Silent Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Silent Lake clear sky chart from 2005-11-06 to 2024-01-16.

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	17% 11% 4 7% 6% 3 5% 4 5% 6% 31%	74722
	Night	16% 11% 4 8% 6% 3 4 4 5% 6% 31%	75082
Transparency	Day	54% 4 10% 20% 11% 1	74428
	Night	54% 4 11% 20% 11% 1	74910
Seeing	Day	25% 14% 31% 19% 9% 3	13288
	Night	23% 12% 31% 24% 10% 1	22665

By Month

Percentage Cloud Cover NE (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	14% 20% 6% 12% 7% 3 3 4 5% 5% 21%	1517
	11th to 20th	Day	18% 17% 9% 10% 7% 3 4 3 3 5% 21%	1490
	21st to end	Day	13% 14% 7% 14% 8% 4 5% 4 4 5% 21%	1782
February	1st to 10th	Day	13% 16% 8% 15% 10% 3 5% 4 4 4 19%	1620
	11th to 20th	Day	13% 16% 6% 11% 8% 4 4 4 3 5% 27%	1573
	21st to end	Day	17% 17% 6% 9% 7% 3 5% 4 4 5% 23%	1394
March	1st to 10th	Day	14% 12% 6% 8% 8% 4 5% 5% 3 5% 29%	1920
	11th to 20th	Day	13% 15% 5% 10% 7% 3 4 4 4 6% 28%	1980
	21st to end	Day	18% 12% 4 5% 5% 3 4 4 4 5% 36%	2204
April	1st to 10th	Day	20% 12% 5% 6% 6% 4 4 4 4 5% 29%	2160
	11th to 20th	Day	22% 10% 3 5% 6% 2 3 4 4 5% 37%	2148
	21st to end	Day	22% 11% 3 7% 5% 3 4 3 4 6% 32%	2340
May	1st to 10th	Day	19% 8% 3 7% 5% 3 5% 4 5% 7% 34%	2443
	11th to 20th	Day	17% 8% 3 6% 6% 3 5% 4 5% 7% 37%	2478
	21st to end	Day	14% 6% 3 5% 6% 4 5% 6% 5% 7% 39%	2725
June	1st to 10th	Day	21% 8% 3 6% 6% 3 5% 5% 5% 7% 32%	2520
	11th to 20th	Day	17% 5% 2 6% 5% 4 6% 5% 6% 8% 36%	2520
	21st to end	Day	17% 7% 3 5% 6% 4 5% 6% 5% 9% 35%	2520
July	1st to 10th	Day	13% 5% 2 5% 6% 4 4 5% 6% 9% 41%	2520
	11th to 20th	Day	12% 7% 3 5% 5% 3 7% 5% 6% 8% 38%	2520
	21st to end	Day	12% 6% 3 6% 7% 4 6% 6% 7% 9% 35%	2727
August	1st to 10th	Day	12% 6% 3 7% 7% 5% 7% 5% 6% 8% 35%	2327
	11th to 20th	Day	13% 7% 3 6% 7% 4 5% 5% 6% 7% 36%	2303
	21st to end	Day	15% 6% 3 5% 5% 4 6% 5% 7% 8% 36%	2439
September	1st to 10th	Day	15% 7% 2 6% 5% 3 5% 4 6% 8% 39%	2160
	11th to 20th	Day	14% 5% 2 5% 5% 3 4 4 5% 7% 43%	2147
	21st to end	Day	17% 7% 3 6% 6% 3 5% 5% 5% 8% 35%	1886
October	1st to 10th	Day	22% 9% 3 7% 5% 3 4 4 5% 6% 33%	1800
	11th to 20th	Day	25% 11% 3 7% 7% 3 4 5% 4 6% 24%	1800
	21st to end	Day	29% 12% 4 7% 6% 3 4 5% 4 5% 22%	1949
November	1st to 10th	Day	17% 12% 4 7% 5% 4 4 5% 5% 5% 32%	1572
	11th to 20th	Day	18% 14% 6% 8% 6% 4 4 4 5% 6% 24%	1520
	21st to end	Day	21% 18% 7% 9% 7% 2 5% 4 4 4 17%	1520
December	1st to 10th	Day	19% 22% 8% 11% 8% 3 4 4 3 5% 14%	1520
	11th to 20th	Day	18% 18% 7% 10% 6% 3 4 3 4 5% 23%	1906
	21st to end	Day	25% 22% 7% 11% 6% 2 3 2 3 3 17%	2772
January	1st to 10th	Night	19% 16% 7% 11% 8% 4 4 4 4 5% 18%	2649
	11th to 20th	Night	17% 17% 7% 12% 9% 4 4 3 4 5% 20%	2596
	21st to end	Night	13% 12% 6% 10% 9% 4 5% 5% 6% 5% 25%	2574
February	1st to 10th	Night	13% 15% 7% 10% 10% 4 6% 5% 6% 6% 18%	2340
