Chester State Park
Clear Sky Chart
History

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

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	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	101246
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 43%	97878
Transparency	Day	38% 7% 12% 20% 18% 6%	104949
	Night	38% 6% 11% 18% 19% 7%	102314
Seeing	Day	17% 9% 25% 25% 18% 7%	15301
	Night	16% 9% 23% 31% 19% 3	25359

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	17% 5% 1 4 3 3 3 3 5% 6% 49%	2836
	11th to 20th	Day	13% 7% 2 5% 4 3 3 3 4 5% 53%	2840
	21st to end	Day	22% 7% 2 6% 3 4 3 3 4 4 43%	3124
February	1st to 10th	Day	15% 7% 2 5% 4 4 4 3 5% 7% 42%	1719
	11th to 20th	Day	21% 6% 2 5% 4 3 4 3 4 4 45%	1848
	21st to end	Day	20% 7% 3 7% 3 4 4 2 4 5% 41%	1608
March	1st to 10th	Day	23% 8% 2 5% 4 3 3 3 4 5% 40%	3435
	11th to 20th	Day	11% 4 2 5% 4 2 4 4 4 6% 53%	3480
	21st to end	Day	19% 7% 2 6% 4 4 3 3 4 5% 42%	3815
April	1st to 10th	Day	11% 4 2 5% 3 4 5% 4 6% 8% 49%	2090
	11th to 20th	Day	12% 6% 1 5% 4 4 4 4 5% 7% 48%	2225
	21st to end	Day	11% 4 2 5% 4 4 4 4 6% 8% 49%	2434
May	1st to 10th	Day	10% 6% 3 6% 5% 5% 6% 5% 7% 10% 37%	4082
	11th to 20th	Day	17% 7% 3 6% 4 5% 4 4 5% 7% 37%	4081
	21st to end	Day	7% 4 2 5% 4 4 5% 4 7% 10% 47%	4476
June	1st to 10th	Day	9% 5% 2 7% 6% 5% 6% 5% 7% 11% 37%	2470
	11th to 20th	Day	7% 4 2 6% 6% 6% 5% 5% 7% 11% 41%	2470
	21st to end	Day	6% 4 2 6% 7% 7% 7% 5% 8% 9% 40%	2470
July	1st to 10th	Day	10% 6% 3 8% 6% 6% 6% 5% 8% 10% 32%	4120
	11th to 20th	Day	7% 5% 2 7% 6% 6% 7% 6% 9% 11% 34%	4120
	21st to end	Day	11% 8% 3 9% 6% 7% 7% 6% 9% 10% 23%	4466
August	1st to 10th	Day	21% 7% 3 7% 5% 6% 6% 5% 7% 9% 24%	4104
	11th to 20th	Day	11% 6% 2 6% 5% 5% 6% 6% 8% 10% 34%	4044
	21st to end	Day	6% 4 2 5% 4 4 5% 4 7% 9% 51%	4227
September	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 4 7% 9% 42%	2090
	11th to 20th	Day	13% 7% 2 8% 5% 4 5% 4 6% 7% 39%	2090
	21st to end	Day	16% 7% 3 5% 4 4 4 4 5% 6% 41%	2090
October	1st to 10th	Day	14% 5% 2 5% 3 4 3 3 4 5% 53%	1990
	11th to 20th	Day	13% 4 2 4 3 2 3 2 3 5% 58%	1900
	21st to end	Day	13% 5% 1 4 2 3 3 3 4 5% 57%	2090
November	1st to 10th	Day	15% 6% 2 4 3 3 3 3 3 6% 53%	1957
	11th to 20th	Day	14% 6% 2 4 2 2 4 3 3 6% 53%	1758
	21st to end	Day	16% 5% 1 5% 4 3 3 3 5% 6% 50%	1710
December	1st to 10th	Day	19% 8% 2 5% 4 4 4 4 5% 6% 39%	1710
	11th to 20th	Day	18% 5% 2 5% 3 3 3 2 4 6% 51%	2153
	21st to end	Day	19% 6% 2 5% 4 4 3 3 5% 6% 43%	3124
January	1st to 10th	Night	18% 5% 2 5% 4 3 4 2 4 5% 48%	4109
	11th to 20th	Night	12% 7% 2 6% 4 4 4 3 6% 5% 47%	4120
	21st to end	Night	21% 9% 2 5% 3 3 3 3 3 4 44%	4532
February	1st to 10th	Night	15% 6% 2 6% 4 4 3 3 4 5% 46%	2456
	11th to 20th	Night	19% 7% 3 6% 3 3 3 3 4 5% 43%	2218
	21st to end	Night	16% 6% 2 6% 4 3 5% 3 5% 8% 42%	1844
