Greene
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greene clear sky chart from 2005-11-06 to 2026-07-31.

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	18% 8% 2 6% 4 4 4 4 5% 7% 37%	137136
	Night	18% 8% 3 7% 4 4 4 3 5% 6% 37%	135888
Transparency	Day	45% 6% 12% 21% 14% 2	140645
	Night	46% 5% 11% 22% 14% 2	140469
Seeing	Day	23% 17% 31% 19% 8% 2	17133
	Night	22% 13% 31% 25% 7%	26071

By Month

Percentage Cloud Cover NE (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	12% 7% 3 9% 5% 5% 5% 4 7% 7% 37%	4661
	11th to 20th	Day	14% 10% 4 6% 4 4 4 3 5% 6% 41%	4650
	21st to end	Day	10% 10% 2 6% 3 4 4 3 5% 5% 46%	5124
February	1st to 10th	Day	15% 9% 2 6% 5% 5% 3 4 6% 5% 38%	1843
	11th to 20th	Day	12% 9% 3 7% 6% 5% 5% 4 5% 5% 39%	2048
	21st to end	Day	15% 10% 3 6% 4 3 6% 4 6% 5% 37%	1730
March	1st to 10th	Day	22% 11% 3 7% 5% 5% 4 3 4 4 32%	4576
	11th to 20th	Day	17% 11% 4 7% 4 4 5% 3 4 5% 36%	4990
	21st to end	Day	26% 9% 2 6% 3 3 3 3 5% 7% 32%	5740
April	1st to 10th	Day	20% 11% 3 6% 4 4 3 3 4 6% 36%	2520
	11th to 20th	Day	19% 7% 2 5% 5% 4 4 4 6% 6% 38%	2602
	21st to end	Day	23% 8% 3 7% 4 4 4 3 4 5% 35%	2730
May	1st to 10th	Day	29% 10% 3 6% 4 4 4 3 5% 6% 26%	7639
	11th to 20th	Day	18% 7% 2 7% 5% 5% 5% 4 5% 7% 33%	7779
	21st to end	Day	20% 7% 2 7% 5% 4 5% 4 6% 7% 33%	9060
June	1st to 10th	Day	22% 8% 3 6% 5% 5% 5% 4 6% 8% 30%	2940
	11th to 20th	Day	17% 6% 2 6% 5% 4 4 4 6% 7% 39%	2940
	21st to end	Day	23% 7% 2 6% 4 5% 5% 4 5% 6% 32%	2940
July	1st to 10th	Day	16% 7% 3 7% 4 5% 5% 5% 7% 8% 32%	6500
	11th to 20th	Day	14% 6% 2 6% 4 5% 5% 4 7% 9% 38%	6500
	21st to end	Day	16% 6% 2 6% 3 4 4 4 6% 8% 42%	7066
August	1st to 10th	Day	16% 6% 2 7% 5% 4 5% 4 7% 9% 35%	4275
	11th to 20th	Day	17% 9% 3 7% 4 4 4 4 6% 7% 35%	4175
	21st to end	Day	10% 5% 2 6% 4 4 5% 5% 6% 8% 46%	4484
September	1st to 10th	Day	13% 4 2 5% 3 4 3 3 5% 8% 49%	2355
	11th to 20th	Day	13% 5% 1 5% 3 3 3 3 5% 5% 55%	2200
	21st to end	Day	16% 5% 2 5% 4 3 4 3 5% 8% 46%	2200
October	1st to 10th	Day	18% 6% 2 6% 5% 3 4 3 4 7% 41%	2200
	11th to 20th	Day	18% 7% 2 6% 4 4 4 3 4 7% 42%	1920
	21st to end	Day	23% 8% 2 5% 4 4 4 3 4 6% 38%	1980
November	1st to 10th	Day	17% 7% 2 6% 3 3 4 3 5% 6% 45%	1851
	11th to 20th	Day	19% 5% 2 5% 4 3 4 3 5% 5% 44%	1890
	21st to end	Day	22% 7% 2 5% 3 2 3 2 5% 6% 41%	1864
December	1st to 10th	Day	17% 10% 3 6% 4 3 4 3 6% 7% 38%	2366
	11th to 20th	Day	19% 8% 2 4 3 3 3 3 4 6% 45%	2750
	21st to end	Day	21% 10% 3 6% 4 4 4 3 5% 6% 35%	4048
January	1st to 10th	Night	12% 9% 3 8% 5% 4 4 3 5% 6% 41%	8234
	11th to 20th	Night	14% 13% 4 10% 5% 5% 5% 3 5% 6% 30%	8235
	21st to end	Night	12% 9% 3 7% 5% 5% 5% 3 5% 6% 41%	9057
February	1st to 10th	Night	15% 9% 3 7% 5% 5% 4 4 6% 6% 35%	2773
	11th to 20th	Night	13% 10% 3 5% 5% 5% 5% 4 5% 5% 41%	2458
	21st to end	Night	14% 10% 2 7% 5% 5% 4 3 5% 6% 40%	2076
