Sawyer Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sawyer Lake clear sky chart from 2005-11-06 to 2025-11-18.

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	12% 9% 3 8% 5% 5% 5% 4 6% 7% 37%	127201
	Night	12% 10% 4 8% 5% 4 4 3 5% 7% 38%	123458
Transparency	Day	45% 5% 12% 24% 13% 1	130665
	Night	45% 4 12% 24% 13% 1	128067
Seeing	Day	19% 10% 31% 24% 12% 4	17457
	Night	18% 8% 30% 31% 11% 1	27302

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	9% 10% 3 10% 7% 6% 6% 4 5% 7% 33%	3617
	11th to 20th	Day	10% 12% 4 9% 6% 6% 6% 5% 7% 7% 28%	3620
	21st to end	Day	10% 14% 6% 12% 5% 4 4 3 5% 6% 31%	3982
February	1st to 10th	Day	8% 12% 4 10% 6% 5% 5% 4 5% 7% 35%	1768
	11th to 20th	Day	9% 12% 3 9% 5% 5% 5% 4 6% 6% 35%	1863
	21st to end	Day	11% 13% 4 9% 6% 5% 3 4 6% 7% 32%	1650
March	1st to 10th	Day	12% 10% 2 5% 4 4 3 3 5% 6% 46%	4480
	11th to 20th	Day	10% 8% 3 9% 6% 6% 5% 4 7% 8% 34%	4699
	21st to end	Day	22% 11% 3 10% 5% 4 4 3 4 5% 28%	5963
April	1st to 10th	Day	15% 13% 3 8% 6% 6% 5% 4 5% 5% 30%	2400
	11th to 20th	Day	19% 10% 3 7% 5% 5% 5% 4 5% 6% 31%	2374
	21st to end	Day	18% 11% 3 7% 5% 4 6% 5% 5% 6% 31%	2555
May	1st to 10th	Day	14% 7% 3 6% 4 4 4 3 4 5% 46%	6173
	11th to 20th	Day	11% 7% 3 7% 4 4 5% 4 6% 7% 42%	6319
	21st to end	Day	14% 9% 3 7% 5% 5% 5% 4 6% 7% 36%	6935
June	1st to 10th	Day	11% 6% 3 7% 5% 6% 5% 5% 6% 8% 40%	2800
	11th to 20th	Day	14% 7% 3 6% 5% 5% 5% 4 6% 7% 37%	2800
	21st to end	Day	12% 6% 2 6% 5% 4 5% 4 7% 10% 37%	2800
July	1st to 10th	Day	11% 5% 2 5% 5% 5% 5% 5% 6% 10% 41%	6360
	11th to 20th	Day	7% 5% 2 4 4 4 5% 4 6% 10% 49%	6360
	21st to end	Day	8% 6% 3 6% 5% 5% 5% 4 7% 8% 44%	6924
August	1st to 10th	Day	10% 6% 2 7% 5% 6% 6% 4 7% 8% 38%	4563
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 4 6% 8% 44%	4119
	21st to end	Day	12% 7% 3 8% 4 5% 5% 4 6% 8% 39%	4312
September	1st to 10th	Day	12% 6% 2 7% 4 4 5% 4 6% 8% 43%	2400
	11th to 20th	Day	11% 6% 2 6% 4 5% 4 5% 6% 8% 43%	2315
	21st to end	Day	12% 8% 3 7% 5% 5% 4 5% 8% 8% 37%	2200
October	1st to 10th	Day	14% 8% 3 6% 4 4 3 4 5% 8% 41%	2065
	11th to 20th	Day	17% 10% 4 8% 5% 4 5% 3 5% 6% 31%	1961
	21st to end	Day	18% 11% 4 10% 4 4 3 4 5% 7% 31%	1980
November	1st to 10th	Day	13% 9% 3 7% 5% 4 5% 4 6% 7% 37%	1852
	11th to 20th	Day	13% 12% 5% 11% 7% 5% 5% 5% 4 6% 28%	1792
	21st to end	Day	14% 12% 3 9% 7% 5% 4 5% 6% 6% 30%	1600
December	1st to 10th	Day	8% 12% 4 13% 7% 7% 6% 4 5% 7% 26%	2610
	11th to 20th	Day	12% 19% 4 10% 5% 5% 4 4 5% 5% 27%	3008
	21st to end	Day	20% 23% 5% 10% 5% 4 3 3 3 4 21%	3982
January	1st to 10th	Night	8% 12% 5% 10% 6% 4 4 4 5% 7% 35%	6348
	11th to 20th	Night	8% 13% 5% 11% 6% 6% 5% 3 6% 8% 28%	6360
	21st to end	Night	8% 13% 7% 12% 6% 5% 4 4 5% 5% 30%	6996
February	1st to 10th	Night	9% 12% 5% 11% 5% 5% 4 3 5% 6% 35%	2630
	11th to 20th	Night	8% 11% 4 9% 5% 5% 5% 3 5% 7% 37%	2423
