Salisbury
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salisbury clear sky chart from 2005-11-06 to 2026-01-02.

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%	127085
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 44%	124279
Transparency	Day	38% 7% 13% 23% 16% 3	130672
	Night	38% 6% 12% 23% 18% 4	128762
Seeing	Day	19% 14% 29% 22% 11% 4	16609
	Night	18% 11% 29% 30% 11% 1	26071

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	14% 5% 1 5% 3 2 3 3 4 6% 53%	3605
	11th to 20th	Day	13% 7% 3 8% 5% 4 3 2 3 4 48%	3950
	21st to end	Day	14% 9% 3 7% 4 4 4 3 4 5% 43%	4466
February	1st to 10th	Day	14% 7% 3 6% 5% 4 5% 4 6% 7% 39%	1800
	11th to 20th	Day	20% 7% 2 4 3 3 4 3 5% 6% 43%	1924
	21st to end	Day	17% 9% 3 5% 5% 3 4 3 5% 5% 40%	1650
March	1st to 10th	Day	19% 7% 1 5% 4 3 4 3 5% 7% 43%	4585
	11th to 20th	Day	9% 6% 2 5% 3 3 3 3 5% 7% 53%	4980
	21st to end	Day	15% 7% 2 7% 4 4 3 3 4 6% 43%	5736
April	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 5% 7% 47%	2400
	11th to 20th	Day	11% 6% 2 5% 4 3 4 4 5% 7% 48%	2374
	21st to end	Day	14% 7% 3 6% 3 3 3 3 5% 7% 46%	2400
May	1st to 10th	Day	18% 8% 3 7% 4 4 4 4 6% 9% 34%	5487
	11th to 20th	Day	19% 7% 2 7% 4 4 5% 4 5% 8% 33%	6306
	21st to end	Day	15% 5% 2 6% 4 4 4 4 6% 9% 39%	6934
June	1st to 10th	Day	11% 5% 2 5% 5% 4 5% 5% 7% 9% 42%	2800
	11th to 20th	Day	11% 6% 2 4 4 4 4 3 7% 10% 45%	2800
	21st to end	Day	8% 5% 2 5% 4 5% 5% 4 7% 10% 45%	2800
July	1st to 10th	Day	8% 4 2 5% 4 4 5% 5% 7% 12% 43%	6360
	11th to 20th	Day	12% 6% 3 7% 5% 6% 6% 5% 9% 12% 30%	6360
	21st to end	Day	8% 4 2 6% 6% 5% 6% 5% 8% 11% 38%	6501
August	1st to 10th	Day	15% 7% 2 6% 4 5% 6% 5% 8% 11% 32%	4184
	11th to 20th	Day	9% 6% 2 7% 6% 5% 6% 5% 7% 10% 37%	3850
	21st to end	Day	8% 5% 2 5% 4 5% 5% 4 7% 9% 46%	4312
September	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 4 5% 7% 43%	2400
	11th to 20th	Day	12% 6% 3 6% 4 4 4 3 5% 7% 44%	2382
	21st to end	Day	20% 7% 3 7% 4 4 4 3 5% 6% 37%	2184
October	1st to 10th	Day	15% 5% 2 6% 4 4 4 3 5% 6% 45%	2000
	11th to 20th	Day	17% 5% 2 5% 3 3 3 2 4 5% 51%	2000
	21st to end	Day	14% 6% 2 5% 4 3 3 3 5% 5% 49%	2200
November	1st to 10th	Day	13% 5% 1 5% 4 3 3 3 5% 6% 52%	1851
	11th to 20th	Day	12% 6% 2 5% 4 4 4 3 5% 7% 48%	1890
	21st to end	Day	16% 4 3 5% 4 3 3 3 5% 6% 48%	1816
December	1st to 10th	Day	12% 5% 2 6% 4 4 3 3 5% 6% 50%	2680
	11th to 20th	Day	19% 8% 3 6% 3 3 3 2 3 5% 46%	3070
	21st to end	Day	12% 6% 2 5% 4 4 4 4 5% 7% 47%	4048
January	1st to 10th	Night	13% 8% 2 4 3 3 3 3 4 5% 51%	6364
	11th to 20th	Night	13% 7% 2 6% 4 3 3 2 3 4 52%	5994
	21st to end	Night	15% 8% 2 6% 3 3 4 3 4 5% 47%	6490
February	1st to 10th	Night	17% 8% 2 5% 4 3 4 3 6% 6% 42%	2600
	11th to 20th	Night	20% 8% 2 4 4 3 4 3 5% 6% 42%	2360
	21st to end	Night	18% 7% 2 5% 3 4 3 3 5% 6% 45%	1980