March	1st to 10th	Night	25% 11% 2 6% 4 4 4 3 4 5% 31%	5484
	11th to 20th	Night	16% 9% 4 7% 4 5% 5% 4 6% 7% 33%	5188
	21st to end	Night	24% 8% 3 7% 4 4 4 4 6% 6% 31%	5430
April	1st to 10th	Night	21% 11% 3 5% 4 4 4 3 4 6% 35%	2100
	11th to 20th	Night	19% 7% 2 6% 6% 4 4 4 4 6% 36%	1966
	21st to end	Night	23% 7% 2 6% 4 4 4 4 5% 5% 36%	1890
May	1st to 10th	Night	30% 9% 3 5% 3 4 4 3 5% 6% 28%	5259
	11th to 20th	Night	19% 8% 3 7% 5% 4 5% 4 6% 8% 33%	5123
	21st to end	Night	18% 8% 3 7% 5% 4 5% 4 6% 7% 34%	5114
June	1st to 10th	Night	21% 7% 3 7% 4 5% 4 4 5% 8% 33%	1680
	11th to 20th	Night	17% 6% 2 5% 5% 3 4 3 6% 8% 39%	1680
	21st to end	Night	21% 8% 3 6% 4 4 4 5% 6% 7% 33%	1680
July	1st to 10th	Night	13% 7% 3 7% 5% 5% 5% 5% 6% 9% 36%	3680
	11th to 20th	Night	15% 8% 3 8% 5% 5% 4 4 5% 7% 37%	3680
	21st to end	Night	12% 4 2 5% 4 4 4 4 7% 8% 47%	4006
August	1st to 10th	Night	21% 7% 3 7% 5% 5% 4 4 5% 6% 33%	2841
	11th to 20th	Night	15% 9% 3 7% 5% 5% 4 4 6% 8% 34%	2872
	21st to end	Night	11% 5% 2 7% 4 4 4 4 6% 9% 44%	3411
September	1st to 10th	Night	13% 6% 2 4 3 3 3 4 5% 7% 50%	2045
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 5% 7% 52%	2200
	21st to end	Night	16% 6% 2 5% 3 4 3 3 5% 6% 47%	2200
October	1st to 10th	Night	18% 7% 2 6% 4 4 4 3 5% 6% 42%	2200
	11th to 20th	Night	18% 6% 2 6% 3 4 4 4 6% 6% 42%	2477
	21st to end	Night	24% 7% 2 5% 3 3 4 3 4 6% 37%	2860
November	1st to 10th	Night	17% 7% 2 5% 4 4 4 3 5% 5% 44%	2667
	11th to 20th	Night	17% 6% 2 4 4 4 4 3 4 5% 45%	2730
	21st to end	Night	17% 7% 2 6% 4 5% 4 3 5% 6% 40%	2749
December	1st to 10th	Night	17% 10% 2 6% 4 4 4 4 6% 7% 36%	5026
	11th to 20th	Night	24% 7% 2 5% 4 3 3 3 4 5% 40%	5667
	21st to end	Night	21% 10% 3 6% 4 3 3 3 4 5% 37%	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	45% 5% 13% 23% 14% 1	4662
	11th to 20th	Day	44% 4 11% 25% 13% 3	4680
	21st to end	Day	39% 5% 10% 22% 19% 5%	5124
February	1st to 10th	Day	46% 4 12% 21% 14% 3	1843
	11th to 20th	Day	47% 5% 11% 20% 14% 3	2057
	21st to end	Day	47% 6% 10% 19% 14% 4	1730
March	1st to 10th	Day	56% 4 8% 11% 14% 7%	4579
	11th to 20th	Day	49% 6% 13% 18% 11% 2	4990
	21st to end	Day	52% 4 6% 17% 17% 5%	5740
April	1st to 10th	Day	51% 4 9% 17% 16% 4	2520
	11th to 20th	Day	44% 6% 11% 21% 14% 3	2602
	21st to end	Day	51% 5% 8% 17% 15% 4	2730
May	1st to 10th	Day	58% 7% 12% 15% 8% 1	7651
	11th to 20th	Day	48% 7% 15% 18% 10% 2	7783
	21st to end	Day	47% 7% 12% 21% 12% 1	9061
June	1st to 10th	Day	50% 7% 12% 21% 10%	2940
	11th to 20th	Day	43% 7% 11% 20% 16% 2	2940
	21st to end	Day	51% 7% 11% 20% 10% 1	2940
July	1st to 10th	Day	46% 8% 13% 22% 11%	6430
	11th to 20th	Day	40% 8% 15% 23% 13% 1	6425
	21st to end	Day	39% 6% 14% 25% 16%	6868
August	1st to 10th	Day	44% 8% 15% 24% 9%	4261
	11th to 20th	Day	47% 6% 16% 23% 8%	4214
