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 2024-01-12.

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	13% 9% 4 7% 6% 4 5% 5% 6% 7% 35%	74784
	Night	13% 9% 4 7% 5% 3 5% 4 5% 7% 37%	74965
Transparency	Day	47% 5% 12% 23% 11% 1	74484
	Night	46% 5% 12% 24% 12% 1	74785
Seeing	Day	19% 9% 30% 25% 13% 4	14831
	Night	18% 8% 30% 32% 11% 1	24843

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	12% 10% 5% 9% 7% 5% 6% 4 5% 6% 32%	1517
	11th to 20th	Day	13% 14% 6% 12% 7% 3 5% 5% 6% 7% 22%	1453
	21st to end	Day	13% 13% 6% 10% 8% 4 3 5% 5% 7% 27%	1584
February	1st to 10th	Day	9% 11% 4 9% 7% 3 5% 5% 5% 7% 35%	1591
	11th to 20th	Day	9% 12% 4 9% 6% 3 4 4 6% 7% 36%	1672
	21st to end	Day	12% 13% 4 8% 7% 4 4 4 6% 7% 30%	1480
March	1st to 10th	Day	12% 11% 4 7% 8% 3 5% 4 5% 5% 35%	1800
	11th to 20th	Day	11% 10% 4 7% 6% 4 4 5% 5% 6% 38%	1867
	21st to end	Day	16% 10% 5% 7% 7% 4 6% 4 5% 7% 30%	2372
April	1st to 10th	Day	15% 11% 4 7% 7% 4 6% 5% 5% 6% 31%	2160
	11th to 20th	Day	21% 10% 3 6% 5% 4 5% 4 4 6% 31%	2134
	21st to end	Day	17% 11% 4 6% 5% 3 6% 6% 4 6% 32%	2299
May	1st to 10th	Day	16% 8% 4 7% 7% 3 5% 5% 5% 7% 34%	2456
	11th to 20th	Day	15% 8% 3 7% 6% 3 5% 5% 4 6% 37%	2479
	21st to end	Day	12% 6% 3 5% 7% 4 6% 5% 6% 8% 38%	2725
June	1st to 10th	Day	11% 5% 3 6% 5% 4 6% 5% 5% 7% 41%	2520
	11th to 20th	Day	13% 6% 3 6% 6% 4 6% 5% 5% 8% 39%	2520
	21st to end	Day	10% 6% 2 6% 6% 3 6% 6% 6% 11% 38%	2520
July	1st to 10th	Day	6% 4 2 4 5% 4 6% 6% 7% 11% 45%	2520
	11th to 20th	Day	7% 5% 2 5% 6% 3 6% 5% 6% 9% 44%	2520
	21st to end	Day	7% 5% 2 5% 6% 4 5% 5% 7% 8% 46%	2743
August	1st to 10th	Day	9% 5% 3 5% 6% 4 6% 6% 7% 10% 40%	2507
	11th to 20th	Day	13% 6% 2 5% 5% 3 5% 5% 6% 8% 41%	2282
	21st to end	Day	13% 6% 2 5% 4 3 4 5% 6% 8% 43%	2376
September	1st to 10th	Day	13% 6% 2 6% 4 3 4 4 6% 7% 43%	2160
	11th to 20th	Day	12% 5% 3 5% 5% 3 5% 5% 6% 8% 43%	2084
	21st to end	Day	13% 8% 3 6% 6% 4 5% 5% 8% 8% 34%	1980
October	1st to 10th	Day	16% 8% 3 5% 5% 3 4 4 5% 8% 39%	1859
	11th to 20th	Day	19% 10% 5% 7% 6% 4 5% 5% 5% 6% 30%	1765
	21st to end	Day	19% 11% 4 9% 6% 3 3 4 5% 6% 30%	1782
November	1st to 10th	Day	12% 9% 3 6% 6% 3 5% 4 6% 7% 37%	1672
	11th to 20th	Day	13% 10% 6% 10% 8% 4 5% 6% 4 7% 27%	1644
	21st to end	Day	14% 11% 4 7% 8% 4 5% 5% 6% 6% 31%	1520
December	1st to 10th	Day	13% 12% 4 9% 6% 4 5% 5% 5% 8% 29%	1520
	11th to 20th	Day	15% 14% 5% 7% 8% 5% 6% 6% 6% 6% 23%	1918
	21st to end	Day	20% 23% 6% 8% 6% 3 4 3 3 5% 19%	2783
January	1st to 10th	Night	11% 11% 5% 7% 6% 4 5% 5% 5% 7% 33%	2648
	11th to 20th	Night	13% 13% 6% 9% 6% 4 4 4 5% 7% 28%	2547
	21st to end	Night	11% 12% 7% 10% 7% 3 5% 6% 5% 7% 26%	2772
February	1st to 10th	Night	9% 11% 5% 10% 6% 4 5% 4 4 7% 35%	2367
	11th to 20th	Night	9% 10% 4 8% 6% 4 6% 4 4 8% 37%	2174
	21st to end	Night	14% 12% 6% 7% 7% 3 4 3 5% 6% 33%	1776
