Greenwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greenwood clear sky chart from 2005-11-06 to 2024-03-01.

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	6% 5% 2 5% 4 3 5% 5% 6% 8% 50%	78396
	Night	5% 5% 2 5% 5% 3 4 5% 6% 8% 53%	81069
Transparency	Day	30% 8% 16% 26% 16% 4	78100
	Night	27% 8% 16% 27% 17% 4	80887
Seeing	Day	15% 20% 35% 22% 7% 2	14884
	Night	13% 19% 34% 26% 8% 1	25069

By Month

Percentage Cloud Cover SW (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	1 3 3 5% 4 3 4 4 6% 10% 57%	2538
	11th to 20th	Day	1 3 3 5% 5% 3 5% 5% 6% 8% 55%	2540
	21st to end	Day	1 3 2 5% 5% 3 4 5% 5% 8% 60%	2794
February	1st to 10th	Day	2 8% 4 8% 6% 4 6% 6% 6% 8% 42%	1705
	11th to 20th	Day	3 7% 4 8% 6% 3 5% 5% 6% 9% 45%	1800
	21st to end	Day	2 7% 4 8% 6% 2 4 5% 7% 8% 45%	1570
March	1st to 10th	Day	3 6% 4 6% 6% 3 5% 5% 6% 9% 48%	1800
	11th to 20th	Day	5% 6% 2 6% 4 3 3 4 5% 8% 52%	1844
	21st to end	Day	8% 12% 4 6% 5% 3 5% 5% 5% 8% 37%	2376
April	1st to 10th	Day	11% 9% 4 6% 3 2 5% 5% 5% 9% 41%	2160
	11th to 20th	Day	11% 11% 4 6% 6% 3 5% 5% 6% 7% 36%	2131
	21st to end	Day	14% 10% 2 5% 5% 3 4 5% 6% 7% 38%	2286
May	1st to 10th	Day	11% 9% 3 6% 6% 3 6% 6% 6% 7% 38%	2409
	11th to 20th	Day	15% 8% 2 5% 4 3 4 5% 6% 10% 36%	2478
	21st to end	Day	17% 7% 2 5% 5% 4 6% 5% 7% 8% 34%	2724
June	1st to 10th	Day	9% 4 2 4 5% 3 5% 6% 7% 9% 45%	2520
	11th to 20th	Day	9% 4 2 4 5% 3 5% 5% 6% 11% 46%	2520
	21st to end	Day	5% 3 1 3 4 3 4 6% 6% 8% 58%	2520
July	1st to 10th	Day	5% 4 1 3 4 3 6% 6% 7% 11% 50%	2520
	11th to 20th	Day	5% 2 1 3 3 2 3 6% 7% 8% 60%	2520
	21st to end	Day	4 3 1 3 3 2 5% 5% 7% 9% 56%	2742
August	1st to 10th	Day	6% 3 2 5% 4 3 5% 6% 9% 10% 49%	2507
	11th to 20th	Day	5% 2 1 3 4 2 5% 5% 6% 9% 59%	2223
	21st to end	Day	5% 3 1 3 3 2 4 5% 6% 7% 62%	2376
September	1st to 10th	Day	7% 4 2 4 3 2 3 3 4 6% 62%	2160
	11th to 20th	Day	8% 4 2 3 3 2 4 4 4 6% 60%	2090
	21st to end	Day	9% 4 2 3 2 2 3 4 4 7% 59%	1980
October	1st to 10th	Day	11% 6% 2 3 4 2 3 4 5% 5% 54%	1878
	11th to 20th	Day	8% 7% 2 4 3 2 4 3 5% 7% 55%	1774
	21st to end	Day	5% 6% 3 4 4 2 3 5% 5% 7% 55%	1782
November	1st to 10th	Day	4 4 2 3 4 2 5% 5% 6% 10% 56%	1673
	11th to 20th	Day	3 4 3 5% 4 2 4 4 5% 9% 56%	1696
