England/Idlewild Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the England/Idlewild Park clear sky chart from 2005-11-06 to 2025-09-19.

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	14% 9% 3 7% 5% 4 5% 4 5% 7% 36%	126269
	Night	14% 10% 3 8% 4 4 4 4 5% 7% 37%	122839
Transparency	Day	46% 4 10% 24% 15% 2	129907
	Night	46% 3 10% 23% 15% 2	127270
Seeing	Day	18% 8% 25% 24% 16% 8%	16527
	Night	20% 7% 24% 31% 17% 2	26177

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	15% 18% 7% 10% 4 3 3 3 4 5% 27%	3617
	11th to 20th	Day	13% 13% 6% 14% 5% 5% 4 3 4 4 29%	3898
	21st to end	Day	21% 11% 7% 8% 5% 5% 5% 3 4 4 26%	4466
February	1st to 10th	Day	18% 13% 5% 8% 4 4 3 3 5% 5% 31%	1930
	11th to 20th	Day	16% 12% 5% 10% 5% 4 4 2 5% 5% 32%	1948
	21st to end	Day	18% 13% 5% 9% 4 3 4 3 4 5% 32%	1650
March	1st to 10th	Day	18% 13% 5% 9% 4 3 4 3 4 4 32%	4480
	11th to 20th	Day	13% 8% 3 6% 4 4 4 3 5% 8% 40%	4979
	21st to end	Day	17% 11% 3 6% 5% 4 5% 4 6% 6% 33%	5465
April	1st to 10th	Day	16% 9% 3 7% 4 4 4 4 5% 8% 34%	2380
	11th to 20th	Day	15% 8% 3 7% 5% 5% 4 4 4 6% 38%	2408
	21st to end	Day	17% 8% 2 7% 5% 5% 4 4 6% 7% 35%	2600
May	1st to 10th	Day	19% 9% 3 7% 6% 5% 6% 4 6% 8% 27%	5862
	11th to 20th	Day	19% 10% 3 7% 4 4 4 3 5% 7% 33%	5861
	21st to end	Day	13% 7% 3 8% 5% 6% 6% 5% 8% 9% 31%	6433
June	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 5% 6% 7% 41%	2616
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 5% 6% 9% 42%	2800
	21st to end	Day	8% 6% 2 7% 5% 5% 6% 5% 6% 10% 40%	2800
July	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 4 7% 10% 41%	6360
	11th to 20th	Day	9% 6% 3 7% 5% 6% 6% 5% 7% 11% 37%	6181
	21st to end	Day	10% 8% 3 9% 6% 7% 6% 6% 7% 9% 30%	6424
August	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 5% 7% 10% 44%	4234
	11th to 20th	Day	8% 6% 2 6% 4 5% 5% 5% 7% 11% 41%	4151
	21st to end	Day	5% 4 2 5% 4 4 4 4 5% 9% 54%	4312
September	1st to 10th	Day	13% 5% 2 6% 3 4 4 4 4 7% 48%	2290
	11th to 20th	Day	8% 4 2 6% 4 3 4 5% 6% 9% 49%	2178
	21st to end	Day	15% 7% 2 6% 4 3 4 3 5% 5% 48%	2090
October	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 3 5% 5% 51%	2090
	11th to 20th	Day	12% 7% 2 6% 5% 3 3 3 6% 7% 46%	1948
	21st to end	Day	18% 8% 3 7% 3 4 3 3 5% 6% 39%	1929
November	1st to 10th	Day	9% 7% 3 6% 4 3 4 2 3 6% 52%	1762
	11th to 20th	Day	14% 10% 4 8% 5% 3 4 3 6% 7% 37%	1800
	21st to end	Day	17% 11% 4 8% 4 3 3 3 4 6% 37%	1800
December	1st to 10th	Day	18% 11% 3 7% 5% 3 3 3 3 5% 40%	2930
	11th to 20th	Day	17% 15% 5% 10% 5% 5% 4 3 5% 4 27%	3373
	21st to end	Day	23% 18% 5% 8% 6% 4 4 3 4 6% 20%	4224
January	1st to 10th	Night	15% 16% 6% 14% 6% 5% 5% 4 4 5% 20%	6348
	11th to 20th	Night	13% 17% 7% 14% 6% 5% 5% 3 4 4 23%	6062
	21st to end	Night	20% 13% 4 8% 5% 4 3 3 4 4 32%	6490
February	1st to 10th	Night	20% 12% 4 10% 5% 4 5% 3 5% 5% 28%	2465
