Chester
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chester clear sky chart from 2005-11-06 to 2024-11-03.

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	15% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	101340
	Night	15% 8% 3 7% 5% 4 5% 4 6% 7% 37%	97652
Transparency	Day	46% 8% 14% 20% 11% 1	101098
	Night	46% 8% 14% 20% 11% 1	97514
Seeing	Day	23% 19% 30% 18% 8% 3	14850
	Night	20% 16% 29% 26% 8% 1	23791

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% 9% 3 10% 6% 5% 5% 4 6% 6% 35%	2517
	11th to 20th	Day	13% 10% 5% 12% 7% 6% 5% 4 5% 4 28%	2520
	21st to end	Day	15% 13% 6% 11% 6% 5% 4 3 5% 5% 26%	2772
February	1st to 10th	Day	12% 10% 4 9% 6% 6% 5% 4 6% 7% 29%	1709
	11th to 20th	Day	9% 9% 5% 10% 6% 6% 5% 5% 6% 7% 33%	1848
	21st to end	Day	16% 11% 4 9% 6% 4 5% 4 5% 5% 32%	1570
March	1st to 10th	Day	19% 16% 4 10% 5% 5% 4 3 4 4 27%	3116
	11th to 20th	Day	13% 9% 3 9% 6% 5% 5% 4 7% 6% 32%	3243
	21st to end	Day	18% 9% 2 7% 6% 5% 4 3 4 6% 34%	4166
April	1st to 10th	Day	17% 11% 3 7% 5% 5% 3 3 5% 6% 35%	2280
	11th to 20th	Day	17% 7% 2 6% 5% 5% 5% 4 6% 7% 36%	2254
	21st to end	Day	20% 8% 3 8% 5% 5% 4 4 5% 6% 32%	2438
May	1st to 10th	Day	22% 11% 3 8% 5% 5% 4 3 6% 6% 28%	4106
	11th to 20th	Day	19% 9% 3 8% 5% 5% 4 4 6% 8% 30%	4384
	21st to end	Day	13% 5% 2 5% 5% 5% 5% 5% 7% 9% 41%	4837
June	1st to 10th	Day	17% 7% 3 7% 6% 6% 5% 4 7% 8% 31%	2660
	11th to 20th	Day	16% 6% 2 5% 5% 4 5% 4 7% 7% 37%	2660
	21st to end	Day	17% 7% 3 7% 6% 5% 5% 5% 6% 7% 32%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 10% 37%	4440
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 9% 11% 37%	4440
	21st to end	Day	15% 6% 2 7% 5% 6% 5% 4 6% 7% 37%	4814
August	1st to 10th	Day	13% 5% 3 7% 5% 5% 6% 5% 6% 9% 36%	4334
	11th to 20th	Day	13% 6% 2 8% 5% 5% 6% 5% 7% 9% 34%	3890
	21st to end	Day	8% 4 2 6% 4 5% 5% 4 7% 11% 43%	4180
September	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 6% 8% 45%	2280
	11th to 20th	Day	12% 5% 2 6% 4 4 4 3 6% 6% 49%	2144
	21st to end	Day	16% 5% 2 6% 4 4 4 3 6% 8% 42%	2090
October	1st to 10th	Day	21% 7% 2 8% 4 5% 4 3 5% 5% 36%	2057
	11th to 20th	Day	14% 7% 2 6% 4 5% 4 4 6% 7% 40%	1842
	21st to end	Day	21% 8% 3 8% 5% 4 4 4 5% 6% 33%	1881
November	1st to 10th	Day	12% 8% 3 7% 3 4 4 3 6% 8% 44%	1689
	11th to 20th	Day	16% 8% 3 6% 5% 4 5% 4 5% 6% 39%	1710
	21st to end	Day	17% 8% 3 7% 4 4 3 5% 7% 7% 35%	1611
December	1st to 10th	Day	17% 12% 4 8% 6% 6% 5% 3 5% 6% 29%	1520
	11th to 20th	Day	21% 11% 3 7% 4 4 3 3 4 5% 36%	1906
	21st to end	Day	21% 12% 4 9% 5% 5% 5% 3 4 5% 27%	2772
January	1st to 10th	Night	15% 8% 2 8% 5% 4 5% 4 6% 7% 37%	4429
	11th to 20th	Night	11% 10% 5% 12% 7% 5% 6% 4 5% 6% 28%	4440
	21st to end	Night	18% 13% 4 10% 5% 5% 5% 4 5% 6% 26%	4884
February	1st to 10th	Night	11% 10% 4 8% 6% 5% 5% 5% 7% 7% 31%	2469
	11th to 20th	Night	9% 8% 3 8% 6% 6% 5% 6% 7% 7% 35%	2218