	21st to end	Day	32% 8% 14% 25% 18% 2	4484
September	1st to 10th	Day	32% 7% 13% 28% 19% 1	2355
	11th to 20th	Day	31% 4 10% 30% 22% 3	2200
	21st to end	Day	37% 5% 12% 28% 17% 1	2200
October	1st to 10th	Day	46% 6% 11% 23% 13% 1	3590
	11th to 20th	Day	35% 4 11% 29% 20% 1	3097
	21st to end	Day	36% 4 11% 25% 21% 3	3180
November	1st to 10th	Day	40% 5% 13% 24% 16% 3	1851
	11th to 20th	Day	40% 6% 11% 21% 19% 3	1890
	21st to end	Day	44% 4 17% 23% 11% 1	1864
December	1st to 10th	Day	44% 5% 14% 24% 12% 1	2366
	11th to 20th	Day	40% 5% 12% 19% 17% 7%	2750
	21st to end	Day	51% 4 9% 18% 13% 5%	4048
January	1st to 10th	Night	44% 4 12% 27% 12% 1	8234
	11th to 20th	Night	53% 6% 11% 16% 12% 2	8280
	21st to end	Night	44% 4 7% 22% 18% 5%	9057
February	1st to 10th	Night	48% 5% 11% 19% 13% 3	2773
	11th to 20th	Night	44% 6% 10% 21% 16% 3	2460
	21st to end	Night	46% 4 10% 22% 15% 4	2076
March	1st to 10th	Night	56% 4 7% 13% 13% 6%	5494
	11th to 20th	Night	47% 7% 17% 19% 8% 2	5189
	21st to end	Night	51% 5% 7% 15% 18% 4	5430
April	1st to 10th	Night	51% 4 9% 17% 15% 3	2100
	11th to 20th	Night	47% 6% 10% 20% 16% 1	1966
	21st to end	Night	49% 5% 11% 18% 14% 4	1890
May	1st to 10th	Night	56% 6% 12% 14% 11% 1	5265
	11th to 20th	Night	48% 7% 12% 25% 7% 1	5124
	21st to end	Night	46% 7% 13% 22% 11% 1	5115
June	1st to 10th	Night	49% 7% 10% 23% 10% 1	1680
	11th to 20th	Night	42% 7% 15% 21% 14% 2	1680
	21st to end	Night	49% 7% 15% 18% 9% 1	1680
July	1st to 10th	Night	42% 7% 16% 23% 11%	3640
	11th to 20th	Night	45% 7% 13% 22% 12%	3632
	21st to end	Night	33% 7% 16% 32% 12% 1	3889
August	1st to 10th	Night	51% 6% 14% 21% 7%	2831
	11th to 20th	Night	46% 8% 15% 20% 10%	2899
	21st to end	Night	35% 8% 15% 27% 15% 1	3411
September	1st to 10th	Night	34% 5% 13% 31% 16%	2045
	11th to 20th	Night	33% 4 12% 30% 19% 2	2200
	21st to end	Night	37% 6% 10% 30% 15% 2	2200
October	1st to 10th	Night	43% 6% 14% 22% 14% 1	3590
	11th to 20th	Night	34% 5% 10% 28% 22% 1	4039
	21st to end	Night	39% 3 11% 27% 16% 2	4610
November	1st to 10th	Night	41% 5% 10% 26% 15% 2	2667
	11th to 20th	Night	42% 4 11% 23% 17% 3	2730
	21st to end	Night	43% 5% 15% 21% 14% 2	2749
December	1st to 10th	Night	46% 5% 10% 29% 10% 1	5026
	11th to 20th	Night	47% 5% 10% 17% 18% 3	5668
	21st to end	Night	50% 5% 9% 18% 17% 1	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	30% 22% 30% 14% 4	220
	11th to 20th	Day	25% 25% 31% 14% 4 1	220
	21st to end	Day	21% 28% 31% 17% 3	242
February	1st to 10th	Day	25% 19% 35% 18% 4	383
	11th to 20th	Day	24% 26% 35% 13% 2	536
	21st to end	Day	26% 20% 36% 16% 3	446
March	1st to 10th	Day	30% 21% 32% 14% 4	540
	11th to 20th	Day	24% 29% 31% 13% 3	540
	21st to end	Day	31% 22% 30% 11% 5% 2	594
April	1st to 10th	Day	32% 25% 26% 13% 4 1	540
	11th to 20th	Day	30% 22% 30% 12% 4 1	532
	21st to end	Day	32% 20% 27% 14% 5% 2	540
