Greencastle
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greencastle clear sky chart from 2005-11-06 to 2026-06-01.

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% 9% 3 8% 5% 4 5% 4 6% 8% 36%	131707
	Night	14% 10% 4 8% 5% 4 4 3 5% 6% 37%	131640
Transparency	Day	45% 6% 11% 23% 14% 2	135286
	Night	46% 5% 10% 22% 15% 2	136123
Seeing	Day	17% 12% 27% 24% 15% 5%	17681
	Night	18% 10% 28% 29% 13% 1	27564

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	14% 13% 6% 12% 6% 4 5% 3 5% 7% 26%	4691
	11th to 20th	Day	9% 12% 7% 14% 8% 6% 5% 5% 5% 5% 24%	4710
	21st to end	Day	18% 15% 6% 13% 6% 5% 4 4 4 5% 22%	5389
February	1st to 10th	Day	16% 13% 6% 9% 6% 4 4 3 5% 5% 28%	2100
	11th to 20th	Day	16% 11% 4 11% 6% 5% 4 3 5% 6% 30%	2048
	21st to end	Day	15% 14% 4 9% 5% 3 3 3 5% 6% 34%	1730
March	1st to 10th	Day	19% 15% 4 7% 3 3 3 2 4 4 36%	4580
	11th to 20th	Day	11% 10% 3 5% 4 4 4 3 6% 8% 42%	4842
	21st to end	Day	17% 11% 4 7% 5% 5% 5% 4 5% 7% 31%	5957
April	1st to 10th	Day	15% 12% 3 8% 5% 3 4 3 5% 8% 35%	2520
	11th to 20th	Day	16% 9% 3 6% 4 5% 4 4 5% 6% 38%	2494
	21st to end	Day	19% 7% 2 7% 4 4 4 3 6% 7% 36%	2651
May	1st to 10th	Day	18% 10% 3 8% 5% 5% 5% 4 6% 8% 28%	5992
	11th to 20th	Day	19% 7% 3 6% 4 4 4 4 5% 7% 36%	5991
	21st to end	Day	13% 7% 3 8% 5% 5% 5% 5% 6% 9% 33%	6854
June	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 5% 5% 8% 43%	2801
	11th to 20th	Day	9% 6% 2 6% 4 5% 5% 5% 7% 9% 44%	2800
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 4 6% 9% 42%	2800
July	1st to 10th	Day	11% 6% 2 6% 4 4 5% 4 6% 11% 42%	6360
	11th to 20th	Day	8% 6% 2 7% 5% 5% 6% 5% 8% 11% 35%	6360
	21st to end	Day	11% 7% 3 7% 5% 4 6% 5% 7% 10% 35%	6839
August	1st to 10th	Day	8% 4 2 5% 4 4 5% 4 7% 10% 48%	4234
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 9% 10% 39%	3885
	21st to end	Day	6% 4 2 5% 4 4 4 3 6% 10% 53%	4312
September	1st to 10th	Day	11% 6% 2 5% 4 4 4 3 6% 8% 46%	2400
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 5% 7% 8% 49%	2200
	21st to end	Day	12% 5% 2 5% 4 4 5% 3 5% 7% 48%	2200
October	1st to 10th	Day	11% 5% 2 5% 4 4 4 3 5% 7% 50%	2200
	11th to 20th	Day	14% 7% 2 6% 4 4 5% 3 5% 6% 44%	2033
	21st to end	Day	18% 9% 2 8% 4 4 4 4 4 5% 37%	1980
November	1st to 10th	Day	10% 7% 2 5% 4 4 4 3 6% 6% 50%	1852
	11th to 20th	Day	17% 10% 3 8% 5% 4 4 2 4 6% 37%	1890
	21st to end	Day	18% 11% 4 9% 4 3 4 3 4 5% 35%	1890
December	1st to 10th	Day	11% 12% 4 9% 4 3 3 3 4 5% 43%	2964
	11th to 20th	Day	15% 15% 6% 10% 6% 5% 5% 4 4 5% 25%	3088
	21st to end	Day	25% 18% 6% 10% 5% 4 4 3 4 5% 15%	4070
January	1st to 10th	Night	15% 14% 7% 13% 6% 4 4 3 4 5% 25%	8232
	11th to 20th	Night	10% 15% 5% 14% 8% 6% 5% 4 4 5% 24%	8280
	21st to end	Night	18% 11% 5% 8% 6% 5% 4 3 5% 6% 29%	8804
February	1st to 10th	Night	18% 12% 5% 9% 5% 4 3 4 5% 6% 29%	2520
