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 2024-01-15.

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	9% 10% 4 8% 7% 4 6% 6% 6% 7% 31%	74536
	Night	8% 12% 5% 9% 8% 4 6% 6% 6% 7% 28%	75222
Transparency	Day	51% 3 14% 21% 10% 1	74222
	Night	54% 4 14% 20% 8% 1	75054
Seeing	Day	15% 12% 24% 25% 17% 7%	14702
	Night	15% 11% 23% 31% 17% 2	23076

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	8% 14% 6% 14% 9% 4 7% 7% 7% 7% 16%	1329
	11th to 20th	Day	8% 10% 7% 13% 9% 6% 6% 6% 7% 7% 22%	1288
	21st to end	Day	6% 14% 7% 12% 9% 5% 6% 5% 7% 6% 22%	1548
February	1st to 10th	Day	9% 16% 7% 11% 9% 4 5% 5% 5% 6% 23%	1498
	11th to 20th	Day	7% 14% 6% 10% 7% 4 5% 7% 5% 8% 26%	1575
	21st to end	Day	4 13% 6% 10% 10% 5% 7% 7% 6% 6% 24%	1381
March	1st to 10th	Day	5% 13% 6% 10% 10% 5% 7% 6% 6% 7% 25%	1800
	11th to 20th	Day	4 12% 6% 10% 8% 5% 9% 6% 7% 8% 26%	1944
	21st to end	Day	6% 12% 6% 11% 9% 4 6% 6% 7% 7% 25%	2299
April	1st to 10th	Day	6% 15% 6% 9% 9% 5% 7% 6% 7% 8% 22%	2160
	11th to 20th	Day	7% 14% 6% 11% 9% 6% 7% 6% 6% 7% 23%	2185
	21st to end	Day	8% 11% 4 9% 10% 5% 7% 7% 6% 7% 26%	2510
May	1st to 10th	Day	10% 12% 5% 9% 7% 5% 5% 5% 5% 8% 29%	2520
	11th to 20th	Day	9% 9% 4 7% 7% 4 6% 6% 7% 8% 31%	2477
	21st to end	Day	14% 9% 4 9% 8% 4 6% 6% 6% 8% 27%	2839
June	1st to 10th	Day	15% 10% 5% 9% 7% 4 6% 5% 6% 7% 26%	2880
	11th to 20th	Day	16% 10% 5% 9% 8% 4 7% 7% 7% 7% 21%	2880
	21st to end	Day	10% 7% 3 7% 7% 4 7% 7% 7% 8% 33%	2880
July	1st to 10th	Day	8% 7% 2 6% 6% 3 5% 6% 8% 8% 40%	2770
	11th to 20th	Day	8% 5% 3 6% 6% 4 5% 6% 7% 7% 44%	2700
	21st to end	Day	7% 4 2 4 5% 3 5% 6% 6% 7% 51%	2816
August	1st to 10th	Day	7% 5% 2 5% 5% 4 5% 6% 6% 9% 48%	2507
	11th to 20th	Day	5% 5% 2 4 5% 3 5% 5% 7% 8% 52%	2434
	21st to end	Day	10% 6% 2 6% 6% 4 6% 6% 6% 9% 38%	2490
September	1st to 10th	Day	10% 6% 3 6% 5% 3 4 4 6% 7% 47%	2160
	11th to 20th	Day	12% 7% 2 6% 6% 4 5% 5% 6% 7% 41%	2160
	21st to end	Day	11% 9% 4 8% 6% 4 5% 5% 5% 7% 36%	1919
October	1st to 10th	Day	12% 9% 3 7% 7% 3 5% 4 6% 7% 37%	1800
	11th to 20th	Day	11% 11% 4 6% 6% 4 5% 5% 5% 7% 35%	1781
	21st to end	Day	12% 12% 5% 7% 6% 3 5% 5% 7% 7% 30%	1764
November	1st to 10th	Day	11% 15% 5% 10% 7% 4 5% 7% 6% 6% 23%	1488
	11th to 20th	Day	9% 12% 5% 9% 8% 5% 7% 6% 6% 8% 25%	1520
	21st to end	Day	9% 15% 6% 10% 9% 5% 6% 7% 8% 7% 19%	1404
December	1st to 10th	Day	9% 13% 6% 11% 11% 5% 8% 7% 7% 6% 18%	1254
	11th to 20th	Day	5% 16% 7% 15% 12% 4 7% 6% 7% 6% 14%	1442
	21st to end	Day	6% 13% 7% 12% 10% 5% 7% 7% 7% 6% 21%	2134
January	1st to 10th	Night	10% 16% 7% 12% 9% 5% 7% 6% 6% 7% 15%	2836
	11th to 20th	Night	7% 14% 6% 13% 10% 5% 6% 6% 7% 8% 17%	2760
	21st to end	Night	7% 12% 6% 11% 10% 5% 7% 7% 7% 7% 22%	2808
