Green Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Green Lake clear sky chart from 2005-11-06 to 2026-02-16.

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	7% 10% 4 9% 6% 6% 6% 5% 7% 8% 33%	134028
	Night	7% 12% 5% 11% 7% 6% 6% 5% 7% 8% 29%	135453
Transparency	Day	48% 4 14% 22% 10% 2	133736
	Night	52% 4 14% 20% 8% 1	135323
Seeing	Day	15% 13% 25% 25% 16% 7%	17429
	Night	15% 11% 24% 31% 17% 2	25797

By Month

Percentage Cloud Cover NW (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 17% 8% 20% 8% 6% 6% 4 6% 6% 14%	4125
	11th to 20th	Day	5% 9% 4 10% 6% 6% 6% 6% 10% 9% 31%	4119
	21st to end	Day	4 13% 5% 13% 8% 6% 6% 4 6% 7% 26%	5066
February	1st to 10th	Day	7% 17% 6% 13% 7% 6% 5% 4 5% 6% 22%	1748
	11th to 20th	Day	6% 15% 5% 11% 6% 5% 5% 5% 5% 8% 28%	1801
	21st to end	Day	4 14% 5% 12% 9% 7% 7% 6% 6% 7% 23%	1540
March	1st to 10th	Day	3 13% 6% 11% 9% 6% 7% 6% 7% 7% 24%	4518
	11th to 20th	Day	2 10% 4 10% 7% 7% 8% 6% 8% 10% 29%	4912
	21st to end	Day	6% 12% 5% 12% 8% 7% 7% 5% 7% 7% 25%	5788
April	1st to 10th	Day	5% 15% 5% 11% 7% 7% 7% 5% 7% 8% 22%	2400
	11th to 20th	Day	7% 15% 5% 11% 7% 7% 7% 5% 6% 7% 24%	2432
	21st to end	Day	7% 12% 4 10% 8% 6% 7% 5% 6% 7% 27%	2790
May	1st to 10th	Day	7% 10% 4 8% 5% 5% 5% 4 6% 8% 39%	6320
	11th to 20th	Day	8% 10% 4 11% 8% 7% 8% 5% 8% 9% 23%	6277
	21st to end	Day	12% 12% 4 10% 6% 5% 5% 5% 7% 9% 26%	7215
June	1st to 10th	Day	14% 10% 4 10% 6% 5% 5% 4 6% 6% 28%	3200
	11th to 20th	Day	15% 10% 4 10% 7% 6% 7% 6% 7% 7% 21%	3200
	21st to end	Day	10% 8% 3 8% 7% 6% 6% 5% 7% 8% 32%	3200
July	1st to 10th	Day	6% 6% 2 7% 4 4 4 4 7% 7% 49%	6948
	11th to 20th	Day	6% 4 2 5% 4 4 4 3 5% 7% 55%	6780
	21st to end	Day	6% 5% 2 5% 4 5% 5% 4 7% 8% 49%	7061
August	1st to 10th	Day	4 4 1 4 4 5% 5% 4 7% 9% 53%	4541
	11th to 20th	Day	3 4 2 5% 5% 5% 6% 5% 9% 11% 44%	4387
	21st to end	Day	9% 5% 2 6% 4 5% 4 4 7% 9% 44%	4510
September	1st to 10th	Day	9% 6% 2 6% 4 3 5% 3 6% 7% 49%	2400
	11th to 20th	Day	11% 8% 2 7% 4 4 5% 3 6% 6% 42%	2400
	21st to end	Day	11% 10% 4 9% 5% 5% 5% 5% 5% 7% 34%	2131
October	1st to 10th	Day	10% 10% 3 8% 6% 5% 6% 4 7% 8% 33%	3280
	11th to 20th	Day	13% 12% 3 8% 5% 5% 5% 4 5% 7% 34%	3214
	21st to end	Day	8% 11% 4 9% 7% 6% 7% 5% 7% 7% 29%	3168
November	1st to 10th	Day	10% 16% 5% 11% 7% 6% 5% 5% 6% 6% 22%	1648