	11th to 20th	Night	15% 11% 4 9% 5% 4 4 3 5% 7% 32%	2458
	21st to end	Night	18% 12% 4 8% 4 3 3 4 5% 5% 34%	2076
March	1st to 10th	Night	20% 15% 4 5% 3 3 3 2 4 5% 36%	5493
	11th to 20th	Night	13% 6% 3 6% 4 4 4 3 4 7% 45%	5336
	21st to end	Night	17% 9% 3 8% 5% 5% 5% 3 5% 6% 33%	5245
April	1st to 10th	Night	14% 10% 3 6% 4 4 4 3 6% 7% 38%	2100
	11th to 20th	Night	17% 8% 2 6% 4 4 3 3 5% 7% 40%	2075
	21st to end	Night	15% 8% 3 6% 5% 4 5% 4 6% 6% 37%	1968
May	1st to 10th	Night	19% 11% 3 8% 5% 4 4 3 5% 6% 31%	4123
	11th to 20th	Night	16% 8% 3 6% 4 4 4 4 6% 8% 38%	4122
	21st to end	Night	14% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	4238
June	1st to 10th	Night	10% 6% 3 7% 3 3 3 3 6% 8% 49%	1600
	11th to 20th	Night	9% 6% 3 6% 4 4 3 4 5% 8% 48%	1600
	21st to end	Night	6% 5% 2 6% 4 4 5% 4 8% 11% 45%	1600
July	1st to 10th	Night	9% 5% 2 6% 4 4 4 3 6% 10% 46%	3618
	11th to 20th	Night	7% 6% 2 6% 4 4 5% 5% 7% 9% 45%	3617
	21st to end	Night	8% 7% 3 8% 5% 4 5% 4 7% 10% 39%	4024
August	1st to 10th	Night	8% 5% 2 6% 3 4 4 3 6% 9% 52%	2915
	11th to 20th	Night	6% 5% 3 6% 4 5% 5% 4 6% 8% 49%	3160
	21st to end	Night	5% 3 1 5% 3 4 4 3 5% 9% 57%	3586
September	1st to 10th	Night	10% 6% 3 5% 3 4 4 4 5% 7% 50%	2000
	11th to 20th	Night	6% 5% 1 4 3 3 4 3 6% 7% 57%	2179
	21st to end	Night	13% 5% 2 5% 3 3 4 3 6% 6% 49%	2200
October	1st to 10th	Night	8% 3 2 5% 4 4 3 3 5% 6% 55%	2200
	11th to 20th	Night	16% 6% 2 5% 3 3 3 2 4 6% 49%	2361
	21st to end	Night	17% 9% 3 5% 4 4 4 3 4 6% 39%	2860
November	1st to 10th	Night	10% 7% 3 5% 4 3 3 3 4 6% 50%	2666
	11th to 20th	Night	13% 10% 3 6% 4 4 4 4 5% 7% 41%	2730
	21st to end	Night	19% 13% 4 7% 4 3 3 3 4 4 34%	2730
December	1st to 10th	Night	15% 10% 4 8% 5% 4 3 3 4 5% 39%	4435
	11th to 20th	Night	17% 12% 5% 10% 5% 4 4 3 5% 5% 29%	5339
	21st to end	Night	27% 18% 6% 9% 5% 4 3 3 3 4 17%	7150

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	57% 4 12% 20% 6% 1	4692
	11th to 20th	Day	60% 3 11% 12% 11% 2	4710
	21st to end	Day	66% 3 8% 16% 5% 2	5389
February	1st to 10th	Day	56% 5% 11% 18% 8% 2	2100
	11th to 20th	Day	55% 4 10% 20% 9% 1	2058
	21st to end	Day	52% 4 11% 22% 9% 2	1730
March	1st to 10th	Day	54% 4 6% 19% 15% 3	4580
	11th to 20th	Day	39% 6% 11% 32% 12% 1	4842
	21st to end	Day	51% 7% 12% 20% 8% 1	5959
April	1st to 10th	Day	47% 7% 11% 20% 14% 1	2520
	11th to 20th	Day	46% 6% 10% 25% 10% 3	2494
	21st to end	Day	47% 6% 11% 23% 10% 3	2651
May	1st to 10th	Day	51% 7% 12% 19% 9%	6027
	11th to 20th	Day	47% 7% 11% 25% 11% 1	5995
	21st to end	Day	44% 8% 12% 20% 14% 2	6868
June	1st to 10th	Day	37% 8% 12% 24% 16% 3	2801
	11th to 20th	Day	34% 8% 12% 22% 20% 3	2800
	21st to end	Day	37% 8% 16% 19% 17% 3	2800
July	1st to 10th	Day	35% 6% 11% 29% 17% 2	6291
	11th to 20th	Day	39% 9% 15% 24% 13% 1	6285
	21st to end	Day	42% 8% 14% 22% 12% 2	6644
August	1st to 10th	Day	29% 8% 15% 32% 15% 1	4221