February	1st to 10th	Night	8% 18% 7% 10% 8% 4 5% 5% 6% 6% 22%	2460
	11th to 20th	Night	7% 13% 6% 10% 7% 4 6% 6% 6% 7% 29%	2272
	21st to end	Night	5% 12% 5% 12% 9% 4 6% 6% 7% 7% 27%	1875
March	1st to 10th	Night	5% 13% 6% 9% 7% 5% 7% 6% 7% 7% 28%	2160
	11th to 20th	Night	3 9% 4 10% 8% 5% 8% 7% 7% 7% 31%	2013
	21st to end	Night	5% 12% 5% 9% 7% 4 8% 7% 6% 8% 29%	2056
April	1st to 10th	Night	5% 11% 5% 10% 10% 4 6% 6% 7% 8% 27%	1800
	11th to 20th	Night	4 12% 5% 9% 9% 5% 7% 7% 7% 7% 29%	1723
	21st to end	Night	8% 12% 4 9% 8% 4 6% 6% 5% 7% 32%	1450
May	1st to 10th	Night	11% 10% 6% 8% 8% 4 6% 6% 6% 6% 29%	1440
	11th to 20th	Night	11% 8% 4 7% 7% 5% 6% 6% 6% 10% 28%	1416
	21st to end	Night	17% 10% 4 9% 7% 5% 6% 5% 6% 7% 25%	1427
June	1st to 10th	Night	15% 8% 5% 8% 7% 5% 6% 6% 7% 6% 28%	1080
	11th to 20th	Night	18% 10% 5% 10% 7% 4 6% 6% 6% 8% 19%	1080
	21st to end	Night	9% 8% 4 8% 7% 4 6% 5% 6% 9% 35%	1080
July	1st to 10th	Night	11% 8% 2 7% 6% 4 6% 6% 6% 9% 36%	1186
	11th to 20th	Night	7% 5% 3 9% 8% 4 6% 6% 7% 8% 36%	1260
	21st to end	Night	8% 4 3 5% 5% 3 5% 5% 7% 10% 45%	1500
August	1st to 10th	Night	7% 4 2 6% 5% 3 6% 6% 8% 8% 46%	1432
	11th to 20th	Night	6% 5% 2 5% 4 3 5% 5% 6% 8% 51%	1464
	21st to end	Night	10% 6% 3 6% 7% 4 7% 6% 6% 10% 36%	1865
September	1st to 10th	Night	8% 7% 3 4 5% 3 5% 5% 6% 7% 47%	1800
	11th to 20th	Night	11% 7% 3 5% 5% 2 4 4 6% 9% 43%	1800
	21st to end	Night	12% 9% 3 5% 5% 3 5% 6% 6% 7% 40%	2038
October	1st to 10th	Night	11% 8% 4 7% 8% 4 5% 4 5% 7% 38%	2160
	11th to 20th	Night	11% 10% 3 7% 6% 4 5% 6% 6% 7% 33%	2178
	21st to end	Night	10% 12% 4 8% 6% 4 4 5% 6% 6% 33%	2589
November	1st to 10th	Night	12% 15% 5% 9% 7% 4 6% 6% 7% 7% 23%	2590
	11th to 20th	Night	8% 13% 5% 9% 9% 5% 5% 7% 7% 7% 25%	2660
	21st to end	Night	9% 16% 7% 10% 8% 5% 6% 6% 7% 7% 20%	2755
December	1st to 10th	Night	7% 13% 6% 11% 9% 5% 6% 7% 6% 7% 21%	2921
	11th to 20th	Night	8% 18% 8% 15% 9% 5% 6% 5% 5% 6% 15%	3750
	21st to end	Night	5% 15% 6% 12% 9% 5% 7% 7% 6% 8% 20%	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	64% 5% 15% 12% 3	1329
	11th to 20th	Day	58% 5% 20% 10% 5% 2	1288
	21st to end	Day	60% 4 14% 17% 5%	1548
February	1st to 10th	Day	63% 5% 11% 11% 9% 1	1498
	11th to 20th	Day	56% 4 16% 15% 9%	1584
	21st to end	Day	58% 3 13% 18% 7% 1	1381
March	1st to 10th	Day	57% 3 12% 16% 12% 1	1800
	11th to 20th	Day	55% 3 13% 21% 8% 1	1944
	21st to end	Day	57% 4 14% 20% 6%	2299
April	1st to 10th	Day	59% 4 13% 16% 8% 1	2160
	11th to 20th	Day	58% 3 9% 18% 10% 1	2185
	21st to end	Day	56% 3 10% 19% 11%	2510
May	1st to 10th	Day	55% 3 11% 18% 12% 1	2520
	11th to 20th	Day	49% 3 12% 25% 10% 1	2480
	21st to end	Day	55% 2 11% 21% 9% 1	2840
June	1st to 10th	Day	56% 3 9% 17% 12% 3	2880
