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 2025-02-06.

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 4 4 5% 7% 37%	108275
	Night	15% 10% 4 8% 4 4 4 3 5% 6% 37%	110100
Transparency	Day	44% 6% 12% 23% 14% 2	111899
	Night	45% 5% 10% 21% 15% 2	114604
Seeing	Day	17% 11% 27% 24% 15% 6%	15880
	Night	18% 9% 28% 29% 14% 1	25831

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% 14% 7% 13% 6% 4 5% 4 5% 6% 24%	3617
	11th to 20th	Day	12% 12% 8% 14% 8% 5% 5% 5% 5% 5% 21%	3620
	21st to end	Day	21% 16% 6% 11% 4 4 3 3 3 5% 25%	4160
February	1st to 10th	Day	17% 13% 6% 9% 6% 4 4 3 5% 5% 28%	1950
	11th to 20th	Day	15% 11% 4 11% 5% 5% 4 3 5% 6% 31%	1848
	21st to end	Day	16% 15% 5% 9% 4 3 3 3 5% 5% 32%	1570
March	1st to 10th	Day	22% 18% 3 7% 4 3 2 2 4 4 31%	3120
	11th to 20th	Day	13% 9% 3 6% 4 3 4 3 5% 7% 44%	3308
	21st to end	Day	16% 10% 4 8% 5% 5% 5% 4 5% 7% 31%	4068
April	1st to 10th	Day	14% 12% 3 7% 5% 3 3 3 5% 8% 36%	2280
	11th to 20th	Day	17% 9% 2 6% 4 4 4 4 5% 6% 39%	2254
	21st to end	Day	20% 7% 2 7% 4 4 4 3 5% 7% 35%	2399
May	1st to 10th	Day	18% 10% 3 8% 5% 5% 5% 4 6% 9% 28%	4082
	11th to 20th	Day	20% 7% 2 6% 4 4 4 4 4 7% 38%	4081
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 5% 6% 9% 40%	4664
June	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 5% 5% 8% 43%	2660
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 9% 45%	2660
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 4 7% 9% 42%	2660
July	1st to 10th	Day	13% 6% 2 7% 4 4 5% 4 6% 10% 38%	4440
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 5% 8% 12% 44%	4440
	21st to end	Day	10% 7% 2 7% 5% 4 6% 5% 7% 10% 35%	4756
August	1st to 10th	Day	8% 4 2 5% 4 4 5% 4 7% 10% 48%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 9% 10% 40%	3764
	21st to end	Day	6% 4 2 5% 4 4 4 3 6% 9% 53%	4180
September	1st to 10th	Day	11% 6% 2 5% 4 4 4 4 5% 8% 45%	2280
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 5% 6% 8% 48%	2090
	21st to end	Day	12% 5% 2 5% 4 4 5% 3 5% 7% 48%	2090
October	1st to 10th	Day	11% 5% 2 5% 4 4 4 3 5% 7% 50%	2090
	11th to 20th	Day	14% 7% 2 6% 4 4 5% 3 5% 6% 43%	1931
	21st to end	Day	18% 9% 2 8% 4 4 4 4 4 6% 37%	1881
November	1st to 10th	Day	10% 7% 2 5% 4 4 4 3 6% 6% 50%	1762
	11th to 20th	Day	17% 10% 3 8% 5% 4 4 2 4 6% 38%	1800
	21st to end	Day	18% 11% 4 8% 4 4 4 3 4 5% 35%	1800
December	1st to 10th	Day	12% 12% 4 8% 4 3 3 3 4 5% 43%	2876
	11th to 20th	Day	15% 15% 6% 9% 6% 5% 5% 4 5% 5% 25%	3008
	21st to end	Day	25% 18% 6% 10% 5% 4 4 3 4 5% 15%	3982
January	1st to 10th	Night	16% 14% 8% 14% 6% 4 5% 3 4 5% 22%	6348
	11th to 20th	Night	13% 18% 6% 13% 8% 5% 5% 4 4 4 20%	6360
	21st to end	Night	20% 13% 5% 8% 5% 5% 3 3 4 5% 29%	6798
February	1st to 10th	Night	19% 12% 5% 10% 5% 4 3 4 5% 5% 28%	2341
	11th to 20th	Night	14% 11% 4 9% 5% 4 5% 3 5% 7% 33%	2218