May	1st to 10th	Day	34% 20% 24% 17% 3 1	543
	11th to 20th	Day	21% 20% 35% 16% 6% 2	567
	21st to end	Day	23% 16% 35% 20% 6%	617
June	1st to 10th	Day	20% 17% 33% 19% 9% 3	570
	11th to 20th	Day	19% 18% 31% 21% 8% 2	570
	21st to end	Day	25% 14% 33% 20% 7% 2	570
July	1st to 10th	Day	18% 9% 39% 24% 8% 2	565
	11th to 20th	Day	15% 10% 37% 25% 10% 3	564
	21st to end	Day	16% 10% 35% 25% 11% 3	616
August	1st to 10th	Day	13% 10% 29% 31% 14% 3	526
	11th to 20th	Day	18% 10% 25% 27% 14% 7%	519
	21st to end	Day	12% 12% 30% 28% 12% 5%	583
September	1st to 10th	Day	16% 10% 30% 24% 17% 4	530
	11th to 20th	Day	15% 13% 27% 20% 15% 9%	530
	21st to end	Day	17% 13% 32% 22% 11% 5%	530
October	1st to 10th	Day	22% 15% 26% 20% 13% 4	530
	11th to 20th	Day	23% 16% 29% 20% 10% 2	425
	21st to end	Day	31% 17% 27% 17% 8%	462
November	1st to 10th	Day	25% 18% 29% 18% 8% 2	425
	11th to 20th	Day	28% 18% 30% 18% 5% 1	430
	21st to end	Day	31% 18% 27% 17% 7%	430
December	1st to 10th	Day	28% 16% 35% 14% 7%	236
	11th to 20th	Day	35% 20% 33% 9% 3	220
	21st to end	Day	31% 20% 26% 18% 5% 1	242
January	1st to 10th	Night	22% 18% 36% 21% 3	840
	11th to 20th	Night	26% 20% 31% 19% 4	840
	21st to end	Night	18% 20% 38% 20% 3	924
February	1st to 10th	Night	22% 18% 33% 23% 4	840
	11th to 20th	Night	22% 19% 39% 18% 3	823
	21st to end	Night	22% 16% 36% 22% 4	692
March	1st to 10th	Night	25% 18% 37% 18% 2	840
	11th to 20th	Night	23% 18% 34% 20% 6%	840
	21st to end	Night	25% 18% 32% 21% 3 1	924
April	1st to 10th	Night	28% 17% 32% 19% 3	840
	11th to 20th	Night	23% 17% 34% 21% 4	722
	21st to end	Night	28% 14% 32% 21% 5%	630
May	1st to 10th	Night	26% 11% 33% 24% 6%	630
	11th to 20th	Night	23% 13% 32% 26% 6%	588
	21st to end	Night	24% 8% 29% 33% 6%	455
June	1st to 10th	Night	25% 7% 30% 30% 9%	420
	11th to 20th	Night	19% 8% 27% 34% 12%	420
	21st to end	Night	25% 5% 26% 35% 9%	420
July	1st to 10th	Night	17% 3 26% 41% 12%	410
	11th to 20th	Night	17% 4 25% 35% 17%	408
	21st to end	Night	15% 3 25% 41% 16% 1	458
August	1st to 10th	Night	16% 3 26% 40% 15% 1	549
	11th to 20th	Night	15% 6% 28% 35% 15% 1	592
	21st to end	Night	13% 7% 26% 35% 16% 2	770
September	1st to 10th	Night	15% 5% 33% 32% 15% 1	800
	11th to 20th	Night	17% 7% 26% 29% 18% 3	800
	21st to end	Night	19% 8% 29% 29% 15% 1	800
October	1st to 10th	Night	21% 11% 25% 29% 14% 1	800
	11th to 20th	Night	21% 12% 31% 26% 10% 1	800
	21st to end	Night	28% 13% 29% 24% 5%	880
November	1st to 10th	Night	23% 13% 33% 23% 7% 1	820
	11th to 20th	Night	23% 14% 32% 22% 7% 1	840
	21st to end	Night	24% 20% 30% 22% 5%	851
December	1st to 10th	Night	26% 15% 34% 20% 5%	950
	11th to 20th	Night	27% 19% 32% 20% 3	931
	21st to end	Night	28% 16% 33% 21% 3	924

Page generated at 2026-07-28 03:25:25. Version ac07

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