	11th to 20th	Day	60% 2 12% 19% 7%	2880
	21st to end	Day	47% 3 15% 22% 10% 2	2880
July	1st to 10th	Day	41% 3 13% 25% 16% 3	2696
	11th to 20th	Day	38% 3 14% 28% 15% 2	2619
	21st to end	Day	30% 2 14% 34% 18% 2	2659
August	1st to 10th	Day	34% 3 15% 32% 16% 1	2490
	11th to 20th	Day	29% 3 20% 31% 15% 3	2434
	21st to end	Day	41% 2 17% 29% 10% 2	2490
September	1st to 10th	Day	37% 3 18% 30% 10% 3	2160
	11th to 20th	Day	44% 3 12% 27% 12% 2	2160
	21st to end	Day	48% 3 16% 20% 11% 2	1919
October	1st to 10th	Day	47% 2 18% 26% 6%	1800
	11th to 20th	Day	49% 3 17% 24% 7%	1781
	21st to end	Day	52% 4 15% 23% 5%	1764
November	1st to 10th	Day	60% 4 11% 18% 7%	1488
	11th to 20th	Day	57% 4 16% 17% 5% 1	1520
	21st to end	Day	60% 5% 16% 12% 6%	1404
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	67% 4 13% 12% 4	2836
	11th to 20th	Night	61% 6% 15% 12% 4 2	2760
	21st to end	Night	59% 5% 14% 16% 5% 1	2808
February	1st to 10th	Night	63% 3 11% 15% 7% 1	2460
	11th to 20th	Night	54% 4 13% 21% 8%	2274
	21st to end	Night	55% 3 14% 20% 8% 1	1875
March	1st to 10th	Night	53% 4 14% 19% 10% 1	2160
	11th to 20th	Night	49% 4 15% 24% 7% 1	2014
	21st to end	Night	52% 4 17% 22% 5%	2056
April	1st to 10th	Night	52% 5% 14% 21% 8%	1800
	11th to 20th	Night	52% 3 9% 23% 11%	1723
	21st to end	Night	52% 3 9% 22% 12% 1	1450
May	1st to 10th	Night	55% 3 11% 20% 10% 1	1440
	11th to 20th	Night	50% 2 15% 22% 9% 1	1416
	21st to end	Night	57% 3 13% 18% 8% 1	1427
June	1st to 10th	Night	54% 3 10% 21% 9% 4	1080
	11th to 20th	Night	62% 3 13% 15% 7%	1080
	21st to end	Night	46% 3 14% 24% 11% 2	1080
July	1st to 10th	Night	46% 4 12% 20% 14% 4	1151
	11th to 20th	Night	42% 3 13% 27% 12% 2	1218
	21st to end	Night	33% 2 14% 31% 18% 2	1417
August	1st to 10th	Night	34% 4 12% 31% 16% 2	1424
	11th to 20th	Night	31% 2 17% 32% 16% 3	1464
	21st to end	Night	42% 3 15% 28% 10% 2	1865
September	1st to 10th	Night	37% 3 14% 32% 13% 2	1800
	11th to 20th	Night	38% 3 14% 28% 13% 4	1800
	21st to end	Night	44% 4 16% 24% 11% 2	2038
October	1st to 10th	Night	47% 3 15% 27% 8%	2160
	11th to 20th	Night	49% 3 15% 25% 8%	2178
	21st to end	Night	51% 3 17% 24% 6%	2589
November	1st to 10th	Night	59% 5% 15% 15% 5% 1	2590
	11th to 20th	Night	56% 6% 16% 16% 7% 1	2660
	21st to end	Night	62% 4 15% 13% 6% 1	2755
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% 16% 27% 23% 19% 2	168
	21st to end	Day	18% 16% 24% 30% 10% 3	176
February	1st to 10th	Day	18% 22% 29% 23% 5% 2	218
	11th to 20th	Day	15% 14% 27% 27% 14% 1	335
	21st to end	Day	11% 18% 31% 25% 12% 4	302
March	1st to 10th	Day	14% 17% 32% 21% 14% 4	420
	11th to 20th	Day	14% 22% 31% 18% 11% 5%	420
	21st to end	Day	18% 19% 26% 22% 9% 6%	462
April	1st to 10th	Day	15% 22% 26% 23% 10% 4	420