	11th to 20th	Day	9% 13% 5% 11% 7% 6% 6% 5% 7% 7% 24%	1680
	21st to end	Day	8% 16% 5% 12% 8% 7% 6% 6% 7% 6% 18%	1551
December	1st to 10th	Day	7% 12% 4 11% 9% 7% 8% 5% 7% 6% 22%	2224
	11th to 20th	Day	5% 15% 6% 16% 10% 6% 7% 5% 7% 6% 15%	2322
	21st to end	Day	4 14% 6% 15% 9% 7% 7% 5% 7% 6% 20%	3132
January	1st to 10th	Night	6% 18% 7% 18% 9% 8% 7% 5% 6% 5% 11%	8770
	11th to 20th	Night	3 10% 4 11% 7% 6% 6% 5% 10% 9% 28%	8779
	21st to end	Night	5% 13% 6% 13% 8% 6% 5% 4 6% 7% 27%	9100
February	1st to 10th	Night	7% 18% 7% 13% 7% 5% 6% 4 5% 5% 23%	2869
	11th to 20th	Night	7% 14% 5% 11% 5% 5% 5% 5% 6% 6% 30%	2597
	21st to end	Night	4 14% 5% 13% 8% 5% 6% 5% 7% 6% 26%	2090
March	1st to 10th	Night	2 12% 6% 11% 6% 6% 7% 6% 9% 9% 25%	5376
	11th to 20th	Night	2 8% 4 11% 7% 7% 7% 6% 8% 9% 32%	5072
	21st to end	Night	6% 12% 4 11% 7% 7% 7% 5% 7% 7% 26%	5186
April	1st to 10th	Night	5% 12% 5% 11% 9% 6% 6% 5% 7% 8% 26%	2000
	11th to 20th	Night	4 13% 4 10% 8% 7% 6% 6% 6% 7% 30%	1916
	21st to end	Night	7% 12% 4 10% 8% 6% 5% 5% 5% 7% 32%	1610
May	1st to 10th	Night	9% 12% 4 9% 5% 5% 5% 4 5% 7% 35%	3640
	11th to 20th	Night	11% 11% 5% 9% 6% 5% 6% 4 6% 8% 29%	3616
	21st to end	Night	16% 12% 4 10% 6% 5% 5% 4 6% 6% 26%	3637
June	1st to 10th	Night	14% 9% 4 8% 6% 6% 6% 5% 7% 6% 30%	1200
	11th to 20th	Night	16% 11% 5% 12% 7% 5% 5% 5% 7% 8% 19%	1200
	21st to end	Night	9% 10% 4 10% 5% 5% 6% 4 6% 8% 33%	1200
July	1st to 10th	Night	7% 6% 2 6% 4 4 4 4 5% 7% 49%	2994
	11th to 20th	Night	6% 4 2 7% 4 3 4 4 6% 8% 51%	3180
	21st to end	Night	8% 6% 3 7% 5% 5% 5% 4 6% 9% 42%	3781
August	1st to 10th	Night	5% 4 2 7% 5% 5% 5% 4 6% 7% 48%	2609
	11th to 20th	Night	7% 6% 2 8% 5% 6% 6% 5% 8% 10% 38%	2661
	21st to end	Night	11% 6% 3 8% 4 5% 5% 4 6% 9% 40%	3403
September	1st to 10th	Night	7% 7% 2 5% 4 5% 5% 3 6% 7% 50%	2000
	11th to 20th	Night	10% 7% 3 6% 4 4 4 4 7% 9% 44%	2000
	21st to end	Night	12% 10% 3 7% 4 4 4 5% 6% 7% 38%	2265
October	1st to 10th	Night	11% 10% 4 10% 7% 6% 5% 4 5% 7% 32%	3920
	11th to 20th	Night	10% 9% 3 8% 5% 5% 6% 5% 7% 9% 34%	3941
	21st to end	Night	9% 10% 4 9% 6% 6% 6% 5% 7% 7% 31%	4628
November	1st to 10th	Night	11% 15% 5% 10% 6% 6% 6% 5% 7% 7% 23%	2870
	11th to 20th	Night	7% 14% 4 10% 8% 7% 6% 6% 7% 7% 24%	2940
	21st to end	Night	8% 17% 6% 12% 8% 6% 7% 5% 7% 6% 19%	3045