	11th to 20th	Night	18% 12% 3 10% 5% 4 3 3 5% 6% 30%	2338
	21st to end	Night	20% 14% 4 8% 3 3 3 3 4 6% 31%	1980
March	1st to 10th	Night	19% 14% 2 6% 4 4 3 3 4 5% 36%	5373
	11th to 20th	Night	12% 7% 2 7% 4 4 4 4 6% 6% 44%	4980
	21st to end	Night	16% 10% 3 9% 5% 4 5% 4 5% 6% 33%	5467
April	1st to 10th	Night	15% 9% 3 6% 5% 4 4 4 6% 7% 37%	2035
	11th to 20th	Night	14% 9% 3 6% 4 4 4 4 6% 7% 40%	1938
	21st to end	Night	17% 7% 3 6% 4 4 4 4 6% 8% 36%	1800
May	1st to 10th	Night	20% 11% 4 8% 5% 4 5% 4 6% 7% 28%	4033
	11th to 20th	Night	16% 7% 3 7% 4 6% 5% 4 7% 9% 32%	4032
	21st to end	Night	12% 7% 3 7% 5% 5% 5% 4 6% 9% 37%	4421
June	1st to 10th	Night	8% 6% 2 5% 4 4 4 3 6% 9% 48%	1778
	11th to 20th	Night	8% 6% 2 5% 4 4 4 4 6% 11% 45%	1600
	21st to end	Night	6% 4 3 5% 5% 4 4 5% 7% 10% 48%	1600
July	1st to 10th	Night	8% 6% 2 6% 4 5% 4 4 6% 9% 47%	3618
	11th to 20th	Night	7% 6% 2 7% 4 5% 5% 4 7% 9% 43%	3784
	21st to end	Night	9% 6% 3 6% 5% 5% 5% 5% 7% 10% 39%	4427
August	1st to 10th	Night	7% 6% 2 7% 4 4 5% 4 7% 10% 45%	2915
	11th to 20th	Night	7% 6% 2 7% 4 5% 4 4 7% 9% 46%	2895
	21st to end	Night	3 3 1 4 3 4 3 4 6% 10% 60%	3586
September	1st to 10th	Night	12% 5% 1 4 3 3 3 4 5% 7% 52%	2090
	11th to 20th	Night	8% 4 2 5% 2 3 4 4 5% 8% 54%	2179
	21st to end	Night	15% 6% 2 5% 4 3 4 2 4 6% 49%	2090
October	1st to 10th	Night	8% 5% 2 5% 4 3 3 3 5% 6% 56%	2090
	11th to 20th	Night	14% 6% 3 6% 3 4 4 3 5% 6% 46%	2232
	21st to end	Night	17% 9% 2 6% 3 4 3 3 5% 6% 41%	2665
November	1st to 10th	Night	12% 7% 2 6% 4 3 4 3 5% 5% 48%	2536
	11th to 20th	Night	15% 9% 3 8% 4 3 4 4 5% 7% 39%	2600
	21st to end	Night	18% 12% 3 7% 5% 4 4 3 4 6% 34%	2600
December	1st to 10th	Night	17% 11% 4 8% 4 4 3 3 4 5% 38%	4250
	11th to 20th	Night	19% 14% 5% 10% 5% 4 4 3 5% 5% 27%	4822
	21st to end	Night	21% 19% 7% 11% 5% 4 4 3 3 5% 17%	6720

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	61% 2 8% 20% 9%	3618
	11th to 20th	Day	59% 3 6% 17% 13% 2	3898
	21st to end	Day	62% 2 8% 19% 7% 2	4466
February	1st to 10th	Day	56% 2 8% 21% 11% 1	1930
	11th to 20th	Day	55% 3 8% 21% 12% 1	1958
	21st to end	Day	55% 2 9% 23% 10% 2	1650
March	1st to 10th	Day	55% 2 6% 19% 14% 5%	4480
	11th to 20th	Day	44% 3 8% 28% 16% 2	4979
	21st to end	Day	51% 3 11% 21% 12% 2	5465
April	1st to 10th	Day	47% 3 10% 23% 14% 1	2380
	11th to 20th	Day	47% 2 8% 24% 16% 3	2408
	21st to end	Day	48% 3 10% 25% 12% 2	2600
May	1st to 10th	Day	55% 4 11% 18% 11% 1	5897
	11th to 20th	Day	50% 3 11% 24% 11% 1	5865
	21st to end	Day	46% 5% 12% 23% 12% 1	6447
June	1st to 10th	Day	40% 4 11% 26% 17% 2	2616
	11th to 20th	Day	38% 5% 13% 24% 20% 2	2800
	21st to end	Day	39% 5% 13% 23% 15% 4	2800
July	1st to 10th	Day	38% 5% 12% 25% 19% 1	6291
	11th to 20th	Day	38% 8% 14% 27% 13% 1	6106
	21st to end	Day	48% 7% 11% 19% 13% 2	6240
August	1st to 10th	Day	32% 6% 15% 33% 13% 1	4221
