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 2026-10-29.

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	17% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	149625
	Night	17% 13% 4 10% 5% 5% 4 3 5% 5% 28%	142439
Transparency	Day	53% 6% 11% 19% 9% 1	153108
	Night	57% 6% 11% 17% 9% 1	147045
Seeing	Day	28% 20% 28% 15% 6% 2	17324
	Night	26% 19% 25% 22% 8% 1	26232

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	11% 15% 7% 19% 8% 5% 5% 3 4 4 19%	4661
	11th to 20th	Day	10% 17% 6% 19% 9% 5% 4 3 4 4 19%	4650
	21st to end	Day	11% 14% 7% 12% 7% 7% 6% 3 4 5% 23%	5124
February	1st to 10th	Day	13% 15% 4 11% 7% 6% 5% 4 5% 6% 23%	1869
	11th to 20th	Day	12% 15% 5% 15% 7% 5% 4 4 4 5% 23%	2044
	21st to end	Day	16% 15% 6% 12% 7% 4 3 3 4 5% 25%	1730
March	1st to 10th	Day	21% 15% 6% 12% 5% 5% 3 3 4 4 23%	4576
	11th to 20th	Day	14% 16% 5% 8% 4 3 4 3 5% 6% 31%	4768
	21st to end	Day	22% 10% 4 10% 5% 4 4 3 4 5% 29%	6102
April	1st to 10th	Day	21% 16% 3 7% 4 4 3 3 4 5% 29%	2520
	11th to 20th	Day	17% 13% 3 7% 6% 4 4 3 4 6% 32%	2494
	21st to end	Day	22% 12% 4 7% 4 4 3 3 5% 6% 31%	2683
May	1st to 10th	Day	29% 11% 3 7% 5% 4 5% 4 5% 5% 20%	7732
	11th to 20th	Day	18% 11% 3 7% 5% 5% 5% 4 6% 7% 30%	8221
	21st to end	Day	20% 10% 3 8% 5% 4 4 4 5% 7% 30%	9060
June	1st to 10th	Day	21% 8% 3 7% 5% 6% 6% 4 6% 7% 28%	2940
	11th to 20th	Day	20% 7% 2 6% 5% 4 5% 4 6% 8% 32%	2940
	21st to end	Day	20% 9% 3 7% 5% 5% 5% 4 6% 6% 29%	2940
July	1st to 10th	Day	14% 7% 2 7% 5% 4 5% 4 7% 10% 33%	8280
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	8280
	21st to end	Day	16% 6% 2 6% 4 4 4 4 6% 8% 38%	8993
August	1st to 10th	Day	16% 8% 3 8% 6% 5% 6% 4 6% 7% 30%	6422
	11th to 20th	Day	15% 7% 2 6% 4 5% 5% 5% 7% 9% 33%	5681
	21st to end	Day	13% 7% 3 6% 4 5% 5% 4 7% 9% 36%	6080
September	1st to 10th	Day	16% 6% 2 5% 3 4 5% 4 6% 6% 42%	2520
	11th to 20th	Day	15% 6% 2 4 3 3 4 3 4 7% 49%	2389
	21st to end	Day	18% 7% 2 6% 3 4 4 4 5% 7% 39%	2310
October	1st to 10th	Day	22% 9% 3 7% 4 4 4 3 5% 5% 35%	2242
	11th to 20th	Day	18% 11% 4 7% 4 5% 4 3 4 8% 34%	2049
	21st to end	Day	24% 13% 3 7% 4 4 4 3 4 5% 30%	2052
November	1st to 10th	Day	16% 13% 4 7% 4 3 4 4 5% 5% 35%	1851
	11th to 20th	Day	16% 15% 4 9% 4 4 4 3 5% 6% 30%	1890
	21st to end	Day	19% 14% 5% 10% 4 5% 4 4 4 6% 26%	1738
December	1st to 10th	Day	15% 21% 5% 15% 6% 4 4 3 5% 6% 16%	2680
	11th to 20th	Day	18% 17% 8% 12% 5% 4 4 2 4 5% 23%	3066
	21st to end	Day	18% 18% 6% 11% 5% 3 4 3 4 5% 23%	4048
January	1st to 10th	Night	12% 16% 8% 19% 7% 4 4 3 3 4 20%	8234
	11th to 20th	Night	11% 19% 7% 20% 9% 6% 5% 3 4 4 13%	8235
	21st to end	Night	13% 13% 6% 12% 7% 8% 6% 4 5% 5% 20%	9057
February	1st to 10th	Night	14% 15% 6% 14% 8% 5% 4 3 5% 5% 22%	2748
	11th to 20th	Night	12% 12% 6% 12% 8% 7% 5% 5% 6% 5% 23%	2460