	21st to end	Night	19% 13% 4 8% 4 3 3 3 5% 5% 32%	1884
March	1st to 10th	Night	21% 17% 3 5% 3 3 3 2 4 5% 33%	3733
	11th to 20th	Night	13% 6% 3 6% 4 4 4 3 4 6% 47%	3650
	21st to end	Night	18% 8% 3 7% 4 4 4 3 4 6% 37%	3579
April	1st to 10th	Night	13% 10% 3 6% 4 4 4 3 6% 7% 39%	1900
	11th to 20th	Night	18% 8% 2 5% 4 3 3 3 5% 7% 41%	1875
	21st to end	Night	16% 9% 3 7% 4 4 5% 4 6% 5% 37%	1781
May	1st to 10th	Night	18% 11% 3 7% 5% 5% 4 3 5% 7% 30%	2813
	11th to 20th	Night	19% 7% 3 5% 4 4 3 4 5% 7% 41%	2812
	21st to end	Night	11% 5% 2 7% 4 4 4 4 6% 8% 44%	2881
June	1st to 10th	Night	9% 6% 3 7% 3 3 3 3 6% 8% 49%	1520
	11th to 20th	Night	8% 6% 2 6% 4 4 3 4 5% 8% 49%	1520
	21st to end	Night	6% 5% 2 5% 5% 4 5% 4 8% 11% 45%	1520
July	1st to 10th	Night	10% 5% 2 6% 3 4 4 3 6% 10% 48%	2530
	11th to 20th	Night	6% 4 2 4 3 3 4 5% 6% 9% 55%	2530
	21st to end	Night	8% 8% 3 7% 4 4 5% 4 7% 10% 40%	2801
August	1st to 10th	Night	8% 4 2 6% 3 4 4 3 5% 9% 52%	2825
	11th to 20th	Night	6% 5% 3 6% 4 5% 5% 4 6% 8% 48%	3061
	21st to end	Night	5% 4 1 5% 3 4 4 3 5% 8% 57%	3476
September	1st to 10th	Night	10% 6% 3 5% 3 4 4 4 5% 7% 50%	1900
	11th to 20th	Night	7% 5% 1 4 3 3 4 3 6% 8% 56%	2070
	21st to end	Night	13% 5% 2 5% 3 3 4 3 6% 7% 49%	2090
October	1st to 10th	Night	8% 3 2 5% 4 4 3 3 5% 6% 55%	2090
	11th to 20th	Night	16% 6% 2 5% 3 3 3 2 4 6% 49%	2243
	21st to end	Night	17% 9% 3 5% 4 4 4 3 4 7% 40%	2717
November	1st to 10th	Night	11% 7% 3 4 4 4 3 3 4 6% 50%	2536
	11th to 20th	Night	13% 10% 3 7% 4 4 4 3 5% 7% 40%	2600
	21st to end	Night	19% 13% 4 7% 4 3 3 3 4 4 34%	2600
December	1st to 10th	Night	15% 10% 4 8% 5% 4 3 3 4 5% 40%	4303
	11th to 20th	Night	18% 12% 5% 10% 5% 4 4 3 5% 5% 29%	5199
	21st to end	Night	27% 18% 6% 9% 5% 4 4 3 3 4 17%	6996

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	60% 4 8% 20% 6% 1	3618
	11th to 20th	Day	64% 4 11% 10% 9% 2	3620
	21st to end	Day	64% 3 8% 16% 6% 2	4160
February	1st to 10th	Day	57% 5% 11% 17% 9% 2	1950
	11th to 20th	Day	54% 5% 11% 20% 9% 1	1858
	21st to end	Day	53% 5% 10% 21% 9% 2	1570
March	1st to 10th	Day	57% 4 7% 17% 12% 2	3120
	11th to 20th	Day	38% 7% 12% 29% 13% 1	3308
	21st to end	Day	50% 9% 14% 22% 5% 1	4068
April	1st to 10th	Day	46% 8% 11% 20% 15% 1	2280
	11th to 20th	Day	45% 6% 9% 25% 10% 4	2254
	21st to end	Day	48% 7% 11% 21% 10% 3	2399
May	1st to 10th	Day	49% 9% 15% 21% 6%	4120
	11th to 20th	Day	45% 8% 12% 25% 9%	4085
	21st to end	Day	37% 10% 12% 19% 19% 2	4677
June	1st to 10th	Day	37% 8% 12% 24% 15% 4	2660
	11th to 20th	Day	33% 8% 12% 23% 21% 3	2660
	21st to end	Day	37% 8% 16% 19% 17% 4	2660
July	1st to 10th	Day	41% 6% 12% 25% 14% 2	4371
	11th to 20th	Day	30% 8% 15% 28% 17% 1	4365
	21st to end	Day	41% 9% 15% 19% 14% 2	4606
August	1st to 10th	Day	30% 8% 15% 31% 16% 1	4091
	11th to 20th	Day	34% 8% 13% 29% 15% 1	3801
