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 2024-10-24.

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	18% 7% 2 6% 4 4 4 3 5% 7% 39%	101091
	Night	19% 8% 2 6% 4 4 4 3 5% 6% 40%	97687
Transparency	Day	25% 49% 6% 12% 8% 1	100848
	Night	25% 49% 6% 12% 8% 1	97550
Seeing	Day	22% 17% 32% 19% 7% 2	15030
	Night	21% 15% 32% 23% 7% 1	24011

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	17% 7% 2 5% 4 4 4 3 4 4 46%	2517
	11th to 20th	Day	17% 9% 2 7% 4 5% 4 4 5% 5% 38%	2520
	21st to end	Day	23% 13% 3 5% 3 3 3 2 5% 5% 34%	2808
February	1st to 10th	Day	18% 9% 2 5% 5% 4 4 4 5% 6% 38%	1805
	11th to 20th	Day	15% 7% 2 5% 5% 4 5% 3 6% 6% 42%	1848
	21st to end	Day	21% 10% 3 5% 4 4 4 3 5% 6% 36%	1570
March	1st to 10th	Day	28% 11% 2 6% 3 3 3 2 4 5% 35%	3116
	11th to 20th	Day	11% 5% 3 5% 4 5% 5% 4 6% 7% 45%	3251
	21st to end	Day	21% 7% 3 6% 4 4 4 3 5% 7% 36%	4154
April	1st to 10th	Day	19% 8% 2 6% 4 4 4 3 5% 7% 38%	2280
	11th to 20th	Day	21% 7% 2 4 3 4 4 3 4 6% 42%	2254
	21st to end	Day	21% 6% 1 6% 4 4 4 3 5% 6% 40%	2405
May	1st to 10th	Day	28% 10% 3 5% 4 3 3 3 5% 7% 30%	4106
	11th to 20th	Day	24% 8% 3 6% 4 4 4 3 5% 7% 33%	4204
	21st to end	Day	16% 5% 2 5% 3 3 4 3 5% 8% 45%	4837
June	1st to 10th	Day	18% 6% 2 6% 5% 5% 5% 4 7% 8% 36%	2660
	11th to 20th	Day	17% 6% 2 5% 4 4 4 4 6% 8% 39%	2660
	21st to end	Day	13% 7% 2 6% 5% 5% 4 4 6% 9% 38%	2660
July	1st to 10th	Day	16% 6% 2 7% 5% 5% 5% 4 6% 8% 35%	4440
	11th to 20th	Day	15% 5% 2 5% 4 4 5% 4 6% 9% 39%	4440
	21st to end	Day	19% 8% 3 7% 5% 4 5% 4 6% 7% 33%	4814
August	1st to 10th	Day	21% 6% 3 7% 4 4 5% 4 6% 8% 32%	4208
	11th to 20th	Day	13% 6% 2 6% 4 5% 4 4 7% 8% 43%	3797
	21st to end	Day	8% 5% 3 6% 4 5% 6% 5% 7% 10% 43%	4180
September	1st to 10th	Day	15% 6% 3 6% 4 3 4 4 5% 6% 46%	2280
	11th to 20th	Day	13% 6% 2 5% 3 3 3 3 4 7% 51%	2128
	21st to end	Day	20% 8% 2 5% 3 4 4 3 5% 6% 40%	2090
October	1st to 10th	Day	22% 7% 2 5% 4 3 3 3 5% 5% 41%	2090
	11th to 20th	Day	14% 6% 2 5% 3 3 4 3 5% 7% 49%	1863
	21st to end	Day	19% 7% 2 6% 3 3 4 3 5% 6% 42%	1809
November	1st to 10th	Day	14% 7% 3 5% 4 4 4 3 4 5% 48%	1671
	11th to 20th	Day	19% 6% 2 4 4 3 3 3 5% 5% 47%	1710
	21st to end	Day	17% 6% 2 5% 4 4 4 3 4 7% 45%	1710
December	1st to 10th	Day	20% 6% 2 6% 5% 4 4 4 5% 6% 38%	1528
	11th to 20th	Day	23% 7% 2 5% 3 3 2 2 4 6% 45%	1906
	21st to end	Day	20% 10% 3 7% 4 4 4 3 4 6% 35%	2772
January	1st to 10th	Night	16% 7% 2 5% 3 3 4 3 4 6% 47%	4429
	11th to 20th	Night	17% 9% 3 7% 4 3 3 3 4 4 43%	4440
	21st to end	Night	24% 12% 3 7% 4 4 3 3 4 4 32%	4843
February	1st to 10th	Night	17% 9% 2 6% 5% 3 4 3 4 5% 41%	2373
	11th to 20th	Night	17% 8% 2 6% 4 3 4 3 5% 6% 41%	2218
	21st to end	Night	21% 8% 2 6% 4 4 3 3 5% 5% 40%	1884
March	1st to 10th	Night	27% 12% 2 5% 3 2 3 2 4 5% 34%	3724
