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 2025-04-11.

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%	113111
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 39%	115159
Transparency	Day	44% 5% 11% 22% 15% 3	116679
	Night	44% 5% 12% 22% 15% 2	119755
Seeing	Day	24% 17% 31% 19% 8% 2	15439
	Night	22% 15% 31% 24% 7% 1	24479

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% 7% 4 7% 6% 6% 5% 5% 5% 6% 36%	3597
	11th to 20th	Day	13% 7% 3 7% 4 4 4 3 5% 6% 44%	3570
	21st to end	Day	15% 9% 2 6% 4 4 4 3 5% 5% 44%	3960
February	1st to 10th	Day	17% 7% 3 5% 5% 5% 6% 5% 6% 6% 35%	1821
	11th to 20th	Day	13% 8% 3 6% 5% 4 4 4 5% 8% 39%	1948
	21st to end	Day	16% 10% 3 8% 5% 4 4 3 6% 5% 36%	1650
March	1st to 10th	Day	20% 11% 3 8% 5% 4 4 3 4 5% 33%	4476
	11th to 20th	Day	16% 8% 2 7% 4 4 5% 4 5% 6% 37%	4750
	21st to end	Day	25% 9% 2 6% 4 4 4 3 5% 7% 32%	5801
April	1st to 10th	Day	20% 9% 3 6% 4 4 4 3 4 7% 36%	2400
	11th to 20th	Day	17% 7% 2 6% 5% 4 5% 4 5% 8% 38%	2273
	21st to end	Day	21% 7% 3 8% 5% 4 4 3 5% 5% 35%	2470
May	1st to 10th	Day	22% 12% 3 8% 5% 5% 4 4 5% 6% 27%	4106
	11th to 20th	Day	21% 7% 3 8% 5% 4 4 4 5% 6% 32%	4225
	21st to end	Day	15% 4 2 5% 4 4 5% 4 6% 8% 43%	4837
June	1st to 10th	Day	19% 6% 3 7% 5% 5% 5% 4 6% 9% 32%	2660
	11th to 20th	Day	16% 5% 3 7% 4 5% 5% 4 7% 8% 37%	2660
	21st to end	Day	18% 6% 3 7% 6% 5% 4 4 6% 7% 34%	2660
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 6% 4 7% 9% 36%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 11% 38%	4440
	21st to end	Day	16% 8% 3 7% 4 4 5% 4 6% 7% 35%	4814
August	1st to 10th	Day	15% 6% 2 7% 5% 6% 5% 5% 6% 8% 34%	4206
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 7% 36%	3999
	21st to end	Day	8% 5% 2 6% 4 5% 6% 4 7% 10% 43%	4180
September	1st to 10th	Day	13% 5% 1 5% 3 4 4 3 6% 7% 47%	2280
	11th to 20th	Day	14% 6% 2 4 3 3 3 3 4 5% 52%	2095
	21st to end	Day	16% 5% 2 6% 4 4 4 3 4 6% 44%	2090
October	1st to 10th	Day	23% 6% 2 6% 3 4 4 3 4 5% 39%	2090
	11th to 20th	Day	15% 5% 2 5% 4 3 4 3 5% 7% 45%	1835
	21st to end	Day	23% 7% 2 5% 4 4 4 3 3 5% 40%	1881
November	1st to 10th	Day	14% 6% 2 6% 4 3 3 3 4 5% 50%	1761
	11th to 20th	Day	19% 5% 2 4 3 3 3 4 4 6% 48%	1800
	21st to end	Day	20% 7% 2 5% 3 4 4 3 4 6% 42%	1790
December	1st to 10th	Day	16% 7% 3 6% 4 4 4 3 5% 7% 41%	2600
	11th to 20th	Day	21% 5% 2 5% 3 4 3 3 5% 5% 44%	2986
	21st to end	Day	20% 10% 3 6% 4 4 4 4 5% 5% 36%	3960
January	1st to 10th	Night	13% 7% 3 6% 4 4 4 3 5% 6% 44%	6349
	11th to 20th	Night	12% 9% 3 9% 6% 5% 4 3 6% 6% 38%	6315
	21st to end	Night	15% 11% 3 7% 4 5% 4 4 5% 5% 38%	6996
February	1st to 10th	Night	16% 9% 3 6% 4 4 4 4 5% 6% 38%	2572
	11th to 20th	Night	13% 9% 2 7% 4 4 5% 4 6% 7% 39%	2338
	21st to end	Night	16% 9% 2 5% 5% 4 4 3 5% 6% 40%	1980