	21st to end	Night	13% 12% 5% 8% 6% 4 4 3 6% 6% 34%	1980
March	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 5% 7% 48%	5373
	11th to 20th	Night	10% 9% 3 8% 5% 4 5% 5% 7% 9% 35%	5305
	21st to end	Night	20% 10% 3 9% 5% 4 4 3 5% 7% 29%	4964
April	1st to 10th	Night	19% 12% 3 7% 5% 4 4 3 5% 6% 32%	2000
	11th to 20th	Night	20% 9% 3 5% 4 4 5% 3 4 6% 37%	1975
	21st to end	Night	16% 9% 3 7% 4 4 4 4 5% 7% 36%	1845
May	1st to 10th	Night	14% 8% 3 6% 3 5% 3 3 5% 6% 43%	3731
	11th to 20th	Night	9% 7% 3 6% 4 4 5% 4 5% 7% 47%	3596
	21st to end	Night	17% 7% 3 7% 4 3 4 4 5% 7% 38%	3942
June	1st to 10th	Night	10% 6% 3 6% 4 5% 5% 4 5% 8% 46%	1600
	11th to 20th	Night	13% 7% 3 8% 6% 5% 5% 4 6% 7% 37%	1600
	21st to end	Night	11% 5% 2 6% 4 4 4 4 7% 9% 44%	1600
July	1st to 10th	Night	12% 5% 2 5% 3 4 4 4 6% 10% 46%	3618
	11th to 20th	Night	9% 4 1 4 3 3 4 3 5% 9% 56%	3617
	21st to end	Night	9% 6% 2 7% 4 3 4 4 5% 7% 49%	3947
August	1st to 10th	Night	11% 5% 3 6% 5% 5% 5% 4 5% 8% 44%	2597
	11th to 20th	Night	12% 5% 2 6% 4 4 5% 4 6% 8% 47%	2929
	21st to end	Night	12% 9% 3 6% 3 3 3 3 4 6% 48%	3586
September	1st to 10th	Night	9% 6% 2 5% 4 3 4 3 5% 6% 52%	2000
	11th to 20th	Night	12% 5% 2 6% 4 3 4 3 5% 8% 50%	2065
	21st to end	Night	13% 7% 2 5% 4 3 4 4 5% 8% 45%	2200
October	1st to 10th	Night	14% 6% 2 6% 3 4 4 3 5% 7% 46%	2332
	11th to 20th	Night	16% 9% 3 7% 4 3 4 4 5% 7% 37%	2438
	21st to end	Night	17% 10% 3 8% 5% 4 4 4 5% 7% 33%	2860
November	1st to 10th	Night	14% 11% 3 6% 4 4 4 3 5% 7% 39%	2666
	11th to 20th	Night	13% 11% 5% 9% 5% 5% 4 4 5% 6% 33%	2760
	21st to end	Night	13% 11% 3 10% 6% 4 5% 3 6% 7% 32%	2800
December	1st to 10th	Night	12% 10% 3 7% 5% 5% 5% 5% 7% 8% 32%	4580
	11th to 20th	Night	11% 17% 7% 12% 6% 4 4 3 4 5% 27%	5199
	21st to end	Night	21% 18% 5% 9% 4 3 3 2 4 5% 25%	6996

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	49% 4 10% 24% 13% 1	3618
	11th to 20th	Day	54% 3 9% 19% 12% 3	3620
	21st to end	Day	55% 3 11% 18% 12% 1	3982
February	1st to 10th	Day	48% 5% 11% 21% 14% 1	1768
	11th to 20th	Day	46% 6% 11% 24% 11% 2	1872
	21st to end	Day	51% 3 10% 22% 12% 2	1650
March	1st to 10th	Day	40% 2 13% 20% 19% 6%	4480
	11th to 20th	Day	45% 6% 14% 21% 13% 1	4699
	21st to end	Day	59% 4 8% 16% 13%	5965
April	1st to 10th	Day	54% 5% 10% 19% 12% 1	2400
	11th to 20th	Day	54% 4 8% 22% 11% 1	2374
	21st to end	Day	53% 5% 9% 18% 13% 2	2555
May	1st to 10th	Day	40% 4 9% 27% 18% 2	6209
	11th to 20th	Day	41% 5% 12% 27% 14% 1	6323
	21st to end	Day	46% 4 9% 23% 17% 1	6949
June	1st to 10th	Day	40% 5% 12% 28% 13% 1	2800
	11th to 20th	Day	45% 5% 15% 22% 13% 1	2800
	21st to end	Day	40% 6% 16% 25% 12% 1	2800
July	1st to 10th	Day	37% 6% 15% 33% 9% 1	6291
	11th to 20th	Day	29% 6% 15% 36% 13% 2	6285
	21st to end	Day	37% 5% 12% 29% 17% 1	6728
August	1st to 10th	Day	41% 6% 14% 24% 14% 1	4548