	11th to 20th	Night	11% 8% 2 7% 5% 5% 4 4 5% 6% 44%	3707
	21st to end	Night	23% 8% 2 5% 3 3 4 3 4 5% 39%	3476
April	1st to 10th	Night	20% 7% 3 6% 5% 4 3 4 5% 6% 37%	1900
	11th to 20th	Night	20% 6% 2 7% 4 4 4 3 5% 6% 40%	1875
	21st to end	Night	22% 6% 2 6% 4 3 3 3 4 4 41%	1773
May	1st to 10th	Night	25% 11% 4 8% 4 5% 4 3 4 6% 28%	2834
	11th to 20th	Night	25% 8% 3 8% 4 4 5% 4 5% 6% 29%	2718
	21st to end	Night	18% 7% 2 5% 4 3 3 3 5% 6% 42%	2738
June	1st to 10th	Night	19% 7% 2 5% 5% 4 4 4 5% 7% 39%	1520
	11th to 20th	Night	18% 7% 2 5% 4 4 4 3 6% 9% 39%	1520
	21st to end	Night	15% 6% 3 4 4 4 5% 3 6% 10% 39%	1520
July	1st to 10th	Night	17% 7% 3 8% 5% 4 5% 5% 6% 8% 32%	2520
	11th to 20th	Night	19% 6% 2 5% 4 5% 3 4 6% 10% 36%	2520
	21st to end	Night	20% 10% 3 6% 4 4 4 4 5% 7% 33%	2739
August	1st to 10th	Night	24% 7% 3 8% 5% 4 5% 4 6% 7% 28%	2688
	11th to 20th	Night	12% 7% 2 7% 5% 5% 6% 4 5% 7% 39%	3027
	21st to end	Night	9% 5% 1 4 3 3 4 3 5% 7% 55%	3476
September	1st to 10th	Night	14% 6% 3 6% 4 4 5% 4 5% 6% 42%	1900
	11th to 20th	Night	13% 6% 2 5% 3 3 3 2 4 5% 54%	2051
	21st to end	Night	19% 7% 2 6% 4 4 5% 3 4 5% 40%	2090
October	1st to 10th	Night	20% 7% 3 5% 4 4 4 3 4 6% 41%	2090
	11th to 20th	Night	16% 5% 3 5% 3 2 4 3 4 6% 49%	2311
	21st to end	Night	21% 7% 3 5% 4 3 3 3 4 5% 41%	2614
November	1st to 10th	Night	14% 5% 2 5% 4 3 3 3 5% 6% 48%	2407
	11th to 20th	Night	19% 7% 2 5% 3 3 3 3 4 6% 46%	2470
	21st to end	Night	16% 6% 2 6% 4 3 4 3 4 6% 47%	2470
December	1st to 10th	Night	21% 7% 3 5% 3 4 4 3 5% 6% 39%	2650
	11th to 20th	Night	21% 7% 2 4 3 4 4 3 5% 5% 42%	3288
	21st to end	Night	22% 11% 3 7% 3 3 3 2 4 5% 37%	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	27% 38% 4 21% 8% 2	2518
	11th to 20th	Day	29% 38% 5% 19% 8% 1	2520
	21st to end	Day	38% 40% 4 11% 6% 1	2808
February	1st to 10th	Day	18% 65% 6% 8% 3	1805
	11th to 20th	Day	16% 64% 2 8% 9% 1	1857
	21st to end	Day	17% 65% 5% 8% 4 2	1570
March	1st to 10th	Day	38% 41% 5% 8% 6% 1	3119
	11th to 20th	Day	16% 44% 8% 22% 9% 1	3251
	21st to end	Day	30% 41% 3 10% 12% 3	4154
April	1st to 10th	Day	19% 65% 3 6% 5% 1	2280
	11th to 20th	Day	15% 65% 3 7% 9%	2254
	21st to end	Day	18% 65% 3 8% 6% 1	2405
May	1st to 10th	Day	36% 43% 9% 6% 5% 1	4120
	11th to 20th	Day	34% 42% 9% 11% 4	4208
	21st to end	Day	23% 42% 5% 17% 14%	4837
June	1st to 10th	Day	16% 65% 3 9% 6%	2660
	11th to 20th	Day	14% 66% 5% 9% 6% 1	2660
	21st to end	Day	14% 64% 4 9% 8%	2660
July	1st to 10th	Day	32% 38% 7% 12% 10% 1	4370
	11th to 20th	Day	28% 38% 11% 14% 8% 1	4365
	21st to end	Day	35% 37% 7% 10% 8% 1	4661
August	1st to 10th	Day	35% 38% 10% 12% 4	4194
	11th to 20th	Day	24% 39% 10% 22% 5%	3835
	21st to end	Day	20% 39% 10% 18% 11% 1	4180