March	1st to 10th	Night	18% 8% 2 5% 3 3 3 3 4 5% 46%	5264
	11th to 20th	Night	13% 8% 2 5% 4 4 3 3 5% 7% 47%	4980
	21st to end	Night	15% 9% 2 6% 4 3 4 3 5% 6% 44%	5195
April	1st to 10th	Night	16% 7% 2 6% 4 4 4 4 5% 6% 40%	2000
	11th to 20th	Night	13% 5% 3 6% 4 3 4 4 4 7% 48%	1975
	21st to end	Night	16% 6% 1 6% 4 4 5% 4 5% 7% 43%	2000
May	1st to 10th	Night	15% 8% 3 8% 5% 5% 5% 4 7% 9% 31%	4406
	11th to 20th	Night	20% 10% 2 6% 4 4 4 3 6% 7% 33%	3630
	21st to end	Night	17% 7% 3 7% 4 5% 4 4 5% 7% 37%	3920
June	1st to 10th	Night	11% 7% 2 6% 4 4 5% 5% 7% 8% 42%	1600
	11th to 20th	Night	9% 6% 2 6% 6% 5% 6% 4 6% 10% 41%	1600
	21st to end	Night	7% 5% 2 5% 5% 5% 5% 6% 7% 12% 41%	1600
July	1st to 10th	Night	10% 5% 2 8% 5% 5% 5% 5% 7% 11% 36%	3598
	11th to 20th	Night	11% 6% 3 7% 6% 6% 5% 5% 8% 11% 32%	3597
	21st to end	Night	11% 7% 2 7% 5% 5% 5% 5% 6% 9% 39%	4332
August	1st to 10th	Night	18% 8% 3 7% 4 4 4 4 6% 9% 34%	2933
	11th to 20th	Night	10% 6% 3 7% 4 5% 4 4 6% 9% 41%	3197
	21st to end	Night	8% 5% 2 5% 4 3 3 3 5% 8% 53%	3586
September	1st to 10th	Night	13% 8% 2 5% 4 3 3 3 5% 7% 47%	2000
	11th to 20th	Night	12% 5% 2 5% 3 3 4 4 5% 8% 49%	2016
	21st to end	Night	19% 8% 3 6% 4 4 4 4 6% 6% 37%	2212
October	1st to 10th	Night	16% 6% 2 6% 3 3 4 4 4 6% 46%	2400
	11th to 20th	Night	17% 5% 2 4 3 3 3 3 4 5% 51%	2400
	21st to end	Night	16% 6% 2 5% 2 3 4 3 4 6% 49%	2640
November	1st to 10th	Night	12% 5% 2 6% 4 3 3 3 5% 6% 51%	2665
	11th to 20th	Night	15% 7% 2 5% 3 4 3 3 4 6% 48%	2730
	21st to end	Night	12% 5% 2 4 5% 4 3 3 5% 7% 50%	2800
December	1st to 10th	Night	10% 7% 2 5% 3 3 3 3 5% 6% 52%	4720
	11th to 20th	Night	20% 7% 3 6% 4 3 4 3 4 6% 39%	5345
	21st to end	Night	14% 7% 3 7% 4 3 4 3 5% 7% 43%	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	33% 3 7% 26% 27% 4	3606
	11th to 20th	Day	41% 3 8% 21% 22% 6%	3950
	21st to end	Day	44% 5% 9% 27% 13% 2	4466
February	1st to 10th	Day	42% 7% 12% 24% 13% 2	1800
	11th to 20th	Day	42% 4 9% 23% 18% 4	1933
	21st to end	Day	45% 5% 12% 18% 16% 4	1650
March	1st to 10th	Day	40% 5% 9% 21% 20% 6%	4585
	11th to 20th	Day	30% 5% 11% 27% 21% 6%	4980
	21st to end	Day	42% 4 9% 17% 20% 8%	5736
April	1st to 10th	Day	37% 6% 12% 22% 18% 5%	2400
	11th to 20th	Day	33% 7% 11% 23% 19% 6%	2374
	21st to end	Day	37% 5% 12% 22% 18% 5%	2400
May	1st to 10th	Day	46% 9% 15% 18% 11% 1	5519
	11th to 20th	Day	46% 9% 12% 21% 11% 1	6310
	21st to end	Day	39% 9% 14% 22% 14% 2	6949
June	1st to 10th	Day	36% 8% 15% 23% 15% 2	2800
	11th to 20th	Day	33% 9% 16% 24% 15% 3	2800
	21st to end	Day	32% 8% 17% 24% 17% 2	2800
July	1st to 10th	Day	31% 11% 23% 20% 13% 2	6290
	11th to 20th	Day	43% 11% 20% 20% 5% 1	6285
	21st to end	Day	36% 11% 15% 21% 17% 1	6315
August	1st to 10th	Day	43% 8% 18% 24% 7%	4171
	11th to 20th	Day	39% 9% 15% 27% 10% 1	3886
	21st to end	Day	32% 9% 13% 27% 18% 2	4312
