11th to 20th	Day	16% 8% 2 7% 5% 6% 5% 5% 6% 8% 32%	3863
	21st to end	Day	15% 6% 2 5% 4 4 5% 4 7% 9% 39%	4180
September	1st to 10th	Day	16% 6% 2 6% 4 4 5% 4 6% 7% 42%	2280
	11th to 20th	Day	16% 6% 2 5% 3 3 4 3 4 7% 48%	2161
	21st to end	Day	17% 7% 2 6% 3 5% 4 4 6% 7% 40%	2090
October	1st to 10th	Day	23% 9% 3 7% 4 4 4 4 4 5% 32%	2028
	11th to 20th	Day	17% 11% 3 7% 4 5% 4 3 4 8% 34%	1854
	21st to end	Day	25% 13% 3 7% 4 4 4 3 4 5% 28%	1881
November	1st to 10th	Day	16% 12% 4 7% 4 3 4 4 5% 5% 35%	1761
	11th to 20th	Day	17% 14% 4 9% 4 4 4 4 5% 5% 31%	1800
	21st to end	Day	19% 13% 5% 9% 4 5% 4 4 4 6% 26%	1655
December	1st to 10th	Day	15% 21% 5% 15% 6% 4 4 3 5% 6% 16%	2600
	11th to 20th	Day	18% 17% 8% 11% 5% 4 4 2 4 5% 23%	2986
	21st to end	Day	19% 18% 6% 11% 5% 3 4 3 4 5% 23%	3960
January	1st to 10th	Night	12% 15% 9% 21% 7% 4 3 2 3 4 21%	6349
	11th to 20th	Night	10% 19% 7% 20% 9% 5% 5% 3 4 4 14%	6315
	21st to end	Night	15% 15% 7% 14% 6% 6% 5% 3 4 5% 21%	6996
February	1st to 10th	Night	15% 16% 6% 13% 8% 5% 4 3 4 5% 20%	2617
	11th to 20th	Night	12% 12% 6% 12% 9% 7% 6% 5% 6% 4 23%	2340
	21st to end	Night	14% 15% 4 13% 6% 5% 4 3 5% 5% 27%	1980
March	1st to 10th	Night	19% 12% 5% 11% 6% 5% 4 3 5% 5% 25%	5364
	11th to 20th	Night	16% 17% 3 7% 4 3 4 3 4 6% 31%	5275
	21st to end	Night	21% 17% 5% 11% 5% 3 3 2 3 4 27%	4962
April	1st to 10th	Night	21% 13% 4 8% 5% 3 4 3 5% 6% 29%	2000
	11th to 20th	Night	20% 14% 4 6% 4 4 4 3 4 6% 31%	1975
	21st to end	Night	20% 13% 5% 6% 4 3 3 2 5% 4 33%	1845
May	1st to 10th	Night	33% 12% 3 7% 4 3 4 2 5% 5% 20%	4018
	11th to 20th	Night	19% 13% 3 9% 5% 4 4 3 5% 6% 28%	3575
	21st to end	Night	22% 10% 3 6% 5% 4 5% 4 6% 6% 29%	3926
June	1st to 10th	Night	21% 8% 2 7% 5% 4 5% 5% 5% 7% 32%	1600
	11th to 20th	Night	22% 7% 2 6% 4 4 4 4 5% 7% 36%	1600
	21st to end	Night	19% 8% 3 6% 5% 4 5% 3 5% 6% 35%	1600
July	1st to 10th	Night	15% 7% 2 8% 5% 6% 6% 5% 6% 8% 33%	2560
	11th to 20th	Night	19% 9% 2 6% 4 4 5% 4 7% 7% 34%	2520
	21st to end	Night	16% 8% 2 7% 5% 4 5% 4 5% 6% 38%	2739
August	1st to 10th	Night	25% 10% 3 6% 5% 4 3 2 4 6% 34%	2520
	11th to 20th	Night	16% 7% 3 8% 5% 3 4 4 6% 8% 37%	2962
	21st to end	Night	13% 8% 2 5% 3 4 4 4 6% 9% 42%	3476
September	1st to 10th	Night	16% 8% 2 5% 3 4 4 4 4 6% 44%	1900
	11th to 20th	Night	16% 5% 2 4 3 3 3 3 4 5% 51%	2019
	21st to end	Night	17% 7% 2 5% 4 4 3 3 5% 6% 44%	2090