	21st to end	Night	14% 8% 3 7% 4 5% 5% 4 8% 7% 36%	1884
March	1st to 10th	Night	22% 13% 2 7% 4 4 3 4 4 6% 30%	3724
	11th to 20th	Night	11% 10% 3 7% 6% 6% 6% 4 5% 7% 36%	3698
	21st to end	Night	17% 11% 3 7% 4 5% 4 3 5% 6% 35%	3466
April	1st to 10th	Night	18% 7% 2 6% 5% 4 4 4 6% 7% 37%	1900
	11th to 20th	Night	17% 8% 3 6% 4 4 4 4 5% 7% 38%	1875
	21st to end	Night	20% 8% 2 6% 5% 3 4 3 5% 7% 37%	1740
May	1st to 10th	Night	25% 9% 3 6% 4 4 4 4 5% 8% 28%	2834
	11th to 20th	Night	15% 9% 4 10% 7% 6% 5% 4 7% 7% 28%	2539
	21st to end	Night	15% 5% 2 5% 4 4 5% 4 6% 8% 42%	2738
June	1st to 10th	Night	18% 5% 2 5% 5% 4 5% 3 6% 8% 38%	1520
	11th to 20th	Night	18% 6% 2 6% 3 3 4 4 6% 8% 41%	1520
	21st to end	Night	13% 7% 2 6% 5% 4 5% 5% 7% 6% 38%	1520
July	1st to 10th	Night	9% 4 3 7% 6% 5% 5% 5% 7% 8% 42%	2520
	11th to 20th	Night	13% 5% 2 5% 4 4 4 4 6% 8% 44%	2520
	21st to end	Night	14% 7% 2 6% 4 3 5% 4 6% 7% 42%	2739
August	1st to 10th	Night	18% 7% 3 7% 4 4 4 4 5% 7% 36%	2565
	11th to 20th	Night	14% 7% 2 7% 5% 4 5% 4 4 8% 41%	2934
	21st to end	Night	9% 4 2 4 3 3 4 3 6% 9% 54%	3476
September	1st to 10th	Night	11% 6% 2 5% 3 3 4 4 5% 8% 51%	1900
	11th to 20th	Night	12% 5% 1 4 3 3 4 3 4 6% 53%	2035
	21st to end	Night	15% 6% 2 4 4 4 4 3 6% 7% 46%	2090
October	1st to 10th	Night	20% 7% 3 6% 4 4 4 4 5% 6% 38%	2120
	11th to 20th	Night	14% 6% 2 6% 4 4 6% 5% 5% 7% 41%	2337
	21st to end	Night	21% 8% 2 6% 4 4 5% 4 6% 6% 34%	2717
November	1st to 10th	Night	13% 7% 3 7% 5% 5% 4 3 5% 6% 43%	2434
	11th to 20th	Night	16% 7% 2 6% 5% 4 4 4 5% 7% 41%	2470
	21st to end	Night	13% 8% 3 6% 5% 4 5% 4 6% 7% 39%	2565
December	1st to 10th	Night	16% 11% 3 8% 6% 5% 4 3 6% 6% 32%	2660
	11th to 20th	Night	19% 9% 3 7% 4 4 4 4 5% 6% 34%	3288
	21st to end	Night	21% 12% 4 9% 5% 4 4 3 5% 5% 26%	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	45% 9% 12% 27% 7%	2518
	11th to 20th	Day	55% 10% 10% 18% 6% 1	2520
	21st to end	Day	58% 7% 10% 17% 6% 1	2772
February	1st to 10th	Day	52% 8% 13% 17% 9% 1	1709
	11th to 20th	Day	48% 10% 11% 19% 11% 2	1857
	21st to end	Day	53% 6% 12% 17% 11% 2	1570
March	1st to 10th	Day	60% 7% 10% 11% 10% 2	3119
	11th to 20th	Day	46% 12% 14% 15% 11% 2	3243
	21st to end	Day	49% 6% 8% 15% 19% 3	4166
April	1st to 10th	Day	50% 6% 10% 19% 12% 3	2280
	11th to 20th	Day	45% 9% 11% 19% 15% 2	2254
	21st to end	Day	52% 7% 10% 16% 12% 3	2438
May	1st to 10th	Day	55% 8% 11% 17% 8% 1	4120
	11th to 20th	Day	50% 10% 14% 16% 9% 1	4388
	21st to end	Day	35% 10% 15% 25% 13% 1	4837
June	1st to 10th	Day	49% 9% 14% 18% 10%	2660
	11th to 20th	Day	44% 8% 14% 18% 14% 2	2660
	21st to end	Day	49% 10% 13% 17% 10% 1	2660
July	1st to 10th	Day	40% 7% 17% 21% 16%	4370
	11th to 20th	Day	37% 7% 20% 25% 11%	4365
	21st to end	Day	43% 6% 16% 22% 12% 1	4661
August	1st to 10th	Day	44% 7% 18% 20% 11%	4320
