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 2024-11-30.

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	8% 10% 4 9% 6% 5% 6% 5% 7% 7% 34%	105601
	Night	8% 12% 5% 11% 7% 6% 6% 5% 6% 7% 29%	102519
Transparency	Day	48% 3 14% 22% 11% 2	105350
	Night	53% 4 14% 20% 8% 1	102416
Seeing	Day	15% 12% 24% 25% 17% 7%	15938
	Night	15% 11% 23% 31% 17% 2	24122

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	6% 16% 7% 20% 7% 5% 5% 4 6% 5% 17%	2219
	11th to 20th	Day	8% 14% 6% 12% 5% 5% 5% 4 10% 8% 23%	2199
	21st to end	Day	6% 17% 6% 15% 9% 7% 6% 4 6% 6% 18%	2730
February	1st to 10th	Day	8% 18% 7% 13% 7% 6% 5% 4 5% 6% 22%	1581
	11th to 20th	Day	6% 15% 6% 11% 6% 5% 5% 6% 5% 8% 28%	1665
	21st to end	Day	4 14% 5% 12% 9% 7% 7% 6% 6% 7% 23%	1465
March	1st to 10th	Day	3 13% 5% 13% 9% 6% 6% 7% 7% 7% 25%	3138
	11th to 20th	Day	3 10% 4 9% 6% 6% 7% 5% 7% 10% 33%	3428
	21st to end	Day	5% 11% 5% 11% 8% 6% 6% 4 7% 7% 30%	4036
April	1st to 10th	Day	6% 16% 5% 11% 7% 7% 6% 5% 7% 8% 22%	2280
	11th to 20th	Day	7% 15% 5% 11% 8% 7% 6% 5% 6% 6% 24%	2309
	21st to end	Day	8% 12% 4 10% 9% 6% 7% 5% 6% 7% 25%	2650
May	1st to 10th	Day	7% 11% 4 8% 5% 5% 5% 4 6% 8% 36%	4420
	11th to 20th	Day	8% 10% 3 9% 7% 5% 7% 5% 8% 9% 28%	4377
	21st to end	Day	14% 15% 5% 12% 7% 5% 6% 4 6% 6% 20%	5027
June	1st to 10th	Day	14% 11% 5% 10% 6% 5% 6% 4 6% 6% 26%	3040
	11th to 20th	Day	15% 11% 4 10% 7% 6% 7% 5% 7% 7% 21%	3040
	21st to end	Day	10% 8% 3 8% 7% 6% 6% 5% 7% 8% 32%	3040
July	1st to 10th	Day	5% 5% 1 5% 4 3 4 4 6% 6% 57%	4852
	11th to 20th	Day	5% 4 1 4 3 3 3 3 5% 6% 63%	4740
	21st to end	Day	7% 5% 2 5% 4 4 5% 4 6% 8% 48%	4921
August	1st to 10th	Day	4 4 1 4 4 5% 5% 4 6% 9% 53%	4401
	11th to 20th	Day	3 4 2 5% 5% 5% 6% 5% 9% 11% 44%	4250
	21st to end	Day	9% 5% 2 6% 4 5% 4 4 7% 10% 42%	4372
September	1st to 10th	Day	9% 5% 2 7% 4 3 4 3 6% 7% 48%	2280
	11th to 20th	Day	12% 8% 2 8% 5% 5% 5% 3 6% 6% 40%	2280
	21st to end	Day	12% 10% 3 9% 5% 5% 5% 5% 5% 7% 35%	2025
October	1st to 10th	Day	9% 10% 3 8% 7% 5% 6% 4 7% 8% 33%	3180
	11th to 20th	Day	13% 12% 3 8% 5% 5% 5% 4 5% 7% 34%	3115
	21st to end	Day	8% 11% 4 9% 7% 6% 7% 5% 7% 7% 29%	3070
November	1st to 10th	Day	10% 17% 5% 11% 7% 6% 5% 5% 6% 6% 22%	1568
	11th to 20th	Day	8% 13% 5% 11% 7% 6% 6% 5% 7% 7% 25%	1600
	21st to end	Day	8% 16% 5% 11% 8% 7% 6% 5% 7% 6% 18%	1473
December	1st to 10th	Day	8% 15% 5% 13% 10% 7% 7% 5% 7% 6% 18%	1254
	11th to 20th	Day	5% 17% 7% 16% 10% 6% 6% 5% 7% 6% 14%	1442
	21st to end	Day	6% 14% 6% 14% 8% 7% 7% 5% 7% 6% 21%	2134
January	1st to 10th	Night	8% 18% 7% 18% 8% 7% 6% 5% 6% 6% 13%	4726
	11th to 20th	Night	6% 15% 6% 14% 8% 6% 5% 5% 8% 8% 20%	4699
	21st to end	Night	7% 15% 6% 17% 10% 7% 6% 5% 6% 6% 16%	4926
February	1st to 10th	Night	7% 19% 7% 12% 7% 5% 6% 4 6% 5% 22%	2597
	11th to 20th	Night	7% 14% 5% 11% 6% 5% 5% 5% 6% 6% 30%	2402
