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 2024-01-27.

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% 8% 4 6% 5% 3 5% 5% 5% 7% 38%	74957
	Night	15% 9% 4 6% 5% 3 4 4 5% 7% 39%	75108
Transparency	Day	45% 7% 12% 21% 13% 2	74661
	Night	45% 6% 11% 21% 15% 3	74925
Seeing	Day	17% 11% 26% 24% 16% 6%	14475
	Night	18% 9% 28% 29% 14% 1	24447

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% 14% 5% 9% 5% 3 4 5% 4 7% 27%	1517
	11th to 20th	Day	18% 13% 5% 9% 7% 4 4 4 5% 5% 25%	1520
	21st to end	Day	15% 15% 8% 9% 6% 3 4 4 5% 7% 25%	1701
February	1st to 10th	Day	18% 12% 7% 9% 7% 3 4 4 4 5% 28%	1800
	11th to 20th	Day	16% 10% 5% 9% 7% 3 5% 4 5% 6% 30%	1748
	21st to end	Day	17% 15% 5% 8% 6% 2 3 4 4 6% 31%	1480
March	1st to 10th	Day	17% 11% 4 7% 6% 3 3 3 5% 6% 34%	1800
	11th to 20th	Day	18% 10% 4 6% 5% 3 4 4 5% 7% 34%	1878
	21st to end	Day	21% 12% 5% 7% 6% 4 5% 3 4 7% 27%	2321
April	1st to 10th	Day	14% 10% 4 6% 6% 3 3 4 5% 8% 37%	2160
	11th to 20th	Day	17% 9% 3 5% 5% 3 4 4 5% 5% 39%	2134
	21st to end	Day	21% 7% 3 6% 6% 4 4 4 5% 7% 35%	2272
May	1st to 10th	Day	18% 9% 3 7% 6% 3 4 5% 4 7% 33%	2340
	11th to 20th	Day	20% 7% 3 6% 5% 3 4 5% 4 8% 36%	2301
	21st to end	Day	10% 5% 3 6% 6% 4 7% 6% 6% 9% 36%	2635
June	1st to 10th	Day	11% 5% 2 5% 6% 3 5% 6% 5% 9% 43%	2520
	11th to 20th	Day	9% 5% 2 5% 5% 3 5% 6% 7% 9% 45%	2520
	21st to end	Day	9% 5% 2 6% 5% 3 6% 5% 7% 9% 42%	2520
July	1st to 10th	Day	9% 5% 2 6% 5% 3 6% 5% 6% 11% 40%	2520
	11th to 20th	Day	8% 4 2 4 4 3 5% 6% 8% 11% 44%	2520
	21st to end	Day	8% 4 3 5% 5% 3 6% 7% 7% 8% 44%	2712
August	1st to 10th	Day	8% 5% 2 5% 4 3 6% 5% 8% 12% 43%	2327
	11th to 20th	Day	10% 4 2 6% 5% 4 6% 6% 7% 9% 41%	2147
	21st to end	Day	6% 4 2 5% 5% 4 5% 5% 6% 9% 50%	2376
September	1st to 10th	Day	12% 6% 3 4 5% 3 5% 4 5% 9% 44%	2160
	11th to 20th	Day	10% 5% 2 4 4 3 4 6% 6% 8% 47%	1980
	21st to end	Day	11% 4 2 4 4 3 5% 4 4 7% 50%	1980
October	1st to 10th	Day	12% 5% 2 4 5% 3 4 4 5% 7% 48%	1980
	11th to 20th	Day	15% 7% 3 6% 5% 3 5% 4 5% 6% 42%	1831
	21st to end	Day	19% 9% 3 7% 5% 3 3 5% 4 6% 36%	1782
November	1st to 10th	Day	10% 6% 3 4 5% 3 4 4 6% 6% 51%	1672
	11th to 20th	Day	17% 8% 3 8% 5% 3 4 3 4 6% 38%	1710
	21st to end	Day	18% 9% 4 7% 5% 2 5% 4 4 6% 36%	1710
December	1st to 10th	Day	18% 14% 5% 7% 6% 2 4 3 4 5% 31%	1682
	11th to 20th	Day	16% 14% 8% 8% 6% 3 4 4 3 6% 29%	1918
	21st to end	Day	21% 20% 8% 10% 6% 3 4 4 4 4 17%	2783
January	1st to 10th	Night	16% 11% 5% 9% 7% 3 5% 5% 4 6% 30%	2648
	11th to 20th	Night	17% 14% 6% 9% 7% 4 4 4 4 5% 26%	2660
	21st to end	Night	17% 13% 7% 9% 6% 4 4 4 4 6% 28%	2797
February	1st to 10th	Night	20% 12% 5% 9% 7% 4 3 4 4 5% 27%	2160
	11th to 20th	Night	15% 10% 5% 8% 7% 2 5% 4 5% 7% 31%	2098
	21st to end	Night	20% 12% 4 7% 5% 2 4 4 4 6% 32%	1776