	11th to 20th	Day	35% 5% 11% 33% 15% 1	4190
	21st to end	Day	27% 4 14% 30% 20% 4	4311
September	1st to 10th	Day	37% 3 9% 25% 20% 5%	2290
	11th to 20th	Day	33% 4 10% 27% 23% 3	2178
	21st to end	Day	39% 3 9% 26% 21% 2	2090
October	1st to 10th	Day	24% 3 7% 32% 33% 2	3480
	11th to 20th	Day	30% 3 7% 30% 28% 2	3214
	21st to end	Day	36% 2 10% 26% 24% 2	3153
November	1st to 10th	Day	35% 3 8% 29% 22% 3	1762
	11th to 20th	Day	47% 3 6% 24% 16% 4	1800
	21st to end	Day	50% 2 9% 23% 15% 1	1800
December	1st to 10th	Day	49% 2 8% 27% 13%	2930
	11th to 20th	Day	62% 3 6% 20% 9% 1	3370
	21st to end	Day	67% 3 10% 13% 6% 1	4224
January	1st to 10th	Night	67% 3 7% 15% 9%	6348
	11th to 20th	Night	67% 2 7% 13% 8% 3	6062
	21st to end	Night	57% 2 6% 23% 11% 1	6490
February	1st to 10th	Night	60% 2 9% 20% 7% 1	2465
	11th to 20th	Night	55% 2 8% 21% 12% 1	2339
	21st to end	Night	56% 2 10% 19% 11% 3	1980
March	1st to 10th	Night	52% 2 5% 27% 12% 3	5373
	11th to 20th	Night	40% 3 9% 28% 19% 1	4980
	21st to end	Night	52% 3 7% 26% 12% 1	5467
April	1st to 10th	Night	46% 3 9% 26% 13% 2	2035
	11th to 20th	Night	43% 2 10% 21% 18% 6%	1938
	21st to end	Night	45% 3 11% 24% 13% 3	1800
May	1st to 10th	Night	55% 5% 10% 20% 8% 2	4060
	11th to 20th	Night	48% 4 13% 24% 9% 1	4033
	21st to end	Night	43% 5% 14% 24% 11% 3	4429
June	1st to 10th	Night	33% 4 12% 26% 22% 3	1778
	11th to 20th	Night	33% 5% 14% 24% 21% 4	1600
	21st to end	Night	29% 6% 18% 24% 18% 6%	1600
July	1st to 10th	Night	34% 6% 11% 24% 20% 4	3580
	11th to 20th	Night	35% 8% 14% 27% 15% 1	3739
	21st to end	Night	39% 6% 13% 25% 14% 3	4297
August	1st to 10th	Night	32% 6% 14% 34% 12% 1	2904
	11th to 20th	Night	33% 6% 11% 31% 18% 1	2922
	21st to end	Night	21% 4 15% 35% 22% 3	3586
September	1st to 10th	Night	31% 4 11% 27% 20% 6%	2090
	11th to 20th	Night	29% 4 9% 28% 27% 4	2179
	21st to end	Night	39% 2 7% 24% 24% 3	2090
October	1st to 10th	Night	22% 2 6% 26% 42% 2	3480
	11th to 20th	Night	27% 2 8% 27% 34% 2	3705
	21st to end	Night	33% 3 7% 23% 29% 5%	4391
November	1st to 10th	Night	38% 3 9% 23% 23% 4	2536
	11th to 20th	Night	45% 2 7% 22% 19% 4	2600
	21st to end	Night	53% 2 9% 21% 13% 1	2600
December	1st to 10th	Night	50% 2 11% 25% 12%	4250
	11th to 20th	Night	59% 3 10% 19% 9% 1	4824
	21st to end	Night	71% 3 8% 14% 4	6720

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	24% 16% 34% 19% 6%	300
	11th to 20th	Day	28% 21% 33% 13% 4	300
	21st to end	Day	29% 18% 34% 17% 2	330
February	1st to 10th	Day	29% 15% 38% 15% 3	300
	11th to 20th	Day	29% 22% 36% 9% 3 1	300
	21st to end	Day	30% 15% 43% 10% 3	249
March	1st to 10th	Day	24% 19% 38% 16% 3	300
	11th to 20th	Day	26% 14% 36% 18% 6% 1	499
	21st to end	Day	31% 15% 30% 18% 6% 1	550
April	1st to 10th	Day	25% 14% 27% 21% 10% 2	500
	11th to 20th	Day	21% 16% 28% 22% 8% 4	492
	21st to end	Day	23% 11% 32% 21% 9% 3	500