December	1st to 10th	Night	5% 11% 5% 11% 8% 6% 7% 6% 9% 9% 22%	5171
	11th to 20th	Night	7% 18% 7% 16% 8% 7% 6% 4 5% 6% 15%	6090
	21st to end	Night	4 15% 6% 13% 8% 7% 7% 5% 6% 7% 21%	8097

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	69% 4 12% 12% 3	4125
	11th to 20th	Day	46% 6% 22% 17% 5% 4	4140
	21st to end	Day	55% 6% 16% 19% 3	5067
February	1st to 10th	Day	63% 5% 10% 12% 10% 1	1748
	11th to 20th	Day	55% 4 15% 16% 10%	1810
	21st to end	Day	58% 3 13% 18% 7% 1	1540
March	1st to 10th	Day	57% 3 11% 21% 9%	4518
	11th to 20th	Day	48% 3 15% 24% 11%	4912
	21st to end	Day	57% 4 11% 20% 8%	5788
April	1st to 10th	Day	57% 4 13% 18% 8% 1	2400
	11th to 20th	Day	57% 3 9% 19% 11% 1	2432
	21st to end	Day	55% 3 10% 20% 12%	2790
May	1st to 10th	Day	43% 2 8% 28% 17% 1	6320
	11th to 20th	Day	55% 3 10% 24% 8%	6280
	21st to end	Day	55% 3 14% 22% 5% 1	7216
June	1st to 10th	Day	54% 3 9% 17% 14% 3	3200
	11th to 20th	Day	59% 3 12% 19% 8%	3200
	21st to end	Day	47% 4 15% 22% 10% 2	3200
July	1st to 10th	Day	32% 4 14% 21% 20% 9%	6874
	11th to 20th	Day	29% 4 14% 28% 20% 5%	6699
	21st to end	Day	30% 5% 17% 29% 15% 4	6863
August	1st to 10th	Day	27% 4 12% 35% 21% 1	4524
	11th to 20th	Day	29% 6% 23% 30% 9% 1	4429
	21st to end	Day	35% 3 26% 25% 8% 2	4509
September	1st to 10th	Day	35% 3 17% 30% 12% 3	2400
	11th to 20th	Day	43% 3 12% 28% 11% 2	2400
	21st to end	Day	49% 3 17% 19% 10% 2	2131
October	1st to 10th	Day	48% 4 21% 20% 7%	3280
	11th to 20th	Day	50% 3 16% 25% 6%	3214
	21st to end	Day	52% 6% 18% 21% 3	3168
November	1st to 10th	Day	60% 4 11% 18% 7%	1648
	11th to 20th	Day	57% 5% 16% 17% 5% 1	1680
	21st to end	Day	62% 5% 16% 11% 6%	1551
December	1st to 10th	Day	60% 5% 20% 12% 2	2224
	11th to 20th	Day	66% 5% 15% 9% 5%	2324
	21st to end	Day	63% 5% 13% 15% 3	3132
January	1st to 10th	Night	73% 5% 10% 9% 4	8770
	11th to 20th	Night	48% 6% 18% 18% 6% 3	8820
	21st to end	Night	56% 6% 15% 20% 3	9100
February	1st to 10th	Night	63% 3 11% 14% 8% 1	2869
	11th to 20th	Night	53% 3 13% 21% 8% 1	2599
	21st to end	Night	56% 3 15% 19% 7%	2090
March	1st to 10th	Night	50% 5% 12% 22% 11%	5376
	11th to 20th	Night	46% 3 16% 25% 10%	5073
	21st to end	Night	55% 4 13% 18% 10%	5186
April	1st to 10th	Night	53% 5% 14% 21% 8%	2000
	11th to 20th	Night	52% 3 9% 24% 12%	1916
	21st to end	Night	52% 3 9% 23% 12% 1	1610