	21st to end	Day	3 6% 2 5% 3 2 4 6% 7% 10% 53%	1520
December	1st to 10th	Day	1 4 3 6% 5% 3 5% 6% 7% 10% 51%	1520
	11th to 20th	Day	2 4 2 3 4 3 4 5% 7% 10% 56%	1926
	21st to end	Day	3 8% 4 6% 5% 3 4 5% 5% 7% 51%	2794
January	1st to 10th	Night	1 4 2 7% 6% 3 5% 6% 6% 7% 54%	4417
	11th to 20th	Night	1 3 2 4 6% 4 6% 6% 7% 10% 51%	4430
	21st to end	Night	1 4 2 4 5% 3 4 5% 6% 8% 59%	4873
February	1st to 10th	Night	3 7% 4 7% 5% 4 6% 6% 6% 8% 46%	2493
	11th to 20th	Night	2 6% 3 6% 6% 3 5% 5% 6% 9% 49%	2267
	21st to end	Night	3 6% 3 6% 5% 3 5% 5% 7% 8% 49%	1884
March	1st to 10th	Night	4 5% 2 6% 6% 3 4 4 6% 8% 52%	2166
	11th to 20th	Night	6% 6% 2 6% 6% 3 4 5% 6% 7% 50%	2113
	21st to end	Night	7% 9% 3 5% 5% 3 5% 5% 6% 10% 40%	1980
April	1st to 10th	Night	11% 6% 3 5% 5% 3 4 4 6% 9% 44%	1800
	11th to 20th	Night	13% 7% 2 5% 5% 3 5% 4 5% 7% 44%	1777
	21st to end	Night	12% 7% 3 4 4 2 4 5% 6% 8% 46%	1673
May	1st to 10th	Night	10% 7% 2 5% 5% 3 4 3 6% 8% 48%	1548
	11th to 20th	Night	12% 8% 2 4 4 3 4 4 4 8% 47%	1417
	21st to end	Night	17% 5% 3 4 3 2 3 4 5% 9% 45%	1552
June	1st to 10th	Night	9% 5% 1 4 4 3 5% 4 6% 10% 50%	1440
	11th to 20th	Night	10% 5% 1 3 5% 3 4 5% 8% 9% 48%	1440
	21st to end	Night	5% 4 1 3 4 2 4 4 6% 8% 58%	1440
July	1st to 10th	Night	6% 2 2 3 3 2 5% 7% 6% 9% 55%	1440
	11th to 20th	Night	4 3 1 3 3 2 3 5% 5% 9% 62%	1440
	21st to end	Night	3 1 1 3 4 2 4 5% 7% 9% 60%	1576
August	1st to 10th	Night	4 3 1 4 5% 3 5% 5% 6% 8% 54%	1432
	11th to 20th	Night	4 2 1 3 4 2 3 4 5% 7% 64%	1674
	21st to end	Night	4 3 1 3 3 2 3 4 6% 8% 63%	1980
September	1st to 10th	Night	6% 3 1 3 3 2 4 4 5% 8% 62%	1800
	11th to 20th	Night	7% 3 1 3 3 2 3 4 4 7% 61%	1869
	21st to end	Night	11% 4 1 3 4 3 3 3 4 6% 59%	1980
October	1st to 10th	Night	12% 7% 2 4 3 2 3 4 4 6% 52%	2078
	11th to 20th	Night	8% 5% 1 4 4 2 3 4 4 7% 57%	2168
	21st to end	Night	7% 7% 2 4 3 2 3 4 5% 8% 54%	2574
November	1st to 10th	Night	4 5% 3 5% 4 3 5% 5% 6% 9% 52%	2405
	11th to 20th	Night	3 4 2 5% 5% 3 4 5% 5% 7% 57%	2479
	21st to end	Night	3 4 3 4 4 3 5% 5% 5% 9% 56%	2660
December	1st to 10th	Night	2 5% 2 5% 4 3 4 5% 6% 8% 55%	2660
	11th to 20th	Night	2 3 2 4 3 2 4 5% 8% 10% 56%	3271
	21st to end	Night	2 7% 3 7% 6% 3 4 4 5% 7% 51%	4873