	11th to 20th	Day	37% 5% 13% 33% 12%	4161
	21st to end	Day	42% 6% 13% 25% 14% 1	4311
September	1st to 10th	Day	39% 5% 14% 28% 14% 1	2400
	11th to 20th	Day	37% 5% 18% 32% 8%	2315
	21st to end	Day	43% 5% 12% 29% 11%	2200
October	1st to 10th	Day	30% 3 12% 32% 22%	3364
	11th to 20th	Day	47% 3 10% 24% 16% 1	3177
	21st to end	Day	48% 4 15% 25% 7%	3180
November	1st to 10th	Day	46% 5% 11% 25% 13% 1	1852
	11th to 20th	Day	56% 5% 10% 18% 9% 1	1792
	21st to end	Day	53% 7% 13% 21% 5% 1	1600
December	1st to 10th	Day	56% 5% 12% 20% 6%	2610
	11th to 20th	Day	59% 5% 8% 14% 13%	3005
	21st to end	Day	68% 2 5% 14% 10%	3982
January	1st to 10th	Night	48% 4 8% 26% 13% 1	6348
	11th to 20th	Night	54% 3 10% 18% 14% 1	6360
	21st to end	Night	54% 4 10% 20% 10% 1	6996
February	1st to 10th	Night	50% 3 8% 23% 13% 3	2630
	11th to 20th	Night	47% 4 10% 24% 12% 2	2424
	21st to end	Night	51% 3 11% 22% 11% 2	1980
March	1st to 10th	Night	37% 3 16% 23% 18% 3	5373
	11th to 20th	Night	45% 5% 16% 21% 11% 2	5305
	21st to end	Night	56% 3 9% 18% 13% 1	4964
April	1st to 10th	Night	52% 5% 7% 17% 17% 1	2000
	11th to 20th	Night	48% 4 9% 22% 13% 3	1975
	21st to end	Night	48% 4 10% 23% 15% 1	1845
May	1st to 10th	Night	42% 4 12% 24% 14% 3	3757
	11th to 20th	Night	36% 6% 12% 27% 17% 2	3597
	21st to end	Night	45% 5% 12% 22% 15% 1	3950
June	1st to 10th	Night	36% 6% 15% 26% 16% 1	1600
	11th to 20th	Night	44% 6% 13% 20% 16% 1	1600
	21st to end	Night	36% 6% 15% 30% 12% 2	1600
July	1st to 10th	Night	33% 5% 19% 31% 9% 2	3580
	11th to 20th	Night	25% 5% 17% 38% 13% 2	3572
	21st to end	Night	34% 5% 15% 26% 19% 1	3832
August	1st to 10th	Night	38% 5% 15% 23% 17% 2	2588
	11th to 20th	Night	35% 6% 15% 29% 14% 2	2953
	21st to end	Night	38% 5% 13% 26% 17% 1	3586
September	1st to 10th	Night	32% 5% 13% 34% 16% 1	2000
	11th to 20th	Night	34% 4 15% 35% 12%	2065
	21st to end	Night	37% 5% 14% 31% 12% 1	2200
October	1st to 10th	Night	30% 3 9% 37% 18% 2	3813
	11th to 20th	Night	37% 4 11% 31% 16%	3961
	21st to end	Night	50% 4 10% 24% 12%	4610
November	1st to 10th	Night	44% 4 10% 26% 14% 1	2666
	11th to 20th	Night	51% 4 13% 19% 12% 1	2760
	21st to end	Night	52% 5% 12% 24% 6% 1	2800
December	1st to 10th	Night	47% 6% 22% 20% 5% 1	4580
	11th to 20th	Night	61% 3 9% 15% 11% 1	5201
	21st to end	Night	63% 3 6% 17% 11%	6996

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	20% 11% 33% 24% 9% 2	300
	11th to 20th	Day	24% 11% 34% 24% 5% 1	300
	21st to end	Day	20% 12% 38% 23% 6% 1	330
February	1st to 10th	Day	17% 17% 38% 19% 6% 2	300
	11th to 20th	Day	21% 20% 41% 13% 5%	300
	21st to end	Day	21% 19% 43% 14% 2	249
March	1st to 10th	Day	19% 16% 45% 16% 4	300
	11th to 20th	Day	24% 13% 34% 20% 7% 2	300
	21st to end	Day	27% 10% 30% 22% 9% 1	546
April	1st to 10th	Day	27% 13% 32% 21% 6% 1	500
	11th to 20th	Day	32% 14% 24% 20% 8% 2	492
