Manchester
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Manchester clear sky chart from 2005-11-06 to 2026-08-15.

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% 7% 2 6% 4 4 4 4 5% 7% 38%	143498
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 40%	138391
Transparency	Day	44% 5% 11% 22% 15% 2	147020
	Night	44% 4 12% 22% 15% 2	142958
Seeing	Day	24% 16% 31% 19% 8% 2	17223
	Night	22% 14% 31% 25% 7%	26043

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% 7% 4 9% 6% 6% 6% 5% 5% 6% 35%	4661
	11th to 20th	Day	14% 8% 3 7% 4 4 4 3 5% 6% 43%	4650
	21st to end	Day	13% 9% 2 6% 4 4 4 3 5% 5% 45%	5124
February	1st to 10th	Day	16% 8% 3 5% 5% 5% 6% 5% 6% 6% 36%	1913
	11th to 20th	Day	13% 8% 2 7% 5% 4 4 5% 5% 8% 39%	2048
	21st to end	Day	16% 10% 3 8% 5% 4 4 3 5% 5% 36%	1730
March	1st to 10th	Day	20% 11% 3 8% 5% 4 4 3 4 5% 33%	4576
	11th to 20th	Day	16% 8% 2 7% 4 4 5% 4 5% 6% 37%	4855
	21st to end	Day	25% 9% 2 6% 4 4 4 3 5% 7% 32%	5929
April	1st to 10th	Day	20% 9% 3 7% 4 4 4 3 4 6% 36%	2520
	11th to 20th	Day	17% 7% 2 6% 5% 4 5% 4 5% 7% 37%	2515
	21st to end	Day	20% 7% 3 8% 5% 4 4 3 5% 5% 36%	2730
May	1st to 10th	Day	28% 9% 2 7% 4 4 4 4 5% 6% 27%	7639
	11th to 20th	Day	19% 7% 3 8% 5% 4 4 4 5% 6% 35%	7881
	21st to end	Day	21% 7% 2 6% 4 4 5% 4 6% 8% 33%	9060
June	1st to 10th	Day	18% 6% 3 7% 5% 5% 5% 4 6% 9% 32%	2940
	11th to 20th	Day	16% 5% 3 7% 5% 5% 5% 4 7% 8% 37%	2940
	21st to end	Day	18% 6% 3 7% 5% 5% 4 4 6% 7% 36%	2940
July	1st to 10th	Day	16% 6% 2 6% 4 5% 5% 4 7% 9% 35%	8280
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 5% 6% 11% 44%	8280
	21st to end	Day	15% 6% 3 6% 4 4 4 4 5% 7% 43%	8993
August	1st to 10th	Day	14% 6% 2 7% 5% 6% 5% 5% 6% 8% 35%	4472
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	4180
	21st to end	Day	8% 5% 2 6% 4 5% 6% 4 7% 10% 44%	4312
September	1st to 10th	Day	13% 5% 1 5% 3 4 4 4 6% 7% 47%	2400
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 4 5% 53%	2205
	21st to end	Day	16% 5% 2 6% 4 4 4 3 4 7% 44%	2200
October	1st to 10th	Day	23% 6% 2 6% 3 3 4 3 4 5% 41%	2200
	11th to 20th	Day	16% 5% 2 5% 4 3 4 3 5% 7% 45%	1931
	21st to end	Day	22% 7% 2 6% 4 4 4 3 4 5% 40%	1980
November	1st to 10th	Day	15% 6% 2 6% 4 3 4 3 4 5% 49%	1851
	11th to 20th	Day	18% 5% 2 5% 3 3 3 4 4 6% 47%	1890
	21st to end	Day	20% 7% 2 5% 3 4 4 3 4 6% 41%	1879
December	1st to 10th	Day	16% 7% 3 6% 4 4 4 3 5% 7% 41%	2680
	11th to 20th	Day	21% 6% 2 5% 3 4 3 3 5% 5% 44%	3066
	21st to end	Day	20% 10% 3 6% 4 4 4 4 5% 5% 36%	4048
January	1st to 10th	Night	14% 7% 3 6% 4 4 4 3 5% 6% 42%	8234
	11th to 20th	Night	14% 10% 3 8% 5% 5% 4 3 5% 6% 36%	8235
	21st to end	Night	13% 10% 3 6% 4 5% 5% 4 5% 6% 40%	9057
February	1st to 10th	Night	15% 9% 3 6% 4 4 4 4 6% 7% 38%	2700
	11th to 20th	Night	13% 9% 2 7% 4 4 5% 4 6% 7% 39%	2458