March	1st to 10th	Night	12% 9% 4 6% 5% 3 4 4 5% 6% 40%	2160
	11th to 20th	Night	12% 9% 4 5% 5% 3 5% 5% 6% 6% 41%	2109
	21st to end	Night	15% 10% 3 6% 6% 3 3 3 5% 7% 38%	1982
April	1st to 10th	Night	19% 10% 5% 6% 5% 3 5% 4 6% 7% 32%	1800
	11th to 20th	Night	20% 8% 3 4 5% 2 5% 4 4 6% 37%	1775
	21st to end	Night	17% 8% 4 7% 6% 3 5% 5% 5% 7% 34%	1661
May	1st to 10th	Night	18% 8% 4 6% 6% 3 5% 5% 5% 6% 33%	1499
	11th to 20th	Night	16% 8% 3 6% 6% 3 4 6% 5% 5% 37%	1416
	21st to end	Night	13% 5% 2 5% 5% 3 5% 5% 6% 11% 40%	1551
June	1st to 10th	Night	10% 5% 3 6% 5% 3 5% 5% 5% 8% 47%	1440
	11th to 20th	Night	11% 6% 3 6% 7% 4 5% 5% 6% 8% 39%	1440
	21st to end	Night	9% 4 3 5% 4 3 5% 5% 6% 10% 46%	1440
July	1st to 10th	Night	7% 3 2 4 3 3 4 5% 6% 10% 54%	1440
	11th to 20th	Night	9% 5% 2 3 4 3 5% 5% 6% 9% 49%	1440
	21st to end	Night	7% 4 2 4 4 2 4 4 5% 8% 56%	1575
August	1st to 10th	Night	8% 3 3 4 5% 5% 6% 6% 6% 9% 45%	1432
	11th to 20th	Night	9% 4 3 5% 5% 3 5% 6% 5% 8% 47%	1615
	21st to end	Night	11% 6% 2 5% 3 2 4 5% 4 7% 51%	1980
September	1st to 10th	Night	10% 6% 2 5% 5% 3 4 4 5% 7% 51%	1800
	11th to 20th	Night	11% 4 2 4 4 3 4 4 5% 8% 51%	1858
	21st to end	Night	13% 8% 3 5% 5% 2 4 5% 5% 8% 42%	1980
October	1st to 10th	Night	15% 6% 2 4 4 3 4 4 5% 8% 45%	2098
	11th to 20th	Night	16% 9% 4 7% 5% 3 4 5% 5% 7% 35%	2194
	21st to end	Night	18% 10% 4 7% 6% 3 5% 5% 5% 7% 32%	2574
November	1st to 10th	Night	13% 10% 3 5% 5% 3 4 4 5% 8% 39%	2406
	11th to 20th	Night	14% 10% 5% 8% 5% 4 5% 5% 5% 7% 33%	2533
	21st to end	Night	14% 10% 4 8% 7% 3 5% 4 5% 8% 33%	2660
December	1st to 10th	Night	12% 13% 4 7% 7% 3 5% 5% 5% 7% 31%	2660
	11th to 20th	Night	11% 14% 5% 9% 7% 3 4 5% 5% 5% 30%	3279
	21st to end	Night	22% 19% 7% 8% 5% 2 3 3 3 4 23%	4884

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	53% 4 10% 22% 11% 1	1518
	11th to 20th	Day	60% 4 9% 17% 8% 1	1453
	21st to end	Day	58% 3 11% 18% 9% 1	1584
February	1st to 10th	Day	48% 5% 11% 21% 13% 1	1591
	11th to 20th	Day	47% 5% 12% 24% 10% 2	1681
	21st to end	Day	54% 3 10% 20% 11% 1	1480
March	1st to 10th	Day	51% 3 12% 20% 12% 2	1800
	11th to 20th	Day	47% 4 13% 22% 11% 2	1867
	21st to end	Day	54% 4 12% 18% 11% 1	2372
April	1st to 10th	Day	54% 5% 11% 18% 12% 1	2160
	11th to 20th	Day	55% 4 7% 21% 11% 1	2134
	21st to end	Day	53% 5% 9% 18% 12% 2	2299
May	1st to 10th	Day	49% 6% 12% 22% 11% 1	2456
	11th to 20th	Day	48% 5% 10% 23% 13% 2	2483
	21st to end	Day	44% 6% 11% 26% 11% 2	2725
June	1st to 10th	Day	40% 5% 13% 28% 13% 1	2520
	11th to 20th	Day	44% 5% 15% 22% 14% 1	2520
	21st to end	Day	39% 6% 16% 27% 11% 1	2520
July	1st to 10th	Day	31% 6% 16% 31% 15% 1	2451
	11th to 20th	Day	35% 6% 13% 28% 15% 3	2445
	21st to end	Day	33% 7% 13% 28% 18% 2	2591
August	1st to 10th	Day	38% 6% 15% 29% 11% 2	2492