September	1st to 10th	Day	39% 8% 15% 18% 17% 4	2400
	11th to 20th	Day	39% 5% 11% 22% 20% 3	2382
	21st to end	Day	48% 6% 9% 18% 16% 3	2184
October	1st to 10th	Day	35% 5% 9% 21% 24% 6%	3260
	11th to 20th	Day	28% 3 6% 24% 29% 9%	3240
	21st to end	Day	24% 4 8% 29% 25% 9%	3538
November	1st to 10th	Day	33% 4 10% 29% 20% 4	1851
	11th to 20th	Day	36% 5% 11% 22% 21% 4	1890
	21st to end	Day	37% 4 9% 29% 17% 3	1816
December	1st to 10th	Day	35% 5% 14% 27% 17% 4	2680
	11th to 20th	Day	43% 3 12% 25% 14% 3	3066
	21st to end	Day	35% 6% 16% 25% 17% 1	4048
January	1st to 10th	Night	35% 4 7% 23% 25% 6%	6364
	11th to 20th	Night	37% 4 8% 26% 21% 5%	5994
	21st to end	Night	40% 4 8% 29% 16% 2	6490
February	1st to 10th	Night	41% 5% 13% 24% 15% 2	2600
	11th to 20th	Night	44% 4 8% 21% 18% 5%	2362
	21st to end	Night	41% 5% 9% 22% 18% 5%	1980
March	1st to 10th	Night	41% 4 8% 21% 16% 9%	5264
	11th to 20th	Night	36% 6% 10% 23% 20% 6%	4980
	21st to end	Night	41% 5% 10% 20% 19% 6%	5195
April	1st to 10th	Night	43% 7% 11% 18% 18% 5%	2000
	11th to 20th	Night	36% 6% 12% 20% 20% 6%	1975
	21st to end	Night	39% 6% 12% 21% 18% 4	2000
May	1st to 10th	Night	47% 8% 15% 20% 8% 2	4436
	11th to 20th	Night	48% 8% 13% 19% 11% 1	3631
	21st to end	Night	44% 8% 14% 20% 12% 1	3927
June	1st to 10th	Night	38% 9% 13% 22% 16% 2	1600
	11th to 20th	Night	38% 8% 15% 24% 14% 2	1600
	21st to end	Night	34% 10% 16% 22% 16% 2	1600
July	1st to 10th	Night	40% 11% 17% 18% 12% 2	3560
	11th to 20th	Night	42% 12% 22% 19% 5%	3552
	21st to end	Night	39% 9% 15% 21% 17%	4205
August	1st to 10th	Night	47% 7% 16% 21% 8%	2922
	11th to 20th	Night	38% 9% 16% 27% 11%	3227
	21st to end	Night	30% 7% 12% 25% 25% 2	3586
September	1st to 10th	Night	37% 6% 15% 22% 16% 4	2000
	11th to 20th	Night	32% 6% 12% 28% 20% 3	2016
	21st to end	Night	46% 7% 11% 17% 15% 3	2212
October	1st to 10th	Night	34% 5% 11% 23% 23% 4	3920
	11th to 20th	Night	25% 4 10% 22% 30% 9%	3899
	21st to end	Night	23% 3 10% 29% 26% 9%	4252
November	1st to 10th	Night	35% 5% 9% 26% 20% 5%	2665
	11th to 20th	Night	39% 4 10% 21% 21% 6%	2730
	21st to end	Night	34% 5% 11% 25% 21% 3	2800
December	1st to 10th	Night	33% 4 13% 26% 21% 3	4720
	11th to 20th	Night	46% 5% 11% 21% 14% 4	5348
	21st to end	Night	40% 5% 15% 23% 16% 1	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	30% 25% 30% 11% 4	202
	11th to 20th	Day	30% 32% 24% 12% 2	277
	21st to end	Day	25% 25% 35% 13% 2	330
February	1st to 10th	Day	24% 31% 31% 10% 3	300
	11th to 20th	Day	35% 22% 31% 10% 2	472
	21st to end	Day	29% 24% 31% 12% 3	414
March	1st to 10th	Day	27% 21% 30% 17% 4	500
	11th to 20th	Day	25% 23% 29% 16% 4 2	500
	21st to end	Day	22% 22% 37% 13% 5% 1	550
April	1st to 10th	Day	22% 25% 33% 14% 5% 1	500
	11th to 20th	Day	18% 18% 36% 19% 6% 2	492
	21st to end	Day	22% 16% 36% 17% 8% 1	500