	11th to 20th	Day	16% 22% 25% 20% 11% 7%	412
	21st to end	Day	16% 17% 23% 27% 11% 7%	420
May	1st to 10th	Day	13% 17% 26% 23% 15% 5%	423
	11th to 20th	Day	16% 8% 21% 31% 16% 9%	448
	21st to end	Day	18% 8% 20% 29% 17% 7%	601
June	1st to 10th	Day	18% 11% 31% 22% 15% 3	810
	11th to 20th	Day	20% 10% 22% 28% 17% 2	810
	21st to end	Day	14% 7% 22% 26% 22% 8%	810
July	1st to 10th	Day	12% 7% 25% 29% 20% 7%	691
	11th to 20th	Day	10% 8% 23% 29% 23% 7%	618
	21st to end	Day	8% 5% 17% 32% 27% 11%	562
August	1st to 10th	Day	9% 5% 14% 31% 28% 13%	447
	11th to 20th	Day	8% 6% 21% 29% 24% 12%	437
	21st to end	Day	12% 10% 22% 25% 19% 12%	495
September	1st to 10th	Day	16% 9% 24% 26% 16% 9%	450
	11th to 20th	Day	16% 10% 19% 22% 22% 10%	450
	21st to end	Day	19% 12% 26% 23% 15% 5%	450
October	1st to 10th	Day	20% 11% 20% 24% 16% 10%	450
	11th to 20th	Day	20% 16% 23% 19% 15% 7%	431
	21st to end	Day	22% 17% 27% 19% 12% 3	288
November	1st to 10th	Day	23% 18% 27% 19% 10% 3	180
	11th to 20th	Day	18% 14% 27% 22% 13% 6%	180
	21st to end	Day	16% 16% 26% 19% 17% 6%	180
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% 33% 14% 2	820
	21st to end	Night	14% 9% 26% 32% 15% 2	808
February	1st to 10th	Night	16% 12% 28% 31% 11% 2	720
	11th to 20th	Night	15% 9% 24% 40% 11% 2	704
	21st to end	Night	12% 10% 23% 35% 18% 1	592
March	1st to 10th	Night	13% 14% 25% 30% 15% 2	720
	11th to 20th	Night	10% 17% 28% 28% 14% 2	720
	21st to end	Night	10% 18% 22% 28% 18% 4	792
April	1st to 10th	Night	10% 12% 25% 31% 18% 4	720
	11th to 20th	Night	12% 12% 26% 30% 18% 2	655
	21st to end	Night	13% 13% 31% 28% 13% 3	370
May	1st to 10th	Night	16% 10% 27% 27% 19% 1	360
	11th to 20th	Night	15% 6% 26% 34% 17% 2	354
	21st to end	Night	21% 6% 20% 28% 23% 2	389
June	1st to 10th	Night	17% 10% 25% 32% 15% 1	360
	11th to 20th	Night	21% 10% 23% 29% 16% 2	360
	21st to end	Night	10% 7% 24% 32% 24% 3	360
July	1st to 10th	Night	15% 4 20% 30% 27% 3	350
	11th to 20th	Night	11% 5% 19% 37% 24% 3	348
	21st to end	Night	9% 3 20% 31% 31% 5%	394
August	1st to 10th	Night	6% 4 13% 33% 38% 6%	358
	11th to 20th	Night	9% 2 14% 33% 37% 5%	396
	21st to end	Night	12% 8% 17% 32% 27% 4	677
September	1st to 10th	Night	13% 6% 18% 37% 23% 3	720
	11th to 20th	Night	14% 5% 18% 27% 29% 7%	720
	21st to end	Night	18% 9% 23% 29% 17% 3	720
October	1st to 10th	Night	17% 11% 19% 30% 20% 3	720
	11th to 20th	Night	18% 11% 21% 30% 17% 2	720
	21st to end	Night	20% 11% 27% 27% 12% 2	792
November	1st to 10th	Night	23% 15% 21% 31% 9% 2	740
	11th to 20th	Night	19% 15% 24% 28% 12% 2	760
	21st to end	Night	19% 13% 26% 28% 12% 2	855
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 2024-01-11 19:33:46. Version ac07

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