	21st to end	Night	13% 16% 5% 13% 6% 5% 4 3 4 5% 28%	2076
March	1st to 10th	Night	19% 12% 5% 11% 6% 5% 4 3 5% 5% 26%	5484
	11th to 20th	Night	16% 17% 4 7% 4 3 4 3 4 6% 30%	5393
	21st to end	Night	22% 17% 5% 11% 5% 3 3 2 3 4 26%	5072
April	1st to 10th	Night	21% 13% 4 8% 5% 3 4 3 5% 6% 29%	2100
	11th to 20th	Night	21% 14% 4 6% 4 4 4 3 4 6% 31%	2075
	21st to end	Night	20% 13% 5% 6% 4 3 3 2 5% 5% 33%	1937
May	1st to 10th	Night	29% 13% 3 7% 4 4 4 3 5% 5% 23%	5210
	11th to 20th	Night	19% 12% 3 9% 5% 4 4 3 5% 7% 28%	4639
	21st to end	Night	22% 9% 3 7% 5% 5% 5% 4 6% 7% 29%	5114
June	1st to 10th	Night	20% 8% 2 7% 5% 4 5% 5% 5% 7% 33%	1680
	11th to 20th	Night	22% 8% 2 5% 4 4 4 4 5% 6% 35%	1680
	21st to end	Night	19% 8% 3 6% 5% 4 5% 3 6% 6% 35%	1680
July	1st to 10th	Night	15% 8% 3 8% 5% 5% 6% 5% 6% 9% 32%	4680
	11th to 20th	Night	17% 8% 2 6% 4 4 5% 3 5% 7% 39%	4680
	21st to end	Night	14% 8% 2 7% 4 4 4 4 5% 6% 41%	5084
August	1st to 10th	Night	23% 10% 3 7% 4 4 4 3 5% 5% 33%	3680
	11th to 20th	Night	18% 8% 3 7% 4 3 4 3 6% 8% 36%	4348
	21st to end	Night	13% 9% 3 6% 4 4 5% 4 6% 9% 37%	5045
September	1st to 10th	Night	16% 8% 2 5% 4 4 4 3 4 6% 44%	2100
	11th to 20th	Night	16% 5% 2 4 3 3 3 3 4 5% 51%	2231
	21st to end	Night	18% 7% 2 5% 4 4 4 3 5% 5% 42%	2310
October	1st to 10th	Night	22% 9% 3 6% 3 3 3 3 4 6% 36%	2376
	11th to 20th	Night	18% 11% 3 7% 5% 4 4 4 5% 6% 33%	2570
	21st to end	Night	22% 13% 3 7% 5% 5% 4 3 5% 5% 28%	2965
November	1st to 10th	Night	18% 13% 4 7% 5% 4 3 3 4 4 33%	2667
	11th to 20th	Night	18% 15% 5% 7% 4 4 4 3 5% 6% 31%	2730
	21st to end	Night	16% 15% 5% 10% 5% 4 4 3 5% 6% 27%	2881
December	1st to 10th	Night	17% 20% 7% 16% 7% 4 4 3 4 4 14%	4720
	11th to 20th	Night	21% 19% 5% 9% 5% 4 3 3 4 4 23%	5348
	21st to end	Night	19% 19% 5% 10% 5% 5% 4 3 4 4 22%	7150

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	68% 5% 8% 15% 3	4662
	11th to 20th	Day	69% 5% 6% 10% 8% 1	4680
	21st to end	Day	63% 6% 9% 13% 8% 2	5124
February	1st to 10th	Day	61% 6% 10% 14% 8% 1	1869
	11th to 20th	Day	62% 6% 8% 16% 7% 1	2053
	21st to end	Day	63% 4 9% 13% 10% 1	1730
March	1st to 10th	Day	64% 6% 8% 9% 9% 4	4579
	11th to 20th	Day	54% 5% 14% 16% 8% 3	4768
	21st to end	Day	58% 4 7% 12% 17% 2	6102
April	1st to 10th	Day	57% 4 8% 18% 11% 2	2520
	11th to 20th	Day	53% 6% 8% 18% 13% 1	2494
	21st to end	Day	55% 6% 8% 17% 12% 2	2683
May	1st to 10th	Day	64% 7% 8% 13% 7% 1	7744
	11th to 20th	Day	52% 7% 13% 18% 8% 1	8225
	21st to end	Day	52% 7% 10% 23% 7%	9061
June	1st to 10th	Day	54% 7% 12% 18% 9%	2940
	11th to 20th	Day	49% 7% 11% 19% 12% 1	2940
	21st to end	Day	54% 8% 10% 18% 9% 1	2940
July	1st to 10th	Day	44% 7% 15% 24% 9%	8210
	11th to 20th	Day	39% 7% 15% 28% 11% 1	8205
	21st to end	Day	43% 6% 14% 27% 9%	8795
August	1st to 10th	Day	52% 8% 14% 16% 10%	6408
	11th to 20th	Day	45% 8% 19% 23% 5%	5720
