Green Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Green Ridge Observatory clear sky chart from 2005-11-06 to 2025-01-22.

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 8% 5% 5% 5% 4 6% 8% 33%	105259
	Night	15% 10% 4 8% 5% 5% 4 4 5% 7% 34%	104000
Transparency	Day	27% 46% 7% 12% 6% 1	108904
	Night	28% 45% 7% 12% 7% 1	108495
Seeing	Day	17% 10% 28% 26% 14% 5%	15289
	Night	19% 9% 28% 30% 13% 2	24700

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	16% 16% 6% 15% 7% 5% 5% 3 5% 5% 16%	2652
	11th to 20th	Day	13% 18% 8% 15% 7% 7% 4 4 5% 5% 13%	2930
	21st to end	Day	25% 19% 8% 12% 5% 4 4 3 4 4 14%	3133
February	1st to 10th	Day	15% 15% 5% 11% 7% 6% 5% 3 5% 7% 21%	1710
	11th to 20th	Day	14% 11% 5% 11% 7% 6% 5% 5% 4 6% 25%	1708
	21st to end	Day	17% 12% 4 11% 8% 5% 5% 3 5% 5% 25%	1570
March	1st to 10th	Day	20% 10% 4 10% 6% 5% 4 3 5% 6% 26%	3311
	11th to 20th	Day	12% 11% 5% 10% 6% 5% 5% 4 4 7% 31%	3480
	21st to end	Day	17% 11% 4 9% 6% 5% 5% 3 5% 6% 31%	3815
April	1st to 10th	Day	15% 12% 3 7% 5% 5% 4 4 6% 9% 31%	2139
	11th to 20th	Day	18% 9% 3 7% 4 5% 5% 4 5% 7% 33%	2442
	21st to end	Day	18% 10% 4 8% 5% 4 4 4 5% 7% 33%	2470
May	1st to 10th	Day	16% 8% 3 7% 5% 4 5% 4 6% 7% 34%	4082
	11th to 20th	Day	16% 8% 3 7% 5% 4 4 4 6% 9% 33%	4081
	21st to end	Day	9% 5% 2 7% 4 4 4 4 6% 9% 45%	4657
June	1st to 10th	Day	10% 7% 2 7% 5% 5% 5% 5% 7% 8% 40%	2660
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 4 7% 9% 41%	2842
	21st to end	Day	9% 6% 2 5% 5% 4 5% 5% 6% 10% 42%	2850
July	1st to 10th	Day	9% 6% 2 6% 4 5% 5% 4 7% 9% 43%	4571
	11th to 20th	Day	8% 5% 2 5% 3 4 4 5% 7% 10% 46%	4226
	21st to end	Day	7% 4 2 7% 5% 6% 6% 5% 7% 9% 42%	4466
August	1st to 10th	Day	14% 5% 2 5% 4 4 5% 4 7% 9% 41%	4104
	11th to 20th	Day	8% 5% 2 7% 5% 4 6% 5% 8% 11% 39%	4044
	21st to end	Day	8% 6% 2 6% 5% 5% 5% 4 7% 8% 43%	4506
September	1st to 10th	Day	10% 6% 2 6% 4 4 6% 4 6% 8% 43%	2176
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 7% 10% 47%	2090
	21st to end	Day	17% 7% 3 6% 4 5% 5% 3 6% 7% 38%	2090
October	1st to 10th	Day	13% 6% 3 7% 4 4 4 4 6% 8% 42%	1970
	11th to 20th	Day	16% 9% 2 7% 5% 6% 5% 4 6% 7% 33%	1900
	21st to end	Day	20% 10% 3 8% 5% 5% 5% 4 6% 7% 29%	2033
November	1st to 10th	Day	13% 8% 3 7% 7% 4 5% 4 6% 9% 34%	1762
	11th to 20th	Day	14% 11% 3 9% 5% 5% 5% 4 5% 8% 31%	1725
	21st to end	Day	18% 12% 5% 11% 6% 5% 4 4 7% 7% 22%	1600
December	1st to 10th	Day	18% 12% 4 9% 6% 5% 5% 5% 6% 8% 23%	2600
	11th to 20th	Day	22% 16% 5% 10% 7% 5% 5% 4 5% 5% 17%	2990
	21st to end	Day	25% 19% 7% 12% 6% 5% 4 3 4 4 12%	3874
January	1st to 10th	Night	16% 14% 5% 10% 5% 6% 5% 4 5% 6% 23%	4496
	11th to 20th	Night	14% 17% 6% 14% 7% 5% 5% 3 4 5% 19%	4250
	21st to end	Night	25% 16% 7% 11% 5% 4 4 3 4 4 17%	4546
February	1st to 10th	Night	17% 15% 5% 10% 6% 5% 5% 4 5% 6% 23%	2470