	11th to 20th	Day	44% 7% 17% 26% 6% 1	3929
	21st to end	Day	33% 6% 20% 27% 13% 1	4180
September	1st to 10th	Day	36% 7% 14% 27% 15% 1	2280
	11th to 20th	Day	35% 6% 12% 26% 19% 1	2144
	21st to end	Day	40% 6% 14% 25% 14% 2	2090
October	1st to 10th	Day	49% 7% 9% 20% 14% 2	2057
	11th to 20th	Day	41% 8% 14% 27% 9% 1	1842
	21st to end	Day	53% 7% 10% 19% 9% 2	1881
November	1st to 10th	Day	39% 8% 15% 23% 15% 1	1689
	11th to 20th	Day	45% 8% 12% 18% 15% 2	1710
	21st to end	Day	47% 8% 17% 19% 7% 1	1611
December	1st to 10th	Day	55% 8% 15% 14% 8% 1	1520
	11th to 20th	Day	52% 7% 11% 18% 11% 1	1906
	21st to end	Day	58% 8% 11% 14% 9%	2772
January	1st to 10th	Night	44% 10% 14% 21% 10% 1	4429
	11th to 20th	Night	53% 9% 11% 16% 8% 1	4440
	21st to end	Night	58% 9% 10% 15% 8% 1	4884
February	1st to 10th	Night	50% 8% 14% 17% 10% 1	2469
	11th to 20th	Night	44% 9% 14% 19% 13% 1	2220
	21st to end	Night	45% 9% 13% 22% 8% 3	1884
March	1st to 10th	Night	54% 6% 11% 18% 9% 2	3734
	11th to 20th	Night	44% 9% 13% 20% 11% 2	3699
	21st to end	Night	48% 6% 9% 13% 20% 3	3466
April	1st to 10th	Night	44% 8% 12% 21% 14% 1	1900
	11th to 20th	Night	44% 7% 11% 22% 14% 1	1875
	21st to end	Night	46% 7% 11% 17% 15% 4	1740
May	1st to 10th	Night	52% 10% 12% 16% 9% 1	2840
	11th to 20th	Night	52% 11% 14% 14% 7% 1	2540
	21st to end	Night	38% 10% 15% 22% 13% 2	2739
June	1st to 10th	Night	43% 8% 15% 22% 12%	1520
	11th to 20th	Night	41% 9% 17% 20% 12% 1	1520
	21st to end	Night	42% 9% 16% 21% 11% 1	1520
July	1st to 10th	Night	39% 7% 18% 23% 14% 1	2480
	11th to 20th	Night	37% 7% 17% 25% 14%	2472
	21st to end	Night	41% 6% 12% 28% 12% 1	2651
August	1st to 10th	Night	47% 8% 15% 21% 9%	2555
	11th to 20th	Night	42% 7% 19% 22% 9%	2961
	21st to end	Night	27% 4 22% 33% 13%	3476
September	1st to 10th	Night	32% 8% 14% 29% 16%	1900
	11th to 20th	Night	32% 7% 12% 29% 19% 1	2035
	21st to end	Night	37% 6% 12% 27% 15% 2	2090
October	1st to 10th	Night	46% 8% 12% 22% 11% 2	2120
	11th to 20th	Night	40% 9% 16% 24% 10% 1	2337
	21st to end	Night	50% 7% 12% 19% 9% 1	2717
November	1st to 10th	Night	41% 8% 13% 21% 13% 3	2434
	11th to 20th	Night	42% 7% 13% 22% 14% 2	2470
	21st to end	Night	44% 8% 17% 21% 9% 1	2565
December	1st to 10th	Night	53% 8% 13% 19% 7%	2660
	11th to 20th	Night	50% 9% 12% 15% 12% 1	3288
	21st to end	Night	57% 8% 12% 18% 6%	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	28% 24% 27% 17% 3	180
	11th to 20th	Day	29% 29% 26% 14% 2 1	180
	21st to end	Day	19% 29% 37% 11% 5%	198
February	1st to 10th	Day	28% 35% 27% 9% 1	284
	11th to 20th	Day	30% 27% 27% 14% 2	456
	21st to end	Day	28% 27% 28% 15% 3	382
March	1st to 10th	Day	29% 20% 34% 15% 2	460
	11th to 20th	Day	28% 28% 28% 11% 3 1	460
	21st to end	Day	32% 23% 27% 10% 5% 3	506
April	1st to 10th	Day	35% 22% 25% 12% 6% 1	460
	11th to 20th	Day	33% 24% 24% 12% 5% 2	452