	21st to end	Day	27% 6% 15% 31% 16% 4	4179
September	1st to 10th	Day	35% 8% 11% 24% 18% 4	2280
	11th to 20th	Day	32% 7% 12% 24% 22% 3	2090
	21st to end	Day	35% 6% 10% 24% 22% 2	2090
October	1st to 10th	Day	22% 4 8% 30% 34% 2	3480
	11th to 20th	Day	30% 5% 9% 26% 29% 1	3173
	21st to end	Day	40% 3 9% 22% 24% 1	3081
November	1st to 10th	Day	35% 4 14% 26% 17% 5%	1762
	11th to 20th	Day	48% 4 9% 20% 14% 4	1800
	21st to end	Day	51% 4 11% 21% 13% 1	1800
December	1st to 10th	Day	45% 4 10% 28% 13%	2876
	11th to 20th	Day	60% 5% 8% 20% 6%	3005
	21st to end	Day	71% 4 10% 10% 4	3982
January	1st to 10th	Night	64% 5% 9% 15% 7%	6348
	11th to 20th	Night	67% 4 8% 10% 8% 3	6360
	21st to end	Night	59% 3 8% 19% 9% 1	6798
February	1st to 10th	Night	58% 4 12% 17% 8% 1	2341
	11th to 20th	Night	51% 6% 11% 18% 13% 1	2219
	21st to end	Night	54% 5% 10% 19% 11% 2	1884
March	1st to 10th	Night	55% 4 8% 22% 10% 2	3733
	11th to 20th	Night	37% 7% 10% 23% 22% 2	3650
	21st to end	Night	46% 7% 12% 26% 8% 1	3579
April	1st to 10th	Night	43% 7% 11% 24% 14% 2	1900
	11th to 20th	Night	43% 5% 10% 20% 16% 5%	1875
	21st to end	Night	46% 7% 10% 20% 13% 4	1781
May	1st to 10th	Night	50% 11% 12% 19% 7% 1	2840
	11th to 20th	Night	41% 8% 14% 27% 10%	2813
	21st to end	Night	35% 9% 13% 21% 18% 4	2889
June	1st to 10th	Night	33% 7% 11% 26% 20% 4	1520
	11th to 20th	Night	31% 7% 12% 23% 21% 6%	1520
	21st to end	Night	31% 9% 16% 21% 19% 4	1520
July	1st to 10th	Night	33% 7% 11% 27% 19% 4	2490
	11th to 20th	Night	24% 7% 14% 31% 23% 2	2482
	21st to end	Night	38% 7% 15% 21% 15% 4	2712
August	1st to 10th	Night	29% 6% 16% 34% 13% 1	2814
	11th to 20th	Night	32% 7% 14% 28% 19% 1	3090
	21st to end	Night	26% 6% 13% 31% 21% 4	3476
September	1st to 10th	Night	33% 7% 12% 23% 19% 6%	1900
	11th to 20th	Night	26% 5% 12% 25% 27% 5%	2070
	21st to end	Night	34% 8% 10% 22% 22% 5%	2090
October	1st to 10th	Night	20% 4 8% 25% 42% 2	3480
	11th to 20th	Night	28% 3 8% 25% 35% 2	3727
	21st to end	Night	36% 3 8% 23% 25% 5%	4467
November	1st to 10th	Night	35% 6% 10% 25% 21% 4	2536
	11th to 20th	Night	43% 4 10% 23% 16% 3	2600
	21st to end	Night	53% 4 9% 21% 12% 1	2600
December	1st to 10th	Night	47% 3 11% 26% 12%	4303
	11th to 20th	Night	56% 6% 11% 17% 10%	5201
	21st to end	Night	72% 5% 8% 11% 5%	6996

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% 33% 19% 5%	300
	11th to 20th	Day	24% 23% 34% 16% 1 1	300
	21st to end	Day	25% 22% 33% 17% 2 1	330
February	1st to 10th	Day	26% 20% 36% 15% 2	285
	11th to 20th	Day	25% 24% 32% 14% 5%	270
	21st to end	Day	31% 15% 39% 12% 3	225
March	1st to 10th	Day	24% 25% 34% 14% 3	270
	11th to 20th	Day	26% 20% 34% 14% 5% 1	353
	21st to end	Day	29% 19% 31% 15% 6%	506
April	1st to 10th	Day	20% 18% 32% 20% 8% 1	460
	11th to 20th	Day	22% 17% 30% 19% 10% 2	452
	21st to end	Day	26% 17% 30% 18% 7% 2	460