	11th to 20th	Night	16% 12% 4 9% 6% 5% 5% 4 5% 6% 27%	2356
	21st to end	Night	19% 10% 4 8% 6% 5% 5% 4 5% 6% 27%	1884
March	1st to 10th	Night	18% 12% 3 7% 6% 5% 4 3 4 5% 33%	3541
	11th to 20th	Night	10% 8% 3 7% 5% 5% 5% 4 6% 8% 39%	3480
	21st to end	Night	16% 10% 3 7% 4 4 4 3 5% 5% 38%	3817
April	1st to 10th	Night	16% 12% 3 6% 6% 4 4 4 5% 6% 35%	2052
	11th to 20th	Night	17% 7% 2 8% 5% 4 3 3 6% 8% 36%	1690
	21st to end	Night	16% 8% 3 7% 5% 5% 4 3 5% 7% 37%	1710
May	1st to 10th	Night	17% 9% 3 7% 4 4 4 4 7% 7% 35%	2813
	11th to 20th	Night	11% 9% 3 9% 6% 6% 5% 5% 6% 8% 33%	2812
	21st to end	Night	10% 5% 2 5% 4 4 4 4 5% 7% 49%	2894
June	1st to 10th	Night	10% 6% 2 6% 4 5% 3 3 6% 9% 45%	1520
	11th to 20th	Night	9% 5% 2 5% 4 5% 5% 4 8% 10% 43%	1332
	21st to end	Night	10% 5% 2 6% 4 5% 4 4 6% 8% 48%	1330
July	1st to 10th	Night	7% 3 2 4 4 4 4 4 5% 11% 51%	2393
	11th to 20th	Night	8% 4 2 4 4 3 4 3 6% 9% 53%	2733
	21st to end	Night	5% 4 2 5% 4 4 5% 5% 7% 9% 49%	3087
August	1st to 10th	Night	11% 6% 2 5% 4 4 4 4 6% 9% 45%	2825
	11th to 20th	Night	7% 5% 2 6% 5% 4 4 4 5% 8% 50%	2785
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 8% 48%	3124
September	1st to 10th	Night	9% 6% 3 6% 4 4 4 4 6% 8% 47%	1993
	11th to 20th	Night	8% 4 2 6% 3 3 4 3 4 6% 56%	2090
	21st to end	Night	15% 7% 2 7% 4 4 4 4 5% 5% 42%	2090
October	1st to 10th	Night	13% 6% 2 6% 4 4 4 4 5% 7% 47%	2209
	11th to 20th	Night	17% 8% 3 7% 4 4 4 4 5% 6% 38%	2280
	21st to end	Night	21% 9% 3 7% 5% 5% 4 4 5% 6% 32%	2560
November	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 6% 7% 42%	2536
	11th to 20th	Night	16% 11% 3 8% 5% 5% 4 4 5% 7% 32%	2672
	21st to end	Night	20% 11% 3 9% 6% 5% 4 3 5% 6% 28%	2800
December	1st to 10th	Night	14% 14% 4 9% 6% 6% 5% 4 7% 7% 23%	4580
	11th to 20th	Night	18% 17% 5% 10% 5% 6% 5% 4 5% 5% 21%	5205
	21st to end	Night	24% 17% 6% 11% 6% 5% 5% 3 4 5% 13%	7045

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	44% 40% 7% 6% 3	2653
	11th to 20th	Day	49% 39% 6% 5% 2	2930
	21st to end	Day	49% 39% 6% 4 2	3133
February	1st to 10th	Day	23% 66% 3 5% 3	1710
	11th to 20th	Day	21% 65% 3 7% 3	1717
	21st to end	Day	18% 66% 3 8% 4 1	1570
March	1st to 10th	Day	37% 42% 5% 13% 2	3311
	11th to 20th	Day	31% 43% 13% 11% 3	3480
	21st to end	Day	31% 42% 7% 11% 8% 1	3815
April	1st to 10th	Day	21% 66% 5% 5% 3	2139
	11th to 20th	Day	18% 66% 4 7% 5% 1	2442
	21st to end	Day	18% 66% 5% 6% 4 1	2470
May	1st to 10th	Day	28% 42% 8% 14% 6% 2	4120
	11th to 20th	Day	28% 44% 13% 14% 1	4085
	21st to end	Day	21% 42% 6% 11% 13% 6%	4671
June	1st to 10th	Day	15% 66% 4 10% 5%	2660
	11th to 20th	Day	16% 66% 4 6% 6% 1	2842
	21st to end	Day	13% 64% 6% 9% 7% 1	2850
July	1st to 10th	Day	27% 36% 9% 17% 9% 2	4502
	11th to 20th	Day	20% 36% 9% 24% 10%	4153
	21st to end	Day	24% 37% 12% 12% 15% 1	4324
August	1st to 10th	Day	26% 37% 9% 16% 11%	4091