October	1st to 10th	Night	23% 9% 3 7% 4 4 3 3 5% 6% 33%	2150
	11th to 20th	Night	18% 11% 3 8% 5% 4 4 4 5% 6% 33%	2325
	21st to end	Night	23% 14% 3 7% 5% 5% 4 3 5% 5% 26%	2717
November	1st to 10th	Night	17% 13% 4 7% 5% 5% 3 3 5% 4 34%	2537
	11th to 20th	Night	18% 14% 5% 7% 4 4 4 3 5% 6% 32%	2600
	21st to end	Night	16% 15% 4 10% 5% 3 4 4 5% 6% 28%	2744
December	1st to 10th	Night	17% 20% 7% 16% 6% 4 4 3 4 4 14%	4580
	11th to 20th	Night	22% 19% 5% 9% 5% 4 3 3 4 4 24%	5208
	21st to end	Night	19% 19% 5% 10% 5% 5% 4 3 4 4 22%	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	69% 4 8% 16% 4	3598
	11th to 20th	Day	67% 5% 7% 12% 8% 2	3600
	21st to end	Day	63% 5% 9% 12% 9% 2	3960
February	1st to 10th	Day	62% 7% 10% 13% 7% 1	1780
	11th to 20th	Day	62% 6% 8% 15% 7% 1	1953
	21st to end	Day	62% 4 9% 13% 10% 1	1650
March	1st to 10th	Day	65% 6% 8% 9% 9% 4	4479
	11th to 20th	Day	53% 5% 15% 17% 8% 3	4666
	21st to end	Day	58% 4 7% 12% 17% 2	5970
April	1st to 10th	Day	57% 4 8% 19% 10% 2	2400
	11th to 20th	Day	53% 6% 8% 18% 13% 1	2374
	21st to end	Day	56% 6% 8% 17% 12% 2	2555
May	1st to 10th	Day	66% 6% 7% 13% 6% 1	5977
	11th to 20th	Day	55% 8% 13% 16% 8% 1	6322
	21st to end	Day	52% 7% 11% 22% 8%	6949
June	1st to 10th	Day	54% 8% 12% 17% 8%	2800
	11th to 20th	Day	49% 7% 11% 20% 12% 1	2800
	21st to end	Day	54% 8% 10% 18% 9% 1	2800
July	1st to 10th	Day	42% 7% 14% 25% 11%	4440
	11th to 20th	Day	43% 9% 15% 25% 7%	4365
	21st to end	Day	45% 8% 14% 24% 9%	4661
August	1st to 10th	Day	50% 8% 14% 19% 9%	4363
	11th to 20th	Day	48% 8% 16% 23% 5%	3902
	21st to end	Day	39% 7% 17% 25% 11% 1	4180
September	1st to 10th	Day	40% 7% 12% 28% 12%	2280
	11th to 20th	Day	37% 6% 9% 30% 17% 1	2161
	21st to end	Day	43% 7% 12% 25% 11% 2	2090
October	1st to 10th	Day	50% 6% 9% 22% 13% 1	3366
	11th to 20th	Day	46% 4 13% 24% 13% 1	3057
	21st to end	Day	43% 6% 11% 28% 10% 1	3081
November	1st to 10th	Day	49% 7% 12% 20% 12%	1761
	11th to 20th	Day	54% 6% 10% 15% 14% 2	1800
	21st to end	Day	59% 6% 15% 15% 5% 1	1655
December	1st to 10th	Day	70% 8% 10% 9% 3	2600
	11th to 20th	Day	65% 4 8% 15% 8% 1	2986
	21st to end	Day	63% 6% 7% 12% 10% 3	3960
January	1st to 10th	Night	68% 4 10% 12% 5%	6349
	11th to 20th	Night	72% 7% 8% 9% 5% 1	6360
	21st to end	Night	65% 5% 8% 10% 10% 2	6996
February	1st to 10th	Night	65% 5% 9% 13% 7% 1	2617
	11th to 20th	Night	61% 6% 9% 14% 9% 1	2342