	11th to 20th	Day	39% 6% 13% 28% 13%	2282
	21st to end	Day	38% 5% 13% 26% 16% 1	2376
September	1st to 10th	Day	40% 5% 13% 28% 14% 1	2160
	11th to 20th	Day	38% 5% 19% 30% 8% 1	2084
	21st to end	Day	46% 5% 13% 27% 9%	1980
October	1st to 10th	Day	43% 5% 14% 30% 7%	1859
	11th to 20th	Day	55% 5% 10% 21% 8% 1	1765
	21st to end	Day	55% 4 13% 19% 8%	1782
November	1st to 10th	Day	45% 5% 11% 25% 13% 1	1672
	11th to 20th	Day	57% 5% 11% 18% 9% 1	1644
	21st to end	Day	52% 7% 13% 21% 5% 1	1520
December	1st to 10th	Day	53% 4 11% 23% 8%	1520
	11th to 20th	Day	59% 7% 11% 14% 9% 1	1915
	21st to end	Day	69% 3 6% 14% 8%	2783
January	1st to 10th	Night	51% 4 11% 22% 10% 2	2648
	11th to 20th	Night	56% 4 11% 21% 8%	2547
	21st to end	Night	57% 4 9% 19% 10% 1	2772
February	1st to 10th	Night	50% 3 8% 24% 12% 3	2367
	11th to 20th	Night	47% 4 11% 24% 12% 3	2175
	21st to end	Night	53% 4 11% 21% 11% 1	1776
March	1st to 10th	Night	44% 4 12% 26% 12% 2	2160
	11th to 20th	Night	42% 4 12% 24% 16% 2	2109
	21st to end	Night	47% 4 10% 23% 13% 2	1982
April	1st to 10th	Night	52% 6% 7% 17% 17% 1	1800
	11th to 20th	Night	48% 4 9% 22% 13% 3	1775
	21st to end	Night	49% 4 9% 22% 14% 1	1661
May	1st to 10th	Night	51% 4 13% 19% 11% 1	1499
	11th to 20th	Night	47% 6% 9% 25% 11% 2	1417
	21st to end	Night	38% 6% 18% 23% 14% 1	1552
June	1st to 10th	Night	35% 6% 16% 27% 15% 1	1440
	11th to 20th	Night	42% 5% 13% 21% 17% 1	1440
	21st to end	Night	34% 6% 16% 32% 11% 2	1440
July	1st to 10th	Night	26% 4 15% 35% 18% 2	1400
	11th to 20th	Night	31% 7% 16% 29% 13% 3	1392
	21st to end	Night	25% 5% 18% 32% 17% 3	1487
August	1st to 10th	Night	35% 6% 14% 29% 13% 3	1423
	11th to 20th	Night	34% 6% 13% 30% 14% 2	1615
	21st to end	Night	33% 6% 13% 27% 18% 2	1980
September	1st to 10th	Night	33% 5% 12% 33% 16% 1	1800
	11th to 20th	Night	33% 4 16% 36% 12%	1858
	21st to end	Night	40% 5% 14% 30% 10% 1	1980
October	1st to 10th	Night	39% 4 13% 31% 12% 1	2098
	11th to 20th	Night	47% 5% 14% 24% 9% 1	2194
	21st to end	Night	52% 5% 12% 20% 10%	2574
November	1st to 10th	Night	43% 5% 10% 26% 15% 1	2406
	11th to 20th	Night	51% 5% 13% 18% 13% 1	2533
	21st to end	Night	51% 5% 13% 24% 6% 1	2660
December	1st to 10th	Night	53% 4 12% 22% 7% 1	2660
	11th to 20th	Night	55% 4 12% 19% 9% 1	3281
	21st to end	Night	66% 3 6% 18% 6%	4884

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	21% 10% 33% 24% 10% 2	270
	11th to 20th	Day	26% 8% 33% 26% 6% 2	245
	21st to end	Day	21% 10% 36% 26% 6% 1	264
February	1st to 10th	Day	18% 15% 40% 21% 6%	240
	11th to 20th	Day	20% 21% 40% 13% 6%	240
	21st to end	Day	22% 17% 44% 15% 1 1	198
March	1st to 10th	Day	18% 15% 45% 17% 5%	240
	11th to 20th	Day	22% 10% 34% 25% 8% 3	240
	21st to end	Day	26% 10% 29% 24% 10% 2	458
April	1st to 10th	Day	24% 11% 34% 23% 7% 1	420
	11th to 20th	Day	32% 11% 24% 22% 9% 2	412
