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 2024-11-12.

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	14% 6% 2 6% 4 4 4 4 6% 8% 42%	101200
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	97918
Transparency	Day	38% 7% 13% 23% 16% 3	104831
	Night	39% 6% 12% 23% 17% 3	102427
Seeing	Day	18% 14% 29% 23% 12% 4	15182
	Night	17% 11% 29% 30% 12% 1	24573

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	15% 7% 2 6% 3 2 3 3 4 6% 49%	2517
	11th to 20th	Day	15% 8% 2 8% 5% 4 3 3 4 6% 42%	2758
	21st to end	Day	17% 11% 3 8% 4 4 4 3 4 4 37%	3124
February	1st to 10th	Day	14% 7% 3 6% 5% 4 5% 4 6% 7% 39%	1710
	11th to 20th	Day	19% 7% 2 4 3 3 4 3 5% 6% 44%	1825
	21st to end	Day	18% 9% 3 6% 5% 4 4 3 6% 5% 38%	1570
March	1st to 10th	Day	23% 9% 2 5% 4 3 3 3 4 7% 37%	3197
	11th to 20th	Day	10% 5% 1 4 2 3 3 3 6% 8% 54%	3480
	21st to end	Day	19% 8% 2 6% 4 4 3 3 4 6% 41%	4002
April	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 5% 7% 48%	2280
	11th to 20th	Day	11% 5% 2 5% 4 3 4 4 5% 7% 49%	2254
	21st to end	Day	14% 7% 3 6% 3 3 3 3 5% 7% 46%	2280
May	1st to 10th	Day	20% 9% 3 7% 4 4 4 3 6% 9% 31%	3819
	11th to 20th	Day	21% 9% 2 7% 5% 5% 5% 4 5% 6% 32%	4386
	21st to end	Day	10% 4 2 6% 4 4 4 4 7% 10% 45%	4823
June	1st to 10th	Day	11% 5% 2 5% 5% 4 5% 5% 7% 9% 42%	2660
	11th to 20th	Day	10% 6% 2 4 4 4 4 3 7% 10% 45%	2660
	21st to end	Day	9% 5% 2 5% 4 5% 5% 4 7% 10% 44%	2660
July	1st to 10th	Day	7% 4 2 5% 4 5% 6% 5% 8% 12% 42%	4440
	11th to 20th	Day	11% 5% 2 7% 5% 5% 5% 5% 8% 11% 37%	4440
	21st to end	Day	10% 5% 3 7% 7% 6% 6% 6% 8% 9% 34%	4515
August	1st to 10th	Day	15% 7% 2 6% 4 5% 6% 5% 8% 11% 31%	4056
	11th to 20th	Day	9% 6% 2 7% 6% 5% 6% 5% 7% 10% 37%	3730
	21st to end	Day	8% 5% 2 5% 4 5% 5% 4 7% 9% 46%	4180
September	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 4 5% 7% 43%	2280
	11th to 20th	Day	12% 6% 2 6% 4 5% 4 3 5% 7% 45%	2263
	21st to end	Day	20% 7% 3 7% 4 4 4 3 5% 5% 38%	2075
October	1st to 10th	Day	16% 5% 2 6% 4 4 4 3 5% 6% 44%	1900
	11th to 20th	Day	17% 5% 2 5% 3 3 3 2 4 5% 51%	1900
	21st to end	Day	14% 6% 2 5% 4 3 3 3 5% 5% 49%	2090
November	1st to 10th	Day	13% 5% 1 5% 4 3 4 3 5% 6% 52%	1761
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 6% 48%	1719
	21st to end	Day	16% 4 3 5% 5% 3 3 3 4 6% 48%	1644
December	1st to 10th	Day	16% 7% 2 6% 4 4 3 4 6% 7% 41%	1520
	11th to 20th	Day	16% 8% 2 6% 4 4 3 2 4 5% 47%	1910
	21st to end	Day	16% 6% 2 5% 4 4 4 4 6% 6% 43%	2772
January	1st to 10th	Night	14% 9% 3 4 3 3 4 3 5% 6% 45%	4429
	11th to 20th	Night	17% 8% 2 6% 4 4 3 3 3 5% 45%	4186
	21st to end	Night	19% 9% 3 6% 4 4 4 2 4 4 41%	4532
February	1st to 10th	Night	16% 8% 2 5% 4 3 4 3 6% 6% 43%	2470
	11th to 20th	Night	19% 8% 2 5% 4 3 4 3 5% 6% 42%	2239
	21st to end	Night	18% 7% 2 5% 2 4 3 3 5% 6% 45%	1884