May	1st to 10th	Day	19% 17% 30% 22% 9% 3	463
	11th to 20th	Day	20% 9% 29% 24% 13% 6%	487
	21st to end	Day	11% 7% 28% 27% 18% 9%	639
June	1st to 10th	Day	12% 6% 26% 32% 18% 5%	680
	11th to 20th	Day	12% 4 25% 35% 20% 5%	680
	21st to end	Day	12% 6% 30% 25% 20% 7%	680
July	1st to 10th	Day	10% 3 19% 27% 25% 16%	671
	11th to 20th	Day	6% 5% 22% 31% 25% 12%	668
	21st to end	Day	11% 3 16% 32% 29% 9%	706
August	1st to 10th	Day	10% 4 14% 27% 31% 14%	486
	11th to 20th	Day	14% 4 19% 30% 24% 10%	479
	21st to end	Day	6% 2 14% 32% 31% 15%	539
September	1st to 10th	Day	10% 4 17% 32% 28% 9%	490
	11th to 20th	Day	9% 2 16% 28% 31% 14%	490
	21st to end	Day	14% 10% 22% 22% 22% 9%	490
October	1st to 10th	Day	10% 7% 27% 32% 19% 5%	490
	11th to 20th	Day	13% 16% 33% 24% 12% 2	371
	21st to end	Day	27% 16% 34% 22% 2	330
November	1st to 10th	Day	13% 19% 31% 23% 12% 3	300
	11th to 20th	Day	23% 19% 32% 17% 8% 1	300
	21st to end	Day	25% 15% 37% 20% 3	300
December	1st to 10th	Day	16% 27% 36% 16% 4 1	300
	11th to 20th	Day	24% 15% 39% 15% 5% 1	300
	21st to end	Day	33% 16% 32% 16% 3	330
January	1st to 10th	Night	22% 16% 34% 24% 4	1000
	11th to 20th	Night	24% 17% 37% 19% 4	1000
	21st to end	Night	21% 16% 36% 24% 3	1075
February	1st to 10th	Night	25% 12% 37% 24% 2	781
	11th to 20th	Night	20% 15% 38% 24% 2	743
	21st to end	Night	26% 14% 38% 20% 3	628
March	1st to 10th	Night	25% 14% 34% 23% 4	760
	11th to 20th	Night	21% 13% 37% 23% 5% 1	760
	21st to end	Night	25% 8% 35% 27% 5% 1	701
April	1st to 10th	Night	18% 12% 35% 28% 7%	570
	11th to 20th	Night	20% 12% 29% 27% 10%	563
	21st to end	Night	21% 10% 36% 26% 7% 1	570
May	1st to 10th	Night	19% 8% 35% 29% 10%	570
	11th to 20th	Night	17% 5% 24% 34% 16% 3	561
	21st to end	Night	10% 4 24% 39% 22% 2	617
June	1st to 10th	Night	10% 4 23% 41% 21% 1	570
	11th to 20th	Night	10% 3 21% 44% 21% 1	570
	21st to end	Night	8% 3 22% 39% 26% 2	570
July	1st to 10th	Night	10% 2 10% 39% 32% 6%	555
	11th to 20th	Night	6% 4 15% 37% 34% 4	552
	21st to end	Night	7% 3 11% 45% 31% 3	624
August	1st to 10th	Night	8% 2 11% 41% 34% 4	567
	11th to 20th	Night	7% 3 12% 42% 33% 4	564
	21st to end	Night	7% 3 12% 31% 41% 6%	627
September	1st to 10th	Night	11% 4 14% 37% 30% 4	570
	11th to 20th	Night	9% 3 14% 36% 34% 4	740
	21st to end	Night	14% 7% 19% 32% 25% 3	760
October	1st to 10th	Night	9% 4 25% 35% 22% 4	760
	11th to 20th	Night	19% 12% 26% 29% 14% 1	760
	21st to end	Night	22% 11% 33% 26% 7% 1	836
November	1st to 10th	Night	15% 9% 35% 30% 11% 1	780
	11th to 20th	Night	18% 15% 32% 27% 9%	800
	21st to end	Night	25% 13% 29% 26% 7%	800
December	1st to 10th	Night	23% 12% 39% 21% 4	827
	11th to 20th	Night	25% 10% 34% 24% 6% 1	1000
	21st to end	Night	32% 13% 32% 19% 4	1100

Page generated at 2025-02-03 03:05:54. Version ac07

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