	21st to end	Night	4 14% 5% 13% 8% 5% 6% 5% 7% 6% 26%	1989
March	1st to 10th	Night	3 13% 6% 11% 6% 6% 6% 5% 9% 9% 26%	3736
	11th to 20th	Night	2 7% 3 8% 5% 6% 7% 6% 8% 11% 38%	3536
	21st to end	Night	5% 14% 4 10% 6% 6% 6% 5% 6% 7% 31%	3616
April	1st to 10th	Night	5% 13% 5% 11% 9% 6% 6% 5% 7% 8% 27%	1900
	11th to 20th	Night	4 12% 4 10% 9% 7% 6% 6% 6% 7% 29%	1819
	21st to end	Night	8% 12% 4 10% 8% 6% 5% 5% 5% 7% 31%	1530
May	1st to 10th	Night	8% 11% 5% 10% 7% 5% 4 4 5% 6% 33%	2540
	11th to 20th	Night	11% 10% 4 9% 6% 6% 6% 4 6% 8% 28%	2516
	21st to end	Night	20% 15% 4 11% 6% 5% 4 3 5% 6% 20%	2525
June	1st to 10th	Night	15% 9% 4 9% 6% 6% 6% 5% 7% 6% 28%	1140
	11th to 20th	Night	17% 11% 5% 12% 6% 5% 6% 5% 7% 8% 19%	1140
	21st to end	Night	9% 9% 3 10% 6% 5% 6% 4 6% 8% 34%	1140
July	1st to 10th	Night	7% 6% 2 6% 4 4 4 4 5% 6% 52%	2090
	11th to 20th	Night	4 3 2 6% 4 3 4 4 6% 8% 55%	2220
	21st to end	Night	10% 7% 4 7% 5% 5% 5% 4 6% 8% 39%	2630
August	1st to 10th	Night	5% 4 2 7% 5% 5% 5% 4 6% 7% 49%	2529
	11th to 20th	Night	7% 6% 2 8% 5% 6% 6% 5% 8% 10% 38%	2579
	21st to end	Night	11% 6% 3 8% 5% 5% 5% 4 6% 9% 38%	3299
September	1st to 10th	Night	7% 7% 2 5% 4 5% 5% 3 6% 7% 49%	1900
	11th to 20th	Night	10% 7% 3 6% 4 3 4 4 7% 9% 42%	1900
	21st to end	Night	12% 10% 2 6% 4 4 5% 5% 6% 7% 39%	2152
October	1st to 10th	Night	11% 10% 4 10% 7% 6% 5% 4 5% 7% 32%	3800
	11th to 20th	Night	10% 9% 3 8% 5% 5% 6% 5% 7% 9% 33%	3820
	21st to end	Night	9% 10% 4 9% 6% 6% 6% 5% 7% 7% 31%	4484
November	1st to 10th	Night	11% 15% 5% 10% 6% 6% 6% 5% 7% 7% 23%	2730
	11th to 20th	Night	7% 13% 4 10% 8% 7% 5% 6% 7% 7% 24%	2800
	21st to end	Night	8% 17% 6% 12% 7% 6% 6% 5% 7% 6% 19%	2900
December	1st to 10th	Night	7% 15% 5% 13% 8% 6% 6% 5% 6% 7% 21%	2921
	11th to 20th	Night	8% 19% 7% 16% 8% 7% 5% 4 5% 6% 14%	3750
	21st to end	Night	5% 16% 6% 13% 8% 7% 7% 5% 6% 8% 19%	5538

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	66% 3 12% 16% 2	2219
	11th to 20th	Day	55% 4 19% 10% 4 8%	2220
	21st to end	Day	65% 6% 15% 12% 3	2730
February	1st to 10th	Day	64% 5% 10% 12% 9% 1	1581
	11th to 20th	Day	55% 4 16% 15% 10%	1674
	21st to end	Day	59% 3 13% 18% 7% 1	1465
March	1st to 10th	Day	57% 2 8% 21% 12%	3138
	11th to 20th	Day	46% 2 17% 27% 7%	3428
	21st to end	Day	53% 2 12% 22% 10%	4036
April	1st to 10th	Day	59% 4 13% 17% 8% 1	2280
	11th to 20th	Day	58% 3 9% 18% 11% 1	2309
	21st to end	Day	57% 3 10% 19% 12%	2650
May	1st to 10th	Day	46% 2 9% 26% 16% 1	4420
	11th to 20th	Day	51% 2 10% 27% 10%	4380
	21st to end	Day	65% 1 9% 17% 6% 1	5028
June	1st to 10th	Day	56% 3 9% 17% 12% 3	3040
	11th to 20th	Day	59% 3 12% 19% 7%	3040
	21st to end	Day	47% 3 15% 22% 11% 2	3040
July	1st to 10th	Day	27% 3 9% 23% 25% 13%	4778
	11th to 20th	Day	23% 2 10% 32% 27% 7%	4659
	21st to end	Day	32% 3 16% 27% 15% 6%	4765
August	1st to 10th	Day	26% 4 12% 36% 22% 1	4384