March	1st to 10th	Night	23% 10% 3 6% 4 3 3 3 4 5% 36%	3652
	11th to 20th	Night	14% 6% 2 5% 3 4 3 3 5% 7% 47%	3480
	21st to end	Night	18% 10% 3 6% 4 3 3 2 4 5% 44%	3629
April	1st to 10th	Night	16% 7% 2 6% 4 4 4 4 5% 6% 41%	1900
	11th to 20th	Night	12% 5% 3 6% 4 3 4 4 4 7% 48%	1875
	21st to end	Night	17% 6% 1 6% 4 4 5% 4 5% 7% 42%	1900
May	1st to 10th	Night	17% 8% 3 8% 5% 5% 4 4 6% 8% 31%	3074
	11th to 20th	Night	23% 10% 2 6% 4 4 4 4 5% 6% 33%	2536
	21st to end	Night	11% 6% 3 6% 5% 5% 4 4 5% 8% 42%	2732
June	1st to 10th	Night	11% 6% 2 6% 4 4 5% 5% 7% 8% 42%	1520
	11th to 20th	Night	8% 5% 2 6% 6% 5% 5% 4 6% 10% 42%	1520
	21st to end	Night	8% 5% 2 5% 5% 5% 5% 6% 7% 11% 40%	1520
July	1st to 10th	Night	8% 5% 2 8% 5% 6% 6% 5% 7% 10% 38%	2520
	11th to 20th	Night	10% 6% 2 6% 6% 5% 5% 5% 7% 11% 39%	2520
	21st to end	Night	14% 9% 3 7% 5% 5% 5% 4 6% 8% 34%	3020
August	1st to 10th	Night	18% 8% 3 7% 4 4 4 4 6% 9% 33%	2843
	11th to 20th	Night	10% 6% 3 7% 4 5% 4 4 6% 9% 41%	3097
	21st to end	Night	8% 5% 2 5% 4 3 3 3 5% 8% 53%	3476
September	1st to 10th	Night	13% 8% 2 5% 4 3 4 3 5% 7% 46%	1900
	11th to 20th	Night	11% 5% 2 5% 3 3 4 4 6% 8% 50%	1915
	21st to end	Night	19% 7% 3 6% 4 4 4 4 6% 6% 38%	2101
October	1st to 10th	Night	16% 6% 2 6% 3 3 4 4 4 6% 45%	2280
	11th to 20th	Night	16% 5% 2 4 3 3 3 3 4 5% 51%	2280
	21st to end	Night	16% 6% 2 5% 2 3 4 3 4 6% 49%	2508
November	1st to 10th	Night	12% 6% 2 6% 4 3 3 3 5% 6% 51%	2535
	11th to 20th	Night	16% 7% 2 5% 3 4 2 3 4 6% 48%	2484
	21st to end	Night	13% 5% 2 4 5% 4 3 3 5% 7% 50%	2532
December	1st to 10th	Night	17% 9% 3 6% 4 4 4 3 5% 6% 39%	2660
	11th to 20th	Night	18% 6% 2 6% 4 3 4 3 4 7% 43%	3285
	21st to end	Night	15% 7% 2 7% 4 4 4 4 5% 7% 40%	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	37% 4 9% 30% 17% 3	2518
	11th to 20th	Day	44% 4 11% 20% 17% 4	2758
	21st to end	Day	50% 6% 9% 21% 12% 2	3124
February	1st to 10th	Day	42% 7% 12% 25% 12% 2	1710
	11th to 20th	Day	41% 4 9% 24% 18% 4	1834
	21st to end	Day	47% 5% 12% 17% 15% 4	1570
March	1st to 10th	Day	47% 5% 9% 21% 15% 3	3197
	11th to 20th	Day	26% 5% 11% 31% 23% 4	3480
	21st to end	Day	46% 4 8% 19% 18% 5%	4002
April	1st to 10th	Day	36% 6% 12% 23% 18% 5%	2280
	11th to 20th	Day	33% 7% 11% 24% 19% 6%	2254
	21st to end	Day	38% 5% 12% 21% 18% 5%	2280
May	1st to 10th	Day	49% 9% 13% 19% 9% 2	3854
	11th to 20th	Day	50% 9% 13% 18% 9% 1	4390
	21st to end	Day	31% 10% 15% 24% 17% 3	4837
June	1st to 10th	Day	35% 9% 16% 24% 14% 2	2660
	11th to 20th	Day	32% 10% 16% 25% 15% 3	2660
	21st to end	Day	32% 8% 17% 24% 17% 2	2660
July	1st to 10th	Day	31% 12% 24% 18% 12% 3	4370
	11th to 20th	Day	38% 9% 21% 25% 6% 1	4365
	21st to end	Day	41% 11% 15% 19% 13% 1	4371
August	1st to 10th	Day	43% 8% 18% 24% 7%	4043
	11th to 20th	Day	38% 8% 15% 27% 11% 1	3766
	21st to end	Day	32% 9% 13% 26% 18% 2	4180