September	1st to 10th	Day	15% 61% 5% 11% 8% 1	2280
	11th to 20th	Day	15% 60% 3 9% 11% 2	2128
	21st to end	Day	21% 60% 4 8% 7% 1	2090
October	1st to 10th	Day	19% 60% 3 7% 7% 3	2090
	11th to 20th	Day	13% 60% 4 11% 12% 1	1863
	21st to end	Day	17% 61% 4 7% 8% 2	1809
November	1st to 10th	Day	18% 59% 6% 8% 8% 1	1671
	11th to 20th	Day	14% 59% 4 9% 12% 2	1710
	21st to end	Day	14% 60% 5% 13% 6% 2	1710
December	1st to 10th	Day	21% 59% 6% 5% 8%	1528
	11th to 20th	Day	23% 48% 6% 8% 13% 3	1906
	21st to end	Day	35% 37% 4 17% 7%	2772
January	1st to 10th	Night	24% 37% 6% 22% 7% 4	4429
	11th to 20th	Night	27% 37% 7% 16% 10% 2	4440
	21st to end	Night	41% 39% 4 9% 5% 1	4843
February	1st to 10th	Night	16% 65% 5% 9% 4 1	2373
	11th to 20th	Night	15% 63% 3 6% 10% 2	2220
	21st to end	Night	17% 64% 3 7% 6% 2	1884
March	1st to 10th	Night	38% 41% 4 10% 5% 1	3734
	11th to 20th	Night	20% 42% 9% 15% 11% 2	3708
	21st to end	Night	31% 41% 3 5% 16% 3	3476
April	1st to 10th	Night	18% 66% 3 7% 5% 1	1900
	11th to 20th	Night	15% 66% 4 7% 7% 1	1875
	21st to end	Night	16% 65% 3 9% 6% 1	1773
May	1st to 10th	Night	38% 42% 8% 9% 3	2840
	11th to 20th	Night	38% 43% 8% 7% 3	2719
	21st to end	Night	26% 42% 8% 17% 7% 1	2739
June	1st to 10th	Night	16% 65% 2 8% 8% 1	1520
	11th to 20th	Night	14% 66% 4 11% 5%	1520
	21st to end	Night	14% 63% 4 11% 7%	1520
July	1st to 10th	Night	35% 38% 7% 11% 8% 1	2480
	11th to 20th	Night	30% 37% 11% 15% 6%	2472
	21st to end	Night	36% 37% 7% 8% 11% 1	2651
August	1st to 10th	Night	40% 39% 7% 8% 5% 1	2678
	11th to 20th	Night	27% 39% 10% 20% 3	3055
	21st to end	Night	13% 38% 13% 22% 14% 1	3476
September	1st to 10th	Night	16% 60% 4 12% 7% 1	1900
	11th to 20th	Night	15% 59% 4 9% 11% 2	2051
	21st to end	Night	22% 60% 3 7% 8% 1	2090
October	1st to 10th	Night	19% 60% 4 9% 6% 2	2090
	11th to 20th	Night	12% 60% 5% 12% 9% 1	2311
	21st to end	Night	17% 61% 4 9% 8% 1	2614
November	1st to 10th	Night	18% 59% 5% 8% 9% 1	2407
	11th to 20th	Night	16% 59% 4 8% 10% 3	2470
	21st to end	Night	15% 60% 4 13% 5% 2	2470
December	1st to 10th	Night	21% 60% 4 8% 6%	2650
	11th to 20th	Night	23% 49% 6% 9% 12% 2	3288
	21st to end	Night	34% 38% 5% 14% 8%	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% 25% 29% 16% 2	180
	11th to 20th	Day	31% 28% 27% 13% 1	180
	21st to end	Day	22% 31% 33% 9% 5%	209
February	1st to 10th	Day	30% 23% 33% 13% 1	365
	11th to 20th	Day	28% 27% 34% 9% 1	456
	21st to end	Day	31% 24% 30% 11% 4	382
March	1st to 10th	Day	26% 24% 34% 13% 2	460
	11th to 20th	Day	25% 25% 35% 11% 3 1	460
	21st to end	Day	30% 24% 31% 11% 3 1	506
April	1st to 10th	Day	29% 27% 27% 12% 5%	460
	11th to 20th	Day	29% 24% 29% 13% 5%	452
	21st to end	Day	29% 18% 33% 14% 4 2	460
May	1st to 10th	Day	32% 19% 30% 14% 5% 1	463