March	1st to 10th	Night	24% 9% 3 7% 4 3 3 3 4 5% 35%	3418
	11th to 20th	Night	11% 5% 2 5% 4 3 4 3 5% 7% 51%	3480
	21st to end	Night	19% 6% 2 5% 4 4 4 3 5% 6% 43%	3817
April	1st to 10th	Night	12% 5% 2 4 4 4 4 4 5% 7% 50%	2090
	11th to 20th	Night	12% 5% 3 5% 3 3 4 3 5% 6% 52%	1904
	21st to end	Night	11% 5% 2 6% 4 3 3 4 5% 8% 51%	1762
May	1st to 10th	Night	12% 6% 2 6% 4 4 5% 3 5% 9% 42%	2813
	11th to 20th	Night	16% 8% 3 6% 4 3 5% 4 6% 8% 38%	2812
	21st to end	Night	6% 5% 2 6% 4 5% 5% 4 8% 12% 43%	3079
June	1st to 10th	Night	11% 6% 2 8% 6% 6% 6% 5% 7% 11% 33%	1710
	11th to 20th	Night	9% 6% 2 6% 6% 4 5% 5% 8% 10% 38%	1710
	21st to end	Night	8% 6% 3 6% 7% 6% 6% 4 8% 10% 36%	1710
July	1st to 10th	Night	11% 8% 3 8% 6% 6% 6% 5% 8% 10% 29%	2840
	11th to 20th	Night	9% 6% 2 8% 5% 5% 6% 6% 10% 12% 30%	2840
	21st to end	Night	14% 11% 4 10% 6% 6% 6% 6% 7% 9% 22%	3087
August	1st to 10th	Night	23% 8% 2 8% 5% 5% 5% 4 7% 9% 24%	2825
	11th to 20th	Night	12% 6% 3 6% 5% 5% 5% 6% 8% 11% 32%	2785
	21st to end	Night	6% 4 2 6% 4 4 5% 5% 7% 9% 48%	3391
September	1st to 10th	Night	9% 6% 2 7% 5% 4 5% 4 6% 10% 43%	2090
	11th to 20th	Night	14% 7% 3 7% 6% 4 4 4 6% 8% 38%	2090
	21st to end	Night	15% 6% 2 7% 4 3 5% 3 6% 6% 42%	2090
October	1st to 10th	Night	15% 4 2 4 3 3 3 3 4 5% 53%	2187
	11th to 20th	Night	13% 6% 2 6% 3 3 3 2 4 6% 54%	2280
	21st to end	Night	12% 5% 2 4 3 3 3 3 3 5% 58%	2508
November	1st to 10th	Night	14% 6% 2 5% 3 3 3 2 4 6% 52%	2341
	11th to 20th	Night	13% 7% 2 4 3 3 3 3 4 6% 52%	2426
	21st to end	Night	14% 6% 2 5% 3 4 4 3 5% 7% 49%	2470
December	1st to 10th	Night	19% 7% 3 6% 3 4 4 3 4 5% 42%	2470
	11th to 20th	Night	18% 5% 2 5% 3 2 3 2 3 5% 52%	3042
	21st to end	Night	20% 6% 2 6% 3 3 4 3 6% 6% 42%	4532

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	36% 3 6% 24% 23% 7%	2837
	11th to 20th	Day	35% 4 6% 17% 31% 7%	2840
	21st to end	Day	45% 4 4 17% 24% 6%	3124
February	1st to 10th	Day	41% 4 10% 20% 19% 5%	1719
	11th to 20th	Day	42% 4 7% 18% 23% 6%	1858
	21st to end	Day	45% 4 9% 14% 20% 7%	1608
March	1st to 10th	Day	48% 4 8% 16% 15% 10%	3435
	11th to 20th	Day	31% 6% 8% 14% 29% 12%	3480
	21st to end	Day	45% 5% 6% 18% 22% 4	3815
April	1st to 10th	Day	33% 4 10% 20% 27% 6%	2090
	11th to 20th	Day	35% 6% 10% 19% 20% 10%	2225
	21st to end	Day	32% 7% 12% 24% 22% 4	2434
May	1st to 10th	Day	39% 9% 16% 21% 12% 2	4120
	11th to 20th	Day	44% 8% 11% 20% 16% 1	4085
	21st to end	Day	29% 9% 16% 23% 20% 3	4489
June	1st to 10th	Day	39% 8% 16% 25% 10% 2	2470
	11th to 20th	Day	34% 10% 18% 23% 14% 1	2470
	21st to end	Day	35% 12% 16% 20% 14% 2	2470
July	1st to 10th	Day	42% 12% 18% 18% 8% 1	4055
	11th to 20th	Day	38% 14% 26% 17% 4 1	4051
	21st to end	Day	50% 13% 16% 15% 5%	4324
August	1st to 10th	Day	52% 10% 17% 15% 5%	4091
	11th to 20th	Day	38% 13% 17% 19% 13% 1	4083
