Green River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Green River Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	3 5% 2 6% 5% 5% 5% 4 6% 8% 51%	105281
	Night	2 5% 2 6% 5% 4 5% 4 6% 8% 51%	102522
Transparency	Day	26% 8% 15% 22% 20% 10%	105036
	Night	25% 8% 16% 24% 19% 8%	102356
Seeing	Day	6% 7% 23% 35% 22% 7%	15603
	Night	4 4 24% 46% 19% 2	25737

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	4 3 9% 7% 6% 6% 5% 9% 11% 40%	2639
	11th to 20th	Day	1 4 2 11% 5% 6% 6% 4 6% 9% 47%	2860
	21st to end	Day	1 5% 3 9% 7% 6% 6% 5% 9% 12% 37%	3146
February	1st to 10th	Day	2 6% 3 8% 6% 5% 5% 4 7% 8% 46%	1710
	11th to 20th	Day	1 8% 4 8% 5% 6% 6% 5% 7% 10% 41%	1665
	21st to end	Day	1 6% 3 8% 6% 4 5% 6% 8% 10% 43%	1495
March	1st to 10th	Day	1 4 3 8% 6% 6% 7% 6% 8% 11% 41%	3444
	11th to 20th	Day	1 5% 2 6% 5% 5% 5% 5% 6% 8% 50%	3490
	21st to end	Day	3 11% 4 13% 8% 7% 6% 5% 7% 9% 27%	3825
April	1st to 10th	Day	2 7% 4 8% 6% 6% 6% 5% 7% 8% 41%	2209
	11th to 20th	Day	3 8% 4 9% 6% 5% 5% 4 7% 9% 39%	2316
	21st to end	Day	5% 8% 4 7% 6% 6% 6% 4 7% 9% 38%	2470
May	1st to 10th	Day	4 8% 4 10% 7% 6% 6% 6% 6% 8% 35%	4110
	11th to 20th	Day	4 6% 2 5% 4 4 5% 5% 6% 8% 50%	4190
	21st to end	Day	5% 7% 2 7% 5% 6% 5% 4 7% 8% 44%	4825
June	1st to 10th	Day	5% 4 2 6% 4 5% 5% 5% 7% 9% 48%	2660
	11th to 20th	Day	4 4 2 5% 4 4 5% 4 6% 8% 55%	2660
	21st to end	Day	3 2 1 4 3 3 4 3 6% 7% 65%	2660
July	1st to 10th	Day	2 2 1 2 2 3 3 3 5% 6% 71%	4430
	11th to 20th	Day	2 2 1 4 3 4 5% 4 7% 9% 59%	4243
	21st to end	Day	4 3 1 4 3 4 5% 4 6% 8% 56%	4454
August	1st to 10th	Day	2 3 1 3 3 4 5% 5% 7% 10% 57%	4092
	11th to 20th	Day	3 2 1 4 4 4 5% 4 5% 7% 60%	4028
	21st to end	Day	2 2 1 4 3 3 4 3 5% 6% 68%	4398
September	1st to 10th	Day	3 3 2 3 3 4 3 3 5% 7% 64%	2280
	11th to 20th	Day	4 4 2 4 3 3 4 3 6% 7% 61%	2112
	21st to end	Day	4 4 1 4 3 3 4 3 3 5% 66%	2090
October	1st to 10th	Day	4 4 1 3 2 2 2 2 4 5% 69%	3180
	11th to 20th	Day	4 5% 2 4 3 4 3 3 5% 7% 60%	3150
	21st to end	Day	3 6% 2 6% 3 3 4 3 5% 7% 59%	3438
November	1st to 10th	Day	4 5% 3 6% 5% 5% 5% 4 5% 8% 52%	1732
	11th to 20th	Day	1 5% 2 5% 5% 4 6% 4 7% 9% 51%	1520
	21st to end	Day	1 6% 2 6% 4 4 5% 3 6% 7% 55%	1520
December	1st to 10th	Day	1 5% 3 7% 6% 5% 5% 5% 7% 8% 48%	1520
	11th to 20th	Day	1 7% 3 7% 5% 5% 5% 5% 9% 12% 42%	1926
	21st to end	Day	1 6% 2 9% 7% 6% 6% 5% 8% 9% 41%	2794
January	1st to 10th	Night	1 4 3 9% 6% 6% 6% 6% 9% 11% 40%	4344
	11th to 20th	Night	1 7% 3 8% 6% 6% 5% 5% 8% 11% 42%	4110
	21st to end	Night	1 8% 4 14% 12% 8% 5% 4 6% 8% 29%	4521
February	1st to 10th	Night	1 5% 2 7% 6% 5% 5% 4 7% 11% 46%	2470
	11th to 20th	Night	2 6% 2 6% 5% 5% 6% 5% 8% 10% 43%	2402
	21st to end	Night	1 5% 3 10% 6% 6% 6% 4 6% 9% 44%	1955
March	1st to 10th	Night	1 5% 2 7% 5% 7% 8% 6% 7% 10% 41%	3430