	21st to end	Night	16% 9% 2 5% 5% 4 4 4 5% 6% 40%	2076
March	1st to 10th	Night	23% 9% 2 5% 4 4 4 3 5% 6% 36%	5484
	11th to 20th	Night	16% 10% 3 7% 5% 4 5% 4 5% 7% 36%	5324
	21st to end	Night	26% 9% 2 4 3 3 4 3 6% 6% 33%	5242
April	1st to 10th	Night	20% 9% 2 6% 5% 4 4 3 4 6% 36%	2100
	11th to 20th	Night	20% 9% 2 5% 4 3 4 3 5% 5% 40%	2054
	21st to end	Night	20% 6% 3 7% 4 3 3 3 4 6% 39%	1890
May	1st to 10th	Night	29% 10% 3 7% 3 4 3 3 5% 6% 27%	5259
	11th to 20th	Night	16% 7% 3 8% 5% 5% 6% 4 6% 7% 33%	5022
	21st to end	Night	22% 7% 2 7% 5% 4 4 4 6% 7% 32%	5114
June	1st to 10th	Night	17% 8% 3 6% 5% 4 4 3 4 7% 39%	1680
	11th to 20th	Night	18% 6% 2 5% 4 4 4 5% 5% 8% 38%	1680
	21st to end	Night	18% 6% 2 6% 4 4 4 4 5% 9% 38%	1680
July	1st to 10th	Night	14% 6% 2 7% 5% 4 5% 3 6% 9% 38%	4680
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 6% 9% 46%	4680
	21st to end	Night	13% 5% 2 6% 3 4 4 3 5% 7% 49%	5084
August	1st to 10th	Night	20% 6% 2 7% 5% 4 5% 4 5% 7% 35%	2865
	11th to 20th	Night	11% 8% 3 7% 5% 5% 6% 4 6% 7% 37%	2939
	21st to end	Night	9% 4 1 5% 3 3 4 3 6% 8% 54%	3586
September	1st to 10th	Night	13% 6% 1 5% 4 4 2 3 6% 6% 50%	2000
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 5% 6% 53%	2195
	21st to end	Night	16% 5% 3 5% 3 3 3 3 5% 7% 47%	2200
October	1st to 10th	Night	20% 6% 2 6% 4 4 4 2 4 6% 42%	2200
	11th to 20th	Night	16% 5% 2 5% 4 4 4 4 6% 7% 44%	2462
	21st to end	Night	22% 6% 2 6% 4 3 3 3 5% 6% 39%	2860
November	1st to 10th	Night	16% 6% 2 5% 4 3 4 4 4 5% 46%	2667
	11th to 20th	Night	16% 7% 2 5% 4 4 3 3 5% 6% 47%	2730
	21st to end	Night	16% 8% 3 5% 5% 3 4 4 5% 6% 43%	2736
December	1st to 10th	Night	16% 10% 3 6% 4 4 4 3 5% 6% 39%	4720
	11th to 20th	Night	22% 8% 2 6% 3 3 3 3 4 5% 41%	5348
	21st to end	Night	19% 10% 3 7% 4 4 4 3 4 5% 38%	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	48% 4 11% 24% 13% 1	4662
	11th to 20th	Day	43% 4 10% 21% 18% 3	4680
	21st to end	Day	40% 4 8% 25% 20% 3	5124
February	1st to 10th	Day	47% 5% 11% 22% 12% 2	1913
	11th to 20th	Day	43% 7% 11% 22% 15% 3	2057
	21st to end	Day	49% 4 10% 20% 14% 3	1730
March	1st to 10th	Day	53% 3 9% 14% 11% 9%	4579
	11th to 20th	Day	45% 5% 14% 23% 11% 2	4855
	21st to end	Day	51% 4 6% 17% 17% 6%	5929
April	1st to 10th	Day	49% 4 9% 17% 17% 4	2520
	11th to 20th	Day	45% 5% 10% 19% 17% 3	2515
	21st to end	Day	49% 4 7% 18% 18% 3	2730
May	1st to 10th	Day	58% 5% 10% 15% 11% 1	7651
	11th to 20th	Day	49% 5% 14% 19% 11% 1	7885
	21st to end	Day	48% 6% 11% 22% 12% 1	9061
June	1st to 10th	Day	47% 6% 12% 22% 12% 1	2940
	11th to 20th	Day	43% 6% 12% 20% 15% 3	2940
	21st to end	Day	47% 5% 13% 21% 13% 1	2940
July	1st to 10th	Day	45% 5% 14% 21% 14%	8210
	11th to 20th	Day	34% 5% 14% 29% 16% 1	8205
	21st to end	Day	40% 4 11% 27% 17% 1	8795
August	1st to 10th	Day	45% 7% 16% 22% 11% 1	4458
	11th to 20th	Day	44% 5% 14% 25% 10% 1	4219