	21st to end	Day	27% 9% 16% 29% 16% 3	4227
September	1st to 10th	Day	36% 9% 15% 18% 18% 4	2090
	11th to 20th	Day	42% 8% 11% 16% 20% 3	2090
	21st to end	Day	44% 6% 9% 20% 15% 6%	2090
October	1st to 10th	Day	30% 5% 7% 20% 28% 10%	3302
	11th to 20th	Day	20% 2 6% 17% 29% 27%	3140
	21st to end	Day	26% 3 5% 23% 28% 15%	3428
November	1st to 10th	Day	34% 4 7% 17% 29% 9%	1957
	11th to 20th	Day	32% 4 7% 22% 26% 9%	1758
	21st to end	Day	35% 5% 8% 20% 22% 9%	1710
December	1st to 10th	Day	45% 5% 7% 21% 17% 5%	1710
	11th to 20th	Day	36% 3 7% 21% 23% 11%	2150
	21st to end	Day	42% 5% 7% 21% 21% 3	3124
January	1st to 10th	Night	37% 4 6% 19% 25% 7%	4109
	11th to 20th	Night	37% 6% 8% 17% 27% 7%	4120
	21st to end	Night	45% 4 4 16% 26% 6%	4532
February	1st to 10th	Night	41% 4 9% 19% 21% 7%	2456
	11th to 20th	Night	44% 3 7% 16% 23% 7%	2219
	21st to end	Night	40% 5% 11% 17% 19% 8%	1844
March	1st to 10th	Night	50% 6% 9% 13% 14% 7%	3418
	11th to 20th	Night	32% 5% 8% 15% 26% 14%	3480
	21st to end	Night	42% 5% 7% 19% 20% 7%	3817
April	1st to 10th	Night	34% 5% 10% 18% 25% 8%	2090
	11th to 20th	Night	32% 5% 9% 23% 21% 10%	1904
	21st to end	Night	32% 5% 11% 27% 21% 5%	1762
May	1st to 10th	Night	38% 8% 14% 23% 15% 2	2840
	11th to 20th	Night	41% 8% 14% 22% 14% 1	2813
	21st to end	Night	29% 11% 15% 27% 17% 2	3087
June	1st to 10th	Night	43% 9% 16% 20% 11% 2	1710
	11th to 20th	Night	38% 12% 16% 20% 12% 2	1710
	21st to end	Night	40% 11% 16% 17% 12% 3	1710
July	1st to 10th	Night	46% 12% 19% 14% 7% 2	2795
	11th to 20th	Night	40% 16% 25% 14% 4 1	2786
	21st to end	Night	56% 12% 14% 13% 4 1	2988
August	1st to 10th	Night	54% 10% 18% 14% 4	2814
	11th to 20th	Night	40% 12% 23% 16% 8% 1	2812
	21st to end	Night	29% 9% 13% 26% 20% 3	3391
September	1st to 10th	Night	36% 8% 15% 18% 16% 5%	2090
	11th to 20th	Night	43% 9% 12% 17% 18% 2	2090
	21st to end	Night	42% 7% 12% 17% 16% 6%	2090
October	1st to 10th	Night	31% 5% 9% 19% 28% 7%	3655
	11th to 20th	Night	23% 3 5% 17% 27% 26%	3779
	21st to end	Night	26% 4 5% 20% 27% 18%	4120
November	1st to 10th	Night	34% 4 7% 17% 26% 12%	2341
	11th to 20th	Night	35% 4 6% 17% 26% 12%	2426
	21st to end	Night	35% 4 6% 20% 27% 7%	2470
December	1st to 10th	Night	44% 5% 8% 18% 20% 6%	2470
	11th to 20th	Night	36% 3 8% 17% 25% 10%	3044
	21st to end	Night	42% 4 8% 21% 22% 3	4532

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	22% 21% 38% 17% 1	270
	11th to 20th	Day	27% 20% 32% 16% 5%	270
	21st to end	Day	24% 18% 43% 11% 4	297
February	1st to 10th	Day	22% 20% 39% 14% 5%	270
	11th to 20th	Day	37% 14% 39% 9% 1	270
	21st to end	Day	27% 20% 35% 17% 2	263
March	1st to 10th	Day	23% 15% 34% 19% 7% 1	460
	11th to 20th	Day	22% 16% 40% 16% 5% 1	460
	21st to end	Day	24% 17% 35% 17% 6% 1	506
April	1st to 10th	Day	22% 13% 34% 20% 9% 2	460
	11th to 20th	Day	15% 17% 33% 23% 11% 3	452