	11th to 20th	Night	1 4 2 7% 6% 6% 8% 7% 10% 10% 39%	3490
	21st to end	Night	3 10% 4 10% 6% 6% 6% 4 6% 7% 38%	3828
April	1st to 10th	Night	4 7% 3 7% 4 4 6% 4 6% 8% 47%	1971
	11th to 20th	Night	4 8% 2 7% 6% 5% 5% 5% 6% 8% 43%	1809
	21st to end	Night	5% 7% 3 7% 4 4 4 3 6% 8% 49%	1710
May	1st to 10th	Night	4 7% 3 8% 6% 5% 5% 4 6% 8% 45%	2860
	11th to 20th	Night	5% 5% 2 4 3 4 4 3 6% 7% 57%	2712
	21st to end	Night	5% 7% 2 5% 4 4 5% 4 6% 7% 53%	2762
June	1st to 10th	Night	4 4 2 4 3 3 4 3 7% 11% 55%	1520
	11th to 20th	Night	5% 4 1 6% 3 2 4 3 4 8% 59%	1520
	21st to end	Night	2 3 1 2 2 2 3 2 5% 7% 69%	1520
July	1st to 10th	Night	2 2 1 3 2 3 3 3 5% 6% 69%	2540
	11th to 20th	Night	1 2 1 3 3 2 3 3 6% 8% 70%	2722
	21st to end	Night	1 1 1 3 3 3 4 4 6% 9% 65%	3109
August	1st to 10th	Night	2 3 1 4 3 4 4 4 6% 7% 62%	2847
	11th to 20th	Night	3 3 1 5% 4 4 4 4 6% 8% 59%	2811
	21st to end	Night	2 2 1 3 3 2 3 3 4 6% 73%	3268
September	1st to 10th	Night	2 3 1 3 3 3 3 3 5% 6% 68%	1900
	11th to 20th	Night	5% 3 2 3 3 3 3 3 5% 7% 63%	2064
	21st to end	Night	4 4 2 3 3 3 2 2 4 5% 68%	2090
October	1st to 10th	Night	4 4 1 3 2 2 2 2 3 4 73%	3790
	11th to 20th	Night	4 6% 3 6% 3 3 4 3 4 6% 57%	3778
	21st to end	Night	4 7% 2 5% 3 4 3 3 5% 8% 54%	4120
November	1st to 10th	Night	4 6% 2 4 4 4 4 4 6% 9% 54%	2425
	11th to 20th	Night	1 4 2 5% 4 4 4 4 7% 8% 57%	2660
	21st to end	Night	2 5% 2 7% 4 3 4 3 6% 7% 56%	2660
December	1st to 10th	Night	2 5% 2 7% 5% 5% 6% 5% 7% 10% 45%	2660
	11th to 20th	Night	1 7% 2 8% 5% 5% 5% 5% 9% 13% 39%	3271
	21st to end	Night	1 6% 3 9% 6% 7% 8% 6% 10% 9% 33%	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	27% 13% 25% 23% 11% 1	2640
	11th to 20th	Day	27% 11% 24% 21% 15% 2	2860
	21st to end	Day	29% 16% 28% 19% 7% 2	3146
February	1st to 10th	Day	32% 10% 23% 21% 11% 2	1710
	11th to 20th	Day	32% 9% 24% 22% 11% 2	1674
	21st to end	Day	31% 11% 23% 22% 12% 3	1495
March	1st to 10th	Day	25% 12% 25% 23% 14% 1	3444
	11th to 20th	Day	26% 9% 23% 28% 13% 1	3490
	21st to end	Day	42% 15% 19% 20% 4 1	3825
April	1st to 10th	Day	36% 11% 18% 22% 12% 2	2209
	11th to 20th	Day	35% 9% 18% 26% 12%	2319
	21st to end	Day	37% 10% 15% 26% 11%	2470
May	1st to 10th	Day	37% 8% 16% 23% 11% 5%	4110
	11th to 20th	Day	25% 8% 16% 29% 17% 5%	4193
	21st to end	Day	31% 8% 15% 27% 17% 2	4825
June	1st to 10th	Day	28% 10% 17% 26% 17% 3	2660
	11th to 20th	Day	24% 7% 12% 19% 27% 11%	2660
	21st to end	Day	18% 4 8% 17% 35% 17%	2660
July	1st to 10th	Day	14% 3 6% 13% 25% 39%	4361
	11th to 20th	Day	18% 5% 5% 13% 26% 31%	4169
	21st to end	Day	23% 5% 6% 13% 33% 19%	4314
August	1st to 10th	Day	19% 6% 7% 20% 26% 21%	4078
	11th to 20th	Day	21% 5% 8% 21% 29% 16%	4067
	21st to end	Day	16% 4 7% 15% 36% 22%	4397
September	1st to 10th	Day	19% 4 10% 16% 31% 21%	2280