	11th to 20th	Day	29% 6% 24% 30% 9% 1	4292
	21st to end	Day	36% 3 27% 25% 7% 1	4371
September	1st to 10th	Day	36% 3 17% 30% 11% 3	2280
	11th to 20th	Day	45% 3 12% 28% 11% 2	2280
	21st to end	Day	49% 3 16% 19% 11% 2	2025
October	1st to 10th	Day	47% 4 21% 21% 7%	3180
	11th to 20th	Day	50% 3 16% 25% 5%	3115
	21st to end	Day	51% 6% 19% 20% 3	3070
November	1st to 10th	Day	60% 4 11% 18% 7%	1568
	11th to 20th	Day	57% 5% 16% 17% 5% 1	1600
	21st to end	Day	62% 5% 16% 11% 6%	1473
December	1st to 10th	Day	66% 6% 11% 14% 3	1254
	11th to 20th	Day	68% 5% 14% 9% 4	1444
	21st to end	Day	62% 5% 15% 15% 4	2134
January	1st to 10th	Night	72% 3 11% 12% 3	4726
	11th to 20th	Night	59% 4 15% 11% 6% 6%	4740
	21st to end	Night	66% 6% 14% 11% 3	4926
February	1st to 10th	Night	64% 3 11% 14% 7% 1	2597
	11th to 20th	Night	54% 3 13% 21% 8% 1	2404
	21st to end	Night	56% 2 14% 19% 7% 1	1989
March	1st to 10th	Night	51% 3 9% 23% 13%	3736
	11th to 20th	Night	40% 2 19% 31% 8% 1	3537
	21st to end	Night	53% 2 14% 19% 12%	3616
April	1st to 10th	Night	53% 5% 14% 21% 8%	1900
	11th to 20th	Night	52% 3 9% 24% 12%	1819
	21st to end	Night	54% 3 9% 22% 12% 1	1530
May	1st to 10th	Night	53% 2 7% 24% 12% 2	2540
	11th to 20th	Night	54% 1 10% 26% 8%	2516
	21st to end	Night	67% 2 10% 16% 5%	2525
June	1st to 10th	Night	53% 3 9% 21% 10% 4	1140
	11th to 20th	Night	61% 3 13% 15% 7%	1140
	21st to end	Night	46% 3 14% 24% 12% 2	1140
July	1st to 10th	Night	32% 3 8% 18% 25% 13%	2055
	11th to 20th	Night	25% 3 9% 30% 29% 4	2178
	21st to end	Night	41% 4 11% 22% 14% 9%	2547
August	1st to 10th	Night	32% 4 9% 32% 22% 1	2521
	11th to 20th	Night	38% 5% 19% 27% 9% 2	2603
	21st to end	Night	42% 4 25% 22% 7% 1	3299
September	1st to 10th	Night	35% 3 14% 32% 15% 2	1900
	11th to 20th	Night	39% 3 15% 27% 12% 4	1900
	21st to end	Night	44% 4 16% 24% 11% 1	2152
October	1st to 10th	Night	52% 4 18% 20% 6%	3800
	11th to 20th	Night	47% 4 16% 26% 6%	3820
	21st to end	Night	49% 6% 18% 23% 4	4484
November	1st to 10th	Night	59% 5% 15% 15% 5% 1	2730
	11th to 20th	Night	56% 6% 15% 15% 7% 1	2800
	21st to end	Night	63% 4 14% 13% 5% 1	2900
December	1st to 10th	Night	61% 6% 14% 14% 4	2921
	11th to 20th	Night	71% 5% 10% 11% 3	3747
	21st to end	Night	63% 4 15% 15% 4	5538

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	15% 12% 30% 27% 9% 6%	180
	11th to 20th	Day	12% 15% 27% 25% 18% 2	180
	21st to end	Day	16% 17% 25% 27% 11% 3	198
February	1st to 10th	Day	17% 22% 29% 24% 6% 3	241
	11th to 20th	Day	14% 13% 28% 27% 15% 2	365
	21st to end	Day	11% 18% 31% 22% 13% 5%	332
March	1st to 10th	Day	14% 17% 30% 22% 14% 4	460
	11th to 20th	Day	13% 21% 29% 19% 12% 6%	460
	21st to end	Day	17% 18% 25% 24% 11% 6%	506
April	1st to 10th	Day	15% 22% 27% 23% 10% 3	460
	11th to 20th	Day	14% 21% 26% 22% 11% 6%	452
	21st to end	Day	15% 17% 23% 27% 11% 7%	460
May	1st to 10th	Day	13% 18% 25% 23% 15% 5%	463