September	1st to 10th	Day	39% 8% 15% 17% 17% 4	2280
	11th to 20th	Day	38% 5% 11% 22% 20% 3	2263
	21st to end	Day	47% 6% 8% 18% 17% 3	2075
October	1st to 10th	Day	36% 5% 9% 20% 24% 6%	3160
	11th to 20th	Day	28% 3 6% 24% 30% 9%	3140
	21st to end	Day	24% 4 9% 30% 25% 9%	3428
November	1st to 10th	Day	33% 4 10% 28% 20% 4	1761
	11th to 20th	Day	37% 5% 11% 22% 21% 4	1719
	21st to end	Day	38% 4 10% 29% 16% 4	1644
December	1st to 10th	Day	43% 6% 14% 23% 12% 3	1520
	11th to 20th	Day	41% 4 9% 29% 14% 4	1906
	21st to end	Day	39% 7% 16% 25% 13%	2772
January	1st to 10th	Night	39% 5% 9% 25% 18% 4	4429
	11th to 20th	Night	43% 5% 10% 25% 16% 2	4186
	21st to end	Night	47% 5% 7% 26% 14% 2	4532
February	1st to 10th	Night	41% 5% 12% 24% 16% 2	2470
	11th to 20th	Night	43% 5% 8% 21% 19% 5%	2241
	21st to end	Night	41% 4 10% 22% 18% 4	1884
March	1st to 10th	Night	50% 5% 10% 20% 14% 2	3652
	11th to 20th	Night	34% 6% 9% 28% 19% 4	3480
	21st to end	Night	43% 4 8% 20% 19% 6%	3629
April	1st to 10th	Night	42% 6% 11% 18% 19% 4	1900
	11th to 20th	Night	35% 6% 13% 20% 20% 6%	1875
	21st to end	Night	40% 6% 12% 22% 17% 3	1900
May	1st to 10th	Night	50% 9% 12% 21% 8% 2	3104
	11th to 20th	Night	50% 9% 12% 19% 9% 1	2537
	21st to end	Night	37% 9% 17% 20% 14% 2	2739
June	1st to 10th	Night	38% 9% 13% 22% 16% 1	1520
	11th to 20th	Night	36% 8% 15% 24% 15% 2	1520
	21st to end	Night	35% 10% 16% 22% 15% 2	1520
July	1st to 10th	Night	38% 12% 18% 20% 10% 2	2480
	11th to 20th	Night	37% 10% 22% 23% 7% 1	2472
	21st to end	Night	46% 8% 15% 18% 13%	2924
August	1st to 10th	Night	47% 7% 16% 21% 8%	2832
	11th to 20th	Night	38% 9% 16% 27% 10%	3127
	21st to end	Night	29% 7% 12% 25% 25% 2	3476
September	1st to 10th	Night	37% 6% 15% 21% 16% 4	1900
	11th to 20th	Night	31% 6% 12% 27% 20% 3	1915
	21st to end	Night	46% 8% 10% 17% 16% 3	2101
October	1st to 10th	Night	34% 5% 11% 23% 23% 4	3800
	11th to 20th	Night	24% 4 10% 22% 30% 9%	3779
	21st to end	Night	23% 3 10% 29% 26% 9%	4120
November	1st to 10th	Night	35% 5% 9% 26% 19% 5%	2535
	11th to 20th	Night	40% 4 9% 20% 21% 5%	2484
	21st to end	Night	34% 5% 11% 25% 21% 4	2532
December	1st to 10th	Night	44% 5% 11% 23% 13% 3	2660
	11th to 20th	Night	42% 5% 9% 23% 19% 3	3288
	21st to end	Night	42% 6% 16% 24% 11% 1	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	27% 24% 33% 12% 4 1	180
	11th to 20th	Day	29% 33% 23% 12% 2	249
	21st to end	Day	25% 24% 35% 13% 2	297
February	1st to 10th	Day	23% 30% 33% 11% 4	270
	11th to 20th	Day	31% 22% 33% 11% 2	433
	21st to end	Day	30% 23% 31% 12% 3	382
March	1st to 10th	Day	27% 21% 30% 18% 4	460
	11th to 20th	Day	26% 23% 29% 17% 3 2	460
	21st to end	Day	22% 21% 37% 15% 5% 1	506
April	1st to 10th	Day	21% 25% 33% 15% 6% 1	460
	11th to 20th	Day	17% 17% 37% 20% 7% 2	452
	21st to end	Day	23% 16% 35% 18% 7% 1	460