	11th to 20th	Day	21% 5% 10% 23% 28% 13%	2112
	21st to end	Day	21% 4 9% 25% 33% 7%	2090
October	1st to 10th	Day	19% 4 7% 21% 31% 17%	3180
	11th to 20th	Day	24% 5% 10% 30% 22% 9%	3150
	21st to end	Day	24% 5% 15% 37% 17% 2	3438
November	1st to 10th	Day	29% 9% 18% 25% 17% 2	1732
	11th to 20th	Day	25% 10% 24% 24% 15% 2	1520
	21st to end	Day	26% 7% 21% 27% 17% 2	1520
December	1st to 10th	Day	28% 12% 25% 19% 12% 4	1520
	11th to 20th	Day	30% 13% 23% 25% 9% 1	1924
	21st to end	Day	30% 11% 18% 19% 14% 9%	2794
January	1st to 10th	Night	27% 10% 21% 25% 15% 1	4344
	11th to 20th	Night	25% 12% 27% 21% 14% 1	4110
	21st to end	Night	38% 12% 25% 16% 7% 2	4521
February	1st to 10th	Night	27% 12% 24% 26% 10% 1	2470
	11th to 20th	Night	28% 10% 24% 23% 13% 2	2403
	21st to end	Night	31% 10% 21% 23% 13% 3	1955
March	1st to 10th	Night	23% 9% 22% 28% 17% 2	3430
	11th to 20th	Night	23% 12% 21% 27% 16% 1	3490
	21st to end	Night	36% 13% 17% 29% 5% 1	3828
April	1st to 10th	Night	31% 8% 20% 23% 13% 5%	1971
	11th to 20th	Night	34% 8% 17% 26% 15% 1	1809
	21st to end	Night	30% 8% 17% 29% 15%	1710
May	1st to 10th	Night	31% 9% 16% 21% 20% 3	2860
	11th to 20th	Night	21% 7% 15% 38% 12% 6%	2713
	21st to end	Night	26% 7% 15% 33% 16% 3	2762
June	1st to 10th	Night	22% 8% 21% 26% 19% 3	1520
	11th to 20th	Night	22% 6% 12% 21% 26% 13%	1520
	21st to end	Night	14% 4 8% 17% 35% 22%	1520
July	1st to 10th	Night	14% 5% 6% 13% 27% 36%	2500
	11th to 20th	Night	13% 3 4 18% 32% 30%	2673
	21st to end	Night	13% 5% 7% 19% 35% 21%	3011
August	1st to 10th	Night	20% 5% 6% 20% 29% 21%	2838
	11th to 20th	Night	22% 4 8% 20% 29% 16%	2838
	21st to end	Night	14% 4 6% 18% 29% 29%	3268
September	1st to 10th	Night	16% 3 8% 18% 32% 22%	1900
	11th to 20th	Night	21% 5% 10% 23% 28% 14%	2064
	21st to end	Night	19% 4 9% 27% 33% 8%	2090
October	1st to 10th	Night	17% 3 7% 22% 39% 11%	3790
	11th to 20th	Night	28% 4 9% 29% 22% 8%	3778
	21st to end	Night	25% 7% 11% 36% 17% 3	4120
November	1st to 10th	Night	25% 9% 16% 27% 20% 3	2425
	11th to 20th	Night	22% 8% 23% 32% 14% 2	2660
	21st to end	Night	26% 7% 19% 29% 16% 3	2660
December	1st to 10th	Night	28% 12% 24% 22% 11% 4	2660
	11th to 20th	Night	30% 11% 22% 23% 14% 1	3272
	21st to end	Night	33% 11% 17% 20% 10% 9%	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	4 5% 20% 45% 19% 7%	270
	11th to 20th	Day	3 6% 20% 44% 21% 6%	270
	21st to end	Day	4 4 18% 51% 20% 4	297
February	1st to 10th	Day	4 12% 38% 32% 12% 2	270
	11th to 20th	Day	5% 6% 29% 43% 14% 3	270
	21st to end	Day	3 11% 26% 41% 16% 2	302
March	1st to 10th	Day	5% 9% 33% 39% 13% 1	460
	11th to 20th	Day	4 7% 30% 37% 21% 1	460
	21st to end	Day	7% 13% 30% 33% 15% 2	506
April	1st to 10th	Day	8% 13% 32% 26% 14% 7%	460
	11th to 20th	Day	8% 19% 31% 24% 15% 4	452