March	1st to 10th	Night	18% 10% 4 6% 5% 3 4 4 4 5% 36%	2160
	11th to 20th	Night	17% 8% 4 6% 4 3 5% 5% 3 7% 38%	2080
	21st to end	Night	22% 9% 4 6% 4 4 3 4 5% 6% 33%	2051
April	1st to 10th	Night	13% 8% 4 6% 5% 3 4 4 6% 8% 40%	1800
	11th to 20th	Night	18% 7% 3 5% 5% 3 4 4 5% 7% 41%	1775
	21st to end	Night	17% 8% 4 5% 5% 3 5% 5% 6% 6% 37%	1688
May	1st to 10th	Night	17% 7% 4 6% 6% 4 5% 4 5% 8% 33%	1620
	11th to 20th	Night	16% 6% 4 5% 5% 3 4 5% 5% 7% 40%	1592
	21st to end	Night	8% 5% 2 6% 6% 3 5% 6% 7% 9% 42%	1637
June	1st to 10th	Night	9% 5% 3 6% 4 2 3 4 6% 8% 49%	1440
	11th to 20th	Night	8% 5% 3 5% 5% 3 4 5% 5% 8% 50%	1440
	21st to end	Night	6% 4 2 5% 5% 3 5% 5% 7% 11% 45%	1440
July	1st to 10th	Night	9% 4 1 5% 4 3 4 5% 7% 12% 46%	1440
	11th to 20th	Night	8% 4 2 3 3 2 4 5% 7% 10% 53%	1440
	21st to end	Night	6% 5% 2 5% 5% 2 4 4 6% 8% 54%	1602
August	1st to 10th	Night	6% 4 2 5% 5% 3 5% 5% 6% 9% 50%	1611
	11th to 20th	Night	7% 3 2 5% 4 4 5% 6% 6% 9% 49%	1750
	21st to end	Night	7% 4 2 4 3 3 4 4 5% 8% 56%	1980
September	1st to 10th	Night	11% 6% 3 5% 3 3 4 4 5% 7% 48%	1800
	11th to 20th	Night	7% 5% 1 3 4 2 4 5% 6% 8% 55%	1961
	21st to end	Night	12% 4 2 4 4 3 4 4 6% 6% 51%	1980
October	1st to 10th	Night	9% 3 3 4 5% 3 4 4 5% 6% 53%	1980
	11th to 20th	Night	17% 6% 2 5% 4 2 3 3 4 6% 47%	2124
	21st to end	Night	18% 9% 3 5% 5% 3 4 4 4 6% 39%	2574
November	1st to 10th	Night	11% 7% 3 4 4 2 4 4 5% 6% 51%	2406
	11th to 20th	Night	13% 9% 4 6% 4 3 4 4 5% 7% 41%	2470
	21st to end	Night	19% 11% 5% 6% 5% 2 4 3 4 4 35%	2470
December	1st to 10th	Night	17% 10% 6% 9% 6% 3 3 4 5% 6% 30%	2495
	11th to 20th	Night	17% 12% 5% 8% 5% 3 4 4 5% 5% 33%	3279
	21st to end	Night	23% 18% 7% 8% 6% 3 4 4 3 4 19%	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	58% 5% 10% 18% 10% 1	1518
	11th to 20th	Day	61% 5% 12% 15% 7%	1520
	21st to end	Day	59% 4 13% 18% 5% 1	1701
February	1st to 10th	Day	58% 5% 10% 17% 8% 1	1800
	11th to 20th	Day	56% 4 11% 19% 8% 1	1758
	21st to end	Day	55% 4 10% 20% 9% 2	1480
March	1st to 10th	Day	50% 6% 11% 22% 11% 1	1800
	11th to 20th	Day	50% 6% 13% 19% 11% 1	1878
	21st to end	Day	59% 5% 10% 19% 5% 1	2321
April	1st to 10th	Day	45% 7% 11% 21% 15% 1	2160
	11th to 20th	Day	46% 6% 10% 25% 10% 4	2134
	21st to end	Day	49% 7% 12% 20% 10% 3	2272
May	1st to 10th	Day	51% 7% 12% 21% 9%	2340
	11th to 20th	Day	47% 8% 12% 18% 14% 1	2305
	21st to end	Day	42% 11% 12% 19% 14% 2	2635
June	1st to 10th	Day	37% 8% 12% 25% 15% 3	2520
	11th to 20th	Day	33% 9% 12% 22% 20% 3	2520
	21st to end	Day	37% 8% 16% 20% 15% 4	2520
July	1st to 10th	Day	37% 8% 15% 22% 14% 3	2451
	11th to 20th	Day	31% 10% 15% 27% 15% 1	2445
	21st to end	Day	34% 11% 14% 23% 15% 3	2561
August	1st to 10th	Day	32% 9% 15% 29% 14% 2	2314
	11th to 20th	Day	36% 9% 14% 24% 14% 2	2147
	21st to end	Day	29% 8% 14% 24% 17% 7%	2376