	21st to end	Day	27% 10% 28% 22% 10% 3	420
May	1st to 10th	Day	22% 14% 32% 21% 9% 3	539
	11th to 20th	Day	20% 9% 35% 23% 10% 4	625
	21st to end	Day	17% 8% 29% 27% 14% 4	679
June	1st to 10th	Day	12% 7% 30% 31% 15% 4	630
	11th to 20th	Day	17% 8% 28% 29% 14% 4	630
	21st to end	Day	12% 7% 28% 31% 17% 5%	630
July	1st to 10th	Day	9% 3 24% 34% 22% 7%	621
	11th to 20th	Day	11% 6% 29% 30% 17% 8%	618
	21st to end	Day	8% 5% 30% 32% 18% 8%	684
August	1st to 10th	Day	12% 4 27% 29% 21% 7%	626
	11th to 20th	Day	17% 4 18% 28% 25% 9%	514
	21st to end	Day	17% 6% 22% 26% 22% 7%	495
September	1st to 10th	Day	18% 8% 22% 26% 18% 8%	450
	11th to 20th	Day	15% 7% 22% 33% 19% 4	450
	21st to end	Day	21% 9% 26% 25% 15% 4	450
October	1st to 10th	Day	23% 8% 25% 26% 14% 4	329
	11th to 20th	Day	24% 19% 36% 16% 4 1	270
	21st to end	Day	27% 14% 38% 17% 4	297
November	1st to 10th	Day	18% 13% 39% 21% 7% 2	270
	11th to 20th	Day	21% 16% 40% 16% 6% 1	270
	21st to end	Day	24% 17% 39% 14% 6% 1	270
December	1st to 10th	Day	20% 12% 43% 18% 5% 1	270
	11th to 20th	Day	26% 17% 34% 17% 5% 1	270
	21st to end	Day	31% 15% 34% 16% 4	297
January	1st to 10th	Night	17% 11% 38% 28% 6%	950
	11th to 20th	Night	20% 9% 37% 25% 8% 1	910
	21st to end	Night	18% 7% 38% 29% 7%	990
February	1st to 10th	Night	15% 12% 38% 28% 7% 1	900
	11th to 20th	Night	16% 13% 35% 29% 7%	779
	21st to end	Night	22% 10% 35% 27% 5%	592
March	1st to 10th	Night	17% 10% 31% 33% 9%	720
	11th to 20th	Night	17% 9% 35% 30% 7% 1	669
	21st to end	Night	20% 6% 28% 34% 11% 1	594
April	1st to 10th	Night	24% 7% 33% 28% 6% 1	540
	11th to 20th	Night	25% 7% 28% 30% 9%	533
	21st to end	Night	23% 5% 29% 32% 10% 1	540
May	1st to 10th	Night	23% 5% 30% 33% 8% 1	540
	11th to 20th	Night	21% 5% 31% 33% 9% 1	531
	21st to end	Night	14% 5% 24% 40% 16% 1	584
June	1st to 10th	Night	11% 5% 24% 43% 16% 1	540
	11th to 20th	Night	17% 4 24% 42% 11% 1	540
	21st to end	Night	11% 4 21% 45% 17% 1	540
July	1st to 10th	Night	9% 2 20% 44% 25% 1	525
	11th to 20th	Night	12% 2 23% 41% 21% 1	522
	21st to end	Night	9% 3 21% 45% 20% 2	591
August	1st to 10th	Night	11% 2 19% 42% 25% 2	537
	11th to 20th	Night	11% 1 15% 39% 29% 4	534
	21st to end	Night	14% 3 20% 37% 25% 2	594
September	1st to 10th	Night	12% 4 23% 36% 20% 5%	540
	11th to 20th	Night	13% 4 26% 35% 19% 3	598
	21st to end	Night	17% 7% 24% 33% 17% 2	720
October	1st to 10th	Night	18% 7% 26% 28% 19% 1	720
	11th to 20th	Night	22% 11% 27% 32% 8%	720
	21st to end	Night	25% 7% 31% 26% 9% 1	792
November	1st to 10th	Night	20% 9% 37% 25% 8% 1	740
	11th to 20th	Night	20% 12% 36% 23% 7% 1	823
	21st to end	Night	20% 12% 33% 29% 6%	950
December	1st to 10th	Night	22% 11% 35% 23% 7% 1	950
	11th to 20th	Night	20% 11% 35% 26% 7% 1	950
	21st to end	Night	28% 10% 34% 24% 4	1045

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