	21st to end	Day	11% 15% 28% 27% 15% 5%	460
May	1st to 10th	Day	10% 18% 28% 25% 14% 6%	463
	11th to 20th	Day	13% 10% 21% 31% 21% 5%	555
	21st to end	Day	12% 8% 20% 28% 24% 8%	734
June	1st to 10th	Day	6% 5% 22% 32% 27% 7%	680
	11th to 20th	Day	6% 9% 26% 37% 20% 3	680
	21st to end	Day	4 5% 19% 38% 27% 6%	680
July	1st to 10th	Day	3 3 18% 35% 32% 8%	671
	11th to 20th	Day	4 2 20% 37% 30% 7%	560
	21st to end	Day	4 2 18% 36% 29% 11%	531
August	1st to 10th	Day	6% 2 21% 33% 28% 11%	487
	11th to 20th	Day	3 2 19% 31% 34% 12%	477
	21st to end	Day	3 5% 20% 32% 28% 12%	539
September	1st to 10th	Day	3 4 22% 30% 27% 13%	490
	11th to 20th	Day	6% 6% 27% 28% 22% 11%	490
	21st to end	Day	6% 8% 21% 28% 27% 10%	490
October	1st to 10th	Day	7% 4 17% 30% 25% 17%	310
	11th to 20th	Day	5% 8% 17% 33% 26% 11%	300
	21st to end	Day	5% 10% 26% 35% 23% 2	330
November	1st to 10th	Day	6% 11% 23% 34% 21% 5%	282
	11th to 20th	Day	3 8% 20% 46% 19% 3	270
	21st to end	Day	3 7% 18% 49% 19% 5%	270
December	1st to 10th	Day	3 5% 20% 47% 21% 4	270
	11th to 20th	Day	4 3 23% 50% 15% 4	270
	21st to end	Day	6% 7% 24% 42% 14% 7%	297
January	1st to 10th	Night	2 4 28% 47% 16% 3	903
	11th to 20th	Night	3 5% 34% 37% 17% 4	760
	21st to end	Night	4 2 27% 51% 14% 3	836
February	1st to 10th	Night	2 5% 35% 44% 11% 2	760
	11th to 20th	Night	4 3 29% 48% 13% 2	744
	21st to end	Night	2 3 33% 50% 10% 1	628
March	1st to 10th	Night	4 3 32% 48% 12% 2	760
	11th to 20th	Night	3 3 25% 53% 16% 1	760
	21st to end	Night	6% 3 28% 44% 16% 1	836
April	1st to 10th	Night	6% 5% 30% 44% 15%	641
	11th to 20th	Night	7% 6% 33% 43% 11% 1	563
	21st to end	Night	7% 8% 28% 37% 19% 1	570
May	1st to 10th	Night	8% 7% 29% 37% 18% 1	570
	11th to 20th	Night	7% 4 20% 41% 26% 2	561
	21st to end	Night	10% 5% 21% 38% 25% 3	617
June	1st to 10th	Night	6% 4 19% 42% 27% 2	570
	11th to 20th	Night	6% 6% 27% 44% 16% 1	570
	21st to end	Night	3 1 16% 54% 25% 1	570
July	1st to 10th	Night	3 1 12% 48% 35% 2	555
	11th to 20th	Night	2 1 11% 54% 31% 1	552
	21st to end	Night	2 7% 52% 38% 1	624
August	1st to 10th	Night	3 2 9% 52% 33% 1	567
	11th to 20th	Night	3 1 8% 52% 34% 2	564
	21st to end	Night	4 1 11% 45% 36% 4	627
September	1st to 10th	Night	3 2 13% 48% 31% 3	570
	11th to 20th	Night	5% 2 13% 47% 28% 5%	734
	21st to end	Night	5% 2 16% 43% 28% 7%	760
October	1st to 10th	Night	8% 1 21% 41% 25% 4	760
	11th to 20th	Night	6% 4 22% 42% 23% 3	760
	21st to end	Night	5% 4 25% 48% 15% 3	836
November	1st to 10th	Night	4 4 26% 49% 15% 2	764
	11th to 20th	Night	2 7% 31% 47% 11% 1	950
	21st to end	Night	4 5% 29% 47% 13% 3	950
December	1st to 10th	Night	3 5% 30% 48% 13% 1	950
	11th to 20th	Night	3 3 30% 53% 10% 1	950
	21st to end	Night	3 6% 31% 44% 13% 3	1045

Page generated at 2024-11-03 00:11:09. Version ac07

Copyright © 2024 Attilla Danko.