	11th to 20th	Night	13% 12% 7% 11% 7% 4 5% 4 4 5% 28%	2273
	21st to end	Night	15% 15% 5% 8% 8% 3 4 5% 5% 6% 26%	1862
March	1st to 10th	Night	14% 12% 5% 9% 7% 3 4 4 4 5% 33%	2024
	11th to 20th	Night	13% 12% 6% 7% 6% 3 4 4 5% 5% 33%	1979
	21st to end	Night	16% 8% 3 8% 6% 3 3 5% 5% 6% 38%	2151
April	1st to 10th	Night	19% 11% 5% 7% 6% 3 4 4 5% 5% 31%	1800
	11th to 20th	Night	18% 9% 4 6% 6% 2 4 4 5% 5% 38%	1775
	21st to end	Night	18% 9% 3 6% 6% 3 5% 4 6% 5% 32%	1620
May	1st to 10th	Night	20% 7% 2 5% 5% 3 4 5% 6% 7% 37%	1514
	11th to 20th	Night	15% 5% 2 5% 5% 3 4 5% 6% 8% 42%	1415
	21st to end	Night	11% 5% 1 5% 4 3 5% 5% 4 8% 48%	1550
June	1st to 10th	Night	16% 7% 3 6% 7% 3 5% 4 6% 8% 37%	1440
	11th to 20th	Night	13% 5% 3 5% 5% 4 5% 4 6% 7% 44%	1440
	21st to end	Night	15% 7% 2 7% 4 4 4 4 5% 7% 40%	1440
July	1st to 10th	Night	8% 4 2 6% 7% 3 5% 5% 5% 8% 48%	1440
	11th to 20th	Night	12% 5% 2 5% 5% 3 5% 4 5% 9% 45%	1440
	21st to end	Night	9% 4 3 4 5% 3 4 5% 6% 9% 47%	1587
August	1st to 10th	Night	9% 5% 2 4 4 3 4 5% 7% 8% 47%	1611
	11th to 20th	Night	10% 6% 3 5% 6% 3 5% 5% 6% 8% 46%	1598
	21st to end	Night	12% 5% 2 5% 6% 3 4 4 6% 7% 46%	1898
September	1st to 10th	Night	11% 5% 2 5% 5% 3 4 4 6% 9% 45%	1800
	11th to 20th	Night	13% 5% 2 5% 4 2 4 4 5% 7% 48%	1810
	21st to end	Night	20% 6% 3 5% 4 3 5% 4 4 5% 42%	2073
October	1st to 10th	Night	19% 7% 3 6% 5% 4 4 4 5% 6% 37%	2160
	11th to 20th	Night	22% 11% 3 8% 6% 4 4 5% 5% 5% 28%	2160
	21st to end	Night	22% 13% 4 8% 6% 3 5% 4 5% 5% 24%	2405
November	1st to 10th	Night	18% 10% 3 7% 6% 4 4 4 5% 6% 34%	2506
	11th to 20th	Night	18% 13% 5% 7% 6% 3 5% 4 5% 7% 28%	2660
	21st to end	Night	20% 14% 5% 8% 7% 4 5% 5% 5% 5% 22%	2660
December	1st to 10th	Night	19% 19% 7% 10% 6% 3 4 5% 4 6% 16%	2660
	11th to 20th	Night	17% 19% 7% 10% 6% 3 3 3 4 5% 23%	3288
	21st to end	Night	26% 20% 7% 11% 6% 3 3 3 3 4 13%	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	66% 3 10% 14% 7%	1518
	11th to 20th	Day	68% 4 7% 10% 10% 2	1490
	21st to end	Day	66% 3 6% 12% 11% 3	1782
February	1st to 10th	Day	70% 3 7% 14% 6% 1	1620
	11th to 20th	Day	62% 3 9% 13% 11% 2	1582
	21st to end	Day	64% 3 7% 14% 11% 1	1394
March	1st to 10th	Day	58% 3 13% 15% 10% 2	1923
	11th to 20th	Day	58% 3 10% 16% 11% 2	1980
	21st to end	Day	52% 3 6% 19% 15% 5%	2204
April	1st to 10th	Day	58% 4 6% 19% 12% 3	2160
	11th to 20th	Day	51% 3 7% 23% 14% 1	2148
	21st to end	Day	55% 3 7% 20% 13% 3	2340
May	1st to 10th	Day	50% 4 8% 21% 14% 3	2443
	11th to 20th	Day	48% 3 6% 25% 16% 2	2482
	21st to end	Day	44% 5% 14% 20% 14% 3	2725
June	1st to 10th	Day	52% 4 10% 20% 13% 1	2520
	11th to 20th	Day	45% 4 11% 25% 13% 2	2520
	21st to end	Day	46% 5% 13% 23% 12% 1	2520
July	1st to 10th	Day	40% 4 10% 29% 15% 2	2450
	11th to 20th	Day	42% 6% 12% 29% 11% 1	2445
	21st to end	Day	43% 6% 12% 27% 11% 1	2574
August	1st to 10th	Day	45% 5% 14% 24% 11% 1	2314