	21st to end	Day	41% 8% 16% 24% 10% 1	6080
September	1st to 10th	Day	41% 7% 11% 28% 12%	2520
	11th to 20th	Day	36% 5% 9% 30% 18% 1	2389
	21st to end	Day	43% 7% 12% 24% 12% 2	2310
October	1st to 10th	Day	48% 6% 9% 22% 14% 1	3580
	11th to 20th	Day	46% 4 12% 24% 13% 1	3252
	21st to end	Day	43% 6% 11% 28% 10% 2	3252
November	1st to 10th	Day	50% 7% 12% 20% 12%	1851
	11th to 20th	Day	55% 6% 10% 15% 13% 2	1890
	21st to end	Day	61% 6% 14% 15% 5% 1	1738
December	1st to 10th	Day	69% 8% 10% 9% 4	2680
	11th to 20th	Day	65% 4 8% 15% 8% 1	3066
	21st to end	Day	63% 6% 7% 12% 10% 3	4048
January	1st to 10th	Night	68% 4 10% 12% 6% 1	8234
	11th to 20th	Night	74% 6% 7% 7% 5% 1	8280
	21st to end	Night	64% 5% 8% 12% 9% 2	9057
February	1st to 10th	Night	63% 5% 9% 14% 7% 1	2748
	11th to 20th	Night	61% 6% 9% 15% 9% 1	2462
	21st to end	Night	60% 4 11% 16% 8% 2	2076
March	1st to 10th	Night	60% 6% 8% 13% 11% 2	5494
	11th to 20th	Night	54% 6% 16% 14% 9% 2	5394
	21st to end	Night	63% 3 5% 12% 15% 2	5072
April	1st to 10th	Night	57% 5% 9% 17% 11% 1	2100
	11th to 20th	Night	54% 6% 9% 19% 12% 1	2075
	21st to end	Night	53% 6% 8% 18% 13% 3	1937
May	1st to 10th	Night	63% 6% 9% 13% 9%	5216
	11th to 20th	Night	55% 7% 11% 19% 7% 1	4640
	21st to end	Night	52% 7% 11% 21% 8% 1	5115
June	1st to 10th	Night	49% 8% 11% 20% 12% 1	1680
	11th to 20th	Night	50% 6% 13% 19% 11% 1	1680
	21st to end	Night	49% 7% 13% 23% 8% 1	1680
July	1st to 10th	Night	47% 7% 16% 20% 9%	4640
	11th to 20th	Night	44% 5% 12% 26% 13%	4632
	21st to end	Night	41% 7% 15% 27% 10%	4967
August	1st to 10th	Night	53% 6% 13% 16% 10% 1	3670
	11th to 20th	Night	46% 7% 17% 23% 7%	4375
	21st to end	Night	42% 7% 18% 23% 10% 1	5045
September	1st to 10th	Night	40% 7% 13% 28% 12%	2100
	11th to 20th	Night	36% 6% 11% 30% 18% 1	2231
	21st to end	Night	43% 5% 12% 23% 15% 2	2310
October	1st to 10th	Night	51% 6% 10% 22% 9% 1	3818
	11th to 20th	Night	47% 5% 11% 21% 16% 1	4106
	21st to end	Night	48% 6% 10% 26% 8% 1	4715
November	1st to 10th	Night	54% 5% 10% 18% 11% 2	2667
	11th to 20th	Night	55% 6% 10% 16% 11% 3	2730
	21st to end	Night	57% 6% 13% 16% 7%	2881
December	1st to 10th	Night	73% 7% 9% 10% 2	4720
	11th to 20th	Night	66% 4 8% 10% 12%	5348
	21st to end	Night	66% 5% 8% 11% 7% 3	7150

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	33% 30% 24% 11% 1	220
	11th to 20th	Day	35% 25% 30% 7% 2	220
	21st to end	Day	27% 30% 32% 9% 2	242
February	1st to 10th	Day	34% 38% 22% 6% 1	319
	11th to 20th	Day	32% 30% 26% 10% 2	532
	21st to end	Day	33% 29% 25% 11% 2	446
March	1st to 10th	Day	36% 24% 28% 11% 2	540
	11th to 20th	Day	34% 27% 25% 11% 2 1	540
	21st to end	Day	35% 26% 23% 10% 4 2	594
April	1st to 10th	Day	42% 20% 24% 10% 4 1	540
	11th to 20th	Day	38% 25% 21% 10% 4 2	532
	21st to end	Day	34% 24% 26% 10% 4 1	540