May	1st to 10th	Night	50% 2 6% 26% 14% 2	3637
	11th to 20th	Night	53% 2 11% 27% 6%	3616
	21st to end	Night	58% 3 13% 21% 5%	3637
June	1st to 10th	Night	52% 3 9% 21% 11% 4	1200
	11th to 20th	Night	61% 4 13% 15% 8%	1200
	21st to end	Night	47% 3 14% 23% 11% 2	1200
July	1st to 10th	Night	34% 4 13% 22% 18% 9%	2959
	11th to 20th	Night	29% 4 12% 30% 22% 3	3138
	21st to end	Night	37% 5% 14% 24% 14% 6%	3674
August	1st to 10th	Night	33% 4 9% 31% 21% 1	2601
	11th to 20th	Night	38% 5% 19% 27% 9% 2	2685
	21st to end	Night	40% 4 25% 22% 8% 2	3403
September	1st to 10th	Night	35% 3 14% 31% 16% 2	2000
	11th to 20th	Night	38% 3 15% 29% 12% 4	2000
	21st to end	Night	44% 4 17% 23% 10% 1	2265
October	1st to 10th	Night	52% 4 18% 20% 6%	3920
	11th to 20th	Night	46% 4 16% 26% 7%	3941
	21st to end	Night	49% 6% 18% 23% 4	4628
November	1st to 10th	Night	58% 5% 15% 16% 6% 1	2870
	11th to 20th	Night	56% 6% 15% 15% 7% 1	2940
	21st to end	Night	62% 5% 15% 13% 5%	3045
December	1st to 10th	Night	54% 8% 22% 13% 3	5171
	11th to 20th	Night	69% 5% 12% 10% 3	6087
	21st to end	Night	60% 5% 15% 16% 3	8097

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	14% 14% 32% 27% 8% 5%	220
	11th to 20th	Day	13% 15% 27% 25% 18% 2	220
	21st to end	Day	15% 18% 25% 26% 13% 2	242
February	1st to 10th	Day	16% 20% 28% 23% 8% 5%	288
	11th to 20th	Day	13% 14% 29% 28% 14% 2	411
	21st to end	Day	12% 19% 32% 21% 13% 4	359
March	1st to 10th	Day	14% 16% 30% 23% 13% 4	500
	11th to 20th	Day	13% 20% 29% 20% 13% 6%	500
	21st to end	Day	18% 18% 24% 23% 10% 6%	550
April	1st to 10th	Day	15% 22% 27% 24% 9% 3	500
	11th to 20th	Day	15% 21% 26% 22% 11% 5%	492
	21st to end	Day	14% 17% 23% 28% 11% 7%	500
May	1st to 10th	Day	13% 19% 26% 23% 15% 5%	503
	11th to 20th	Day	16% 9% 21% 30% 17% 8%	528
	21st to end	Day	18% 10% 21% 28% 16% 6%	703
June	1st to 10th	Day	17% 11% 31% 23% 15% 3	930
	11th to 20th	Day	19% 10% 22% 28% 18% 3	930
	21st to end	Day	13% 8% 23% 27% 21% 8%	930
July	1st to 10th	Day	11% 9% 25% 29% 20% 7%	798
	11th to 20th	Day	9% 8% 23% 30% 23% 7%	718
	21st to end	Day	8% 5% 18% 32% 26% 11%	658
August	1st to 10th	Day	8% 5% 15% 31% 28% 14%	527
	11th to 20th	Day	8% 7% 22% 26% 24% 13%	517
	21st to end	Day	11% 9% 20% 25% 21% 14%	583
September	1st to 10th	Day	14% 8% 21% 26% 19% 12%	530