	11th to 20th	Day	45% 4 15% 26% 9% 1	2303
	21st to end	Day	43% 5% 13% 27% 11% 1	2439
September	1st to 10th	Day	43% 4 11% 29% 12% 1	2160
	11th to 20th	Day	41% 4 12% 30% 14% 1	2147
	21st to end	Day	47% 4 13% 25% 10%	1886
October	1st to 10th	Day	52% 4 10% 21% 12% 1	1800
	11th to 20th	Day	62% 4 11% 15% 7% 1	1800
	21st to end	Day	66% 4 9% 15% 6% 1	1949
November	1st to 10th	Day	53% 4 14% 21% 7% 1	1572
	11th to 20th	Day	59% 4 12% 14% 9% 1	1520
	21st to end	Day	70% 4 9% 11% 6% 1	1520
December	1st to 10th	Day	74% 3 8% 11% 5%	1520
	11th to 20th	Day	65% 4 9% 11% 9% 1	1906
	21st to end	Day	74% 2 5% 14% 4	2772
January	1st to 10th	Night	69% 3 8% 13% 7%	2649
	11th to 20th	Night	68% 3 7% 12% 9% 1	2596
	21st to end	Night	61% 3 7% 16% 12% 1	2574
February	1st to 10th	Night	64% 3 9% 16% 7% 1	2340
	11th to 20th	Night	59% 2 9% 19% 10% 1	2275
	21st to end	Night	58% 2 9% 20% 10% 1	1862
March	1st to 10th	Night	54% 3 10% 18% 13% 2	2034
	11th to 20th	Night	53% 3 10% 21% 11% 2	1980
	21st to end	Night	48% 4 7% 22% 16% 3	2151
April	1st to 10th	Night	55% 3 6% 21% 12% 2	1800
	11th to 20th	Night	48% 3 8% 24% 15% 2	1775
	21st to end	Night	52% 3 9% 18% 15% 2	1620
May	1st to 10th	Night	47% 3 9% 21% 17% 3	1514
	11th to 20th	Night	40% 4 9% 26% 18% 3	1416
	21st to end	Night	35% 4 15% 24% 19% 3	1551
June	1st to 10th	Night	45% 4 12% 24% 14% 1	1440
	11th to 20th	Night	38% 4 11% 27% 18% 1	1440
	21st to end	Night	44% 4 14% 25% 12% 1	1440
July	1st to 10th	Night	34% 5% 11% 28% 20% 3	1400
	11th to 20th	Night	37% 4 13% 33% 13%	1392
	21st to end	Night	32% 6% 17% 31% 13% 1	1499
August	1st to 10th	Night	33% 7% 18% 29% 12% 1	1600
	11th to 20th	Night	35% 5% 18% 28% 13% 1	1598
	21st to end	Night	37% 5% 14% 30% 12% 1	1898
September	1st to 10th	Night	36% 5% 18% 27% 15% 1	1800
	11th to 20th	Night	35% 4 15% 35% 12% 1	1810
	21st to end	Night	45% 4 11% 30% 11%	2073
October	1st to 10th	Night	49% 4 11% 22% 14%	2160
	11th to 20th	Night	58% 4 12% 20% 6%	2160
	21st to end	Night	61% 5% 11% 14% 9% 1	2405
November	1st to 10th	Night	51% 4 13% 23% 9%	2506
	11th to 20th	Night	56% 4 12% 18% 8% 2	2660
	21st to end	Night	63% 4 12% 16% 5%	2660
December	1st to 10th	Night	70% 3 9% 13% 5%	2660
	11th to 20th	Night	65% 3 9% 15% 8%	3288
	21st to end	Night	77% 2 6% 11% 4	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	23% 20% 36% 16% 4 1	180
	11th to 20th	Day	29% 16% 35% 17% 3 1	174
	21st to end	Day	28% 19% 34% 15% 5%	264
February	1st to 10th	Day	32% 22% 38% 6% 2	240
	11th to 20th	Day	32% 26% 36% 5% 1	240
	21st to end	Day	37% 20% 33% 10% 1	260
March	1st to 10th	Day	25% 19% 37% 15% 4	420
	11th to 20th	Day	29% 17% 33% 15% 5% 1	420
	21st to end	Day	32% 17% 29% 15% 6% 2	462
April	1st to 10th	Day	28% 17% 33% 14% 7%	420
	11th to 20th	Day	33% 19% 24% 11% 10% 2	412
	21st to end	Day	30% 18% 31% 15% 5% 2	420