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	23% 7% 24% 29% 15% 1	2539
	11th to 20th	Day	26% 8% 20% 27% 14% 5%	2540
	21st to end	Day	22% 8% 21% 33% 14% 2	2794
February	1st to 10th	Day	39% 9% 16% 22% 11% 3	1705
	11th to 20th	Day	36% 7% 18% 22% 14% 4	1810
	21st to end	Day	33% 9% 16% 22% 14% 5%	1570
March	1st to 10th	Day	32% 8% 17% 27% 14% 3	1800
	11th to 20th	Day	31% 5% 17% 31% 14% 3	1844
	21st to end	Day	44% 9% 14% 23% 9% 1	2376
April	1st to 10th	Day	39% 8% 18% 21% 11% 3	2160
	11th to 20th	Day	44% 9% 14% 21% 10% 2	2134
	21st to end	Day	44% 7% 17% 24% 8% 1	2286
May	1st to 10th	Day	43% 7% 18% 24% 8% 1	2409
	11th to 20th	Day	43% 8% 19% 24% 6%	2482
	21st to end	Day	44% 10% 19% 19% 6% 2	2724
June	1st to 10th	Day	33% 11% 19% 25% 10% 2	2520
	11th to 20th	Day	31% 8% 18% 27% 13% 3	2520
	21st to end	Day	22% 8% 17% 29% 21% 4	2520
July	1st to 10th	Day	26% 9% 16% 29% 17% 4	2451
	11th to 20th	Day	20% 7% 13% 26% 24% 10%	2445
	21st to end	Day	21% 6% 15% 27% 21% 9%	2590
August	1st to 10th	Day	26% 10% 16% 27% 15% 6%	2491
	11th to 20th	Day	22% 6% 16% 32% 19% 5%	2223
	21st to end	Day	20% 5% 13% 25% 27% 10%	2376
September	1st to 10th	Day	23% 4 11% 27% 25% 9%	2160
	11th to 20th	Day	24% 6% 13% 26% 25% 6%	2090
	21st to end	Day	26% 4 12% 34% 22% 2	1980
October	1st to 10th	Day	32% 5% 14% 24% 21% 4	1878
	11th to 20th	Day	29% 5% 12% 30% 18% 6%	1774
	21st to end	Day	27% 5% 21% 25% 18% 4	1782
November	1st to 10th	Day	22% 10% 16% 25% 22% 4	1673
	11th to 20th	Day	25% 7% 15% 29% 19% 5%	1696
	21st to end	Day	24% 7% 17% 30% 17% 4	1520
December	1st to 10th	Day	27% 11% 17% 25% 18% 2	1520
	11th to 20th	Day	21% 7% 21% 34% 14% 3	1924
	21st to end	Day	32% 7% 10% 25% 22% 4	2794
January	1st to 10th	Night	27% 9% 13% 32% 16% 3	4417
	11th to 20th	Night	25% 13% 19% 24% 15% 4	4430
	21st to end	Night	22% 9% 20% 32% 15% 3	4873
February	1st to 10th	Night	35% 9% 19% 22% 13% 3	2493
	11th to 20th	Night	31% 8% 18% 25% 15% 4	2267
	21st to end	Night	30% 8% 15% 24% 16% 6%	1884
March	1st to 10th	Night	28% 8% 18% 26% 17% 3	2166
	11th to 20th	Night	32% 6% 15% 26% 18% 3	2113
	21st to end	Night	37% 8% 19% 23% 11% 2	1980
April	1st to 10th	Night	37% 8% 16% 25% 13% 2	1800
	11th to 20th	Night	37% 7% 16% 24% 13% 2	1777
	21st to end	Night	36% 7% 18% 26% 12% 1	1673
May	1st to 10th	Night	35% 8% 16% 29% 11% 1	1548
	11th to 20th	Night	36% 7% 20% 27% 10%	1418
	21st to end	Night	36% 8% 19% 25% 10% 1	1552
June	1st to 10th	Night	30% 9% 22% 27% 12% 1	1440
	11th to 20th	Night	31% 9% 23% 21% 14% 2	1440
	21st to end	Night	23% 7% 17% 28% 21% 4	1440
July	1st to 10th	Night	24% 8% 17% 31% 17% 4	1400
	11th to 20th	Night	19% 6% 13% 28% 24% 9%	1392
	21st to end	Night	18% 6% 16% 29% 24% 7%	1488
August	1st to 10th	Night	25% 8% 13% 28% 18% 6%	1424
	11th to 20th	Night	20% 6% 12% 31% 24% 7%	1674
	21st to end	Night	18% 6% 12% 25% 29% 9%	1980
September	1st to 10th	Night	21% 5% 9% 30% 25% 10%	1800
	11th to 20th	Night	23% 5% 13% 27% 25% 8%	1869
	21st to end	Night	27% 5% 9% 30% 24% 5%	1980
October	1st to 10th	Night	33% 5% 13% 23% 22% 3	2078
	11th to 20th	Night	27% 5% 13% 29% 20% 7%	2168
	21st to end	Night	28% 6% 18% 23% 19% 6%	2574
November	1st to 10th	Night	28% 7% 17% 22% 21% 6%	2405
	11th to 20th	Night	25% 6% 17% 27% 20% 5%	2479
	21st to end	Night	25% 6% 18% 27% 19% 5%	2660
December	1st to 10th	Night	25% 8% 19% 26% 18% 4	2660
	11th to 20th	Night	20% 10% 17% 37% 15% 2	3272
	21st to end	Night	31% 8% 12% 28% 18% 4	4873