	21st to end	Day	34% 6% 12% 29% 18% 2	4312
September	1st to 10th	Day	35% 6% 12% 25% 20% 2	2400
	11th to 20th	Day	34% 5% 8% 27% 24% 2	2205
	21st to end	Day	41% 5% 8% 23% 20% 3	2200
October	1st to 10th	Day	44% 5% 7% 23% 19% 3	3590
	11th to 20th	Day	33% 4 8% 30% 22% 3	3121
	21st to end	Day	35% 4 7% 32% 20% 3	3180
November	1st to 10th	Day	39% 3 12% 26% 17% 2	1851
	11th to 20th	Day	38% 5% 10% 22% 22% 3	1890
	21st to end	Day	44% 5% 15% 22% 13% 1	1879
December	1st to 10th	Day	43% 4 15% 28% 10% 1	2680
	11th to 20th	Day	43% 4 11% 18% 20% 4	3066
	21st to end	Day	50% 5% 8% 19% 14% 5%	4048
January	1st to 10th	Night	42% 3 13% 28% 12% 2	8234
	11th to 20th	Night	49% 4 10% 19% 14% 4	8280
	21st to end	Night	45% 4 8% 20% 19% 5%	9057
February	1st to 10th	Night	44% 5% 13% 22% 14% 2	2700
	11th to 20th	Night	42% 5% 12% 22% 15% 3	2460
	21st to end	Night	44% 5% 9% 24% 14% 4	2076
March	1st to 10th	Night	50% 4 9% 16% 15% 6%	5494
	11th to 20th	Night	47% 5% 16% 18% 12% 2	5325
	21st to end	Night	51% 3 6% 13% 21% 5%	5242
April	1st to 10th	Night	49% 4 10% 17% 17% 3	2100
	11th to 20th	Night	46% 4 9% 21% 18% 2	2054
	21st to end	Night	46% 4 10% 18% 18% 4	1890
May	1st to 10th	Night	58% 4 12% 14% 11% 1	5265
	11th to 20th	Night	49% 5% 14% 21% 10% 1	5023
	21st to end	Night	51% 5% 13% 22% 9% 1	5115
June	1st to 10th	Night	47% 5% 11% 24% 12% 1	1680
	11th to 20th	Night	44% 8% 12% 21% 13% 2	1680
	21st to end	Night	43% 8% 15% 21% 13% 1	1680
July	1st to 10th	Night	43% 5% 15% 23% 14%	4640
	11th to 20th	Night	35% 5% 15% 25% 19% 1	4632
	21st to end	Night	35% 4 12% 32% 15% 1	4967
August	1st to 10th	Night	49% 6% 13% 20% 11% 1	2855
	11th to 20th	Night	44% 7% 15% 23% 10% 1	2966
	21st to end	Night	28% 5% 16% 30% 21% 1	3586
September	1st to 10th	Night	34% 5% 12% 27% 20% 1	2000
	11th to 20th	Night	33% 4 10% 26% 24% 2	2195
	21st to end	Night	39% 4 10% 28% 17% 2	2200
October	1st to 10th	Night	42% 4 14% 23% 15% 2	3590
	11th to 20th	Night	29% 4 10% 27% 26% 3	4011
	21st to end	Night	37% 4 11% 32% 15% 2	4610
November	1st to 10th	Night	39% 5% 10% 24% 19% 3	2667
	11th to 20th	Night	40% 4 10% 24% 20% 3	2730
	21st to end	Night	42% 4 15% 26% 13% 1	2736
December	1st to 10th	Night	46% 4 10% 28% 11% 1	4720
	11th to 20th	Night	47% 4 13% 16% 20% 2	5348
	21st to end	Night	48% 5% 8% 22% 15% 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	30% 24% 30% 14% 3	220
	11th to 20th	Day	30% 24% 33% 10% 2 1	220
	21st to end	Day	26% 26% 31% 13% 3	242
February	1st to 10th	Day	29% 23% 33% 13% 2	398
	11th to 20th	Day	31% 26% 29% 13% 1	536
	21st to end	Day	28% 22% 33% 13% 3	446
March	1st to 10th	Day	31% 19% 34% 13% 3	540
	11th to 20th	Day	31% 25% 29% 10% 4 1	540
	21st to end	Day	33% 21% 29% 11% 4 2	594
April	1st to 10th	Day	34% 21% 26% 12% 5% 1	540
	11th to 20th	Day	32% 21% 29% 12% 5% 2	532
	21st to end	Day	28% 19% 31% 14% 6% 2	540