	11th to 20th	Day	15% 9% 20% 23% 23% 10%	530
	21st to end	Day	21% 13% 28% 21% 12% 4	530
October	1st to 10th	Day	21% 13% 21% 22% 14% 9%	530
	11th to 20th	Day	21% 17% 23% 18% 15% 6%	508
	21st to end	Day	22% 16% 27% 21% 11% 3	352
November	1st to 10th	Day	23% 20% 30% 16% 9% 2	220
	11th to 20th	Day	20% 14% 30% 21% 11% 5%	220
	21st to end	Day	15% 15% 29% 20% 16% 5%	220
December	1st to 10th	Day	15% 9% 25% 27% 16% 9%	220
	11th to 20th	Day	15% 14% 30% 25% 11% 6%	220
	21st to end	Day	17% 15% 29% 26% 9% 4	242
January	1st to 10th	Night	20% 12% 28% 29% 10% 1	950
	11th to 20th	Night	15% 11% 24% 35% 13% 2	950
	21st to end	Night	14% 9% 27% 33% 15% 2	945
February	1st to 10th	Night	15% 13% 29% 30% 11% 3	840
	11th to 20th	Night	15% 9% 24% 40% 11% 2	804
	21st to end	Night	13% 12% 23% 33% 17% 1	660
March	1st to 10th	Night	12% 16% 24% 30% 16% 2	800
	11th to 20th	Night	10% 17% 28% 29% 15% 2	800
	21st to end	Night	10% 18% 22% 29% 18% 4	880
April	1st to 10th	Night	11% 12% 26% 31% 17% 3	800
	11th to 20th	Night	12% 12% 26% 30% 17% 2	728
	21st to end	Night	12% 12% 31% 29% 14% 3	410
May	1st to 10th	Night	16% 11% 26% 28% 19% 1	400
	11th to 20th	Night	15% 7% 26% 34% 17% 2	394
	21st to end	Night	21% 7% 21% 28% 21% 2	433
June	1st to 10th	Night	16% 11% 25% 32% 15% 1	400
	11th to 20th	Night	20% 10% 22% 30% 17% 2	400
	21st to end	Night	10% 8% 23% 34% 22% 4	400
July	1st to 10th	Night	14% 5% 20% 31% 28% 3	390
	11th to 20th	Night	10% 5% 19% 38% 25% 3	388
	21st to end	Night	10% 3 19% 32% 31% 5%	438
August	1st to 10th	Night	6% 5% 13% 33% 37% 6%	398
	11th to 20th	Night	9% 3 15% 33% 35% 5%	441
	21st to end	Night	11% 8% 16% 32% 28% 5%	753
September	1st to 10th	Night	12% 6% 17% 36% 25% 5%	800
	11th to 20th	Night	13% 5% 18% 28% 30% 7%	800
	21st to end	Night	19% 10% 24% 29% 16% 3	800
October	1st to 10th	Night	18% 12% 20% 30% 19% 3	800
	11th to 20th	Night	18% 11% 22% 30% 17% 2	800
	21st to end	Night	20% 13% 28% 27% 11% 2	880
November	1st to 10th	Night	23% 16% 22% 29% 9% 1	820
	11th to 20th	Night	20% 16% 23% 28% 11% 2	840
	21st to end	Night	18% 13% 27% 28% 11% 2	945
December	1st to 10th	Night	14% 11% 24% 33% 15% 2	1091
	11th to 20th	Night	18% 13% 24% 33% 10% 1	1160
	21st to end	Night	17% 14% 28% 32% 9% 1	1259

Page generated at 2026-02-12 22:42:17. Version ac07

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