	21st to end	Day	16% 9% 31% 25% 14% 5%	460
May	1st to 10th	Day	14% 13% 33% 22% 14% 5%	463
	11th to 20th	Day	17% 7% 22% 29% 17% 8%	487
	21st to end	Day	15% 5% 18% 28% 21% 13%	529
June	1st to 10th	Day	12% 3 17% 37% 23% 9%	490
	11th to 20th	Day	9% 4 19% 28% 28% 11%	490
	21st to end	Day	9% 3 15% 34% 27% 11%	490
July	1st to 10th	Day	9% 1 10% 27% 34% 18%	485
	11th to 20th	Day	9% 2 9% 31% 33% 15%	484
	21st to end	Day	7% 2 12% 35% 32% 12%	532
August	1st to 10th	Day	17% 4 14% 26% 25% 14%	486
	11th to 20th	Day	15% 3 12% 27% 30% 14%	479
	21st to end	Day	10% 2 14% 31% 26% 17%	539
September	1st to 10th	Day	9% 4 13% 31% 32% 12%	490
	11th to 20th	Day	17% 4 15% 27% 26% 12%	490
	21st to end	Day	19% 6% 18% 29% 23% 5%	490
October	1st to 10th	Day	16% 4 24% 28% 20% 8%	490
	11th to 20th	Day	12% 8% 26% 27% 21% 6%	490
	21st to end	Day	17% 7% 24% 27% 20% 6%	539
November	1st to 10th	Day	21% 8% 25% 26% 17% 3	495
	11th to 20th	Day	17% 13% 37% 23% 8% 2	318
	21st to end	Day	13% 11% 36% 26% 12% 2	270
December	1st to 10th	Day	26% 13% 37% 19% 5%	270
	11th to 20th	Day	24% 12% 35% 20% 7% 3	270
	21st to end	Day	27% 14% 33% 15% 7% 3	297
January	1st to 10th	Night	24% 16% 29% 26% 6%	760
	11th to 20th	Night	20% 14% 32% 28% 6%	760
	21st to end	Night	21% 16% 31% 29% 3	836
February	1st to 10th	Night	19% 14% 32% 30% 4	760
	11th to 20th	Night	24% 15% 36% 22% 1	743
	21st to end	Night	20% 16% 35% 26% 4	628
March	1st to 10th	Night	21% 11% 32% 29% 6%	760
	11th to 20th	Night	19% 13% 35% 25% 8%	760
	21st to end	Night	18% 14% 34% 27% 7%	836
April	1st to 10th	Night	15% 16% 31% 28% 9%	760
	11th to 20th	Night	16% 13% 27% 32% 12% 1	751
	21st to end	Night	13% 7% 30% 34% 16%	622
May	1st to 10th	Night	11% 8% 28% 37% 16%	570
	11th to 20th	Night	15% 5% 24% 34% 21% 1	561
	21st to end	Night	11% 3 14% 35% 33% 3	617
June	1st to 10th	Night	13% 3 15% 39% 27% 3	570
	11th to 20th	Night	12% 3 17% 30% 31% 8%	570
	21st to end	Night	9% 2 14% 37% 33% 6%	570
July	1st to 10th	Night	10% 3 8% 34% 36% 8%	555
	11th to 20th	Night	11% 2 6% 31% 41% 10%	552
	21st to end	Night	9% 4 10% 31% 39% 6%	624
August	1st to 10th	Night	15% 3 10% 27% 37% 7%	567
	11th to 20th	Night	12% 2 10% 31% 39% 6%	564
	21st to end	Night	12% 2 10% 29% 40% 7%	768
September	1st to 10th	Night	11% 3 11% 31% 39% 6%	760
	11th to 20th	Night	16% 4 12% 29% 35% 4	760
	21st to end	Night	18% 5% 13% 32% 27% 4	760
October	1st to 10th	Night	16% 4 18% 29% 28% 6%	760
	11th to 20th	Night	16% 8% 23% 29% 21% 3	760
	21st to end	Night	14% 9% 20% 33% 22% 2	836
November	1st to 10th	Night	17% 6% 23% 33% 18% 3	780
	11th to 20th	Night	15% 12% 26% 34% 12% 1	763
	21st to end	Night	16% 11% 24% 35% 13% 1	760
December	1st to 10th	Night	22% 12% 25% 33% 7% 1	760
	11th to 20th	Night	20% 9% 25% 33% 12% 1	760
	21st to end	Night	26% 14% 22% 30% 8%	836

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