	11th to 20th	Day	24% 16% 41% 14% 5% 1	487
	21st to end	Day	20% 14% 31% 24% 9% 1	529
June	1st to 10th	Day	20% 13% 34% 22% 10% 2	490
	11th to 20th	Day	18% 17% 34% 22% 8% 1	490
	21st to end	Day	16% 14% 34% 23% 10% 2	490
July	1st to 10th	Day	18% 8% 32% 26% 14% 2	485
	11th to 20th	Day	14% 7% 31% 32% 13% 3	484
	21st to end	Day	15% 10% 39% 27% 8% 1	532
August	1st to 10th	Day	14% 9% 30% 33% 10% 4	486
	11th to 20th	Day	16% 8% 31% 29% 13% 4	479
	21st to end	Day	11% 11% 34% 25% 14% 5%	539
September	1st to 10th	Day	19% 10% 29% 24% 15% 3	490
	11th to 20th	Day	14% 11% 33% 23% 12% 8%	490
	21st to end	Day	23% 13% 34% 19% 9% 2	490
October	1st to 10th	Day	28% 12% 25% 21% 10% 4	490
	11th to 20th	Day	19% 21% 29% 22% 8% 2	470
	21st to end	Day	24% 18% 30% 19% 7% 2	405
November	1st to 10th	Day	20% 16% 32% 22% 9% 1	365
	11th to 20th	Day	25% 23% 28% 18% 6%	370
	21st to end	Day	23% 21% 29% 21% 6%	370
December	1st to 10th	Day	26% 24% 30% 15% 5%	188
	11th to 20th	Day	33% 26% 29% 9% 3	180
	21st to end	Day	27% 26% 28% 15% 4 1	198
January	1st to 10th	Night	21% 23% 36% 17% 3	760
	11th to 20th	Night	29% 20% 33% 17% 2	760
	21st to end	Night	20% 24% 35% 18% 2	836
February	1st to 10th	Night	23% 20% 35% 20% 1	760
	11th to 20th	Night	24% 22% 38% 13% 1	743
	21st to end	Night	27% 22% 32% 15% 3	628
March	1st to 10th	Night	25% 19% 35% 18% 3	760
	11th to 20th	Night	23% 18% 37% 18% 3 1	760
	21st to end	Night	24% 21% 35% 17% 3	836
April	1st to 10th	Night	24% 20% 35% 19% 3	760
	11th to 20th	Night	22% 16% 36% 22% 3	751
	21st to end	Night	24% 16% 37% 18% 6% 1	633
May	1st to 10th	Night	25% 14% 32% 22% 6%	570
	11th to 20th	Night	23% 14% 38% 20% 5%	506
	21st to end	Night	20% 7% 29% 34% 9% 1	411
June	1st to 10th	Night	23% 6% 29% 32% 9% 1	380
	11th to 20th	Night	20% 6% 29% 36% 9%	380
	21st to end	Night	17% 5% 31% 37% 9%	380
July	1st to 10th	Night	15% 5% 28% 34% 16% 1	370
	11th to 20th	Night	15% 3 26% 40% 15% 1	368
	21st to end	Night	18% 4 27% 40% 10% 1	416
August	1st to 10th	Night	12% 4 30% 39% 14% 1	482
	11th to 20th	Night	15% 4 26% 36% 18% 2	704
	21st to end	Night	14% 5% 25% 35% 18% 2	836
September	1st to 10th	Night	15% 5% 32% 33% 13% 2	760
	11th to 20th	Night	17% 7% 25% 30% 18% 3	760
	21st to end	Night	21% 9% 28% 27% 14% 2	760
October	1st to 10th	Night	21% 11% 29% 24% 12% 2	760
	11th to 20th	Night	19% 14% 33% 24% 10%	760
	21st to end	Night	26% 13% 34% 19% 8%	805
November	1st to 10th	Night	17% 15% 34% 22% 11% 1	740
	11th to 20th	Night	23% 19% 32% 20% 5% 1	760
	21st to end	Night	21% 20% 32% 21% 6%	760
December	1st to 10th	Night	27% 18% 30% 19% 5% 1	760
	11th to 20th	Night	25% 21% 32% 19% 3	760
	21st to end	Night	26% 17% 38% 17% 2	836

Page generated at 2024-10-21 02:20:05. Version ac07

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