	11th to 20th	Day	24% 39% 9% 25% 3	4083
	21st to end	Day	24% 38% 9% 22% 6%	4506
September	1st to 10th	Day	14% 61% 7% 11% 6%	2176
	11th to 20th	Day	13% 61% 6% 12% 8%	2090
	21st to end	Day	18% 60% 5% 10% 6%	2090
October	1st to 10th	Day	19% 37% 11% 18% 15% 1	3269
	11th to 20th	Day	25% 37% 6% 18% 15%	3140
	21st to end	Day	25% 37% 11% 19% 6%	3335
November	1st to 10th	Day	24% 57% 5% 9% 4 1	1762
	11th to 20th	Day	23% 58% 6% 8% 5%	1725
	21st to end	Day	28% 59% 6% 5% 2	1600
December	1st to 10th	Day	38% 37% 12% 10% 4	2600
	11th to 20th	Day	49% 33% 7% 6% 5%	2986
	21st to end	Day	57% 29% 5% 7% 2	3874
January	1st to 10th	Night	37% 41% 9% 10% 3	4496
	11th to 20th	Night	43% 39% 8% 8% 2	4250
	21st to end	Night	46% 40% 5% 7% 2	4546
February	1st to 10th	Night	24% 65% 3 6% 2	2470
	11th to 20th	Night	19% 65% 4 8% 5%	2358
	21st to end	Night	20% 65% 4 7% 4 1	1884
March	1st to 10th	Night	35% 41% 9% 12% 3	3541
	11th to 20th	Night	24% 43% 11% 11% 11% 1	3480
	21st to end	Night	27% 42% 7% 12% 12% 1	3817
April	1st to 10th	Night	20% 66% 4 6% 4	2052
	11th to 20th	Night	18% 66% 4 7% 5% 1	1690
	21st to end	Night	16% 65% 5% 8% 5% 1	1710
May	1st to 10th	Night	28% 42% 6% 11% 10% 3	2840
	11th to 20th	Night	30% 44% 8% 14% 4	2813
	21st to end	Night	20% 42% 6% 12% 16% 3	2901
June	1st to 10th	Night	13% 65% 4 11% 6% 1	1520
	11th to 20th	Night	15% 66% 3 10% 5% 1	1332
	21st to end	Night	13% 64% 5% 9% 9%	1330
July	1st to 10th	Night	18% 36% 9% 22% 11% 5%	2353
	11th to 20th	Night	19% 36% 10% 21% 14% 1	2683
	21st to end	Night	21% 38% 11% 14% 16% 2	2988
August	1st to 10th	Night	25% 37% 9% 16% 12% 2	2814
	11th to 20th	Night	23% 39% 8% 20% 9%	2812
	21st to end	Night	24% 38% 7% 21% 11%	3124
September	1st to 10th	Night	13% 61% 6% 11% 8% 1	1993
	11th to 20th	Night	12% 60% 4 12% 11% 1	2090
	21st to end	Night	19% 60% 4 11% 6%	2090
October	1st to 10th	Night	14% 37% 4 22% 21% 1	3690
	11th to 20th	Night	29% 37% 5% 14% 15%	3779
	21st to end	Night	23% 36% 10% 21% 10%	4208
November	1st to 10th	Night	23% 57% 6% 8% 6% 1	2536
	11th to 20th	Night	21% 57% 6% 10% 6%	2672
	21st to end	Night	26% 58% 6% 6% 4	2800
December	1st to 10th	Night	38% 36% 13% 11% 2	4580
	11th to 20th	Night	45% 33% 7% 10% 5%	5208
	21st to end	Night	55% 29% 8% 7% 2	7045

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	21% 16% 37% 18% 6% 1	300
	11th to 20th	Day	25% 16% 42% 11% 4 1	300
	21st to end	Day	27% 14% 32% 22% 4 1	300
February	1st to 10th	Day	19% 21% 38% 18% 4	270
	11th to 20th	Day	24% 18% 37% 17% 4	270
	21st to end	Day	25% 21% 41% 12% 1	225
March	1st to 10th	Day	21% 17% 34% 22% 6% 1	383
	11th to 20th	Day	20% 13% 37% 23% 6% 1	460
	21st to end	Day	25% 14% 32% 24% 5% 1	506
April	1st to 10th	Day	16% 12% 40% 23% 8% 1	460
	11th to 20th	Day	26% 13% 29% 20% 8% 4	452
	21st to end	Day	23% 11% 33% 24% 8% 2	460