May	1st to 10th	Day	24% 17% 34% 15% 7% 2	463
	11th to 20th	Day	19% 14% 36% 22% 7% 2	487
	21st to end	Day	16% 10% 27% 29% 14% 5%	529
June	1st to 10th	Day	13% 12% 29% 30% 13% 3	490
	11th to 20th	Day	10% 11% 29% 29% 15% 5%	490
	21st to end	Day	11% 8% 29% 36% 13% 4	490
July	1st to 10th	Day	12% 4 23% 36% 18% 7%	485
	11th to 20th	Day	4 2 25% 36% 25% 7%	484
	21st to end	Day	9% 5% 27% 34% 18% 7%	532
August	1st to 10th	Day	13% 4 22% 32% 21% 8%	486
	11th to 20th	Day	9% 5% 22% 34% 23% 7%	479
	21st to end	Day	8% 5% 25% 27% 24% 11%	539
September	1st to 10th	Day	13% 6% 25% 25% 17% 13%	490
	11th to 20th	Day	12% 7% 26% 29% 18% 9%	490
	21st to end	Day	24% 12% 28% 21% 10% 4	490
October	1st to 10th	Day	20% 8% 26% 24% 13% 8%	490
	11th to 20th	Day	18% 13% 29% 23% 14% 2	490
	21st to end	Day	17% 14% 34% 21% 12% 3	539
November	1st to 10th	Day	17% 13% 29% 23% 13% 4	395
	11th to 20th	Day	19% 19% 31% 21% 9% 1	373
	21st to end	Day	22% 19% 25% 22% 9% 3	304
December	1st to 10th	Day	27% 22% 33% 12% 6% 1	180
	11th to 20th	Day	28% 22% 29% 13% 7%	180
	21st to end	Day	22% 24% 27% 18% 9%	198
January	1st to 10th	Night	20% 19% 34% 23% 4	760
	11th to 20th	Night	21% 16% 33% 25% 4	760
	21st to end	Night	20% 18% 36% 24% 2	836
February	1st to 10th	Night	20% 15% 36% 25% 3	760
	11th to 20th	Night	23% 23% 34% 18% 2	743
	21st to end	Night	22% 19% 36% 19% 4	628
March	1st to 10th	Night	21% 17% 34% 22% 5%	760
	11th to 20th	Night	23% 18% 34% 19% 5% 1	760
	21st to end	Night	20% 16% 35% 25% 4	836
April	1st to 10th	Night	21% 16% 40% 19% 4	760
	11th to 20th	Night	15% 15% 36% 29% 5%	751
	21st to end	Night	20% 10% 36% 28% 6%	760
May	1st to 10th	Night	18% 12% 37% 25% 6% 1	730
	11th to 20th	Night	16% 7% 32% 37% 7%	402
	21st to end	Night	13% 4 25% 39% 17% 1	411
June	1st to 10th	Night	12% 5% 26% 45% 11% 1	380
	11th to 20th	Night	8% 2 27% 45% 17% 1	380
	21st to end	Night	8% 1 27% 45% 18%	380
July	1st to 10th	Night	10% 2 20% 45% 22% 2	370
	11th to 20th	Night	6% 2 14% 49% 29% 1	368
	21st to end	Night	7% 2 17% 44% 28% 2	583
August	1st to 10th	Night	9% 3 13% 44% 28% 3	572
	11th to 20th	Night	11% 4 16% 41% 25% 3	750
	21st to end	Night	9% 4 15% 39% 29% 4	836
September	1st to 10th	Night	16% 3 17% 36% 24% 4	760
	11th to 20th	Night	12% 3 18% 36% 27% 4	760
	21st to end	Night	23% 6% 22% 32% 16% 2	760
October	1st to 10th	Night	19% 5% 22% 32% 17% 5%	760
	11th to 20th	Night	18% 11% 23% 31% 16% 1	760
	21st to end	Night	19% 11% 29% 27% 13% 2	836
November	1st to 10th	Night	16% 8% 32% 29% 13% 3	780
	11th to 20th	Night	18% 14% 29% 30% 8% 1	765
	21st to end	Night	17% 13% 29% 29% 11% 1	760
December	1st to 10th	Night	23% 14% 33% 21% 8% 1	760
	11th to 20th	Night	20% 15% 36% 24% 6%	760
	21st to end	Night	18% 15% 33% 30% 5%	836

Page generated at 2024-11-08 22:45:38. Version ac07

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