May	1st to 10th	Day	34% 18% 29% 13% 4 1	543
	11th to 20th	Day	22% 17% 38% 17% 5% 1	567
	21st to end	Day	21% 16% 34% 22% 7% 1	617
June	1st to 10th	Day	18% 15% 38% 18% 11% 1	570
	11th to 20th	Day	18% 16% 36% 19% 9% 2	570
	21st to end	Day	19% 15% 35% 21% 8% 3	570
July	1st to 10th	Day	19% 8% 31% 29% 11% 3	565
	11th to 20th	Day	14% 8% 35% 28% 12% 4	564
	21st to end	Day	15% 8% 35% 28% 11% 3	620
August	1st to 10th	Day	13% 7% 32% 29% 15% 4	566
	11th to 20th	Day	16% 8% 29% 27% 14% 5%	535
	21st to end	Day	13% 10% 32% 26% 14% 4	583
September	1st to 10th	Day	18% 11% 25% 23% 16% 7%	530
	11th to 20th	Day	18% 12% 25% 19% 15% 10%	530
	21st to end	Day	19% 11% 33% 21% 12% 5%	530
October	1st to 10th	Day	27% 13% 24% 21% 12% 4	530
	11th to 20th	Day	23% 13% 32% 18% 11% 2	467
	21st to end	Day	29% 14% 29% 22% 6% 1	462
November	1st to 10th	Day	23% 19% 28% 20% 9% 1	425
	11th to 20th	Day	31% 17% 27% 19% 5% 1	430
	21st to end	Day	31% 21% 26% 17% 5%	419
December	1st to 10th	Day	22% 27% 31% 14% 5%	220
	11th to 20th	Day	31% 25% 29% 12% 2	220
	21st to end	Day	31% 21% 27% 17% 3 1	242
January	1st to 10th	Night	23% 21% 35% 18% 3	840
	11th to 20th	Night	28% 20% 30% 20% 2	840
	21st to end	Night	22% 20% 37% 17% 3	924
February	1st to 10th	Night	23% 19% 35% 22% 2	840
	11th to 20th	Night	24% 20% 36% 18% 2	823
	21st to end	Night	25% 19% 35% 18% 3	692
March	1st to 10th	Night	26% 19% 35% 18% 2	840
	11th to 20th	Night	24% 21% 31% 20% 4	840
	21st to end	Night	27% 19% 33% 18% 4	924
April	1st to 10th	Night	28% 18% 32% 18% 4	840
	11th to 20th	Night	26% 18% 33% 18% 5%	810
	21st to end	Night	23% 19% 33% 21% 3	630
May	1st to 10th	Night	26% 14% 33% 21% 5%	630
	11th to 20th	Night	21% 14% 34% 26% 5%	552
	21st to end	Night	22% 6% 33% 33% 6%	455
June	1st to 10th	Night	18% 10% 32% 31% 8% 1	420
	11th to 20th	Night	19% 7% 32% 32% 9% 1	420
	21st to end	Night	17% 6% 32% 38% 7%	420
July	1st to 10th	Night	14% 5% 32% 38% 9% 1	410
	11th to 20th	Night	14% 3 25% 43% 14% 1	408
	21st to end	Night	13% 4 29% 42% 12%	460
August	1st to 10th	Night	15% 3 27% 40% 14%	539
	11th to 20th	Night	14% 6% 29% 35% 14% 1	622
	21st to end	Night	14% 6% 25% 37% 17% 2	880
September	1st to 10th	Night	17% 5% 32% 31% 15% 1	800
	11th to 20th	Night	16% 7% 27% 31% 18% 2	800
	21st to end	Night	18% 8% 29% 29% 14% 2	800
October	1st to 10th	Night	24% 10% 25% 27% 14% 1	800
	11th to 20th	Night	19% 12% 32% 26% 10% 1	800
	21st to end	Night	25% 16% 28% 25% 6%	880
November	1st to 10th	Night	21% 13% 31% 27% 7% 1	820
	11th to 20th	Night	23% 17% 32% 21% 7%	840
	21st to end	Night	24% 18% 30% 22% 6%	840
December	1st to 10th	Night	25% 18% 36% 19% 3	840
	11th to 20th	Night	27% 20% 30% 20% 3	840
	21st to end	Night	26% 20% 31% 21% 3	924

Page generated at 2026-08-12 03:37:16. Version ac07

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