May	1st to 10th	Day	22% 12% 27% 27% 10% 2	463
	11th to 20th	Day	17% 8% 27% 27% 17% 4	487
	21st to end	Day	12% 6% 24% 30% 23% 5%	529
June	1st to 10th	Day	12% 8% 28% 34% 15% 4	490
	11th to 20th	Day	11% 6% 30% 35% 16% 2	672
	21st to end	Day	12% 6% 29% 35% 15% 3	680
July	1st to 10th	Day	9% 3 23% 33% 24% 8%	671
	11th to 20th	Day	12% 3 23% 30% 21% 10%	547
	21st to end	Day	9% 2 20% 32% 27% 10%	532
August	1st to 10th	Day	10% 4 18% 30% 25% 12%	486
	11th to 20th	Day	12% 5% 15% 34% 21% 13%	479
	21st to end	Day	9% 4 18% 32% 26% 11%	539
September	1st to 10th	Day	12% 3 21% 29% 23% 11%	490
	11th to 20th	Day	8% 3 18% 27% 31% 13%	490
	21st to end	Day	20% 6% 23% 29% 15% 8%	490
October	1st to 10th	Day	17% 7% 25% 27% 18% 6%	490
	11th to 20th	Day	17% 14% 33% 24% 10% 3	490
	21st to end	Day	25% 12% 35% 21% 7% 1	482
November	1st to 10th	Day	14% 19% 35% 22% 7% 2	300
	11th to 20th	Day	24% 19% 30% 19% 7% 2	263
	21st to end	Day	22% 13% 40% 21% 5% 1	200
December	1st to 10th	Day	23% 18% 32% 19% 9% 1	200
	11th to 20th	Day	30% 15% 34% 20% 3	200
	21st to end	Day	30% 18% 31% 16% 4	233
January	1st to 10th	Night	25% 15% 35% 18% 6% 1	954
	11th to 20th	Night	28% 13% 34% 22% 3	800
	21st to end	Night	22% 11% 34% 27% 6%	841
February	1st to 10th	Night	24% 12% 35% 25% 4	760
	11th to 20th	Night	22% 13% 32% 25% 6%	743
	21st to end	Night	25% 11% 39% 22% 2	628
March	1st to 10th	Night	21% 11% 33% 29% 6%	760
	11th to 20th	Night	19% 10% 37% 26% 8% 1	760
	21st to end	Night	21% 10% 33% 27% 8% 1	836
April	1st to 10th	Night	21% 11% 33% 29% 5% 1	760
	11th to 20th	Night	20% 9% 33% 28% 9% 1	566
	21st to end	Night	20% 7% 34% 31% 8% 1	570
May	1st to 10th	Night	18% 5% 29% 33% 14% 1	570
	11th to 20th	Night	14% 5% 26% 39% 14% 2	561
	21st to end	Night	11% 3 22% 40% 22% 1	509
June	1st to 10th	Night	12% 5% 27% 42% 14%	380
	11th to 20th	Night	11% 4 21% 47% 16% 1	380
	21st to end	Night	11% 3 25% 42% 18% 1	380
July	1st to 10th	Night	7% 1 14% 43% 31% 3	470
	11th to 20th	Night	11% 3 16% 38% 29% 3	552
	21st to end	Night	9% 3 13% 45% 28% 3	624
August	1st to 10th	Night	9% 1 13% 40% 32% 5%	567
	11th to 20th	Night	7% 3 13% 37% 34% 6%	564
	21st to end	Night	11% 2 16% 37% 30% 5%	627
September	1st to 10th	Night	12% 4 17% 35% 27% 6%	752
	11th to 20th	Night	10% 4 15% 35% 30% 7%	760
	21st to end	Night	18% 4 21% 31% 19% 6%	760
October	1st to 10th	Night	15% 6% 25% 32% 19% 3	760
	11th to 20th	Night	20% 11% 28% 27% 12% 2	760
	21st to end	Night	25% 10% 31% 28% 6% 1	836
November	1st to 10th	Night	16% 12% 29% 28% 13% 2	780
	11th to 20th	Night	22% 14% 34% 23% 7% 1	800
	21st to end	Night	27% 13% 31% 23% 7%	800
December	1st to 10th	Night	25% 15% 34% 20% 6% 1	800
	11th to 20th	Night	23% 15% 36% 23% 3	800
	21st to end	Night	29% 13% 32% 23% 3	930

Page generated at 2025-01-19 03:06:46. Version ac07

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