May	1st to 10th	Day	24% 19% 33% 15% 7% 2	503
	11th to 20th	Day	19% 15% 37% 21% 7% 2	527
	21st to end	Day	18% 11% 27% 27% 13% 4	573
June	1st to 10th	Day	13% 12% 29% 29% 13% 3	530
	11th to 20th	Day	10% 12% 29% 30% 14% 5%	530
	21st to end	Day	10% 8% 28% 35% 15% 4	530
July	1st to 10th	Day	13% 4 23% 36% 18% 7%	525
	11th to 20th	Day	4 2 25% 36% 25% 7%	524
	21st to end	Day	9% 4 26% 36% 19% 7%	576
August	1st to 10th	Day	13% 4 23% 31% 21% 8%	526
	11th to 20th	Day	10% 4 21% 34% 23% 7%	519
	21st to end	Day	8% 5% 27% 27% 22% 10%	583
September	1st to 10th	Day	14% 7% 26% 25% 16% 12%	530
	11th to 20th	Day	12% 7% 26% 29% 18% 8%	530
	21st to end	Day	25% 11% 29% 21% 9% 5%	530
October	1st to 10th	Day	20% 7% 26% 25% 13% 9%	530
	11th to 20th	Day	21% 13% 29% 21% 14% 2	530
	21st to end	Day	18% 15% 33% 20% 11% 3	583
November	1st to 10th	Day	19% 15% 29% 21% 13% 3	425
	11th to 20th	Day	21% 18% 32% 20% 8% 1	430
	21st to end	Day	24% 19% 25% 21% 8% 3	356
December	1st to 10th	Day	27% 21% 35% 11% 5%	220
	11th to 20th	Day	30% 20% 31% 13% 6%	220
	21st to end	Day	24% 23% 28% 17% 8%	242
January	1st to 10th	Night	21% 20% 33% 21% 4	805
	11th to 20th	Night	21% 16% 33% 25% 4	800
	21st to end	Night	20% 18% 37% 23% 2	880
February	1st to 10th	Night	20% 16% 36% 24% 3	800
	11th to 20th	Night	25% 23% 33% 18% 2	783
	21st to end	Night	22% 19% 37% 19% 3	660
March	1st to 10th	Night	22% 18% 34% 22% 5%	800
	11th to 20th	Night	23% 18% 34% 19% 5% 1	800
	21st to end	Night	20% 17% 35% 24% 4	880
April	1st to 10th	Night	21% 17% 40% 18% 4	800
	11th to 20th	Night	15% 15% 35% 29% 5%	791
	21st to end	Night	20% 10% 36% 28% 7%	800
May	1st to 10th	Night	18% 13% 37% 25% 6% 1	768
	11th to 20th	Night	16% 8% 31% 37% 7%	423
	21st to end	Night	14% 5% 25% 38% 16% 1	433
June	1st to 10th	Night	12% 6% 26% 46% 11% 1	400
	11th to 20th	Night	9% 3 26% 45% 17% 1	400
	21st to end	Night	8% 1 27% 44% 19% 1	400
July	1st to 10th	Night	11% 2 19% 44% 22% 2	390
	11th to 20th	Night	6% 2 14% 47% 29% 1	388
	21st to end	Night	7% 2 16% 44% 28% 3	614
August	1st to 10th	Night	10% 3 13% 43% 27% 3	602
	11th to 20th	Night	12% 4 16% 40% 25% 3	790
	21st to end	Night	9% 4 16% 39% 28% 4	880
September	1st to 10th	Night	16% 4 17% 36% 23% 4	800
	11th to 20th	Night	13% 3 17% 37% 26% 4	800
	21st to end	Night	23% 6% 22% 32% 15% 2	800
October	1st to 10th	Night	19% 5% 21% 32% 17% 6%	800
	11th to 20th	Night	19% 12% 22% 30% 16% 1	800
	21st to end	Night	19% 11% 29% 28% 12% 2	880
November	1st to 10th	Night	16% 8% 32% 29% 12% 3	820
	11th to 20th	Night	18% 15% 30% 29% 7%	840
	21st to end	Night	18% 15% 28% 29% 10% 1	840
December	1st to 10th	Night	23% 14% 34% 21% 8% 1	840
	11th to 20th	Night	21% 15% 34% 24% 5%	840
	21st to end	Night	18% 15% 32% 29% 5%	924

Page generated at 2025-12-30 01:14:11. Version ac07

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