	21st to end	Day	27% 11% 30% 20% 9% 3	500
May	1st to 10th	Day	21% 13% 32% 23% 8% 3	633
	11th to 20th	Day	19% 10% 34% 24% 9% 3	725
	21st to end	Day	19% 10% 30% 25% 13% 4	789
June	1st to 10th	Day	14% 8% 31% 30% 15% 3	730
	11th to 20th	Day	19% 9% 29% 27% 12% 3	730
	21st to end	Day	14% 8% 30% 28% 15% 5%	730
July	1st to 10th	Day	9% 4 25% 35% 21% 6%	721
	11th to 20th	Day	10% 7% 29% 31% 16% 7%	718
	21st to end	Day	8% 6% 29% 32% 18% 7%	794
August	1st to 10th	Day	12% 5% 26% 29% 21% 7%	726
	11th to 20th	Day	16% 5% 20% 28% 23% 8%	602
	21st to end	Day	15% 8% 24% 26% 21% 7%	583
September	1st to 10th	Day	17% 9% 24% 25% 17% 8%	530
	11th to 20th	Day	15% 6% 21% 35% 19% 4	530
	21st to end	Day	19% 8% 25% 27% 16% 4	530
October	1st to 10th	Day	21% 10% 28% 25% 13% 3	395
	11th to 20th	Day	23% 19% 36% 16% 4 1	330
	21st to end	Day	24% 14% 39% 18% 4	363
November	1st to 10th	Day	21% 13% 39% 19% 6% 2	330
	11th to 20th	Day	25% 15% 38% 15% 6% 1	321
	21st to end	Day	24% 18% 38% 13% 5% 1	300
December	1st to 10th	Day	20% 13% 44% 17% 4 1	300
	11th to 20th	Day	24% 20% 34% 17% 4 1	300
	21st to end	Day	32% 14% 33% 17% 4	330
January	1st to 10th	Night	17% 11% 38% 28% 6%	1000
	11th to 20th	Night	20% 10% 38% 24% 7% 1	1000
	21st to end	Night	18% 8% 37% 30% 7%	1100
February	1st to 10th	Night	15% 13% 37% 26% 8% 1	1000
	11th to 20th	Night	15% 15% 34% 29% 6%	868
	21st to end	Night	21% 10% 37% 27% 5%	660
March	1st to 10th	Night	18% 11% 32% 32% 8%	800
	11th to 20th	Night	17% 11% 35% 29% 7% 1	743
	21st to end	Night	20% 7% 29% 33% 10% 1	660
April	1st to 10th	Night	26% 7% 32% 28% 6% 1	600
	11th to 20th	Night	25% 9% 28% 29% 9%	593
	21st to end	Night	23% 6% 30% 32% 9% 1	600
May	1st to 10th	Night	22% 6% 30% 33% 8% 1	600
	11th to 20th	Night	19% 5% 31% 34% 9% 1	591
	21st to end	Night	14% 6% 25% 39% 15% 1	650
June	1st to 10th	Night	12% 6% 26% 42% 14% 1	600
	11th to 20th	Night	19% 5% 24% 40% 11% 1	600
	21st to end	Night	13% 6% 22% 43% 16% 1	600
July	1st to 10th	Night	9% 2 21% 44% 23% 1	585
	11th to 20th	Night	11% 3 22% 42% 21% 1	582
	21st to end	Night	9% 3 22% 44% 20% 2	657
August	1st to 10th	Night	11% 2 19% 41% 24% 2	597
	11th to 20th	Night	12% 2 16% 40% 27% 4	594
	21st to end	Night	14% 3 20% 37% 25% 2	660
September	1st to 10th	Night	13% 5% 23% 35% 21% 5%	600
	11th to 20th	Night	13% 4 24% 35% 21% 3	665
	21st to end	Night	16% 7% 23% 35% 18% 1	800
October	1st to 10th	Night	18% 8% 27% 28% 19% 1	800
	11th to 20th	Night	22% 11% 28% 31% 7%	800
	21st to end	Night	24% 8% 31% 26% 10% 1	880
November	1st to 10th	Night	21% 10% 37% 24% 8% 1	820
	11th to 20th	Night	21% 13% 36% 22% 7% 1	897
	21st to end	Night	20% 13% 34% 28% 5%	1000
December	1st to 10th	Night	22% 12% 35% 23% 7% 1	1000
	11th to 20th	Night	21% 12% 34% 25% 7% 1	1000
	21st to end	Night	28% 10% 33% 24% 5%	1100

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