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	11% 20% 32% 24% 10% 3	270
	11th to 20th	Day	17% 22% 32% 19% 7% 2	270
	21st to end	Day	18% 33% 31% 13% 5% 1	297
February	1st to 10th	Day	17% 28% 41% 11% 3	270
	11th to 20th	Day	14% 30% 40% 13% 2	270
	21st to end	Day	16% 28% 41% 13% 1	225
March	1st to 10th	Day	11% 30% 41% 11% 5% 1	240
	11th to 20th	Day	16% 25% 37% 15% 6% 1	280
	21st to end	Day	24% 24% 32% 15% 5% 1	462
April	1st to 10th	Day	21% 30% 34% 12% 2	420
	11th to 20th	Day	26% 33% 33% 6% 1	412
	21st to end	Day	22% 21% 33% 18% 5% 1	546
May	1st to 10th	Day	21% 23% 27% 20% 7% 2	603
	11th to 20th	Day	25% 14% 31% 20% 7% 2	625
	21st to end	Day	21% 18% 32% 20% 8% 2	679
June	1st to 10th	Day	10% 14% 32% 30% 11% 2	630
	11th to 20th	Day	15% 21% 38% 19% 6% 1	630
	21st to end	Day	9% 16% 36% 27% 10% 2	630
July	1st to 10th	Day	7% 10% 36% 35% 11% 1	621
	11th to 20th	Day	5% 12% 40% 31% 11% 1	618
	21st to end	Day	6% 9% 36% 35% 13% 2	684
August	1st to 10th	Day	6% 9% 38% 34% 13% 1	626
	11th to 20th	Day	7% 8% 39% 32% 10% 4	497
	21st to end	Day	5% 14% 36% 33% 9% 3	495
September	1st to 10th	Day	8% 17% 38% 27% 7% 3	450
	11th to 20th	Day	12% 12% 33% 30% 11% 3	380
	21st to end	Day	19% 22% 30% 16% 11% 2	270
October	1st to 10th	Day	21% 16% 29% 21% 10% 3	270
	11th to 20th	Day	21% 29% 30% 12% 6% 3	270
	21st to end	Day	17% 26% 35% 17% 4 1	297
November	1st to 10th	Day	15% 26% 33% 20% 4 2	270
	11th to 20th	Day	18% 25% 36% 16% 5%	270
	21st to end	Day	14% 24% 34% 21% 6% 1	270
December	1st to 10th	Day	17% 28% 32% 17% 4 1	270
	11th to 20th	Day	16% 26% 40% 15% 2	270
	21st to end	Day	18% 26% 33% 19% 4 1	297
January	1st to 10th	Night	13% 26% 33% 20% 7% 1	950
	11th to 20th	Night	15% 29% 32% 16% 7% 1	950
	21st to end	Night	13% 29% 36% 17% 4	1045
February	1st to 10th	Night	13% 29% 34% 18% 5%	783
	11th to 20th	Night	12% 26% 35% 20% 6% 1	744
	21st to end	Night	11% 22% 40% 20% 6%	628
March	1st to 10th	Night	11% 26% 37% 22% 4 1	722
	11th to 20th	Night	12% 17% 41% 22% 7% 1	716
	21st to end	Night	17% 18% 32% 25% 7% 1	594
April	1st to 10th	Night	19% 16% 37% 24% 4	540
	11th to 20th	Night	23% 18% 36% 20% 2 1	533
	21st to end	Night	19% 16% 27% 29% 7% 1	540
May	1st to 10th	Night	15% 12% 31% 29% 12% 1	540
	11th to 20th	Night	18% 13% 30% 28% 11% 1	531
	21st to end	Night	20% 15% 36% 21% 8% 1	584
June	1st to 10th	Night	11% 14% 31% 32% 12% 1	540
	11th to 20th	Night	12% 15% 39% 28% 6%	540
	21st to end	Night	7% 11% 36% 37% 9% 1	540
July	1st to 10th	Night	7% 7% 31% 40% 14% 1	525
	11th to 20th	Night	6% 5% 35% 43% 10% 1	522
	21st to end	Night	3 4 33% 47% 13%	591
August	1st to 10th	Night	6% 6% 29% 46% 12% 1	537
	11th to 20th	Night	5% 5% 31% 42% 17% 1	534
	21st to end	Night	6% 9% 26% 41% 17% 2	594
September	1st to 10th	Night	8% 9% 29% 40% 13% 2	540
	11th to 20th	Night	10% 10% 27% 40% 12% 1	540
	21st to end	Night	14% 17% 30% 30% 8% 1	540
October	1st to 10th	Night	19% 15% 29% 28% 9% 1	638
	11th to 20th	Night	16% 18% 35% 23% 7% 1	728
	21st to end	Night	17% 21% 34% 22% 7% 1	990
November	1st to 10th	Night	10% 24% 38% 22% 5% 2	925
	11th to 20th	Night	13% 25% 37% 19% 5% 1	950
	21st to end	Night	11% 29% 36% 21% 3	950
December	1st to 10th	Night	14% 28% 35% 17% 5% 1	950
	11th to 20th	Night	12% 25% 37% 21% 5% 1	950
	21st to end	Night	16% 28% 31% 19% 5%	1045

Page generated at 2024-02-27 04:30:12. Version ac07

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