	11th to 20th	Day	34% 8% 13% 29% 15% 1	3922
	21st to end	Day	26% 6% 15% 31% 17% 4	4311
September	1st to 10th	Day	34% 8% 12% 25% 19% 4	2400
	11th to 20th	Day	31% 7% 12% 25% 23% 3	2200
	21st to end	Day	35% 6% 10% 23% 24% 2	2200
October	1st to 10th	Day	22% 4 8% 30% 34% 2	3590
	11th to 20th	Day	31% 4 9% 26% 29% 1	3275
	21st to end	Day	40% 3 9% 22% 24% 1	3180
November	1st to 10th	Day	35% 4 13% 27% 17% 5%	1852
	11th to 20th	Day	48% 4 9% 21% 14% 4	1890
	21st to end	Day	52% 4 10% 21% 13% 1	1890
December	1st to 10th	Day	46% 3 10% 28% 13%	2964
	11th to 20th	Day	60% 5% 8% 20% 6%	3085
	21st to end	Day	71% 4 10% 10% 4	4070
January	1st to 10th	Night	61% 5% 10% 18% 6%	8233
	11th to 20th	Night	63% 4 8% 12% 11% 3	8280
	21st to end	Night	57% 3 10% 21% 9% 1	8804
February	1st to 10th	Night	57% 4 11% 18% 8% 1	2520
	11th to 20th	Night	52% 5% 11% 19% 12% 1	2459
	21st to end	Night	53% 5% 10% 20% 10% 2	2076
March	1st to 10th	Night	52% 3 6% 24% 11% 4	5493
	11th to 20th	Night	38% 6% 9% 26% 19% 1	5336
	21st to end	Night	50% 5% 10% 26% 8% 1	5245
April	1st to 10th	Night	44% 6% 11% 24% 13% 2	2100
	11th to 20th	Night	43% 5% 11% 20% 17% 5%	2075
	21st to end	Night	45% 7% 10% 23% 12% 3	1968
May	1st to 10th	Night	52% 8% 10% 18% 10% 1	4150
	11th to 20th	Night	43% 7% 12% 26% 12%	4123
	21st to end	Night	44% 8% 14% 19% 13% 3	4246
June	1st to 10th	Night	33% 6% 10% 26% 21% 4	1600
	11th to 20th	Night	33% 7% 11% 23% 21% 5%	1600
	21st to end	Night	31% 9% 15% 22% 20% 4	1600
July	1st to 10th	Night	33% 7% 10% 28% 19% 3	3580
	11th to 20th	Night	32% 8% 15% 27% 16% 1	3572
	21st to end	Night	39% 7% 15% 25% 12% 3	3908
August	1st to 10th	Night	29% 6% 16% 35% 13% 1	2904
	11th to 20th	Night	32% 6% 14% 28% 18% 1	3189
	21st to end	Night	25% 5% 13% 31% 22% 4	3586
September	1st to 10th	Night	32% 7% 11% 24% 19% 6%	2000
	11th to 20th	Night	25% 5% 12% 25% 28% 4	2179
	21st to end	Night	35% 8% 10% 21% 23% 5%	2200
October	1st to 10th	Night	20% 4 8% 24% 42% 2	3590
	11th to 20th	Night	28% 3 8% 25% 34% 2	3845
	21st to end	Night	37% 3 8% 22% 25% 5%	4610
November	1st to 10th	Night	35% 5% 10% 25% 22% 4	2666
	11th to 20th	Night	43% 4 10% 24% 16% 3	2730
	21st to end	Night	54% 4 9% 21% 11% 1	2730
December	1st to 10th	Night	48% 3 11% 25% 12%	4435
	11th to 20th	Night	56% 6% 11% 17% 10%	5341
	21st to end	Night	72% 4 8% 11% 5%	7150

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% 19% 34% 18% 5%	330
	11th to 20th	Day	24% 26% 34% 15% 1 1	330
	21st to end	Day	25% 24% 33% 16% 2 1	363
February	1st to 10th	Day	25% 18% 39% 15% 3	330
	11th to 20th	Day	27% 24% 33% 12% 4	330
	21st to end	Day	29% 17% 40% 12% 2	273
March	1st to 10th	Day	24% 25% 36% 13% 2	330
	11th to 20th	Day	27% 21% 34% 13% 4	422
	21st to end	Day	27% 21% 32% 15% 5%	594
April	1st to 10th	Day	23% 19% 31% 20% 6% 1	540
	11th to 20th	Day	23% 18% 29% 19% 9% 2	532