March	1st to 10th	Night	23% 9% 2 5% 4 4 4 3 5% 6% 35%	5364
	11th to 20th	Night	16% 10% 3 6% 5% 4 5% 4 5% 6% 37%	5209
	21st to end	Night	26% 9% 2 4 3 3 4 3 6% 6% 33%	5128
April	1st to 10th	Night	19% 9% 2 6% 5% 4 5% 4 4 7% 36%	2000
	11th to 20th	Night	20% 9% 2 5% 4 3 4 3 5% 5% 40%	1863
	21st to end	Night	20% 6% 3 6% 4 4 4 4 4 6% 38%	1710
May	1st to 10th	Night	24% 12% 3 8% 4 4 4 3 5% 7% 26%	2834
	11th to 20th	Night	18% 8% 3 9% 5% 6% 6% 4 6% 6% 27%	2698
	21st to end	Night	16% 6% 2 6% 4 4 4 4 6% 8% 41%	2738
June	1st to 10th	Night	17% 9% 3 7% 5% 4 4 3 5% 7% 37%	1520
	11th to 20th	Night	19% 6% 2 5% 4 4 5% 5% 5% 8% 38%	1520
	21st to end	Night	18% 6% 2 6% 4 4 4 4 5% 10% 37%	1520
July	1st to 10th	Night	11% 5% 2 7% 6% 6% 6% 4 7% 9% 37%	2520
	11th to 20th	Night	13% 6% 3 7% 4 4 5% 4 6% 9% 41%	2520
	21st to end	Night	16% 6% 3 7% 4 4 5% 3 6% 7% 40%	2739
August	1st to 10th	Night	21% 6% 2 7% 5% 4 5% 4 4 6% 34%	2693
	11th to 20th	Night	12% 8% 3 7% 5% 5% 6% 4 6% 8% 37%	2811
	21st to end	Night	9% 4 1 5% 3 3 4 3 6% 8% 54%	3476
September	1st to 10th	Night	13% 6% 1 5% 4 4 2 3 6% 6% 50%	1900
	11th to 20th	Night	14% 6% 2 5% 3 2 3 3 5% 6% 52%	2085
	21st to end	Night	16% 5% 3 5% 3 3 3 3 5% 7% 47%	2090
October	1st to 10th	Night	21% 6% 2 6% 4 4 4 2 4 6% 40%	2090
	11th to 20th	Night	15% 5% 2 5% 4 4 4 4 6% 7% 44%	2338
	21st to end	Night	22% 6% 3 6% 4 3 3 3 5% 6% 39%	2717
November	1st to 10th	Night	15% 6% 2 5% 4 3 4 4 4 5% 47%	2537
	11th to 20th	Night	17% 7% 2 5% 4 4 3 3 4 5% 47%	2600
	21st to end	Night	16% 8% 2 5% 5% 4 3 4 5% 6% 43%	2605
December	1st to 10th	Night	17% 10% 3 6% 4 4 4 3 5% 6% 38%	4580
	11th to 20th	Night	23% 8% 2 6% 3 3 3 3 4 5% 41%	5208
	21st to end	Night	19% 10% 3 7% 4 4 4 3 4 5% 38%	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	47% 5% 9% 26% 14% 1	3598
	11th to 20th	Day	41% 4 12% 23% 17% 3	3600
	21st to end	Day	43% 5% 7% 22% 19% 4	3960
February	1st to 10th	Day	47% 5% 12% 22% 11% 2	1821
	11th to 20th	Day	43% 7% 11% 20% 15% 4	1957
	21st to end	Day	49% 4 10% 20% 14% 3	1650
March	1st to 10th	Day	53% 3 9% 14% 11% 9%	4479
	11th to 20th	Day	45% 5% 14% 23% 11% 2	4750
	21st to end	Day	51% 4 5% 17% 17% 6%	5801
April	1st to 10th	Day	49% 5% 8% 18% 17% 4	2400
	11th to 20th	Day	45% 5% 11% 20% 17% 3	2273
	21st to end	Day	51% 5% 7% 17% 17% 3	2470
May	1st to 10th	Day	57% 6% 10% 15% 10% 1	4120
	11th to 20th	Day	50% 7% 15% 16% 10% 2	4229
	21st to end	Day	36% 7% 13% 24% 18% 2	4837
June	1st to 10th	Day	48% 7% 12% 21% 11% 1	2660
	11th to 20th	Day	43% 7% 12% 19% 15% 3	2660
	21st to end	Day	48% 6% 13% 21% 12% 1	2660
July	1st to 10th	Day	43% 6% 12% 21% 17% 1	4370
	11th to 20th	Day	39% 6% 16% 25% 13% 1	4365
	21st to end	Day	46% 5% 12% 21% 14% 2	4661
August	1st to 10th	Day	46% 7% 15% 22% 10%	4192
	11th to 20th	Day	45% 5% 14% 25% 9% 1	4038
	21st to end	Day	34% 6% 12% 29% 17% 2	4180