September	1st to 10th	Day	36% 8% 12% 24% 16% 4	2160
	11th to 20th	Day	33% 7% 12% 24% 21% 3	1980
	21st to end	Day	32% 7% 11% 25% 23% 3	1980
October	1st to 10th	Day	35% 6% 11% 25% 20% 3	1980
	11th to 20th	Day	41% 6% 10% 23% 20% 1	1831
	21st to end	Day	49% 5% 10% 22% 13% 1	1782
November	1st to 10th	Day	34% 4 14% 26% 17% 5%	1672
	11th to 20th	Day	48% 4 9% 21% 15% 4	1710
	21st to end	Day	50% 4 11% 21% 13% 1	1710
December	1st to 10th	Day	57% 5% 10% 18% 10%	1682
	11th to 20th	Day	57% 5% 7% 22% 7% 1	1915
	21st to end	Day	69% 5% 10% 10% 5%	2783
January	1st to 10th	Night	55% 6% 9% 18% 11% 1	2648
	11th to 20th	Night	61% 5% 11% 16% 7% 1	2660
	21st to end	Night	58% 5% 11% 17% 9% 1	2797
February	1st to 10th	Night	60% 5% 12% 16% 6% 1	2160
	11th to 20th	Night	52% 6% 12% 18% 11% 2	2099
	21st to end	Night	55% 5% 10% 19% 10% 2	1776
March	1st to 10th	Night	51% 4 9% 22% 12% 2	2160
	11th to 20th	Night	47% 6% 12% 21% 13% 2	2080
	21st to end	Night	52% 5% 12% 21% 8% 2	2051
April	1st to 10th	Night	42% 6% 11% 25% 14% 2	1800
	11th to 20th	Night	43% 5% 11% 20% 17% 5%	1775
	21st to end	Night	47% 7% 10% 20% 13% 4	1688
May	1st to 10th	Night	49% 7% 11% 20% 11% 1	1620
	11th to 20th	Night	42% 8% 14% 21% 14% 1	1593
	21st to end	Night	36% 10% 14% 20% 15% 5%	1638
June	1st to 10th	Night	33% 6% 11% 25% 21% 4	1440
	11th to 20th	Night	31% 8% 12% 23% 21% 5%	1440
	21st to end	Night	31% 9% 16% 21% 19% 4	1440
July	1st to 10th	Night	29% 11% 16% 22% 18% 5%	1400
	11th to 20th	Night	24% 8% 16% 29% 20% 3	1392
	21st to end	Night	28% 6% 13% 31% 19% 4	1513
August	1st to 10th	Night	30% 9% 14% 27% 19% 2	1600
	11th to 20th	Night	30% 8% 15% 26% 19% 2	1750
	21st to end	Night	25% 6% 15% 25% 22% 7%	1980
September	1st to 10th	Night	34% 8% 13% 23% 18% 6%	1800
	11th to 20th	Night	26% 6% 12% 26% 25% 4	1961
	21st to end	Night	32% 8% 10% 23% 23% 5%	1980
October	1st to 10th	Night	30% 6% 12% 24% 23% 4	1980
	11th to 20th	Night	40% 4 7% 25% 21% 3	2124
	21st to end	Night	46% 4 10% 21% 16% 3	2574
November	1st to 10th	Night	35% 6% 10% 24% 21% 4	2406
	11th to 20th	Night	42% 4 10% 24% 16% 3	2470
	21st to end	Night	52% 4 9% 22% 12% 1	2470
December	1st to 10th	Night	55% 5% 10% 19% 10% 1	2495
	11th to 20th	Night	51% 7% 11% 18% 13% 1	3281
	21st to end	Night	70% 6% 8% 10% 6% 1	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	24% 17% 33% 19% 6%	270
	11th to 20th	Day	26% 20% 34% 17% 1 1	270
	21st to end	Day	26% 21% 33% 17% 2 1	282
February	1st to 10th	Day	28% 20% 37% 13% 3	240
	11th to 20th	Day	27% 24% 31% 14% 5%	240
	21st to end	Day	31% 16% 39% 12% 3	198
March	1st to 10th	Day	23% 25% 35% 14% 3	240
	11th to 20th	Day	27% 19% 34% 14% 5% 1	318
	21st to end	Day	30% 18% 29% 16% 6%	462
April	1st to 10th	Day	19% 16% 34% 21% 8% 1	420
	11th to 20th	Day	21% 17% 29% 19% 11% 2	412