May	1st to 10th	Day	29% 13% 30% 19% 6% 4	423
	11th to 20th	Day	21% 15% 35% 19% 7% 2	447
	21st to end	Day	20% 16% 32% 19% 10% 3	485
June	1st to 10th	Day	26% 10% 34% 22% 7% 1	450
	11th to 20th	Day	18% 13% 33% 23% 10% 3	450
	21st to end	Day	21% 12% 34% 21% 11% 2	450
July	1st to 10th	Day	15% 8% 31% 28% 15% 4	445
	11th to 20th	Day	17% 10% 30% 25% 14% 5%	444
	21st to end	Day	15% 9% 35% 27% 11% 3	488
August	1st to 10th	Day	15% 6% 31% 29% 13% 5%	446
	11th to 20th	Day	15% 5% 24% 33% 15% 7%	439
	21st to end	Day	19% 9% 29% 23% 14% 7%	495
September	1st to 10th	Day	15% 9% 34% 21% 14% 6%	450
	11th to 20th	Day	17% 9% 27% 20% 17% 10%	450
	21st to end	Day	20% 12% 28% 22% 12% 5%	450
October	1st to 10th	Day	27% 14% 25% 17% 15% 2	450
	11th to 20th	Day	32% 15% 31% 15% 5% 1	450
	21st to end	Day	37% 15% 28% 16% 4	480
November	1st to 10th	Day	29% 13% 33% 18% 6% 1	266
	11th to 20th	Day	33% 19% 31% 11% 4 2	180
	21st to end	Day	33% 18% 38% 8% 3 1	180
December	1st to 10th	Day	33% 19% 30% 16% 2 1	180
	11th to 20th	Day	38% 21% 28% 11% 2 1	180
	21st to end	Day	35% 20% 29% 11% 5% 1	198
January	1st to 10th	Night	29% 18% 32% 16% 4 1	760
	11th to 20th	Night	30% 14% 32% 19% 5%	744
	21st to end	Night	20% 15% 34% 23% 7% 1	792
February	1st to 10th	Night	24% 20% 34% 19% 2	720
	11th to 20th	Night	22% 18% 39% 17% 4	703
	21st to end	Night	25% 19% 33% 18% 4	592
March	1st to 10th	Night	24% 19% 35% 19% 3	720
	11th to 20th	Night	24% 16% 35% 19% 5% 1	720
	21st to end	Night	22% 12% 35% 22% 9% 1	792
April	1st to 10th	Night	27% 13% 32% 23% 5%	720
	11th to 20th	Night	25% 17% 29% 20% 9% 1	711
	21st to end	Night	24% 10% 30% 24% 11%	540
May	1st to 10th	Night	27% 7% 26% 25% 13% 2	434
	11th to 20th	Night	17% 10% 33% 31% 8%	354
	21st to end	Night	14% 7% 35% 30% 12% 1	389
June	1st to 10th	Night	18% 8% 33% 33% 8% 1	360
	11th to 20th	Night	15% 9% 28% 35% 12% 1	360
	21st to end	Night	18% 7% 26% 36% 13%	360
July	1st to 10th	Night	7% 7% 30% 39% 16% 1	350
	11th to 20th	Night	13% 5% 28% 35% 19% 1	348
	21st to end	Night	10% 4 31% 37% 16% 1	407
August	1st to 10th	Night	14% 3 21% 35% 26% 2	537
	11th to 20th	Night	11% 4 20% 37% 25% 3	534
	21st to end	Night	13% 5% 29% 31% 20% 2	710
September	1st to 10th	Night	15% 6% 30% 29% 18% 3	720
	11th to 20th	Night	15% 5% 26% 29% 21% 4	720
	21st to end	Night	22% 10% 21% 27% 16% 4	720
October	1st to 10th	Night	23% 10% 28% 23% 15% 2	720
	11th to 20th	Night	30% 12% 30% 20% 8% 1	720
	21st to end	Night	31% 14% 29% 20% 5%	792
November	1st to 10th	Night	24% 14% 29% 25% 8% 1	740
	11th to 20th	Night	27% 15% 31% 17% 8% 1	760
	21st to end	Night	30% 15% 29% 20% 5% 1	760
December	1st to 10th	Night	33% 16% 31% 15% 4	760
	11th to 20th	Night	27% 18% 34% 17% 3 1	760
	21st to end	Night	34% 13% 33% 16% 3	836

Page generated at 2024-01-13 19:28:27. Version ac07

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