May	1st to 10th	Day	24% 9% 31% 22% 10% 4	503
	11th to 20th	Day	23% 6% 22% 27% 15% 7%	527
	21st to end	Day	15% 5% 25% 25% 19% 10%	573
June	1st to 10th	Day	15% 4 20% 29% 23% 10%	546
	11th to 20th	Day	10% 3 20% 36% 23% 8%	730
	21st to end	Day	11% 3 22% 32% 21% 11%	730
July	1st to 10th	Day	15% 2 12% 26% 25% 20%	721
	11th to 20th	Day	10% 2 19% 31% 25% 13%	643
	21st to end	Day	13% 1 12% 33% 26% 16%	576
August	1st to 10th	Day	11% 2 12% 26% 29% 20%	526
	11th to 20th	Day	13% 2 13% 33% 25% 15%	519
	21st to end	Day	9% 2 14% 27% 32% 16%	583
September	1st to 10th	Day	13% 4 13% 27% 31% 12%	530
	11th to 20th	Day	9% 2 14% 25% 32% 18%	522
	21st to end	Day	19% 5% 19% 24% 23% 9%	490
October	1st to 10th	Day	10% 3 20% 36% 22% 8%	490
	11th to 20th	Day	16% 12% 28% 25% 15% 4	490
	21st to end	Day	24% 6% 37% 22% 10% 1	378
November	1st to 10th	Day	14% 11% 34% 28% 9% 4	300
	11th to 20th	Day	22% 15% 33% 19% 9% 2	300
	21st to end	Day	25% 9% 35% 22% 8%	300
December	1st to 10th	Day	22% 17% 36% 17% 7% 1	300
	11th to 20th	Day	21% 14% 41% 16% 7% 1	300
	21st to end	Day	32% 13% 32% 19% 4 1	330
January	1st to 10th	Night	22% 14% 31% 27% 5%	1000
	11th to 20th	Night	30% 13% 32% 20% 4	871
	21st to end	Night	26% 11% 35% 24% 4	880
February	1st to 10th	Night	28% 11% 33% 26% 3	800
	11th to 20th	Night	27% 15% 33% 23% 3	783
	21st to end	Night	28% 12% 34% 24% 2	660
March	1st to 10th	Night	25% 12% 28% 30% 5%	800
	11th to 20th	Night	24% 11% 32% 24% 8% 1	800
	21st to end	Night	23% 11% 30% 29% 7%	880
April	1st to 10th	Night	20% 9% 32% 30% 9%	635
	11th to 20th	Night	21% 9% 27% 32% 10% 1	593
	21st to end	Night	20% 5% 34% 31% 10% 1	600
May	1st to 10th	Night	21% 4 30% 30% 14% 1	600
	11th to 20th	Night	19% 3 20% 36% 19% 3	591
	21st to end	Night	11% 3 18% 37% 26% 4	650
June	1st to 10th	Night	11% 2 18% 44% 24% 2	600
	11th to 20th	Night	11% 3 13% 39% 30% 3	600
	21st to end	Night	7% 2 17% 41% 29% 4	600
July	1st to 10th	Night	12% 2 9% 32% 35% 10%	585
	11th to 20th	Night	9% 1 9% 37% 39% 5%	582
	21st to end	Night	12% 1 8% 38% 36% 4	657
August	1st to 10th	Night	9% 1 7% 37% 40% 5%	597
	11th to 20th	Night	10% 1 8% 40% 35% 5%	594
	21st to end	Night	7% 1 7% 36% 41% 8%	660
September	1st to 10th	Night	15% 2 10% 33% 34% 6%	690
	11th to 20th	Night	11% 2 10% 31% 40% 6%	793
	21st to end	Night	18% 3 18% 33% 24% 3	760
October	1st to 10th	Night	11% 3 20% 36% 25% 5%	760
	11th to 20th	Night	18% 7% 22% 35% 16% 2	760
	21st to end	Night	23% 6% 29% 29% 12% 1	836
November	1st to 10th	Night	18% 7% 26% 32% 17% 1	780
	11th to 20th	Night	22% 11% 28% 28% 11% 1	800
	21st to end	Night	26% 10% 26% 28% 9% 1	800
December	1st to 10th	Night	28% 8% 34% 24% 6%	800
	11th to 20th	Night	26% 9% 31% 25% 7% 1	800
	21st to end	Night	31% 10% 29% 25% 4	980

Page generated at 2025-09-16 01:49:10. Version ac07

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