September	1st to 10th	Day	36% 6% 12% 25% 20% 2	2280
	11th to 20th	Day	35% 5% 8% 27% 23% 2	2095
	21st to end	Day	41% 5% 8% 23% 21% 2	2090
October	1st to 10th	Day	45% 5% 7% 22% 18% 2	3480
	11th to 20th	Day	33% 4 8% 30% 22% 3	3025
	21st to end	Day	35% 4 7% 31% 20% 3	3081
November	1st to 10th	Day	39% 3 12% 27% 17% 2	1761
	11th to 20th	Day	38% 5% 10% 22% 22% 3	1800
	21st to end	Day	44% 5% 15% 22% 13% 2	1790
December	1st to 10th	Day	43% 4 15% 28% 9% 1	2600
	11th to 20th	Day	43% 4 11% 18% 20% 4	2986
	21st to end	Day	50% 5% 8% 19% 14% 5%	3960
January	1st to 10th	Night	40% 4 12% 30% 12% 2	6349
	11th to 20th	Night	46% 5% 12% 21% 13% 3	6360
	21st to end	Night	48% 4 9% 17% 17% 6%	6996
February	1st to 10th	Night	45% 6% 13% 21% 13% 2	2572
	11th to 20th	Night	43% 6% 12% 20% 16% 3	2340
	21st to end	Night	44% 6% 9% 23% 14% 4	1980
March	1st to 10th	Night	50% 4 9% 16% 15% 6%	5374
	11th to 20th	Night	47% 5% 16% 18% 12% 2	5210
	21st to end	Night	51% 3 6% 13% 22% 5%	5128
April	1st to 10th	Night	49% 4 10% 17% 16% 3	2000
	11th to 20th	Night	46% 4 9% 21% 18% 2	1863
	21st to end	Night	46% 5% 11% 19% 16% 4	1710
May	1st to 10th	Night	57% 5% 12% 16% 8% 2	2840
	11th to 20th	Night	54% 8% 14% 15% 8% 2	2699
	21st to end	Night	40% 7% 17% 21% 13% 2	2739
June	1st to 10th	Night	48% 5% 12% 22% 12% 1	1520
	11th to 20th	Night	44% 8% 12% 21% 13% 3	1520
	21st to end	Night	43% 8% 14% 21% 13% 1	1520
July	1st to 10th	Night	42% 7% 14% 23% 14% 1	2480
	11th to 20th	Night	41% 7% 14% 23% 15%	2472
	21st to end	Night	43% 5% 11% 24% 15% 1	2651
August	1st to 10th	Night	50% 6% 13% 20% 11% 1	2683
	11th to 20th	Night	45% 7% 15% 23% 11% 1	2838
	21st to end	Night	28% 5% 16% 30% 21% 1	3476
September	1st to 10th	Night	35% 5% 13% 27% 20% 1	1900
	11th to 20th	Night	34% 4 11% 26% 24% 2	2085
	21st to end	Night	38% 4 10% 28% 18% 2	2090
October	1st to 10th	Night	43% 4 14% 23% 14% 2	3480
	11th to 20th	Night	29% 4 10% 27% 26% 3	3887
	21st to end	Night	36% 4 11% 32% 15% 2	4467
November	1st to 10th	Night	39% 5% 10% 24% 19% 3	2537
	11th to 20th	Night	40% 4 9% 23% 20% 3	2600
	21st to end	Night	41% 4 15% 26% 13% 1	2605
December	1st to 10th	Night	47% 4 11% 28% 10%	4580
	11th to 20th	Night	47% 4 13% 15% 20% 2	5208
	21st to end	Night	48% 5% 8% 22% 14% 3	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	32% 24% 28% 14% 3	200
	11th to 20th	Day	31% 23% 33% 11% 3 1	200
	21st to end	Day	26% 24% 32% 14% 4	220
February	1st to 10th	Day	31% 24% 31% 12% 2	366
	11th to 20th	Day	32% 27% 27% 13% 1	496
	21st to end	Day	29% 23% 32% 13% 3	414
March	1st to 10th	Day	31% 19% 34% 13% 2	500
	11th to 20th	Day	31% 25% 29% 10% 4 1	500
	21st to end	Day	33% 21% 29% 12% 4 2	550
April	1st to 10th	Day	34% 22% 26% 12% 5% 1	500
	11th to 20th	Day	31% 21% 29% 13% 5% 2	452
	21st to end	Day	28% 20% 31% 14% 6% 2	460