	21st to end	Day	24% 17% 31% 19% 7% 1	540
May	1st to 10th	Day	20% 17% 30% 22% 8% 3	543
	11th to 20th	Day	20% 10% 31% 23% 12% 5%	567
	21st to end	Day	13% 8% 28% 26% 17% 8%	739
June	1st to 10th	Day	13% 6% 27% 32% 18% 5%	731
	11th to 20th	Day	12% 5% 24% 34% 19% 5%	730
	21st to end	Day	12% 6% 29% 25% 21% 7%	730
July	1st to 10th	Day	10% 3 18% 28% 25% 16%	721
	11th to 20th	Day	7% 4 22% 31% 25% 12%	718
	21st to end	Day	11% 3 16% 32% 29% 9%	759
August	1st to 10th	Day	10% 4 14% 27% 31% 14%	526
	11th to 20th	Day	13% 4 18% 30% 24% 10%	519
	21st to end	Day	6% 2 15% 32% 30% 14%	583
September	1st to 10th	Day	9% 5% 18% 31% 29% 9%	530
	11th to 20th	Day	8% 2 15% 28% 32% 15%	530
	21st to end	Day	14% 10% 21% 23% 23% 9%	530
October	1st to 10th	Day	10% 7% 25% 33% 20% 5%	530
	11th to 20th	Day	13% 15% 31% 26% 13% 2	405
	21st to end	Day	27% 17% 33% 21% 2	363
November	1st to 10th	Day	13% 20% 32% 22% 11% 2	330
	11th to 20th	Day	24% 21% 31% 16% 8% 1	330
	21st to end	Day	27% 14% 37% 20% 2	330
December	1st to 10th	Day	17% 25% 38% 15% 4 1	330
	11th to 20th	Day	24% 16% 40% 14% 5% 1	330
	21st to end	Day	32% 16% 35% 15% 2	363
January	1st to 10th	Night	22% 16% 35% 24% 4	1050
	11th to 20th	Night	23% 18% 37% 19% 3	1050
	21st to end	Night	21% 16% 37% 23% 3	1129
February	1st to 10th	Night	23% 12% 37% 25% 2	840
	11th to 20th	Night	21% 16% 37% 23% 2	823
	21st to end	Night	25% 13% 40% 20% 2	692
March	1st to 10th	Night	26% 15% 33% 23% 3	840
	11th to 20th	Night	22% 13% 37% 23% 5%	840
	21st to end	Night	25% 9% 35% 26% 4 1	775
April	1st to 10th	Night	19% 12% 35% 27% 6%	630
	11th to 20th	Night	20% 13% 30% 26% 10%	623
	21st to end	Night	20% 10% 35% 27% 7% 1	630
May	1st to 10th	Night	19% 7% 35% 29% 9%	630
	11th to 20th	Night	17% 6% 26% 33% 15% 2	621
	21st to end	Night	11% 4 24% 38% 21% 2	683
June	1st to 10th	Night	11% 4 24% 41% 21% 1	600
	11th to 20th	Night	11% 3 20% 44% 20% 1	600
	21st to end	Night	8% 3 21% 39% 27% 2	600
July	1st to 10th	Night	10% 2 10% 39% 33% 6%	585
	11th to 20th	Night	6% 4 15% 37% 33% 4	582
	21st to end	Night	7% 3 11% 44% 32% 3	657
August	1st to 10th	Night	8% 2 11% 41% 34% 4	597
	11th to 20th	Night	7% 3 12% 41% 34% 3	594
	21st to end	Night	7% 2 12% 33% 40% 5%	660
September	1st to 10th	Night	11% 4 15% 37% 30% 4	600
	11th to 20th	Night	9% 3 13% 37% 34% 4	779
	21st to end	Night	14% 6% 19% 32% 25% 3	800
October	1st to 10th	Night	9% 5% 24% 36% 23% 4	800
	11th to 20th	Night	18% 12% 25% 30% 14% 1	800
	21st to end	Night	22% 12% 33% 26% 7% 1	880
November	1st to 10th	Night	15% 9% 35% 30% 10% 1	820
	11th to 20th	Night	18% 15% 33% 26% 8%	840
	21st to end	Night	25% 14% 29% 26% 7%	840
December	1st to 10th	Night	24% 12% 39% 21% 4	869
	11th to 20th	Night	24% 11% 35% 23% 6% 1	1050
	21st to end	Night	32% 14% 32% 18% 4	1155

Page generated at 2026-05-29 01:53:29. Version ac07

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