May	1st to 10th	Day	38% 23% 23% 10% 4 1	543
	11th to 20th	Day	26% 20% 34% 16% 4 2	567
	21st to end	Day	24% 19% 34% 17% 5% 2	617
June	1st to 10th	Day	26% 19% 32% 17% 6% 1	570
	11th to 20th	Day	27% 15% 33% 17% 8%	570
	21st to end	Day	25% 19% 32% 18% 4 1	570
July	1st to 10th	Day	20% 13% 36% 20% 8% 2	565
	11th to 20th	Day	15% 15% 39% 24% 7% 1	564
	21st to end	Day	19% 12% 38% 22% 6% 2	620
August	1st to 10th	Day	17% 13% 29% 27% 11% 3	566
	11th to 20th	Day	19% 15% 28% 21% 11% 6%	559
	21st to end	Day	18% 15% 28% 23% 11% 5%	627
September	1st to 10th	Day	19% 15% 28% 22% 11% 5%	570
	11th to 20th	Day	19% 14% 23% 19% 18% 8%	570
	21st to end	Day	22% 15% 30% 18% 11% 5%	570
October	1st to 10th	Day	29% 13% 27% 18% 11% 2	570
	11th to 20th	Day	29% 19% 26% 17% 9%	540
	21st to end	Day	34% 20% 26% 15% 5% 1	486
November	1st to 10th	Day	31% 22% 24% 15% 7% 1	425
	11th to 20th	Day	29% 27% 25% 13% 5% 1	430
	21st to end	Day	35% 27% 28% 9% 1 1	278
December	1st to 10th	Day	32% 32% 25% 8% 2	220
	11th to 20th	Day	41% 29% 22% 6% 1	220
	21st to end	Day	35% 25% 26% 10% 3	242
January	1st to 10th	Night	25% 30% 30% 14% 2	840
	11th to 20th	Night	31% 25% 25% 16% 2	840
	21st to end	Night	21% 27% 30% 18% 3	924
February	1st to 10th	Night	24% 26% 34% 15% 2	840
	11th to 20th	Night	24% 30% 28% 17% 2	823
	21st to end	Night	26% 25% 32% 15% 2	692
March	1st to 10th	Night	27% 24% 30% 17% 3	840
	11th to 20th	Night	31% 23% 26% 15% 4	840
	21st to end	Night	31% 21% 26% 16% 6%	924
April	1st to 10th	Night	31% 21% 25% 19% 4	840
	11th to 20th	Night	30% 23% 24% 16% 7%	831
	21st to end	Night	30% 19% 24% 20% 5% 1	677
May	1st to 10th	Night	32% 15% 27% 19% 7%	619
	11th to 20th	Night	21% 16% 29% 27% 6% 1	414
	21st to end	Night	22% 11% 26% 31% 10% 1	455
June	1st to 10th	Night	22% 9% 27% 29% 12%	420
	11th to 20th	Night	26% 9% 21% 32% 12% 1	420
	21st to end	Night	22% 8% 25% 34% 11% 1	420
July	1st to 10th	Night	18% 5% 21% 42% 12% 2	410
	11th to 20th	Night	18% 4 24% 37% 16% 1	408
	21st to end	Night	15% 4 28% 36% 17%	460
August	1st to 10th	Night	19% 5% 17% 38% 21%	419
	11th to 20th	Night	20% 7% 21% 33% 17% 3	735
	21st to end	Night	19% 6% 21% 32% 20% 2	924
September	1st to 10th	Night	21% 9% 22% 30% 16% 2	840
	11th to 20th	Night	19% 9% 19% 28% 21% 4	840
	21st to end	Night	22% 11% 23% 27% 15% 2	840
October	1st to 10th	Night	28% 13% 19% 24% 14% 2	840
	11th to 20th	Night	26% 16% 24% 23% 10% 1	840
	21st to end	Night	30% 19% 24% 19% 6%	913
November	1st to 10th	Night	28% 20% 26% 18% 7%	820
	11th to 20th	Night	27% 23% 25% 17% 7% 1	840
	21st to end	Night	28% 28% 23% 15% 5% 1	840
December	1st to 10th	Night	32% 26% 24% 14% 3	840
	11th to 20th	Night	31% 27% 23% 16% 3	840
	21st to end	Night	31% 25% 26% 15% 3	924

Page generated at 2026-10-26 04:37:48. Version ac07

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