May	1st to 10th	Day	32% 18% 30% 14% 5% 1	463
	11th to 20th	Day	21% 16% 37% 18% 5% 1	487
	21st to end	Day	19% 15% 35% 23% 7% 1	529
June	1st to 10th	Day	18% 16% 38% 16% 10% 1	490
	11th to 20th	Day	17% 15% 37% 20% 9% 2	490
	21st to end	Day	19% 16% 35% 20% 7% 3	490
July	1st to 10th	Day	19% 8% 30% 28% 12% 3	485
	11th to 20th	Day	14% 7% 35% 28% 12% 3	484
	21st to end	Day	15% 8% 35% 29% 11% 2	532
August	1st to 10th	Day	14% 8% 30% 29% 15% 2	486
	11th to 20th	Day	17% 9% 29% 26% 14% 4	479
	21st to end	Day	14% 10% 31% 26% 14% 5%	539
September	1st to 10th	Day	19% 12% 25% 22% 17% 7%	490
	11th to 20th	Day	20% 13% 25% 18% 14% 10%	490
	21st to end	Day	19% 11% 33% 21% 12% 4	490
October	1st to 10th	Day	28% 13% 24% 21% 11% 4	490
	11th to 20th	Day	22% 14% 32% 19% 11% 2	433
	21st to end	Day	30% 13% 28% 21% 6% 1	429
November	1st to 10th	Day	21% 19% 29% 20% 9% 2	395
	11th to 20th	Day	32% 17% 26% 19% 5% 1	400
	21st to end	Day	32% 20% 26% 16% 5% 1	390
December	1st to 10th	Day	21% 30% 31% 14% 6%	200
	11th to 20th	Day	31% 26% 30% 12% 3	200
	21st to end	Day	29% 21% 28% 17% 4 1	220
January	1st to 10th	Night	23% 22% 34% 18% 3	800
	11th to 20th	Night	27% 20% 30% 20% 3	800
	21st to end	Night	22% 20% 37% 18% 3	880
February	1st to 10th	Night	24% 19% 35% 21% 2	800
	11th to 20th	Night	25% 21% 36% 17% 2	783
	21st to end	Night	25% 19% 34% 18% 3	660
March	1st to 10th	Night	26% 20% 35% 18% 2	800
	11th to 20th	Night	24% 21% 31% 20% 4	800
	21st to end	Night	27% 19% 32% 18% 4	880
April	1st to 10th	Night	28% 18% 32% 18% 4	800
	11th to 20th	Night	25% 19% 33% 18% 5%	735
	21st to end	Night	24% 19% 33% 21% 3	570
May	1st to 10th	Night	25% 15% 34% 21% 5%	570
	11th to 20th	Night	22% 14% 34% 25% 5%	499
	21st to end	Night	21% 6% 33% 33% 7%	411
June	1st to 10th	Night	19% 11% 33% 30% 7% 1	380
	11th to 20th	Night	20% 7% 31% 31% 9% 1	380
	21st to end	Night	17% 6% 33% 37% 7%	380
July	1st to 10th	Night	15% 5% 32% 38% 9% 1	370
	11th to 20th	Night	15% 4 24% 42% 15% 1	368
	21st to end	Night	14% 4 29% 42% 11%	416
August	1st to 10th	Night	16% 3 29% 39% 14%	487
	11th to 20th	Night	15% 6% 29% 35% 14% 1	578
	21st to end	Night	14% 6% 24% 37% 18% 2	836
September	1st to 10th	Night	17% 5% 32% 30% 15% 1	760
	11th to 20th	Night	16% 7% 27% 29% 18% 2	760
	21st to end	Night	18% 8% 30% 28% 13% 2	760
October	1st to 10th	Night	25% 10% 25% 27% 12% 1	760
	11th to 20th	Night	18% 12% 32% 26% 11% 1	760
	21st to end	Night	26% 16% 28% 24% 6%	836
November	1st to 10th	Night	20% 13% 32% 27% 7% 1	780
	11th to 20th	Night	24% 17% 31% 20% 8% 1	800
	21st to end	Night	25% 18% 31% 21% 6%	800
December	1st to 10th	Night	25% 18% 36% 18% 4	800
	11th to 20th	Night	27% 20% 30% 20% 3	800
	21st to end	Night	25% 20% 31% 21% 3	880

Page generated at 2025-04-08 09:17:27. Version ac07

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