	21st to end	Night	60% 4 12% 16% 7% 2	1980
March	1st to 10th	Night	60% 6% 8% 13% 11% 2	5374
	11th to 20th	Night	54% 6% 16% 14% 9% 2	5276
	21st to end	Night	63% 3 5% 12% 15% 2	4962
April	1st to 10th	Night	57% 5% 9% 18% 10% 1	2000
	11th to 20th	Night	54% 6% 9% 19% 12% 1	1975
	21st to end	Night	54% 6% 8% 18% 12% 3	1845
May	1st to 10th	Night	66% 6% 7% 13% 7% 1	4024
	11th to 20th	Night	56% 7% 11% 18% 7% 1	3576
	21st to end	Night	54% 8% 12% 16% 9% 1	3927
June	1st to 10th	Night	50% 8% 11% 19% 11% 1	1600
	11th to 20th	Night	49% 7% 14% 19% 11% 1	1600
	21st to end	Night	49% 7% 13% 23% 8% 1	1600
July	1st to 10th	Night	48% 8% 14% 18% 11% 1	2520
	11th to 20th	Night	46% 7% 13% 25% 8%	2472
	21st to end	Night	45% 6% 12% 26% 10% 1	2651
August	1st to 10th	Night	53% 6% 12% 19% 9%	2510
	11th to 20th	Night	44% 7% 18% 22% 8%	2989
	21st to end	Night	37% 7% 18% 26% 11% 1	3476
September	1st to 10th	Night	39% 7% 13% 28% 12%	1900
	11th to 20th	Night	35% 6% 11% 30% 17% 1	2019
	21st to end	Night	42% 5% 12% 24% 14% 2	2090
October	1st to 10th	Night	53% 7% 11% 21% 8% 1	3592
	11th to 20th	Night	47% 5% 11% 21% 15% 1	3861
	21st to end	Night	49% 6% 11% 27% 7% 1	4467
November	1st to 10th	Night	53% 6% 10% 18% 11% 2	2537
	11th to 20th	Night	54% 6% 10% 17% 11% 3	2600
	21st to end	Night	56% 6% 13% 17% 7%	2744
December	1st to 10th	Night	73% 7% 9% 10% 2	4580
	11th to 20th	Night	66% 4 7% 10% 12%	5208
	21st to end	Night	66% 5% 8% 11% 7% 4	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	35% 31% 23% 11% 2	200
	11th to 20th	Day	35% 23% 33% 8% 2 1	200
	21st to end	Day	25% 30% 33% 9% 3	220
February	1st to 10th	Day	36% 40% 19% 4 1	290
	11th to 20th	Day	33% 30% 25% 10% 2	492
	21st to end	Day	35% 27% 25% 11% 2	414
March	1st to 10th	Day	35% 24% 28% 11% 2	500
	11th to 20th	Day	32% 27% 26% 12% 2 1	500
	21st to end	Day	33% 27% 23% 11% 5% 2	550
April	1st to 10th	Day	42% 19% 24% 10% 4 1	500
	11th to 20th	Day	38% 25% 20% 11% 4 2	492
	21st to end	Day	35% 23% 27% 10% 4 1	500
May	1st to 10th	Day	38% 22% 23% 11% 4 1	503
	11th to 20th	Day	24% 19% 34% 17% 4 2	527
	21st to end	Day	22% 19% 34% 18% 6% 2	573
June	1st to 10th	Day	27% 19% 32% 16% 5% 1	530
	11th to 20th	Day	27% 15% 32% 18% 8%	530
	21st to end	Day	25% 19% 32% 18% 4 1	530
July	1st to 10th	Day	21% 14% 32% 21% 9% 2	505
	11th to 20th	Day	14% 13% 40% 24% 8% 1	484
	21st to end	Day	17% 13% 40% 23% 6% 2	532
August	1st to 10th	Day	18% 14% 29% 26% 11% 3	486