	11th to 20th	Day	15% 8% 22% 30% 16% 9%	488
	21st to end	Day	18% 9% 21% 29% 16% 7%	652
June	1st to 10th	Day	18% 11% 31% 22% 14% 3	870
	11th to 20th	Day	20% 11% 22% 27% 17% 3	870
	21st to end	Day	14% 8% 23% 27% 21% 8%	870
July	1st to 10th	Day	11% 7% 25% 29% 20% 7%	744
	11th to 20th	Day	10% 7% 22% 30% 24% 7%	668
	21st to end	Day	8% 5% 18% 32% 26% 11%	610
August	1st to 10th	Day	8% 4 15% 31% 28% 14%	487
	11th to 20th	Day	7% 6% 20% 28% 25% 14%	477
	21st to end	Day	12% 9% 22% 25% 20% 11%	539
September	1st to 10th	Day	15% 8% 23% 27% 18% 9%	490
	11th to 20th	Day	16% 10% 20% 22% 23% 10%	490
	21st to end	Day	20% 12% 28% 22% 13% 4	490
October	1st to 10th	Day	21% 12% 21% 22% 14% 9%	490
	11th to 20th	Day	21% 16% 23% 19% 14% 6%	469
	21st to end	Day	21% 16% 27% 21% 11% 3	320
November	1st to 10th	Day	23% 18% 30% 18% 10% 3	200
	11th to 20th	Day	20% 14% 28% 21% 12% 6%	200
	21st to end	Day	15% 15% 28% 20% 18% 6%	199
December	1st to 10th	Day	13% 8% 22% 31% 17% 11%	180
	11th to 20th	Day	12% 12% 31% 24% 14% 7%	180
	21st to end	Day	15% 13% 29% 29% 10% 5%	198
January	1st to 10th	Night	21% 11% 28% 28% 10% 2	850
	11th to 20th	Night	16% 10% 25% 34% 14% 2	850
	21st to end	Night	15% 9% 27% 32% 15% 2	854
February	1st to 10th	Night	16% 12% 28% 31% 11% 2	760
	11th to 20th	Night	15% 8% 24% 39% 12% 2	744
	21st to end	Night	13% 11% 23% 34% 18% 1	628
March	1st to 10th	Night	12% 15% 26% 30% 16% 2	760
	11th to 20th	Night	10% 17% 27% 29% 15% 2	760
	21st to end	Night	9% 17% 22% 29% 18% 4	836
April	1st to 10th	Night	11% 12% 26% 30% 17% 3	760
	11th to 20th	Night	12% 12% 26% 31% 17% 2	691
	21st to end	Night	12% 12% 32% 28% 13% 3	390
May	1st to 10th	Night	15% 10% 27% 27% 19% 1	380
	11th to 20th	Night	15% 6% 26% 34% 17% 2	374
	21st to end	Night	21% 7% 20% 28% 21% 2	411
June	1st to 10th	Night	17% 11% 25% 32% 15% 1	380
	11th to 20th	Night	20% 10% 22% 29% 17% 2	380
	21st to end	Night	10% 7% 23% 33% 23% 4	380
July	1st to 10th	Night	15% 5% 19% 31% 28% 3	370
	11th to 20th	Night	11% 5% 19% 38% 25% 3	368
	21st to end	Night	10% 3 19% 32% 30% 5%	416
August	1st to 10th	Night	6% 4 13% 33% 38% 6%	378
	11th to 20th	Night	9% 3 14% 33% 37% 5%	419
	21st to end	Night	12% 8% 17% 32% 27% 4	715
September	1st to 10th	Night	13% 6% 18% 36% 24% 3	760
	11th to 20th	Night	13% 5% 17% 28% 30% 7%	760
	21st to end	Night	19% 9% 23% 30% 16% 3	760
October	1st to 10th	Night	18% 12% 19% 29% 19% 3	760
	11th to 20th	Night	18% 11% 22% 30% 17% 2	760
	21st to end	Night	20% 12% 28% 27% 12% 2	836
November	1st to 10th	Night	23% 16% 21% 30% 9% 2	780
	11th to 20th	Night	20% 16% 23% 28% 12% 2	800
	21st to end	Night	19% 13% 26% 28% 12% 2	900
December	1st to 10th	Night	15% 10% 23% 34% 16% 2	983
	11th to 20th	Night	18% 12% 25% 34% 10% 1	1040
	21st to end	Night	16% 13% 27% 34% 10% 1	1129

Page generated at 2024-11-27 14:30:48. Version ac07

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