	21st to end	Day	29% 21% 29% 14% 5% 1	460
May	1st to 10th	Day	29% 25% 26% 12% 7% 2	463
	11th to 20th	Day	20% 19% 36% 19% 4 2	487
	21st to end	Day	19% 14% 33% 24% 8% 2	529
June	1st to 10th	Day	20% 17% 36% 18% 9% 1	490
	11th to 20th	Day	18% 17% 33% 19% 10% 2	490
	21st to end	Day	19% 19% 35% 17% 7% 3	490
July	1st to 10th	Day	15% 12% 32% 25% 13% 3	485
	11th to 20th	Day	14% 7% 39% 26% 12% 2	484
	21st to end	Day	13% 11% 40% 23% 11% 2	532
August	1st to 10th	Day	11% 13% 30% 28% 14% 4	486
	11th to 20th	Day	14% 10% 33% 22% 15% 6%	479
	21st to end	Day	12% 14% 28% 25% 14% 7%	539
September	1st to 10th	Day	16% 12% 26% 23% 16% 7%	490
	11th to 20th	Day	15% 13% 26% 18% 17% 10%	490
	21st to end	Day	16% 14% 29% 22% 12% 7%	490
October	1st to 10th	Day	23% 17% 24% 20% 12% 4	490
	11th to 20th	Day	21% 17% 27% 23% 10% 2	459
	21st to end	Day	31% 16% 26% 19% 7% 1	429
November	1st to 10th	Day	23% 19% 24% 23% 11% 1	371
	11th to 20th	Day	30% 22% 25% 17% 5% 1	370
	21st to end	Day	29% 21% 28% 17% 4	271
December	1st to 10th	Day	24% 30% 26% 15% 5%	180
	11th to 20th	Day	37% 23% 30% 7% 3	180
	21st to end	Day	32% 21% 30% 14% 3	198
January	1st to 10th	Night	21% 20% 36% 21% 3	760
	11th to 20th	Night	25% 19% 32% 21% 2	760
	21st to end	Night	17% 22% 34% 22% 4	836
February	1st to 10th	Night	22% 21% 37% 18% 2	760
	11th to 20th	Night	20% 24% 36% 18% 2	743
	21st to end	Night	25% 23% 30% 20% 2	628
March	1st to 10th	Night	26% 18% 33% 21% 2	760
	11th to 20th	Night	24% 23% 30% 20% 4	760
	21st to end	Night	24% 20% 28% 21% 6%	836
April	1st to 10th	Night	25% 20% 29% 22% 4	760
	11th to 20th	Night	22% 23% 28% 20% 7%	751
	21st to end	Night	25% 18% 29% 24% 5%	600
May	1st to 10th	Night	26% 16% 28% 23% 7%	570
	11th to 20th	Night	16% 16% 32% 29% 6%	405
	21st to end	Night	17% 9% 30% 31% 12% 1	411
June	1st to 10th	Night	18% 10% 28% 32% 12%	380
	11th to 20th	Night	17% 11% 25% 34% 13%	380
	21st to end	Night	14% 7% 30% 38% 10% 1	380
July	1st to 10th	Night	12% 9% 21% 43% 14% 1	370
	11th to 20th	Night	12% 4 24% 39% 19% 2	368
	21st to end	Night	12% 5% 27% 38% 17% 1	416
August	1st to 10th	Night	11% 4 21% 45% 18% 1	411
	11th to 20th	Night	13% 7% 27% 33% 18% 3	649
	21st to end	Night	15% 6% 21% 35% 21% 2	836
September	1st to 10th	Night	13% 7% 28% 33% 18% 1	760
	11th to 20th	Night	14% 9% 23% 29% 19% 5%	760
	21st to end	Night	17% 9% 25% 31% 15% 3	760
October	1st to 10th	Night	23% 14% 19% 29% 14% 1	760
	11th to 20th	Night	18% 14% 27% 30% 11% 1	760
	21st to end	Night	26% 16% 28% 24% 6%	836
November	1st to 10th	Night	18% 19% 27% 28% 8% 1	749
	11th to 20th	Night	21% 19% 30% 23% 7% 1	760
	21st to end	Night	22% 19% 29% 22% 6% 1	760
December	1st to 10th	Night	23% 22% 33% 17% 4	760
	11th to 20th	Night	26% 21% 29% 21% 3	760
	21st to end	Night	27% 22% 30% 19% 2	836

Page generated at 2024-10-31 03:39:23. Version ac07

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