	11th to 20th	Day	20% 14% 28% 21% 11% 6%	479
	21st to end	Day	19% 14% 27% 23% 12% 5%	539
September	1st to 10th	Day	18% 15% 29% 21% 11% 6%	490
	11th to 20th	Day	19% 15% 22% 18% 18% 8%	490
	21st to end	Day	20% 15% 29% 19% 11% 5%	490
October	1st to 10th	Day	29% 13% 27% 18% 11% 2	490
	11th to 20th	Day	28% 18% 26% 19% 9%	465
	21st to end	Day	35% 21% 24% 15% 4	429
November	1st to 10th	Day	29% 22% 24% 16% 8% 1	395
	11th to 20th	Day	29% 27% 25% 13% 6% 1	400
	21st to end	Day	34% 25% 29% 9% 2 1	255
December	1st to 10th	Day	31% 34% 25% 8% 2 1	200
	11th to 20th	Day	41% 29% 22% 7% 2	200
	21st to end	Day	35% 25% 27% 10% 4	220
January	1st to 10th	Night	25% 30% 30% 14% 2	800
	11th to 20th	Night	30% 25% 26% 17% 3 1	800
	21st to end	Night	20% 27% 31% 18% 3	880
February	1st to 10th	Night	25% 28% 33% 13% 2	800
	11th to 20th	Night	25% 30% 27% 16% 2	783
	21st to end	Night	26% 25% 31% 16% 2	660
March	1st to 10th	Night	27% 25% 29% 17% 3	800
	11th to 20th	Night	30% 23% 27% 15% 5%	800
	21st to end	Night	30% 21% 25% 16% 7%	880
April	1st to 10th	Night	31% 22% 25% 19% 4	800
	11th to 20th	Night	29% 23% 24% 16% 7%	791
	21st to end	Night	31% 20% 23% 20% 5% 1	645
May	1st to 10th	Night	33% 15% 26% 19% 7%	590
	11th to 20th	Night	21% 16% 28% 28% 6% 1	394
	21st to end	Night	21% 11% 26% 31% 10% 1	433
June	1st to 10th	Night	23% 9% 28% 28% 12% 1	400
	11th to 20th	Night	25% 9% 22% 32% 12% 1	400
	21st to end	Night	22% 8% 25% 33% 12% 1	400
July	1st to 10th	Night	18% 5% 21% 41% 13% 2	380
	11th to 20th	Night	18% 3 23% 37% 17% 1	368
	21st to end	Night	16% 4 28% 35% 17%	416
August	1st to 10th	Night	19% 5% 16% 38% 21% 1	379
	11th to 20th	Night	19% 6% 21% 33% 17% 3	664
	21st to end	Night	20% 6% 20% 32% 21% 2	836
September	1st to 10th	Night	20% 9% 22% 30% 17% 2	760
	11th to 20th	Night	20% 9% 19% 26% 22% 5%	760
	21st to end	Night	22% 11% 23% 26% 15% 3	760
October	1st to 10th	Night	29% 12% 18% 24% 13% 2	760
	11th to 20th	Night	25% 16% 24% 23% 11% 1	760
	21st to end	Night	31% 20% 24% 18% 6%	836
November	1st to 10th	Night	26% 21% 26% 18% 8% 1	780
	11th to 20th	Night	27% 22% 25% 18% 7% 1	800
	21st to end	Night	28% 28% 23% 15% 5% 1	800
December	1st to 10th	Night	32% 27% 23% 14% 4	800
	11th to 20th	Night	30% 27% 22% 17% 4	800
	21st to end	Night	31% 25% 26% 15% 3	880

Page generated at 2025-07-03 01:30:15. Version ac07

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