	21st to end	Day	26% 17% 30% 18% 7% 2	420
May	1st to 10th	Day	20% 17% 30% 22% 9% 3	423
	11th to 20th	Day	20% 9% 29% 24% 13% 5%	447
	21st to end	Day	11% 5% 28% 26% 20% 10%	589
June	1st to 10th	Day	13% 5% 26% 33% 19% 6%	630
	11th to 20th	Day	12% 4 24% 33% 20% 6%	630
	21st to end	Day	12% 6% 29% 26% 20% 7%	630
July	1st to 10th	Day	10% 3 17% 27% 26% 17%	621
	11th to 20th	Day	6% 5% 21% 31% 25% 12%	618
	21st to end	Day	11% 3 16% 30% 30% 10%	653
August	1st to 10th	Day	10% 4 12% 28% 32% 15%	446
	11th to 20th	Day	13% 4 17% 30% 25% 11%	439
	21st to end	Day	6% 2 15% 31% 30% 16%	495
September	1st to 10th	Day	11% 4 17% 30% 28% 10%	450
	11th to 20th	Day	10% 2 15% 27% 32% 14%	450
	21st to end	Day	12% 10% 22% 23% 24% 9%	450
October	1st to 10th	Day	11% 7% 28% 32% 17% 5%	450
	11th to 20th	Day	14% 17% 33% 25% 10% 1	338
	21st to end	Day	29% 16% 34% 21% 1	297
November	1st to 10th	Day	12% 19% 29% 24% 13% 3	270
	11th to 20th	Day	23% 19% 31% 18% 9% 1	270
	21st to end	Day	24% 14% 37% 21% 3	270
December	1st to 10th	Day	17% 26% 34% 17% 4 1	270
	11th to 20th	Day	23% 15% 40% 15% 6% 1	270
	21st to end	Day	31% 18% 33% 15% 3	297
January	1st to 10th	Night	22% 16% 34% 24% 4	950
	11th to 20th	Night	24% 16% 37% 19% 4	950
	21st to end	Night	22% 15% 36% 24% 3	1003
February	1st to 10th	Night	25% 12% 36% 24% 2	720
	11th to 20th	Night	22% 15% 37% 23% 2	703
	21st to end	Night	26% 13% 39% 19% 3	592
March	1st to 10th	Night	25% 14% 34% 24% 4	720
	11th to 20th	Night	22% 13% 36% 23% 5% 1	720
	21st to end	Night	26% 8% 34% 27% 5% 1	665
April	1st to 10th	Night	17% 11% 34% 30% 7%	540
	11th to 20th	Night	20% 11% 29% 29% 11%	533
	21st to end	Night	22% 9% 35% 26% 7% 1	540
May	1st to 10th	Night	19% 7% 35% 29% 10%	540
	11th to 20th	Night	17% 6% 25% 34% 16% 2	531
	21st to end	Night	10% 3 23% 38% 23% 3	584
June	1st to 10th	Night	11% 3 23% 42% 21% 1	540
	11th to 20th	Night	10% 3 21% 44% 21% 1	540
	21st to end	Night	8% 3 21% 39% 27% 1	540
July	1st to 10th	Night	9% 2 10% 38% 34% 7%	525
	11th to 20th	Night	6% 3 15% 37% 34% 5%	522
	21st to end	Night	7% 3 11% 45% 32% 3	591
August	1st to 10th	Night	8% 2 11% 41% 34% 4	537
	11th to 20th	Night	7% 2 11% 41% 34% 4	534
	21st to end	Night	8% 3 12% 31% 41% 6%	594
September	1st to 10th	Night	12% 4 14% 37% 30% 4	540
	11th to 20th	Night	10% 3 14% 36% 34% 4	701
	21st to end	Night	12% 7% 19% 33% 26% 3	720
October	1st to 10th	Night	10% 4 25% 34% 22% 4	720
	11th to 20th	Night	19% 12% 26% 29% 13% 1	720
	21st to end	Night	23% 12% 33% 26% 6% 1	792
November	1st to 10th	Night	16% 8% 35% 30% 11% 1	740
	11th to 20th	Night	17% 15% 31% 28% 9%	760
	21st to end	Night	24% 13% 30% 26% 7%	760
December	1st to 10th	Night	23% 12% 38% 21% 5%	785
	11th to 20th	Night	24% 10% 34% 25% 6% 1	950
	21st to end	Night	31% 13% 32% 19% 4	1045

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